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Ivana Postic, Laura Wells, Geetha Mahavedan, Heather Sheardown; A Minimally Invasive, Controllable Photosensitive Device for Posterior Drug Delivery. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3231.
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Most current treatments of posterior eye disorders require repeat injections of drugs into the vitreous. This technique, however, is quite invasive and can be uncomfortable for the patient. To improve this practice, research has focused on developing resources for long-term, sustained release of drugs. A photosensitive gel can provide controlled drug dosage by adjusting the cross-linking density using UV-wavelengths of light. By joining this gel to a microneedle, the need for an injection using conventional needles is not needed. With only the microneedle penetrating scleral tissue, this external device could potentially be reloaded with drug as necessary, and controlled release reinstated by exposing the photogel to UV wavelengths.
Initially, a polyethylene glycol-anthracene (PEG-anthracene) molecule was grafted to a hyaluronic-acid (HA) backbone, creating a photosensitive gel. The gel was loaded with varying concentrations of model dyes (including Fast Green and Coomassi blue) and a UV light source crosslinked the photo-sensitive anthacene. Hollow, glass microneedles were etched using hydrofluoric acid and later penetrated though a polydimethylsiloxane (PDMS) disc. The photogel was then placed in a PDMS well, and the PDMS disc was used to encapsulate the gel, creating the device. Release of model molecules through the microneedle was performed at 37°C into phosphate-buffered saline solution. Released molecules were detected at their individual wavelengths.
UV penetration results show that wavelengths specific to crosslinking and de-crosslinking anthracene are able to penetrate the PDMS exterior and crosslink the photogel. Photogels alone are able to load 22.6 ± 0.35 mg/g of Coomassie blue and 1.3 ± 0.65 mg/g gel of Fast Green with 30 minute UV exposure time, resulting in 82% and 62% decrease in diffusion coefficients respectively. Glass microneedles of sizes varying from 165um (outer diameter (OD)) and 365OD have been successfully inserted through PDMS discs to allow an exitway of model molecules.
Results show that photogels are able to control the release of model molecules through PDMS encapsulation and microneedles provide a minimally invasive alternative for small molecule delivery. By combining these technologies, we have the potential to deliver drugs to the back of the eye from a prolonged period of time.
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