Microneedles for controlled and sustained intraocular drug delivery

Microneedles (MNs) have emerged as a promising technology for minimally invasive drug delivery, offering significant advantages in the treatment of ocular diseases. These miniaturized needles enable precise, localized drug delivery directly into specific tissues of the eye, such as the cornea, sclera, vitreous, or retina, while minimizing pain and discomfort. MNs can be fabricated from various biocompatible materials, including metals, silicon, and biodegradable polymers, making them highly adaptable to various clinical applications. Recent advancements in MN design include the integration of 3D printing technologies to create highly customized geometries for improved drug delivery precision, the use of smart materials that enable stimuli-responsive and sustained drug release, and the development of hybrid microneedles combining different polymers to enhance both mechanical strength and controlled drug release. These innovations have established MNs as a superior alternative to traditional methods like eye drops or intravitreal injections, which often face issues of limited bioavailability and patient compliance. This review summarizes the current state of research on MN-based ocular drug delivery, focusing on material developments, fabrication methods, drug release mechanisms, and implantation techniques. Future directions for MN technology in ophthalmology are also discussed, highlighting its potential to improve treatment outcomes for complex ocular diseases.