Shear-thinning hydrogels are particularly promising for use in the minimally-invasive implantation of biofunctional materials for a variety of biomedical applications, including as reinforcing tissue fillers or delivery vehicles for encapsulated cells or drugs. The formation of a robust, injectable implant that can withstand typical stresses in the physiological environment over desired timescales is an ongoing challenge.  To address this need while meeting demands for clinically-relevant storage and processing conditions, one strategy has been to engineer thermoresponsive hydrogels that can be injected at low temperatures, but will responsively self-assemble to a reinforced state at high temperatures.  Hybrid triblock copolymers made from artificially-engineered associative protein midblocks with poly(N-isopropylacrylamide) (PNIPAM) endblocks form nanostructured associative polymer gels at elevated temperatures, exhibiting large increases in stiffness and toughness, with significant decreases in creep and erosion. Alternative synthetic routes to either all-protein-based elastin-like polypeptide (ELP) triblock fusions or PNIPAM triblocks with dimethylacrylamide-co-N-acryoyl-dopamine midblocks led to responsive hydrogels with altered thermodynamic and mechanical behavior. These designs provide new mechanisms for control over macromolecular structure and association nature. Monodisperse ELP fusions undergo spherical-to-cylindrical transitions at lower concentrations than the hybrid PNIPAM triblocks, while iron-coordinating dopamine-functionalized triblocks exhibit unique pH, temperature, and metal ion-dependent reversible and irreversible behavior. The multiple embodiments of nanostructured associative polymer gels investigated in this study explore new routes to achieving complex morphologies for tuning the reinforcement and toughness of shear-thinning hydrogels for biomedical applications. 

Engineering network associations for control of responsive reinforcement in nanostructured physical hydrogels

247th National Meeting (2014)

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