The degree of cross-linking induced at resin manufacture can affect pore diameter. Inorganic electrolytes permeating the matrix are sufficiently small such that porosity should not affect their diffusion rates. In contrast, drug molecules are usually many times larger which can influence diffusion through the matrix. Cross-linking also affects matrix swellability which in turn can affect diffusion. Swellability can also be affected by the polymerization process at resin manufacture . Drug release rate can be affected by particle size of the resinate. Release can be faster from smaller particles due to their greater surface area. Larger particles may be utilized to provide slower release.
Drug release is usually rapid from resins that possess weak cationic or anionic (carboxylic acid or ammonium/primary amine) functional groups. Gradual release is provided by resins with strong cationic or anionic capacities (sulphonic acid or
tertiary ammonium functional groups). The pKa value of the resin functional group can also significantly affect release rate in acidic media. Such differences can enable selection of an appropriate resin matrix to influence drug release.
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