Biophysics of freezing of tissue equivalents

Understanding the biophysics of freezing a tissue equivalent (TE) is the first step to its successful cryopreservation. TEs are formed by entrapping human dermal fibroblasts (HDFs) in collagen or in fibrin gel. Freezing studies are done using a Linkam cryostage with different controlled cooling rates. Typically, freezing results in dehydration or intracellular ice formation (IIF), both of which can be potentially lethal to cells. Quantification of the biophysics involves determining the water permeability parameters, E _Lp and L _pg, and the intracellular ice nucleation parameters, Ωo and κo. HDFs in suspension show 55% IIF whereas HDFs in collagen and in fibrin TE 100% IIF at 130 C/min cooling rate. Cell-cell and cell-matrix interactions are found to play a significant role during freezing as observed from the obtained biophysical parameters.