Dilute self-healing hydrogels of silk-collagen-like block copolypeptides at neutral pH

We report on self-healing, pH-responsive hydrogels that are entirely protein-based. The protein is a denovo designed recombinant triblock polypeptide of 66 kg/mol consisting of a silk-like middle block (GAGAGAGH)48, flanked by two long collagen-inspired hydrophilic random coil side blocks. The pH-dependent charge on the histidines in the silk block controls folding and stacking of the silk block. At low pH the protein exists as monomers, but above pH 6 it readily self-assembles into long fibers. At higher concentrations the fibers form self-healing physical gels. Optimal gel strength and self-healing are found at a pH of around 7. The modulus of a 2 wt % gel at pH 7 is G' = 1700 Pa. Being protein-based, and amenable to further sequence engineering, we expect that these proteins are promising scaffold materials to be developed for a broad range of biomedical applications.