An experiment has demonstrated that genetically engineered unstructured proteins with covalent and reversible crosslinking (due to metal coordination and hydrophobic interactions) yield hydrogels with extremely high strength, toughness, stretchability, and self-adhesion in Zn 2+ solutions. Genes encoding for proteins were constructed using the recursive directional ligation by plasmid reconstruction method. The monomer was created by annealing together complementary single-stranded DNA chains that encode for the desired amino acid sequence with sticky end overhangs. The two cut vectors were complementary to one another such that when ligated together the monomer sequence is doubled. This process was continued until the desired length of protein was achieved. The same procedure applied for insertion of crosslinking domains. The genes encoding for the final sequence of CCP, MCP1, and MCP2 were confirmed by DNA sequencing. The genes encoding for CCP, MCP1, and MCP2 were transformed into chemically competent Escherichia coli BL21 cells. The cells were incubated overnight and one colony was used to inoculate a starter culture of sterilized terrific broth media supplemented with kanamycin. Because the molecular structures of the proteins can be precisely controlled, a systematic optimization of various mechanisms for dissipating mechanical energy and maintaining high elasticity, as well as observing the interactions and inherent properties of polypeptides dictated by their sequence may lead to protein-based materials with further enhanced physical properties. In addition, the strong, tough, stretchable and self-adhesive materials developed here provide a robust scaffold for use in biomedical and other applications.
Strong, Tough, Stretchable, and Self-Adhesive Hydrogels from Intrinsically Unstructured Proteins