Multiscale investigation of Snomax effects on supercooling with application to high-subzero cryopreservation:...

This is a multiscale experimental investigation to study supercooling effects in selected cryoprotective agents (CPAs), in the presence and absence of the commercial ice nucleation promoter Snomax. Microscale and macroscale experiments were conducted using differential scanning calorimetry (DSC) and cryomacroscopy, respectively. The distinction between the different scales in this study is related to heat transfer considerations, where the microsample behaves as a thermally lumped system, such as the case in cells in suspension and microorganisms. On the other hand, the macrosample is characterized by a significant temperature distribution, which is relevant to cryopreservation of large tissues and organs. While the ice modulation effects of Snomax have been investigated in microsamples over the past three decades, its application to organ cryopreservation gained traction only in recent years, where the related application is popularly known as partial freezing. While the current study focuses on cryopreservation, the term partial freezing has also been used previously for different applications in thermal sciences and in the food industry. While the addition of Snomax to microsample generated the expected effect of reducing the extent of supercooling, the supercooling reduction at the center of macrosamples in the current study is found marginal, where the effect of Snomax is virtually nonexistent. This study demonstrates how ice nucleation in macrosamples is dominated by surface tension, surface roughness, other geometrical features, and patterns of ice growth thereafter, but not as much on the presence of Snomax. Interestingly, no volumetric ice nucleation was observed in the macrosamples, but only ice growth from surfaces, regardless of Snomax concentration. Finally, this study discusses the impracticality of high subzero (HSZ) organ preservation in supercooling conditions as an alternative to partial freezing.