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Assessment of hydrogel cross-linking by postformation swelling

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The ability of PdBT, CS/PdBT, BMPm/PdBT, and NC/PdBT to cross-link P(NIPAAm-co-GMA) was assessed by a study in which fabricated hydrogels were swollen in excess PBS and then assessed for degree of mass swelling, i.e., the ability to resist the natural tendency of P(NIPAAm-co-GMA) to shrink and expel water mass after formation (3). In this study, hydrogels were weighed immediately after fabrication (Wf) and then weighed again after equilibrium swelling (Ws) in 1.5 ml of PBS at pH 7.4 for 24 hours at 37°C. Swollen hydrogels were then flash-frozen in liquid N2 and lyophilized to obtain the dry weight (Wd). From these weights, the initial formation swelling ratio was calculated as $Wf−WdWd$, while the equilibrium swelling ratio was calculated as $Ws−WdWd$. The minimum PdBT, CS/PdBT, BMPm/PdBT, and NC/PdBT concentrations that resulted in a greater equilibrium swelling ratio than the initial formation swelling ratio, indicating sufficiently cross-linked systems, were then used for all further hydrogel characterization.

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