Multiresponsive 4D Printable Hydrogels with Anti-Inflammatory Properties

Multiresponsive hydrogels are valuable as biomaterials due to their ability to respond to multiple biologically relevant stimuli, i.e., temperature, pH, or reactive oxygen species (ROS), which can be present simultaneously in the body. In this work, we synthesize triple-responsive hydrogels through UV light photopolymerization of selected monomer compositions that encompass thermoresponsive N-isopropylacrylamide (NIPAM), pH-responsive methacrylic acid (MAA), and a tailor-made ROS-responsive diacrylate thioether monomer (EG₃SA). As a result, smart P[NIPAM_x-co-MAA_y-co-(EG₃SA)_z] hydrogels capable of being manufactured by digital light processing (DLP) 4D printing are obtained. The thermo-, pH-, and ROS-response of the hydrogels are studied by swelling tests and rheological measurements at different temperatures (25 and 37 °C), pHs (3, 5, 7.4, and 11), and in the absence or presence of ROS (H₂O₂). The hydrogels are employed as matrixes for the encapsulation of ketoprofen (KET), an anti-inflammatory drug that shows a tunable release, depending on the hydrogel composition and stimuli applied. The cytotoxicity properties of the hydrogels are tested in vitro with mouse embryonic fibroblasts (NIH 3T3) and RAW 264.7 murine macrophage (RAW) cells. Finally, the anti-inflammatory properties are assessed, and the results exhibit a ≈70% nitric oxide reduction up to base values of pro-inflammatory RAW cells, which highlights the anti-inflammatory capacity of P[NIPAM₈₀-co-MAA₁₅-co-(EG₃SA)₅] hydrogels, per se, without being necessary to encapsulate an anti-inflammatory drug within their network. It opens the route for the fabrication of customizable 4D printable scaffolds for the effective treatment of inflammatory pathologies.