Rheological Properties of GuHCl/Type I Collagen Dispersions

Collagen was extracted from the outer skin of pig using a pepsin digestion method. The isolated collagen was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier transform infrared spectroscopy (FTIR) and ultraviolet (UV). According to the electrophoretic pattern, the isolated collagen consisted of two different alpha-chains (alpha(1), alpha(2)) and one beta-chain, indicating type I collagen. FTIR and UV results confirmed the presence of triple helical structure in the collagen molecule. The rheological properties of GuHCl/type I collagen dispersions were investigated as a function of guanidine hydrochloride (GuHCl) concentration and action time. The results of flow curves indicated that the pseudoplastic flow behavior of GuHCl/collagen dispersions gradually close to the Newtonian fluid with the increase of GuHCl concentration in the range of 0-6. 0 mol/L and action time in the range of 6-48 h. The linear oscillatory shear, steady shear and thixotropic loop experiments were performed to investigate thixotropic behavior of the GuHCl/collagen dispersions. It was found that the thixotropic type of GuHCl/collagen dispersions transformed from positive thixotropy to complex thixotropy and then to negative thixotropy with the increase of GuHCl concentration. The thixotropic type of collagen dispersion transformed from complex thixotropy to negative thixotropy with the increase of action time of 1. 0 mol/L GuHCl. It should be note that the complex thixotropy in GuHCl/collagen dispersions has not been reported in the similar systems so far. And we tentatively discussed this novel discovery on the basis of the interactions between GuHCl molecule and collagen. Meanwhile, this work would be helpful to deeply understand the mechanism of thixotropy.