Fabrication of Multifunctional Stimuli-Responsive Hydrogels Susceptible to both pH and Metal Cation for Visual Detections

Advances in several areas of contemporary biomaterial science are closely related to the design of stimuli-responsive smart materials. An important aspect that governs widespread adaptation of a synthetic biomaterial depends on its ease of synthesis, as well as facile functionalization. In this study, readily available homo-bifunctional PEG-based diamines are mixed with a tetra-arm epoxide based cross-linker to yield hydrogels through the epoxy-amine addition reaction. Hydrogels obtained with varying chain lengths of PEG polymer are characterized for their morphology, swelling, and rheological properties. The residual epoxide groups within the hydrogel are used for post-gelation functionalization to obtain a functional material. In particular, functionalization with an amine-containing rhodamine derivative yields a hydrogel that serves as a colorimetric sensor for acidic pH environment, and indicates the presence of Fe3+ cation with high specificity.