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V. Rajendra, Y. Chen, M. A. Brook; Structuring Silicone Elastomers for Drug Delivery. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5304.
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While silicone elastomers possess many interesting properties for use as biomaterials, their hydrophobicity, particularly when the objective to deliver polar drugs, including proteins, is problematic: it is challenging to disperse the polar drug into the elastomer, and subsequent controlled release is also problematic. Our objective was to develop strategies that would permit the controlled synthesis of hydrophilic structures within a silicone elastomer, with the idea that this hydrophilic control could be linked to desired delivery protocols. Surface biocompatibility is an issue when considering implantation of these materials within the eye for drug delivery. As a result, investigating the growth of Human Corneal Epithelial Cells (HCEC) was important to this study.
Room Temperature Vulcanization (RTV) of silicones involves the condensation of hydroxy-terminated polydimethylsiloxane (PDMS) with tetraethyl orthosilicate (TEOS). Aminopropyl-terminated PDMS (ATPDMS) was used as the catalyst and poly(ethylene glycol) (PEG), which provided hydrophilic domains, was doped into the elastomer formulation. The silicone/PEO surfactant DC-3225c was also added in certain experiments. After cure, human corneal epithelial cells were grown on select elastomers and analyzed.
Asymmetric cure, surface roughness, internal hydrophilic structuring and cell growth were the parameters that were examined as a function of the synthetic formulations. By varying simple parameters such as the weight% of crosslinker, catalyst, surfactant and relative humidity, we were able to control the homogeneity of our elastomers, achieve surface roughness values (Rq) ranging from 400nm - 65µm, and create internal hydrophilic structures ranging from dispersed globules to interconnected channels. Cell growth was also analyzed as a function of criteria above as well as the biocompatibility of these materials.
We have shown a simple method to control the structuring of silicone elastomers, which affects the biocompatibility of these materials, by simply modifying elastomer formulations. Controlling the internal structure of the material should also facilitate drug release with defined profiles.
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