Inorganic biomaterials for ocular drug delivery: A comprehensive review

Since last few decades, a wide range of biomaterials have been employed for ocular drug delivery applications, including natural and synthetic polymers, proteins and peptides, inorganic biomaterials, engineered biomaterials, etc. Amongst these, inorganic biomaterials have already been demonstrated to control biological responses, including cell-matrix interaction. Metals (like gold, silver, titanium, etc.), metal oxides like silicon dioxide (SiO2), magnetic iron oxide (Fe3O4), titanium dioxide (TiO2), zinc oxide (ZnO2), etc., ceramics, mesoporous silica nanoparticles (MSNs), carbon-based inorganics, etc., are some of the most often used inorganic biomaterials for ocular drug delivery applications. This review article outlines different inorganic biomaterials, their classification, properties, and applications in ocular drug delivery. The ocular toxicity of inorganic biomaterials has also been comprehensively reviewed. Several metals and metal oxides have shown their antioxidant with high chemical stability in ocular drug delivery therapeutics. Different carbon-based inorganics like carbon dots (CDs), carbon nanotubes (CNTs), graphene, etc., with their bioinert, biocompatibility, and biomimicking activity have also demonstrated a promising usefulness in ocular therapeutics. The unique physicochemical, chemical, mechanical, optical, and magnetic properties of inorganic biomaterials make them highly efficient for drug targeting. The therapeutic capabilities of inorganic biomaterials can be modified using attachment of ligands to enrich their attraction towards the molecules at the target site, which makes them more appealing for efficient target-specific drug delivery with bioimaging (diagnostic) applications.