Cryosolvents effects on low temperature gel structure of denatured collagen.

Water flux and crystallization are major problems for cryopreservation. The gel approach relies on the concept that a biological gel network might sufficiently entrap fluid within its pores, so as to maintain its osmotically inactive under the stresses usually encountered in the course of cryopreservation and limit the extent of crystallization. It could even induce vitrification. The effects of some cryosolvents on the structure of denatured collagen gels were studied as a function of temperature by hydraulic conductivity measurements and electron microscopy observations, so as to explore the porosity and fluid behavior of the gels. Gels formed in the presence of methanol exhibit a large increase in pore size as gelation temperature drops, whereas almost no variation is detected with ethylene glycol, where the porosity is finer. Gels in the presence of ethylene glycol display a larger fluid content, smaller flow rates, and better pressure resistance than those in the presence of methanol. Electron micrographs confirm the variations in gel structures depending on the cryosolvent and the temperature. Rheological measurements also support these observations. Upon rapid cooling, vitrification occurs only in gels with ethylene glycol. Ethylene glycol seems to have a specific interaction with denatured collagen gels which induces a finer network better adapted for trapping fluid osmotically inactive in the course of cryopreservation.