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He Wen, S Kevin Li; Development and characterization of silicone pressure sensitive adhesive episcleral implant. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5051.
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Ocular implants provide prolonged delivery of therapeutic agents to the eye, minimize systemic drug exposure, and reduce the need of multiple intraocular drug injections. Episcleral implants are ocular drug delivery systems that prolong drug delivery through the transscleral route. Materials currently available for constructing ocular implants are limited. Silicone pressure sensitive adhesives (PSA) are non-toxic and highly compressible, have high cohesive strength, and offer good adhesion to biological substrates. This material can form a polymer-drug matrix that improves drug compactibility and allows prolonged drug release at low polymer content. The objectives of this study were to develop and characterize a silicone PSA episcleral implant system for transscleral delivery of small molecules and macromolecules.
Dexamethasone, atenolol, and bovine serum albumin (BSA) were selected as the model drugs. Silicone PSA 7-4302 was the polymer used to construct the episcleral implant. The implant had an average diameter of 3.5 mm and thickness of 0.7 mm. In vitro drug release experiments were conducted with implants of varying polymer to drug mass ratios in a well-stirred vial system.
The silicone PSA episcleral implants provided sustained drug release that could last for over one month in the present study in vitro. Drug release from the implants followed a dissolution controlled release mechanism with the higher water solubility drug showing faster release rate than the low solubility drug. Increasing polymer content in the implant led to a significant decrease in the drug release rate.
Drug release from the silicone PSA episcleral implant is influenced by the solubility of the drug and the polymer content in the implant. The episcleral implant demonstrates the ability to provide drug release for an extended period of time, and therefore has the potential to offer safe and effective treatment to chronic ocular diseases via the transscleral route.
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