Fig. 5. Swelling, reaction kinetics, hydrolytic degradation, and cytocompatibility of PdBT cross-linked hydrogels.

(A) Swelling study performed to assess the cross-linking of 10% (w/v) P(NIPAAm-co-GMA) hydrogels mixed with varying concentrations of PdBT, CS/PdBT, BMPm/PdBT, or NC/PdBT. Data are reported as means ± SD for a sample size of n = 3. Number sign (#) indicates statistical significance of a greater equilibrium swelling ratio than initial swelling ratio at a given concentration, which represents formation of a well–cross-linked system. Representative pictures are shown for 3.5% (w/v) PdBT, 4.66% (w/v) CS/PdBT, 10.5% (w/v) BMPm/PdBT, and 3.5% (w/v) NC/PdBT, which were used for all further studies. (B) Cross-linking kinetics of the aforementioned hydrogel formulations characterized by differential scanning calorimetry of heat flow produced by each cross-linking reaction. Samples were held at 4°C for the first 5 min and then immediately elevated to 37°C to induce gelation and cross-linking. (C) Hydrolytic degradability of PdBT cross-linkers assessed by an accelerated degradation study comparing the degradation kinetics of PdBT, CS/PdBT, BMPm/PdBT, and NC/PdBT cross-linked hydrogels placed in 0.1 M HCl at 37°C. Data are reported as means ± SD for a sample size of n = 3. (D) Cytocompatibility of cross-linked hydrogels, as demonstrated by a leachable cytotoxicity assay. Data are reported as means ± SD for a sample size of n = 3. Number sign (#) indicates statistical significance from live controls.