Enhanced Release of Drugs from Silicone Elastomers (II): Induction of Swelling and Changes in Microstructure

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Abstract
Incorporation of glycerol into silicone elastomers was found to enhance the release of hydrophilic drugs as well as to cause the polymeric device to swell as a result of water uptake. There are similarities between the kinetics of drug release from the matrix of silicone elastomers and the kinetics of swelling, water uptake, and leaching of tritiated glycerol, in that they all follow a matrix diffusion-controlled mechanism. The results of absorption, desorption, and resorption kinetic studies suggest that the two processes of swelling and water uptake are reversible. The amount of glycerol which leached out from devices containing up to 20% glycerol was only 4 → 10−4 to 6 → 10−4% of the amount of glycerol that had been originally incorporated into the device. A scanning electron microscopic examination of a silicone device containing glycerol revealed a microstructure in which glycerol vesicles are dispersed. In contrast to this, the matrix of a silicone device containing no glycerol was shown to be a continuous network. The microstructure of a glycerol-containing silicone device became more “spongy” after leaching than it was before leaching.