After having established that microparticles remain largely stationary in TiTannic gels, we investigated the diffusion rate of a small molecule: glucose (0.18 kDa). Glucose-permeable hydrogels are of interest clinically, as these types of gels are being explored to encapsulate insulin-producing cells for the treatment of diabetes. In the present investigation, we developed a glucose permeability assay (Figure ) to compare glucose permeability of the TiTannic gel system to Pluronic F127 gels, an in vivo gelation system which has previously been explored for the treatment of diabetes. In the glucose permeability assay, the gel was cast in a porous well insert (membrane with 0.4 µm pores) and PBS was added both underneath and above the gel following gelation (Figure ). Concentrated glucose was then added above the gel, while a glucose probe was situated underneath the gel (Figure ). In the empty well control (i.e. free diffusion), the glucose concentration was measured as equilibrated within the first three hours, and for the TiTannic control sample (no glucose added) the signal remained low, as expected (Figure ). For both Pluronic F127 and TiTannic gels, retarded diffusion relative to the empty well (free diffusion) was observed. While there is a large overlap in the observed glucose concentration increase during the first few hours (Figure ), Pluronic F127 gels appeared to stabilize at longer time points (>10 hours) at a higher concentration than the TiTannic gels (Figure ). Pluronic F127 gels are known to dissolve over time which may contribute to this difference. Polyphenols are known to interact with carbohydrates, and this may contribute to the observed lower glucose level detected. Nevertheless, the results demonstrate that Pluronic F127 gels and TiTannic gels are both permeable to glucose. TiTannic gels are stable and well tolerated after subcutaneous injection in mice. For initial assessment of TiTannic gel tolerability, an individual mouse was injected subcutaneously on the right flank with 50 µL of gel precursors (precursors were always mixed immediately before injection). This was followed by a second mouse injected subcutaneously with 100 µL of gel precursors. The gels formed a solid disc-shaped mass within ~15 minutes, which was palpable underneath the skin. As no systemic or local adverse effects were observed for these first mice, a subsequent group of mice was subcutaneously injected with 100 µL of TiTannic gel precursor and culled at selected time points up to week 14 post-injection. The injection site was investigated and resected for histological assessment.