Opposite effects have been also described. For instance, the inclusion of iron oxide NPs in a GelMA matrix, or silver NPs in a CS/PDA hydrogel, increased crosslinking and induced an alteration of the gel porous network, which adversely affected its water absorption capacity. Similarly, PDA-coated Au NPs, impeded water diffusion within a PNAAm hydrogel, resulting in slower water uptake. In the case of a PNIPAAm hydrogel encapsulating PDA NPs, the reduced equilibrium swelling ratio primarily arose from polymer/particle entanglement that impeded polymer chains extension. The swelling ratio can also be affected by the pH of the surrounding medium. This is particularly important for systems intended for oral administration, which are confronted with the gastrointestinal pH gradient.