Bioactive silica-based drug delivery systems containing doxorubicin hydrochloride: In vitro studies

This study reports the applicability of sol-gel derived silica and silica-polydimethylsiloxane (silica-PDMS) composites as a potential bioactive implantable drug delivery system for doxorubicin hydrochloride (DOX). These composites also contain calcium chloride (CaCl₂) and triethylphosphate as precursors of Ca²⁺ and (PO₄)^3- ions. These composites were immersed for 20 days in a simulated body fluid (SBF) at 37°C to study the release rate of the DOX, dissolution of the silica and the formation of hydroxyapatite on the composites' surface. The results show that the release rate of the DOX can be effectively tailored by either the addition of a polydimethylsiloxane (PDMS), or by varying the amount of CaCl₂, where the elution rate of DOX increases with increasing amount of the CaCl₂ precursor. Importantly, irrespective of the amount of CaCl₂, no burst release of DOX has been observed in any of the silica-PDMS system investigated. On the other hand, a slow release of DOX has been observed with a trend that followed a zero (0)-order kinetics for a total of 20 days of elusion. The dissolution of silica in SBF was ca. two-times faster than that of silica-PDMS, with the former reaching an average saturation level of 80μg/mL whilst the latter reached 46μg/mL within 20 days. Both the silica and the silica-PDMS composites show bioactivity i.e. they absorb calcium phosphate from SBF. Within 10 days, a ten-fold increase in the concentration of calcium phosphate deposit has been observed on the silica-PDMS relative to the silica. The constant rates of DOX release observed for the silica-PDMS composites indicate that the calcium phosphate deposit do not obstruct controlled release of the drug.