Effect of Pre-shearing Treatment on Molecular Structure, Fibrillogenesis Behavior and Gel Properties of Collagen
Shear treatment is always accompanied by the extraction, preparation and research of collagen materials. This study aimed to investigate the effect of pre-shearing treatment of neutral bovine tendon collagen solution on collagen molecular structure, assembly behavior and gel properties. Rheological and assembly degree (AD) tests showed that with the increase of shear rate or the extension of shear time in pre-shearing treatment, the equilibrium moduli and AD of collagen gels assembled from pretreated samples gradually decreased. Scanning electron microscope (SEM) results indicated that with the deepening of pre-shearing treatment (shear rate or shear time increased), the diameter of resultant collagen fibers gradually decreased, and their pore size and porosity became larger as a whole. The viscosity test of collagen solution after pre-shearing revealed that the whole viscosity of samples became lower than that of the sample devoid of pre-shearing. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and circular dichroism (CD) analysis manifested that the molecular weights and CD characteristic peaks of collagen molecules remained unchanged in the sheared solution. However, with the deepening of pre-shearing treatment, the proportion of α chains in the SDS-PAGE picture increased, while the total content of β and γ chains decreased; the triple-helix structure of collagen in the CD spectrum decreased and the random coiled structure increased. Moreover, transmission electron microscope (TEM) displayed that the D-periods of fibers assembled from the sheared samples were also decreasing. A mechanism for the effect of pre-shearing treatment of collagen solution on collagen molecular structure, assembly behavior and gel properties was proposed, and findings in this work may provide new understanding and theory for the physical modification of proteins and construction of new materials from polymer systems aggregated or assembled based on weak intermolecular interactions.