The Raman probe provides spectral information of a local volume (~1 mm from the probe tip) and these data therefore suggest that local coordination occurs rapidly (within 1 minute), which is in agreement with previously reported metal-phenolic nanoscale films and coatings. Shorter range (nanoscale) interactions in the material may thus be completed within seconds, while longer range interactions needed to form the stable gel were observed to take around 15 minutes for the composition used here. It is noted that for other compositions, gelation time can vary drastically, from <1 minute to >1 day. Hydrogel porosity and permeability. To further investigate the porosity of the hydrated material, particle tracking analysis was used (Figure ). In this method, microparticles are dispersed in the gel (through co-gelation) and their movement is tracked over time using optical microscopy. This information can then be used to explore the porosity and functional tortuosity of a material. We compared the movement of embedded 1 µm polystyrene particles in Pluronic F127 hydrogels and in TiTannic gels at 37 ºC. Pluronic F127 gelation is a well-established gelation system (in this study acting as comparative control samples) that is thermoresponsive and where the gelation occurs through a micellar-packing mechanism. In the Pluronic F127 gel, a particle movement of around 50 µm (median displacement distance) per minute was observed (Figure ). That particles can easily move around is expected as the micellar-packing structure can accommodate substantial flexibility and movement inside the gel. In contrast, for TiTannic gels the median displacement distance per minute was 10-fold lower (<5 µm; Figure ). The largely stationary behavior of particles embedded in the TiTannic hydrogels indicate that the effective hydrated pore size is smaller than the particle diameter (i.e., 1 µm). This difference in effective pore size between the two different gel systems may be explained by the differences in chemistry and assembly mechanism: whereas Pluronic F127 gels are composed of macromolecules (poloxamers, >10 kDa) that form micelles, TiTannic gels are instead assembled through molecular coordination between metal ions and low molecular weight polyphenol (TA, 1.7 kDa).