Effect of Ionic Interaction on the Entrapping of Drug into Porous Microspheres and Drug Release Characteristics

Abstract

Polymer-coated porous microspheres containing salicylic acid as a model drug were prepared by graft copolymerization by a pre-irradiation method using gamma rays. Methyl methacrylate (MMA), dimethylaminoethyl methacrylate (DM), and diethylaminoethyl methacrylate (DE) were used as monomers. Irradiated spheres were brought in contact with monomer solution containing the drug. The amount of salicylic acid entrapped increased linearly with increasing extent of graft polymerization of DM-MMA and DE-MMA. The amount of salicylic acid released was proportional to the square root of time, and diffusion of salicylic acid through solution-filled pores in the matrix was the rate-limiting step. The diffusion rate constant of salicylic acid increased with increasing content of amino ester in the graft copolymer.