1
|
Subject-specific multiscale modeling of aortic valve biomechanics. Biomech Model Mechanobiol 2021; 20:1031-1046. [PMID: 33792805 PMCID: PMC8154826 DOI: 10.1007/s10237-021-01429-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 01/28/2021] [Indexed: 11/13/2022]
Abstract
A Finite Element workflow for the multiscale analysis of the aortic valve biomechanics was developed and applied to three physiological anatomies with the aim of describing the aortic valve interstitial cells biomechanical milieu in physiological conditions, capturing the effect of subject-specific and leaflet-specific anatomical features from the organ down to the cell scale. A mixed approach was used to transfer organ-scale information down to the cell-scale. Displacement data from the organ model were used to impose kinematic boundary conditions to the tissue model, while stress data from the latter were used to impose loading boundary conditions to the cell level. Peak of radial leaflet strains was correlated with leaflet extent variability at the organ scale, while circumferential leaflet strains varied over a narrow range of values regardless of leaflet extent. The dependency of leaflet biomechanics on the leaflet-specific anatomy observed at the organ length-scale is reflected, and to some extent emphasized, into the results obtained at the lower length-scales. At the tissue length-scale, the peak diastolic circumferential and radial stresses computed in the fibrosa correlated with the leaflet surface area. At the cell length-scale, the difference between the strains in two main directions, and between the respective relationships with the specific leaflet anatomy, was even more evident; cell strains in the radial direction varied over a relatively wide range (\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$$0.36-0.87$$\end{document}0.36-0.87) with a strong correlation with the organ length-scale radial strain (\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$$R^{2}= 0.95$$\end{document}R2=0.95); conversely, circumferential cell strains spanned a very narrow range (\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$$0.75-0.88$$\end{document}0.75-0.88) showing no correlation with the circumferential strain at the organ level (\documentclass[12pt]{minimal}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsbsy}
\usepackage{mathrsfs}
\usepackage{upgreek}
\setlength{\oddsidemargin}{-69pt}
\begin{document}$$R^{2}= 0.02$$\end{document}R2=0.02). Within the proposed simulation framework, being able to account for the actual anatomical features of the aortic valve leaflets allowed to gain insight into their effect on the structural mechanics of the leaflets at all length-scales, down to the cell scale.
Collapse
|
2
|
Al-Shammari H, Latif N, Sarathchandra P, McCormack A, Rog-Zielinska EA, Raja S, Kohl P, Yacoub MH, Peyronnet R, Chester AH. Expression and function of mechanosensitive ion channels in human valve interstitial cells. PLoS One 2020; 15:e0240532. [PMID: 33057457 PMCID: PMC7561104 DOI: 10.1371/journal.pone.0240532] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 09/28/2020] [Indexed: 11/21/2022] Open
Abstract
Background The ability of heart valve cells to respond to their mechanical environment represents a key mechanism by which the integrity and function of valve cusps is maintained. A number of different mechanotransduction pathways have been implicated in the response of valve cells to mechanical stimulation. In this study, we explore the expression pattern of several mechanosensitive ion channels (MSC) and their potential to mediate mechanosensitive responses of human valve interstitial cells (VIC). Methods MSC presence and function were probed using the patch clamp technique. Protein abundance of key MSC was evaluated by Western blotting in isolated fibroblastic VIC (VICFB) and in VIC differentiated towards myofibroblastic (VICMB) or osteoblastic (VICOB) phenotypes. Expression was compared in non-calcified and calcified human aortic valves. MSC contributions to stretch-induced collagen gene expression and to VIC migration were assessed by pharmacological inhibition of specific channels. Results Two MSC types were recorded in VICFB: potassium selective and cation non-selective channels. In keeping with functional data, the presence of both TREK-1 and Kir6.1 (potassium selective), as well as TRPM4, TRPV4 and TRPC6 (cationic non-selective) channels was confirmed in VIC at the protein level. Differentiation of VICFB into VICMB or VICOB phenotypes was associated with a lower expression of TREK-1 and Kir6.1, and a higher expression of TRPV4 and TRPC6. Differences in MSC expression were also seen in non-calcified vs calcified aortic valves where TREK-1, TRPM4 and TRPV4 expression were higher in calcified compared to control tissues. Cyclic stretch-induced expression of COL I mRNA in cultured VICFB was blocked by RN-9893, a selective inhibitor of TRPV4 channels while having no effect on the stretch-induced expression of COL III. VICFB migration was blocked with the non-specific MSC blocker streptomycin and by GSK417651A an inhibitor of TRPC6/3. Conclusion Aortic VIC express a range of MSC that play a role in functional responses of these cells to mechanical stimulation. MSC expression levels differ in calcified and non-calcified valves in ways that are in part compatible with the change in expression seen between VIC phenotypes. These changes in MSC expression, and associated alterations in the ability of VIC to respond to their mechanical environment, may form novel targets for intervention during aortic valvulopathies.
Collapse
Affiliation(s)
- Hessah Al-Shammari
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Najma Latif
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
- Heart Science Centre, Magdi Yacoub Institute, Harefield, United Kingdom
| | | | - Ann McCormack
- Heart Science Centre, Magdi Yacoub Institute, Harefield, United Kingdom
| | - Eva A. Rog-Zielinska
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg, Bad Krozingen, and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Shahzad Raja
- Harefield Hospital, Royal Brompton & Harefield NHS Foundation Trust, Harefield, United Kingdom
| | - Peter Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg, Bad Krozingen, and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Magdi H. Yacoub
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
- Heart Science Centre, Magdi Yacoub Institute, Harefield, United Kingdom
| | - Rémi Peyronnet
- Heart Science Centre, Magdi Yacoub Institute, Harefield, United Kingdom
- Institute for Experimental Cardiovascular Medicine, University Heart Center Freiburg, Bad Krozingen, and Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Adrian H. Chester
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
- Heart Science Centre, Magdi Yacoub Institute, Harefield, United Kingdom
- * E-mail:
| |
Collapse
|
3
|
Chester AH, Grande-Allen KJ. Which Biological Properties of Heart Valves Are Relevant to Tissue Engineering? Front Cardiovasc Med 2020; 7:63. [PMID: 32373630 PMCID: PMC7186395 DOI: 10.3389/fcvm.2020.00063] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Accepted: 03/27/2020] [Indexed: 12/30/2022] Open
Abstract
Over the last 20 years, the designs of tissue engineered heart valves have evolved considerably. An initial focus on replicating the mechanical and structural features of semilunar valves has expanded to endeavors to mimic the biological behavior of heart valve cells as well. Studies on the biology of heart valves have shown that the function and durability of native valves is underpinned by complex interactions between the valve cells, the extracellular matrix, and the mechanical environment in which heart valves function. The ability of valve interstitial cells to synthesize extracellular matrix proteins and remodeling enzymes and the protective mediators released by endothelial cells are key factors in the homeostasis of valve function. The extracellular matrix provides the mechanical strength and flexibility required for the valve to function, as well as communicating with the cells that are bound within. There are a number of regulatory mechanisms that influence valve function, which include neuronal mechanisms and the tight regulation of growth and angiogenic factors. Together, studies into valve biology have provided a blueprint for what a tissue engineered valve would need to be capable of, in order to truly match the function of the native valve. This review addresses the biological functions of heart valve cells, in addition to the influence of the cells' environment on this behavior and examines how well these functions are addressed within the current strategies for tissue engineering heart valves in vitro, in vivo, and in situ.
Collapse
Affiliation(s)
- Adrian H Chester
- Heart Science Centre, The Magdi Yacoub Institute, Harefield, United Kingdom
| | | |
Collapse
|
4
|
Anssari-Benam A, Screen HR, Bucchi A. Insights into the micromechanics of stress-relaxation and creep behaviours in the aortic valve. J Mech Behav Biomed Mater 2019; 93:230-245. [DOI: 10.1016/j.jmbbm.2019.02.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2018] [Revised: 10/30/2018] [Accepted: 02/11/2019] [Indexed: 12/20/2022]
|
5
|
Zündel M, Ehret AE, Mazza E. The multiscale stiffness of electrospun substrates and aspects of their mechanical biocompatibility. Acta Biomater 2019; 84:146-158. [PMID: 30447336 DOI: 10.1016/j.actbio.2018.11.012] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Revised: 10/10/2018] [Accepted: 11/07/2018] [Indexed: 02/04/2023]
Abstract
In contrast to homogeneous materials, the mechanical properties of fibrous substrates depend on the probing lengthscale. This suggests that cells feel very different mechanical cues than expected from the macroscale characterisation of the substrate materials. By means of multiscale computational analyses we study here the mechanical environment of cells adhering to typical electrospun networks used in biomedical applications, with comparable macroscopic stiffness but different fibre diameters. The stiffness evaluated at the level of focal adhesions varies significantly, and the overall magnitude is strongly affected by the fibre diameter. The microscopic stiffness evaluated at cell scale depends substantially on the network topology and is about one order of magnitude lower than the macroscopic stiffness of the substrate, and two to three orders of magnitude below the fibres' elastic modulus. Moreover, the translation of stiffness over the scales is modulated by global deformations of the scaffold. In particular, uniaxial or biaxial stretching of the substrate induces nonlinear microscopic stiffening. Finally, although electrospun networks allow long-range transmission of cell-induced deformations, the comparison between the range of forces measured in cell traction force microscopy and those required to markedly deform typical electrospun networks reveals an order of magnitude difference, suggesting that these scaffolds provide a rather rigid environment for cells. All these results underline that the achievement of mechanical biocompatibility at all relevant lengthscales, and over the whole range of physiological loading states is extremely challenging. At the same time, the study shows that the diameter, length and curvature of fibre segments might be tunable towards achieving this goal. STATEMENT OF SIGNIFICANCE: Electrospun fabrics have growing use as substrates and scaffolds in tissue engineering and other biomedical applications. Based on multiscale computational analyses, this study shows that substrates of comparable macroscopic stiffness can provide tremendously different mechanical micro-environments, and that cells adhering to fibrous substrates may thus experience by orders of magnitude different mechanical cues than it would be expected from macroscale material characterisation. The simulations further reveal that the transfer of stiffness over the length scales changes with macroscopic deformation, and identify some key parameters that govern the transfer ratio. We believe that such refined understanding of the multiscale aspects of mechanical biocompatibility is key to the development of successful scaffold materials.
Collapse
Affiliation(s)
- Manuel Zündel
- ETH Zürich, Institute for Mechanical Systems, 8092 Zürich, Switzerland
| | - Alexander E Ehret
- ETH Zürich, Institute for Mechanical Systems, 8092 Zürich, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
| | - Edoardo Mazza
- ETH Zürich, Institute for Mechanical Systems, 8092 Zürich, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
| |
Collapse
|
6
|
Anssari-Benam A, Bucchi A. Modeling
the Deformation of the Elastin Network in the Aortic
Valve. J Biomech Eng 2017; 140:2654665. [DOI: 10.1115/1.4037916] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2017] [Indexed: 12/20/2022]
Abstract
Abstract
This paper is concerned with proposing a suitable structurally motivated strain energy function, denoted by Weelastin network, for modeling the deformation of the elastin network within the aortic valve (AV) tissue. The AV elastin network is the main noncollagenous load-bearing component of the valve matrix, and therefore, in the context of continuum-based modeling of the AV, the Weelastin network strain energy function would essentially serve to model the contribution of the “isotropic matrix.” To date, such a function has mainly been considered as either a generic neo-Hookean term or a general exponential function. In this paper, we take advantage of the established structural analogy between the network of elastin chains and the freely jointed molecular chain networks to customize a structurally motivated Weelastin network function on this basis. The ensuing stress–strain (force-stretch) relationships are thus derived and fitted to the experimental data points reported by (Vesely, 1998, “The Role of Elastin in Aortic Valve Mechanics,” J. Biomech., 31, pp. 115–123) for intact AV elastin network specimens under uniaxial tension. The fitting results are then compared with those of the neo-Hookean and the general exponential models, as the frequently used models in the literature, as well as the “Arruda–Boyce” model as the gold standard of the network chain models. It is shown that our proposed Weelastin network function, together with the general exponential and the Arruda–Boyce models provide excellent fits to the data, with R2 values in excess of 0.98, while the neo-Hookean function is entirely inadequate for modeling the AV elastin network. However, the general exponential function may not be amenable to rigorous interpretation, as there is no structural meaning attached to the model. It is also shown that the parameters estimated by the Arruda–Boyce model are not mathematically and structurally valid, despite providing very good fits. We thus conclude that our proposed strain energy function Weelastin network is the preferred choice for modeling the behavior of the AV elastin network and thereby the isotropic matrix. This function may therefore be superimposed onto that of the anisotropic collagen fibers family in order to develop a structurally motivated continuum-based model for the AV.
Collapse
Affiliation(s)
| | - Andrea Bucchi
- The BIONEER Centre,Cardiovascular Engineering ResearchLaboratory (CERL),School of Engineering,University of Portsmouth,Anglesea Road,Portsmouth PO1 3DJ, UK
| |
Collapse
|
7
|
Thrombospondins: A Role in Cardiovascular Disease. Int J Mol Sci 2017; 18:ijms18071540. [PMID: 28714932 PMCID: PMC5536028 DOI: 10.3390/ijms18071540] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Revised: 07/05/2017] [Accepted: 07/13/2017] [Indexed: 12/16/2022] Open
Abstract
Thrombospondins (TSPs) represent extracellular matrix (ECM) proteins belonging to the TSP family that comprises five members. All TSPs have a complex multidomain structure that permits the interaction with various partners including other ECM proteins, cytokines, receptors, growth factors, etc. Among TSPs, TSP1, TSP2, and TSP4 are the most studied and functionally tested. TSP1 possesses anti-angiogenic activity and is able to activate transforming growth factor (TGF)-β, a potent profibrotic and anti-inflammatory factor. Both TSP2 and TSP4 are implicated in the control of ECM composition in hypertrophic hearts. TSP1, TSP2, and TSP4 also influence cardiac remodeling by affecting collagen production, activity of matrix metalloproteinases and TGF-β signaling, myofibroblast differentiation, cardiomyocyte apoptosis, and stretch-mediated enhancement of myocardial contraction. The development and evaluation of TSP-deficient animal models provided an option to assess the contribution of TSPs to cardiovascular pathology such as (myocardial infarction) MI, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis. Targeting of TSPs has a significant therapeutic value for treatment of cardiovascular disease. The activation of cardiac TSP signaling in stress and pressure overload may be therefore beneficial.
Collapse
|
8
|
Wu S, Duan B, Qin X, Butcher JT. Living nano-micro fibrous woven fabric/hydrogel composite scaffolds for heart valve engineering. Acta Biomater 2017; 51:89-100. [PMID: 28110071 DOI: 10.1016/j.actbio.2017.01.051] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Revised: 12/27/2016] [Accepted: 01/17/2017] [Indexed: 02/07/2023]
Abstract
Regeneration and repair of injured or diseased heart valves remains a clinical challenge. Tissue engineering provides a promising treatment approach to facilitate living heart valve repair and regeneration. Three-dimensional (3D) biomimetic scaffolds that possess heterogeneous and anisotropic features that approximate those of native heart valve tissue are beneficial to the successful in vitro development of tissue engineered heart valves (TEHV). Here we report the development and characterization of a novel composite scaffold consisting of nano- and micro-scale fibrous woven fabrics and 3D hydrogels by using textile techniques combined with bioactive hydrogel formation. Embedded nano-micro fibrous scaffolds within hydrogel enhanced mechanical strength and physical structural anisotropy of the composite scaffold (similar to native aortic valve leaflets) and also reduced its compaction. We determined that the composite scaffolds supported the growth of human aortic valve interstitial cells (HAVIC), balanced the remodeling of heart valve ECM against shrinkage, and maintained better physiological fibroblastic phenotype in both normal and diseased HAVIC over single materials. These fabricated composite scaffolds enable the engineering of a living heart valve graft with improved anisotropic structure and tissue biomechanics important for maintaining valve cell phenotypes. STATEMENT OF SIGNIFICANCE Heart valve-related disease is an important clinical problem, with over 300,000 surgical repairs performed annually. Tissue engineering offers a promising strategy for heart valve repair and regeneration. In this study, we developed and tissue engineered living nano-micro fibrous woven fabric/hydrogel composite scaffolds by using textile technique combined with bioactive hydrogel formation. The novelty of our technique is that the composite scaffolds can mimic physical structure anisotropy and the mechanical strength of natural aortic valve leaflet. Moreover, the composite scaffolds prevented the matrix shrinkage, which is major problem that causes the failure of TEHV, and better maintained physiological fibroblastic phenotype in both normal and diseased HAVIC. This work marks the first report of a combination composite scaffold using 3D hydrogel enhanced by nano-micro fibrous woven fabric, and represents a promising tissue engineering strategy to treat heart valve injury.
Collapse
|
9
|
Huang S, Huang HYS. Biaxial stress relaxation of semilunar heart valve leaflets during simulated collagen catabolism: Effects of collagenase concentration and equibiaxial strain state. Proc Inst Mech Eng H 2016; 229:721-31. [PMID: 26405097 DOI: 10.1177/0954411915604336] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Heart valve leaflet collagen turnover and remodeling are innate to physiological homeostasis; valvular interstitial cells routinely catabolize damaged collagen and affect repair. Moreover, evidence indicates that leaflets can adapt to altered physiological (e.g. pregnancy) and pathological (e.g. hypertension) mechanical load states, tuning collagen structure and composition to changes in pressure and flow. However, while valvular interstitial cell-secreted matrix metalloproteinases are considered the primary effectors of collagen catabolism, the mechanisms by which damaged collagen fibers are selectively degraded remain unclear. Growing evidence suggests that the collagen fiber strain state plays a key role, with the strain-dependent configuration of the collagen molecules either masking or presenting proteolytic sites, thereby protecting or accelerating collagen proteolysis. In this study, the effects of equibiaxial strain state on collagen catabolism were investigated in porcine aortic valve and pulmonary valve tissues. Bacterial collagenase (0.2 and 0.5 mg/mL) was utilized to simulate endogenous matrix metalloproteinases, and biaxial stress relaxation and biochemical collagen concentration served as functional and compositional measures of collagen catabolism, respectively. At a collagenase concentration of 0.5 mg/mL, increasing the equibiaxial strain imposed during stress relaxation (0%, 37.5%, and 50%) yielded significantly lower median collagen concentrations in the aortic valve (p = 0.0231) and pulmonary valve (p = 0.0183), suggesting that relatively large strain magnitudes may enhance collagen catabolism. Collagen concentration decreases were paralleled by trends of accelerated normalized stress relaxation rate with equibiaxial strain in aortic valve tissues. Collectively, these in vitro results indicate that biaxial strain state is capable of affecting the susceptibility of valvular collagens to catabolism, providing a basis for further investigation of how such phenomena may manifest at different strain magnitudes or in vivo.
Collapse
Affiliation(s)
- Siyao Huang
- Department of Mechanical & Aerospace Engineering, North Carolina State University, Raleigh, NC, USA
| | - Hsiao-Ying Shadow Huang
- Department of Mechanical & Aerospace Engineering, North Carolina State University, Raleigh, NC, USA
| |
Collapse
|
10
|
Anssari-Benam A, Barber AH, Bucchi A. Evaluation of bioprosthetic heart valve failure using a matrix-fibril shear stress transfer approach. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2016; 27:42. [PMID: 26715134 DOI: 10.1007/s10856-015-5657-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 12/20/2015] [Indexed: 06/05/2023]
Abstract
A matrix-fibril shear stress transfer approach is devised and developed in this paper to analyse the primary biomechanical factors which initiate the structural degeneration of the bioprosthetic heart valves (BHVs). Using this approach, the critical length of the collagen fibrils l c and the interface shear acting on the fibrils in both BHV and natural aortic valve (AV) tissues under physiological loading conditions are calculated and presented. It is shown that the required critical fibril length to provide effective reinforcement to the natural AV and the BHV tissue is l c = 25.36 µm and l c = 66.81 µm, respectively. Furthermore, the magnitude of the required shear force acting on fibril interface to break a cross-linked fibril in the BHV tissue is shown to be 38 µN, while the required interfacial force to break the bonds between the fibril and the surrounding extracellular matrix is 31 µN. Direct correlations are underpinned between these values and the ultimate failure strength and the failure mode of the BHV tissue compared with the natural AV, and are verified against the existing experimental data. The analyses presented in this paper explain the role of fibril interface shear and critical length in regulating the biomechanics of the structural failure of the BHVs, for the first time. This insight facilitates further understanding into the underlying causes of the structural degeneration of the BHVs in vivo.
Collapse
Affiliation(s)
- Afshin Anssari-Benam
- School of Engineering, University of Portsmouth, Anglesea Road, Portsmouth, PO1 3DJ, UK.
| | - Asa H Barber
- School of Engineering, University of Portsmouth, Anglesea Road, Portsmouth, PO1 3DJ, UK
| | - Andrea Bucchi
- School of Engineering, University of Portsmouth, Anglesea Road, Portsmouth, PO1 3DJ, UK
| |
Collapse
|
11
|
Huang S, Huang HYS. Prediction of matrix-to-cell stress transfer in heart valve tissues. J Biol Phys 2014; 41:9-22. [PMID: 25298285 DOI: 10.1007/s10867-014-9362-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Accepted: 08/12/2014] [Indexed: 11/27/2022] Open
Abstract
Non-linear and anisotropic heart valve leaflet tissue mechanics manifest principally from the stratification, orientation, and inhomogeneity of their collagenous microstructures. Disturbance of the native collagen fiber network has clear consequences for valve and leaflet tissue mechanics and presumably, by virtue of their intimate embedment, on the valvular interstitial cell stress-strain state and concomitant phenotype. In the current study, a set of virtual biaxial stretch experiments were conducted on porcine pulmonary valve leaflet tissue photomicrographs via an image-based finite element approach. Stress distribution evolution during diastolic valve closure was predicted at both the tissue and cellular levels. Orthotropic material properties consistent with distinct stages of diastolic loading were applied. Virtual experiments predicted tissue- and cellular-level stress fields, providing insight into how matrix-to-cell stress transfer may be influenced by the inhomogeneous collagen fiber architecture, tissue anisotropic material properties, and the cellular distribution within the leaflet tissue. To the best of the authors' knowledge, this is the first study reporting on the evolution of stress fields at both the tissue and cellular levels in valvular tissue and thus contributes toward refining our collective understanding of valvular tissue micromechanics while providing a computational tool enabling the further study of valvular cell-matrix interactions.
Collapse
Affiliation(s)
- Siyao Huang
- Mechanical and Aerospace Engineering Department, North Carolina State University, R3158 Engineering Building 3, Campus Box 7910, 911 Oval Drive, Raleigh, NC, 27695, USA
| | | |
Collapse
|
12
|
Masoumi N, Howell MC, Johnson KL, Niesslein MJ, Gerber G, Engelmayr GC. Design and testing of a cyclic stretch and flexure bioreactor for evaluating engineered heart valve tissues based on poly(glycerol sebacate) scaffolds. Proc Inst Mech Eng H 2014; 228:576-586. [PMID: 24898445 DOI: 10.1177/0954411914534837] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Cyclic flexure and stretch are essential to the function of semilunar heart valves and have demonstrated utility in mechanically conditioning tissue-engineered heart valves. In this study, a cyclic stretch and flexure bioreactor was designed and tested in the context of the bioresorbable elastomer poly(glycerol sebacate). Solid poly(glycerol sebacate) membranes were subjected to cyclic stretch, and micromolded poly(glycerol sebacate) scaffolds seeded with porcine aortic valvular interstitial cells were subjected to cyclic stretch and flexure. The results demonstrated significant effects of cyclic stretch on poly(glycerol sebacate) mechanical properties, including significant decreases in effective stiffness versus controls. In valvular interstitial cell-seeded scaffolds, cyclic stretch elicited significant increases in DNA and collagen content that paralleled maintenance of effective stiffness. This work provides a basis for investigating the roles of mechanical loading in the formation of tissue-engineered heart valves based on elastomeric scaffolds.
Collapse
Affiliation(s)
- Nafiseh Masoumi
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - M Christian Howell
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - Katherine L Johnson
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - Matthew J Niesslein
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - Gene Gerber
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| | - George C Engelmayr
- Department of Bioengineering, The Pennsylvania State University, University Park, PA, USA
| |
Collapse
|
13
|
Biomechanical properties of native and tissue engineered heart valve constructs. J Biomech 2014; 47:1949-63. [DOI: 10.1016/j.jbiomech.2013.09.023] [Citation(s) in RCA: 179] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Revised: 09/09/2013] [Accepted: 09/10/2013] [Indexed: 11/18/2022]
|
14
|
Masoumi N, Larson BL, Annabi N, Kharaziha M, Zamanian B, Shapero KS, Cubberley AT, Camci-Unal G, Manning KB, Mayer JE, Khademhosseini A. Electrospun PGS:PCL microfibers align human valvular interstitial cells and provide tunable scaffold anisotropy. Adv Healthc Mater 2014; 3:929-39. [PMID: 24453182 PMCID: PMC4053480 DOI: 10.1002/adhm.201300505] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Revised: 10/09/2013] [Indexed: 12/23/2022]
Abstract
Tissue engineered heart valves (TEHV) can be useful in the repair of congenital or acquired valvular diseases due to their potential for growth and remodeling. The development of biomimetic scaffolds is a major challenge in heart valve tissue engineering. One of the most important structural characteristics of mature heart valve leaflets is their intrinsic anisotropy, which is derived from the microstructure of aligned collagen fibers in the extracellular matrix (ECM). In the present study, a directional electrospinning technique is used to fabricate fibrous poly(glycerol sebacate):poly(caprolactone) (PGS:PCL) scaffolds containing aligned fibers, which resemble native heart valve leaflet ECM networks. In addition, the anisotropic mechanical characteristics of fabricated scaffolds are tuned by changing the ratio of PGS:PCL to mimic the native heart valve's mechanical properties. Primary human valvular interstitial cells (VICs) attach and align along the anisotropic axes of all PGS:PCL scaffolds with various mechanical properties. The cells are also biochemically active in producing heart-valve-associated collagen, vimentin, and smooth muscle actin as determined by gene expression. The fibrous PGS:PCL scaffolds seeded with human VICs mimick the structure and mechanical properties of native valve leaflet tissues and would potentially be suitable for the replacement of heart valves in diverse patient populations.
Collapse
Affiliation(s)
- Nafiseh Masoumi
- Department of Bioengineering, The Pennsylvania State University, 205 Hallowell Building, Sate College, PA, USA. Center for Biomedical Engineering, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Harvard-MIT Division of Health Sciences and Technology Massachusetts Institute of Technology, 65 Landsdowne St., Cambridge, 02139 MA, USA. Department of Cardiac Surgery, Boston Children Hospital and Harvard Medical School 300 Longwood Ave, Boston, MA 02115, USA
| | - Benjamin L. Larson
- Harvard-MIT Division of Health Sciences and Technology and the David Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, 500 Main Street, Cambridge, MA 02139, USA
| | - Nasim Annabi
- Center for Biomedical Engineering, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Harvard-MIT Division of Health Sciences and Technology Massachusetts Institute of Technology, 65 Landsdowne St., Cambridge, 02139 MA, USA. Wyss Institute for Biologically Inspired Engineering, Harvard University, 3 Blackfan Cir, Boston, MA 02115, USA
| | - Mahshid Kharaziha
- Center for Biomedical Engineering, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Harvard-MIT Division of Health Sciences and Technology Massachusetts Institute of Technology, 65 Landsdowne St., Cambridge, 02139 MA, USA
| | - Behnam Zamanian
- Center for Biomedical Engineering, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Harvard-MIT Division of Health Sciences and Technology Massachusetts Institute of Technology, 65 Landsdowne St., Cambridge, 02139 MA, USA
| | - Kayle S. Shapero
- Department of Cardiac Surgery, Boston Children Hospital and Harvard Medical School, 300 Longwood Ave, Boston, MA 02115, USA
| | - Alexander T. Cubberley
- Department of Cardiac Surgery, Boston Children Hospital and Harvard Medical School, 300 Longwood Ave, Boston, MA 02115, USA
| | - Gulden Camci-Unal
- Department of Bioengineering, The Pennsylvania State University, 205 Hallowell Building, Sate College, PA, USA
| | - Keefe. B. Manning
- Department of Bioengineering, The Pennsylvania State University, 205 Hallowell Building, Sate College, PA, USA
| | - John E. Mayer
- Department of Cardiac Surgery, Boston Children Hospital and Harvard Medical School, 300 Longwood Ave, Boston, MA 02115, USA
| | - Ali Khademhosseini
- Center for Biomedical Engineering, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Harvard-MIT Division of Health Sciences and Technology Massachusetts Institute of Technology, 65 Landsdowne St., Cambridge, 02139 MA, USA. Wyss Institute for Biologically Inspired Engineering, Harvard University, 3 Blackfan Cir, Boston, MA 02115, USA
| |
Collapse
|
15
|
Huang HYS, Huang S. Real-time strain mapping via biaxial stretching in heart valve tissues. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2013; 2012:6653-6. [PMID: 23367455 DOI: 10.1109/embc.2012.6347520] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Previous studies show that the collagen fiber architecture is key to the heart valves tissue mechanical property. We report a real-time strain mapping approach that provides displacement vectors and principal strain directions during the mechanical characterization of heart valve tissues. The strain maps reported in the current study allows an individual to quickly identify the approximate strain imposed on a location of the sample. The result shows that when samples are biaxially stretched under 18% strain, less anisotropy is observed in both aortic and pulmonary valve leaflet samples. Moreover, when samples are stretched from 28% to 35%, pulmonary valves leaflet samples exhibits a stronger anisotropic effect than aortic valve. Therefore, a higher degree of straightening is required for collagen fibers to be fully aligned. This work provides an easy approach to quantify mechanical properties with the corresponding strain maps of heart valve tissues and potentially facilitates the developments of tissue engineering heart valves.
Collapse
Affiliation(s)
- Hsiao-Ying Shadow Huang
- Department of Mechanical Engineering, North Carolina State University, Raleigh, NC 27695, USA.
| | | |
Collapse
|
16
|
Masoumi N, Johnson KL, Howell MC, Engelmayr GC. Valvular interstitial cell seeded poly(glycerol sebacate) scaffolds: toward a biomimetic in vitro model for heart valve tissue engineering. Acta Biomater 2013; 9:5974-88. [PMID: 23295404 DOI: 10.1016/j.actbio.2013.01.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2012] [Revised: 11/24/2012] [Accepted: 01/01/2013] [Indexed: 01/01/2023]
Abstract
Tissue engineered replacement heart valves may be capable of overcoming the lack of growth potential intrinsic to current non-viable prosthetics, and thus could potentially serve as permanent replacements in the surgical repair of pediatric valvular lesions. However, the evaluation of candidate combinations of cells and scaffolds lacks a biomimetic in vitro model with broadly tunable, anisotropic and elastomeric structural-mechanical properties. Toward establishing such an in vitro model, in the current study, porcine aortic and pulmonary valvular interstitial cells (i.e. biomimetic cells) were cultivated on anisotropic, micromolded poly(glycerol sebacate) scaffolds (i.e. biomimetic scaffolds). Following 14 and 28 days of static culture, cell-seeded scaffolds and unseeded controls were assessed for their mechanical properties, and cell-seeded scaffolds were further characterized by confocal fluorescence and scanning electron microscopy, and by collagen and DNA assays. Poly(glycerol sebacate) micromolding yielded scaffolds with anisotropic stiffnesses resembling those of native valvular tissues in the low stress-strain ranges characteristic of physiologic valvular function. Scaffold anisotropy was largely retained upon cultivation with valvular interstitial cells; while the mechanical properties of unseeded scaffolds progressively diminished, cell-seeded scaffolds either retained or exceeded initial mechanical properties. Retention of mechanical properties in cell-seeded scaffolds paralleled the accretion of collagen, which increased significantly from 14 to 28 days. This study demonstrates that valvular interstitial cells can be cultivated on anisotropic poly(glycerol sebacate) scaffolds to yield biomimetic in vitro models with which clinically relevant cells and future scaffold designs can be evaluated.
Collapse
|
17
|
Huang S, Huang HYS. Virtualisation of stress distribution in heart valve tissue. Comput Methods Biomech Biomed Engin 2013; 17:1696-704. [PMID: 23477432 DOI: 10.1080/10255842.2013.763937] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
This study presents an image-based finite element analysis incorporating histological photomicrographs of heart valve tissues. We report stress fields inside heart valve tissues, where heterogeneously distributed collagen fibres are responsible for transmitting forces into cells. Linear isotropic and anisotropic tissue material property models are incorporated to quantify the overall stress distributions in heart valve tissues. By establishing an effective predictive method with new computational tools and by performing virtual experiments on the heart valve tissue photomicrographs, we clarify how stresses are transferred from matrix to cell. The results clearly reveal the roles of heterogeneously distributed collagen fibres in mitigating stress developments inside heart valve tissues. Moreover, most local peak stresses occur around cell nuclei, suggesting that higher stress may be mediated by cells for biomechanical regulations.
Collapse
Affiliation(s)
- Siyao Huang
- a Mechanical and Aerospace Engineering Department , North Carolina State University , 3002 EBIII, Campus Box 7910, 911 Oval Drive, Raleigh , NC 27695-7910 , USA
| | | |
Collapse
|
18
|
Huang HYS, Balhouse BN, Huang S. Application of simple biomechanical and biochemical tests to heart valve leaflets: implications for heart valve characterization and tissue engineering. Proc Inst Mech Eng H 2013. [PMID: 23185957 DOI: 10.1177/0954411912455004] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
A simple biomechanical test with real-time displacement and strain mapping is reported, which provides displacement vectors and principal strain directions during the mechanical characterization of heart valve tissues. The maps reported in the current study allow us to quickly identify the approximate strain imposed on a location in the samples. The biomechanical results show that the aortic valves exhibit stronger anisotropic mechanical behavior than that of the pulmonary valves before 18% strain equibiaxial stretching. In contrast, the pulmonary valves exhibit stronger anisotropic mechanical behavior than aortic valves beyond 28% strain equibiaxial stretching. Simple biochemical tests are also conducted. Collagens are extracted at different time points (24, 48, 72, and 120 h) at different locations in the samples. The results show that extraction time plays an important role in determining collagen concentration, in which a minimum of 72 h of extraction is required to obtain saturated collagen concentration. This work provides an easy approach for quantifying biomechanical and biochemical properties of semilunar heart valve tissues, and potentially facilitates the development of tissue engineered heart valves.
Collapse
Affiliation(s)
- Hsiao-Ying S Huang
- Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC, USA.
| | | | | |
Collapse
|
19
|
Masoumi N, Jean A, Zugates JT, Johnson KL, Engelmayr GC. Laser microfabricated poly(glycerol sebacate) scaffolds for heart valve tissue engineering. J Biomed Mater Res A 2012; 101:104-14. [PMID: 22826211 DOI: 10.1002/jbm.a.34305] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2011] [Revised: 05/01/2012] [Accepted: 05/22/2012] [Indexed: 02/04/2023]
Abstract
Microfabricated poly(glycerol sebacate) (PGS) scaffolds may be applicable to tissue engineering heart valve leaflets by virtue of their controllable microstructure, stiffness, and elasticity. In this study, PGS scaffolds were computationally designed and microfabricated by laser ablation to match the anisotropy and peak tangent moduli of native bovine aortic heart valve leaflets. Finite element simulations predicted PGS curing conditions, scaffold pore shape, and strut width capable of matching the scaffold effective stiffnesses to the leaflet peak tangent moduli. On the basis of simulation predicted effective stiffnesses of 1.041 and 0.208 MPa for the scaffold preferred (PD) and orthogonal, cross-preferred (XD) material directions, scaffolds with diamond-shaped pores were microfabricated by laser ablation of PGS cured 12 h at 160°C. Effective stiffnesses measured for the scaffold PD (0.83 ± 0.13 MPa) and XD (0.21 ± 0.03 MPa) were similar to both predicted values and peak tangent moduli measured for bovine aortic valve leaflets in the circumferential (1.00 ± 0.16 MPa) and radial (0.26 ± 0.03 MPa) directions. Scaffolds cultivated with fibroblasts for 3 weeks accumulated collagen (736 ± 193 μg/g wet weight) and DNA (17 ± 4 μg/g wet weight). This study provides a basis for the computational design of biomimetic microfabricated PGS scaffolds for tissue-engineered heart valves.
Collapse
Affiliation(s)
- Nafiseh Masoumi
- Department of Bioengineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
| | | | | | | | | |
Collapse
|
20
|
Anssari-Benam A, Gupta HS, Screen HRC. Strain Transfer Through the Aortic Valve. J Biomech Eng 2012; 134:061003. [DOI: 10.1115/1.4006812] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The complex structural organization of the aortic valve (AV) extracellular matrix (ECM) enables large and highly nonlinear tissue level deformations. The collagen and elastin (elastic) fibers within the ECM form an interconnected fibrous network (FN) and are known to be the main load-bearing elements of the AV matrix. The role of the FN in enabling deformation has been investigated and documented. However, there is little data on the correlation between tissue level and FN-level strains. Investigating this correlation will help establish the mode of strain transfer (affine or nonaffine) through the AV tissue as a key feature in microstructural modeling and will also help characterize the local FN deformation across the AV sample in response to applied tissue level strains. In this study, the correlation between applied strains at tissue level, macrostrains across the tissue surface, and local FN strains were investigated. Results showed that the FN strain distribution across AV samples was inhomogeneous and nonuniform, as well as anisotropic. There was no direct transfer of the deformation applied at tissue level to the fibrous network. Loading modes induced in the FN are different than those applied at the tissue as a result of different local strains in the valve layers. This nonuniformity of local strains induced internal shearing within the FN of the AV, possibly exposing the aortic valve interstitial cells (AVICs) to shear strains and stresses.
Collapse
Affiliation(s)
- Afshin Anssari-Benam
- School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, E1 4NS London, UK
| | - Himadri S. Gupta
- School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, E1 4NS London, UK
| | - Hazel R. C. Screen
- School of Engineering and Materials Science, Queen Mary, University of London, Mile End Road, E1 4NS London, UK
| |
Collapse
|