The relationship between drug release rate, particle size and swelling of silicone matrices

Matrices composed of silicone elastomer (polydimethylsiloxane) have been used extensively as implantable controlled release drug delivery systems. This study examined the relationship between drug particle size, release rate and swelling of silastic matrices, by using a model drug (potassium dichromate) and two types of silicone polymer. The drug particles were found to be the driving force for water uptake by the matrix. The release rate was directly proportional to the degree of swelling, which in turn was directly proportional to the drug particle size. The release rate and swelling of matrices composed of silastic 382 increased with decreasing drug particle size, while increasing drug particle size resulted in increased release rate and decreased swelling of silastic Q7 matrices, probably because air is entrapped during fabrication of these matrices. More retarded release and swelling was exhibited by silastic Q7 matrices in comparison to matrices composed of silastic 382, probably due to the different physical properties of these silicones.