A06 Plenary Lecture 2
2014
Mazur, P. (Peter)
This presentation will attempt to relate some fundamental aspects of cryobiology to the problems of cryosurgery. Much understanding of the fundamentals has come from studies on cryopreservation, but cryopreservation and cryosurgery differ in important ways aside from their ultimate aims. The following are the topics to be discussed:A. Extrinsic factors or variables: Extracellular medium Cooling rate Can be constant in cryopreservation * Can not be constant in cryosurgical freezing Temperature Minimum temperature Usually uniform in cryopreservation Can not be uniform in cryosurgical freezing Time at subzero temperature Warming rate Number of repeat freezing thawing cyclesB. Physical events: Extra-cellular and inter-cellular ice formation Osmotic dehydration Permeation of permeating solutes Cell supercoiling Is cell position perturbed by ice front? Intracellular ice formation Vitrification Recrystallization of ice Post-thaw osmotic excursionsC. Intrinsic cellular factors Cell size Permeability to water Permeability to solutes. Possession of aquaporins or not Chill sensitivity Sensitivity to osmotic excursionsD. Major differences between:Cryopreservation freezingCryosurgical freezingCooling is from outside-InCooling is from inside-outAll parts of the system reach equilibrium with temperature of −196°C throughoutSystem reaches steady state with temps.varying from −160°C near probe to −0.5°C at ice-ball surfaceCryoprotective agents are always addedCryoprotective agents are never added. But..Survivals of ⩾50% are usually acceptableSurvivals of <1% are mandatory
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