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Dehghani H, Holzapfel GA, Mittelbronn M, Zilian A. Cell adhesion affects the properties of interstitial fluid flow: A study using multiscale poroelastic composite modeling. J Mech Behav Biomed Mater 2024; 153:106486. [PMID: 38428205 DOI: 10.1016/j.jmbbm.2024.106486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 02/20/2024] [Accepted: 02/26/2024] [Indexed: 03/03/2024]
Abstract
In this study, we conduct a multiscale, multiphysics modeling of the brain gray matter as a poroelastic composite. We develop a customized representative volume element based on cytoarchitectural features that encompass important microscopic components of the tissue, namely the extracellular space, the capillaries, the pericapillary space, the interstitial fluid, cell-cell and cell-capillary junctions, and neuronal and glial cell bodies. Using asymptotic homogenization and direct numerical simulation, the effective properties at the tissue level are identified based on microscopic properties. To analyze the influence of various microscopic elements on the effective/macroscopic properties and tissue response, we perform sensitivity analyses on cell junction (cluster) stiffness, cell junction diameter (dimensions), and pericapillary space width. The results of this study suggest that changes in cell adhesion can greatly affect both mechanical and hydraulic (interstitial fluid flow and porosity) features of brain tissue, consistent with the effects of neurodegenerative diseases.
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Affiliation(s)
- Hamidreza Dehghani
- Institute of Computational Engineering and Sciences, Department of Engineering, Faculty of Science, Technology and Medicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg.
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, 8010 Graz, Austria; Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway
| | - Michel Mittelbronn
- National Center of Pathology (NCP), Laboratoire National de Santé (LNS), Dudelange, Luxembourg; Luxembourg Centre for Systems Biomedicine (LCSB), University of Luxembourg, Belval, Luxembourg; Luxembourg Center of Neuropathology (LCNP), Dudelange, Luxembourg; Department of Oncology (DONC), Luxembourg Institute of Health (LIH), Luxembourg; Department of Life Sciences and Medicine (DLSM), University of Luxembourg, Esch-sur-Alzette, Luxembourg; Faculty of Science, Technology and Medicine (FSTM), University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Andreas Zilian
- Institute of Computational Engineering and Sciences, Department of Engineering, Faculty of Science, Technology and Medicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg
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Pukaluk A, Sommer G, Holzapfel GA. Multimodal experimental studies of the passive mechanical behavior of human aortas: Current approaches and future directions. Acta Biomater 2024; 178:1-12. [PMID: 38401775 DOI: 10.1016/j.actbio.2024.02.026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2023] [Revised: 02/14/2024] [Accepted: 02/15/2024] [Indexed: 02/26/2024]
Abstract
Cardiovascular diseases are the leading cause of death worldwide and include, among others, critical conditions of the aortic wall. Importantly, such critical conditions require effective diagnosis and treatment, which are not yet accurate enough. However, they could be significantly strengthened with predictive material models of the aortic wall. In particular, such predictive models could support surgical decisions, preoperative planning, and estimation of postoperative tissue remodeling. However, developing a predictive model requires experimental data showing both structural parameters and mechanical behavior. Such experimental data can be obtained using multimodal experiments. This review therefore discusses the current approaches to multimodal experiments. Importantly, the strength of the aortic wall is determined primarily by its passive components, i.e., mainly collagen, elastin, and proteoglycans. Therefore, this review focuses on multimodal experiments that relate the passive mechanical behavior of the human aortic wall to the structure and organization of its passive components. In particular, the multimodal experiments are classified according to the expected results. Multiple examples are provided for each experimental class and summarized with highlighted advantages and disadvantages of the method. Finally, future directions of multimodal experiments are envisioned and evaluated. STATEMENT OF SIGNIFICANCE: Multimodal experiments are innovative approaches that have gained interest very quickly, but also recently. This review presents therefore a first clear summary of groundbreaking research in the field of multimodal experiments. The benefits and limitations of various types of multimodal experiments are thoroughly discussed, and a comprehensive overview of possible results is provided. Although this review focuses on multimodal experiments performed on human aortic tissues, the methods used and described are not limited to human aortic tissues but can be extended to other soft materials.
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Affiliation(s)
- Anna Pukaluk
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering (NTNU), Trondheim, Norway.
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Agrafiotis E, Zimpfer D, Mächler H, Holzapfel GA. Review of Systemic Mock Circulation Loops for Evaluation of Implantable Cardiovascular Devices and Biological Tissues. J Endovasc Ther 2024:15266028241235876. [PMID: 38528650 DOI: 10.1177/15266028241235876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/27/2024]
Abstract
CLINICAL IMPACT On needs-based ex vivo monitoring of implantable devices or tissues/organs in cardiovascular simulators provides new insights and paves new paths for device prototypes. The insights gained could not only support the needs of patients, but also inform engineers, scientists and clinicians about undiscovered aspects of diseases (during routine monitoring). We analyze seminal and current work and highlight a variety of opportunities for developing preclinical tools that would improve strategies for future implantable devices. Holistically, mock circulation loop studies can bridge the gap between in vivo and in vitro approaches, as well as clinical and laboratory settings, in a mutually beneficial manner.
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Affiliation(s)
| | - Daniel Zimpfer
- Division of Cardiac Surgery, Medical University of Graz, Graz, Austria
| | - Heinrich Mächler
- Division of Cardiac Surgery, Medical University of Graz, Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
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Kan X, Ma T, Jiang X, Holzapfel GA, Dong Z, Xu XY. Towards biomechanics-based pre-procedural planning for thoracic endovascular aortic repair of aortic dissection. Comput Methods Programs Biomed 2024; 244:107994. [PMID: 38159449 DOI: 10.1016/j.cmpb.2023.107994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 12/17/2023] [Accepted: 12/21/2023] [Indexed: 01/03/2024]
Abstract
BACKGROUND AND OBJECTIVE Although thoracic aortic endovascular repair (TEVAR) has shown promising outcomes in the treatment of patients with complicated type B aortic dissection, complications still occur after TEVAR that can lead to catastrophic events. Biomechanical interactions between the stent-graft (SG) and the local aortic tissue play a critical role in determining the outcome of TEVAR. Different SG design may cause different biomechanical responses in the treated aorta, but such information is not known at the time of pre-procedural planning. By developing patient-specific virtual stent-graft deployment tools, it is possible to analyse and compare the biomechanical impact of different SGs on the local aorta for individual patients. METHODS A finite element based virtual SG deployment model was employed in this study. Computational simulations were performed on a patient-specific model of type B aortic dissection, accounting for details of the SG design and the hyperelastic behaviour of the aortic wall. Based on the geometry reconstructed from the pre-TEVAR CTA scan, the patient-specific aortic dissection model was created and pre-stressed. Parametric models of three different SG products (SG1, SG2 and SG3) were built with two different lengths for each design. The SG models incorporated different stent and graft materials, stent strut patterns, and assembly approaches. Using our validated SG deployment simulation framework, virtual trials were performed on the patient-specific aortic dissection model using different SG products and varying SG lengths. CONCLUSION Simulation results for different SG products suggest that SG3 with a longer length (SG3-long) would be the most appropriate device for the individual patient. Compared to SG1-short (the SG deployed in the patient), SG3-long followed the true lumen tortuosity closely, resulted in a more uniform true lumen expansion and a significant reduction in peak stress in the distal landing zone. These simulation results are promising and demonstrate the feasibility of using the virtual SG deployment model to assist clinicians in pre-procedural planning.
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Affiliation(s)
- Xiaoxin Kan
- Centre for Vascular Surgery and Wound Care, Jinshan Hospital, Fudan University, Shanghai, China; Department of Chemical Engineering, Imperial College London, London, United Kingdom
| | - Tao Ma
- Department of Vascular Surgery, Zhongshan Hospital, Fudan University, Shanghai, China; Institute of Vascular Surgery, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Xiaolang Jiang
- Department of Vascular Surgery, Zhongshan Hospital, Fudan University, Shanghai, China; Institute of Vascular Surgery, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria; Norwegian University of Science and Technology (NTNU), Department of Structural Engineering, Trondheim, Norway
| | - Zhihui Dong
- Centre for Vascular Surgery and Wound Care, Jinshan Hospital, Fudan University, Shanghai, China; Department of Vascular Surgery, Zhongshan Hospital, Fudan University, Shanghai, China; Institute of Vascular Surgery, Zhongshan Hospital, Fudan University, Shanghai, China
| | - Xiao Yun Xu
- Department of Chemical Engineering, Imperial College London, London, United Kingdom.
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Alberini R, Spagnoli A, Sadeghinia MJ, Skallerud B, Terzano M, Holzapfel GA. Fourier transform-based method for quantifying the three-dimensional orientation distribution of fibrous units. Sci Rep 2024; 14:1999. [PMID: 38263352 DOI: 10.1038/s41598-024-51550-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Accepted: 01/06/2024] [Indexed: 01/25/2024] Open
Abstract
Several materials and tissues are characterized by a microstructure composed of fibrous units embedded in a ground matrix. In this paper, a novel three-dimensional (3D) Fourier transform-based method for quantifying the distribution of fiber orientations is presented. The method allows for an accurate identification of individual fiber families, their in-plane and out-of-plane dispersion, and showed fast computation times. We validated the method using artificially generated 3D images, in terms of fiber dispersion by considering the error between the standard deviation of the reconstructed and the prescribed distributions of the artificial fibers. In addition, we considered the measured mean orientation angles of the fibers and validated the robustness using a measure of fiber density. Finally, the method is employed to reconstruct a full 3D view of the distribution of collagen fiber orientations based on in vitro second harmonic generation microscopy of collagen fibers in human and mouse skin. The dispersion parameters of the reconstructed fiber network can be used to inform mechanical models of soft fiber-reinforced materials and biological tissues that account for non-symmetrical fiber dispersion.
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Affiliation(s)
- Riccardo Alberini
- Department of Engineering and Architecture, University of Parma, Parma, Italy
| | - Andrea Spagnoli
- Department of Engineering and Architecture, University of Parma, Parma, Italy.
| | - Mohammad Javad Sadeghinia
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Bjørn Skallerud
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
| | - Michele Terzano
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Gerhard A Holzapfel
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
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6
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Holzer CS, Pukaluk A, Viertler C, Regitnig P, Caulk AW, Eschbach M, Contini EM, Holzapfel GA. Biomechanical characterization of the passive porcine stomach. Acta Biomater 2024; 173:167-183. [PMID: 37984627 DOI: 10.1016/j.actbio.2023.11.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 11/02/2023] [Accepted: 11/07/2023] [Indexed: 11/22/2023]
Abstract
The complex mechanics of the gastric wall facilitates the main digestive tasks of the stomach. However, the interplay between the mechanical properties of the stomach, its microstructure, and its vital functions is not yet fully understood. Importantly, the pig animal model is widely used in biomedical research for preliminary or ethically prohibited studies of the human digestion system. Therefore, this study aims to thoroughly characterize the mechanical behavior and microstructure of the porcine stomach. For this purpose, multiple quasi-static mechanical tests were carried out with three different loading modes, i.e., planar biaxial extension, radial compression, and simple shear. Stress-relaxation tests complemented the quasi-static experiments to evaluate the deformation and strain-dependent viscoelastic properties. Each experiment was conducted on specimens of the complete stomach wall and two separate layers, mucosa and muscularis, from each of the three gastric regions, i.e., fundus, body, and antrum. The significant preconditioning effects and the considerable regional and layer-specific differences in the tissue response were analyzed. Furthermore, the mechanical experiments were complemented with histology to examine the influence of the microstructural composition on the macrostructural mechanical response and vice versa. Importantly, the shear tests showed lower stresses in the complete wall compared to the single layers which the loose network of submucosal collagen might explain. Also, the stratum arrangement of the muscularis might explain mechanical anisotropy during tensile tests. This study shows that gastric tissue is characterized by a highly heterogeneous microstructure with regional variations in layer composition reflecting not only functional differences but also diverse mechanical behavior. STATEMENT OF SIGNIFICANCE: Unfortunately, only few experimental data on gastric tissue are available for an adequate material parameter and model estimation. The present study therefore combines layer- and region-specific stomach wall mechanics obtained under multiple loading conditions with histological insights into the heterogeneous microstructure. On the one hand, the extensive data sets of this study expand our understanding of the interplay between gastric mechanics, motility and functionality, which could help to identify and treat associated pathologies. On the other hand, such data sets are of high relevance for the constitutive modeling of stomach tissue, and its application in the field of medical engineering, e.g., in the development of surgical staplers and the improvement of bariatric surgical interventions.
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Affiliation(s)
| | - Anna Pukaluk
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Christian Viertler
- Diagnostic and Research Institute of Pathology, Medical University of Graz, Austria
| | - Peter Regitnig
- Diagnostic and Research Institute of Pathology, Medical University of Graz, Austria
| | | | | | | | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, NTNU, Trondheim, Norway.
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7
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Amor M, Bianco V, Buerger M, Lechleitner M, Vujić N, Dobrijević A, Akhmetshina A, Pirchheim A, Schwarz B, Pessentheiner AR, Baumgartner F, Rampitsch K, Schauer S, Klobučar I, Degoricija V, Pregartner G, Kummer D, Svecla M, Sommer G, Kolb D, Holzapfel GA, Hoefler G, Frank S, Norata GD, Kratky D. Genetic deletion of MMP12 ameliorates cardiometabolic disease by improving insulin sensitivity, systemic inflammation, and atherosclerotic features in mice. Cardiovasc Diabetol 2023; 22:327. [PMID: 38017481 PMCID: PMC10685620 DOI: 10.1186/s12933-023-02064-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Accepted: 11/13/2023] [Indexed: 11/30/2023] Open
Abstract
BACKGROUND Matrix metalloproteinase 12 (MMP12) is a macrophage-secreted protein that is massively upregulated as a pro-inflammatory factor in metabolic and vascular tissues of mice and humans suffering from cardiometabolic diseases (CMDs). However, the molecular mechanisms explaining the contributions of MMP12 to CMDs are still unclear. METHODS We investigated the impact of MMP12 deficiency on CMDs in a mouse model that mimics human disease by simultaneously developing adipose tissue inflammation, insulin resistance, and atherosclerosis. To this end, we generated and characterized low-density lipoprotein receptor (Ldlr)/Mmp12-double knockout (DKO) mice fed a high-fat sucrose- and cholesterol-enriched diet for 16-20 weeks. RESULTS DKO mice showed lower cholesterol and plasma glucose concentrations and improved insulin sensitivity compared with LdlrKO mice. Untargeted proteomic analyses of epididymal white adipose tissue revealed that inflammation- and fibrosis-related pathways were downregulated in DKO mice. In addition, genetic deletion of MMP12 led to alterations in immune cell composition and a reduction in plasma monocyte chemoattractant protein-1 in peripheral blood which indicated decreased low-grade systemic inflammation. Aortic en face analyses and staining of aortic valve sections demonstrated reduced atherosclerotic plaque size and collagen content, which was paralleled by an improved relaxation pattern and endothelial function of the aortic rings and more elastic aortic sections in DKO compared to LdlrKO mice. Shotgun proteomics revealed upregulation of anti-inflammatory and atheroprotective markers in the aortas of DKO mice, further supporting our data. In humans, MMP12 serum concentrations were only weakly associated with clinical and laboratory indicators of CMDs. CONCLUSION We conclude that the genetic deletion of MMP12 ameliorates obesity-induced low-grade inflammation, white adipose tissue dysfunction, biomechanical properties of the aorta, and the development of atherosclerosis. Therefore, therapeutic strategies targeting MMP12 may represent a promising approach to combat CMDs.
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Affiliation(s)
- Melina Amor
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Valentina Bianco
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Martin Buerger
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Margarete Lechleitner
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Nemanja Vujić
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Anja Dobrijević
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
- Institute for Vascular Biology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Alena Akhmetshina
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Anita Pirchheim
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Birgit Schwarz
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
| | - Ariane R Pessentheiner
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
- Institute for Molecular Biosciences, University of Graz, Graz, Austria
| | | | | | - Silvia Schauer
- Diagnostics and Research Institute of Pathology, Medical University of Graz, Graz, Austria
| | - Iva Klobučar
- Sisters of Charity, University Hospital Centre, Zagreb, Croatia
| | - Vesna Degoricija
- University of Zagreb School of Medicine, Zagreb, Croatia
- Department of Medicine, Sisters of Charity, University Hospital Centre, Zagreb, Croatia
| | - Gudrun Pregartner
- Institute for Medical Informatics, Statistics and Documentation, Medical University of Graz, Graz, Austria
| | - Daniel Kummer
- Gottfried Schatz Research Center, Cell Biology, Histology and Embryology, Medical University of Graz, Graz, Austria
| | - Monika Svecla
- Department of Pharmacological and Biomolecular Sciences, University of Milan, Milan, Italy
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- BioTechMed-Graz, Graz, Austria
| | - Dagmar Kolb
- Gottfried Schatz Research Center, Cell Biology, Histology and Embryology, Medical University of Graz, Graz, Austria
- Core Facility Ultrastructural Analysis, Medical University of Graz, Graz, Austria
- BioTechMed-Graz, Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- BioTechMed-Graz, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Gerald Hoefler
- Diagnostics and Research Institute of Pathology, Medical University of Graz, Graz, Austria
- BioTechMed-Graz, Graz, Austria
| | - Saša Frank
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria
- BioTechMed-Graz, Graz, Austria
| | - Giuseppe Danilo Norata
- Department of Pharmacological and Biomolecular Sciences, University of Milan, Milan, Italy
| | - Dagmar Kratky
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Neue Stiftingtalstrasse 6/4, Graz, 8010, Austria.
- BioTechMed-Graz, Graz, Austria.
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8
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Saeidi S, Kainz MP, Dalbosco M, Terzano M, Holzapfel GA. Histology-informed multiscale modeling of human brain white matter. Sci Rep 2023; 13:19641. [PMID: 37949949 PMCID: PMC10638412 DOI: 10.1038/s41598-023-46600-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Accepted: 11/02/2023] [Indexed: 11/12/2023] Open
Abstract
In this study, we propose a novel micromechanical model for the brain white matter, which is described as a heterogeneous material with a complex network of axon fibers embedded in a soft ground matrix. We developed this model in the framework of RVE-based multiscale theories in combination with the finite element method and the embedded element technique for embedding the fibers. Microstructural features such as axon diameter, orientation and tortuosity are incorporated into the model through distributions derived from histological data. The constitutive law of both the fibers and the matrix is described by isotropic one-term Ogden functions. The hyperelastic response of the tissue is derived by homogenizing the microscopic stress fields with multiscale boundary conditions to ensure kinematic compatibility. The macroscale homogenized stress is employed in an inverse parameter identification procedure to determine the hyperelastic constants of axons and ground matrix, based on experiments on human corpus callosum. Our results demonstrate the fundamental effect of axon tortuosity on the mechanical behavior of the brain's white matter. By combining histological information with the multiscale theory, the proposed framework can substantially contribute to the understanding of mechanotransduction phenomena, shed light on the biomechanics of a healthy brain, and potentially provide insights into neurodegenerative processes.
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Affiliation(s)
- Saeideh Saeidi
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Manuel P Kainz
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Misael Dalbosco
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- GRANTE - Department of Mechanical Engineering, Federal University of Santa Catarina, Florianópolis, SC, Brazil
| | - Michele Terzano
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria.
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
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9
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Dalbosco M, Terzano M, Carniel TA, Fancello EA, Holzapfel GA. A two-scale numerical study on the mechanobiology of abdominal aortic aneurysms. J R Soc Interface 2023; 20:20230472. [PMID: 37907092 PMCID: PMC10618057 DOI: 10.1098/rsif.2023.0472] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Accepted: 10/11/2023] [Indexed: 11/02/2023] Open
Abstract
Abdominal aortic aneurysms (AAAs) are a serious condition whose pathophysiology is related to phenomena occurring at different length scales. To gain a better understanding of the disease, this work presents a multi-scale computational study that correlates AAA progression with microstructural and mechanical alterations in the tissue. Macro-scale geometries of a healthy aorta and idealized aneurysms with increasing diameter are developed on the basis of existing experimental data and subjected to physiological boundary conditions. Subsequently, microscopic representative volume elements of the abluminal side of each macro-model are employed to analyse the local kinematics at the cellular scale. The results suggest that the formation of the aneurysm disrupts the micromechanics of healthy tissue, which could trigger collagen growth and remodelling by mechanosensing cells. The resulting changes to the macro-mechanics and microstructure of the tissue seem to establish a new homeostatic state at the cellular scale, at least for the diameter range investigated.
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Affiliation(s)
- Misael Dalbosco
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- GRANTE—Department of Mechanical Engineering, Federal University of Santa Catarina, Florianópolis, Santa Catarina, Brazil
| | - Michele Terzano
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Thiago A. Carniel
- Polytechnic School, Community University of Chapecó Region, Chapecó, Santa Catarina, Brazil
- Graduate Program in Health Sciences, Community University of Chapecó Region, Chapecó, Santa Catarina, Brazil
| | - Eduardo A. Fancello
- GRANTE—Department of Mechanical Engineering, Federal University of Santa Catarina, Florianópolis, Santa Catarina, Brazil
- LEBm—University Hospital, Federal University of Santa Catarina, Florianópolis, Santa Catarina, Brazil
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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10
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Zhang W, Jadidi M, Razian SA, Holzapfel GA, Kamenskiy A, Nordsletten DA. A viscoelastic constitutive model for human femoropopliteal arteries. Acta Biomater 2023; 170:68-85. [PMID: 37699504 PMCID: PMC10802972 DOI: 10.1016/j.actbio.2023.09.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 09/06/2023] [Accepted: 09/07/2023] [Indexed: 09/14/2023]
Abstract
High failure rates present challenges for surgical and interventional therapies for peripheral artery disease of the femoropopliteal artery (FPA). The FPA's demanding biomechanical environment necessitates complex interactions with repair devices and materials. While a comprehensive understanding of the FPA's mechanical characteristics could improve medical treatments, the viscoelastic properties of these muscular arteries remain poorly understood, and the constitutive model describing their time-dependent behavior is absent. We introduce a new viscoelastic constitutive model for the human FPA grounded in its microstructural composition. The model is capable of detailing the contributions of each intramural component to the overall viscoelastic response. Our model was developed utilizing fractional viscoelasticity and tested using biaxial experimental data with hysteresis and relaxation collected from 10 healthy human subjects aged 57 to 65 and further optimized for high throughput and automation. The model accurately described the experimental data, capturing significant nonlinearity and hysteresis that were particularly pronounced circumferentially, and tracked the contribution of passive smooth muscle cells to viscoelasticity that was twice that of the collagen fibers. The high-throughput parameter estimation procedure we developed included a specialized objective function and modifications to enhance convergence for the common exponential-type fiber laws, facilitating computational implementation. Our new model delineates the time-dependent behavior of human FPAs, which will improve the fidelity of computational simulations investigating device-artery interactions and contribute to their greater physical accuracy. Moreover, it serves as a useful tool to investigate the contribution of arterial constituents to overall tissue viscoelasticity, thereby expanding our knowledge of arterial mechanophysiology. STATEMENT OF SIGNIFICANCE: The demanding biomechanical environment of the femoropopliteal artery (FPA) necessitates complex interactions with repair devices and materials, but the viscoelastic properties of these muscular arteries remain poorly understood with the constitutive model describing their time-dependent behavior being absent. We hereby introduce the first viscoelastic constitutive model for the human FPA grounded in its microstructures. This model was tested using biaxial mechanical data collected from 10 healthy human subjects between the ages of 57 to 65. It can detail the contributions of each intramural component to the overall viscoelastic response, showing that the contribution of passive smooth muscle cells to viscoelasticity is twice that of collagen fibers. The usefulness of this model as tool to better understand arterial mechanophysiology was demonstrated.
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Affiliation(s)
- Will Zhang
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
| | - Majid Jadidi
- Department of Biomechanics, University of Nebraska at Omaha, Omaha, NE, USA.
| | | | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz Univerisity of Technology, Graz, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
| | - Alexey Kamenskiy
- Department of Biomechanics, University of Nebraska at Omaha, Omaha, NE, USA.
| | - David A Nordsletten
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA; Division of Biomedical Engineering and Imaging Sciences, Department of Biomedical Engineering, King's College London, London, UK.
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11
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Laurence DW, Wang S, Xiao R, Qian J, Mir A, Burkhart HM, Holzapfel GA, Lee CH. An investigation of how specimen dimensions affect biaxial mechanical characterizations with CellScale BioTester and constitutive modeling of porcine tricuspid valve leaflets. J Biomech 2023; 160:111829. [PMID: 37826955 PMCID: PMC10995110 DOI: 10.1016/j.jbiomech.2023.111829] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 08/19/2023] [Accepted: 10/03/2023] [Indexed: 10/14/2023]
Abstract
Biaxial mechanical characterizations are the accepted approach to determine the mechanical response of many biological soft tissues. Although several computational and experimental studies have examined how experimental factors (e.g., clamped vs. suture mounting) affect the acquired tissue mechanical behavior, little is known about the role of specimen dimensions in data acquisition and the subsequent modeling. In this study, we combined our established mechanical characterization framework with an iterative size-reduction protocol to test the hypothesis that specimen dimensions affect the observed mechanical behavior of biaxial characterizations. Our findings indicated that there were non-significant differences in the peak equibiaxial stretches of tricuspid valve leaflets across four specimen dimensions ranging from 4.5×4.5mm to 9 × 9mm. Further analyses revealed that there were significant differences in the low-tensile modulus of the circumferential tissue direction. These differences resulted in significantly different constitutive model parameters for the Tong-Fung model between different specimen dimensions of the posterior and septal leaflets. Overall, our findings demonstrate that specimen dimensions play an important role in experimental characterizations, but not necessarily in constitutive modeling of soft tissue mechanical behavior during biaxial testing with the commercial CellScale BioTester.
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Affiliation(s)
- Devin W Laurence
- Biomechanics and Biomaterials Design Laboratory, The University of Oklahoma, USA
| | - Shuodao Wang
- School of Mechanical and Aerospace Engineering, Oklahoma State University, USA
| | - Rui Xiao
- Department of Engineering Mechanics, Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, Hangzhou 310027, China
| | - Jin Qian
- Department of Engineering Mechanics, Key Laboratory of Soft Machines and Smart Devices of Zhejiang Province, Zhejiang University, Hangzhou 310027, China
| | - Arshid Mir
- Department of Pediatrics, University of Oklahoma Health Sciences Center, USA
| | - Harold M Burkhart
- Department of Surgery, University of Oklahoma Health Sciences Center, USA
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Norway
| | - Chung-Hao Lee
- Biomechanics and Biomaterials Design Laboratory, The University of Oklahoma, USA; Institute for Biomedical Engineering, Science and Technology, The University of Oklahoma, USA; Department of Bioengineering, The University of California, Riverside, USA.
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12
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Pineda-Castillo SA, Acar H, Detamore MS, Holzapfel GA, Lee CH. Modulation of Smooth Muscle Cell Phenotype for Translation of Tissue-Engineered Vascular Grafts. Tissue Eng Part B Rev 2023; 29:574-588. [PMID: 37166394 PMCID: PMC10618830 DOI: 10.1089/ten.teb.2023.0006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Accepted: 04/25/2023] [Indexed: 05/12/2023]
Abstract
Translation of small-diameter tissue-engineered vascular grafts (TEVGs) for the treatment of coronary artery disease (CAD) remains an unfulfilled promise. This is largely due to the limited integration of TEVGs into the native vascular wall-a process hampered by the insufficient smooth muscle cell (SMC) infiltration and extracellular matrix deposition, and low vasoactivity. These processes can be promoted through the judicious modulation of the SMC toward a synthetic phenotype to promote remodeling and vascular integration; however, the expression of synthetic markers is often accompanied by a decrease in the expression of contractile proteins. Therefore, techniques that can precisely modulate the SMC phenotypical behavior could have the potential to advance the translation of TEVGs. In this review, we describe the phenotypic diversity of SMCs and the different environmental cues that allow the modulation of SMC gene expression. Furthermore, we describe the emerging biomaterial approaches to modulate the SMC phenotype in TEVG design and discuss the limitations of current techniques. In addition, we found that current studies in tissue engineering limit the analysis of the SMC phenotype to a few markers, which are often the characteristic of early differentiation only. This limited scope has reduced the potential of tissue engineering to modulate the SMC toward specific behaviors and applications. Therefore, we recommend using the techniques presented in this review, in addition to modern single-cell proteomics analysis techniques to comprehensively characterize the phenotypic modulation of SMCs. Expanding the holistic potential of SMC modulation presents a great opportunity to advance the translation of living conduits for CAD therapeutics.
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Affiliation(s)
- Sergio A. Pineda-Castillo
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, Oklahoma, USA
- Stephenson School of Biomedical Engineering, The University of Oklahoma, Norman, Oklahoma, USA
| | - Handan Acar
- Stephenson School of Biomedical Engineering, The University of Oklahoma, Norman, Oklahoma, USA
- Institute for Biomedical Engineering, Science and Technology, The University of Oklahoma, Norman, Oklahoma, USA
| | - Michael S. Detamore
- Stephenson School of Biomedical Engineering, The University of Oklahoma, Norman, Oklahoma, USA
- Institute for Biomedical Engineering, Science and Technology, The University of Oklahoma, Norman, Oklahoma, USA
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Chung-Hao Lee
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, Oklahoma, USA
- Institute for Biomedical Engineering, Science and Technology, The University of Oklahoma, Norman, Oklahoma, USA
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13
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Avril S, Holzapfel GA. Foreword to the special issue entitled "Progress and future directions in soft tissue mechanics" in the Journal Biomechanics and Modeling in Mechanobiology. Biomech Model Mechanobiol 2023; 22:1461-1464. [PMID: 37707686 DOI: 10.1007/s10237-023-01770-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Accepted: 08/28/2023] [Indexed: 09/15/2023]
Affiliation(s)
- Stéphane Avril
- Mines Saint-Etienne, Université Jean Monnet Saint-Etienne, INSERM, SAINBIOSE U1059, 42023, Saint-Etienne, France.
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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14
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Cosentino F, Sherifova S, Sommer G, Raffa G, Pilato M, Pasta S, Holzapfel GA. Regional biomechanical characterization of human ascending aortic aneurysms: Microstructure and biaxial mechanical response. Acta Biomater 2023; 169:107-117. [PMID: 37579911 DOI: 10.1016/j.actbio.2023.08.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2023] [Revised: 07/17/2023] [Accepted: 08/09/2023] [Indexed: 08/16/2023]
Abstract
The ascending thoracic aortic aneurysm (ATAA) is a permanent dilatation of the vessel with a high risk of adverse events, and shows heterogeneous properties. To investigate regional differences in the biomechanical properties of ATAAs, tissue samples were collected from 10 patients with tricuspid aortic valve phenotype and specimens from minor, anterior, major, and posterior regions were subjected to multi-ratio planar biaxial extension tests and second-harmonic generation (SHG) imaging. Using the data, parameters of a microstructure-motivated constitutive model were obtained considering fiber dispersion. SHG imaging showed disruptions in the organization of the layers. Structural and material parameters did not differ significantly between regions. The non-symmetric fiber dispersion model proposed by Holzapfel et al. [25] was used to fit the data. The mean angle of collagen fibers was negatively correlated between minor and anterior regions, and the parameter associated with collagen fiber stiffness was positively correlated between minor and major regions. Furthermore, correlations were found between the stiffness of the ground matrix and the mean fiber angle, and between the parameter associated with the collagen fiber stiffness and the out-of-plane dispersion parameter in the posterior and minor regions, respectively. The experimental data collected in this study contribute to the biomechanical data available in the literature on human ATAAs. Region-specific parameters for the constitutive models are fundamental to improve the current risk stratification strategies, which are mainly based on aortic size. Such investigations can facilitate the development of more advanced finite element models capable of capturing the regional heterogeneity of pathological tissues. STATEMENT OF SIGNIFICANCE: Tissue samples of human ascending thoracic aortic aneurysms (ATAA) were collected. Samples from four regions underwent multi-ratio planar biaxial extension tests and second-harmonic generation imaging. Region-specific parameters of a microstructure-motivated model considering fiber dispersion were obtained. Structural and material parameters did not differ significantly between regions, however, the mean fiber angle was negatively correlated between minor and anterior regions, and the parameter associated with collagen fiber stiffness was positively correlated between minor and major regions. Furthermore, correlations were found between the stiffness of the ground matrix and the mean fiber angle, and between the parameter associated with the collagen fiber stiffness and the out-of-plane dispersion parameter in the posterior and minor regions, respectively. This study provides a unique set of mechanical and structural data, supporting the microstructural influence on the tissue response. It may facilitate the development of better finite element models capable of capturing the regional tissue heterogeneity.
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Affiliation(s)
- Federica Cosentino
- Ri.MED Foundation, Palermo, Italy; Department of Engineering, University of Palermo, Italy
| | - Selda Sherifova
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Giuseppe Raffa
- Department for the Treatment and Study of Cardiothoracic Diseases and Cardiothoracic Transplantation, IRCCS-ISMETT, Palermo, Italy
| | - Michele Pilato
- Department for the Treatment and Study of Cardiothoracic Diseases and Cardiothoracic Transplantation, IRCCS-ISMETT, Palermo, Italy
| | - Salvatore Pasta
- Department of Engineering, University of Palermo, Italy; Department for the Treatment and Study of Cardiothoracic Diseases and Cardiothoracic Transplantation, IRCCS-ISMETT, Palermo, Italy
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, Norwegian Institute of Science and Technology (NTNU), Trondheim, Norway.
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15
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Holzapfel GA, DeAnda A, Rajagopal K. Commentary: May the force(s) be with you: Loading conditions and the aorta. J Thorac Cardiovasc Surg 2023; 166:714-715. [PMID: 34657717 DOI: 10.1016/j.jtcvs.2021.10.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 10/01/2021] [Accepted: 10/04/2021] [Indexed: 11/20/2022]
Affiliation(s)
- Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Abe DeAnda
- Division of Cardiovascular and Thoracic Surgery, Department of Surgery, University of Texas Medical Branch-Galveston, Galveston, Tex.
| | - Keshava Rajagopal
- Department of Clinical Sciences, University of Houston College of Medicine, Houston, Tex
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16
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Terzano M, Wollner MP, Kainz MP, Rolf-Pissarczyk M, Götzen N, Holzapfel GA. Modelling the anisotropic inelastic response of polymeric scaffolds for in situ tissue engineering applications. J R Soc Interface 2023; 20:20230318. [PMID: 37700713 PMCID: PMC10498354 DOI: 10.1098/rsif.2023.0318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 08/18/2023] [Indexed: 09/14/2023] Open
Abstract
In situ tissue engineering offers an innovative solution for replacement valves and grafts in cardiovascular medicine. In this approach, a scaffold, which can be obtained by polymer electrospinning, is implanted into the human body and then infiltrated by cells, eventually replacing the scaffold with native tissue. In silico simulations of the whole process in patient-specific models, including implantation, growth and degradation, are very attractive to study the factors that might influence the end result. In our research, we focused on the mechanical behaviour of the polymeric scaffold and its short-term response. Following a recently proposed constitutive model for the anisotropic inelastic behaviour of fibrous polymeric materials, we present here its numerical implementation in a finite element framework. The numerical model is developed as user material for commercial finite element software. The verification of the implementation is performed for elementary deformations. Furthermore, a parallel-plate test is proposed as a large-scale representative example, and the model is validated by comparison with experiments.
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Affiliation(s)
- Michele Terzano
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | | | - Manuel P. Kainz
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | | | - Nils Götzen
- 4RealSim Services BV, IJsselstein, The Netherlands
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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17
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Pukaluk A, Wolinski H, Viertler C, Regitnig P, Holzapfel GA, Sommer G. Changes in the microstructure of the human aortic adventitia under biaxial loading investigated by multi-photon microscopy. Acta Biomater 2023; 161:154-169. [PMID: 36812954 DOI: 10.1016/j.actbio.2023.02.027] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 02/01/2023] [Accepted: 02/17/2023] [Indexed: 02/23/2023]
Abstract
Among the three layers of the aortic wall, the media is primarily responsible for its mechanical properties, but the adventitia prevents the aorta from overstretching and rupturing. The role of the adventitia is therefore crucial with regard to aortic wall failure, and understanding the load-induced changes in tissue microstructure is of high importance. Specifically, the focus of this study is on the changes in collagen and elastin microstructure in response to macroscopic equibiaxial loading applied to the aortic adventitia. To observe these changes, multi-photon microscopy imaging and biaxial extension tests were performed simultaneously. In particular, microscopy images were recorded at 0.02 stretch intervals. The microstructural changes of collagen fiber bundles and elastin fibers were quantified with the parameters of orientation, dispersion, diameter, and waviness. The results showed that the adventitial collagen was divided from one into two fiber families under equibiaxial loading conditions. The almost diagonal orientation of the adventitial collagen fiber bundles remained unchanged, but the dispersion was substantially reduced. No clear orientation of the adventitial elastin fibers was observed at any stretch level. The waviness of the adventitial collagen fiber bundles decreased under stretch, but the adventitial elastin fibers showed no change. These original findings highlight differences between the medial and adventitial layers and provide insight into the stretching process of the aortic wall. STATEMENT OF SIGNIFICANCE: To provide accurate and reliable material models, it is essential to understand the mechanical behavior of the material and its microstructure. Such understanding can be enhanced with tracking of the microstructural changes caused by mechanical loading of the tissue. This study provides therefore a unique dataset of structural parameters of the human aortic adventitia obtained under equibiaxial loading. The structural parameters describe orientation, dispersion, diameter, and waviness of collagen fiber bundles and elastin fibers. Eventually, the microstructural changes in the human aortic adventitia are compared with the microstructural changes in the human aortic media from a previous study. This comparison reveals the cutting-edge findings on the differences in the response to the loading between these two human aortic layers.
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Affiliation(s)
- Anna Pukaluk
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Heimo Wolinski
- Institute of Molecular Biosciences, University of Graz, Austria; Field of Excellence BioHealth, University of Graz, Austria
| | - Christian Viertler
- Diagnostic and Research Institute of Pathology, Medical University of Graz, Austria
| | - Peter Regitnig
- Diagnostic and Research Institute of Pathology, Medical University of Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering (NTNU), Trondheim, Norway
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Austria.
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18
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Giovanniello F, Asgari M, Breslavsky ID, Franchini G, Holzapfel GA, Tabrizian M, Amabili M. Development and mechanical characterization of decellularized scaffolds for an active aortic graft. Acta Biomater 2023; 160:59-72. [PMID: 36792047 DOI: 10.1016/j.actbio.2023.02.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Revised: 02/02/2023] [Accepted: 02/07/2023] [Indexed: 02/16/2023]
Abstract
Decellularized porcine aortas are proposed as scaffolds for revolutionary active aortic grafts. A change in the static and dynamic mechanical properties, associated with the microstructure of elastin and collagen fibers, corresponds to alteration in the cyclic expansion and perfusion, in addition to possible graft damage. Therefore, the present study thoroughly investigates the mechanical response of the decellularized scaffolds of human and porcine origin to static and dynamic mechanical loads. The responses of the native human and porcine aortas are also compared; this is unavailable in the literature. Because the aorta is subjected to pulsatile blood pressure, dynamical responses to cyclic loads and their associated viscoelastic properties are particularly relevant for advanced graft design. In parallel, this study examines the microstructure of the decellularized aorta. The resulting data are compared to the analogous data obtained for the native human and porcine tissues. The results indicate that by using an optimized decellularization protocol - based on sodium dodecyl sulfate (SDS) and DNase - that minimizes mechanical and structural changes of the tissue, layered scaffolds with static and dynamic properties very similar to natural human aortas are obtained. In particular, a decellularized porcine aorta is non-inferior to a decellularized human aorta. STATEMENT OF SIGNIFICANCE: About 55,000 patients undergo abdominal aortic aneurysm repair annually in the USA. The currently implanted grafts present a large mechanical mismatch with the native tissue. This increases the pulsatile nature of the blood flow with negative consequences to the organ perfusion. For this reason, biomimetic and mechanically compatible grafts for aortic repair are urgently needed and they can be obtained through tissue engineering. In this study, scaffolds from porcine and human aortas are obtained from an optimized decellularization protocol. They are accurately compared to the native tissue and present the ideal static and dynamic mechanical properties for developing innovative aortic grafts.
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Affiliation(s)
| | - Meisam Asgari
- Department of Mechanical Engineering, McGill University, Montreal, Canada
| | - Ivan D Breslavsky
- Department of Mechanical Engineering, McGill University, Montreal, Canada
| | - Giulio Franchini
- Department of Mechanical Engineering, McGill University, Montreal, Canada
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Maryam Tabrizian
- Department of Biomedical Engineering, McGill University, Montreal, Canada; Faculty of Dental Medicine and Oral Health Sciences, McGill University, Montreal, Canada
| | - Marco Amabili
- Department of Mechanical Engineering, McGill University, Montreal, Canada; Advanced Materials Research Center, Technology Innovation Institute (TII), Abu Dhabi, UAE.
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Sadeghinia MJ, Aguilera HM, Holzapfel GA, Urheim S, Persson RM, Ellensen VS, Haaverstad R, Skallerud B, Prot V. Mechanical Behavior and Collagen Structure of Degenerative Mitral Valve Leaflets and a Finite Element Model of Primary Mitral Regurgitation. Acta Biomater 2023; 164:269-281. [PMID: 37003496 DOI: 10.1016/j.actbio.2023.03.029] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 03/03/2023] [Accepted: 03/20/2023] [Indexed: 04/03/2023]
Abstract
Degenerative mitral valve disease is the main cause of primary mitral regurgitation with two phenotypes: fibroelastic deficiency (FED) often with localized myxomatous degeneration and diffuse myxomatous degeneration or Barlow's disease. Myxomatous degeneration disrupts the microstructure of the mitral valve leaflets, particularly the collagen fibers, which affects the mechanical behavior of the leaflets. The present study uses biaxial mechanical tests and second harmonic generation microscopy to examine the mechanical behavior of Barlow and FED tissue. Three tissue samples were harvested from a FED patient and one sample is from a Barlow patient. Then we use an appropriate constitutive model by excluding the collagen fibers under compression. Finally, we built an FE model based on the echocardiography of patients diagnosed with FED and Barlow and the characterized material model and collagen fiber orientation. The Barlow sample and the FED sample from the most affected segment showed different mechanical behavior and collagen structure compared to the other two FED samples. The FE model showed very good agreement with echocardiography with 2.02±1.8 mm and 1.05±0.79 mm point-to-mesh distance errors for Barlow and FED patients, respectively. It has also been shown that the exclusion of collagen fibers under compression provides versatility for the material model; it behaves stiff in the belly region, preventing excessive bulging, while it behaves very softly in the commissures to facilitate folding. STATEMENT OF SIGNIFICANCE: None.
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Affiliation(s)
- Mohammad Javad Sadeghinia
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
| | - Hans Martin Aguilera
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Gerhard A Holzapfel
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway; Institute of Biomechanics, Graz University of Technology, Austria
| | - Stig Urheim
- Haukeland University Hospital, Department of Heart Disease, Bergen, Norway; Institute of Clinical Science, University of Bergen, Bergen, Norway
| | - Robert Matongo Persson
- Haukeland University Hospital, Department of Heart Disease, Bergen, Norway; Institute of Clinical Science, University of Bergen, Bergen, Norway
| | | | - Rune Haaverstad
- Haukeland University Hospital, Department of Heart Disease, Bergen, Norway; Institute of Clinical Science, University of Bergen, Bergen, Norway
| | - Bjørn Skallerud
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Victorien Prot
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
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20
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Agrafiotis E, Mayer C, Grabenwöger M, Zimpfer D, Regitnig P, Mächler H, Holzapfel GA. Global and local stiffening of ex vivo-perfused stented human thoracic aortas: A mock circulation study. Acta Biomater 2023; 161:170-183. [PMID: 36849029 DOI: 10.1016/j.actbio.2023.02.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Revised: 01/25/2023] [Accepted: 02/20/2023] [Indexed: 02/27/2023]
Abstract
The effects of thoracic endovascular repair (TEVAR) on the biomechanical properties of aortic tissue have not been adequately studied. Understanding these features is important for the management of endograft-triggered complications of a biomechanical nature. This study aims to examine how stent-graft implantation affects the elastomechanical behavior of the aorta. Non-pathological human thoracic aortas (n=10) were subjected to long-standing perfusion (8h) within a mock circulation loop under physiological conditions. To quantify compliance and its mismatch in the test periods without and with a stent, the aortic pressure and the proximal cyclic circumferential displacement were measured. After perfusion, biaxial tension tests (stress-stretch) were carried out to examine the stiffness profiles between non-stented and stented tissue, followed by a histological assessment. Experimental evidence shows: (i) a significant reduction in aortic distensibility after TEVAR, indicating aortic stiffening and compliance mismatch, (ii) a stiffer behavior of the stented samples compared to the non-stented samples with an earlier entry into the nonlinear part of the stress-stretch curve and (iii) strut-induced histological remodeling of the aortic wall. The biomechanical and histological comparison of the non-stented and stented aortas provides new insights into the interaction between the stent-graft and the aortic wall. The knowledge gained could refine the stent-graft design to minimize the stent-induced impacts on the aortic wall and the resulting complications. STATEMENT OF SIGNIFICANCE: Stent-related cardiovascular complications occur the moment the stent-graft expands on the human aortic wall. Clinicians base their diagnosis on the anatomical morphology of CT scans while neglecting the endograft-triggered biomechanical events that compromise aortic compliance and wall mechanotransduction. Experimental replication of endovascular repair in cadaver aortas within a mock circulation loop may have a catalytic effect on biomechanical and histological findings without an ethical barrier. Demonstrating interactions between the stent and the wall can help clinicians make a broader diagnosis such as ECG-triggered oversizing and stent-graft characteristics based on patient-specific anatomical location and age. In addition, the results can be used to optimize towards more aortophilic stent grafts.
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Affiliation(s)
| | - Christian Mayer
- Department of Cardiac Surgery, Medical University of Graz, Austria
| | - Martin Grabenwöger
- Department of Cardiovascular Surgery, Clinic Floridsdorf, Vienna, Austria
| | - Daniel Zimpfer
- Department of Cardiac Surgery, Medical University of Graz, Austria
| | - Peter Regitnig
- Institute of Pathology, Medical University of Graz, Austria
| | - Heinrich Mächler
- Department of Cardiac Surgery, Medical University of Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria; Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
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21
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Jafarinia A, Melito GM, Müller TS, Rolf-Pissarczyk M, Holzapfel GA, Brenn G, Ellermann K, Hochrainer T. Morphological parameters affecting false lumen thrombosis following type B aortic dissection: a systematic study based on simulations of idealized models. Biomech Model Mechanobiol 2023; 22:885-904. [PMID: 36630014 PMCID: PMC10167197 DOI: 10.1007/s10237-023-01687-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Accepted: 01/02/2023] [Indexed: 01/12/2023]
Abstract
Type B aortic dissection (TBAD) carries a high risk of complications, particularly with a partially thrombosed or patent false lumen (FL). Therefore, uncovering the risk factors leading to FL thrombosis is crucial to identify high-risk patients. Although studies have shown that morphological parameters of the dissected aorta are related to FL thrombosis, often conflicting results have been reported. We show that recent models of thrombus evolution in combination with sensitivity analysis methods can provide valuable insights into how combinations of morphological parameters affect the prospect of FL thrombosis. Based on clinical data, an idealized geometry of a TBAD is generated and parameterized. After implementing the thrombus model in computational fluid dynamics simulations, a global sensitivity analysis for selected morphological parameters is performed. We then introduce dimensionless morphological parameters to scale the results to individual patients. The sensitivity analysis demonstrates that the most sensitive parameters influencing FL thrombosis are the FL diameter and the size and location of intimal tears. A higher risk of partial thrombosis is observed when the FL diameter is larger than the true lumen diameter. Reducing the ratio of the distal to proximal tear size increases the risk of FL patency. In summary, these parameters play a dominant role in classifying morphologies into patent, partially thrombosed, and fully thrombosed FL. In this study, we point out the predictive role of morphological parameters for FL thrombosis in TBAD and show that the results are in good agreement with available clinical studies.
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Affiliation(s)
- Alireza Jafarinia
- Institute of Strength of Materials, Graz University of Technology, Graz, Austria.
| | - Gian Marco Melito
- Institute of Mechanics, Graz University of Technology, Graz, Austria.
| | - Thomas Stephan Müller
- Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology, Graz, Austria
| | | | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria.,Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Günter Brenn
- Institute of Fluid Mechanics and Heat Transfer, Graz University of Technology, Graz, Austria
| | - Katrin Ellermann
- Institute of Mechanics, Graz University of Technology, Graz, Austria
| | - Thomas Hochrainer
- Institute of Strength of Materials, Graz University of Technology, Graz, Austria
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22
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Kainz MP, Greiner A, Hinrichsen J, Kolb D, Comellas E, Steinmann P, Budday S, Terzano M, Holzapfel GA. Poro-viscoelastic material parameter identification of brain tissue-mimicking hydrogels. Front Bioeng Biotechnol 2023; 11:1143304. [PMID: 37101751 PMCID: PMC10123293 DOI: 10.3389/fbioe.2023.1143304] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 03/27/2023] [Indexed: 04/28/2023] Open
Abstract
Understanding and characterizing the mechanical and structural properties of brain tissue is essential for developing and calibrating reliable material models. Based on the Theory of Porous Media, a novel nonlinear poro-viscoelastic computational model was recently proposed to describe the mechanical response of the tissue under different loading conditions. The model contains parameters related to the time-dependent behavior arising from both the viscoelastic relaxation of the solid matrix and its interaction with the fluid phase. This study focuses on the characterization of these parameters through indentation experiments on a tailor-made polyvinyl alcohol-based hydrogel mimicking brain tissue. The material behavior is adjusted to ex vivo porcine brain tissue. An inverse parameter identification scheme using a trust region reflective algorithm is introduced and applied to match experimental data obtained from the indentation with the proposed computational model. By minimizing the error between experimental values and finite element simulation results, the optimal constitutive model parameters of the brain tissue-mimicking hydrogel are extracted. Finally, the model is validated using the derived material parameters in a finite element simulation.
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Affiliation(s)
- Manuel P. Kainz
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Alexander Greiner
- Department Mechanical Engineering, Institute of Applied Mechanics, Friedrich Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Jan Hinrichsen
- Department Mechanical Engineering, Institute of Applied Mechanics, Friedrich Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Dagmar Kolb
- Center for Medical Research, Gottfried Schatz Research Center, Core Facility Ultrastructure Analysis, Medical University of Graz, Graz, Austria
- Division of Cell Biology, Histology and Embryology, Gottfried Schatz Research Center, Medical University of Graz, Graz, Austria
| | - Ester Comellas
- Department of Physics, Serra Húnter Fellow, Universitat Politècnica de Catalunya (UPC), Barcelona, Spain
| | - Paul Steinmann
- Department Mechanical Engineering, Institute of Applied Mechanics, Friedrich Alexander-University Erlangen-Nürnberg, Erlangen, Germany
- Glasgow Computational Engineering Centre, University of Glasgow, Glasgow, United Kingdom
| | - Silvia Budday
- Department Mechanical Engineering, Institute of Applied Mechanics, Friedrich Alexander-University Erlangen-Nürnberg, Erlangen, Germany
| | - Michele Terzano
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
- *Correspondence: Gerhard A. Holzapfel,
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23
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Almer G, Opriessnig P, Wolinski H, Sommer G, Diwoky C, Lechleitner M, Kolb D, Bubalo V, Brunner MS, Schwarz AN, Leitinger G, Schoiswohl G, Marsche G, Niedrist T, Schauer S, Oswald W, Groselj-Strele A, Paar M, Cvirn G, Hoefler G, Rechberger GN, Herrmann M, Frank S, Holzapfel GA, Kratky D, Mangge H, Hörl G, Tehlivets O. Deficiency of B vitamins leads to cholesterol-independent atherogenic transformation of the aorta. Biomed Pharmacother 2022; 154:113640. [PMID: 36081286 DOI: 10.1016/j.biopha.2022.113640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2022] [Revised: 08/24/2022] [Accepted: 08/30/2022] [Indexed: 11/02/2022] Open
Abstract
Atherosclerosis, the leading cause of cardiovascular disease responsible for the majority of deaths worldwide, cannot be sufficiently explained by established risk factors, including hypercholesterolemia. Elevated plasma homocysteine is an independent risk factor for atherosclerosis and is strongly linked to cardiovascular mortality. However, the role of homocysteine in atherosclerosis is still insufficiently understood. Previous research in this area has been also hampered by the lack of reproducible in vivo models of atherosclerosis that resemble the human situation. Here, we have developed and applied an automated system for vessel wall injury that leads to more homogenous damage and more pronounced atherosclerotic plaque development, even at low balloon pressure. Our automated system helped to glean vital details of cholesterol-independent changes in the aortic wall of balloon-injured rabbits. We show that deficiency of B vitamins, which are required for homocysteine degradation, leads to atherogenic transformation of the aorta resulting in accumulation of macrophages and lipids, impairment of its biomechanical properties and disorganization of aortic collagen/elastin in the absence of hypercholesterolemia. A combination of B vitamin deficiency and hypercholesterolemia leads to thickening of the aorta, decreased aortic water diffusion, increased LDL-cholesterol and impaired vascular reactivity compared to any single condition. Our findings suggest that deficiency of B vitamins leads to atherogenic transformation of the aorta even in the absence of hypercholesterolemia and aggravates atherosclerosis development in its presence.
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Affiliation(s)
- Gunter Almer
- Clinical Institute for Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Graz, Austria
| | - Peter Opriessnig
- Division of General Neurology, Department of Neurology, Medical University of Graz, Graz, Austria; Division of Pediatric Radiology, Department of Radiology, Medical University of Graz, Graz, Austria
| | - Heimo Wolinski
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Clemens Diwoky
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | - Margarete Lechleitner
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Graz, Austria
| | - Dagmar Kolb
- Gottfried Schatz Research Center, Cell Biology, Histology and Embryology, Medical University of Graz, Graz, Austria; Center for Medical Research, Ultrastructure Analysis, Medical University of Graz, Graz, Austria
| | - Vladimir Bubalo
- Division of Biomedical Research, Medical University of Graz, Graz, Austria
| | - Markus S Brunner
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | - Andreas N Schwarz
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | - Gerd Leitinger
- Gottfried Schatz Research Center, Cell Biology, Histology and Embryology, Medical University of Graz, Graz, Austria
| | - Gabriele Schoiswohl
- Institute of Molecular Biosciences, University of Graz, Graz, Austria; Department of Pharmacology and Toxicology, University of Graz, Graz, Austria
| | - Gunther Marsche
- Otto Loewi Research Center, Pharmacology, Medical University of Graz, Graz, Austria
| | - Tobias Niedrist
- Clinical Institute for Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Graz, Austria
| | - Silvia Schauer
- Diagnostic and Research Institute of Pathology, Medical University of Graz, Graz, Austria
| | - Wolfgang Oswald
- Department of Surgery, Clinical Division of Vascular Surgery, Medical University of Graz, Graz, Austria
| | - Andrea Groselj-Strele
- Center for Medical Research, Computational Bioanalytics, Medical University of Graz, Graz, Austria
| | - Margret Paar
- Otto Loewi Research Center, Division of Medicinal Chemistry, Medical University of Graz, Graz, Austria
| | - Gerhard Cvirn
- Otto Loewi Research Center, Division of Medicinal Chemistry, Medical University of Graz, Graz, Austria
| | - Gerald Hoefler
- Diagnostic and Research Institute of Pathology, Medical University of Graz, Graz, Austria
| | | | - Markus Herrmann
- Clinical Institute for Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Graz, Austria
| | - Saša Frank
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Dagmar Kratky
- Gottfried Schatz Research Center, Molecular Biology and Biochemistry, Medical University of Graz, Graz, Austria
| | - Harald Mangge
- Clinical Institute for Medical and Chemical Laboratory Diagnostics, Medical University of Graz, Graz, Austria
| | - Gerd Hörl
- Otto Loewi Research Center, Division of Medicinal Chemistry, Medical University of Graz, Graz, Austria.
| | - Oksana Tehlivets
- Institute of Molecular Biosciences, University of Graz, Graz, Austria; Division of General Radiology, Department of Radiology, Medical University of Graz, Graz, Austria.
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24
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Pukaluk A, Wolinski H, Viertler C, Regitnig P, Holzapfel GA, Sommer G. Changes in the microstructure of the human aortic medial layer under biaxial loading investigated by multi-photon microscopy. Acta Biomater 2022; 151:396-413. [PMID: 35970481 DOI: 10.1016/j.actbio.2022.08.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Revised: 07/29/2022] [Accepted: 08/08/2022] [Indexed: 11/01/2022]
Abstract
Understanding the correlation between tissue architecture, health status, and mechanical properties is essential for improving material models and developing tissue engineering scaffolds. Since structural-based material models are state of the art, there is an urgent need for experimentally obtained structural parameters. For this purpose, the medial layer of nine human abdominal aortas was simultaneously subjected to equibiaxial loading and multi-photon microscopy. At each loading interval of 0.02, collagen and elastin fibers were imaged based on their second-harmonic generation signal and two-photon excited autofluorescence, respectively. The structural alterations in the fibers were quantified using the parameters of orientation, diameter, and waviness. The results of the mechanical tests divided the sample cohort into the ruptured and non-ruptured, and stiff and non-stiff groups, which were covered by the findings from histological investigations. The alterations in structural parameters provided an explanation for the observed mechanical behavior. In addition, the waviness parameters of both collagen and elastin fibers showed the potential to serve as indicators of tissue strength. The data provided address deficiencies in current material models and bridge multiscale mechanisms in the aortic media. STATEMENT OF SIGNIFICANCE: Available material models can reproduce, but cannot predict, the mechanical behavior of human aortas. This deficiency could be overcome with the help of experimentally validated structural parameters as provided in this study. Simultaneous multi-photon microscopy and biaxial extension testing revealed the microstructure of human aortic media at different stretch levels. Changes in the arrangement of collagen and elastin fibers were quantified using structural parameters such as orientation, diameter and waviness. For the first time, structural parameters of human aortic tissue under continuous loading conditions have been obtained. In particular, the waviness parameters at the reference configuration have been associated with tissue stiffness, brittleness, and the onset of atherosclerosis.
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Affiliation(s)
- Anna Pukaluk
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Heimo Wolinski
- Institute of Molecular Biosciences, University of Graz, Austria; Field of Excellence BioHealth - University of Graz, Austria
| | | | - Peter Regitnig
- Institute of Pathology, Medical University of Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, NTNU, Trondheim, Norway
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Austria.
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25
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Pineda-Castillo SA, Aparicio-Ruiz S, Burns MM, Laurence DW, Bradshaw E, Gu T, Holzapfel GA, Lee CH. Linking the region-specific tissue microstructure to the biaxial mechanical properties of the porcine left anterior descending artery. Acta Biomater 2022; 150:295-309. [PMID: 35905825 PMCID: PMC10230544 DOI: 10.1016/j.actbio.2022.07.036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 07/14/2022] [Accepted: 07/20/2022] [Indexed: 11/16/2022]
Abstract
Coronary atherosclerosis is the main cause of death worldwide. Advancing the understanding of coronary microstructure-based mechanics is fundamental for the development of therapeutic tools and surgical procedures. Although the passive biaxial properties of the coronary arteries have been extensively explored, their regional differences and the relationship between tissue microstructure and mechanics have not been fully characterized. In this study, we characterized the passive biaxial mechanical properties and microstructural properties of the proximal, medial, and distal regions of the porcine left anterior descending artery (LADA). We also attempted to relate the biaxial stress-stretch response of the LADA and its respective birefringent responses to the polarized light for obtaining information about the load-dependent microstructural variations. We found that the LADA extensibility is reduced in the proximal-to-distal direction and that the medial region exhibits more heterogeneous mechanical behavior than the other two regions. We have also observed highly dynamic microstructural behavior where fiber families realign themselves depending on loading. In addition, we found that the microstructure of the distal region exhibited highly aligned fibers along the longitudinal axis of the artery. To verify this microstructural feature, we imaged the LADA specimens with multi-photon microscopy and observed that the adventitia microstructure transitioned from a random fiber network in the proximal region to highly aligned fibers in the distal region. Our findings could offer new perspectives for understanding coronary mechanics and aid in the development of tissue-engineered vascular grafts, which are currently limited due to their mismatch with native tissue in terms of mechanical properties and microstructural features. STATEMENT OF SIGNIFICANCE: The tissue biomechanics of coronary arteries is fundamental for the development of revascularization techniques such as coronary artery bypass. These therapeutics require a deep understanding of arterial mechanics, microstructure, and mechanobiology to prevent graft failure and reoperation. The present study characterizes the unique regional mechanical and microstructural properties of the porcine left anterior descending artery using biaxial testing, polarized-light imaging, and confocal microscopy. This comprehensive characterization provides an improved understanding of the collagen/elastin architecture in response to mechanical loads using a region-specific approach. The unique tissue properties obtained from this study will provide guidance for the selection of anastomotic sites in coronary artery bypass grafting and for the design of tissue-engineered vascular grafts.
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Affiliation(s)
- Sergio A Pineda-Castillo
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA; Stephenson School of Biomedical Engineering, The University of Oklahoma, USA
| | - Santiago Aparicio-Ruiz
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Madison M Burns
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Devin W Laurence
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Elizabeth Bradshaw
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA
| | - Tingting Gu
- Samuel Roberts Noble Microscopy Laboratory, The University of Oklahoma, USA
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Norway
| | - Chung-Hao Lee
- Biomechanics and Biomaterials Design Lab, School of Aerospace and Mechanical Engineering, The University of Oklahoma, USA.
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26
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Bernecker C, Lima M, Kolesnik T, Lampl A, Ciubotaru C, Leita R, Kolb D, Fröhlich E, Schlenke P, Holzapfel GA, Dorn I, Cojoc D. Biomechanical properties of native and cultured red blood cells–Interplay of shape, structure and biomechanics. Front Physiol 2022; 13:979298. [PMID: 36051915 PMCID: PMC9424772 DOI: 10.3389/fphys.2022.979298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 07/25/2022] [Indexed: 11/13/2022] Open
Abstract
Modern medicine increases the demand for safe blood products. Ex vivo cultured red blood cells (cRBC) are eagerly awaited as a standardized, safe source of RBC. Established culture models still lack the terminal cytoskeletal remodeling from reticulocyte to erythrocyte with changes in the biomechanical properties and interacts with membrane stiffness, viscosity of the cytoplasm and the cytoskeletal network. Comprehensive data on the biomechanical properties of cRBC are needed to take the last step towards translation into clinical use in transfusion medicine. Aim of the study was the comparative analysis of topographical and biomechanical properties of cRBC, generated from human CD34+ adult hematopoietic stem/progenitor cells, with native reticulocytes (nRET) and erythrocytes (nRBC) using cell biological and biomechanical technologies. To gain the desired all-encompassing information, a single method was unsatisfactory and only the combination of different methods could lead to the goal. Topographical information was matched with biomechanical data from optical tweezers (OT), atomic force microscopy (AFM) and digital holographic microscopy (DHM). Underlying structures were investigated in detail. Imaging, deformability and recovery time showed a high similarity between cRBC and nRBC. Young’s modulus and plasticity index also confirmed this similarity. No significant differences in membrane and cytoskeletal proteins were found, while lipid deficiency resulted in spherical, vesiculated cells with impaired biomechanical functionality. The combination of techniques has proven successful and experiments underscore a close relationship between lipid content, shape and biomechanical functionality of RBC.
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Affiliation(s)
- Claudia Bernecker
- Department for Blood Group Serology and Transfusion Medicine, Medical University of Graz, Graz, Austria
| | - Maria Lima
- CNR-IOM, National Research Council of Italy - Institute of Materials, Trieste, Italy
- University of Trieste, Physics Department, Trieste, Italy
| | - Tatjana Kolesnik
- Core Facility Imaging, Center for Medical Research, Medical University of Graz, Graz, Austria
| | - Annika Lampl
- Department for Blood Group Serology and Transfusion Medicine, Medical University of Graz, Graz, Austria
| | - Catalin Ciubotaru
- CNR-IOM, National Research Council of Italy - Institute of Materials, Trieste, Italy
| | - Riccardo Leita
- CNR-IOM, National Research Council of Italy - Institute of Materials, Trieste, Italy
| | - Dagmar Kolb
- Core Facility Ultrastructure Analysis, Center for Medical Research, Medical University of Graz, Graz, Austria
- Gottfried Schatz Research Center for Cell Signaling, Metabolism and Aging, Division of Cell Biology, Histology and Embryology, Medical University of Graz, Graz, Austria
| | - Eleonore Fröhlich
- Core Facility Imaging, Center for Medical Research, Medical University of Graz, Graz, Austria
| | - Peter Schlenke
- Department for Blood Group Serology and Transfusion Medicine, Medical University of Graz, Graz, Austria
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Isabel Dorn
- Department for Blood Group Serology and Transfusion Medicine, Medical University of Graz, Graz, Austria
- *Correspondence: Dan Cojoc, ; Isabel Dorn,
| | - Dan Cojoc
- CNR-IOM, National Research Council of Italy - Institute of Materials, Trieste, Italy
- *Correspondence: Dan Cojoc, ; Isabel Dorn,
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27
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Dalbosco M, Carniel TA, Fancello EA, Holzapfel GA. Multiscale simulations suggest a protective role of neo-adventitia in abdominal aortic aneurysms. Acta Biomater 2022; 146:248-258. [PMID: 35526737 DOI: 10.1016/j.actbio.2022.04.049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Revised: 04/22/2022] [Accepted: 04/28/2022] [Indexed: 11/01/2022]
Abstract
Abdominal aortic aneurysms (AAAs) are a dangerous cardiovascular disease, the pathogenesis of which is not yet fully understood. In the present work a recent mechanopathological theory, which correlates AAA progression with microstructural and mechanical alterations in the tissue, is investigated using multiscale models. The goal is to combine these changes, within the framework of mechanobiology, with possible mechanical cues that are sensed by vascular cells along the AAA pathogenesis. Particular attention is paid to the formation of a 'neo-adventitia' on the abluminal side of the aortic wall, which is characterized by a highly random (isotropic) distribution of collagen fibers. Macro- and micro-scale results suggest that the formation of an AAA, as expected, perturbs the micromechanical state of the aortic tissue and triggers a growth and remodeling (G&R) reaction by mechanosensing cells such as fibroblasts. This G&R then leads to the formation of a thick neo-adventitia that appears to bring the micromechanical state of the tissue closer to the original homeostatic level. In this context, this new layer could act like a protective sheath, similar to the tunica adventitia in healthy aortas. This potential 'attempt at healing' by vascular cells would have important implications on the stability of the AAA wall and thus on the risk of rupture. STATEMENT OF SIGNIFICANCE: Current clinical criteria for risk assessment in AAAs are still empirical, as the causes and mechanisms of the disease are not yet fully understood. The strength of the arterial tissue is closely related to its microstructure, which in turn is remodeled by mechanosensing cells in the course of the disease. In this study, multiscale simulations show a possible connection between mechanical cues at the microscopic level and collagen G&R in AAA tissue. It should be emphasized that these micromechanical cues cannot be visualized in vivo. Therefore, the results presented here will help to advance our current understanding of the disease and motivate future experimental studies, with important implications for AAA risk assessment.
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28
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Niestrawska JA, Pukaluk A, Babu AR, Holzapfel GA. Differences in Collagen Fiber Diameter and Waviness between Healthy and Aneurysmal Abdominal Aortas. Microsc Microanal 2022; 28:1-15. [PMID: 35545876 DOI: 10.1017/s1431927622000629] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Collagen plays a key role in the strength of aortic walls, so studying micro-structural changes during disease development is critical to better understand collagen reorganization. Second-harmonic generation microscopy is used to obtain images of human aortic collagen in both healthy and diseased states. Methods are being developed in order to efficiently determine the waviness, that is, tortuosity and amplitude, as well as the diameter, orientation, and dispersion of collagen fibers, and bundles in healthy and aneurysmal tissues. The results show layer-specific differences in the collagen of healthy tissues, which decrease in samples of aneurysmal aortic walls. In healthy tissues, the thick collagen bundles of the adventitia are characterized by greater waviness, both in the tortuosity and in the amplitude, compared to the relatively thin and straighter collagen fibers of the media. In contrast, most aneurysmal tissues tend to have a more uniform structure of the aortic wall with no significant difference in collagen diameter between the luminal and abluminal layers. An increase in collagen tortuosity compared to the healthy media is also observed in the aneurysmal luminal layer. The data set provided can help improve related material and multiscale models of aortic walls and aneurysm formation.
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Affiliation(s)
- Justyna A Niestrawska
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16, 8010Graz, Austria
| | - Anna Pukaluk
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16, 8010Graz, Austria
| | - Anju R Babu
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16, 8010Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16, 8010Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), 7491Trondheim, Norway
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29
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Zhang W, Sommer G, Niestrawska JA, Holzapfel GA, Nordsletten D. The effects of viscoelasticity on residual strain in aortic soft tissues. Acta Biomater 2022; 140:398-411. [PMID: 34823042 DOI: 10.1016/j.actbio.2021.11.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 11/14/2021] [Accepted: 11/15/2021] [Indexed: 11/15/2022]
Abstract
Residual stress is thought to play a critical role in modulating stress distributions in soft biological tissues and in maintaining the mechanobiological stress environment of cells. Residual stresses in arteries and other tissues are classically assessed through opening angle experiments, which demonstrate the continuous release of residual stresses over hours. These results are then assessed through nonlinear biomechanical models to provide estimates of the residual stresses in the intact state. Although well studied, these analyses typically focus on hyperelastic material models despite significant evidence of viscoelastic phenomena over both short and long timescales. In this work, we extended the state-of-the-art structural tensor model for arterial tissues from Holzapfel and Ogden for fractional viscoelasticity. Models were tuned to capture consistent levels of hysteresis observed in biaxial experiments, while also minimizing the fractional viscoelastic weighting and opening angles to correctly capture opening angle dynamics. Results suggest that a substantial portion of the human abdominal aorta is viscoelastic, but exhibits a low fractional order (i.e. more elastically). Additionally, a significantly larger opening angle in the fully unloaded state is necessary to produce comparable hysteresis in biaxial testing. As a consequence, conventional estimates of residual stress using hyperelastic approaches over-estimate their viscoelastic counterparts by a factor of 2. Thus, a viscoelastic approach, such as the one illustrated in this study, in combination with an additional source of rate-controlled viscoelastic data is necessary to accurately analyze the residual stress distribution in soft biological tissues. STATEMENT OF SIGNIFICANCE: Residual stress plays a crucial role in achieving a homeostatic stress environment in soft biological tissues. However, the analysis of residual stress typically focuses on hyperelastic material models despite evidence of viscoelastic behavior. This work is the first attempt at analyzing the effects of viscoelasticity on residual stress. The application of viscoelasticity was crucial for producing realistic opening dynamics in arteries. The overall residual stresses were estimated to be 50% less than those from using hyperelastic material models, while the opening angles were projected to be 25% more than those measured after 16 hours, suggesting underestimated residual strain. This study highlights the importance viscoelasticity in the analysis of residual stress even in weakly dissipative materials like the human aorta.
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Affiliation(s)
- Will Zhang
- Department of Biomedical Engineering, University of Michigan, North Campus Research Center, Building 20, 2800 Plymouth Rd, Ann Arbor 48109, USA.
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, AT, Austria
| | - Justyna A Niestrawska
- Gottfried Schatz Research Center, Division of Macroscopic and Clinical Anatomy, Medical University of Graz, Harrachgasse 21, 8010 Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, AT, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, NO, Norway
| | - David Nordsletten
- Division of Biomedical Engineering and Imaging Sciences, Department of Biomedical Engineering, King's College London, UK; Departments of Biomedical Engineering and Cardiac Surgery, University of Michigan, Ann Arbor, USA
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Nordsletten D, Capilnasiu A, Zhang W, Wittgenstein A, Hadjicharalambous M, Sommer G, Sinkus R, Holzapfel GA. A viscoelastic model for human myocardium. Acta Biomater 2021; 135:441-457. [PMID: 34487858 DOI: 10.1016/j.actbio.2021.08.036] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 08/22/2021] [Accepted: 08/24/2021] [Indexed: 01/06/2023]
Abstract
Understanding the biomechanics of the heart in health and disease plays an important role in the diagnosis and treatment of heart failure. The use of computational biomechanical models for therapy assessment is paving the way for personalized treatment, and relies on accurate constitutive equations mapping strain to stress. Current state-of-the art constitutive equations account for the nonlinear anisotropic stress-strain response of cardiac muscle using hyperelasticity theory. While providing a solid foundation for understanding the biomechanics of heart tissue, most current laws neglect viscoelastic phenomena observed experimentally. Utilizing experimental data from human myocardium and knowledge of the hierarchical structure of heart muscle, we present a fractional nonlinear anisotropic viscoelastic constitutive model. The model is shown to replicate biaxial stretch, triaxial cyclic shear and triaxial stress relaxation experiments (mean error ∼7.68%), showing improvements compared to its hyperelastic (mean error ∼24%) counterparts. Model sensitivity, fidelity and parameter uniqueness are demonstrated. The model is also compared to rate-dependent biaxial stretch as well as different modes of biaxial stretch, illustrating extensibility of the model to a range of loading phenomena. STATEMENT OF SIGNIFICANCE: The viscoelastic response of human heart tissues has yet to be integrated into common constitutive models describing cardiac mechanics. In this work, a fractional viscoelastic modeling approach is introduced based on the hierarchical structure of heart tissue. From these foundations, the current state-of-the-art biomechanical models of the heart muscle are transformed using fractional viscoelasticity, replicating passive muscle function across multiple experimental tests. Comparisons are drawn with current models to highlight the improvements of this approach and predictive responses show strong qualitative agreement with experimental data. The proposed model presents the first constitutive model aimed at capturing viscoelastic nonlinear response across multiple testing regimes, providing a platform for better understanding the biomechanics of myocardial tissue in health and disease.
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Affiliation(s)
- David Nordsletten
- Division of Biomedical Engineering and Imaging Sciences, Department of Biomedical Engineering, King's College London, UK; Departments of Biomedical Engineering and Cardiac Surgery, University of Michigan, North Campus Research Center, Building 20, 2800 Plymouth Rd, Ann Arbor 48109, MI, USA.
| | - Adela Capilnasiu
- Division of Biomedical Engineering and Imaging Sciences, Department of Biomedical Engineering, King's College London, UK
| | - Will Zhang
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, USA
| | - Anna Wittgenstein
- Division of Biomedical Engineering and Imaging Sciences, Department of Biomedical Engineering, King's College London, UK
| | | | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Austria
| | - Ralph Sinkus
- Division of Biomedical Engineering and Imaging Sciences, Department of Biomedical Engineering, King's College London, UK; Inserm U1148, LVTS, University Paris Diderot, University Paris 13, Paris, France
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
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Ross CJ, Laurence DW, Echols AL, Babu AR, Gu T, Duginski GA, Johns CH, Mullins BT, Casey KM, Laurence KA, Zhao YD, Amini R, Fung KM, Mir A, Burkhart HM, Wu Y, Holzapfel GA, Lee CH. Effects of enzyme-based removal of collagen and elastin constituents on the biaxial mechanical responses of porcine atrioventricular heart valve anterior leaflets. Acta Biomater 2021; 135:425-440. [PMID: 34481053 DOI: 10.1016/j.actbio.2021.08.043] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 08/22/2021] [Accepted: 08/26/2021] [Indexed: 12/24/2022]
Abstract
The leaflets of the atrioventricular heart valves (AHVs) regulate the one-directional flow of blood through a coordination of the extracellular matrix components, including the collagen fibers, elastin, and glycosaminoglycans. Dysfunction of the AHVs, such as those caused by unfavorable microstructural remodeling, lead to valvular heart diseases and improper blood flow, which can ultimately cause heart failure. In order to better understand the mechanics and remodeling of the AHV leaflets and how therapeutics can inadvertently cause adverse microstructural changes, a systematic characterization of the role of each constituent in the biomechanical properties is appropriate. Previous studies have quantified the contributions of the individual microstructural components to tissue-level behavior for the semilunar valve cusps, but not for the AHV leaflets. In this study, for the first time, we quantify the relationships between microstructure and mechanics of the AHV leaflet using a three-step experimental procedure: (i) biaxial tension and stress relaxation testing of control (untreated) porcine AHV anterior leaflet specimens; (ii) enzyme treatment to remove a portion of either the collagen or elastin constituent; and (iii) biaxial tensile and stress relaxation testing of the constituent-removed (treated) specimens. We have observed that the removal of ∼100% elastin resulted in a ∼10% decrease in the tissue extensibility with biaxial tension and a ∼10% increase in the overall stress reduction with stress relaxation. In contrast, removal of 46% of the collagen content insignificantly affected tissue extensibility with biaxial tension and significantly increased stress decay (10%) with stress relaxation. These findings provide an insight into the microstructure-mechanics relationship of the AHVs and will be beneficial for future developments and refinements of microstructurally informed constitutive models for the simulation of diseased and surgically intervened AHV function. STATEMENT OF SIGNIFICANCE: This study presents, for the first time, a thorough mechanical characterization of the atrioventricular heart valve leaflets before and after enzymatic removal of elastin and collagen. We found that the biaxial tensile properties of elastin-deficient tissues and collagen-deficient are stiffer. The fact of elastin supporting low-stress valve function and collagen as the main load-bearing component was evident in a decrease in the low-tension modulus for elastin-deficient tissues and in the high-tension modulus for collagen-deficient tissues. Our quantification and experimental technique could be useful in predicting the disease-related changes in heart valve mechanics. The information obtained from this work is valuable for refining the constitutive models that describe the essential microstructure-mechanics relationship.
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Rolf-Pissarczyk M, Wollner MP, Pacheco DRQ, Holzapfel GA. Efficient computational modelling of smooth muscle orientation and function in the aorta. Proc Math Phys Eng Sci 2021. [DOI: 10.1098/rspa.2021.0592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Understanding the mechanical effects of smooth muscle cell (SMC) contraction on the initiation and the propagation of cardiovascular diseases such as aortic dissection is critical. Framed by elastic lamellar sheets in the lamellar unit, there are SMCs in the media with a distinct radial tilt, which indicates their contribution to the radial strength. However, the mechanical effects of this type of anisotropy have not been fully discussed. Therefore, in this study, we propose a constitutive framework that models the passive and active mechanics of the aorta, taking into account the dispersed nature of the aortic constituents by applying the discrete fibre dispersion method. We suggest an isoparametric approach by evaluating various numerical integration methods and introducing a non-uniform discretization of the unit hemisphere to increase its computational efficiency. Finally, the constitutive parameters are fitted to layer-specific experimental data and initial computational results are briefly presented. The radial tilt of SMCs is also analysed, which has a noticeable influence on the mechanical behaviour of the aorta. In the absence of sufficient experimental data, the results indicate that the active contribution of SMCs has a remarkable impact on the mechanics of the healthy aorta.
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Affiliation(s)
| | - Maximilian P. Wollner
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Institute for Solid Mechanics, Dresden University of Technology, Dresden, Germany
| | | | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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Amabili M, Asgari M, Breslavsky ID, Franchini G, Giovanniello F, Holzapfel GA. Microstructural and mechanical characterization of the layers of human descending thoracic aortas. Acta Biomater 2021; 134:401-421. [PMID: 34303867 DOI: 10.1016/j.actbio.2021.07.036] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2021] [Revised: 07/10/2021] [Accepted: 07/15/2021] [Indexed: 12/13/2022]
Abstract
The mechanical properties of human aortas are linked to the layered tissue and its microstructure at different length scales. Each layer has specific mechanical and structural properties. While the ground substance and the elastin play an important role in tissue stiffness at small strain, collagen fibers carry most of the load at larger strains, which corresponds to the physiological conditions of the aorta at maximum pulsatile blood pressure. In fact, collagen fibers are crimped in the unloaded state. Collagen fibers show different orientation distributions when they are observed in a plane that is tangent to the aortic wall (in-plane section) or along a direction orthogonal to it (out-of-plane section). This was systematically investigated using large images (2500 × 2500 µm) with high resolution obtained by second harmonic generation (SHG) in order to homogenize tissue heterogeneity after a convergence analysis, which is a main goal of the study. In addition, collagen fibers show lateral interactions due to entanglements and the presence of transverse elastin fibers, observed on varying length scales using atomic force microscopy and a three-dimensional rendering obtained by stacking a sequence of SHG and two-photon fluorescence images; this is another important contribution. Human descending thoracic aortas from 13 heartbeat donors aged 28 to 66 years were examined. Uniaxial tensile tests were carried out on the longitudinal and circumferential strips of the aortic wall and the three separated layers (intima, media and adventitia). A structurally-motivated material model with (i) a term to describe the combined response of ground substance and elastin and (ii) terms to consider four families of collagen fibers with different directions was applied. The exclusion of compressed fibers was implemented in the fitting process of the experimental data, which was optimized by a genetic algorithm. The results show that a single fiber family with directional and dispersion parameters measured from SHG images can describe the mechanical response of all 39 layers (3 layers for each of the 13 aortas) with very good accuracy when a second (auxiliary) family of aligned fibers is introduced in the orthogonal direction to account for lateral fiber interaction. Indeed, all observed distributions of collagen directions can be accurately fitted by a single bivariate von Mises distribution. Statistical analysis of in-plane and out-of-plane dispersion of fiber orientations reveals structural differences between the three layers and a change of collagen dispersion parameters with age. STATEMENT OF SIGNIFICANCE: The stiffness of healthy young aortas is adjusted so that a diameter expansion of about 10 % is possible during the heartbeat. This creates the Windkessel effect, which smooths out the pulsating nature of blood flow and benefits organ perfusion. The specific elastic properties of the aorta that are required to achieve this effect are related to the microstructure of the aortic tissue at different length scales. An increase in the aortic stiffness, in addition to reducing cyclic expansion and worsening perfusion, is a risk factor for clinical hypertension. The present study relates the microstructure of healthy human aortas to the mechanical response and examines the changes in microstructural parameters with age, which is a key factor in increasing stiffness.
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Agrafiotis E, Geith MA, Golkani MA, Hergesell V, Sommer G, Spiliopoulos S, Holzapfel GA. An active approach of pressure waveform matching for stress-based testing of arteries. Artif Organs 2021; 45:1562-1575. [PMID: 34519059 PMCID: PMC9292962 DOI: 10.1111/aor.14064] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 08/11/2021] [Accepted: 08/30/2021] [Indexed: 01/04/2023]
Abstract
BACKGROUND Arterial compliance assists the cardiovascular system with three key roles: (i) storing up to 50% of the stroke volume; (ii) ensuring blood flow during diastole; (iii) dampening pressure oscillations through arterial distension. In mock circulation loops (MCLs), arterial compliance was simulated either with membrane, spring, or Windkessel chambers. Although they have been shown to be suitable for cardiac device testing, their passive behavior can limit stress-based testing of arteries. Here we present an active compliance chamber with a feedback control of variable compliance as part of an MCL designed for biomechanical evaluation of arteries under physiological waveforms. MATERIALS AND METHODS The chamber encloses a piston that changes the volume via a cascaded controller when there is a difference between the real-time pressure and the physiological reference pressure with the aim to equilibrate both pressures. RESULTS The experimental results showed repeatable physiological waveforms of aortic pressure in health (80-120 mm Hg), systemic hypertension (90-153 mm Hg), and heart failure reduced ejection fraction (78-108 mm Hg). Statistical validation (n = 20) of the function of the chamber is presented against compared raw data. CONCLUSION We demonstrate that the active compliance chamber can track the actual pressure of the MCL and balance it in real time (every millisecond) with the reference values in order to shape the given pressure waveform. The active compliance chamber is an advanced tool for MCL applications for biomechanical examination of stented arteries and for preclinical evaluation of vascular implants.
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Affiliation(s)
| | - Markus A Geith
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Mohammad A Golkani
- Institute of Automation and Control, Graz University of Technology, Graz, Austria
| | - Vera Hergesell
- Department of Cardiac Surgery, Medical University of Graz, Graz, Austria
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | | | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria.,Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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Abstract
The constitutive modelling of soft biological tissues has rapidly gained attention over the last 20 years. Current constitutive models can describe the mechanical properties of arterial tissue. Predicting these properties from microstructural information, however, remains an elusive goal. To address this challenge, we are introducing a novel hybrid modelling framework that combines advanced theoretical concepts with deep learning. It uses data from mechanical tests, histological analysis and images from second-harmonic generation. In this first proof of concept study, our hybrid modelling framework is trained with data from 27 tissue samples only. Even such a small amount of data is sufficient to be able to predict the stress–stretch curves of tissue samples with a median coefficient of determination of R2 = 0.97 from microstructural information, as long as one limits the scope to tissue samples whose mechanical properties remain in the range commonly encountered. This finding suggests that deep learning could have a transformative impact on the way we model the constitutive properties of soft biological tissues.
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Affiliation(s)
- Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2, 8010 Graz, Austria.,Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Kevin Linka
- Institute for Continuum and Material Mechanics, Hamburg University of Technology, Eißendorfer Straße 42, 21073 Hamburg, Germany
| | - Selda Sherifova
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2, 8010 Graz, Austria
| | - Christian J Cyron
- Institute for Continuum and Material Mechanics, Hamburg University of Technology, Eißendorfer Straße 42, 21073 Hamburg, Germany.,Institute of Material Systems Modeling, Helmholtz-Zentrum Hereon, Max-Planck-Straße 1, 21502 Geesthacht, Germany
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Franchini G, Breslavsky ID, Holzapfel GA, Amabili M. Viscoelastic characterization of human descending thoracic aortas under cyclic load. Acta Biomater 2021; 130:291-307. [PMID: 34082105 DOI: 10.1016/j.actbio.2021.05.025] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 05/21/2021] [Accepted: 05/26/2021] [Indexed: 12/20/2022]
Abstract
Experiments were carried out on 15 human descending thoracic aortas from heart-beating healthy donors who donated organs for transplant. The aortas were kept refrigerated in organ preservation solution and tested were completed within 48 hours from explant. Donors' age was comprised between 25 and 70 years, with an average of 51.7 ± 12.8 years. Quasi-static and dynamic uniaxial tensile test were carried out in thermally controlled physiological saline solution in order to characterize the viscoelastic behavior. Strips were tested under harmonic deformation of different frequency, between 1 and 11 Hz, at three initial pre-stretches. Cyclic deformations of two different amplitudes were used: a physiological one and a small one, the latter one for comparison purposes to understand the accuracy limits of viscoelastic models. Aortic strips in circumferential and longitudinal directions were cut from each aorta. Some strips were dissected to separate the three layers: intima, media and adventitia. They were tested individually in order to obtain layer-specific data. However, strips of the intact wall were also tested. Therefore, 8 strips per donors were tested. Viscoelastic parameters are accurately evaluated from the hysteresis loops. Results show that small-amplitude cyclic strain over-estimate the storage modulus and under-estimate the loss-factor. Therefore, cyclic deformation of physiological amplitude is necessary to obtain correct viscoelastic data of aortic tissue. The value of the applied pre-stretch is significant on the dynamic stiffness ratio (storage modulus divided by the corresponding quasi-static stiffness), while it is less significant for the loss factor. The median of the dynamic stiffness ratios, in physiological conditions, varies between 1.14 and 1.33 for the different layers and the intact wall; the corresponding median of the loss factors varies between 0.050 and 0.066. The lowest dynamic stiffness ratios and loss factors were obtained from donors of the youngest age group. STATEMENT OF SIGNIFICANCE: There is an increasing interest in replacing traditional Dacron grafts used to repair thoracic aortas after acute dissection and aneurysm, with grafts in innovative biomaterials that mimic the mechanical properties and the dynamic behavior of the aorta. The human aorta is a complex laminated structure with hyperelastic and viscoelastic material properties and residual stresses. This study aims to characterize the nonlinear viscoelastic properties of ex-vivo human descending thoracic aortas by measuring hysteresis loops of physiological amplitude under harmonic strain. Results show the necessity to characterize the viscoelastic material properties of the aorta under physiological conditions, as well as the necessity to introduce improved models that take better into account the influence of the initial pre-stretch and amplitude of the cyclic load.
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Affiliation(s)
- Giulio Franchini
- Department of Mechanical Engineering, McGill University, Montreal, Canada
| | - Ivan D Breslavsky
- Department of Mechanical Engineering, McGill University, Montreal, Canada
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway
| | - Marco Amabili
- Department of Mechanical Engineering, McGill University, Montreal, Canada; Dipartimento di Ingegneria e Architettura, University of Parma, Parma, Italy.
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Haspinger DC, Klinge S, Holzapfel GA. Numerical analysis of the impact of cytoskeletal actin filament density alterations onto the diffusive vesicle-mediated cell transport. PLoS Comput Biol 2021; 17:e1008784. [PMID: 33939706 PMCID: PMC8130967 DOI: 10.1371/journal.pcbi.1008784] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 05/18/2021] [Accepted: 02/09/2021] [Indexed: 11/21/2022] Open
Abstract
The interior of a eukaryotic cell is a highly complex composite material which consists of water, structural scaffoldings, organelles, and various biomolecular solutes. All these components serve as obstacles that impede the motion of vesicles. Hence, it is hypothesized that any alteration of the cytoskeletal network may directly impact or even disrupt the vesicle transport. A disruption of the vesicle-mediated cell transport is thought to contribute to several severe diseases and disorders, such as diabetes, Parkinson’s and Alzheimer’s disease, emphasizing the clinical relevance. To address the outlined objective, a multiscale finite element model of the diffusive vesicle transport is proposed on the basis of the concept of homogenization, owed to the complexity of the cytoskeletal network. In order to study the microscopic effects of specific nanoscopic actin filament network alterations onto the vesicle transport, a parametrized three-dimensional geometrical model of the actin filament network was generated on the basis of experimentally observed filament densities and network geometries in an adenocarcinomic human alveolar basal epithelial cell. Numerical analyzes of the obtained effective diffusion properties within two-dimensional sampling domains of the whole cell model revealed that the computed homogenized diffusion coefficients can be predicted statistically accurate by a simple two-parameter power law as soon as the inaccessible area fraction, due to the obstacle geometries and the finite size of the vesicles, is known. This relationship, in turn, leads to a massive reduction in computation time and allows to study the impact of a variety of different cytoskeletal alterations onto the vesicle transport. Hence, the numerical simulations predicted a 35% increase in transport time due to a uniformly distributed four-fold increase of the total filament amount. On the other hand, a hypothetically reduced expression of filament cross-linking proteins led to sparser filament networks and, thus, a speed up of the vesicle transport. Many vital processes in our eukaryotic cells and organs require an astonishingly precise routing of intermediate products to various intra- and extracellular destinations using vesicles as transporters. This can be illustrated by numerous examples, such as the production and destruction of proteins, the export of neurotransmitters or insulin to the extracellular domain, etc. However, the inside of a cell is tightly packed with numerous structural scaffoldings (filaments), which serve as obstacles and impede the vesicle motion. It is thought that any disturbances of the vesicle-mediated cell transport contribute to numerous degenerative diseases and disorders, which highlights the clinical relevance for investigating this intracellular transport mechanism by developing computational models and performing experimental studies. In this study, we numerically quantified how different specific alterations of the filament density inside a human lung cell—due to changed mechanical loadings or genetic disorders of proteins being responsible for filament branching—affect the diffusion of vesicles inside the intracellular fluid. Therefore, based on the concept of homogenization, a computationally efficient numerical method was developed and utilized to simulate the diffusion of vesicles inside the whole cell, considering the detailed structural information of the filament network.
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Affiliation(s)
| | - Sandra Klinge
- Chair of Structural Mechanics and Analysis, TU Berlin, Berlin, Germany
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Faculty of Engineering Science and Technology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
- * E-mail:
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Saxena AK, Biro E, Sommer G, Holzapfel GA. Esophagus stretch tests: Biomechanics for tissue engineering and possible implications on the outcome of esophageal atresia repairs performed under excessive tension. Esophagus 2021; 18:346-352. [PMID: 32816188 DOI: 10.1007/s10388-020-00769-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Accepted: 08/13/2020] [Indexed: 02/03/2023]
Abstract
BACKGROUND Esophageal biomechanical studies are important to understand structural changes resulting from stretches during repair of esophageal atresias as well as to obtain values to compare with the biomechanics of tissue-engineered esophagus in the future. This study aimed to investigate light microscopic changes after uniaxial stretching of the ovine esophagus. METHODS In vitro uniaxial stretching was performed on esophagi (n = 20) of 1-month-old lambs within 4-6 h post-mortem. Esophagi were divided into 5 groups: control and stretched (1.1, 1.2, 1.3 and 1.4). Force and lengthening were measured with 5 cycles performed on every specimen using a PBS organ bath at 37 °C. Histological studies were performed on the 5 groups. RESULTS Low forces of ~ 2 N (N) were sufficient for a 1.2-1.25 stretch in the 1st cycle, whereas a three times higher force (~ 6 N) was needed for a stretch of 1.3. In the 2nd to 5th cycle, the tissue weakened and a force of ~ 3 N was sufficient for a stretch of 1.3. Histologically, in the 1.3-1.4 stretch groups, rupture of muscle fibers and capillaries were observed, respectively. Changes in mucosa and collagen fibers could not be observed. CONCLUSIONS These results offer norm values from the native esophagus to compare with the biomechanics of future tissue-engineered esophagus. Esophageal stretching > 1.3 leads to tears in muscle fibers and to rupture of capillaries. These findings can explain the decrease in microcirculation and scarring in mobilized tissue and possibly offer clues to impaired motility in esophagus atresias repaired under excessive tension.
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Affiliation(s)
- Amulya K Saxena
- Department of Pediatric Surgery, Chelsea Children's Hospital, Chelsea and Westminster Hospital NHS Fdn Trust, Imperial College London, 369 Fulham Road, London, SW10 9NH, UK.
| | - Ede Biro
- Department of Pediatric Surgery, Medical University of Pecs, Pecs, Hungary
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria.,Norwegian University of Science and Technology, Trondheim, Norway
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Laurence DW, Homburg H, Yan F, Tang Q, Fung KM, Bohnstedt BN, Holzapfel GA, Lee CH. A pilot study on biaxial mechanical, collagen microstructural, and morphological characterizations of a resected human intracranial aneurysm tissue. Sci Rep 2021; 11:3525. [PMID: 33568740 PMCID: PMC7876029 DOI: 10.1038/s41598-021-82991-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2020] [Accepted: 01/25/2021] [Indexed: 02/08/2023] Open
Abstract
Intracranial aneurysms (ICAs) are focal dilatations that imply a weakening of the brain artery. Incidental rupture of an ICA is increasingly responsible for significant mortality and morbidity in the American’s aging population. Previous studies have quantified the pressure-volume characteristics, uniaxial mechanical properties, and morphological features of human aneurysms. In this pilot study, for the first time, we comprehensively quantified the mechanical, collagen fiber microstructural, and morphological properties of one resected human posterior inferior cerebellar artery aneurysm. The tissue from the dome of a right posterior inferior cerebral aneurysm was first mechanically characterized using biaxial tension and stress relaxation tests. Then, the load-dependent collagen fiber architecture of the aneurysm tissue was quantified using an in-house polarized spatial frequency domain imaging system. Finally, optical coherence tomography and histological procedures were used to quantify the tissue’s microstructural morphology. Mechanically, the tissue was shown to exhibit hysteresis, a nonlinear stress-strain response, and material anisotropy. Moreover, the unloaded collagen fiber architecture of the tissue was predominantly aligned with the testing Y-direction and rotated towards the X-direction under increasing equibiaxial loading. Furthermore, our histological analysis showed a considerable damage to the morphological integrity of the tissue, including lack of elastin, intimal thickening, and calcium deposition. This new unified characterization framework can be extended to better understand the mechanics-microstructure interrelationship of aneurysm tissues at different time points of the formation or growth. Such specimen-specific information is anticipated to provide valuable insight that may improve our current understanding of aneurysm growth and rupture potential.
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Affiliation(s)
- Devin W Laurence
- Biomechanics and Biomaterials Design Laboratory (BBDL), School of Aerospace and Mechanical Engineering, The University of Oklahoma, 865 Asp Ave., Felgar Hall 219C, Norman, 73019, USA
| | - Hannah Homburg
- Department of Neurosurgery, The University of Oklahoma Health Sciences Center, Oklahoma City, 73104, USA
| | - Feng Yan
- Biophotonic Imaging Laboratory, Stephenson School of Biomedical Engineering, The University of Oklahoma, Norman, 73019, USA
| | - Qinggong Tang
- Biophotonic Imaging Laboratory, Stephenson School of Biomedical Engineering, The University of Oklahoma, Norman, 73019, USA
| | - Kar-Ming Fung
- Department of Pathology, The University of Oklahoma Health Sciences Center, Oklahoma City, 73104, USA.,Stephenson Cancer Center, The University of Oklahoma Health Sciences Center, Oklahoma City, 73104, USA
| | - Bradley N Bohnstedt
- Department of Neurological Surgery, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, 8010, Graz, Austria.,Department of Structural Engineering, Norwegian University of Science and Technology, 7491, Trondheim, Norway
| | - Chung-Hao Lee
- Biomechanics and Biomaterials Design Laboratory (BBDL), School of Aerospace and Mechanical Engineering, The University of Oklahoma, 865 Asp Ave., Felgar Hall 219C, Norman, 73019, USA. .,Institute for Biomedical Engineering, Science and Technology, The University of Oklahoma, Norman, OK, 73019, USA.
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Jadidi M, Sherifova S, Sommer G, Kamenskiy A, Holzapfel GA. Constitutive modeling using structural information on collagen fiber direction and dispersion in human superficial femoral artery specimens of different ages. Acta Biomater 2021; 121:461-474. [PMID: 33279711 PMCID: PMC8464405 DOI: 10.1016/j.actbio.2020.11.046] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Revised: 11/27/2020] [Accepted: 11/27/2020] [Indexed: 12/29/2022]
Abstract
Arterial mechanics plays an important role in vascular pathophysiology and repair, and advanced imaging can inform constitutive models of vascular behavior. We have measured the mechanical properties of 14 human superficial femoral arteries (SFAs) (age 12-70, mean 48±19 years) using planar biaxial extension, and determined the preferred collagen fiber direction and dispersion using multiphoton microscopy. The collagen fiber direction and dispersion were evaluated using second-harmonic generation imaging and modeled using bivariate von Mises distributions. The microstructures of elastin and collagen were assessed using two-photon fluorescence imaging and conventional bidirectional histology. The mechanical and structural data were used to describe the SFA mechanical behavior using two- and four-fiber family invariant-based constitutive models. Older SFAs were stiffer and mechanically more nonlinear than younger specimens. In the adventitia, collagen fibers were undulated and diagonally-oriented, while in the media, they were straight and circumferentially-oriented. The media was rich in collagen that surrounded the circumferentially-oriented smooth muscle cells, and the elastin was present primarily in the internal and external elastic laminae. Older SFAs had a more circumferential collagen fiber alignment, a decreased circumferential-radial fiber dispersion, but the same circumferential-longitudinal fiber dispersion as younger specimens. Both the two- and the four-fiber family constitutive models were able to capture the experimental data, and the fits were better for the four-fiber family formulation. Our data provide additional details on the SFA intramural structure and inform structurally-based constitutive models.
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Yang Y, Li K, Sommer G, Yung KL, Holzapfel GA. Mechanical characterization of porcine liver properties for computational simulation of indentation on cancerous tissue. Math Med Biol 2020; 37:469-490. [PMID: 32424396 DOI: 10.1093/imammb/dqaa006] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2019] [Revised: 04/06/2020] [Accepted: 04/06/2020] [Indexed: 11/13/2022]
Abstract
An accurate characterization of soft biological tissue properties is essential for a realistic simulation of surgical procedures. Unconfined uniaxial compression tests with specimens affixed to the fixtures are often performed to characterize the stress-stretch curves of soft biological tissues, with which the material parameters can be obtained. However, the constrained boundary condition causes non-uniform deformation during the uniaxial test, posing challenges for accurate measurement of tissue deformation. In this study, we measured the deformation locally at the middle of liver specimens and obtained the corresponding stress-stretch curves. Since the effect of the constrained boundary condition on the local deformation of specimen is minimized, the stress-stretch curves are thus more realistic. Subsequently, we fitted the experimental stress-stretch curves with several constitutive models and found that the first-order Ogden hyperelastic material model was most suitable for characterizing the mechanical properties of porcine liver tissues. To further verify the characterized material properties, we carried out indentation tests on porcine liver specimens and compared the experimental data with computational results by using finite element simulations. A good agreement was achieved. Finally, we constructed computational models of liver tissue with a tumor and investigated the effect of the tumor on the mechanical response of the tissue under indentation. The computational results revealed that the liver specimen with tumor shows a stiffer response if the distance between the tumor and the indenter is small.
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Affiliation(s)
- Yingqiao Yang
- Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, 1 Yuk Road, Hung Hom, Kowloon, Hong Kong
| | - Kewei Li
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16-II, 8010 Graz, Austria
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16-II, 8010 Graz, Austria
| | - Kai-Leung Yung
- Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, 1 Yuk Road, Hung Hom, Kowloon, Hong Kong
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16-II, 8010 Graz, Austria and Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway
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Sajjadinia SS, Carpentieri B, Holzapfel GA. A backward pre-stressing algorithm for efficient finite element implementation of in vivo material and geometrical parameters into fibril-reinforced mixture models of articular cartilage. J Mech Behav Biomed Mater 2020; 114:104203. [PMID: 33234496 DOI: 10.1016/j.jmbbm.2020.104203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 11/06/2020] [Accepted: 11/09/2020] [Indexed: 10/23/2022]
Abstract
Classical continuum mechanics has been widely used for implementation of the material models of articular cartilage (AC) mainly with the aid of the finite element (FE) method, which, in many cases, considers the stress-free configuration as the initial configuration. On the contrary, the AC experimental tests typically begin with the pre-stressed state of both material and geometrical properties. Indeed, imposing the initial pre-stress onto AC models with the in vivo values as the initial state would result in nonphysiologically expansion of the FE mesh due to the soft nature of AC. This change in the model configuration can also affect the material behavior kinematically in the mixture models of cartilage due to the intrinsic compressibility of the tissue. Although several different fixed-point backward algorithms, as the most straightforward pre-stressing methods, have already been developed to incorporate these initial conditions into FE models iteratively, such methods focused merely on the geometrical parameters, and they omitted the material variations of the anisotropic mixture models of AC. To address this issue, we propose an efficient algorithm generalizing the backward schemes to restore stress-free conditions by optimizing both the involving variables, and we hypothesize that it can affect the results considerably. To this end, a comparative simulation was implemented on an advanced and validated multiphasic model by the new and conventional algorithms. The results are in support of the hypothesis, as in our illustrative general AC model, the material parameters experienced a maximum error of 16% comparing to the initial in vivo data when the older algorithm was employed, and it led to a maximum variation of 44% in the recorded stresses comparing to the results of the new method. We conclude that our methodology enhanced the model fidelity, and it is applicable in most of the existing FE solvers for future mixture studies with accurate stress distributions.
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Affiliation(s)
| | - Bruno Carpentieri
- Faculty of Computer Science, Free University of Bozen-Bolzano, Bozen-Bolzano, 39100, Italy.
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2, Graz, 8010, Austria; Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
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Geith MA, Nothdurfter L, Heiml M, Agrafiotis E, Gruber M, Sommer G, Schratzenstaller TG, Holzapfel GA. Quantifying stent-induced damage in coronary arteries by investigating mechanical and structural alterations. Acta Biomater 2020; 116:285-301. [PMID: 32858190 DOI: 10.1016/j.actbio.2020.08.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2020] [Revised: 07/28/2020] [Accepted: 08/12/2020] [Indexed: 11/18/2022]
Abstract
Vascular damage develops with diverging severity during and after percutaneous coronary intervention with stent placement and is the prevailing stimulus for in-stent restenosis. Previous work has failed to link mechanical data obtained in a realistic in vivo or in vitro environment with data collected during imaging processes. We investigated whether specimens of porcine right coronary arteries soften when indented with a stent strut shaped structure, and if the softening results from damage mechanisms inside the fibrillar collagen structure. To simulate the multiaxial loading scenario of a stented coronary artery, we developed the testing device 'LAESIO' that can measure differences in the stress-stretch behavior of the arterial wall before and after the indentation of a strut-like stamp. The testing protocol was optimized according to preliminary experiments, more specifically equilibrium and relaxation tests. After chemical fixation of the specimens and subsequent tissue clearing, we performed three-dimensional surface and second-harmonic generation scans on the deformed specimens. We analyzed and correlated the mechanical response with structural parameters of high-affected tissue located next to the stamp indentation and low-affected tissue beyond the injured area. The results reveal that damage mechanisms, like tissue compression as well as softening, fiber dispersion, and the lesion extent, are direction-dependent, and the severity of them is linked to the strut orientation, indentation pressure, and position. The findings highlight the need for further investigations by applying the proposed methods to human coronary arteries. Additional data and insights might help to incorporate the observed damage mechanisms into material models for finite element analyses to perform more accurate simulations of stent-implantations.
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Affiliation(s)
- Markus A Geith
- Institute of Biomechanics, Graz University of Technology, Graz, Austria; Biomedical Engineering Department, King's College London, London, United Kingdom
| | | | - Manuel Heiml
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | | | | | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Thomas G Schratzenstaller
- Medical Device Laboratory, Regensburg Center of Biomedical Engineering, Technical University of Applied Sciences Regensburg, Regensburg, Germany
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria; Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
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Pepe A, Li J, Rolf-Pissarczyk M, Gsaxner C, Chen X, Holzapfel GA, Egger J. Detection, segmentation, simulation and visualization of aortic dissections: A review. Med Image Anal 2020; 65:101773. [DOI: 10.1016/j.media.2020.101773] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 06/01/2020] [Accepted: 07/06/2020] [Indexed: 12/16/2022]
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Ross CJ, Hsu MC, Baumwart R, Mir A, Burkhart HM, Holzapfel GA, Wu Y, Lee CH. Quantification of load-dependent changes in the collagen fiber architecture for the strut chordae tendineae-leaflet insertion of porcine atrioventricular heart valves. Biomech Model Mechanobiol 2020; 20:223-241. [PMID: 32809131 PMCID: PMC8008705 DOI: 10.1007/s10237-020-01379-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Accepted: 08/08/2020] [Indexed: 10/23/2022]
Abstract
Atrioventricular heart valves (AHVs) regulate the unidirectional flow of blood through the heart by opening and closing of the leaflets, which are supported in their functions by the chordae tendineae (CT). The leaflets and CT are primarily composed of collagen fibers that act as the load-bearing component of the tissue microstructures. At the CT-leaflet insertion, the collagen fiber architecture is complex, and has been of increasing focus in the previous literature. However, these previous studies have not been able to quantify the load-dependent changes in the tissue's collagen fiber orientations and alignments. In the present study, we address this gap in knowledge by quantifying the changes in the collagen fiber architecture of the mitral and tricuspid valve's strut CT-leaflet insertions in response to the applied loads by using a unique approach, which combines polarized spatial frequency domain imaging with uniaxial mechanical testing. Additionally, we characterized these microstructural changes across the same specimen without the need for tissue fixatives. We observed increases in the collagen fiber alignments in the CT-leaflet insertion with increased loading, as described through the degree of optical anisotropy. Furthermore, we used a leaflet-CT-papillary muscle entity method during uniaxial testing to quantify the chordae tendineae mechanics, including the derivation of the Ogden-type constitutive modeling parameters. The results from this study provide a valuable insight into the load-dependent behaviors of the strut CT-leaflet insertion, offering a research avenue to better understand the relationship between tissue mechanics and the microstructure, which will contribute to a deeper understanding of AHV biomechanics.
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Affiliation(s)
- Colton J Ross
- Biomechanics and Biomaterial Design Laboratory (BBDL), School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, OK, 73019, USA
| | - Ming-Chen Hsu
- Department of Mechanical Engineering, Iowa State University, Ames, IA, 50011, USA
| | - Ryan Baumwart
- Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, WA, 99164, USA
| | - Arshid Mir
- Department of Pediatric Cardiology, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Harold M Burkhart
- Department of Surgery, The University of Oklahoma Health Sciences Center, Oklahoma City, OK, 73104, USA
| | - Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Graz, Austria.,Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Yi Wu
- Biomechanics and Biomaterial Design Laboratory (BBDL), School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, OK, 73019, USA
| | - Chung-Hao Lee
- Biomechanics and Biomaterial Design Laboratory (BBDL), School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, OK, 73019, USA. .,School of Aerospace and Mechanical Engineering, Affiliated Faculty, Institute for Biomedical Engineering, Science and Technology (IBEST), The University of Oklahoma, 865 Asp Ave., Felgar Hall Rm. 219C, Norman, OK, 73019, USA.
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Laurence DW, Johnson EL, Hsu MC, Baumwart R, Mir A, Burkhart HM, Holzapfel GA, Wu Y, Lee CH. A pilot in silico modeling-based study of the pathological effects on the biomechanical function of tricuspid valves. Int J Numer Method Biomed Eng 2020; 36:e3346. [PMID: 32362054 PMCID: PMC8039906 DOI: 10.1002/cnm.3346] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 03/23/2020] [Accepted: 04/22/2020] [Indexed: 05/12/2023]
Abstract
Current clinical assessment of functional tricuspid valve regurgitation relies on metrics quantified from medical imaging modalities. Although these clinical methodologies are generally successful, the lack of detailed information about the mechanical environment of the valve presents inherent challenges for assessing tricuspid valve regurgitation. In the present study, we have developed a finite element-based in silico model of one porcine tricuspid valve (TV) geometry to investigate how various pathological conditions affect the overall biomechanical function of the TV. There were three primary observations from our results. Firstly, the results of the papillary muscle (PM) displacement study scenario indicated more pronounced changes in the TV biomechanical function. Secondly, compared to uniform annulus dilation, nonuniform dilation scenario induced more evident changes in the von Mises stresses (83.8-125.3 kPa vs 65.1-84.0 kPa) and the Green-Lagrange strains (0.52-0.58 vs 0.47-0.53) for the three TV leaflets. Finally, results from the pulmonary hypertension study scenario showed opposite trends compared to the PM displacement and annulus dilation scenarios. Furthermore, various chordae rupture scenarios were simulated, and the results showed that the chordae tendineae attached to the TV anterior and septal leaflets may be more critical to proper TV function. This in silico modeling-based study has provided a deeper insight into the tricuspid valve pathologies that may be useful, with moderate extensions, for guiding clinical decisions. NOVELTY STATEMENT: The novelties of the research are summarized below: A comprehensive in silico pilot study of how isolated functional tricuspid regurgitation pathologies and ruptured chordae tendineae would alter the tricuspid valve function; An extensive analysis of the tricuspid valve function, including mechanical quantities (eg, the von Mises stress and the Green-Lagrange strain) and clinically-relevant geometry metrics (eg, the tenting area and the coaptation height); and A developed computational modeling pipeline that can be extended to evaluate patient-specific tricuspid valve geometries and enhance the current clinical diagnosis and treatment of tricuspid regurgitation.
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Affiliation(s)
- Devin W. Laurence
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, OK 73019, USA
| | - Emily L. Johnson
- Computational Fluid-Structure Interaction Laboratory, Department of Mechanical Engineering, Iowa State University, Ames, IA 50011, USA
| | - Ming-Chen Hsu
- Computational Fluid-Structure Interaction Laboratory, Department of Mechanical Engineering, Iowa State University, Ames, IA 50011, USA
| | - Ryan Baumwart
- Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK 74078, USA
| | - Arshid Mir
- Division of Pediatric Cardiology, Department of Pediatrics, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Harold M. Burkhart
- Division of Cardiothoracic Surgery, Department of Surgery, The University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/2 8010 Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway
| | - Yi Wu
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, OK 73019, USA
| | - Chung-Hao Lee
- Biomechanics and Biomaterials Design Laboratory, School of Aerospace and Mechanical Engineering, The University of Oklahoma, Norman, OK 73019, USA
- Institute for Biomedical Engineering, Science, and Technology, The University of Oklahoma, Norman, OK 73019, USA
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Geith MA, Eckmann JD, Haspinger DC, Agrafiotis E, Maier D, Szabo P, Sommer G, Schratzenstaller TG, Holzapfel GA. Experimental and mathematical characterization of coronary polyamide-12 balloon catheter membranes. PLoS One 2020; 15:e0234340. [PMID: 32579587 PMCID: PMC7313739 DOI: 10.1371/journal.pone.0234340] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Accepted: 05/23/2020] [Indexed: 11/18/2022] Open
Abstract
The experimental quantification and modeling of the multiaxial mechanical response of polymer membranes of coronary balloon catheters have not yet been carried out. Due to the lack of insights, it is not shown whether isotropic material models can describe the material response of balloon catheter membranes expanded with nominal or higher, supra-nominal pressures. Therefore, for the first time, specimens of commercial polyamide-12 balloon catheters membranes were investigated during uniaxial and biaxial loading scenarios. Furthermore, the influence of kinematic effects on the material response was observed by comparing results from quasi-static and dynamic biaxial extension tests. Novel clamping techniques are described, which allow to test even tiny specimens taken from the balloon membranes. The results of this study reveal the semi-compliant, nonlinear, and viscoelastic character of polyamide-12 balloon catheter membranes. Above nominal pressure, the membranes show a pronounced anisotropic mechanical behavior with a stiffer response in the circumferential direction. The anisotropic feature intensifies with an increasing strain-rate. A modified polynomial model was applied to represent the realistic mechanical response of the balloon catheter membranes during dynamic biaxial extension tests. This study also includes a compact set of constitutive model parameters for the use of the proposed model in future finite element analyses to perform more accurate simulations of expanding balloon catheters.
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Affiliation(s)
- Markus A. Geith
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Biomedical Engineering Department, King’s College London, London, United Kingdom
- * E-mail: (GAH); (MAG)
| | - Jakob D. Eckmann
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Daniel Ch. Haspinger
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Emmanouil Agrafiotis
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Dominik Maier
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Patrick Szabo
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Gerhard Sommer
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
| | - Thomas G. Schratzenstaller
- Medical Device Laboratory, Regensburg Center of Biomedical Engineering, Technical University of Applied Sciences Regensburg, Regensburg, Germany
| | - Gerhard A. Holzapfel
- Faculty of Computer Science and Biomedical Engineering, Institute of Biomechanics, Graz University of Technology, Graz, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
- * E-mail: (GAH); (MAG)
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Holzapfel GA, Ogden RW. A damage model for collagen fibres with an application to collagenous soft tissues. Proc Math Phys Eng Sci 2020; 476:20190821. [PMID: 32398939 DOI: 10.1098/rspa.2019.0821] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Accepted: 03/19/2020] [Indexed: 11/12/2022] Open
Abstract
We propose a mechanical model to account for progressive damage in collagen fibres within fibrous soft tissues. The model has a similar basis to the pseudoelastic model that describes the Mullins effect in rubber but it also accounts for the effect of cross-links between collagen fibres. We show that the model is able to capture experimental data obtained from rat tail tendon fibres, and the combined effect of damage and collagen cross-links is illustrated for a simple shear test. The proposed three-dimensional framework allows a straightforward implementation in finite-element codes, which are needed to analyse more complex boundary-value problems for soft tissues under supra-physiological loading or tissues weakened by disease.
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Affiliation(s)
- Gerhard A Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16-II, 8010 Graz, Austria.,Norwegian University of Science and Technology (NTNU), Faculty of Engineering Science and Technology, 7491 Trondheim, Norway
| | - Ray W Ogden
- School of Mathematics and Statistics, University of Glasgow, University Place, Glasgow G12 8SQ, UK
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Zhang W, Capilnasiu A, Sommer G, Holzapfel GA, Nordsletten DA. An efficient and accurate method for modeling nonlinear fractional viscoelastic biomaterials. Comput Methods Appl Mech Eng 2020; 362:112834. [PMID: 34136022 PMCID: PMC7610983 DOI: 10.1016/j.cma.2020.112834] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Computational biomechanics plays an important role in biomedical engineering: using modeling to understand pathophysiology, treatment and device design. While experimental evidence indicates that the mechanical response of most tissues is viscoelastic, current biomechanical models in the computational community often assume hyperelastic material models. Fractional viscoelastic constitutive models have been successfully used in literature to capture viscoelastic material response; however, the translation of these models into computational platforms remains limited. Many experimentally derived viscoelastic constitutive models are not suitable for three-dimensional simulations. Furthermore, the use of fractional derivatives can be computationally prohibitive, with a number of current numerical approximations having a computational cost that is 𝒪 ( N T 2 ) and a storage cost that is 𝒪(NT ) (NT denotes the number of time steps). In this paper, we present a novel numerical approximation to the Caputo derivative which exploits a recurrence relation similar to those used to discretize classic temporal derivatives, giving a computational cost that is 𝒪(NT ) and a storage cost that is fixed over time. The approximation is optimized for numerical applications, and an error estimate is presented to demonstrate the efficacy of the method. The method, integrated into a finite element solid mechanics framework, is shown to be unconditionally stable in the linear viscoelastic case. It was then integrated into a computational biomechanical framework, with several numerical examples verifying the accuracy and computational efficiency of the method, including in an analytic test, in an analytic fractional differential equation, as well as in a computational biomechanical model problem.
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Affiliation(s)
- Will Zhang
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, USA
| | - Adela Capilnasiu
- School of Biomedical Engineering and Imaging Sciences, King’s College London, London, UK
| | - Gerhard Sommer
- Institute of Biomechanics, Graz University of Technology, AT, Austria
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, AT, Austria
- Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, NO, Norway
| | - David A. Nordsletten
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, USA
- Department of Cardiac Surgery, University of Michigan, Ann Arbor, USA
- School of Biomedical Engineering and Imaging Sciences, King’s College London, London, UK
- Corresponding author at: B20 212W, NCRC, 2800 Plymouth Rd, Ann Arbor, MI, USA, 48109. (D.A. Nordsletten)
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Anssari-Benam A, Tseng YT, Holzapfel GA, Bucchi A. Rate-dependent mechanical behaviour of semilunar valves under biaxial deformation: From quasi-static to physiological loading rates. J Mech Behav Biomed Mater 2020; 104:103645. [PMID: 32174403 DOI: 10.1016/j.jmbbm.2020.103645] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 01/15/2020] [Accepted: 01/16/2020] [Indexed: 11/29/2022]
Abstract
In this study we investigate the rate-dependency of the mechanical behaviour of semilunar heart valves under biaxial deformation, from quasi-static to physiological loading rates. This work extends and complements our previous undertaking, where the rate-dependency in the mechanical behaviour of semilunar valve specimens was documented in sub-physiological rate domains (Acta Biomater. 2019; https://doi.org/10.1016/j.actbio.2019.02.008). For the first time we demonstrate herein that the stress-stretch curves obtained from specimens under physiological rates too are markedly different to those at sufficiently lower rates and at quasi-static conditions. The results importantly underline that the mechanical behaviour of semilunar heart valves is rate dependent, and the physiological mechanical behaviour of the valves may not be correctly obtained via material characterisation tests at arbitrary low deformation rates. Presented results in this work provide an inclusive dataset for material characterisation and modelling of semilunar heart valves across a 10,000 fold deformation rate, both under equi-biaxial and 1:3 ratio deformation rates. The important application of these results is to inform the development of appropriate mechanical testing protocols, as well as devising new models, for suitable determination of the rate-dependent constitutive mechanical behaviour of the semilunar valves.
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Affiliation(s)
- Afshin Anssari-Benam
- Cardiovascular Engineering Research Laboratory (CERL), School of Mechanical and Design Engineering, University of Portsmouth, Anglesea Road, Portsmouth, PO1 3DJ, United Kingdom.
| | - Yuan-Tsan Tseng
- National Heart and Lung Institute, Heart Science Centre, Imperial College London, Middlesex, United Kingdom
| | - Gerhard A Holzapfel
- Graz University of Technology, Institute of Biomechanics, Graz, Austria; Norwegian University of Science and Technology (NTNU), Department of Structural Engineering, Trondheim, Norway
| | - Andrea Bucchi
- Cardiovascular Engineering Research Laboratory (CERL), School of Mechanical and Design Engineering, University of Portsmouth, Anglesea Road, Portsmouth, PO1 3DJ, United Kingdom
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