Polarized light scanning cryomacroscopy, part I: Experimental apparatus and observations of vitrification, crystallization, and photoelasticity effects

Abstract

Cryomacroscopy is an effective means to observe physical events affecting cryopreservation success in large-size specimens. The current study aims at integrating polarized-light in the study of large-size cryopreservation, using the scanning cryomacroscope as a development platform. Results of this study demonstrate polarized light as a visualization enhancement means, including the following effects: contaminants in the CPA solution, crystallization, fracture formation, thermal contraction, and solute precipitation. In addition, photoelasticity effects are used to demonstrate the development of residual stresses and the potential for stress relaxation above the glass transition temperature. Furthermore, this study suggests that the ability to periodically switch between non-polarized light and polarized light is an essential feature of investigation. When using polarized light for example, a dark region may represent a free-of-stress and free-of-crystals material, or fully crystallized material, which may potentially experience mechanical stress; switching to a non-polarized light would help to distinguish between the different cases. The analysis of thermo-mechanical stress in cryopreservation is essentially based on four key elements: identification of physical events, knowledge of physical properties, thermal analysis of the specimen, and description of the mechanical behavior of the cryopreserved material (also known as the constitutive law). With the above knowledge, one can investigate the conditions to preserve structural integrity. While the current study aims at identification of physical events, critical knowledge on physical properties and mechanical behavior has already been developed in previous studies. The companion manuscript (Part II) aims at providing means for thermal analysis in the specimen, which will serve as the basis for a multi-scale analysis of thermo-mechanical stress in large-size specimens.

Polarized light scanning cryomacroscopy, part II: Thermal modeling and analysis of experimental observations

“…2(a) of Part I [9]. The overall contact area with the cuvette base is less than 10% of the area of the cuvette bottom surface and less than 0.7% of the overall cuvette outer surface.…”

“…The overall contact area with the cuvette base is less than 10% of the area of the cuvette bottom surface and less than 0.7% of the overall cuvette outer surface. Furthermore, the cuvette base is a 3D-printed structure, made of Acrylonitrile Butadiene Styrene (ABS) [9], which is considered a thermal insulator $false(k=0.15\frac{W}{m-°\mathrm{normalC}}false)$. With this particular thermal design of the cuvette holder, heat transfer by forced convection is assumed from the remaining 90% of the cuvette bottom surface [9].…”

“…Furthermore, the cuvette base is a 3D-printed structure, made of Acrylonitrile Butadiene Styrene (ABS) [9], which is considered a thermal insulator $false(k=0.15\frac{W}{m-°\mathrm{normalC}}false)$. With this particular thermal design of the cuvette holder, heat transfer by forced convection is assumed from the remaining 90% of the cuvette bottom surface [9]. Finally, due to the 3D-printed cap of the cuvette [9], only free convection is assumed at the CPA-cooling chamber interface (upper surface).…”

“…The observed convection currents within the CPA at higher cryogenic temperatures, as indicated by circulation of contaminants (Fig. 3(a) of Part I of this study [9]), call for a special heat transfer analysis in this temperature range. Furthermore, the rate of heat transfer between the cuvette and its cryogenic environment cannot be predicted a priori and must be analyzed from specific experimental data.…”

“…Cryomacroscopy has been demonstrated as an effective means to observe physical events affecting cryopreservation success in large-size specimens [9]. In Part I of this study, polarized light capabilities have been demonstrated in two modes: (i) as a means to detect physical effects such as contamination in the CPA solution, crystallization, fracture formation, thermal contraction, and solute precipitation; and (ii) as a tool to study thermo-mechanical stress by means of photoelasticity.…”