There is a great demand for blood and stem cells in clinic. It is difficult to achieve high throughput and to increase the cooling rate at the same time during vitrification. In this paper, a micro-droplet spray system with a container collection device was fabricated, and HepG2 cells were sprayed by this system for high-throughput vitrification. First, the container collection device and a cryo-paper were used to receive micro-droplets in the spray vitrification system. The results showed that the cell survival rate and 24h adhesion rate in container collection vitrification group were significantly higher than those in cryo-paper collection group. Second, HepG2 cells were sprayed and vitrified at increased cell density, and it was found that the results of micro-droplet spray vitrification did not change significantly. Finally, micro-droplet spray vitrification is compared with slow freezing. Cell processing capacity in the vitrification group increased, meanwhile, the cell survival rate and 24h adhesion rate in the vitrification group were significantly higher than those in slow freezing group. The results indicated that the micro-droplet spray vitrification system with container collection device designed in this paper can achieve high-throughput cell vitrification, which is of great significance for mass preservation of small cells.
Ultra-rapid cooling and rewarming rate is a critical technical approach to achieve ice-free cells during the freezing and melting process. A set of ultra-rapid solid surface freeze-thaw visualization system was developed based on a sapphire flim, and experiments on droplet freeze-thaw were carried out under different cryoprotectant components, volumes and laser energies. The results showed that the cooling rate of 1 μL mixed cryoprotectant [1.5 mol/L propylene glycol (PG) + 1.5 mol/L ethylene glycol (EG) + 0.5 mol/L trehalose (TRE)] could be 9.2×103 °C/min. The volume range of 1–8 μL droplets could be vitrified. After comparing the proportions of multiple cryoprotectants, the combination of equal proportion mixed permeability protectant and trehalose had the best vitrification freezing effect and more uniform crystallization characteristics. During the rewarming operation, the heating curve of glassy droplets containing gold nanoparticles was measured for the first time under the action of 400–1 200 W laser power, and the rewarming rate was up to the order of 106 °C/min. According to the droplet images of different power rewarming processes, the laser power range for ice-free rewarming with micron-level resolution was clarified to be 1 400–1 600 W. The work of this paper simultaneously realizes the ultra-high-speed temperature ramp-up, transient visual observation and temperature measurement of droplets, providing technical means for judging the ice free droplets during the freeze-thaw process. It is conducive to promoting the development of ultra-rapid freeze-thaw technology for biological cells and tissues.