SMART HYDROGELS IN OCULAR DRUG DELIVERY: MECHANISMS, MATERIALS, AND THERAPEUTIC APPLICATIONS

Smart hydrogels represent a rapidly evolving class of stimuli-responsive biomaterials with transformative potential in ocular drug delivery. Unlike conventional ophthalmic formulations, smart hydrogels are designed to undergo controlled physicochemical transitions in response to physiological or external stimuli, including temperature, pH, ionic strength, enzymatic activity, light, and electric fields. These intelligent systems significantly improve precorneal residence time, enhance drug bioavailability, and enable sustained and site-specific drug release in both anterior and posterior ocular segments. This review presents a comprehensive analysis of smart hydrogel systems, encompassing their fundamental mechanisms, polymer classifications, stimuli-responsive behaviour, and therapeutic applications across a broad spectrum of ocular diseases. Key polymer matrices including chitosan, alginate, poly(N-isopropylacrylamide) (PNIPAAm), polyethylene glycol (PEG), and natural polysaccharides are critically evaluated. Special emphasis is placed on recent formulation advances, literature evidence from 2019–2026, and the challenges surrounding clinical translation such as biocompatibility, sterilisation, regulatory compliance, and scalable manufacturing. The review concludes with a forward-looking perspective on multi-stimuli-responsive systems, regenerative ophthalmic applications, and the integration of nanotechnology with smart hydrogel platforms as future directions for precision ocular therapeutics.