Chemistry between crosslinks affects the properties of peptide hydrogels

Protein hydrogels were prepared by substituting ovalbumin with different concentrations of ethyl vinyl sulfone (EVS) or acrylic acid (AA) and crosslinking with divinyl sulfone (DVS). Fourier transform-infrared (FT-IR) spectroscopic studies confirmed the addition of EVS, AA, and DVS onto the protein. Swelling was assessed as a function of pH in the range of 2.5 to 9.4 and ionic strength. The elastic modulus of the gels was determined in shear and compression. Stress relaxation was assessed in compression. The substituent highly affected swelling and modulus with both hydrogels displaying non-Gaussian behavior in the range of hydrogel environments studied. Acrylic acid substituted ovalbumin exhibited a decreasing modulus with increasing swelling behaving as a polyelectrolyte with low added salt content. Ethyl vinyl sulfone substituted ovalbumin displayed an increasing modulus with swelling originating in the finite extensibility of the highly swollen chains. AA-substituted ovalbumin showed higher modulus and reduced swelling compared to EVS-substituted ovalbumin because of its ability to hydrogen and ionic bond to other molecules.