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Gangwar L, Phatak SS, Etheridge M, Bischof JC. A guide to successful mL to L scale vitrification and rewarming. Cryo Letters 2022; 43:316-321. [PMID: 36629824 PMCID: PMC10217567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Cryopreservation by vitrification to achieve an "ice free" glassy state is an effective technique for preserving biomaterials including cells, tissues, and potentially even whole organs. The major challenges in cooling to and rewarming from a vitrified state remain ice crystallization and cracking/fracture. Ice crystallization can be inhibited by the use of cryoprotective agents (CPAs), though the inhibition further depends upon the rates achieved during cooling and rewarming. The minimal rate required to prevent any ice crystallization or recrystallization/devitrification in a given CPA is called the critical cooling rate (CCR) or critical warming rate (CWR), respectively. On the other hand, physical cracking is mainly related to thermomechanical stresses, which can be avoided by maintaining temperature differences below a critical threshold. In this simplified analysis, we calculate deltaT as the largest temperature difference occurring in a system during cooling or rewarming in the brittle/glassy phase. This deltaT is then used in a simple "thermal shock equation" to estimate thermal stress within the material to decide if the material is above the yield strength and to evaluate the potential for fracture failure. In this review we aimed to understand the limits of success and failure at different length scales for cryopreservation by vitrification, due to both ice crystallization and cracking. Here we use thermal modeling to help us understand the magnitude and trajectory of these challenges as we scale the biomaterial volume for a given CPA from the milliliter to liter scale. First, we solved the governing heat transfer equations in a cylindrical geometry for three common vitrification cocktails (i.e., VS55, DP6, and M22) to estimate the cooling and warming rates during convective cooling and warming and nanowarming (volumetric heating). Second, we estimated the temperature difference deltaT and compared it to a tolerable threshold (deltaTmax) based on a simplified "thermal shock" equation for the same cooling and rewarming conditions. We found, not surprisingly, that M22 achieves vitrification more easily during convective cooling and rewarming for all volumes compared to VS55 or DP6 due to its considerably lower CCR and CWR. Further, convective rewarming (boundary rewarming) leads to larger temperature differences and smaller rates compared to nanowarming (volumetric rewarming) for all CPAs with increasing failure at larger volumes. We conclude that as more and larger systems are vitrified and rewarmed with standard CPA cocktails, this work can serve as a practical guide to successful implementation based on the characteristic length (volume/surface area) of the system and the specific conditions of cooling and warming. doi.org/10.54680/fr22610110112.
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Affiliation(s)
- L Gangwar
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, 55455 USA
| | - S S Phatak
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, 55455 USA
| | - M Etheridge
- Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, 55455 USA
| | - J C Bischof
- Department of Mechanical Engineering; Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, 55455 USA.
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Han Z, Gangwar L, Magnuson E, Etheridge ML, Bischof JC, Choi J, Pringle CO. Supplemented phase diagrams for vitrification CPA cocktails: DP6, VS55 and M22. Cryobiology 2022; 106:113-121. [PMID: 35276219 DOI: 10.1016/j.cryobiol.2022.02.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 02/24/2022] [Accepted: 02/25/2022] [Indexed: 11/03/2022]
Abstract
DP6, VS55 and M22 are the most commonly used cryoprotective agent (CPA) cocktails for vitrification experiments in tissues and organs. However, complete phase diagrams for the three CPAs are often unavailable or incomplete (only available for full strength CPAs) thereby hampering optimization of vitrification and rewarming procedures. In this paper, we used differential scanning calorimetry (DSC) to measure the transition temperatures including heterogeneous nucleation temperatures (Thet), glass transition temperatures (Tg), rewarming phase crystallization (devitrification and/or recrystallization) temperatures (Td) and melting temperatures (Tm) while cooling or warming the CPA sample at 5 °C/min and plotted the obtained transition temperatures for different concentrations of CPAs into the phase diagrams. We also used cryomicroscopy cooling or warming the sample at the same rate to record the ice crystallization during the whole process, and we presented the cryomicroscopic images at the transition temperatures, which agreed with the DSC presented phenomena.
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Affiliation(s)
- Z Han
- Department of Mechanical Engineering, University of Minnesota, 111 Church St., Minneapolis, MN, 55455, USA
| | - L Gangwar
- Department of Mechanical Engineering, University of Minnesota, 111 Church St., Minneapolis, MN, 55455, USA
| | - E Magnuson
- Department of Mechanical Engineering, University of Minnesota, 111 Church St., Minneapolis, MN, 55455, USA
| | - M L Etheridge
- Department of Mechanical Engineering, University of Minnesota, 111 Church St., Minneapolis, MN, 55455, USA
| | - J C Bischof
- Department of Mechanical Engineering, Department of Biomedical Engineering, University of Minnesota, 111 Church St., Minneapolis, MN, 55455, USA.
| | - J Choi
- Department of Engineering Technologies, Safety, and Construction, Central Washington University, 400 E. University Way, Ellensburg, WA, 98926, USA.
| | - C O Pringle
- Department of Engineering Technologies, Safety, and Construction, Central Washington University, 400 E. University Way, Ellensburg, WA, 98926, USA
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