Different polymers may be used for manufacturing IVRs intended to prevent HIV-1 infection, but the range of materials used is limited by the requirement for high drug permeability, flexibility and mainly biocompatibility. Silicone and thermoplastic elastomers are the two most widely used compounds.
Silicone elastomers are polymers exhibiting two methyl groups called polydimethylsiloxane. They present an excellent biocompatibility and biodurability. Dapivirine (TMC120), maraviroc, UC781 and MC1220 were shown to have physicochemical properties very similar to those of steroid molecules, which means that it may be relatively easy to obtain a controlled release of these compounds by using silicone-made IVRs.
Thermoplastic elastomers are copolymers with both thermoplastic and elastomeric properties; they are formed by crosslinking bonds, which impart high elastic properties. The compounds that are the most used in manufacturing IVRs are polyethylene vinyl acetate and polyurethane. They are particularly adapted to some polar anti-HIV drugs such as TFV, or its precursor TFV disoproxil fumarate (TDF), that are not released at efficient rates by silicone elastomers because of their high hydrophilicity and resultant low solubility in silicone.
Future Virology. 2014;9(3):227-230. © 2014 Future Medicine Ltd.