Multiresponsive\n4D Printable Hydrogels with Anti-Inflammatory\nProperties

Multiresponsive hydrogels are valuable as biomaterials\ndue to their\nability to respond to multiple biologically relevant stimuli, i.e.,\ntemperature, pH, or reactive oxygen species (ROS), which can be present\nsimultaneously in the body. In this work, we synthesize triple-responsive\nhydrogels through UV light photopolymerization of selected monomer\ncompositions that encompass thermoresponsive <i>N</i>-isopropylacrylamide\n(NIPAM), pH-responsive methacrylic acid (MAA), and a tailor-made ROS-responsive\ndiacrylate thioether monomer (EG<sub>3</sub>SA). As a result, smart\nP[NIPAM<sub><i>x</i></sub>-<i>co</i>-MAA<sub><i>y</i></sub>-<i>co</i>-(EG<sub>3</sub>SA)<sub><i>z</i></sub>] hydrogels capable of being manufactured by digital\nlight processing (DLP) 4D printing are obtained. The thermo-, pH-,\nand ROS-response of the hydrogels are studied by swelling tests and\nrheological measurements at different temperatures (25 and 37 °C),\npHs (3, 5, 7.4, and 11), and in the absence or presence of ROS (H<sub>2</sub>O<sub>2</sub>). The hydrogels are employed as matrixes for\nthe encapsulation of ketoprofen (KET), an anti-inflammatory drug that\nshows a tunable release, depending on the hydrogel composition and\nstimuli applied. The cytotoxicity properties of the hydrogels are\ntested <i>in vitro</i> with mouse embryonic fibroblasts\n(NIH 3T3) and RAW 264.7 murine macrophage (RAW) cells. Finally, the\nanti-inflammatory properties are assessed, and the results exhibit\na ≈70% nitric oxide reduction up to base values of pro-inflammatory\nRAW cells, which highlights the anti-inflammatory capacity of P[NIPAM<sub>80</sub>-<i>co</i>-MAA<sub>15</sub>-<i>co</i>-(EG<sub>3</sub>SA)<sub>5</sub>] hydrogels, <i>per se</i>, without being necessary to encapsulate an anti-inflammatory drug\nwithin their network. It opens the route for the fabrication of customizable\n4D printable scaffolds for the effective treatment of inflammatory\npathologies.