Numerical investigation into thermal effects of pre-cooling zone in vitrification-based cryopreservation process.

Most studies on ultra-fast cryopreservation assume an immediate placement of the cryopreservation tube in the liquid nitrogen tank. However, in practice, before the tube is placed into the liquid nitrogen, it passes through a space containing gaseous nitrogen (pre-cooling zone) formed via the evaporation of the bulk liquid nitrogen. Comparing with ultra-fast cryopreservation, the cooling rate is insufficiently high during the falling transition to vitrify the liquid.