Reinforcement of Shear Thinning Protein Hydrogels by Responsive Block Copolymer Self-Assembly

Shear thinning hydrogels are promising materials that exhibit rapid self-healing following the cessation of shear, making them attractive for applications including injectable biomaterials. Here, self-assembly is demonstrated as a strategy to introduce a reinforcing network within shear thinning artificially engineered protein gels, enabling a responsive transition from an injectable state at low temperatures with a low yield stress to a stiffened state at physiological temperatures with resistance to shear thinning, higher toughness, and reduced erosion rates and creep compliance. Protein-polymer triblock copolymers capable of the responsive self-assembly of two orthogonal networks are synthesized. Midblock association forms a shear-thinning network, while endblock aggregation at elevated temperatures introduces a second, independent physical network into the protein hydrogel. These reversible crosslinks introduce extremely long relaxation times and lead to a five-fold increase in the elastic modulus, significantly larger than is expected from transient network theory. Thermoresponsive reinforcement reduces the high temperature creep compliance by over four orders of magnitude, decreases the erosion rate by at least a factor of five, and increases the yield stress by up to a factor of seven. Combined with the demonstrated potential of shear thinning artificial protein hydrogels for various uses, this reinforcement mechanism broadens the range of applications that can be addressed with shear-thinning physical gels.