Postthaw

Postthaw refers to the period after a biological sample stored by cryopreservation has been thawed. It encompasses the immediate handling, recovery, and evaluation of the sample as it returns from storage to a functional state. In practice, postthaw is used in cryobiology, biobanking, regenerative medicine, and assisted reproduction to describe the condition and viability of cells, tissues, or embryos after warming.

During postthaw, cells experience osmotic and thermal stress, potential ice recrystallization, and residual cryoprotectant exposure. The outcome depends on factors such as cooling rate, warming rate, cryoprotectant choice, sample type, and storage duration. Common cryoprotectants include DMSO for mammalian cells; glycerol for some cell types; alternatives are being researched.

Process and handling in the postthaw period typically involve rapid warming to minimize ice-related damage, followed by removal or dilution of cryoprotectants, gentle handling, and plating or culture for recovery. Postthaw processing often includes washing, centrifugation, or transfer to appropriate medium with reduced CPA concentration, to support cell survival and function.

Assessment of postthaw samples combines viability and functional tests. Viability can be measured by dye exclusion or fluorescence-based live/dead assays, while metabolic activity may be assessed with MTT or ATP-based assays. Functional evaluations may include proliferation, differentiation, colony formation, or developmental potential for embryos.

Optimization efforts focus on reducing cryo-injury through adjusted cooling and warming rates, CPA concentration and exposure, stepwise dilution, and improved postthaw culture conditions. Additional strategies include alternative CPAs and supportive additives tailored to specific cell types.

See also cryopreservation, cryoprotectants, viability assays.