"The microneedle is about as long as a regular hypodermic needle is wide," says Mark Prausnitz of Georgia Tech. "It enables us to reach not just the eye in general, but specific places in the eye—exactly where the medication needs to be."
Neither of the eminent PhDs can pin down the first time they exchanged details about what each of them was investigating in the lab.
But both of these researchers—the Emory Eye Center's Henry Edelhauser, former director of research, a multiple-award-winner and an acclaimed expert in drug delivery, and Mark Prausnitz, professor of chemical and biomolecular engineering at the Georgia Institute of Technology—are quick to cite the question that linked their interests: How can we deliver drugs to the back of the eye more efficiently and effectively?
A key question
A number of serious conditions can affect the retina (the receptive "screen" at the back of the eye where images are formed), such as age-related macular degeneration, the most common cause of severe vision loss among people over age 60; and diabetes-related disorders, the leading cause of blindness in people under 60. Unfortunately, the retina historically has proven difficult to target directly with newly available drugs.
Traditionally, medications for the eye have been delivered in the form of eye drops. Injections directly into the eye (intravitreal injections) have historically been used for treatment of acute disorders, such as an acute intraocular infection. Intravitreal injections, however, have become a mainstay of clinical management since 2006 for common disorders such as wet age-related macular degeneration and diabetic retinopathy. Alternative methods of delivering drugs to the eye are to simply take a pill, which delivers drug to the entire body, including the eye, or to inject a medication around the eye and allow it to diffuse through the porous white part (sclera) into the target tissues within the eye.
A big problem
None of these options, though, selectively targets the retina. Together, Edelhauser and Prausnitz stepped up to meet that challenge. Edelhauser brought to the partnership his years of notable research in drug delivery to the eye, particularly a long-term investigation into a transscleral approach, which he and Timothy Olsen, director of the Emory Eye Center, have shared. Prausnitz, having worked extensively in drug delivery to the skin, had already begun researching the use of very small needles along with his Georgia Tech colleague, Mark Allen, and was interested in ophthalmic drug delivery.
"Joining forces, we looked at the possibility that a microneedle could serve as a targeted delivery conduit in ophthalmology," Edelhauser says.
The right moment
Not only were the two researchers well matched, but, according to Prausnitz, "The timing was lucky. Thanks to advances in the electronics industry, it was no longer difficult to make structures of these micron dimensions."
For injections in the skin as well as in the eye, physicians use regular hypodermic needles, even when the surface for penetration is very thin. The microneedle's tiny size—about half a millimeter long (approximately equal to the thickness of a dime)—makes the new implement an ideal alternative.
"For comparison," Prausnitz says, "the microneedle is about as long as a regular hypodermic needle is wide. It enables us to reach not just the eye in general, but specific places in the eye—exactly where the medication needs to be."