| dc.description | For the first time a novel thermomechanical approach has been used to study the dynamics of the rapid thermal denaturation of two different collagenous tissues (bovine pericardium and mitral chordae tendineae) and the various factors influencing this important event. Specifically, a custom-made, computer-controlled, dynamic hydrothermal isometric tension (DHIT) system allowed for the rapid change of tissue temperature, from 25°C to 90°C in less than 1 s, while the samples are held under isometric constraint. The data for all the experiments were well-fitted using the Levenberg-Marquardt nonlinear least-squares method and a 3-exponential function each having unique time constant taui; and corresponding coefficients (Ci). The data for all tissues revealed that rapid thermal denaturation of the collagenous tissues was a dynamic, 3-step process, and that the first step, as characterized by (tau1) was both the fastest, and the most significant (as indicated by C1) during the entire denaturation process. The reversibility experiments indicated that the rapid step-change in temperature in both collagenous tissues, under isometric and isothermal conditions led to the observation that the first heating cycle resulted in the transformation of ordered, native collagenous tissues into less ordered and rubber elastic materials. The molecular events occurring during the first heating cycle represented the only irreversible transitions; the thermoelastic contraction and relaxation of the rubbery, denatured collagen during the subsequent thermal and cooling cycles occurred in a repeatable manner. The effects of increased loads and various concentrations of NaCl on the dynamics of rapid thermal denaturation indicated that both factors delayed the dynamics of thermal denaturation and, more importantly that the denaturation remained a dynamic 3-staged event. Finally, the DHIT system was used to comparatively investigate the structure-function relations in various load-bearing components of bovine heart including: mitral and tricuspid chordae tendineae, aortic and mitral valves, and pericardium. It was shown that tissues sustaining higher mechanical loads were less thermally stable, perhaps due to a higher level of immature crosslinks than those under lower stress. This new thermomechanical approach demonstrated that rapid thermal denaturation of different collagenous tissues, under isometric constraints and isothermal heating conditions, is a dynamic, largely irreversible, 3-step mechanism. | en_US |
