Heat-induced changes in the mechanics of a collagenous tissue: isothermal free shrinkage

We present data from isothermal free-shrinkage tests (i.e., performed in the absence of mechanical loads) wherein bovine chordae tendineae were subjected to temperatures from 65 to 85 degrees C for 120 to 1200 s. These data reveal four new insights into heat-induced denaturation of a collagenous tissue. First, a characteristic time for the free shrinkage appears to exhibit an Arrhenius-type relationship with temperature. Second, scaling the actual heating time via the characteristic time results in a single correlation between free shrinkage and the duration of heating; this correlation suggests a time-temperature equivalence. Third, it is the cumulative, not current, heating time that governs the free shrinkage. And fourth, heat-induced free shrinkage is partially recovered when the tissue is returned to 37 degrees C, this recovery also being time-dependent. Although these findings will help guide future experimentation and constitutive modeling, as well as the design of new heat-based clinical therapies, there is a pressing need to collect additional isothermal data, particularly in the presence of well-defined mechanical loads.