The preparation of poly(γ-glutamic acid)-NHS ester as a natural cross-linking agent of collagen

γ-PGA-NHS ester, which was prepared using poly(γ-glutamic acid) (γ-PGA) and N-hydroxysuccinimide (NHS) as the raw materials, was synthesized to be a novel cross-linker of collagen. Fourier transform infrared spectra analysis suggested that the products displayed the characteristic absorption peak of ester. Results from nuclear magnetic resonance analysis indicated that the esterification degree of γ-PGA-NHS ester was increased with the increase of NHS. Modified collagen was prepared and characterized. The results of circular dichroism analysis indicated modified collagen retained the triple helix structure of natural collagen. Sodium dodecyl sulphate polyacrylamide gel electrophoresis revealed that the molecular weight of collagen was increased after cross-linking. Peptide mapping of collagen suggested that cross-linked collagen possessed an enhanced resistance to trypsin degradation. Differential scanning calorimeter results showed that the denaturation temperature of collagen was improved from 68.1±0.4 to 91.2±0.5°C (p<0.05). Dynamic viscoelastic measurements demonstrated the improvement of thermal stability and reflected the exponential increase in η*. The cross-linked collagen retained porous structure and the pore size became larger as observed by scanning electron microscopy. The investigation results provided useful information to produce collagen with improved physicochemical properties, particularly the thermal stability via the use of γ-PGA-NHS ester as a biomacromolecule-based cross-linker.