Various types of cells are routinely cryopreserved in modern regenerative and cell-based medicines. For instance, the oocyte is one of the most demanding cells to be cryopreserved in genetic engineering and human-assisted reproductive technology (ART). However, the usage of cryopreserved oocytes in ART clinics is still limited mainly because of the unstable survival rate. This is due to the fact that oocytes are more prone to be damaged by ice crystals in comparison to other cells, as oocytes are larger in size and surface area. Meanwhile, oocytes contain more water, and thus, ice crystals are easier to form inside the cells. Currently, to avoid injury by the formed ice crystals, cryopreservation (CP) of oocytes has to use large amounts of small molecules as cryoprotectants such as dimethyl sulfoxide (DMSO) and ethylene glycol (EG), which can permeate into the cell and prevent ice formation inside. However, these molecules are chemically and epigenetically toxic to cells. Therefore, great efforts have been focused on reducing the amount of DMSO and EG used for oocyte CP. In nature, the antifreeze (glyco)­proteins (AFGPs) locate extracellularly with the ability to protect living organisms from freezing damage via controlling ice growth. Inspired by this, biocompatible and nontoxic L-proline oligomers (L-Pro n ), which have the same polyproline II helix structure as that of AFGPs, are first employed for the CP of oocytes. The experimental results reveal that L-Pro8 has a profound activity in inhibiting ice growth as that of AFGP8. Also, by the addition of 50 mM L-Pro8, the amount of DMSO and EG can be greatly reduced by ca. 1.8 M for oocyte CP; moreover, the survival rate of the cryopreserved oocytes is increased up to 99.11%, and the coefficient of variance of the survival rate is decreased from 7.47 to 2.15%. These results mean that almost all oocytes can survive after CP with our method; importantly, the mitochondrial function as a critical criterion for the quality of the frozen–thawed oocytes is also improved. It is proposed that with the addition of L-Pro8, the extracellular ice growth is slowed down, which prevents the direct injuries of cells by large ice crystals and the accompanying osmotic pressure increase. As such, this work is not only significant for meeting the ever-increasing demand by the ART clinics but also gives guidance for designing materials in controlling ice growth during CP of other cells and tissues.

Heterogeneous ice nucleation (HIN) triggered by mineral surfaces typically exposed to various ions can have a significant impact on the regional atmosphere and climate. However, the dependence of HIN on the nature of the mineral surface ions is still largely unexplored due to the complexity of mineral surfaces. Because K + on the atomically flat (001) surface of mica can be readily replaced by different cations through ion exchange, muscovite mica was selected; its simple nature provides a very straightforward system that can serve as the model for investigating the effects of mineral surface ions on HIN. Our experiments show that the surface (001) of H + -exchanged mica displays markedly higher HIN efficiencies than that of Na-/K-mica. Vibrational sum-frequency generation spectroscopy reveals that H-mica induces substantially less orientation ordering than Na-/K-mica within the contact water layer at the interface. Molecular dynamics simulations suggest that the HIN efficiency of mica depends on the positional arrangement and orientation of the interfacial water. The formation of the hexagonal ice Ih basal-type structure in the first water layer atop the mica surface facilitates HIN, which is determined by the size of the protruding ions atop the mica surface and by the surface adsorption energy. The orientational distribution is optimal for HIN when 25% of the water molecules in the first water layer atop the mica surface have one OH group pointing up and 25% have one OH group pointing down, which, in turn, is determined by the surface charge distribution.