Cryotropic structuring of aqueous dispersions of fibrous collagen: influence of the initial pH values

The formation of macroporous anisotropic non-covalent cryogels stabilised by H-bonds and hydrophobic interactions as a result of the freezing–thawing of aqueous dispersions of fibrous collagen (protein concentration >4%) possessing pH values of 1.5–4.6 or 10–11.9 was observed. Collagen cryogels formed at pH 12–12.5 were additionally stabilised by covalent links. It was shown that the stability of cryogels in aqueous medium was determined by the changes in supramolecular packing of collagen during freezing–thawing. As this took place the swelling extent of the dispersed particles must be no more than 5–6 g of bound solvent per gram of protein. It was established that for the formation of spongy structures of cryogels the portion of solvent bound by protein should not exceed two thirds of the total amount of solvent in the system and be equal to 0.35–0.65 by weight. One may control the degree of solvent binding in the dispersed system by varying the pH value and ionic composition of the solvent.