Physicochemical and functional characterization of the collagen-polyvinylpyrrolidone copolymer

Collagen-polyvinylpyrrolidone (C-PVP) is a copolymer that is generated from the γ irradiation of a mixture of type I collagen and low-molecular-weight PVP. It is characterized by immunomodulatory, fibrolytic, and antifibrotic properties. Here, we used various physicochemical and biological strategies to characterize the structure, biochemical susceptibility, as well as its effects on metabolic activity in fibroblasts. C-PVP contained 16 times more PVP than collagen, but only 55.8% of PVP was bonded. Nevertheless, the remaining PVP exerted strong structural activity due to the existence of weak bonds that provided shielding in the NMR spectra. On SEM and AFM, freeze-dried C-PVP appeared as a film that uniformly covered the collagen fibers. Size analysis revealed the presence of abundant PVP molecules in the solution of the copolymer with a unique dimension related to macromolecular combinations. Calorimetric analysis showed that the copolymer in solution exhibited structural changes at 110 °C, whereas the lyophilized form showed such changes at temperatures below 50 °C. The copolymer presented a rheopectic behavior, with a predominant effect of the collagen. C-PVP had biological effects on the expression of integrin α2 and prolyl-hydroxylase but did not interact with cells through the collagen receptors because it did not inhibit or slow contraction.