TY - JOUR

T1 - Cooling dynamics of droplets exposed to solid surface freezing and vitrification

AU - Liu, Dejia

AU - Oldenhof, Harriëtte

AU - Luo, Xing

AU - Braun, Tobias

AU - Sieme, Harald

AU - Wolkers, Willem F.

N1 - Funding Information: The work described in this study was financially supported via grant WO1735/6–2 and SI1462/4–2 of the German Research Foundation (DFG: Deutsche Forschungsgemeinschaft), and HEMOFORCE (E/U2ED/MD010/LF551, Deutsche Bundeswehr). We kindly acknowledge the Institute for Transfusion Medicine (Hannover Medical School) for providing blood samples.

PY - 2024/6

Y1 - 2024/6

N2 - Solid surface freezing or vitrification (SSF/SSV) can be done by depositing droplets of a sample, e.g., cells in a preservation solution, onto a pre-cooled metal surface. It is used to achieve higher cooling rates and concomitant higher cryosurvival rates compared to immersion of samples into liquid nitrogen. In this study, numerical simulations of SSF/SSV were conducted by modeling the cooling dynamics of droplets of cryoprotective agent (CPA) solutions. It was assumed that deposited droplets attain a cylindrical bottom part and half-ellipsoidal shaped upper part. Material properties for heat transfer simulations including density, heat capacity and thermal conductivity were obtained from the literature and extrapolated using polynomial fitting. The impact of CPA type, i.e., glycerol (GLY) and dimethyl sulfoxide (DMSO), CPA concentration, and droplet size on the cooling dynamics was simulated at different CPA mass fractions at temperatures ranging from −196 to 25 °C. Simulations show that glycerol solutions cool faster compared to DMSO solutions, and cooling rates increase with decreasing CPA concentration. However, we note that material property data for GLY and DMSO solutions were obtained in different temperature and concentration ranges under different conditions, which complicated making an accurate comparison. Experimental studies show that samples that freeze have a delayed cooling response early on, whereas equilibration times are similar compared to samples that vitrify. Finally, as proof of concept, droplets of human red blood cells (RBCs) were cryopreserved using SSV/SSF comparing the effect of GLY and DMSO on cryopreservation outcome. At 20% (w/w), similar hemolysis rates were found for GLY and DMSO, whereas at 40%, GLY outperformed DMSO.

AB - Solid surface freezing or vitrification (SSF/SSV) can be done by depositing droplets of a sample, e.g., cells in a preservation solution, onto a pre-cooled metal surface. It is used to achieve higher cooling rates and concomitant higher cryosurvival rates compared to immersion of samples into liquid nitrogen. In this study, numerical simulations of SSF/SSV were conducted by modeling the cooling dynamics of droplets of cryoprotective agent (CPA) solutions. It was assumed that deposited droplets attain a cylindrical bottom part and half-ellipsoidal shaped upper part. Material properties for heat transfer simulations including density, heat capacity and thermal conductivity were obtained from the literature and extrapolated using polynomial fitting. The impact of CPA type, i.e., glycerol (GLY) and dimethyl sulfoxide (DMSO), CPA concentration, and droplet size on the cooling dynamics was simulated at different CPA mass fractions at temperatures ranging from −196 to 25 °C. Simulations show that glycerol solutions cool faster compared to DMSO solutions, and cooling rates increase with decreasing CPA concentration. However, we note that material property data for GLY and DMSO solutions were obtained in different temperature and concentration ranges under different conditions, which complicated making an accurate comparison. Experimental studies show that samples that freeze have a delayed cooling response early on, whereas equilibration times are similar compared to samples that vitrify. Finally, as proof of concept, droplets of human red blood cells (RBCs) were cryopreserved using SSV/SSF comparing the effect of GLY and DMSO on cryopreservation outcome. At 20% (w/w), similar hemolysis rates were found for GLY and DMSO, whereas at 40%, GLY outperformed DMSO.

KW - Cryopreservation

KW - Droplet generation

KW - Numerical simulation

KW - Red blood cells

KW - Solid surface vitrification/freezing

KW - Vitrification

UR - http://www.scopus.com/inward/record.url?scp=85187327217&partnerID=8YFLogxK

U2 - 10.1016/j.cryobiol.2024.104879

DO - 10.1016/j.cryobiol.2024.104879

M3 - Article

C2 - 38447705

AN - SCOPUS:85187327217

VL - 115

JO - CRYOBIOLOGY

JF - CRYOBIOLOGY

SN - 0011-2240

M1 - 104879

ER -