Survival of directionally solidified B-lymphoblasts under various crystal growth conditions

Abstract

Reduction of temperature during freezing brings about two complex and interrelated phenomena: (1) crystal nucleation and subsequent growth processes and (2) change in biophysical properties of a biological system. The purpose of this investigation is to relate the morphology of the solid phase with the survival of a cell. To this end, B-lymphoblasts were exposed to directional solidification in phosphate-buffered saline + 0.5 M dimethyl sulfoxide. Directional solidification is a freezing technique which allows the morphology of the interface to be varied without varying the chemical history that a cell would experience during a constant cooling rate protocol. Results indicated that, for the range of experimental conditions tested, a maximum survival of approximately 78% could be achieved using a temperature gradient of 25(10) 3 K/m and an interface velocity of 23(10) −6 m/s (cooling rate: 35 K/min). Survival dropped off sharply for freezing at faster cooling rates with little or no variation in survival for different crystal growth conditions. Survival at slower cooling rates decreased with decreasing cooling rate. It was observed, however, that the presence of secondary branches in the ice phase correlated with lower survival for a given cooling rate. These results indicated that not only is the redistribution of solute during freezing a potential source of damage during freezing but ice/cell interactions are also. Thus, the cooling rate alone may not be adequate to describe the freezing process.