Multiaxial thermal damage of collagenous membranes

There is a pressing need to evaluate the effects of multiaxial stresses on the kinetics of thermal denaturation and conversely to evaluate the effects of heating on the subsequent multiaxial properties. No such data are available. We present data on bovine epicardium that reveal the effects of two special cases of mechanical loading during isothermal heating: biaxial isotonic and biaxial isometric tests. General findings include: (1) free-shrinkage condition yields a much more compliant and extensible tissue; (2) isometric condition near the original natural configuration yields a much less extensible and stiffer material; (3) high strain isometric and high load isotonic conditions yield a spectrum of alterations, with less general deviation from the native response; (4) increased isotonic load both delays onset of shrinkage and decreases equilibrium shrinkage; (5) increased temperature both hastens shrinkage and increases equilibrium shrinkage. Thermal damage under multiaxial stresses is thus a very complex process, one that merits much greater attention.