Graphene oxide protects sperm from ice
In a study published in Angewandte Chemie, researchers from China have used graphene oxide as a cryoprotectant to preserve the activity of horse sperm during freezing. Cryopreservation is a procedure where tissues, cells, organs or other biological materials susceptible to damage caused by unregulated chemical kinetics are preserved by cooling to very low temperature. Since the discovery of cryopreservation in the 1950s, it has been widely used in fields including medicine, biology and agronomy. However, the inevitable ice growth during the cryopreserve procedure can cause severe ice injuries. Commercial cryoprotectants including glycerol and DMSO are limited by their low ice recrystallization inhibition efficiency and high toxicity. Furthermore, these cryoprotectants cause severe cell dehydration at high concentrations.
Inspired by the fact that natural AntiFreeze Proteins (AFPs) protect a broad range of biological organisms inhabiting subzero environments, Professor Wang Jianjun from the Institute of Chemistry of the Chinese Academy of Sciences (CAS), Professor Fang Haiping and Dr. Wang Chunlei from Shanghai Institute of Applied Physics of CAS previously investigated how AFPs decrease freezing temperature and inhibit ice growth and recrystallization. They found that the ordered arrangement of the hydrophobic and hydrophilic functional groups protruding in the ice-binding face facilitated the formation of ice-like water, which provided the driving force for binding to the ice surface and inhibited the growth of ice crystal. Using their findings on AFPs, the researchers made use of the unique structure of graphene to investigate the effectiveness of graphene oxide in controlling ice formation.
The results showed that graphene oxide inhibited the growth and recrystallization of ice crystal, and shaped ice crystals into a hexagon. Molecular dynamics simulation analysis revealed the formation of stable ice-like water on the surface of the graphene oxide. Thus, graphene oxide formed more hydrogen bonds with ice in comparison with liquid water, which led to the formation of a curve and poisoned the continuous growth of the ice lattice due to the Gibbs-Thompson effect. The researchers also reported using graphene oxide as a cryopreservation agent for horse sperm for the first time. Their results unambiguously showed that the graphene oxide prevented ice recrystallization in horse sperm. Compared with commercial cryoprotectants, the addition of just 0.01% graphene oxide into the culture medium increased the sperm motility from 24.3 percent to 71.3 percent. This study not only opens a new avenue for the application of 2D materials but also helps establish a molecular level understanding of AFPs in controlling ice formation, the researchers said.