Microencapsulation Facilitates Low-Cryoprotectant Vitrification of Human Umbilical Vein Endothelial Cells

Vitrification has become one of the promising cryopreservation methods for biosamples including cells and tissues because the vitreous state reduces the damage of ice crystals to cells. However, besides extremely high cooling rates, routine vitrification protocols require a high concentration of penetrating cryoprotectants (pCPAs, ∼6-8 M), which is toxic for cells and brings trouble when removing pCPAs. Therefore, reducing the concentration of toxic pCPAs in vitrification remains a challenge, and advanced strategies are urgently needed. Hydrogel encapsulation has become one effective method to achieve low-cryoprotectant (CPA) concentration preservation of stem cells with rapid cooling, but there are very few related studies about endothelial cells (ECs). In this study, we achieved pCPA concentration (up to 3 M) vitrification by encapsulating human umbilical vein endothelial cells (HUVECs) into core-shell alginate hydrogel microcapsules. Alginate encapsulation increased HUVEC cryosurvival up to 80%, which is 60% improvement compared to control without encapsulation. Furthermore, two different sizes of capsules (diameter: ∼900 and 400 μm) were produced to explore the effects of microcapsule volume on the cell preservation results, and it was found that larger capsules (∼900 μm) have no significant effect on cell survival while improving encapsulation efficiency. This encapsulation method provides a new strategy for EC preservation and serves as an improvement to optimize the preservation of biosamples.