Master of Science in Mechanical Engineering (MSME)
This thesis addresses optimization techniques for cryopreservation of biological systems. A part of the thesis (Chapter 2) reports a simplified procedure to predict the optimal rate of freezing biological systems once the cell level parameters are known a priori. The key cell level parameters investigated were, reference permeability of the membrane to water (Lpg), apparent activation energy (ELp), inactive cell volume (Vb), diameter (D), and the ratio of the available surface area for water transport to the initial volume of intracellular water (SA/WV). The simplified procedure was developed by performing a thorough analysis of the water transport model over a physiologically relevant range for the various cell level parameters. The results from the parametric analysis are analyzed and used to develop a Generic Optimal Cooling Rate Chart (GOCRC) and a Generic Optimal Cooling Rate Equation (GOCRE). The use of GOCRC and GOCRE greatly simplifies the prediction of the optimal rate of freezing of biological systems without resorting to complex numerical simulations. The second and last part of the thesis (Chapter 3) reports the membrane permeability parameters (Lpg and ELp) of canine sperm cells during freezing using a differential scanning calorimeter (DSC) technique. In this study a well established shape independent Differential Scanning Calorimeter (DSC) technique was used to measure the dehydration response during freezing of ejaculated canine sperm cells. Volumetric shrinkage during freezing of canine sperm cell suspensions was obtained at cooling rates of 5 and 10 oC/min in the presence of extracellular ice and with or without cryoprotective agents (CPAs). By fitting a model of water transport to the experimentally obtained volumetric shrinkage data the best fit membrane permeability parameters (Lpg and ELp) were determined. Numerical simulations of water transport in canine sperm cells were then performed under a variety of cooling rates (5 to 100 oC/min) using the experimentally determined membrane permeability parameters (Lpg and ELp). The simulation results were analyzed to predict the amount of water left in the cell after dehydration ceased, in the absence of IIF and the "optimal cooling" rates for canine sperm cryopreservation.
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Thirumala, Sreedhar, "Optimal rate of freezing biological systems" (2004). LSU Master's Theses. 3131.