Slow release from a coated sphere with a slightly deformed coating

Effects of a slight deformation of the coating film on the concentration distribution and the slow release characteristics of a coated drug particle is theoretically investigated in this work. A perturbation technique is employed for transformation of the deformed spherical problem into a series of concentric spherical problems with the degree of deformation considered as the perturbation parameter. In addition, the governing equations are solved analytically by further restricting the deformation shape function. Results in this study indicate that if the deformation is slight or only the average release rate is of interest, the effects of coating shape deformation are secondary. However, if the deformation is not so small and if the drug diffusivity in the film is low, the shape deformation could have a significant effect on the concentration profiles and/or the release rate from different parts of the particle surface.