Structure and Physicochemical Properties of Collagen Gels Treated with Hyaluronic Acid

The parameters of the condensed state and structure of fibrillar collagen and the composition and structuring of calcium phosphates in collagen gel samples obtained from rat tail tendons were studied. After the acid extraction and gelation at 37°С, fibrillar collagen preserves the domain organization and undergoes dispersion to the subfibrillar level and aggregation; the extrafibrillar space is filled with a viscous liquid. The dilatancy arises at 37–40°С at low and medium shear stresses and rates. In the course of acid extraction, fibrillar collagen undergoes amorphization, its primary peptide chains are hydrated and undergo heterogeneous strengthening/softening; the interchain spaces undergo contraction/expansion. Calcium phosphates originating from the initial tendons and medium 199 undergo structuring into hydroxyapatites in the course of gelation. These hydroxyapatites undergo decarbonation on introducing hyaluronic acid and become close to hydroxyapatite Са 10 (РО 4 ) 6 (ОН) 2 in the structure. The gels treated with hyaluronic acid form strong networks and fibrillar nodes of increased connection, shifting the dilatancy toward higher shear rates and stresses. Collagen fibers undergo aggregation to form thickened platelike structures tending to exfoliation. The water-filled interfibrillar spaces are expanded. Hyaluronic acid prevents the amorphization of fibrillar collagen, reduces the intermolecular contact strength, and suppresses the growth of hydroxyapatite structural precursors.