009 Solid mechanics aspects in scale-up vitrification: From visualization of physical effects to the analysis of structural damage

Abstract

The coupled phenomena affecting cryopreservation success display a quite complex picture, with effects typically classified as resulting from the kinetics of ice crystallization, the toxicity of ice-controlling agents (ICAs), the degradation of biological material in a suspended state, and the development of thermo-mechanical stress—the focus of the current presentation. Cryopreservation success is not merely dependent upon the instantaneous state of the material, but primarily on the evolution of events along the cryopreservation protocol, which makes the process path dependent. While the analysis of cryopreservation effects in small specimens frequently benefits from spatial uniformity in temperature and in ICA concentration, higher complexity is introduced to the analysis of large-size specimens, resulting from significant temperature and concentration gradients. In vitrification of large specimens for example, the cooling rate history as a function of temperature vary across the specimen, leading to spatial distributions of the probability to suppress crystallization and the toxicity potential. Furthermore, the temperature gradients drive a non-uniform thermal expansion distribution in the material, potentially giving rise to thermo-mechanical stress, with fracture formation as its most dramatic outcome. In the absence of alternative means, the analysis of scale-up cryopreservation represents an integration of inspections at end states—at cryogenic storage temperature and at room temperature, with extrapolation from small-scale effects—observed with cryomicroscopy. Recently recorded movies of the path-dependent process of vitrification in large specimens are displayed in the current presentation, obtained with the scanning cryomacroscope—a new visualization device for the analysis of scale-up cryopreservation. The principles of thermo-mechanical stress are reviewed in the current presentation to explain the observed phenomena and draw conclusions from corresponding computer simulations. Finally, effects of combining synthetic ice modulators (SIMs) with cryoprotective agents (CPAs) in the ICA cocktail are discussed based on recently measured physical properties. In conclusion, this presentation provides a broader view on the role of solid mechanics analysis in the development of scale-up vitrification. Source of funding: This project is supported by Award Number R21EB009370 from the National Institute of Biomedical Imaging and Bioengineering, Award Number 5R21RR026210 from the National Center for Research Resources, and Award Number 8R21GM103407 from the National Institute of General Medical Sciences. Conflict of interest: None declared. rabin@cmu.edu