Rejection and capture of cells by ice crystals on freezing aqueous solutions

Abstract

The results of an experimental study of the processes of cell rejection or capture by growing ice crystals are discussed. Cell suspensions were frozen in a cryochamber placed on a microscope stage fitted for programmed cooling of flat preparations with automatic maintenance of a temperature gradient of 100°C/cm, which stabilized the crystallization front even in the presence of impurities. It is shown that all cells are rejected, if the front movement is slower than a first critical rate ( V < V 1), and that a ll cells are captured by the crystal, forming inclusions, if the rate of the crystallization front movement is higher than the second critical rate ( V > V 2). The dependence of the critical rates on the concentrations of impurities such as NaCl and HN 4Cl, and cryoprotectants such as glycerol and polyethylene glycol of average M.W. 300 have been determined. The character of the dependence on concentration of the critical rates supports the view that the mechanism of cell capture by the crystal is caused by the hydrodynamic instability of the fluid film in the gap between cell and crystal. The analysis of the results demonstrates that the structural component of the disjoining pressure built up in the thin film of the fluid filling the gap between cell and crystal makes a major contribution to the repulsion of cells from the ice crystal front.