Measurement of layer-specific mechanical properties in multilayered biomaterials by micropipette aspiration.

Many biomaterials and tissues are complex multilayered structures in which the individual layers have distinct mechanical properties that influence the mechanical behavior and define the local cellular microenvironment. Characterization of the mechanical properties of individual layers in intact tissues is technically challenging. Micropipette aspiration (MA) is a proven method for the analysis of local mechanical properties of soft single-layer biomaterials, but its applicability for multilayer structures has not been demonstrated. We sought to determine and validate MA experimental parameters that would permit measurement of the mechanical properties of only the top layer of an intact multilayer biomaterial or tissue. To do so, we performed parametric nonlinear finite-element (FE) analyses and validation experiments using a multilayer gelatin system. The parametric FE analyses demonstrated that measurement of the properties of only the top layer of a multilayer structure is sensitive to the ratio of the pipette inner diameter (D) to top layer thickness (ttop), and that accurate measurement of the top layer modulus requires D/ttop<1. These predictions were confirmed experimentally by MA of the gelatin system. Using this approach and an inverse FE method, the mean effective modulus of the fibrosa layer of intact porcine aortic valve leaflets was determined to be greater than that of the ventricularis layer (P<0.01), consistent with data obtained by tensile testing of dissected layers. This study provides practical guidelines for the use of MA to measure the mechanical properties of single layers in intact multilayer biomaterials and tissues.

[1]  Frank P T Baaijens,et al.  Mechanical characterization of anisotropic planar biological soft tissues using large indentation: a computational feasibility study. , 2005, Journal of biomechanical engineering.

[2]  R. Ogden,et al.  Biomechanics of Soft Tissue in Cardiovascular Systems , 2003 .

[3]  Frank P T Baaijens,et al.  Mechanical characterization of anisotropic planar biological soft tissues using finite indentation: experimental feasibility. , 2008, Journal of biomechanics.

[4]  Frederick J Schoen,et al.  Dynamic and reversible changes of interstitial cell phenotype during remodeling of cardiac valves. , 2004, The Journal of heart valve disease.

[5]  J. Lagarde,et al.  In vivo model of the mechanical properties of the human skin under suction , 2000, Skin research and technology : official journal of International Society for Bioengineering and the Skin (ISBS) [and] International Society for Digital Imaging of Skin (ISDIS) [and] International Society for Skin Imaging.

[6]  Toshiro Ohashi,et al.  Pipette aspiration technique for the measurement of nonlinear and anisotropic mechanical properties of blood vessel walls under biaxial stretch. , 2005, Journal of biomechanics.

[7]  D. Frankel,et al.  Nanoscale viscoelastic properties of an aligned collagen scaffold , 2009, Journal of materials science. Materials in medicine.

[8]  Gábor Székely,et al.  Inverse Finite Element Characterization of Soft Tissues , 2001, MICCAI.

[9]  Thomas Boudou,et al.  An extended relationship for the characterization of Young's modulus and Poisson's ratio of tunable polyacrylamide gels. , 2006, Biorheology.

[10]  Takao Furukawa,et al.  Residual stress and strain in the lamellar unit of the porcine aorta: experiment and analysis. , 2004, Journal of biomechanics.

[11]  Roger R Markwald,et al.  Transitions in Early Embryonic Atrioventricular Valvular Function Correspond With Changes in Cushion Biomechanics That Are Predictable by Tissue Composition , 2007, Circulation research.

[12]  Toshiro Ohashi,et al.  Local elastic modulus of atherosclerotic lesions of rabbit thoracic aortas measured by pipette aspiration method. , 2002, Physiological measurement.

[13]  H. Zahouani,et al.  In vivo characterization of viscoelastic properties of human skin using dynamic micro-indentation , 2007, 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society.

[14]  Takeo Matsumoto,et al.  The pipette aspiration applied to the local stiffness measurement of soft tissues , 1997, Annals of Biomedical Engineering.

[15]  R. Ogden,et al.  Mechanics of biological tissue , 2006 .

[16]  Michael S Sacks,et al.  The effects of cellular contraction on aortic valve leaflet flexural stiffness. , 2006, Journal of biomechanics.

[17]  Ferenc Horkay,et al.  Determination of elastic moduli of thin layers of soft material using the atomic force microscope. , 2002, Biophysical journal.

[18]  Ruogang Zhao,et al.  Comparison of analytical and inverse finite element approaches to estimate cell viscoelastic properties by micropipette aspiration. , 2009, Journal of biomechanics.

[19]  Andrew D. McCulloch,et al.  Computational Methods for Soft Tissue Biomechanics , 2003 .

[20]  Chwee Teck Lim,et al.  Finite Element Simulation of the Micropipette Aspiration of a Living Cell Undergoing Large Viscoelastic Deformation , 2005 .

[21]  Toshiro Ohashi,et al.  lntramural Distribution of Elastic Moduli in Thoracic Aortas and Its Relationship to Histology : Comparison between Porcine and Bovine Thoracic Aortas , 1999 .

[22]  C. Simmons,et al.  Cofilin is a marker of myofibroblast differentiation in cells from porcine aortic cardiac valves. , 2008, American journal of physiology. Heart and circulatory physiology.

[23]  Craig A Simmons,et al.  Calcification by Valve Interstitial Cells Is Regulated by the Stiffness of the Extracellular Matrix , 2009, Arteriosclerosis, thrombosis, and vascular biology.

[24]  Michael S Sacks,et al.  Synergistic effects of cyclic tension and transforming growth factor-beta1 on the aortic valve myofibroblast. , 2007, Cardiovascular pathology : the official journal of the Society for Cardiovascular Pathology.

[25]  Y C Fung,et al.  Determination of the mechanical properties of the different layers of blood vessels in vivo. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[26]  An improved microindentation technique to measure changes in properties of arterial intima during atherogenesis. , 1983, Journal of biomechanics.

[27]  Farshid Guilak,et al.  Alterations in the mechanical properties of the human chondrocyte pericellular matrix with osteoarthritis. , 2003, Journal of biomechanical engineering.

[28]  David E. Schmidt,et al.  On the biomechanics of heart valve function. , 2009, Journal of biomechanics.

[29]  M. Sato,et al.  Comparison of spinal cord gray matter and white matter softness: measurement by pipette aspiration method. , 2001, Journal of neurosurgery.

[30]  Michael S Sacks,et al.  On the biaxial mechanical properties of the layers of the aortic valve leaflet. , 2005, Journal of biomechanical engineering.

[31]  I Vesely,et al.  Micromechanics of the fibrosa and the ventricularis in aortic valve leaflets. , 1992, Journal of biomechanics.

[32]  Thomas Boudou,et al.  An extended modeling of the micropipette aspiration experiment for the characterization of the Young's modulus and Poisson's ratio of adherent thin biological samples: numerical and experimental studies. , 2006, Journal of biomechanics.