Cryopreservation of Collagen-Based Tissue Equivalents. II. Improved Freezing in the Presence of Cryoprotective Agents

In Part I of this study we determined an optimal cooling rate for cryopreservation of collagen-based tissue equivalents (TEs) that preserves both the postthaw cell viability and mechanical properties, but results in tissue contraction and an overall loss of opacity. The empirically determined optimal cooling rate (5°C/min) was obtained in a freezing medium consisting solely of phosphate-buffered saline (PBS) at physiological concentration (1x). In the present study we report the effect of freezing on TEs in the presence of PBS and two cryoprotective agents (CPAs) (glycerol and dimethyl sulfoxide [Me2SO]), at two different concentrations (0.5 and 1.0 M), to two different end temperatures (-80 and -160°C), at a cooling rate of 5°C/min. The controlled rate freezing experiments, postthaw cell viability, and mechanical property measurements were performed as described in Part I of this study. In addition to studying the effect of CPAs on the postthaw properties of TEs, we also investigated (1) the effect of fr...