Emerging trends in ophthalmic products: Microneedles, hydrogels, and ocular inserts

People worldwide suffer from eye illnesses, resulting in visual impairment or blindness. Conventional treatment uses eye drops, with a limited bioavailability, requiring frequent administration and sometimes increasing the dose. Notably, drug loss has been a major challenge due to the physiological processes of the ocular system, including blinking, baseline tear production, reflex tear production, and tear drainage. To this end, over the decades, there has been a surplus of evidence that has shown explicative research in the development of more effective drug delivery methods that are necessary to address current constraints. These delivery systems improve the penetration of therapeutic biomolecules across the cornea and increase systemic bioavailability. Microneedles, hydrogel, and ocular inserts, among others, have been recommended as modern and novel ophthalmic drug delivery systems. These delivery systems are considered noninvasive or minimally invasive drug delivery systems. Microneedles are micron-sized needles that permeate the corneal barrier and get dissolved in the physiological fluid. The dissolvability of the needles is governed by the materials used for their fabrication. The drug release can be tuned, either immediate or sustained release, based on the selection of these materials. These are the dissolvable microneedles that control the release of the therapeutics incorporated within the microneedle cavities. The other types include solid, coated, and hollow microneedles. Hydrogels are biphasic materials with porous and permeable solid networks, made up of natural, synthetic, or composite polymers. As hydrogels tend to show a desired swelling behavior, as a response to a change in the environment, they are termed smart or stimuli-responsive hydrogels. These are influenced by temperature, pH, and ions, among others, that govern the drug residence time and sustain the release of the drugs. The short precorneal residence time can be overcome by the application of ocular inserts, which are sterile, thin, and multilayered devices that are inserted into the cul-de-sac or conjunctival sac of the eye. They are supported by a polymeric material that may or may not contain drugs. Based on these modern developments, various ophthalmic products are now well-established in clinical studies, showing desired results in the management of certain ocular ailments. Nevertheless, there have been studies that also show the 3D-printed manufacturing techniques of these drug delivery systems as an advanced and effective delivery of therapeutics. Taken together, this chapter delves into the progressive developments and interests of ophthalmic products based on microneedle, hydrogel, and ocular inserts drug delivery platforms.