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Lim W. Effect of novel diagonal stretching combining trunk rotation and trunk flexion on contralateral knee extension. ISOKINET EXERC SCI 2022. [DOI: 10.3233/ies-220026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
BACKGROUND: Most previous studies have focused on increasing hamstring flexibility when knee extension range of motion (KE ROM) is restricted. However, it was demonstrated that the tensile force generated in the upper body could be transmitted to the contralateral lower extremity. OBJECTIVE: This study examined the effect of novel diagonal stretching combining trunk rotation and trunk flexion on the contralateral KE ROM. METHODS: Two different positions (sitting with a neutral pelvis position and sitting with trunk rotation) were randomly selected and the contralateral and ipsilateral KE ROM was measured in each position. As for the stretching intervention, trunk rotation and slight trunk flexion were applied in sitting with a neutral pelvic position. RESULTS: On the contralateral side, KE ROM was significantly different in all pairwise comparisons (p< 0.001). On the ipsilateral side, a significant difference in KE ROM was only observed between measurements taken after stretching compared to measurements taken during trunk rotation (p= 0.005). CONCLUSIONS: The tensile force in the upper body significantly affects tissue extensibility in the lower extremity in the contralateral side, leading to the restriction of active maximum knee extension. Diagonal stretching techniques may successfully enhance mobility in the contralateral leg.
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Affiliation(s)
- Wootaek Lim
- Department of Physical Therapy, College of Health and Welfare, Woosong University, Daejeon, Korea
- Woosong Institute of Rehabilitation Science, Woosong University, Daejeon, Korea
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2
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Volumetric growth of soft tissues evaluated in the current configuration. Biomech Model Mechanobiol 2022; 21:569-588. [PMID: 35044527 PMCID: PMC8940838 DOI: 10.1007/s10237-021-01549-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 12/17/2021] [Indexed: 11/02/2022]
Abstract
AbstractThe growth and remodelling of soft tissues plays a significant role in many physiological applications, particularly in understanding and managing many diseases. A commonly used approach for soft tissue growth and remodelling is volumetric growth theory, introduced in the framework of finite elasticity. In such an approach, the total deformation gradient tensor is decomposed so that the elastic and growth tensors can be studied separately. A critical element in this approach is to determine the growth tensor and its evolution with time. Most existing volumetric growth theories define the growth tensor in the reference (natural) configuration, which does not reflect the continuous adaptation processes of soft tissues under the current configuration. In a few studies where growth from a loaded configuration was considered, simplifying assumptions, such as compatible deformation or geometric symmetries, were introduced. In this work, we propose a new volumetric growth law that depends on fields evaluated in the current configuration, which is residually stressed and loaded, without any geometrical restrictions. We illustrate our idea using a simplified left ventricle model, which admits inhomogeneous growth in the current configuration. We compare the residual stress distribution of our approach with the traditional volumetric growth theory, that assumes growth occurring from the natural reference configuration. We show that the proposed framework leads to qualitative agreements with experimental measurements. Furthermore, using a cylindrical model, we find an incompatibility index that explains the differences between the two approaches in more depth. We also demonstrate that results from both approaches reach the same steady solution published previously at the limit of a saturated growth. Although we used a left ventricle model as an example, our theory is applicable in modelling the volumetric growth of general soft tissues.
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3
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Membrane curvature and connective fiber alignment in guinea pig round window membrane. Acta Biomater 2021; 136:343-362. [PMID: 34563725 DOI: 10.1016/j.actbio.2021.09.036] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 09/14/2021] [Accepted: 09/17/2021] [Indexed: 11/23/2022]
Abstract
The round window membrane (RWM) covers an opening between the perilymph fluid-filled inner ear space and the air-filled middle ear space. As the only non-osseous barrier between these two spaces, the RWM is an ideal candidate for aspiration of perilymph for diagnostics purposes and delivery of medication for treatment of inner ear disorders. Routine access across the RWM requires the development of new surgical tools whose design can only be optimized with a thorough understanding of the RWM's structure and properties. The RWM possesses a layer of collagen and elastic fibers so characterization of the distribution and orientation of these fibers is essential. Confocal and two-photon microscopy were conducted on intact RWMs in a guinea pig model to characterize the distribution of collagen and elastic fibers. The fibers were imaged via second-harmonic-generation, autofluorescence, and Rhodamine B staining. Quantitative analyses of both fiber orientation and geometrical properties of the RWM uncovered a significant correlation between mean fiber orientations and directions of zero curvature in some portions of the RWM, with an even more significant correlation between the mean fiber orientations and linear distance along the RWM in a direction approximately parallel to the cochlear axis. The measured mean fiber directions and dispersions can be incorporated into a generalized structure tensor for use in the development of continuum anisotropic mechanical constitutive models that in turn will enable optimization of surgical tools to access the cochlea. STATEMENT OF SIGNIFICANCE: The Round Window Membrane (RWM) is the only non-osseous barrier separating the middle and inner ear spaces, and thus is an ideal portal for medical access to the cochlea. An understanding of RWM structure and mechanical response is necessary to optimize the design of surgical tools for this purpose. The RWM geometry and the connective fiber orientation and dispersion are measured via confocal and 2-photon microscopy. A region of the RWM geometry is characterized as a hyperbolic paraboloid and another region as a tapered parabolic cylinder. Predominant fiber directions correlate well with directions of zero curvature in the hyperbolic paraboloid region. Overall fiber directions correlate well with position along a line approximately parallel to the central axis of the cochlea's spiral.
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Goodwin RL, Kheradvar A, Norris RA, Price RL, Potts JD. Collagen Fibrillogenesis in the Mitral Valve: It's a Matter of Compliance. J Cardiovasc Dev Dis 2021; 8:jcdd8080098. [PMID: 34436240 PMCID: PMC8397013 DOI: 10.3390/jcdd8080098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 07/30/2021] [Accepted: 08/16/2021] [Indexed: 11/16/2022] Open
Abstract
Collagen fibers are essential structural components of mitral valve leaflets, their tension apparatus (chordae tendineae), and the associated papillary muscles. Excess or lack of collagen fibers in the extracellular matrix (ECM) in any of these structures can adversely affect mitral valve function. The organization of collagen fibers provides a sophisticated framework that allows for unidirectional blood flow during the precise opening and closing of this vital heart valve. Although numerous ECM molecules are essential for the differentiation, growth, and homeostasis of the mitral valve (e.g., elastic fibers, glycoproteins, and glycans), collagen fibers are key to mitral valve integrity. Besides the inert structural components of the tissues, collagen fibers are dynamic structures that drive outside-to-inside cell signaling, which informs valvular interstitial cells (VICs) present within the tissue environment. Diversity of collagen family members and the closely related collagen-like triple helix-containing proteins found in the mitral valve, will be discussed in addition to how defects in these proteins may lead to valve disease.
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Affiliation(s)
- Richard L. Goodwin
- Department of Biomedical Sciences, School of Medicine Greenville, University of South Carolina, Greenville, SC 29605, USA
- Correspondence:
| | - Arash Kheradvar
- Department of Biomedical Engineering, The Henry Samueli School of Engineering, University of California, Irvine, CA 92697, USA;
| | - Russell A. Norris
- Department of Regenerative Medicine, School of Medicine, Medical University of South Carolina, Charleston, SC 29425, USA;
| | - Robert L. Price
- Department of Cell Biology and Anatomy, School of Medicine, University of South Carolina, Greenville, SC 29605, USA; (R.L.P.); (J.D.P.)
| | - Jay D. Potts
- Department of Cell Biology and Anatomy, School of Medicine, University of South Carolina, Greenville, SC 29605, USA; (R.L.P.); (J.D.P.)
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5
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Ma Z, Bao G, Li J. Multifaceted Design and Emerging Applications of Tissue Adhesives. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2007663. [PMID: 33956371 DOI: 10.1002/adma.202007663] [Citation(s) in RCA: 88] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 12/04/2020] [Indexed: 05/24/2023]
Abstract
Tissue adhesives can form appreciable adhesion with tissues and have found clinical use in a variety of medical settings such as wound closure, surgical sealants, regenerative medicine, and device attachment. The advantages of tissue adhesives include ease of implementation, rapid application, mitigation of tissue damage, and compatibility with minimally invasive procedures. The field of tissue adhesives is rapidly evolving, leading to tissue adhesives with superior mechanical properties and advanced functionality. Such adhesives enable new applications ranging from mobile health to cancer treatment. To provide guidelines for the rational design of tissue adhesives, here, existing strategies for tissue adhesives are synthesized into a multifaceted design, which comprises three design elements: the tissue, the adhesive surface, and the adhesive matrix. The mechanical, chemical, and biological considerations associated with each design element are reviewed. Throughout the report, the limitations of existing tissue adhesives and immediate opportunities for improvement are discussed. The recent progress of tissue adhesives in topical and implantable applications is highlighted, and then future directions toward next-generation tissue adhesives are outlined. The development of tissue adhesives will fuse disciplines and make broad impacts in engineering and medicine.
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Affiliation(s)
- Zhenwei Ma
- Department of Mechanical Engineering, McGill University, Montréal, QC, H3A 0C3, Canada
| | - Guangyu Bao
- Department of Mechanical Engineering, McGill University, Montréal, QC, H3A 0C3, Canada
| | - Jianyu Li
- Department of Mechanical Engineering, McGill University, Montréal, QC, H3A 0C3, Canada
- Department of Biomedical Engineering, McGill University, Montréal, QC, H3A 2B4, Canada
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6
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Spatiotemporal remodeling of embryonic aortic arch: stress distribution, microstructure, and vascular growth in silico. Biomech Model Mechanobiol 2020; 19:1897-1915. [DOI: 10.1007/s10237-020-01315-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Accepted: 02/17/2020] [Indexed: 02/07/2023]
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Ambrosi D, Ben Amar M, Cyron CJ, DeSimone A, Goriely A, Humphrey JD, Kuhl E. Growth and remodelling of living tissues: perspectives, challenges and opportunities. J R Soc Interface 2019; 16:20190233. [PMID: 31431183 PMCID: PMC6731508 DOI: 10.1098/rsif.2019.0233] [Citation(s) in RCA: 76] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Accepted: 07/26/2019] [Indexed: 12/29/2022] Open
Abstract
One of the most remarkable differences between classical engineering materials and living matter is the ability of the latter to grow and remodel in response to diverse stimuli. The mechanical behaviour of living matter is governed not only by an elastic or viscoelastic response to loading on short time scales up to several minutes, but also by often crucial growth and remodelling responses on time scales from hours to months. Phenomena of growth and remodelling play important roles, for example during morphogenesis in early life as well as in homeostasis and pathogenesis in adult tissues, which often adapt to changes in their chemo-mechanical environment as a result of ageing, diseases, injury or surgical intervention. Mechano-regulated growth and remodelling are observed in various soft tissues, ranging from tendons and arteries to the eye and brain, but also in bone, lower organisms and plants. Understanding and predicting growth and remodelling of living systems is one of the most important challenges in biomechanics and mechanobiology. This article reviews the current state of growth and remodelling as it applies primarily to soft tissues, and provides a perspective on critical challenges and future directions.
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Affiliation(s)
- Davide Ambrosi
- Dipartimento di Matematica, Politecnico di Milano, Milan, Italy
| | - Martine Ben Amar
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris, France
| | - Christian J. Cyron
- Institute of Continuum Mechanics and Materials, Hamburg University of Technology, Hamburg, Germany
- Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany
| | - Antonio DeSimone
- Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy
| | - Alain Goriely
- Mathematical Institute, University of Oxford, Oxford, UK
| | - Jay D. Humphrey
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Ellen Kuhl
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
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Apelqvist J, Willy C, Fagerdahl AM, Fraccalvieri M, Malmsjö M, Piaggesi A, Probst A, Vowden P. EWMA Document: Negative Pressure Wound Therapy. J Wound Care 2019; 26:S1-S154. [PMID: 28345371 DOI: 10.12968/jowc.2017.26.sup3.s1] [Citation(s) in RCA: 95] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
1. Introduction Since its introduction in clinical practice in the early 1990's negative pressure wounds therapy (NPWT) has become widely used in the management of complex wounds in both inpatient and outpatient care.1 NPWT has been described as a effective treatment for wounds of many different aetiologies2,3 and suggested as a gold standard for treatment of wounds such as open abdominal wounds,4-6 dehisced sternal wounds following cardiac surgery7,8 and as a valuable agent in complex non-healing wounds.9,10 Increasingly, NPWT is being applied in the primary and home-care setting, where it is described as having the potential to improve the efficacy of wound management and help reduce the reliance on hospital-based care.11 While the potential of NPWT is promising and the clinical use of the treatment is widespread, highlevel evidence of its effectiveness and economic benefits remain sparse.12-14 The ongoing controversy regarding high-level evidence in wound care in general is well known. There is a consensus that clinical practice should be evidence-based, which can be difficult to achieve due to confusion about the value of the various approaches to wound management; however, we have to rely on the best available evidence. The need to review wound strategies and treatments in order to reduce the burden of care in an efficient way is urgent. If patients at risk of delayed wound healing are identified earlier and aggressive interventions are taken before the wound deteriorates and complications occur, both patient morbidity and health-care costs can be significantly reduced. There is further a fundamental confusion over the best way to evaluate the effectiveness of interventions in this complex patient population. This is illustrated by reviews of the value of various treatment strategies for non-healing wounds, which have highlighted methodological inconsistencies in primary research. This situation is confounded by differences in the advice given by regulatory and reimbursement bodies in various countries regarding both study design and the ways in which results are interpreted. In response to this confusion, the European Wound Management Association (EWMA) has been publishing a number of interdisciplinary documents15-19 with the intention of highlighting: The nature and extent of the problem for wound management: from the clinical perspective as well as that of care givers and the patients Evidence-based practice as an integration of clinical expertise with the best available clinical evidence from systematic research The nature and extent of the problem for wound management: from the policy maker and healthcare system perspectives The controversy regarding the value of various approaches to wound management and care is illustrated by the case of NPWT, synonymous with topical negative pressure or vacuum therapy and cited as branded VAC (vacuum-assisted closure) therapy. This is a mode of therapy used to encourage wound healing. It is used as a primary treatment of chronic wounds, in complex acute wounds and as an adjunct for temporary closure and wound bed preparation preceding surgical procedures such as skin grafts and flap surgery. Aim An increasing number of papers on the effect of NPWT are being published. However, due to the low evidence level the treatment remains controversial from the policy maker and health-care system's points of view-particularly with regard to evidence-based medicine. In response EWMA has established an interdisciplinary working group to describe the present knowledge with regard to NPWT and provide overview of its implications for organisation of care, documentation, communication, patient safety, and health economic aspects. These goals will be achieved by the following: Present the rational and scientific support for each delivered statement Uncover controversies and issues related to the use of NPWT in wound management Implications of implementing NPWT as a treatment strategy in the health-care system Provide information and offer perspectives of NPWT from the viewpoints of health-care staff, policy makers, politicians, industry, patients and hospital administrators who are indirectly or directly involved in wound management.
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Affiliation(s)
- Jan Apelqvist
- Department of Endocrinology, University Hospital of Malmö, 205 02 Malmö, Sweden and Division for Clinical Sciences, University of Lund, 221 00 Lund, Sweden
| | - Christian Willy
- Department of Trauma & Orthopedic Surgery, Septic & Reconstructive Surgery, Bundeswehr Hospital Berlin, Research and Treatment Center for Complex Combat Injuries, Federal Armed Forces of Germany, 10115 Berlin, Germany
| | - Ann-Mari Fagerdahl
- Department of Clinical Science and Education, Karolinska Institutet, and Wound Centre, Södersjukhuset AB, SE-118 83 Stockholm, Sweden
| | - Marco Fraccalvieri
- Plastic Surgery Unit, ASO Città della Salute e della Scienza of Turin, University of Turin, 10100 Turin, Italy
| | | | - Alberto Piaggesi
- Department of Endocrinology and Metabolism, Pisa University Hospital, 56125 Pisa, Italy
| | - Astrid Probst
- Kreiskliniken Reutlingen GmbH, 72764 Reutlingen, Germany
| | - Peter Vowden
- Faculty of Life Sciences, University of Bradford, and Honorary Consultant Vascular Surgeon, Bradford Royal Infirmary, Duckworth Lane, Bradford, BD9 6RJ, United Kingdom
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9
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Ciambella J, Nardinocchi P. Torque-induced reorientation in active fibre-reinforced materials. SOFT MATTER 2019; 15:2081-2091. [PMID: 30741294 DOI: 10.1039/c8sm02346h] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We introduce a continuum model for a fibre reinforced material in which the reference orientation of the fibre may evolve with time, under the influence of external stimuli. The model is formulated in the framework of large strain hyperelasticity and the kinematics of the continuum is described by both a position vector and by a remodelling tensor which, in the present context, is an orthogonal tensor representing the fibre reorientation process. By imposing suitable thermodynamical restrictions on the constitutive equation, we obtain an evolution equation of the remodelling tensor governed by the Eshelby torque, whose stationary solutions are studied in absence of any external source terms. It is shown that the fibres reorient themselves in a configuration that minimises the elastic energy and get aligned along a direction that may or may not be of principal strain. The explicit analysis of the Hessian of the strain energy density allows us to discriminate among the stationary solutions, which ones are stable. Examples are given for passive reorientation processes driven by applied strains or external boundary tractions. Applications of the proposed theory to biological tissues, nematic or magneto-electro active elastomers are foreseen.
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10
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Rakhsha M, Smith CR, Recuero A, Brandon SCE, Vignos MF, Thelen DG, Negrut D. Simulation of surface strain in tibiofemoral cartilage during walking for the prediction of collagen fiber orientation. COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING. IMAGING & VISUALIZATION 2018; 7:396-405. [PMID: 31886037 PMCID: PMC6934360 DOI: 10.1080/21681163.2018.1442751] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 02/15/2018] [Indexed: 06/10/2023]
Abstract
The collagen fibers in the superficial layer of tibiofemoral articular cartilage exhibit distinct patterns in orientation revealed by split lines. In this study, we introduce a simulation framework to predict cartilage surface loading during walking to investigate if split line orientations correspond with principal strain directions in the cartilage surface. The two-step framework uses a multibody musculoskeletal model to predict tibiofemoral kinematics which are then imposed on a deformable surface model to predict surface strains. The deformable surface model uses absolute nodal coordinate formulation (ANCF) shell elements to represent the articular surface and a system of spring-dampers and internal pressure to represent the underlying cartilage. Simulations were performed to predict surface strains due to osmotic pressure, loading induced by walking, and the combination of both loading due to pressure and walking. Time-averaged magnitude-weighted first principal strain directions agreed well with split line maps from the literature for both the osmotic pressure and combined cases. This result suggests there is indeed a connection between collagen fiber orientation and mechanical loading, and indicates the importance of accounting for the pre-strain in the cartilage surface due to osmotic pressure.
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Affiliation(s)
- Milad Rakhsha
- Simulation Based Engineering Laboratory (SBEL), Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Colin R Smith
- Neuromuscular Biomechanics Laboratory (NMBL), Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Antonio Recuero
- Simulation Based Engineering Laboratory (SBEL), Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Scott C E Brandon
- Neuromuscular Biomechanics Laboratory (NMBL), Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Michael F Vignos
- Neuromuscular Biomechanics Laboratory (NMBL), Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Darryl G Thelen
- Neuromuscular Biomechanics Laboratory (NMBL), Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Dan Negrut
- Simulation Based Engineering Laboratory (SBEL), Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706
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11
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Comellas E, Gasser TC, Bellomo FJ, Oller S. A homeostatic-driven turnover remodelling constitutive model for healing in soft tissues. J R Soc Interface 2016; 13:rsif.2015.1081. [PMID: 27009177 DOI: 10.1098/rsif.2015.1081] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 03/01/2016] [Indexed: 01/08/2023] Open
Abstract
Remodelling of soft biological tissue is characterized by interacting biochemical and biomechanical events, which change the tissue's microstructure, and, consequently, its macroscopic mechanical properties. Remodelling is a well-defined stage of the healing process, and aims at recovering or repairing the injured extracellular matrix. Like other physiological processes, remodelling is thought to be driven by homeostasis, i.e. it tends to re-establish the properties of the uninjured tissue. However, homeostasis may never be reached, such that remodelling may also appear as a continuous pathological transformation of diseased tissues during aneurysm expansion, for example. A simple constitutive model for soft biological tissues that regards remodelling as homeostatic-driven turnover is developed. Specifically, the recoverable effective tissue damage, whose rate is the sum of a mechanical damage rate and a healing rate, serves as a scalar internal thermodynamic variable. In order to integrate the biochemical and biomechanical aspects of remodelling, the healing rate is, on the one hand, driven by mechanical stimuli, but, on the other hand, subjected to simple metabolic constraints. The proposed model is formulated in accordance with continuum damage mechanics within an open-system thermodynamics framework. The numerical implementation in an in-house finite-element code is described, particularized for Ogden hyperelasticity. Numerical examples illustrate the basic constitutive characteristics of the model and demonstrate its potential in representing aspects of remodelling of soft tissues. Simulation results are verified for their plausibility, but also validated against reported experimental data.
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Affiliation(s)
- Ester Comellas
- International Center for Numerical Methods in Engineering (CIMNE), Campus Nord UPC, Building C1, c/Gran Capita s/n, 08034 Barcelona, Spain Department of Strength of Materials and Structural Engineering, ETSECCPB, Universitat Politcnica de Catalunya, Barcelona Tech (UPC), Campus Nord, Building C1, c/Jordi Girona 1-3, 08034 Barcelona, Spain
| | - T Christian Gasser
- Department of Solid Mechanics, School of Engineering Sciences, KTH Royal Institute of Technology, Teknikringen 8, 100 44 Stockholm, Sweden
| | - Facundo J Bellomo
- INIQUI (CONICET), Faculty of Engineering, National University of Salta, Av. Bolivia 5150, 4400 Salta, Argentina
| | - Sergio Oller
- International Center for Numerical Methods in Engineering (CIMNE), Campus Nord UPC, Building C1, c/Gran Capita s/n, 08034 Barcelona, Spain Department of Strength of Materials and Structural Engineering, ETSECCPB, Universitat Politcnica de Catalunya, Barcelona Tech (UPC), Campus Nord, Building C1, c/Jordi Girona 1-3, 08034 Barcelona, Spain
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12
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Mullen CA, Vaughan TJ, Billiar KL, McNamara LM. The effect of substrate stiffness, thickness, and cross-linking density on osteogenic cell behavior. Biophys J 2016; 108:1604-1612. [PMID: 25863052 DOI: 10.1016/j.bpj.2015.02.022] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Revised: 02/15/2015] [Accepted: 02/23/2015] [Indexed: 11/16/2022] Open
Abstract
Osteogenic cells respond to mechanical changes in their environment by altering their spread area, morphology, and gene expression profile. In particular, the bulk modulus of the substrate, as well as its microstructure and thickness, can substantially alter the local stiffness experienced by the cell. Although bone tissue regeneration strategies involve culture of bone cells on various biomaterial scaffolds, which are often cross-linked to enhance their physical integrity, it is difficult to ascertain and compare the local stiffness experienced by cells cultured on different biomaterials. In this study, we seek to characterize the local stiffness at the cellular level for MC3T3-E1 cells plated on biomaterial substrates of varying modulus, thickness, and cross-linking concentration. Cells were cultured on flat and wedge-shaped gels made from polyacrylamide or cross-linked collagen. The cross-linking density of the collagen gels was varied to investigate the effect of fiber cross-linking in conjunction with substrate thickness. Cell spread area was used as a measure of osteogenic differentiation. Finite element simulations were used to examine the effects of fiber cross-linking and substrate thickness on the resistance of the gel to cellular forces, corresponding to the equivalent shear stiffness for the gel structure in the region directly surrounding the cell. The results of this study show that MC3T3 cells cultured on a soft fibrous substrate attain the same spread cell area as those cultured on a much higher modulus, but nonfibrous substrate. Finite element simulations predict that a dramatic increase in the equivalent shear stiffness of fibrous collagen gels occurs as cross-linking density is increased, with equivalent stiffness also increasing as gel thickness is decreased. These results provide an insight into the response of osteogenic cells to individual substrate parameters and have the potential to inform future bone tissue regeneration strategies that can optimize the equivalent stiffness experienced by a cell.
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Affiliation(s)
- Conleth A Mullen
- Centre for Biomechanics Research (BMEC), Department of Biomedical Engineering, NUI Galway, Galway, Ireland; National Centre for Biomedical Engineering Science (NCBES), NUI Galway, Galway, Ireland
| | - Ted J Vaughan
- Centre for Biomechanics Research (BMEC), Department of Biomedical Engineering, NUI Galway, Galway, Ireland
| | - Kristen L Billiar
- Department Biomedical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts
| | - Laoise M McNamara
- Centre for Biomechanics Research (BMEC), Department of Biomedical Engineering, NUI Galway, Galway, Ireland; National Centre for Biomedical Engineering Science (NCBES), NUI Galway, Galway, Ireland.
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13
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Alavi SH, Sinha A, Steward E, Milliken JC, Kheradvar A. Load-dependent extracellular matrix organization in atrioventricular heart valves: differences and similarities. Am J Physiol Heart Circ Physiol 2015; 309:H276-84. [DOI: 10.1152/ajpheart.00164.2015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Accepted: 05/17/2015] [Indexed: 12/31/2022]
Abstract
The extracellular matrix of the atrioventricular (AV) valves' leaflets has a key role in the ability of these valves to properly remodel in response to constantly varying physiological loads. While the loading on mitral and tricuspid valves is significantly different, no information is available on how collagen fibers change their orientation in response to these loads. This study delineates the effect of physiological loading on AV valves' leaflets microstructures using Second Harmonic Generation (SHG) microscopy. Fresh natural porcine tricuspid and mitral valves' leaflets ( n = 12/valve type) were cut and prepared for the experiments. Histology and immunohistochemistry were performed to compare the microstructural differences between the valves. The specimens were imaged live during the relaxed, loading, and unloading phases using SHG microscopy. The images were analyzed with Fourier decomposition to mathematically seek changes in collagen fiber orientation. Despite the similarities in both AV valves as seen in the histology and immunohistochemistry data, the microstructural arrangement, especially the collagen fiber distribution and orientation in the stress-free condition, were found to be different. Uniaxial loading was dependent on the arrangement of the fibers in their relaxed mode, which led the fibers to reorient in-line with the load throughout the depth of the mitral leaflet but only to reorient in-line with the load in deeper layers of the tricuspid leaflet. Biaxial loading arranged the fibers in between the two principal axes of the stresses independently from their relaxed states. Unlike previous findings, this study concludes that the AV valves' three-dimensional extracellular fiber arrangement is significantly different in their stress-free and uniaxially loaded states; however, fiber rearrangement in response to the biaxial loading remains similar.
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Affiliation(s)
- S. Hamed Alavi
- The Edwards Lifesciences Center for Advanced Cardiovascular Technology, University of California, Irvine, Irvine, California
- Department Biomedical Engineering, University of California, Irvine, Irvine, California; and
| | - Aditi Sinha
- The Edwards Lifesciences Center for Advanced Cardiovascular Technology, University of California, Irvine, Irvine, California
- Department Biomedical Engineering, University of California, Irvine, Irvine, California; and
| | - Earl Steward
- Division of Cardiothoracic Surgery, University of California, Irvine, Irvine, California
| | - Jeffrey C. Milliken
- Division of Cardiothoracic Surgery, University of California, Irvine, Irvine, California
| | - Arash Kheradvar
- The Edwards Lifesciences Center for Advanced Cardiovascular Technology, University of California, Irvine, Irvine, California
- Department Biomedical Engineering, University of California, Irvine, Irvine, California; and
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14
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Lanir Y, Namani R. Reliability of structure tensors in representing soft tissues structure. J Mech Behav Biomed Mater 2015; 46:222-8. [DOI: 10.1016/j.jmbbm.2015.02.012] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 02/16/2015] [Accepted: 02/18/2015] [Indexed: 11/16/2022]
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15
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A theoretical model of the endothelial cell morphology due to different waveforms. J Theor Biol 2015; 379:16-23. [PMID: 25956359 DOI: 10.1016/j.jtbi.2015.04.038] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Revised: 04/14/2015] [Accepted: 04/26/2015] [Indexed: 11/21/2022]
Abstract
Endothelial cells are key units in the regulatory biological process of blood vessels. They represent an interface to transmit variations on the fluid dynamic changes. They are able to adapt its cytoskeleton, by means of microtubules reorientation and F-actin reorganization, due to new mechanical environments. Moreover, they are responsible for initiating a huge cascade of biological processes, such as the release of endothelins (ET-1), in charge of the constriction of the vessel and growth factors such as TGF-β and PDGF. Although a huge efforts have been made in the experimental characterization and description of these two issues the computational modeling has not gained such an attention. In this work we study the 3D remodeling of endothelial cells based on the main features of blood flow. In particular we study how different oscillatory shear index and the time average wall shear stresses modify the endothelial cell shape. We found our model fitted the experimental works presented before in in vitro studies. We also include our model within a computational fluid dynamics simulation of a carotid artery to evaluate endothelial cell shape index which is a key predictor of atheroma plaque formation. Moreover, our approach can be coupled with models of collagen and smooth muscle cell growth, where remodeling and the associated release of chemical substance are involved.
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16
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Sáez P, Peña E, Tarbell JM, Martínez MA. Computational model of collagen turnover in carotid arteries during hypertension. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2015; 31:e02705. [PMID: 25643608 DOI: 10.1002/cnm.2705] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Revised: 01/15/2015] [Accepted: 01/15/2015] [Indexed: 06/04/2023]
Abstract
It is well known that biological tissues adapt their properties because of different mechanical and chemical stimuli. The goal of this work is to study the collagen turnover in the arterial tissue of hypertensive patients through a coupled computational mechano-chemical model. Although it has been widely studied experimentally, computational models dealing with the mechano-chemical approach are not. The present approach can be extended easily to study other aspects of bone remodeling or collagen degradation in heart diseases. The model can be divided into three different stages. First, we study the smooth muscle cell synthesis of different biological substances due to over-stretching during hypertension. Next, we study the mass-transport of these substances along the arterial wall. The last step is to compute the turnover of collagen based on the amount of these substances in the arterial wall which interact with each other to modify the turnover rate of collagen. We simulate this process in a finite element model of a real human carotid artery. The final results show the well-known stiffening of the arterial wall due to the increase in the collagen content.
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Affiliation(s)
- P Sáez
- Group of Applied Mechanics and Bioengineering. Aragón Institute of Engineering Research, University of Zaragoza, Zaragoza, Spain; Centro de Investigación Biomédica en Red en Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Zaragoza, Spain; Mathematical Institute, University of Oxford, Oxford, UK
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17
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CILINGIR AHMETC. EFFECTS OF CULTURE PERIODS AND LOADING ON BIOMECHANICAL PROPERTIES OF SHEEP COLLAGEN FASCICLES. J MECH MED BIOL 2014. [DOI: 10.1142/s0219519414400107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Soft tissues (e.g., tendon, skin, cartilage) change their dimensions and properties in response to applied mechanical stress/strain, which is called remodeling. Experimental studies using tissue cultures were performed to understand the biomechanical properties of collagen fascicles under mechanical loads. Collagen fascicles were dissected from sheep Achilles tendons and loaded under 1, 2, and 3 kg for 2, 4, and 6 days under culture. The mechanical properties of collagen fascicles after being loaded into the culture media were determined using tensile tester, and resultant stress–strain curves, tangent modulus, tensile strength, and strain at failure values were compared with those in a non-loaded and non-cultured control group of fascicles. The tangent modulus and tensile strength of the collagen fascicles increased with the increasing remodeling load after two days of culture. However, these values gradually decreased with the increasing culture period compared with the control group. According to the results obtained in this study, the mechanical properties of collagen fascicles were improved by loading at two days of culture, most likely due to the remodeling of collagen fibers. However, after a period of remodeling, local strains on the collagen fibrils increased, and finally, the collagen fibrils broke down, decreasing the mechanical properties of the tissue.
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Affiliation(s)
- AHMET C. CILINGIR
- Mechanical Engineering Department, Sakarya University, Esentepe Campus, 54187 Sakarya, Turkey
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18
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Ateshian GA, Nims RJ, Maas S, Weiss JA. Computational modeling of chemical reactions and interstitial growth and remodeling involving charged solutes and solid-bound molecules. Biomech Model Mechanobiol 2014; 13:1105-20. [PMID: 24558059 PMCID: PMC4141041 DOI: 10.1007/s10237-014-0560-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 02/05/2014] [Indexed: 10/25/2022]
Abstract
Mechanobiological processes are rooted in mechanics and chemistry, and such processes may be modeled in a framework that couples their governing equations starting from fundamental principles. In many biological applications, the reactants and products of chemical reactions may be electrically charged, and these charge effects may produce driving forces and constraints that significantly influence outcomes. In this study, a novel formulation and computational implementation are presented for modeling chemical reactions in biological tissues that involve charged solutes and solid-bound molecules within a deformable porous hydrated solid matrix, coupling mechanics with chemistry while accounting for electric charges. The deposition or removal of solid-bound molecules contributes to the growth and remodeling of the solid matrix; in particular, volumetric growth may be driven by Donnan osmotic swelling, resulting from charged molecular species fixed to the solid matrix. This formulation incorporates the state of strain as a state variable in the production rate of chemical reactions, explicitly tying chemistry with mechanics for the purpose of modeling mechanobiology. To achieve these objectives, this treatment identifies the specific theoretical and computational challenges faced in modeling complex systems of interacting neutral and charged constituents while accommodating any number of simultaneous reactions where reactants and products may be modeled explicitly or implicitly. Several finite element verification problems are shown to agree with closed-form analytical solutions. An illustrative tissue engineering analysis demonstrates tissue growth and swelling resulting from the deposition of chondroitin sulfate, a charged solid-bound molecular species. This implementation is released in the open-source program FEBio ( www.febio.org ). The availability of this framework may be particularly beneficial to optimizing tissue engineering culture systems by examining the influence of nutrient availability on the evolution of inhomogeneous tissue composition and mechanical properties, the evolution of construct dimensions with growth, the influence of solute and solid matrix electric charge on the transport of cytokines, the influence of binding kinetics on transport, the influence of loading on binding kinetics, and the differential growth response to dynamically loaded versus free-swelling culture conditions.
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Affiliation(s)
- Gerard A Ateshian
- Departments of Mechanical Engineering and Biomedical Engineering, Columbia University, New York, NY, 10027, USA,
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19
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Pregnancy-Induced Remodeling of Collagen Architecture and Content in the Mitral Valve. Ann Biomed Eng 2014; 42:2058-71. [DOI: 10.1007/s10439-014-1077-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 07/23/2014] [Indexed: 10/24/2022]
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20
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Lanir Y. Mechanistic micro-structural theory of soft tissues growth and remodeling: tissues with unidirectional fibers. Biomech Model Mechanobiol 2014; 14:245-66. [DOI: 10.1007/s10237-014-0600-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Accepted: 05/23/2014] [Indexed: 10/25/2022]
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21
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Valentín A, Humphrey JD, Holzapfel GA. A finite element-based constrained mixture implementation for arterial growth, remodeling, and adaptation: theory and numerical verification. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2013; 29:822-49. [PMID: 23713058 PMCID: PMC3735847 DOI: 10.1002/cnm.2555] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 04/09/2013] [Accepted: 04/09/2013] [Indexed: 05/02/2023]
Abstract
We implemented a constrained mixture model of arterial growth and remodeling in a nonlinear finite element framework to facilitate numerical analyses of diverse cases of arterial adaptation and maladaptation, including disease progression, resulting in complex evolving geometries and compositions. This model enables hypothesis testing by predicting consequences of postulated characteristics of cell and matrix turnover, including evolving quantities and orientations of fibrillar constituents and nonhomogenous degradation of elastin or loss of smooth muscle function. The nonlinear finite element formulation is general within the context of arterial mechanics, but we restricted our present numerical verification to cylindrical geometries to allow comparisons with prior results for two special cases: uniform transmural changes in mass and differential growth and remodeling within a two-layered cylindrical model of the human aorta. The present finite element model recovers the results of these simplified semi-inverse analyses with good agreement.
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Affiliation(s)
- A. Valentín
- Institute of Biomechanics, Center of Biomedical Engineering, Graz University of Technology, Kronesgasse 5-I, 8010 Graz, Austria
| | - J. D. Humphrey
- Department of Biomedical Engineering, Yale University, New Haven CT 06520, USA
| | - G. A. Holzapfel
- Institute of Biomechanics, Center of Biomedical Engineering, Graz University of Technology, Kronesgasse 5-I, 8010 Graz, Austria
- Royal Institute of Technology (KTH), Department of Solid Mechanics, School of Engineering Sciences, Osquars Backe 1, 100 44 Stockholm, Sweden
- Corresponding author ()
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22
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A new multiscale model for the mechanical behavior of vein walls. J Mech Behav Biomed Mater 2013; 23:32-43. [PMID: 23660303 DOI: 10.1016/j.jmbbm.2013.04.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Revised: 03/21/2013] [Accepted: 04/02/2013] [Indexed: 11/24/2022]
Abstract
The purpose of the present work is to propose a new multiscale model for the prediction of the mechanical behavior of vein walls. This model is based on one of our previous works which considered scale transitions applied to undulated collagen fibers. In the present work, the scale below was added to take the anisotropy of collagen fibrils into account. One scale above was also added, modeling the global reorientation of collagen fibers inside the vessel wall. The model was verified on experimental data from the literature, leading to a satisfactory agreement. The proposed multiscale approach also allows the extraction of local stresses and strains at each scale. This approach is presented here in the case of vein walls, but can easily be extended to other tissues which contain similar constituents.
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23
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Characterizing the collagen fiber orientation in pericardial leaflets under mechanical loading conditions. Ann Biomed Eng 2012. [PMID: 23180029 DOI: 10.1007/s10439-012-0696-z] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
When implanted inside the body, bioprosthetic heart valve leaflets experience a variety of cyclic mechanical stresses such as shear stress due to blood flow when the valve is open, flexural stress due to cyclic opening and closure of the valve, and tensile stress when the valve is closed. These types of stress lead to a variety of failure modes. In either a natural valve leaflet or a processed pericardial tissue leaflet, collagen fibers reinforce the tissue and provide structural integrity such that the very thin leaflet can stand enormous loads related to cyclic pressure changes. The mechanical response of the leaflet tissue greatly depends on collagen fiber concentration, characteristics, and orientation. Thus, understating the microstructure of pericardial tissue and its response to dynamic loading is crucial for the development of more durable heart valve, and computational models to predict heart valves' behavior. In this work, we have characterized the 3D collagen fiber arrangement of bovine pericardial tissue leaflets in response to a variety of different loading conditions under Second-Harmonic Generation Microscopy. This real-time visualization method assists in better understanding of the effect of cyclic load on collagen fiber orientation in time and space.
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24
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Li HY, Chen M, Yang JF, Yang CQ, Xu L, Wang F, Tong JB, Lv Y, Suonan C. Fluid flow along venous adventitia in rabbits: is it a potential drainage system complementary to vascular circulations? PLoS One 2012; 7:e41395. [PMID: 22848483 PMCID: PMC3406065 DOI: 10.1371/journal.pone.0041395] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Accepted: 06/25/2012] [Indexed: 12/02/2022] Open
Abstract
Background Our previous research and other studies with radiotracers showed evidence of a centripetal drainage pathway, separate from blood or lymphatic vessels, that can be visualized when a small amount of low molecular weight tracer is injected subcutaneously into a given region on skin of humans. In order to further characterize this interesting biological phenomenon, animal experiments are designed to elucidate histological and physiologic characteristics of these visualized pathways. Methods Multiple tracers are injected subcutaneously into an acupuncture point of KI3 to visualize centripetal pathways by magnetic resonance imaging or fluorescein photography in 85 healthy rabbits. The pathways are compared with venography and indirect lymphangiography. Fluid flow through the pathways is observed by methods of altering their hydrated state, hydrolyzing by different collagenases, and histology is elucidated by optical, fluorescein and electron microscopy. Results Histological and magnetic imaging examinations of these visualized pathways show they consist of perivenous loose connective tissues. As evidenced by examinations of tracers’ uptake, they appear to function as a draining pathway for free interstitial fluid. Fluorescein sodium from KI3 is found in the pathways of hind limbs and segments of the small intestines, partial pulmonary veins and results in pericardial effusion, suggesting systematical involvement of this perivenous pathway. The hydraulic conductivity of these pathways can be compromised by the collapse of their fiber-rich beds hydrolyzed by either of collagenase type I, III, IV or V. Conclusions The identification of pathways comprising perivenous loose connective tissues with a high hydraulic conductivity draining interstitial fluid in hind limbs of a mammal suggests a potential drainage system complementary to vascular circulations. These findings may provide new insights into a systematically distributed collagenous connective tissue with a circulatory function and their potential relevance to the nature of acupuncture meridians.
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Affiliation(s)
- Hong-yi Li
- Cardiology Division, Beijing Hospital of the Ministry of Health, Beijing, People's Republic of China.
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25
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Zeugolis DI, Li B, Lareu RR, Chan CK, Raghunath M. Collagen solubility testing, a quality assurance step for reproducible electro-spun nano-fibre fabrication. A technical note. JOURNAL OF BIOMATERIALS SCIENCE-POLYMER EDITION 2012; 19:1307-17. [DOI: 10.1163/156856208786052344] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- D. I. Zeugolis
- a Tissue Modulation Laboratory, National University of Singapore, 117510, Singapore; National University of Singapore Tissue Engineering Programme (NUSTEP), National University of Singapore, 117510, Singapore; Division of Bioengineering, Faculty of Engineering, National University of Singapore, 117576, Singapore; Immunology Programme, Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, 117456, Singapore
| | - B. Li
- b Division of Bioengineering, Faculty of Engineering, National University of Singapore, 117576, Singapore; National University of Singapore Science and Nanobiotechnoloy Initiative (NUSSNI), National University of Singapore, 117576, Singapore
| | - R. R. Lareu
- c Tissue Modulation Laboratory, National University of Singapore, 117510, Singapore; National University of Singapore Tissue Engineering Programme (NUSTEP), National University of Singapore, 117510, Singapore; Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, 117597, Singapore
| | - C. K. Chan
- d Division of Bioengineering, Faculty of Engineering, National University of Singapore, 117576, Singapore; National University of Singapore Science and Nanobiotechnoloy Initiative (NUSSNI), National University of Singapore, 117576, Singapore; Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, 117597, Singapore
| | - M. Raghunath
- e Tissue Modulation Laboratory, National University of Singapore, 117510, Singapore; Division of Bioengineering, Faculty of Engineering, National University of Singapore, 117576, Singapore; Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, 117597, Singapore
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26
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Tawhai M, Bischoff J, Einstein D, Erdemir A, Guess T, Reinbolt J. Multiscale modeling in computational biomechanics. ACTA ACUST UNITED AC 2011; 28:41-9. [PMID: 19457733 DOI: 10.1109/memb.2009.932489] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Merryn Tawhai
- Auckland Bioengineering Institute, The University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand.
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27
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Remodelling of collagen fibre transition stretch and angular distribution in soft biological tissues and cell-seeded hydrogels. Biomech Model Mechanobiol 2011; 11:325-39. [DOI: 10.1007/s10237-011-0313-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Accepted: 05/02/2011] [Indexed: 10/18/2022]
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28
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Schmid H, Pauli L, Paulus A, Kuhl E, Itskov M. Consistent formulation of the growth process at the kinematic and constitutive level for soft tissues composed of multiple constituents. Comput Methods Biomech Biomed Engin 2011; 15:547-61. [PMID: 21347909 DOI: 10.1080/10255842.2010.548325] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Previous studies have investigated the possibilities of modelling the change in volume and change in density of biomaterials. This can be modelled at the constitutive or the kinematic level. This work introduces a consistent formulation at the kinematic and constitutive level for growth processes. Most biomaterials consist of many constituents and can be approximated as being incompressible. These two conditions (many constituents and incompressibility) suggest a straightforward implementation in the context of the finite element (FE) method which could now be validated more easily against histological measurements. Its key characteristic variable is the normalised partial mass change. Using the concept of homeostatic equilibrium, we suggest two complementary growth laws in which the evolution of the normalised partial mass change is governed by an ordinary differential equation in terms of either the Piola-Kirchhoff stress or the Green-Lagrange strain. We combine this approach with the classical incompatibility condition and illustrate its algorithmic implementation within a fully nonlinear FE approach. This approach is first illustrated for a simple uniaxial tension and extension test for pure volume change and pure density change and is validated against previous numerical results. Finally, a physiologically based example of a two-phase model is presented which is a combination of volume and density changes. It can be concluded that the effect of hyper-restoration may be due to the systemic effect of degradation and adaptation of given constituents.
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Affiliation(s)
- H Schmid
- Department of Continuum Mechanics, RWTH Aachen University, Eilfschornsteinstrasse 18, 56062 Aachen, Germany.
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29
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Live en face imaging of aortic valve leaflets under mechanical stress. Biomech Model Mechanobiol 2011; 11:355-61. [PMID: 21604147 DOI: 10.1007/s10237-011-0315-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Accepted: 05/08/2011] [Indexed: 11/26/2022]
Abstract
Soft tissues, such as tendons, skin, arteries, or lung, are constantly subject to mechanical stresses in vivo. None more so than the aortic heart valve that experiences an array of forces including shear stress, cyclic pressure, strain, and flexion. Anisotropic biaxial cyclic stretch maintains valve homeostasis; however, abnormal forces are implicated in disease progression. The response of the valve endothelium to deviations from physiological levels has not been fully characterized. Here, we show the design and validation of a novel stretch apparatus capable of applying biaxial stretch to viable heart valve tissue, while simultaneously allowing for live en face endothelial cell imaging via confocal laser scanning microscopy (CLSM). Real-time imaging of tissue is possible while undergoing highly characterized mechanical conditions and maintaining the native extracellular matrix. Thus, it provides significant advantages over traditional cell culture or in vivo animal models. Planar biaxial tissue stretching with simultaneous live cell imaging could prove useful in studying the mechanobiology of any soft tissue.
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30
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Kroon M. Modeling of fibroblast-controlled strengthening and remodeling of uniaxially constrained collagen gels. J Biomech Eng 2010; 132:111008. [PMID: 21034149 DOI: 10.1115/1.4002666] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
A theoretical model for the remodeling of collagen gels is proposed. The collagen fabric is modeled as a network of collagen fibers, which in turn are composed of collagen fibrils. In the model, the strengthening of collagen fabric is accomplished by fibroblasts, which continuously recruit and attach more collagen fibrils to existing collagen fibers. The fibroblasts also accomplish a reorientation of collagen fibers. Fibroblasts are assumed to reorient collagen fibers toward the direction of maximum material stiffness. The proposed model is applied to experiments in which fibroblasts were inserted into a collagen gel. The model is able to predict the force-strain curves for the experimental collagen gels, and the final distribution of collagen fibers also agrees qualitatively with the experiments.
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Affiliation(s)
- Martin Kroon
- Department of Solid Mechanics, Royal Institute of Technology, Stockholm, Sweden.
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31
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Regional structure-function relationships in mouse aortic valve tissue. J Biomech 2010; 44:77-83. [PMID: 20863504 DOI: 10.1016/j.jbiomech.2010.08.026] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Revised: 07/29/2010] [Accepted: 08/19/2010] [Indexed: 01/06/2023]
Abstract
Site-specific biomechanical properties of the aortic valve play an important role in native valve function, and alterations in these properties may reflect mechanisms of degeneration and disease. Small animals such as targeted mutagenesis mice provide a powerful approach to model human valve disease pathogenesis; however, physical mechanical testing in small animals is limited by valve tissue size. Aortic valves are comprised of highly organized extracellular matrix compartmentalized in cusp and annulus regions, which have different functions. The objective of this study was to measure regional mechanical properties of mouse aortic valve tissue using a modified micropipette aspiration technique. Aortic valves were isolated from juvenile, adult and aged adult C57BL/6 wild type mice. Tissue tensile stiffness was determined for annulus and cusp regions using a half-space punch model. Stiffness for the annulus region was significantly higher compared to the cusp region at all stages. Further, aged adult valve tissue had decreased stiffness in both the cusp and annulus. Quantitative histochemical analysis revealed a collagen-rich annulus and a proteoglycan-rich cusp at all stages. In aged adult valves, there was proteoglycan infiltration of the annulus hinge, consistent with the observed mechanical differences over time. These findings indicate that valve tissue biomechanical properties vary in wild type mice in a region-specific and age-related manner. The micropipette aspiration technique provides a promising approach for studies of valve structure and function in small animal models, such as transgenic mouse models of valve disease.
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On the correlation between continuum mechanics entities and cell activity in biological soft tissues: Assessment of three possible criteria for cell-controlled fibre reorientation in collagen gels and collagenous tissues. J Theor Biol 2010; 264:66-76. [DOI: 10.1016/j.jtbi.2009.12.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Revised: 12/22/2009] [Accepted: 12/24/2009] [Indexed: 11/17/2022]
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Nagel T, Kelly DJ. Mechano-regulation of mesenchymal stem cell differentiation and collagen organisation during skeletal tissue repair. Biomech Model Mechanobiol 2009; 9:359-72. [PMID: 20039092 DOI: 10.1007/s10237-009-0182-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2009] [Accepted: 12/03/2009] [Indexed: 01/13/2023]
Abstract
A number of mechano-regulation theories have been proposed that relate the differentiation pathway of mesenchymal stem cells (MSCs) to their local biomechanical environment. During spontaneous repair processes in skeletal tissues, the organisation of the extracellular matrix is a key determinant of its mechanical fitness. In this paper, we extend the mechano-regulation theory proposed by Prendergast et al. (J Biomech 30(6):539-548, 1997) to include the role of the mechanical environment on the collagen architecture in regenerating soft tissues. A large strain anisotropic poroelastic material model is used in a simulation of tissue differentiation in a fracture subject to cyclic bending (Cullinane et al. in J Orthop Res 20(3):579-586, 2002). The model predicts non-union with cartilage and fibrous tissue formation in the defect. Predicted collagen fibre angles, as determined by the principal decomposition of strain- and stress-type tensors, are similar to the architecture seen in native articular cartilage and neoarthroses induced by bending of mid-femoral defects in rats. Both stress and strain-based remodelling stimuli successfully predicted the general patterns of collagen fibre organisation observed in vivo. This provides further evidence that collagen organisation during tissue differentiation is determined by the mechanical environment. It is envisioned that such predictive models can play a key role in optimising MSC-based skeletal repair therapies where recapitulation of the normal tissue architecture is critical to successful repair.
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Affiliation(s)
- Thomas Nagel
- Trinity Centre for Bioengineering, Department of Mechanical and Manufacturing Engineering, School of Engineering, Trinity College Dublin, Dublin 2, Ireland
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35
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Wan W, Hansen L, Gleason RL. A 3-D constrained mixture model for mechanically mediated vascular growth and remodeling. Biomech Model Mechanobiol 2009; 9:403-19. [PMID: 20039091 DOI: 10.1007/s10237-009-0184-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Accepted: 12/08/2009] [Indexed: 11/29/2022]
Abstract
In contrast to the widely applied approach to model soft tissue remodeling employing the concept of volumetric growth, microstructurally motivated models are capable of capturing many of the underlying mechanisms of growth and remodeling; i.e., the production, removal, and remodeling of individual constituents at different rates and to different extents. A 3-dimensional constrained mixture computational framework has been developed for vascular growth and remodeling, considering new, microstructurally motivated kinematics and constitutive equations and new stress and muscle activation mediated evolution equations. Our computational results for alterations in flow and pressure, using reasonable physiological values for rates of constituent growth and turnover, concur with findings in the literature. For example, for flow-induced remodeling, our simulations predict that, although the wall shear stress is restored completely, the circumferential stress is not restored employing realistic physiological rate parameters. Also, our simulations predict different levels of thickening on inner versus outer wall locations, as shown in numerous reports of pressure-induced remodeling. Whereas the simulations are meant to be illustrative, they serve to highlight the experimental data currently lacking to fully quantify mechanically mediated adaptations in the vasculature.
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Affiliation(s)
- William Wan
- The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, 30332, USA
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Yang JY, Ting YC, Lai JY, Liu HL, Fang HW, Tsai WB. Quantitative analysis of osteoblast-like cells (MG63) morphology on nanogrooved substrata with various groove and ridge dimensions. J Biomed Mater Res A 2009; 90:629-40. [PMID: 18563818 DOI: 10.1002/jbm.a.32130] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Nanotextured silicon substrata with parallel ridges separated by grooves with equal width from 90 to 500 nm, were fabricated by electron beam lithography and dry etching techniques. Osteoblast-like cells, MG-63, were cultured on the sterilized nanopatterned substrata for 4 or 24 h, and then imaged by scanning electron microscopy. The influence of substrate topography on cell morphology was analyzed by image software. We found the initially cells spread faster on the nanopatterned surfaces than on the flat surface, suggesting that surface anisotropic feature facilitates initial cell extension along its direction. However, because of inhibition of cell lateral expansion across nanogrooved surfaces, the cells on the nanogrooved surface did not further expand laterally, and cell spreading area was less than that on the flat surface after 24 h of incubation. Cells elongated and aligned along the direction of grooves on all the nanopatterned substrata. Furthermore, fluorescence staining of cell nuclei indicated that the nuclei of the cells cultured on the nanopatterned surfaces also displayed a more elongated and aligned morphology along the direction of the grooves. Since cell shape and orientation influence cell functions and alignment of extracellular matrix secreted by cells, our results may provide the information regarding responses of osteoblasts to the nanostructure of collagen fibrils, and benefit bone tissue engineering and surface design of orthopedic implants.
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Girard MJA, Suh JKF, Bottlang M, Burgoyne CF, Downs JC. Scleral biomechanics in the aging monkey eye. Invest Ophthalmol Vis Sci 2009; 50:5226-37. [PMID: 19494203 PMCID: PMC2883469 DOI: 10.1167/iovs.08-3363] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
PURPOSE To investigate the age-related differences in the inhomogeneous, anisotropic, nonlinear biomechanical properties of posterior sclera from old (22.9 +/- 5.3 years) and young (1.5 +/- 0.7 years) rhesus monkeys. METHODS The posterior scleral shell of each eye was mounted on a custom-built pressurization apparatus, then intraocular pressure (IOP) was elevated from 5 to 45 mm Hg while the 3D displacements of the scleral surface were measured with speckle interferometry. Each scleral shell's geometry was digitally reconstructed from data generated by a 3-D digitizer (topography) and 20-MHz ultrasound (thickness). An inverse finite element (FE) method incorporating a fiber-reinforced constitutive model was used to extract a unique set of biomechanical properties for each eye. Displacements, thickness, stress, strain, tangent modulus, structural stiffness, and preferred collagen fiber orientation were mapped for each posterior sclera. RESULTS The model yielded 3-D deformations of posterior sclera that matched well with those observed experimentally. The posterior sclera exhibited inhomogeneous, anisotropic, nonlinear mechanical behavior. The sclera was significantly thinner (P = 0.038) and tangent modulus and structural stiffness were significantly higher in old monkeys (P < 0.0001). On average, scleral collagen fibers were circumferentially oriented around the optic nerve head (ONH). No difference was found in the preferred collagen fiber orientation and fiber concentration factor between age groups. CONCLUSIONS Posterior sclera of old monkeys is significantly stiffer than that of young monkeys and is therefore subject to higher stresses but lower strains at all levels of IOP. Age-related stiffening of the sclera may significantly influence ONH biomechanics and potentially contribute to age-related susceptibility to glaucomatous vision loss.
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Affiliation(s)
- Michaël J. A. Girard
- Department of Biomedical Engineering, Tulane University, 6823 St. Charles Avenue, New Orleans LA, 70118
- Ocular Biomechanics Laboratory, Devers Eye Institute, 1225 NE 2nd Avenue, Portland, OR 97232
- Current affiliation: Department of Bioengineering, Imperial College London, London UK, SW7 2AZ
| | - J-K. Francis Suh
- Department of Biomedical Engineering, Tulane University, 6823 St. Charles Avenue, New Orleans LA, 70118
- Convergence Technology Laboratory, Korea Institute of Science and Technology, Hawolgok-Dong 39-1, Seongbuk-Gu, Seoul, Korea
| | - Michael Bottlang
- Biomechanics Laboratory, Legacy Health Research, 1225 NE 2nd Avenue, Portland, OR 97232
| | - Claude F. Burgoyne
- Department of Biomedical Engineering, Tulane University, 6823 St. Charles Avenue, New Orleans LA, 70118
- Optic Nerve Head Research Laboratory, Devers Eye Institute, 1225 NE 2nd Avenue, Portland, OR 97232
| | - J. Crawford Downs
- Department of Biomedical Engineering, Tulane University, 6823 St. Charles Avenue, New Orleans LA, 70118
- Ocular Biomechanics Laboratory, Devers Eye Institute, 1225 NE 2nd Avenue, Portland, OR 97232
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Need for a Continuum Biochemomechanical Theory of Soft Tissue and Cellular Growth and Remodeling. BIOMECHANICAL MODELLING AT THE MOLECULAR, CELLULAR AND TISSUE LEVELS 2009. [DOI: 10.1007/978-3-211-95875-9_1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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39
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The modelling of fibre reorientation in soft tissue. Biomech Model Mechanobiol 2008; 8:359-70. [DOI: 10.1007/s10237-008-0142-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2008] [Accepted: 10/23/2008] [Indexed: 10/21/2022]
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40
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Zeugolis D, Paul R, Attenburrow G. Post-self-assembly experimentation on extruded collagen fibres for tissue engineering applications. Acta Biomater 2008; 4:1646-56. [PMID: 18590987 DOI: 10.1016/j.actbio.2008.05.015] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Revised: 05/08/2008] [Accepted: 05/15/2008] [Indexed: 10/22/2022]
Abstract
Extruded collagen fibres have been shown to constitute a biomimetic three-dimensional scaffold with numerous tissue engineering applications. The multi-step fabrication process of this material provides opportunities for further advancements to improve the properties of the final product. Herein we investigated the influence of the post-self-assembly washing baths on the structural, mechanical and thermal properties of these fibres. The surface morphology and the inter-fibre packing were similar for every treatment. The overnight incubation in isopropanol yielded fibres with the highest temperature and energy of denaturation (p<0.013). Typical s- and j-shape stress-strain curves were obtained for all treatments in the dry and wet state respectively. Rehydration of the fibres resulted in increased fibre diameter (p<0.006) and reduced stress (p<0.001), force (p<0.001) and modulus (p<0.002) values for every treatment. In the dry state, the alcohol-treated fibres were characterized by the highest stress (p<0.002) values; whilst in the wet state the Tris-HCl-treated fibres were the weakest (p<0.006). For every treatment, in both dry and wet state, a strong and inverse relationship between the fibre diameter and the stress at break was observed. Overall, the fibres produced were characterized by properties similar to those of native tissues.
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41
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Girard MJA, Downs JC, Burgoyne CF, Suh JKF. Experimental surface strain mapping of porcine peripapillary sclera due to elevations of intraocular pressure. J Biomech Eng 2008; 130:041017. [PMID: 18601459 DOI: 10.1115/1.2948416] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
To experimentally characterize 2D surface mapping of the deformation pattern of porcine peripapillary sclera following acute elevations of intraocular pressure (IOP) from 5 mm Hg to 45 mm Hg. Four porcine eyes were obtained within 48 h postmortem and dissected to the sclera. After the anterior chamber was removed, each posterior scleral shell was individually mounted at the equator on a custom-built pressurization device, which internally pressurized the scleral samples with isotonic saline at 22 degrees C. Black polystyrene microspheres (10 microm in diameter) were randomly scattered and attached to the scleral surface. IOP was incrementally increased from 5 mm Hg to 45 mm Hg (+/-0.15 mm Hg), and the surface deformation of the peripapillary sclera immediately adjacent to the dural insertion was optically tracked at a resolution of 2 micrompixel one quadrant at a time, for each of four quadrants (superior, nasal, inferior, and temporal). The 2D displacement data of the microsphere markers were extracted using the optical flow equation, smoothed by weighting function interpolation, and converted to the corresponding Lagrangian finite surface strain. In all four quadrants of each eye, the principal strain was highest and primarily circumferential immediately adjacent to the scleral canal. Average maximum Lagrangian strain across all quadrants for all eyes was 0.013+/-0.005 from 5 mm Hg to 10 mm Hg, 0.014+/-0.004 from 10 mm Hg to 30 mm Hg and 0.004+/-0.001 from 30 mm Hg to 45 mm Hg, demonstrating the nonlinearity in the IOP-strain relationship. For each scleral shell, the observed surface strain mapping implied that the scleral stiffness was relatively low between 5 mm Hg and 10 mm Hg, but dramatically increased for each IOP elevation increment beyond 10 mm Hg. Peripapillary deformation following an acute IOP elevation may be governed by the underlying scleral collagen microstructure and is likely in the high-stiffness region of the scleral stress-strain curve when IOP is above 10 mm Hg.
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Affiliation(s)
- Michaël J A Girard
- Department of Biomedical Engineering, Tulane University, 6823 St. Charles Avenue, New Orleans, LA 70118, USA.
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42
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Cox MA, Gawlitta D, Driessen NJ, Oomens CW, Baaijens FP. The non-linear mechanical properties of soft engineered biological tissues determined by finite spherical indentation. Comput Methods Biomech Biomed Engin 2008; 11:585-92. [DOI: 10.1080/10255840701771768] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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43
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Stress related collagen ultrastructure in human aortic valves—implications for tissue engineering. J Biomech 2008; 41:2612-7. [DOI: 10.1016/j.jbiomech.2008.06.031] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2007] [Revised: 06/17/2008] [Accepted: 06/19/2008] [Indexed: 11/27/2022]
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O'Connell MK, Murthy S, Phan S, Xu C, Buchanan J, Spilker R, Dalman RL, Zarins CK, Denk W, Taylor CA. The three-dimensional micro- and nanostructure of the aortic medial lamellar unit measured using 3D confocal and electron microscopy imaging. Matrix Biol 2007; 27:171-81. [PMID: 18248974 DOI: 10.1016/j.matbio.2007.10.008] [Citation(s) in RCA: 248] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Revised: 10/29/2007] [Accepted: 10/29/2007] [Indexed: 11/20/2022]
Abstract
Changes in arterial wall composition and function underlie all forms of vascular disease. The fundamental structural and functional unit of the aortic wall is the medial lamellar unit (MLU). While the basic composition and organization of the MLU is known, three-dimensional (3D) microstructural details are tenuous, due (in part) to lack of three-dimensional data at micro- and nano-scales. We applied novel electron and confocal microscopy techniques to obtain 3D volumetric information of aortic medial microstructure at micro- and nano-scales with all constituents present. For the rat abdominal aorta, we show that medial elastin has three primary forms: with approximately 71% of total elastin as thick, continuous lamellar sheets, 27% as thin, protruding interlamellar elastin fibers (IEFs), and 2% as thick radial struts. Elastin pores are not simply holes in lamellar sheets, but are indented and gusseted openings in lamellae. Smooth muscle cells (SMCs) weave throughout the interlamellar elastin framework, with cytoplasmic extensions abutting IEFs, resulting in approximately 20 degrees radial tilt (relative to the lumen surface) of elliptical SMC nuclei. Collagen fibers are organized as large, parallel bundles tightly enveloping SMC nuclei. Quantification of the orientation of collagen bundles, SMC nuclei, and IEFs reveal that all three primary medial constituents have predominantly circumferential orientation, correlating with reported circumferentially dominant values of physiological stress, collagen fiber recruitment, and tissue stiffness. This high resolution three-dimensional view of the aortic media reveals MLU microstructure details that suggest a highly complex and integrated mural organization that correlates with aortic mechanical properties.
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Affiliation(s)
- Mary K O'Connell
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
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Humphrey JD, Wells PB, Baek S, Hu JJ, McLeroy K, Yeh AT. A theoretically-motivated biaxial tissue culture system with intravital microscopy. Biomech Model Mechanobiol 2007; 7:323-34. [PMID: 17701064 DOI: 10.1007/s10237-007-0099-5] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Accepted: 04/29/2007] [Indexed: 11/29/2022]
Abstract
Many cell types produce, remodel, and degrade extracellular matrix in response to diverse stimuli, including mechanical loads. Much is known about the molecular biology and biochemistry of the deposition and degradation of collagen, the primary structural constituent of the extracellular matrix in many tissues, yet there has been little modeling of the associated mechanobiology. For example, we do not have quantitative descriptions, or rules, for the kinetics of collagen turnover as a function of altered mechanical loading and we do not know what governs the orientation and pre-stretch at which new fibers are incorporated within extant tissue. In this paper, we use a constrained mixture theory for growth and remodeling of planar soft tissues to motivate a new experimental approach for investigating competing hypotheses on, for example, how new collagen is aligned by synthetic cells. In particular, because stress and strain fields can be homogeneous in a central region of a biaxially tested tissue, and because biaxial testing admits diverse protocols wherein equal stresses can be imposed in the presence of unequal strains or stresses can be maintained in the absence of strain, we report simulations that illustrate the potential utility of biaxial culture studies. Finally, we describe the associated design of a computer-controlled system that allows intravital microscopic quantification of collagen density, orientation, and cross-linking at various stages during the adaptation of a native tissue or the development of a tissue engineered equivalent, each subjected to well controlled biaxial loads.
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Affiliation(s)
- J D Humphrey
- Department of Biomedical Engineering, Texas A&M University, 337 Zachry Engineering Center, 3120 TAMU, College Station, TX 77843-3120, USA,
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Dahl SLM, Vaughn ME, Niklason LE. An ultrastructural analysis of collagen in tissue engineered arteries. Ann Biomed Eng 2007; 35:1749-55. [PMID: 17566861 PMCID: PMC2605788 DOI: 10.1007/s10439-007-9340-8] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2006] [Accepted: 06/06/2007] [Indexed: 11/30/2022]
Abstract
Collagen is the structural molecule that is most correlated with strength in blood vessels. In this study, we compared the properties of collagen in engineered and native blood vessels. Transmission electron microscopy (TEM) was used to image sections of engineered and native arteries. Band periodicities of engineered and native collagen fibrils indicated that spacing between collagen molecules was similar in engineered and native tissues. Engineered arteries, however, had thinner collagen fibrils and fibers than native arteries. Further, collagen fibrils were more loosely packed within collagen fibers in engineered arteries than in native arteries. The sensitivity of TEM analysis allowed measurement of the relative frequency of observation for alignment of collagen. These observations showed that collagen in both engineered and native arteries was aligned circumferentially, helically, and axially, but that engineered arteries had less circumferential collagen and more axial collagen than native arteries. Given that collagen is primarily responsible for dictating the ultimate mechanical properties of arterial tissue, future efforts should focus on using relative frequency of observation for alignment of collagen as a descriptive input for models of the mechanical properties of engineered or native tissues.
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Affiliation(s)
- Shannon L M Dahl
- Department of Biomedical Engineering, Duke University, Durham, NC 27708, USA.
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47
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Driessen NJB, Cox MAJ, Bouten CVC, Baaijens FPT. Remodelling of the angular collagen fiber distribution in cardiovascular tissues. Biomech Model Mechanobiol 2007; 7:93-103. [PMID: 17354005 PMCID: PMC2792349 DOI: 10.1007/s10237-007-0078-x] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2006] [Accepted: 01/14/2007] [Indexed: 11/18/2022]
Abstract
Understanding collagen fiber remodelling is desired to optimize the mechanical conditioning protocols in tissue-engineering of load-bearing cardiovascular structures. Mathematical models offer strong possibilities to gain insight into the mechanisms and mechanical stimuli involved in these remodelling processes. In this study, a framework is proposed to investigate remodelling of angular collagen fiber distribution in cardiovascular tissues. A structurally based model for collagenous cardiovascular tissues is extended with remodelling laws for the collagen architecture, and the model is subsequently applied to the arterial wall and aortic valve. For the arterial wall, the model predicts the presence of two helically arranged families of collagen fibers. A branching, diverging hammock-type fiber architecture is predicted for the aortic valve. It is expected that the proposed model may be of great potential for the design of improved tissue engineering protocols and may give further insight into the pathophysiology of cardiovascular diseases.
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Affiliation(s)
- Niels J B Driessen
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
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48
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Driessen NJB, Mol A, Bouten CVC, Baaijens FPT. Modeling the mechanics of tissue-engineered human heart valve leaflets. J Biomech 2007; 40:325-34. [PMID: 16529755 DOI: 10.1016/j.jbiomech.2006.01.009] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Accepted: 01/09/2006] [Indexed: 11/30/2022]
Abstract
Mathematical models can provide valuable information to assess and evaluate the mechanical behavior of tissue-engineered constructs. In this study, a structurally based model is applied to describe and analyze the mechanics of tissue-engineered human heart valve leaflets. The results from two orthogonal uniaxial tensile tests are used to determine the model parameters of the constructs after two, three and four weeks of culturing. Subsequently, finite element analyses are performed to simulate the mechanical response of the engineered leaflets to a pressure load. The stresses in the leaflets induced by the pressure load increase monotonically with culture time due to a decrease in the construct's thickness. The strains, on the other hand, eventually decrease as a result of an increase in the elastic modulus. Compared to native porcine leaflets, the mechanical response of the engineered tissues after four weeks of culturing is more linear, stiffer and less anisotropic.
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Affiliation(s)
- Niels J B Driessen
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
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49
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Wilson W, Driessen NJB, van Donkelaar CC, Ito K. Prediction of collagen orientation in articular cartilage by a collagen remodeling algorithm. Osteoarthritis Cartilage 2006; 14:1196-202. [PMID: 16797194 DOI: 10.1016/j.joca.2006.05.006] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2006] [Accepted: 05/09/2006] [Indexed: 02/02/2023]
Abstract
OBJECTIVE Tissue engineering is a promising method to treat damaged cartilage. So far it has not been possible to create tissue-engineered cartilage with an appropriate structural organization. It is envisaged that cartilage tissue engineering will significantly benefit from knowledge of how the collagen fiber orientation is directed by mechanical conditions. The goal of the present study is to evaluate whether a collagen remodeling algorithm based on mechanical loading can be corroborated by the collagen orientation in healthy cartilage. METHODS According to the remodeling algorithm, collagen fibrils align with a preferred fibril direction, situated between the positive principal strain directions. The remodeling algorithm was implemented in an axisymmetric finite element model of the knee joint. Loading as a result of typical daily activities was represented in three different phases: rest, standing and gait. RESULTS In the center of the tibial plateau the collagen fibrils run perpendicular to the subchondral bone. Just below the articular surface they bend over to merge with the articular surface. Halfway between the center and the periphery, the collagen fibrils bend over earlier, resulting in a thicker superficial and transitional zones. Near the periphery fibrils in the deep zone run perpendicular to the articular surface and slowly bend over to angles of -45 degrees and +45 degrees with the articular surface. CONCLUSION The collagen structure as predicted with the collagen remodeling algorithm corresponds very well with the collagen structure in healthy knee joints. This remodeling algorithm is therefore considered to be a valuable tool for developing loading protocols for tissue engineering of articular cartilage.
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Affiliation(s)
- W Wilson
- Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
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50
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Hariton I, de Botton G, Gasser TC, Holzapfel GA. Stress-driven collagen fiber remodeling in arterial walls. Biomech Model Mechanobiol 2006; 6:163-75. [PMID: 16912884 DOI: 10.1007/s10237-006-0049-7] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Accepted: 03/22/2006] [Indexed: 10/24/2022]
Abstract
A stress-driven model for the relation between the collagen morphology and the loading conditions in arterial walls is proposed. We assume that the two families of collagen fibers in arterial walls are aligned along preferred directions, located between the directions of the two maximal principal stresses. For the determination of these directions an iterative finite element based procedure is developed. As an example the remodeling of a section of a human common carotid artery is simulated. We find that the predicted fiber morphology correlates well with experimental observations. Interesting outcomes of the model including local shear minimization and the possibility of axial compressions due to high blood pressure are revealed and discussed.
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Affiliation(s)
- I Hariton
- The Pearlstone Center for Aeronautical Studies, Department of Mechanical Engineering, Ben-Gurion University, Beer-Sheva, Israel
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