Revolutionizing Eye Care: Exploring the Potential of Microneedle Drug Delivery

Abstract

Microneedle technology revolutionizes ocular drug delivery by addressing challenges in treating ocular diseases. This review explores its potential impact, recent advancements, and clinical uses. This minimally invasive technique offers precise control of drug delivery to the eye, with various microneedle types showing the potential to penetrate barriers in the cornea and sclera, ensuring effective drug delivery. Recent advancements have improved safety and efficacy, offering sustained and controlled drug delivery for conditions like age-related macular degeneration and glaucoma. While promising, challenges such as regulatory barriers and long-term biocompatibility persist. Overcoming these through interdisciplinary research is crucial. Ultimately, microneedle drug delivery presents a revolutionary method with the potential to significantly enhance ocular disease treatment, marking a new era in eye care.

Keywords: biocompatibility; eye care; glaucoma; microneedles; ocular drug delivery.

Figure 1

(1) The complex structure of the eye contains three coats to enclose the optically clear aqueous humor, lens, and vitreous body. The outermost coat consists of the cornea and sclera, and the middle coat consists of blood supply to the eye involving the choroid, ciliary body, and iris. (2) Diabetic retinopathy contains “Cotton-wool spots”, which are tiny white areas on the retina, the layer of light-sensing cells lining the back of the eye. (3) Cataracts can develop on aging or injury, resulting in changes in the eye lens involving the breakdown of the protein and fibers to make vision hazy or cloudy. (4) Glaucoma is a chronic, progressive eye disease caused by optic nerve damage leading to visual field loss. An abnormality in the eye drainage causing fluid to build up results in excessive pressure, causing damage to the optic nerve.

Figure 2

The transdermal microneedle structure and poke and patch mechanism of solid microneedles. The design of the microneedle consists of a flow channel from the drug reservoir, a flow channel opening on the needle side, a hollow microneedle, and a microneedle lumen. The poke and patch mechanism consists of using (1) microneedles to pierce the stratum corneum. (2) The micro-conduits are created in the stratum corneum, (3) a reservoir of the drug applied to the skin and diffuses through the prepared channels to reach the deeper layers of the epidermis.

Figure 3

(a): The drug release mechanisms through different types of microneedle patches involve the following: 1. Solid microneedle drugs diffuse into the dermis and the systemic circulation. 2. Hollow microneedles involve the application of a slight pressure or pump system to deliver the drug through the hollow channels into the skin. 3. Dissolving microneedles penetrate the skin and begin dissolving into the skin interstitial fluid for drug release. 4. Degradable microneedles degrade over time and allow for gradual drug release directly into the systemic circulation. (b): Drug release mechanisms: A. Poke and patch including pore-forming pretreatment with a drug formulation. B. Poke and flow involving the hole into the tip of the microneedle for drug flow across the skin. C. Poke and dissolve involves the dissolution and release of therapeutic agents into the skin. D. Coat and poke involving the solid microneedles coated with a water-soluble drug before application. E. Poke and release includes the release of encapsulated drugs through water-soluble microneedles.

Figure 4

Photolithography: The wafer undergoes a cleaning process to eliminate undesired contaminants. A spin-coating technique is employed to apply the photoresist onto the wafer. The photomask is positioned over the photoresist, and ultraviolet (UV) light is directed through the mask. Solvents remove the unexposed portion of the photoresist, leaving behind the desired patterns.

Figure 5

Three-dimensional printing of microneedles by fused deposition modeling.

Figure 6

The ophthalmic medication routes involving injection sites for better therapeutics.

Figure 7

Image of the back of the eye showing intermediate age-related macular degeneration and use of microneedle for the same.

Figure 8

A summary of the onset of glaucoma, which results in increased intraocular pressure and optic nerve damage, along with the use of microneedles for effective glaucoma therapeutics.

Figure 9

SCS Microinjector^® device in comparison with microneedles and ultrasound.