Influence of Drug Loading and Gel Structure on in-Vitro Release Kinetics from Photopolymerized Gels

Abstract

Precious work has shown that stabls and homogenous poly HEMA gels can be prepared using a visible light sensitive initiator system. Gels were prepared from solutions of water and poly-2-hydroxyethyl methacrylate monomer. At concentrations of water greater than 10% v/v, translucent gel resulted. However, polymerization solvents such as glycerol and tertiary butyl alcohol (T.B.T.A) gave transparent, flexible gels over a wider range of concentrations. Subsequent work showed that changes in polymerization solvent and monomer concentration brought about changes in the mechanical and structural properties of the gels.

In this work, the effects of drug loading and polymerization solvents on in vitro drug release rate from the photopolymerized polyHEMA gels were studied. Polymerization solvents used included glycerol and tertiary butyl alcohol. Results indicated that the release rate in vitro was a diffusion-controlled process except at high drug concentrations in poly HEMA - T.B.T.A. gels when a departure from root-time kinetics occurred. Poly HEMA T.B.T.A. gels presented greater hindeirance to the mobility of the drug than polyHEMA - glycerol gels. Higuch's model for release from incoluble homogenous matrices containing dispersed solute was found to be inappropriate for the analysis of the release of the drug from the gels. A simple equation based on the modelling of desorption in diffusion was found more appropriate. Estimates of drug release rates in vitro may be made from measurements of the physical crosslinking density of the polymer (if matrix-diffusion controlled release is operative). Quantitative drug loading was achieved in the gels as evidenced from variation in crosslinking density and in vitro release rate with drug loading.