Formation of Coacervates from Charged Polypeptides for Cryopreservation

Bioinspired antifreeze polypeptides can be used as macromolecular cryoprotectants, but the wide application of charged polypeptides remains a challenge for cell cryopreservation due to the possible membrane-destructive activity. In this work, positively charged poly(l-methionine) derivatives tethering threonine-mimetic methyl and hydroxyl groups (PMOH) are synthesized, which can form coacervates with anionic γ-poly(glutamic acid) (PGA) with or without trehalose via liquid-liquid phase separation. The coacervate consisting of PMOH and PGA each at 20 mg/mL with 0.2 M trehalose exhibits a strong ice recrystallization inhibition activity with a mean largest grain size of 22.2 ± 1.9% relative to PBS, attributable to the depressed diffusion of water molecules through the highly confined water and contribution of trehalose. The coacervation of PMOH/PGA could also promote ice nucleation owing to the charged nature of the polymers. Actually, the PMOH/PGA coacervates show acceptable cytocompatibility and cryopreservative effects on cell cryopreservation by reducing half of the dimethyl sulfoxide dosage. This work offers a valuable strategy for the utility of charged polypeptides in cryopreservation.