Abstract
This study investigates the effects of the thermal protocol on the development and relaxation of thermo-mechanical stress in cryopreservation by means of glass formation, also known as vitrification. The cryopreserved medium is modeled as a homogeneous viscoelastic domain, constrained within either a stiff cylindrical container or a highly compliant bag. Annealing effects during the cooling phase of the cryopreservation protocol are analyzed. Results demonstrate that an intermediate temperature-hold period can significantly reduce the maximum tensile stress, thereby decreasing the potential for structural damage. It is also demonstrated that annealing at temperatures close to glass transition significantly weakens the dependency of thermo-mechanical stress on the cooling rate. Furthermore, a slower initial rewarming rate after cryogenic storage may drastically reduce the maximum tensile stress in the material, which supports previous experimental observations on the likelihood of fracture at this stage. This study discusses the dependency of the various stress components on the storage temperature. Finally, it is demonstrated that the stiffness of the container wall can affect the location of maximum stress, with implications on the development of cryopreservation protocols.
Highlights
Ice formation is known to be harmful to cells, structured tissues, and organs [1,2,3,4,5]
As part of an ongoing effort to investigate thermo-mechanical effects in cryopreservation [6,11,17,18,19,20,21,22,23,24,25,26], the current study aims at investigating the potential contribution of including a temperature-hold step in cryopreservation protocols, in order to facilitate annealing and thereby reducing the risk to structural damage
This study is theoretical by nature, encapsulating the underlying principles of thermomechanical stress in viscoelastic materials, as they pertain to experimental observations collected in previous studies
Summary
Ice formation is known to be harmful to cells, structured tissues, and organs [1,2,3,4,5]. The high cooling rates required to facilitate vitrification result in significant thermal gradients within a large-size sample, where each layer of the material may display a different tendency to contract. Since adjacent layers of the material cannot overlap, thermal stress develops, making the resulting strain compatible. If this stress exceeds a critical threshold, permanent damage may occur with fracture formation as its most dramatic outcome [6,7]. It follows that, the magnitude of the resulting thermo-mechanical stress elevates with the increasing size of the specimens
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