Hydrogels as versatile colloidal platforms to combat skin cancer – Physicochemical features, strategies and advances

• Polymer-based hydrogels are highly versatile colloidal systems to effectively fight skin cancer. • A comprehensive and systematic overview of strategies undertaking this serious problem is presented. • Hydrogels have been researched as direct drug reservoirs, as nanocarrier scaffolds and as nanogels. • Physicochemical, colloidal and biomedical features of investigated hydrogels are highlighted. • General outlook and future perspectives are also presented. The incidence of skin cancer is rising globally. Hydrogels are among the most extensively studied systems in the plight to combat this disease due to their unique features—such as versatility, biocompatibility, capacity for stimuli-responsiveness, common non-invasiveness, photodynamic therapy capability, and ability to contain smaller delivery structures embedded—and their potential for continuous enhancement. Herein, we review the major strategies and findings concerning the development of hydrogel-based colloidal systems for skin cancer treatment, dividing the literature into three main areas: hydrogels as direct drug delivery systems; hydrogels as scaffolds for drug-loaded nanostructures and sensitizers; and hydrogels in the form of nanogels. Hydrogels have been employed as slow-release drug reservoirs, which can be administered topically or injected directly into the tumor mass, yielding potent anticancer effects. Hydrogel scaffolds embedded with drug-loaded nanostructures—encompassing vesicles, micelles, emulsions or nanocapsules—have emerged as hybrid systems that significantly enhance bioavailability at the tumor site, demonstrating high efficacy against skin cancer. Additionally, solid nanoparticles benefit greatly from the hydrogel network, which serves not only as a scaffold to enhance photothermal therapy but also as a bioactive compound, promoting cancer cell death and wound healing. Finally, nanogels are highly versatile and very effective systems against metastization as they can be administered intravenously. We conclude by presenting perspectives on future directions in this field and challenges yet to be addressed.