Here, we demonstrate that metal-phenolic supramolecular gelation occurs in vivo and investigate the host response to the material over 14 weeks (Figure ). Liquid precursors (tannic acid solution and Ti IV solution) were prepared and filter-sterilized. The composition was tailored to achieve a gelation time of around 15 minutes, which was deemed suitable for allowing careful injection. Prior to animal studies, the gel system was characterized using electron microscopy and Raman spectroscopy, and permeability and porosity were assessed using a glucose permeability assay and particle tracking analysis, respectively. For the animal studies, the two sterile precursors were mixed immediately prior to subcutaneous injection in the flanks of immunocompetent mice. At specified time points during the 14-week period, external and internal photographs of the injection sites were taken and histological sections were prepared. Additionally, tissue samples were collected for titanium biodistribution studies using mass spectroscopy. Titanium remained largely at basal levels for most studied tissues and time points, indicating low to negligible titanium accumulation. Finally, drug loading and elution studies were performed in vitro using the corticosteroid dexamethasone, and drug elution from the TiTannic gels was observed over a period of >10 days, which can be compared to <1 day for the Pluronic F127 hydrogels prepared as controls.