Biotechnology and Bioengineering, Vol.92, No.3, 372-383, 2005
Transport phenomena during freezing of adipose tissue derived adult stem cells
In the present study 6 well-established differential scanning calorimeter (DSC) technique is used to measure the water transport phenomena during freezing of stromal vascular fraction (SVF) and adipose tissue derived adult stem (AIDAS) cells at different passages (Passages 0 and 2). Volumetric shrinkage during freezing of adipose derived cells was obtained at a cooling rate of 20 degrees C/min in the presence of extracellular ice and two different, commonly used, cryoprotective agents, CPAs (10% DMSO and 10% Glycerol). The adipose derived cells were modeled as spheres of 50 pm diameter with an osmotically inactive volume (V-b) of 0.6V(o), where V-o is the isotonic cell volume. By fitting a model of water transport to the experimentally obtained volumetric shrinkage data, the "best-fit" membrane permeability parameters (reference membrane permeability to water, L-pg or L-pg [cpa] and the activation energy, E-Lp or E-Lp[cpa]) were determined. The "best-fit" membrane permeability parameters for adipose derived cells in the absence and presence of CPAs ranged from: Lpg 23.1-111.5x 10(-15) m(3)/Ns (0.135-0.652 mu m/min-atm) and E-Lp = 43.1-168.8 kJ/mol (9.7-40.4 kcal/mol). Numerical simulations of water transport were then performed under a variety of cooling rates (5-100 degrees C/min) using the experimentally determined membrane permeability parameters. And finally, the simulation results were analyzed to predict the optimal rates of freezing adipose derived cells in the presence and absence of CPAs. (c) 2005 Wiley Periodicals, Inc.
Keywords:adipose derived stem cells;stromal vascular fraction;cryopreservation;differential scanning calorimeter;water transport