The blunt tip probe, shown above left, produces a spherical iceball in the prostae, shown above right.
The flat probe, shown above left, produces a hemispherical iceball in the prostate, shown above right
There is a sequence of events that cells experience in the hypertonic solutions, between ice crystals .At lower temperatures, as the extracellular concentration increases cells shrink. This shrinkage is caused by the fact that the unfrozen cells are super-cooled relative to the extracellular solution, which is in thermodynamic equilibrium with the ice. To equilibrate the difference in chemical potential between the extracellular and intracellular solutions, water will leave the cell through the cell membrane that is readily permeable to water. This causes an increase in the intracellular solute concentration, with a decrease in temperature. Increased hypertonic extracellular solutions damage the cells. The mechanisms are not entirely clear and they could relate to chemical damage or osmolality induced changes in the cell structure. This is consistent with the hypertonic extracellular solution mechanism of damage, as the hypertonic extracellular concentration also increases gradually with a decrease in temperature.
There are several additional phenomena worth mentioning in relation to the hypertonic mode of damage. While cell death increases with extracellular concentration time affects survival only during the first few minutes of exposure after which a plateau is reached and the percentage of death cells remains constant. This is because while the mesoscale processes that occur during exposure of cells to hypertonic solutions, cell shrinkage as water leaves through the cell membrane, have been observed and are understood, the nanoscale processes are not. However, in cryosurgery these mechanisms of damage are more important than in cryopreservation because many cells in the frozen region will remain throughout the procedure in the region dominated by hyperosmotic phenomena where the solution is partially frozen and the cells are not.
There are, however, additional mechanism of damage in the region of temperatures and cooling rates associated with hypertonic solution damage. Experiments have shown that the percentage of death cells after freezing is larger than the percentage of death cells after exposure to a similar extracellular hypertonic solution. This suggests that mechanical interaction between ice and cells may contribute to cell death. This is a reasonable assumption, since ice rejects cells in the space between ice crystals. This may generate a mechanical force on the cells, whose cellular cytoskeleton is weakened by cold, and destroy them. Another possible mode of damage is the contact and interaction between ice and the lipid bilayer, which by itself may be damaging.