Biomechanical characterization of aortic valve tissue in humans and common animal models

Abstract

Aortic valve disease develops in an escalating fashion in elderly patients. Current treatments including total valve replacement and valve repair techniques are still suboptimal. A thorough understanding of the animal and human valve tissue properties, particularly their differences, is crucial for the establishment of preclinical animal models and strategies for evaluating new valve treatment techniques, such as transcatheter valve intervention and tissue engineered valves. The goal of this study was to characterize and compare the biomechanical properties and histological structure of healthy ovine, porcine, and human aortic valve leaflets. The biaxial mechanical properties of the aortic valve leaflets of 10 ovine (~1 year), 10 porcine (6–9 months), and 10 aged human (80.6 ± 8.34) hearts were quantified. Tissue microstructure was analyzed via histological techniques. Aged human aortic valve leaflets were significantly less compliant than both ovine and porcine leaflets, with the ovine leaflets being the most compliant. Histological analysis revealed structural differences between the species: the human and porcine leaflets contained more collagen and elastin than the ovine leaflets. Significant mechanical and structural differences in the aortic valve tissues of 6- to 9-month-old porcine models and 1-year-old ovine models with respect to those of aged humans, suggest that these animal models may not be representative of the typical patient undergoing aortic valve replacement.

A Computational Tool for the Microstructure Optimization of a Polymeric Heart Valve Prosthesis

“…The optimized microstructure leads to a smaller circumferential strain and a higher radial strain than those found in an isotropic valve, in accordance with the studies of Billiar et al [16,50], and Martin et al [51] on the native valve, which highlighted how the natural tissue is mainly stretched in the radial direction due to the collagen fibers organization.…”

Effects of Valve Geometry and Tissue Anisotropy on the Radial Stretch and Coaptation Area of Tissue-Engineered Heart Valves

“…Regurgitation is mainly caused by cell-mediated retraction of the leaflets (Dijkman et al, 2012;van Vlimmeren et al, 2011van Vlimmeren et al, , 2012, and to ensure valve closure, these contractile cellular forces should be counteracted by the pressure applied to the valve during diastole. In native valves, the diastolic pressure applied to the valve indeed causes an extension of the tissue in primarily the radial direction (Billiar and Sacks, 2000a,b;Martin and Sun, 2012). In TEHVs, however, the tissue primarily extends in circumferential direction and radial strains can even become negative (Driessen et al, 2007).…”

Efficient computational simulation of actin stress fiber remodeling

“…The mechanical properties of soft tissues depend to a large extent on the organization of the collagen network, which is considered as the main loadbearing component in most tissues and the principal contributor to their anisotropic mechanical properties. For example, in heart valves, circumferentially aligned collagen fibers have been observed (Billiar & Sacks 2000a;Martin & Sun 2012) that transfer the pressure applied on the closed heart valve to the aortic wall (Peskin & McQueen 1994). Furthermore, they reinforce the circumferential direction enabling the stretch in the radial direction for a proper closure of the heart valve (Billiar & Sacks 2000a, 2000bSacks et al 2009;Martin & Sun 2012;Fan et al 2013;Loerakker et al 2013).…”

“…For example, in heart valves, circumferentially aligned collagen fibers have been observed (Billiar & Sacks 2000a;Martin & Sun 2012) that transfer the pressure applied on the closed heart valve to the aortic wall (Peskin & McQueen 1994). Furthermore, they reinforce the circumferential direction enabling the stretch in the radial direction for a proper closure of the heart valve (Billiar & Sacks 2000a, 2000bSacks et al 2009;Martin & Sun 2012;Fan et al 2013;Loerakker et al 2013). Next to external loads (Ruberti & Hallab 2005;Bhole et al 2009;Wyatt et al 2009;De Jonge et al 2013), the collagen network is remodeled by contractile forces exerted by the cells along their principal direction, which is determined by the organization of actin stress fibers (Wang et al 2003;Ghibaudo et al 2008;Faust et al 2011).…”