Thermomechanical stress analysis of rabbit kidney and human kidney during cryopreservation by vitrification with the application of radiofrequency heating.

This study presents a computational framework for thermomechanical stress analysis in a specimen undergoing cryopreservation, with emphasis on radiofrequency (RF) heating for recovering from cryogenic storage. In particular, this study addresses cryopreservation by vitrification, where the specimen is stored in the amorphous phase (vitreous means glassy). In broad terms, the relatively high cooling and rewarming rates necessary for vitrification result in differential thermal expansion in the specimen, which is the driving force for thermomechanical stress. Thermomechanical stress can lead to structural damage, such as fractures or plastic deformation, rendering the specimen useless. Not without technical difficulties, those hazardous effects during the rewarming phase of the protocol can be mitigated by applying volumetric heating, with RF heating as an attractive means. The proposed computational framework in this study addresses the coupled electromagnetic, thermal and solid mechanics fields, using commercially available solvers. This study advances from a spherical-case benchmark to realistic models of the rabbit kidney and the human kidney. Results of this study suggest that structural damage to the brittle material can be prevented when stress relaxation is facilitated around the glass transition temperature. Furthermore, this study suggests that volumetric heating is necessary to surpass the critical rewarming rate, while benefiting from lowering the overall thermomechanical stress during recovery from cryogenic storage. More broadly, the computational framework presented here can be used for the optimization of the RF heating parameters, chamber specifics, specimen container shape, and the thermal protocol in order to preserve structural integrity in the specimen.