Micromechanical modeling of heart valve materials

Load bearing soft tissues, such as mitral valve chordae, tendon, pericardium and heart valves, have stiff fibers embedded in a soft matrix. Mechanical interactions between these material constituents are poorly understood. To analyze the effect of the microstructure on the mechanical behavior of specific tissues, we used a high-fidelity micromechanics model for the viscoelastic response of periodic materials characterized by a repeating unit cell with an arbitrary microstructure.;The objective of this study is to model the micromechanical behavior of heart valve materials by using their microstructure. We modeled the microstructural differences in mitral valve chordae tendinae by using their differences in collagen crimp period and fibril distribution. Our results demonstrated that the crimp period is more important than the fibril distribution for duplicating the stress/strain behavior of mitral valve chordae. We also looked at the effect of microstructure on the viscoelastic properties of the chordae. The microstructural differences, such as collagen crimp period and fibril distribution, were not sufficient to explain the difference in the stress relaxation behavior of the different chordal types.;We used crossectional TEM images of tissue-engineered chordae and native chordae to analyze the effects of its microstructural differences on its mechanical behavior. Our model successfully retrieved the stress/strain behavior of tissue-engineered chordae. We used the material parameters that are optimized for the native chordae and microstructure representation for the tissue-engineered chordae. The resultant stress/strain behavior matched the mechanical behavior of tissue-engineered chordae quite well.;One of the purposes of this project is to study the elastin degradation and loss as a failure mechanism in porcine aortic bioprosthetic heart valves to better understand the microstructural interaction of the constituents of soft tissues. We calculated elastin degradation and loss by measuring the amount of desmosine and isodesmosine---which are cross-linking amino acids specific to elastin. Our results suggested a significant loss of elastin with implant duration at a rate of 3.20 %/year which is higher than the rate of degradation of the total protein content (0.74 %/year). There was no significant effect of implantation position and gender on the rate of elastin degradation.