Modeling and experimental studies of enhanced cooling by medical gauze for cell cryopreservation by vitrification

Vitrification is considered as an important alternative approach to traditional slow freezing method for cryopreservation of cells. A typical cell vitrification procedure involves a non-equilibrium cooling process commonly accomplished in liquid nitrogen, while in which film boiling is believed to greatly hinder heat transfer surrounding the sample, resulting in incomplete vitrification or a much higher critical concentration. In this study, we developed a simple while effective approach, wrapping traditional French-type straw with medical gauze, to greatly enhance convective heat transfer during cooling by suppress film boiling. We further established a coupled heat transfer model for cooling and warming of cell suspensions to investigate the inherent thermodynamic mechanism in this approach. The model describes both the macroscale thermal distributions in extracellular solution and the microscale ice crystallization inside the cells. The simulation indicated that straws wrapped with medical gauze would increase cell survival subject to vitrification cryopreservation by significantly increasing the cooling rate to inhibit intracellular ice formation (IIF). Our experiments on human umbilical vein endothelial cells (HUVECs) further confirmed the predictions in that the cell survival rate was significantly increased by wrapping straws with medical gauze.