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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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Chen H, Zhao M, Li Y, Wang Q, Xing Y, Bian C, Li J. A study on the ultimate mechanical properties of middle-aged and elderly human aorta based on uniaxial tensile test. Front Bioeng Biotechnol 2024; 12:1357056. [PMID: 38576445 PMCID: PMC10991712 DOI: 10.3389/fbioe.2024.1357056] [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] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2023] [Accepted: 03/07/2024] [Indexed: 04/06/2024] Open
Abstract
Background The mechanical properties of the aorta are particularly important in clinical medicine and forensic science, serving as basic data for further exploration of aortic disease or injury mechanisms. Objective To study the influence of various factors (age, gender, test direction, anatomical location, and pathological characteristics) on the mechanical properties and thickness of the aorta. Methods In this study, a total of 24 aortas (age range: 54-88 years old) were collected, one hundred and seventy-four dog-bone-shaped samples were made, and then the uniaxial tensile test was run, finally, pathological grouping was performed through histological staining. Results Atherosclerotic plaques were mainly distributed near the openings of blood vessel branches. The distribution was most severe in the abdominal aorta, followed by the aortic arch. Aortic atherosclerosis was a more severe trend in the male group. In the comparison of thickness, there were no significant differences in age (over 50 years) and test direction, the average thickness of the aorta was greater in the male group than the female group and decreased progressively from the ascending aorta to the abdominal aorta. Comparing the mechanical parameters, various parameters are mainly negatively correlated with age, especially in the circumferential ascending aorta (εp "Y = -0.01402*X + 1.762, R2 = 0.6882", εt "Y = -0.01062*X + 1.250, R2 = 0.6772"); the parameters of males in the healthy group were larger, while the parameters of females were larger in atherosclerosis group; the aorta has anisotropy, the parameters in the circumferential direction were greater than those in the axial direction; the parameters of the ascending aorta were the largest in the circumferential direction, the ultimate stress [σp "1.69 (1.08,2.32)"] and ultimate elastic modulus [E2"8.28 (6.67,10.25)"] of the abdominal aorta were significantly larger in the axial direction; In the circumferential direction, the stress [σp "2.2 (1.31,3.98)", σt "0.13 (0.09,0.31)"] and ultimate elastic modulus (E2 "14.10 ± 7.21") of adaptive intimal thickening were greater than those of other groups, the strain (εp "0.82 ± 0.17", εt "0.53 ± 0.14") of pathological intimal thickening was the largest in the pathological group. Conclusion The present study systematically analyzed the influence of age, sex, test direction, anatomical site, and pathological characteristics on the biomechanical properties of the aorta, described the distribution of aortic atherosclerosis, and illustrated the characteristics of aortic thickness changes. At the same time, new insights into the grouping of pathological features were presented.
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Affiliation(s)
- Hongbing Chen
- Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China
- Chongqing Engineering Research Center for Criminal Investigation Technology, Chongqing, China
- Chongqing Key Laboratory of Forensic Medicine, Chongqing, China
| | - Minzhu Zhao
- Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China
- Chongqing Engineering Research Center for Criminal Investigation Technology, Chongqing, China
- Chongqing Key Laboratory of Forensic Medicine, Chongqing, China
| | - Yongguo Li
- Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China
- Chongqing Engineering Research Center for Criminal Investigation Technology, Chongqing, China
- Chongqing Key Laboratory of Forensic Medicine, Chongqing, China
| | - Qi Wang
- Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China
- Chongqing Engineering Research Center for Criminal Investigation Technology, Chongqing, China
- Chongqing Key Laboratory of Forensic Medicine, Chongqing, China
| | - Yu Xing
- Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China
- Chongqing Engineering Research Center for Criminal Investigation Technology, Chongqing, China
- Chongqing Key Laboratory of Forensic Medicine, Chongqing, China
| | - Cunhao Bian
- Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China
- Chongqing Engineering Research Center for Criminal Investigation Technology, Chongqing, China
- Chongqing Key Laboratory of Forensic Medicine, Chongqing, China
| | - Jianbo Li
- Department of Forensic Medicine, College of Basic Medicine, Chongqing Medical University, Chongqing, China
- Chongqing Engineering Research Center for Criminal Investigation Technology, Chongqing, China
- Chongqing Key Laboratory of Forensic Medicine, Chongqing, China
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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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Arbănaşi EM, Russu E, Arbănaşi EM, Ciucanu CC, Mureșan AV, Suzuki S, Chirilă TV. Effect of Ultraviolet Radiation on the Enzymolytic and Biomechanical Profiles of Abdominal Aortic Adventitia Tissue. J Clin Med 2024; 13:633. [PMID: 38276139 PMCID: PMC10817471 DOI: 10.3390/jcm13020633] [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: 11/21/2023] [Revised: 01/10/2024] [Accepted: 01/19/2024] [Indexed: 01/27/2024] Open
Abstract
BACKGROUND The abdominal aortic aneurysm (AAA) is defined as an increase in aortic diameter by more than 50% and is associated with a high risk of rupture and mortality without treatment. The aim of this study is to analyze the role of aortic adventitial collagen photocrosslinking by UV-A irradiation on the biomechanical profile of the aortic wall. METHODS This experimental study is structured in two parts: the first part includes in vitro uniaxial biomechanical evaluation of porcine adventitial tissue subjected to either short-term elastolysis or long-term collagenolysis in an attempt to duplicate two extreme situations as putative stages of aneurysmal degeneration. In the second part, we included biaxial biomechanical evaluation of in vitro human abdominal aortic adventitia and human AAA adventitia specimens. Biomechanical profiles were examined for porcine and human aortic tissue before and after irradiation with UV-A light (365 nm wavelength). RESULTS On the porcine aortic sample, the enhancing effect of irradiation was evident both on the tissue subjected to elastolysis, which had a high collagen-to-elastin ratio, and on the tissue subjected to prolonged collagenolysis despite being considerably depleted in collagen. Further, the effect of irradiation was conclusively demonstrated in the human adventitia samples, where significant post-irradiation increases in Cauchy stress (longitudinal axis: p = 0.001, circumferential axis: p = 0.004) and Young's modulus (longitudinal axis: p = 0.03, circumferential axis: p = 0.004) were recorded. Moreover, we have a stronger increase in the strengthening of the AAA adventitia samples following the exposure to UV-A irradiation (p = 0.007) and a statistically significant but not very important increase (p = 0.021) regarding the stiffness in the circumferential axis. CONCLUSIONS The favorable effect of UV irradiation on the strength and stiffness of degraded aortic adventitia in experimental situations mimicking early and later stages of aneurysmal degeneration is essential for the development and potential success of procedures to prevent aneurysmal ruptures. The experiments on human normal and aneurysmal adventitial tissue confirmed the validity and potential success of a procedure based on exposure to UV-A radiation.
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Affiliation(s)
- Emil-Marian Arbănaşi
- Doctoral School of Medicine and Pharmacy, George Emil Palade University of Medicine, Pharmacy, Sciences and Technology of Targu Mures (UMFST), 540142 Targu Mures, Romania; (E.-M.A.); (E.-M.A.); (C.C.C.)
- Clinic of Vascular Surgery, Mures County Emergency Hospital, 540136 Targu Mures, Romania;
- Department of Vascular Surgery, George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540139 Targu Mures, Romania
- Centre for Advanced Medical and Pharmaceutical Research (CCAMF), George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540139 Targu Mures, Romania; (S.S.); (T.V.C.)
| | - Eliza Russu
- Clinic of Vascular Surgery, Mures County Emergency Hospital, 540136 Targu Mures, Romania;
- Department of Vascular Surgery, George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540139 Targu Mures, Romania
| | - Eliza-Mihaela Arbănaşi
- Doctoral School of Medicine and Pharmacy, George Emil Palade University of Medicine, Pharmacy, Sciences and Technology of Targu Mures (UMFST), 540142 Targu Mures, Romania; (E.-M.A.); (E.-M.A.); (C.C.C.)
| | - Constantin Claudiu Ciucanu
- Doctoral School of Medicine and Pharmacy, George Emil Palade University of Medicine, Pharmacy, Sciences and Technology of Targu Mures (UMFST), 540142 Targu Mures, Romania; (E.-M.A.); (E.-M.A.); (C.C.C.)
- Clinic of Vascular Surgery, Mures County Emergency Hospital, 540136 Targu Mures, Romania;
| | - Adrian Vasile Mureșan
- Clinic of Vascular Surgery, Mures County Emergency Hospital, 540136 Targu Mures, Romania;
- Department of Vascular Surgery, George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540139 Targu Mures, Romania
| | - Shuko Suzuki
- Centre for Advanced Medical and Pharmaceutical Research (CCAMF), George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540139 Targu Mures, Romania; (S.S.); (T.V.C.)
- Queensland Eye Institute, South Brisbane, QLD 4101, Australia
| | - Traian V. Chirilă
- Centre for Advanced Medical and Pharmaceutical Research (CCAMF), George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540139 Targu Mures, Romania; (S.S.); (T.V.C.)
- Queensland Eye Institute, South Brisbane, QLD 4101, Australia
- Faculty of Medicine, George Emil Palade University of Medicine, Pharmacy, Science, and Technology of Targu Mures, 540139 Targu Mures, Romania
- School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD 4001, Australia
- Australian Institute of Bioengineering and Nanotechnology (AIBN), University of Queensland, St. Lucia, QLD 4072, Australia
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Gkousioudi A, Razzoli M, Moreira JD, Wainford RD, Zhang Y. Renal denervation restores biomechanics of carotid arteries in a rat model of hypertension. Sci Rep 2024; 14:495. [PMID: 38177257 PMCID: PMC10767006 DOI: 10.1038/s41598-023-50816-8] [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: 08/17/2023] [Accepted: 12/26/2023] [Indexed: 01/06/2024] Open
Abstract
The prevalence of hypertension increases with aging and is associated with increased arterial stiffness. Resistant hypertension is presented when drug treatments fail to regulate a sustained increased blood pressure. Given that the mechanisms between the sympathetic nervous system and the kidney play an important role in blood regulation, renal denervation (RDN) has emerged as a therapeutic potential in resistant hypertension. In this study, we investigated the effects of RDN on the biomechanical response and microstructure of elastic arteries. Common carotid arteries (CCA) excised from 3-month, 8-month, and 8-month denervated rats were subjected to biaxial extension-inflation test. Our results showed that hypertension developed in the 8-month-old rats. The sustained elevated blood pressure resulted in arterial remodeling which was manifested as a significant stress increase in both axial and circumferential directions after 8 months. RDN had a favorable impact on CCAs with a restoration of stresses in values similar to control arteries at 3 months. After biomechanical testing, arteries were imaged under a multi-photon microscope to identify microstructural changes in extracellular matrix (ECM). Quantification of multi-photon images showed no significant alterations of the main ECM components, elastic and collagen fibers, indicating that arteries remained intact after RDN. Regardless of the experimental group, our microstructural analysis of the multi-photon images revealed that reorientation of the collagen fibers might be the main microstructural mechanism taking place during pressurization with their straightening happening during axial stretching.
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Affiliation(s)
- Anastasia Gkousioudi
- Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA
| | - Margherita Razzoli
- Department of Biomedical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA
| | - Jesse D Moreira
- Department of Pharmacology & Experimental Therapeutics, School of Medicine, Boston University Avedisian and Chobanian, Boston, MA, USA
| | - Richard D Wainford
- Department of Pharmacology & Experimental Therapeutics, School of Medicine, Boston University Avedisian and Chobanian, Boston, MA, USA.
- Division of Cardiology, School of Medicine, HSRB II, Emory University, 1750 Haygood Drive, Atlanta, GA, 30322, USA.
| | - Yanhang Zhang
- Department of Mechanical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA.
- Department of Biomedical Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA.
- Division of Materials Science & Engineering, Boston University, 110 Cummington Mall, Boston, MA, 02215, USA.
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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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Gkousioudi A, Razzoli M, Moreira JD, Wainford RD, Zhang Y. Renal denervation restores biomechanics of carotid arteries in a rat model of hypertension. Res Sq 2023:rs.3.rs-3273236. [PMID: 37720022 PMCID: PMC10503847 DOI: 10.21203/rs.3.rs-3273236/v1] [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] [Subscribe] [Scholar Register] [Indexed: 09/19/2023]
Abstract
The prevalence of hypertension increases with aging and is associated with increased arterial stiffness. Resistant hypertension is presented when drug treatments fail to regulate a sustained increased blood pressure. Given that the mechanisms between the sympathetic nervous system and the kidney play an important role in blood regulation, renal denervation (RDN) has emerged as a therapeutic potential in resistant hypertension. In this study, we investigated the effects of RDN on the biomechanical response and microstructure of elastic arteries. Common carotid arteries (CCA) were excised from 3-, 8- and 8-month-old denervated rats, and subjected to biaxial extension-inflation test. Our results showed that hypertension developed in the 8-month-old rats. The sustained elevated blood pressure resulted in arterial remodeling which was manifested as a significant stress increase in both axial and circumferential directions after 8 months. RDN had a favorable impact on CCAs with a restoration of stresses in values similar to control arteries at 3 months. After biomechanical testing, arteries were imaged under a multi-photon microscope to identify microstructural changes in extracellular matrix (ECM). Quantification of multi-photon images showed no significant alterations of the main ECM components, elastic and collagen fibers, indicating that arteries remained intact after RDN. Regardless of the experimental group, our microstructural analysis of the multi-photon images revealed that reorientation of the collagen fibers might be the main microstructural mechanism taking place during pressurization with their straightening happening during axial stretching.
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Affiliation(s)
| | | | - Jesse D Moreira
- Boston University Avedisian and Chobanian School of Medicine
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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: 6] [Impact Index Per Article: 6.0] [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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Dwivedi KK, Lakhani P, Yadav A, Kumar S, Kumar N. Location specific multi-scale characterization and constitutive modeling of pig aorta. J Mech Behav Biomed Mater 2023; 142:105809. [PMID: 37116311 DOI: 10.1016/j.jmbbm.2023.105809] [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] [Received: 01/09/2023] [Revised: 03/18/2023] [Accepted: 03/25/2023] [Indexed: 04/03/2023]
Abstract
The mechanical and structural behavior of the aorta depend on physiological functions and vary from proximal to distal. Understanding the relation between regionally varying mechanical and multi-scale structural response of aorta can be helpful to assess the disease outcomes. Therefore, this study investigated the variation in mechanical and multi-scale structural properties among the major segments of aorta such as ascending aorta (AA), descending aorta (DA) and abdominal aorta (ABA), and established a relation between mechanical and multi-structural parameters. The obtained results showed significant increase in anisotropy and nonlinearity from proximal to distal aorta. The change in periphery length and radii between load and stress free configuration was also found increasing far from the heart. Opening angle was significantly large for ABA than AA and DA (AA/DA vs ABA; p = 0.001). Mean circumferential residual stretch (ratio of mean periphery length at load and stress free configurations) was found decreasing between AA and DA, and then increasing between DA to ABA and its value was significantly more for ABA (AA vs DA; p = 0.041, AA vs ABA; p = 0.001, DA vs ABA; p = 0.001). The waviness of collagen fibers, collagen fiber content, collagen fibril diameter and total protein content were found significantly increasing from proximal to distal. Pearson correlation test showed a significant linear correlation between variation in mechanical and multi-scale structural parameters over the aortic length. Residual stretch was found positively correlated with collagen fiber content (r = 0.82) whereas opening angel was found positively correlated with total protein content (TPC) (r = 0.76).
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Affiliation(s)
| | | | - Ashu Yadav
- Department of Automobile Engineering, Manipal University Jaipur, Jaipur, India
| | - Sachin Kumar
- Department of Mechanical Engineering, IIT Ropar, India.
| | - Navin Kumar
- Department of Biomedical Engineering, IIT Ropar, India; Department of Mechanical Engineering, IIT Ropar, India.
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