Figure 1.

A modular strategy to confer new chemical properties to clickable hydrogels via sequential CuAAC reactions. (A) Schematic of sequential CuAAC reactions to introduce cleavable chemical functions to clickable poly(acrylamide-co-propargyl acrylate) (pAPA) gels. To emphasize the modularity of the sequential in-gel CuAAC reaction approach, we depict reacting species as LEGO®-like blocks where protruding ends represent pendant alkynes and indented ends represent azides. In a model system, we functionalized pAPA gels with cleavable Rhodamine110 groups through an initial in-gel CuAAC reaction with the bifunctional N₃-SS-N₃ linker followed by a second reaction with a Rhodamine110-alkyne capping group. (B) Representative photograph of pAPA gel regions independently exposed to Rhodamine110-N₃ shows retention of the chromophore in the gel due to the in-gel CuAAC reaction. Scale bar = 6.5 mm (C) Representative UV-Vis absorbance spectra of pAPA gel regions exposed to 500 μM solutions of Rhodamine110-N₃ for increasing amounts of time. (D) Reaction progress curve for the first in-gel CuAAC reaction between alkyne groups on the pAPA gels and 500 μM solutions of Rhodamine110-N₃. (E) Reaction progress curve for the second in-gel CuAAC reaction, where we first exposed pAPA gels to 500 μM solutions of the N₃-SS-N₃ linker for 90 min followed by a second reaction with 250 μM solutions of Rhodamine110-alkyne. All error bars represent one standard deviation of the mean of 5 independent measurements per condition.