Dynamic thermomechanical studies on collagen denaturation: a comparative study of bovine pericardium and chordae...

Denaturation of the collagen molecule is a kinetic process, and hence a function of both temperature and duration of heating. Simple isothermal tests have traditionally provided the easiest way to isolate the role of heating in denaturation. In the present experiments, a Dynamic Hydrothermal Isometric Tension (DHIT) system has been custom-built and used to impose near-step changes temperature as a means to studying the dynamics of denaturation in fresh and crosslinked bovine Pericardium (PC) and Chordac Tendinae (CT). Irrespective of their treatment, both PC and CT followed the same pattern of force rise following a step in temperature. The force-time data were well-fitted using the Levenberg-Marquardt nonlinear least-squares method and 3 exponential functions with unique time constants (tau 1, tau 2, tau 3). This suggests the presence of three discrete mechanisms in the denaturation process. The tau 1 values for PC and CT were significantly shorter than either tau 2, or tau 3. Also, the tau 1 values of the untreated groups (either PC or CT) were similar and significantly different than those for the crosslinked tissues. This indicates that crosslinking dramatically slows the dynamic denaturation in both tissues (identified with tau 1) to the same extent. This is of considerable interest since each tissue has unique and distinct collagen architecture; therefore the dynamics of denaturation depend more on the collagen molecule than on fibrous architecture. This is the first study to identify discrete mechanisms leading to isometric denaturation changes in two collagenous tissues. While it is believed that the mechanisms identified represent (i) progressive hydration and (ii) denaturation of collagen structure, more precise identification of the processes remain to be done.