The Unusual Properties of Polytetrafluoroethylene Enable Massive‐Volume Vitrification of Stem Cells with Low‐Concentration Cryoprotectants

Abstract Injectable stem cell‐hydrogel constructs hold great potential for regenerative medicine and cell‐based therapies. However, their clinical application is still challenging due to their short shelf‐life at ambient temperature and the time‐consuming fabrication procedure. Banking the constructs at cryogenic temperature may offer the possibility for their “off‐the‐shelf” availability to end‐users. However, ice formation during the cryopreservation process may compromise the construct quality and cell viability. Vitrification, cooling biological samples without apparent ice formation, has been explored to resolve the challenge. However, contemporary vitrification methods are limited to very small volume (up to ≈0.25 mL) and/or need highly toxic and high concentration (up to ≈8 m) of permeable cryoprotectants (pCPAs). Here, it is shown that polytetrafluoroethylene (PTFE, best known as Teflon for making nonstick cookware) capillary is flexible and unusually stable at cryogenic temperatures. By using the PTFE capillary as a flexible cryopreservation vessel together with alginate hydrogel microencapsulation and Fe₃O₄ nanoparticle‐mediated nanowarming to suppress ice formation, massive‐volume (e.g., 10 mL) vitrification of cell‐alginate hydrogel constructs with low concentrations (≈2.5 m) of pCPAs can be achieved. This may greatly facilitate the use of stem cell‐based constructs for tissue regeneration and cell based therapies in the clinic.