Ficoll is a synthetic, high-molecular-weight polymer of sucrose that functions as a non-penetrating (extracellular) cryoprotectant. It is particularly valued for its low toxicity and its ability to facilitate vitrification, often allowing for the reduction or replacement of more toxic penetrating agents like dimethyl sulfoxide (DMSO).
Mechanism of Cryoprotection
As a large, hydrophilic polymer that remains outside the cell, Ficoll protects biological material through several interrelated physical mechanisms.
- Inhibition of Ice Nucleation and Growth: Molecular dynamics simulations show that Ficoll molecules create a steric barrier, preventing water molecules from approaching pre-existing ice nuclei and simultaneously lowering the activity of the surrounding water. This action helps suppress damaging ice crystal formation during cooling.
- Ice Recrystallization Inhibition (IRI): During warming, small ice crystals can merge into larger, more damaging ones—a process called recrystallization. Ficoll minimizes this recrystallization, which is particularly important for maintaining cell viability during storage at non-cryogenic temperatures (e.g., −80 °C).
- Promotion of Vitrification: Ficoll contributes to a solution's physical vitrification properties, helping it form a stable, glassy state rather than crystalline ice. This is a key function in vitrification protocols.
- Low Toxicity Profile: A major advantage of Ficoll is its low toxicity compared to other polymers like polyvinylpyrrolidone (PVP). Studies on mouse embryos and hepatocytes have identified Ficoll as the least toxic additive, allowing for extended exposure times without compromising cell function.
