1989 Volume 35 Pages 32-38
To elucidate the means by which polymer solutions protect cells from freezing injury, we cooled human monocytes to -80℃ in the presence of various polymers. Differential scanning calorimetry revealed that those polymers which protect cells best have an equilibrium glass transition temperature, Tg, of about -20℃; those with a Tg significantly higher or lower did not protect. Freeze-etch electron micrographs indicated that intracellular ice crystals had formed during freezing, but remained small in about the same proportion of cells as survived rapid thawing. We conclude that cryoprotection of slowly frozen monocytes by polymers is a consequence of a Tg of -20℃. Glass formation limits the injurious osmotic stress which cells face during freezing by preventing further osmotic stress below -20℃. At the same time, it allows cells to concentrate their cytoplasm sufficiently to restrict lethal intracellular ice formation between -20℃ and the intracellular Tg.
