Polyvinylpyrrolidone (PVP) is a synthetic, high-molecular-weight polymer that functions primarily as a non-penetrating (extracellular) cryoprotectant (CPA). It is widely used, particularly in vitrification protocols, often in combination with a penetrating CPA like dimethyl sulfoxide (DMSO) or ethylene glycol (EG), to protect cells and tissues from freezing damage.
Mechanism of Cryoprotection
As a large polymer that remains outside the cell, PVP protects biological material through several interrelated physical mechanisms.
- Vitrification Promotion and Ice Inhibition: PVP is a key macromolecular additive that promotes the formation of a glassy, amorphous state instead of crystalline ice during freezing. It does this by markedly reducing the cooling rates required to avoid ice crystallization, thereby facilitating successful vitrification.
- Reduction of CPA Toxicity: A major advantage of PVP is its ability to reduce the toxicity of penetrating CPAs. By combining PVP with a permeating agent, researchers can lower the concentration of the toxic component while maintaining an effective vitrification solution. Studies on ovarian tissue show that PVP can reduce DMSO toxicity without compromising vitrification efficacy.
- Membrane and Cellular Stabilization: PVP helps stabilize the osmotic environment and protects cells from the mechanical damage caused by ice crystals during freezing and thawing.
