Figure 1.

Schematics of microliter sized droplet vitrification using 2 m permeable CPA. A) Gold nanorods (GNRs) and biomaterials (i.e., stem cells) were first mixed with CPA for subsequent droplet printing. When a droplet was printed directly to LN₂, the instantaneous boiling of LN₂ created a “vapor blanket”, known as the Leidenfrost effect. This nitrogen vapor held the droplet floating, slowed down the cooling rate, and eventually led to crystallization. B) Droplet was printed onto a cryogenic copper dish floating on the LN₂. Faster cooling rate through heat conduction can be achieved by avoiding the Leidenfrost issue, leading to successful vitrification. C) For convective rewarming, a vitrified droplet was directly dropped to the CPA unloading solution. Devitrification occurred due to slow warming rate. D) For laser warming, a vitrified droplet on the cryoholder was brought up to the millisecond pulse laser beam. E) After laser warming, biomaterials were released into CPA unloading solution. 2 m propylene glycol (PG) and 1 m trehalose was used as the CPA in this study.