Curing behavior of silicone elastomer in the presence of two corticosteroid drugs

Silicone rubbers are widely used as carriers for delivery of drugs intended for parenteral administration as implantable devices. Drugs having different functional groups can significantly affect curing profile of silicone rubber, which in turn may negatively affect their biological applicability due to the loss in mechanical and drug retaining properties. To this end, the effects of two corticosteroid analogs (up to 2 %w/w of drug loading) that is, dexamethasone (DEX) and its sodium phosphate ester (DSP) on curing behavior of a non-restricted, two part RTV silicone rubber was studied using different characterization techniques including spectroscopic (FTIR), calorimetric (DSC), oscillating disk rheometry, and swelling studies. The results showed that curing time extends longer for DSP-loaded samples compared to the non-loaded silicone rubber. The presence of DSP in the formulation interferes in the curing of silicone elastomers, probably due to the thermal decomposition of DSP according to the spectral changes observed in FTIR spectra as confirmed by DSC analysis. Rheometric studies showed depreciated properties for silicone elastomers upon compounding with DSP. Swelling measurements indicated to lowered crosslink density for networks and increasing M(c) upon adding DSP to the formulations which can be attributed to disruption in crosslinking reaction by sodium phosphate moieties of DSP.