Solute release from a porous polymeric matrix: inwardly tapered disk with a central releasing hole.

Diffusional solute release from an inert porous polymeric matrix was evaluated using sodium salicylate released from fused, inwardly tapered, polyethylene disk matrices (1.27 cm in diameter) with a central releasing hole. Two types of matrix were made by compressing (175 MPa) a sodium salicylate-melt polyethylene mixture with two different sets of circular conical punches having angles of 20 degrees and 30 degrees, with an axis perpendicular to the cone. The matrix sodium salicylate loading was greater than its solubility limit in the release medium. The fused matrices were coated with wax and perforated in their center to create a surface available for solute release. Flat disks with a central cylindrical hole were also made to compare the release profiles. An approximate solution was developed for these inwardly tapered disks and tested against experimental results. The theoretical model and experimental results showed good agreement and indicated that this type of matrix geometry may be useful as a pharmaceutical dosage form to approximate zero-order release.