Cellular and Molecular Bioengineering

, Volume 11, Issue 4, pp 291–306 | Cite as

The Three-Dimensional Microenvironment of the Mitral Valve: Insights into the Effects of Physiological Loads

  • Salma Ayoub
  • Karen C. Tsai
  • Amir H. Khalighi
  • Michael S. SacksEmail author



In the mitral valve (MV), numerous pathological factors, especially those resulting from changes in external loading, have been shown to affect MV structure and composition. Such changes are driven by the MV interstitial cell (MVIC) population via protein synthesis and enzymatic degradation of extracellular matrix (ECM) components.


While cell phenotype, ECM composition and regulation, and tissue level changes in MVIC shape under stress have been studied, a detailed understanding of the three-dimensional (3D) microstructural mechanisms are lacking. As a first step in addressing this challenge, we applied focused ion beam scanning electron microscopy (FIB-SEM) to reveal novel details of the MV microenvironment in 3D.


We demonstrated that collagen is organized into large fibers consisting of an average of 605 ± 113 fibrils, with a mean diameter of 61.2 ± 9.8 nm. In contrast, elastin was organized into two distinct structural subtypes: (1) sheet-like lamellar elastin, and (2) circumferentially oriented elastin struts, based on both the aspect ratio and transmural tilt. MVICs were observed to have a large cytoplasmic volume, as evidenced by the large mean surface area to volume ratio 3.68 ± 0.35, which increased under physiological loading conditions to 4.98 ± 1.17.


Our findings suggest that each MVIC mechanically interacted only with the nearest 3–4 collagen fibers. This key observation suggests that in developing multiscale MV models, each MVIC can be considered a mechanically integral part of the local fiber ensemble and is unlikely to be influenced by more distant structures.


Heart valves Ultrastructure Valve interstitial cells Extracellular matrix Collagen Elastin 



The authors would like to acknowledge Dr. Hua Gua (Rice University) and Dr. Dwight Romanovicz (UT Austin) for their assistance with the FIB-SEM and TEM instruments, as well as Sarah Poletti, Ethan Kwan, and Michelle Lu for their assistance with heart valve tissue isolation and preparation. This work was supported by the National Institutes of Health Grant [R01HL119297] to MSS and the American Heart Association Pre-Doctoral Fellowship [PRE33420135] to SA.

Conflict of interest

None of the authors of this work, Salma Ayoub, Karen C. Tsai, Amir H. Khalighi, and Michael S. Sacks, have a conflict of interest.

Ethical Approval

This article does not contain any studies with human participants or animal studies performed by any of the authors.

Supplementary material

Video 1. Video of the 3D reconstruction of the mitral valve interstitial cell and its surrounding microenvironment showing the serial 2D FIB-SEM images (horizontal field width of 53.6 µm), followed by the 3D reconstruction of the nucleus, cytoplasm, collagen, and elastin. This video highlights the complexity of the interconnection between the valve interstitial cell and the surrounding extracellular matrix. Reconstruction of 77 serial sections (total thickness = 15.4 µm) with a slice thickness of 200 nm. Supplementary material 1 (MP4 102833 kb)

Video 2. Video of the 3D reconstruction of the mitral valve interstitial microenvironment showing the serial 2D FIB-SEM images (horizontal field width of 20.7 µm), followed by the 3D reconstruction of the collagen fibers and the elastin structures. Reconstruction of 30 serial sections (total thickness = 1.50 µm) with a slice thickness of 50 nm. Supplementary material 2 (MP4 94609 kb)


  1. 1.
    Ali, M. S., X. Wang, and C. M. Lacerda. A survey of membrane receptor regulation in valvular interstitial cells cultured under mechanical stresses. Exp. Cell Res. 351(2):150–156, 2017.CrossRefGoogle Scholar
  2. 2.
    Ayoub, S., G. Ferrari, R. C. Gorman, J. H. Gorman, F. J. Schoen, and M. S. Sacks. Heart valve biomechanics and underlying mechanobiology. Compr. Physiol. 6(4):1743–1780, 2016.CrossRefGoogle Scholar
  3. 3.
    Ayoub, S., C.-H. Lee, K. H. Driesbaugh, W. Anselmo, C. T. Hughes, G. Ferrari, R. C. Gorman, J. H. Gorman, and M. S. Sacks. Regulation of valve interstitial cell homeostasis by mechanical deformation: implications for heart valve disease and surgical repair. J. R. Soc. Interface 14(135):20170580, 2017.CrossRefGoogle Scholar
  4. 4.
    Balachandran, K., P. W. Alford, J. Wylie-Sears, J. A. Goss, A. Grosberg, J. Bischoff, E. Aikawa, R. A. Levine, and K. K. Parker. Cyclic strain induces dual-mode endothelial-mesenchymal transformation of the cardiac valve. Proc. Natl. Acad. Sci. USA 108(50):19943–19948, 2011.CrossRefGoogle Scholar
  5. 5.
    Balachandran, K., S. Konduri, P. Sucosky, H. Jo, and A. Yoganathan. An ex vivo study of the biological properties of porcine aortic valves in response to circumferential cyclic stretch. Ann. Biomed. Eng. 34(11):1655–1665, 2006.CrossRefGoogle Scholar
  6. 6.
    Balachandran, K., P. Sucosky, H. Jo, and A. P. Yoganathan. Elevated cyclic stretch alters matrix remodeling in aortic valve cusps: implications for degenerative aortic valve disease. Am. J. Physiol. Heart Circ. Physiol. 296(3):H756–H764, 2009.CrossRefGoogle Scholar
  7. 7.
    Bloodworth, C. H., E. L. Pierce, T. F. Easley, A. Drach, A. H. Khalighi, M. Toma, M. O. Jensen, M. S. Sacks, and A. P. Yoganathan. Ex vivo methods for informing computational models of the mitral valve. Ann. Biomed. Eng. 45(2):496–507, 2017.CrossRefGoogle Scholar
  8. 8.
    Buchanan, R. M., and M. S. Sacks. Interlayer micromechanics of the aortic heart valve leaflet. Biomech. Model. Mechanobiol. 3(4):813–826, 2013.CrossRefGoogle Scholar
  9. 9.
    Bushby, A. J., K. M. P’ng, R. D. Young, C. Pinali, C. Knupp, and A. J. Quantock. Imaging three-dimensional tissue architectures by focused ion beam scanning electron microscopy. Nat. Protoc. 6(6):845–858, 2011.CrossRefGoogle Scholar
  10. 10.
    Carruthers, C. A., B. Good, A. D’Amore, J. Liao, R. Amini, S. C. Watkins, and M. S. Sacks. Alterations in the microstructure of the anterior mitral valve leaflet under physiological stress. In: ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, Fajardo, Puerto Rico, 2012, pp. 227–228Google Scholar
  11. 11.
    Cole, W. G., D. Chan, A. J. Hickey, and D. E. Wilcken. Collagen composition of normal and myxomatous human mitral heart valves. Biochem. J. 219(2):451–460, 1984.CrossRefGoogle Scholar
  12. 12.
    Dal-Bianco, J. P., E. Aikawa, J. Bischoff, J. L. Guerrero, M. D. Handschumacher, S. Sullivan, B. Johnson, J. S. Titus, Y. Iwamoto, J. Wylie-Sears, R. A. Levine, and A. Carpentier. Active adaptation of the tethered mitral valve: insights into a compensatory mechanism for functional mitral regurgitation. Circulation 120(4):334–342, 2009.CrossRefGoogle Scholar
  13. 13.
    Dal-Bianco, J. P., E. Aikawa, J. Bischoff, J. L. Guerrero, J. Hjortnaes, J. Beaudoin, C. Szymanski, P. E. Bartko, M. M. Seybolt, M. D. Handschumacher, S. Sullivan, M. L. Garcia, A. Mauskapf, J. S. Titus, J. Wylie-Sears, W. S. Irvin, M. Chaput, E. Messas, A. A. Hagege, A. Carpentier, and R. A. Levine. Myocardial infarction alters adaptation of the tethered mitral valve. J. Am. Coll. Cardiol. 67(3):275–287, 2016.CrossRefGoogle Scholar
  14. 14.
    De Winter, D. A., C. T. Schneijdenberg, M. N. Lebbink, B. Lich, A. J. Verkleij, M. R. Drury, and B. M. Humbel. Tomography of insulating biological and geological materials using focused ion beam (FIB) sectioning and low-kV BSE imaging. J. Microsc. 233(3):372–383, 2009.MathSciNetCrossRefGoogle Scholar
  15. 15.
    Denk, W., and H. Horstmann. Serial block-face scanning electron microscopy to reconstruct three-dimensional tissue nanostructure. PLoS Biol. 2(11):e329, 2004.CrossRefGoogle Scholar
  16. 16.
    Drach, A., A. H. Khalighi, and M. S. Sacks. A comprehensive pipeline for multi-resolution modeling of the mitral valve: Validation, computational efficiency, and predictive capability. Int. J. Numer. Method. Biomed. Eng. 34(2):e2921, 2018.CrossRefGoogle Scholar
  17. 17.
    Dunkman, A. A., M. R. Buckley, M. J. Mienaltowski, S. M. Adams, S. J. Thomas, A. Kumar, D. P. Beason, R. V. Iozzo, D. E. Birk, and L. J. Soslowsky. The injury response of aged tendons in the absence of biglycan and decorin. Matrix Biol. 2013. Scholar
  18. 18.
    Dunkman, A. A., M. R. Buckley, M. J. Mienaltowski, S. M. Adams, S. J. Thomas, L. Satchell, A. Kumar, L. Pathmanathan, D. P. Beason, and R. V. Iozzo. Decorin expression is important for age-related changes in tendon structure and mechanical properties. Matrix Biol. 32(1):3–13, 2013.CrossRefGoogle Scholar
  19. 19.
    Giannuzzi, L. A., D. Phifer, N. J. Giannuzzi, and M. J. Capuano. Two-dimensional and 3-dimensional analysis of bone/dental implant interfaces with the use of focused ion beam and electron microscopy. J. Oral Maxillofac. Surg. 65(4):737–747, 2007.CrossRefGoogle Scholar
  20. 20.
    Go, A. S., D. Mozaffarian, V. L. Roger, E. J. Benjamin, J. D. Berry, M. J. Blaha, S. Dai, E. S. Ford, C. S. Fox, S. Franco, H. J. Fullerton, C. Gillespie, S. M. Hailpern, J. A. Heit, V. J. Howard, M. D. Huffman, S. E. Judd, B. M. Kissela, S. J. Kittner, D. T. Lackland, J. H. Lichtman, L. D. Lisabeth, R. H. Mackey, D. J. Magid, G. M. Marcus, A. Marelli, D. B. Matchar, D. K. McGuire, E. R. Mohler, 3rd, C. S. Moy, M. E. Mussolino, R. W. Neumar, G. Nichol, D. K. Pandey, N. P. Paynter, M. J. Reeves, P. D. Sorlie, J. Stein, A. Towfighi, T. N. Turan, S. S. Virani, N. D. Wong, D. Woo, and M. B. Turner. Heart disease and stroke statistics–2014 update: a report from the American Heart Association. Circulation 129(3):e28–e292, 2014.CrossRefGoogle Scholar
  21. 21.
    Grande-Allen, K. J., B. P. Griffin, N. B. Ratliff, D. M. Cosgrove, and I. Vesely. Glycosaminoglycan profiles of myxomatous mitral leaflets and chordae parallel the severity of mechanical alterations. J. Am. Coll. Cardiol. 42(2):271–277, 2003.CrossRefGoogle Scholar
  22. 22.
    Grande-Allen, K. J., and J. Liao. The heterogeneous biomechanics and mechanobiology of the mitral valve: implications for tissue engineering. Curr. Cardiol. Rep. 13(2):113–120, 2011.CrossRefGoogle Scholar
  23. 23.
    Gupta, V., H. Tseng, B. D. Lawrence, and K. J. Grande-Allen. Effect of cyclic mechanical strain on glycosaminoglycan and proteoglycan synthesis by heart valve cells. Acta Biomater. 5(2):531–540, 2009.CrossRefGoogle Scholar
  24. 24.
    Hekking, L. H., M. N. Lebbink, D. A. De Winter, C. T. Schneijdenberg, C. M. Brand, B. M. Humbel, A. J. Verkleij, and J. A. Post. Focused ion beam-scanning electron microscope: exploring large volumes of atherosclerotic tissue. J. Microsc. 235(3):336–347, 2009.MathSciNetCrossRefGoogle Scholar
  25. 25.
    Heymann, J. A., D. Shi, S. Kim, D. Bliss, J. L. Milne, and S. Subramaniam. 3D imaging of mammalian cells with ion-abrasion scanning electron microscopy. J. Struct. Biol. 166(1):1–7, 2009.CrossRefGoogle Scholar
  26. 26.
    Huang, H. Y., J. Liao, and M. S. Sacks. In-situ deformation of the aortic valve interstitial cell nucleus under diastolic loading. J. Biomech. Eng. 129(6):880–889, 2007.CrossRefGoogle Scholar
  27. 27.
    Khalighi, A. H., A. Drach, C. H. T. Bloodworth, E. L. Pierce, A. P. Yoganathan, R. C. Gorman, J. H. Gorman, 3rd, and M. S. Sacks. Mitral valve chordae tendineae: topological and geometrical characterization. Ann. Biomed Eng. 45(2):378–393, 2017.CrossRefGoogle Scholar
  28. 28.
    Khalighi, A. H., A. Drach, R. C. Gorman, J. H. Gorman, and M. S. Sacks. Multi-resolution geometric modeling of the mitral heart valve leaflets. Biomech Model Mechanobiol 17(2):351–366, 2018.CrossRefGoogle Scholar
  29. 29.
    Khalighi, A. H., A. Drach, F. M. ter Huurne, C.-H. Lee, C. Bloodworth, E. L. Pierce, M. O. Jensen, A. P. Yoganathan, and M. S. Sacks. A comprehensive framework for the characterization of the complete mitral valve geometry for the development of a population-averaged model. In: Functional Imaging and Modeling of the Heart: 8th International Conference, FIMH 2015, Maastricht, The Netherlands, June 25–27, edited by H. van Assen, P. Bovendeerd, T. Delhaas. Proceedings, Springer International Publishing, Cham, 2015, pp. 164–171.Google Scholar
  30. 30.
    Kizilyaprak, C., J. Daraspe, and B. M. Humbel. Focused ion beam scanning electron microscopy in biology. J. Microsc. 254(3):109–114, 2014.CrossRefGoogle Scholar
  31. 31.
    Lamers, E., X. F. Walboomers, M. Domanski, G. McKerr, B. M. O’Hagan, C. A. Barnes, L. Peto, R. Luttge, L. A. Winnubst, H. J. Gardeniers, and J. A. Jansen. Cryo DualBeam focused ion beam-scanning electron microscopy to evaluate the interface between cells and nanopatterned scaffolds. Tissue Eng Part C 17(1):1–7, 2011.CrossRefGoogle Scholar
  32. 32.
    Lanir, Y. Constitutive equations for fibrous connective tissues. J. Biomech. 16(1):1–12, 1983.CrossRefGoogle Scholar
  33. 33.
    Lee, C. H., C. A. Carruthers, S. Ayoub, R. C. Gorman, J. H. Gorman, 3rd, and M. S. Sacks. Quantification and simulation of layer-specific mitral valve interstitial cells deformation under physiological loading. J. Theor. Biol. 373:26–39, 2015.CrossRefzbMATHGoogle Scholar
  34. 34.
    Lee, C.-H., and M. S. Sacks. Fibers to organs: how collagen fiber properties modulate the closing behavior of the mitral valve. In: Structure-Based Mechanics of Tissues and Organs, edited by G. S. Kassab, and M. S. Sacks. Boston: Springer, 2016, pp. 365–381.CrossRefGoogle Scholar
  35. 35.
    Lee, C.-H., W. Zhang, K. Feaver, R. C. Gorman, J. H. Gorman, and M. S. Sacks. On the in vivo function of the mitral heart valve leaflet: insights into tissue–interstitial cell biomechanical coupling. Biomech. Model. Mechanobiol. 16(5):1613–1632, 2017.CrossRefGoogle Scholar
  36. 36.
    Lee, C. H., W. Zhang, J. Liao, C. A. Carruthers, J. I. Sacks, and M. S. Sacks. On the presence of affine fibril and fiber kinematics in the mitral valve anterior leaflet. Biophys. J. 108(8):2074–2087, 2015.CrossRefGoogle Scholar
  37. 37.
    Leser, V., M. Milani, F. Tatti, Z. P. Tkalec, J. Strus, and D. Drobne. Focused ion beam (FIB)/scanning electron microscopy (SEM) in tissue structural research. Protoplasma 246(1–4):41–48, 2010.CrossRefGoogle Scholar
  38. 38.
    Levine, R. A., A. A. Hagege, D. P. Judge, M. Padala, J. P. Dal-Bianco, E. Aikawa, J. Beaudoin, J. Bischoff, N. Bouatia-Naji, P. Bruneval, J. T. Butcher, A. Carpentier, M. Chaput, A. H. Chester, C. Clusel, F. N. Delling, H. C. Dietz, C. Dina, R. Durst, L. Fernandez-Friera, M. D. Handschumacher, M. O. Jensen, X. P. Jeunemaitre, H. L. Marec, T. L. Tourneau, R. R. Markwald, J. Merot, E. Messas, D. P. Milan, T. Neri, R. A. Norris, D. Peal, M. Perrocheau, V. Probst, M. Puceat, N. Rosenthal, J. Solis, J. J. Schott, E. Schwammenthal, S. A. Slaugenhaupt, J. K. Song, and M. H. Yacoub. Mitral valve disease-morphology and mechanisms. Nat. Rev. Cardiol. 12(12):689–710, 2015.CrossRefGoogle Scholar
  39. 39.
    Lidke, D. S., and K. A. Lidke. Advances in high-resolution imaging–techniques for three-dimensional imaging of cellular structures. J Cell Sci 125(11):2571–2580, 2012.CrossRefGoogle Scholar
  40. 40.
    Medeiros, L. C., W. De Souza, C. Jiao, H. Barrabin, and K. Miranda. Visualizing the 3D architecture of multiple erythrocytes infected with Plasmodium at nanoscale by focused ion beam-scanning electron microscopy. PLoS ONE 7(3):e33445, 2012.CrossRefGoogle Scholar
  41. 41.
    Merryman, W. D., H. D. Lukoff, R. A. Long, G. C. Engelmayr, Jr, R. A. Hopkins, and M. S. Sacks. Synergistic effects of cyclic tension and transforming growth factor-beta1 on the aortic valve myofibroblast. Cardiovasc. Pathol. 16(5):268–276, 2007.CrossRefGoogle Scholar
  42. 42.
    Murphy, G. E., K. Narayan, B. C. Lowekamp, L. M. Hartnell, J. A. Heymann, J. Fu, and S. Subramaniam. Correlative 3D imaging of whole mammalian cells with light and electron microscopy. J. Struct. Biol. 176(3):268–278, 2011.CrossRefGoogle Scholar
  43. 43.
    Nalla, R. K., A. E. Porter, C. Daraio, A. M. Minor, V. Radmilovic, E. A. Stach, A. P. Tomsia, and R. O. Ritchie. Ultrastructural examination of dentin using focused ion-beam cross-sectioning and transmission electron microscopy. Micron 36(7–8):672–680, 2005.CrossRefGoogle Scholar
  44. 44.
    Narayan, K., and S. Subramaniam. Focused ion beams in biology. Nat Methods 12(11):1021, 2015.CrossRefGoogle Scholar
  45. 45.
    O’Connell, M. K., S. Murthy, S. Phan, C. Xu, J. Buchanan, R. Spilker, and C. A. Taylor. The three-dimensional micro- and nanostructure of the aortic medial lamellar unit measured using 3D confocal and electron microscopy imaging. Matrix Biol. 27(3):171–181, 2008.CrossRefGoogle Scholar
  46. 46.
    Peddie, C. J., and L. M. Collinson. Exploring the third dimension: volume electron microscopy comes of age. Micron 61:9–19, 2014.CrossRefGoogle Scholar
  47. 47.
    Rabkin, E., M. Aikawa, J. R. Stone, Y. Fukumoto, P. Libby, and F. J. Schoen. Activated interstitial myofibroblasts express catabolic enzymes and mediate matrix remodeling in myxomatous heart valves. Circulation 104(21):2525–2532, 2001.CrossRefGoogle Scholar
  48. 48.
    Rabkin-Aikawa, E., M. Farber, M. Aikawa, and F. J. Schoen. Dynamic and reversible changes of interstitial cell phenotype during remodeling of cardiac valves. J Heart Valve Dis 13(5):841–847, 2004.Google Scholar
  49. 49.
    Raspanti, M., M. Reguzzoni, M. Protasoni, and D. Martini. Evidence of a discrete axial structure in unimodal collagen fibrils. Biomacromolecules 12(12):4344–4347, 2011.CrossRefGoogle Scholar
  50. 50.
    Rego, B. V., S. Ayoub, A. H. Khalighi, A. Drach, R. Gorman, J. Gorman, and M. S. Sacks. Alterations in mechanical properties and in vivo geometry of the mitral valve following myocardial infarction. In: Proceedings of the 2017 Summer Biomechanics, Bioengineering and Biotransport Conference, pp. SB3C2017-1, 2017.Google Scholar
  51. 51.
    Rego, B. V., A. H. Khalighi, A. Drach, E. K. Lai, A. M. Pouch, R. C. Gorman, J. H. Gorman, and M. S. Sacks. A non-invasive method for the determination of in vivo mitral valve leaflet strains. Int. J. Numer. Method. Biomed. Eng. (in press)Google Scholar
  52. 52.
    Rego, B. V., and M. S. Sacks. A functionally graded material model for the transmural stress distribution of the aortic valve leaflet. J. Biomech. 54:88–95, 2017.CrossRefGoogle Scholar
  53. 53.
    Rego, B. V., S. M. Wells, C. H. Lee, and M. S. Sacks. Mitral valve leaflet remodelling during pregnancy: insights into cell-mediated recovery of tissue homeostasis. J. R. Soc. Interface 13(125):20160709, 2016.CrossRefGoogle Scholar
  54. 54.
    Reznikov, N., R. Almany-Magal, R. Shahar, and S. Weiner. Three-dimensional imaging of collagen fibril organization in rat circumferential lamellar bone using a dual beam electron microscope reveals ordered and disordered sub-lamellar structures. Bone 52(2):676–683, 2013.CrossRefGoogle Scholar
  55. 55.
    Robinson, P. S., K. A. Derwin, R. V. Iozzo, L. J. Soslowsky, T. W. Lin, and P. R. Reynolds. Strain-rate sensitive mechanical properties of tendon fascicles from mice with genetically engineered alterations in collagen and decorin. J. Biomech. Eng. 126(2):252–257, 2004.CrossRefGoogle Scholar
  56. 56.
    Robinson, P. S., T.-F. Huang, E. Kazam, R. V. Iozzo, L. J. Soslowsky, and D. E. Birk. Influence of decorin and biglycan on mechanical properties of multiple tendons in knockout mice. J. Biomech. Eng. 127(1):181–185, 2005.CrossRefGoogle Scholar
  57. 57.
    Ruggeri, A., F. Reale, and E. Benazzo. Collagen fibrils with straight and helicoidal microfibrils: a freeze-fracture and thin-section study. J. Ultrastruct. Res. 68(1):101–108, 1979.CrossRefGoogle Scholar
  58. 58.
    Sacks, M. S., A. Khalighi, B. Rego, S. Ayoub, and A. Drach. On the need for multi-scale geometric modelling of the mitral heart valve. Healthc. Technol Lett 4(5):150, 2017.CrossRefGoogle Scholar
  59. 59.
    Sacks, M. S., W. D. Merryman, and D. E. Schmidt. On the biomechanics of heart valve function. J. Biomech. 42(12):1804–1824, 2009.CrossRefGoogle Scholar
  60. 60.
    Sacks, M. S., and A. P. Yoganathan. Heart valve function: a biomechanical perspective. Philos. Trans. R. Soc. Lond. B 363(1502):2481, 2008.CrossRefGoogle Scholar
  61. 61.
    Schertel, A., N. Snaidero, H. M. Han, T. Ruhwedel, M. Laue, M. Grabenbauer, and W. Mobius. Cryo FIB-SEM: volume imaging of cellular ultrastructure in native frozen specimens. J. Struct. Biol. 184(2):355–360, 2013.CrossRefGoogle Scholar
  62. 62.
    Schneider, P., M. Meier, R. Wepf, and R. Muller. Towards quantitative 3D imaging of the osteocyte lacuno-canalicular network. Bone 47(5):848–858, 2010.CrossRefGoogle Scholar
  63. 63.
    Schneider, P., M. Meier, R. Wepf, and R. Muller. Serial FIB/SEM imaging for quantitative 3D assessment of the osteocyte lacuno-canalicular network. Bone 49(2):304–311, 2011.CrossRefGoogle Scholar
  64. 64.
    Schoen, F. Aortic valve structure-function correlations: role of elastic fibers no longer a stretch of the imagination. J. Heart Valve Dis. 6:1–6, 1997.Google Scholar
  65. 65.
    Scott, M., and I. Vesely. Aortic valve cusp microstructure: the role of elastin. Ann. Thorac. Surg. 60:S391–S394, 1995.CrossRefGoogle Scholar
  66. 66.
    Scott, M. J., and I. Vesely. Morphology of porcine aortic valve cusp elastin. J Heart Valve Dis. 5(5):464–471, 1996.Google Scholar
  67. 67.
    Starborg, T., N. S. Kalson, Y. Lu, A. Mironov, T. F. Cootes, D. F. Holmes, and K. E. Kadler. Using transmission electron microscopy and 3View to determine collagen fibril size and three-dimensional organization. Nat. Protoc. 8(7):1433–1448, 2013.CrossRefGoogle Scholar
  68. 68.
    Stella, J. A., and M. S. Sacks. On the biaxial mechanical properties of the layers of the aortic valve leaflet. J. Biomech. Eng. 129(5):757–766, 2007.CrossRefGoogle Scholar
  69. 69.
    Stephens, E., C. Durst, J. Swanson, K. J. Grande-Allen, N. Ingels, Jr, and D. C. Miller. Functional coupling of valvular interstitial cells and collagen via α2β1 integrins in the mitral leaflet. Cell. Mol. Bioeng. 3(4):428–437, 2010.CrossRefGoogle Scholar
  70. 70.
    Taylor, P. M., P. Batten, N. J. Brand, P. S. Thomas, and M. H. Yacoub. The cardiac valve interstitial cell. Int. J. Biochem. Cell Biol. 35(2):113–118, 2003.CrossRefGoogle Scholar
  71. 71.
    Thayer, P., K. Balachandran, S. Rathan, C. H. Yap, S. Arjunon, H. Jo, and A. P. Yoganathan. The effects of combined cyclic stretch and pressure on the aortic valve interstitial cell phenotype. Ann. Biomed. Eng. 39(6):1654–1667, 2011.CrossRefGoogle Scholar
  72. 72.
    Timmermans, F. J., and C. Otto. Contributed review: Review of integrated correlative light and electron microscopy. Rev. Sci. Instrum. 86(1):011501, 2015.CrossRefGoogle Scholar
  73. 73.
    Titze, B., and C. Genoud. Volume scanning electron microscopy for imaging biological ultrastructure. Biol. Cell 108(11):307–323, 2016.CrossRefGoogle Scholar
  74. 74.
    Upton, M. L., J. Chen, F. Guilak, and L. A. Setton. Differential effects of static and dynamic compression on meniscal cell gene expression. J. Orthop. Res. 21(6):963–969, 2003.CrossRefGoogle Scholar
  75. 75.
    Vesely, I. The role of elastin in aortic valve mechanics. J. Biomech. 31(2):115–123, 1998.CrossRefGoogle Scholar
  76. 76.
    Weinberg, E. J., and M. R. K. Mofrad. A multiscale computational comparison of the bicuspid and tricuspid aortic valves in relation to calcific aortic stenosis. J. Biomech. 41(16):3482–3487, 2008.CrossRefGoogle Scholar
  77. 77.
    Weinberg, E. J., D. Shahmirzadi, and M. R. K. Mofrad. On the multiscale modeling of heart valve biomechanics in health and disease. Biomech. Modeling Mechanobiol. 9(4):373–387, 2010.CrossRefGoogle Scholar
  78. 78.
    Zaefferer, S., S. I. Wright, and D. Raabe. Three-dimensional orientation microscopy in a focused ion beam-scanning electron microscope: a new dimension of microstructure characterization. Metall. Mater. Trans. A 39(2):374–389, 2008.CrossRefGoogle Scholar
  79. 79.
    Zhang, W., S. Ayoub, J. Liao, and M. S. Sacks. A meso-scale layer-specific structural constitutive model of the mitral heart valve leaflets. Acta Biomater. 32:238–255, 2015.CrossRefGoogle Scholar

Copyright information

© Biomedical Engineering Society 2018

Authors and Affiliations

  • Salma Ayoub
    • 1
  • Karen C. Tsai
    • 1
  • Amir H. Khalighi
    • 1
  • Michael S. Sacks
    • 1
    Email author
  1. 1.Willerson Center for Cardiovascular Modeling and Simulation, Institute for Computational Engineering and Sciences and the Department of Biomedical EngineeringThe University of Texas at AustinAustinUSA

Personalised recommendations