Drug delivery to the eye faces various challenges in the form of physiological (blinking, nasolacrimal drainage), anatomical (static and dynamic), and metabolic barriers. Drugs injected systemically are not able to cross the blood– retinal barrier into the retina. Nanocarrier-loaded in situ gels have gained popularity in the drug delivery system for their targeted administration and stimuli-responsive behavior. Nanogels emerged as an innovative approach over the conventional treatment for ocular drug delivery, by providing dual benefits of hydrogels and nanoparticles (NPs) in one dosage form. Nanogels are polymer-based 3-D hydrogel materials. Nanogels can be designed in the form of in-situ nanogels to exhibit sensitivity toward internal and external stimuli, such as light, temperature, pH, redox, and ionic strength, for controlled drug release. In addition, the incorporation of NPs in the gel decreases the burst release issues associated with NPs. In-situ gels are liquid during administration to the eye and get rapidly converted in the cul-de-sac of the eye into a gel form that releases the drug gradually. This article is going to review in-situ nanogels and their applications in the treatment of ocular diseases. In addition, the challenges as well as the progress made by nanogels in ocular delivery are also reviewed in detail.
Key words: nanogels, ocular administration, stimuli, in situ gels, application, safety
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