If we were certain of future repair, it would make much more sense to immediately thrust cryonics patients into liquid nitrogen upon deanimation rather than to waste time or expense on cryoprotectant perfusion. Cryoprotectants are perfused into the blood vessels of a cryonics patient and diffuse from capillaries into cells and intracellular spaces. Aside from the choice of cryoprotectants, a major concern is the way cryoprotectant is administered. There is evidence that gradual introduction is less damaging.
Cells are much more permeable to water than they are to glycerol.
When a cell is exposed to high-strength glycerol, osmosis causes water to rush out of the cells, causing the cells to shrink. Only very gradually does the glycerol cross cell membranes to enter the cell. Rapid shrinking of cells can kill them. Not only is cell shrinkage damaging, but rapid passage of water across cell membranes physically damages the membranes. Also, allowing more time for glycerol equilibration gives time for cells more distant from blood vessels to receive glycerol.