A06 Plenary Lecture 2 : Cryosurgery as the anti-christ of cryopreservation

Abstract

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 cycles B. 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 excursions C. Intrinsic cellular factors • Cell size • Permeability to water • Permeability to solutes. • Possession of aquaporins or not • Chill sensitivity • Sensitivity to osmotic excursions D. Major differences between: Cryopreservation freezing Cryosurgical freezing Cooling is from outside-In Cooling is from inside-out All parts of the system reach equilibrium with temperature of −196 °C throughout System reaches steady state with temps.varying from −160 °C near probe to −0.5 °C at ice-ball surface Cryoprotective agents are always added Cryoprotective agents are never added. But.. Survivals of ⩾50% are usually acceptable Survivals of <1% are mandatory