By avoiding chemical crosslinking reactions, and hence the use of additional reagents that may produce toxic residues, these hydrogels are generally considered safer for biological applications. Interactions in these systems are reversible, meaning that the network that breaks under the effect of an applied stress will reform once the stress has been removed, therefore ensuring injectability and self-healing. Such reversibility can be leveraged for the controlled release of therapeutics, also upon application of an external trigger such as NIR light. With charged polymers such as CS and ALG, gel formation can be simply achieved by ionic gelation with the introduction of oppositely charged species. For instance, hybrid nanocomposite hydrogels made of ALG and nanostructured lipid carriers, CS micelles, liposomes (Figure ) were obtained by drop-by-drop addition of the polymer dispersion containing the nano-objects into a CaCl2 solution. In the case of CS-based hydrogel beads containing CuO NPs, sodium tripolyphosphate served as the crosslinking agent. .