Study on Leidenfrost effect of cryoprotectant droplets on liquid nitrogen with IR imaging technology and non-isothermal crystallization kinetics model

Droplet vitrification is one of the most attractive tools for cells cryopreservation due to its ultra-rapid cooling rate. However, this method has its own limitation because of the Leidenfrost phenomenon. In this work, the infrared imaging technology was utilized to investigate the effects of cryoprotective agents (CPA) concentrations and volumes on levitating velocities and durations of CPA droplets on liquid nitrogen (LN2), and the model of non-isothermal crystallization kinetics was also adopted here for theoretical analysis of the temperature distributions and degree of crystallization inside the droplets. The experimental results showed that the movements of droplets on LN2 became slower when increasing the CPA concentrations, but they were independent on the volumes except for higher CPA concentration cases (i.e., 50% glycerol and VS55). And the Leidenfrost effect time (i.e. the levitation time on the liquid nitrogen) became longer as increasing both the CPA concentrations and volumes. The theoretical results indicated that the final crystallinity inside droplets reached 1 for both water and 20% glycerol cases, a magnitude of 1 × 10−6 for 50% glycerol and 1 × 10−13 for VS55, respectively. Furthermore, the motion of droplets was strongly related to the crystallinity rates and cooling rates inside the droplets.