Inorganic nanomaterials for ocular drug delivery: route-specific design rules, biological interfaces, and...

Ocular therapy is constrained by multiple physiological and anatomical barriers that severely limit drug exposure at diseased sites. Conventional dosage forms often suffer from low bioavailability, poor target-site accumulation, and the need for frequent administration, thereby compromising therapeutic efficacy and patient adherence. The rapid development of nanotechnology has accelerated the design of nanoscale delivery systems for ophthalmic applications, among which inorganic nanomaterials are particularly attractive because of their tunable physicochemical properties, structural robustness, and versatile surface chemistry. In this review, we summarize recent progress in the use of inorganic nanomaterials for ocular drug delivery and discuss the translational challenges that continue to hinder their clinical implementation. Particular emphasis is placed on route-specific design rules that link carrier properties to the biological interfaces, transport barriers, and local microenvironments encountered across different ocular delivery routes. Focusing on various representative inorganic nanoplatform systems, we highlight how particle size, interfacial chemistry, and pore architecture can be leveraged to regulate drug loading, tissue penetration, retention, and release behavior. We further discuss key translational considerations, including standardized physicochemical characterization, route-relevant safety evaluation, and batch-to-batch consistency during scale-up. Finally, we outline the major challenges and future opportunities for the rational development of inorganic nanocarriers in ophthalmic therapeutics.