In addition to act on the rheological and mechanical properties, covalent coupling between NPs and the gel matrix can also enable specific functionalities/responsiveness to be retained. For instance, the formation of an acid-labile Schiff base bond between cationic PAMAM G5 dendrimers and aldehyde-modified Dex (Dex-CHO) offered an interesting opportunity to crosslink it and to acquire pH responsiveness (Figure ). In this case, acidification of the medium caused both degradation of the imine bond and protonation of the tertiary amines in the dendrimers compromising the ability to coordinate Ag NPs loaded into the dendrimer core (G5-Ag). Taking advantage of the acidification of the medium in the presence of proliferating bacteria, this approach may facilitate a site-specific release of antimicrobial particles. The same type of reaction allowed to incorporate PDA-coated bioactive glass NPs into a F127 /polylysine hydrogel, yielding to controlled accumulation of photothermal features within the hydrogel matrix. Figure . Schematic representation of the formulation of hybrid system in which Ag-loaded, amine-terminated dendrimers are covalently linked to Dex-CHO via Schiff base and the mechanism of its degradation in an acidic environment. Adapted with permission. Copyright 2018 American Chemical Society.