forming hydrogels are of interest for diverse biomedical applications due to their ease-of-use and minimal invasiveness and therefore high translational potential. Supramolecular hydrogels that can be assembled using metal–phenolic coordination of naturally occurring polyphenols and group IV metal ions ( Ti IV or Zr IV ) provide a versatile and robust platform for engineering such materials. However, the formation and response to this new class of materials has not yet been reported. Here, we demonstrate that metal–phenolic supramolecular gelation occurs successfully and we investigate the host response to the material over 14 weeks. The Ti IV –tannic acid materials form stable gels that are well-tolerated following subcutaneous injection. Histology reveals a mild foreign body reaction, and titanium biodistribution studies show low accumulation in distal tissues. Compared to poloxamer-based hydrogels (commonly used for gelation), Ti IV –tannic acid materials show a ...