Understanding Cryopreservation of Oyster Oocytes from a Physical Chemistry Perspective

Abstract

Cryopreservation applies to the freezing, storage (usually long-term) at a very low temperature, thawing, and successful recovery of living cells. There are seven basic steps in cryopreservation protocols: sample collection, maintenance of collected material in extender solutions, quality assessment, refrigerated storage, freezing, thawing, and viability assessment (Tiersch 2000). Cell viability can be affected at any of these steps, although most damage occurs due to exposure of cells to high concentrations of intra- and extracellular solutes or due to intracellular ice formation (IIF) during cooling and/or thawing. It has been suggested that the growth and propagation of intracellular ice crystals cause cell death through disruption of the cell membrane. Extracellular ice has also been shown to cause mechanical damage of cells (Sterling 1968; Rubinsky et al. 1990). The formation of extracellular ice also increases solute concentration in the remaining unfrozen matrix (Mazur et al. 1972; Pegg 2002), which leads to additional stress such as solute toxicity (Mazur et al. 1972) and causes cells to shrink osmotically (Lovelock 1953; Steponkus et al. 1983). The consequences of the freezing process on a cell are represented schematically in Fig. 1.