Insight into the rheological behaviors of a polyanionic collagen fabricated with poly(γ-glutamic acid)-NHS ester

The rheological behaviors of a polyanionic collagen, fabricated using poly(γ-glutamic acid)-N-hydroxysuccinimide (γ-PGA-NHS) as a novel modifier, were investigated in this study. It was found that both of the native and modified collagen solutions were pseudoplastic fluids, as shown from the steady-shear tests. While the storage modulus and loss modulus of collagen increased with increasing the amount of γ-PGA-NHS, or with increasing the degree of esterification of γ-PGA-NHS; meanwhile, the dynamic denaturation temperature determined by dynamic temperature sweep was also increased, indicating an improved thermal stability of collagen solution modified by γ-PGA-NHS. The creep-recovery measurements showed that the resistance to deformation was enhanced for modified collagen, probably due to the cross-linking occurred between the ε-amino groups of collagen molecules and α-COOH groups of γ-PGA-NHS, as well as the electrostatic interaction and hydrogen-bond interactions between the two molecules. Furthermore, the aggregation of collagen fibers was promoted due to these interactions between collagen and γ-PGA-NHS as observed by atomic force morphology. In addition, the modified collagen exhibited good cytocompatibility as demonstrated by cell growth culturing. The obtained information was expected to give valuable clues to the design and fabrication of controlled stable collagen-based products for applications in various biomedical fields.