Bio-inspired DMSO-free ice controlling strategy for the cryopreservation of oocytes

Oocyte cryopreservation (CP) is indispensable for genetic breeding and fertility preservation. Nowadays, vitrification is widely used for the CP of oocytes in clinics, which aims to completely prevent ice formation (i.e., ice-free state) by using high concentration of cryoprotectants (CPAs), including bio-incompatible dimethyl sulfoxide (DMSO), for the protection of oocytes from ice damages. Significant efforts have been dedicated to reducing DMSO use in oocyte CP. In nature, ice binding proteins, such as antifreeze (glycol) proteins (AF(G)Ps), control ice crystal size and morphology to minimize the detrimental effects of ice to freezing tolerance organisms, rather than trying to entirely prevent ice formation. Inspired by this, we firstly employ biocompatible and FDA approved poly(vinyl alcohol) (PVA) as an effective mimic of AF(G)Ps to eliminate DMSO in the CP of mouse and human oocytes via controlling ice growth and morphology instead of fully suppressing ice formation. Our results show that oocytes cryopreserved with PVA have higher survival rates, better mitochondria function and significantly improved genetic stability, e.g., DNA integrity and normal spindle recovery rate as compared to the oocytes frozen-thawed with vitrification media containing DMSO. As the bio-inspired ice controlling strategy can circumvent the use of DMSO, it will be promising for the CP of tissues and organs.