In situ mechanical reinforcement of polymer hydrogels via metal-coordinated crosslink mineralization.

Biological organic-inorganic materials remain a popular source of inspiration for bioinspired materials design and engineering. Inspired by the self-assembling metal-reinforced mussel holdfast threads, we tested if metal-coordinate polymer networks can be utilized as simple composite scaffolds for direct in situ crosslink mineralization. Starting with aqueous solutions of polymers end-functionalized with metal-coordinating ligands of catechol or histidine, here we show that inter-molecular metal-ion coordination complexes can serve as mineral nucleation sites, whereby significant mechanical reinforcement is achieved upon nanoscale particle growth directly at the metal-coordinate network crosslink sites.

Rheology as a Mechanoscopic Method to Monitor Mineralization in Hydrogels.

Biominerals have been widely studied due to their unique mechanical properties, afforded by their inorganic-organic composite structure and well-controlled growth in macromolecular environments. However, a lack of suitable characterization techniques for inorganic minerals in organic-rich media has prevented a full understanding of biomineralization. Here, we applied rheometry to study mineral nucleation and growth dynamics by measuring viscoelastic material properties of a hydrogel system during mineralization. Our proof-of-concept system consists of a gelatin hydrogel matrix preloaded with calcium ions and a reservoir of carbonate ions, which diffuse through the gel to initiate mineralization. We found that gels with diffused carbonate show an increase in low frequency energy dissipation, which scales with carbonate concentration and gel pH. Using this signal, and recognizing that mineralization occurs simultaneously with carbonate diffusion in our system, we have mechanoscopically tracked mineral growth in situ, showcasing the potential of rheometry for studying mineralization kinetics in real time.