A novel concept of determining optimized coolingprotocols for freezing three-dimensional organs has beendeveloped and its feasibility examined computationally. Theconcept is based on determining correct spatial variation oftemperature distribution on the walls of a freezing container atevery instant of time during the cooling process so that localthermal stresses in the heterogeneous organ are always keptbelow a specified level while maximizing the local cooling rates.The cryo-preservation medium must be gelatin which preventsthermal convection. The optimized cooling protocol wassimulated by developing a time-accurate finite element computerprogram to predict unsteady heat conduction with phase changeand thermal stresses within a realistically shaped and sized organmade of tissues with temperature-dependent physical properties.A micro-genetic optimization algorithm was then used toachieve nonlinear constrained optimization of parameterizedtime-varying container wall temperature distribution so that theprescribed maximum allowable thermal stresses are neverexceeded in the organ.
