Surface Roughness on Film Coated Extrudates Investigated Using Photometric Imaging

Development of controlled release dosages forms requires thorough understanding of the formulation and process parameters as well as robust process control solutions. In this study the effect of four selected process parameters; coating amount, concentration of the polymer in coating solution, spray rate of the coating solution and fluidising air flow rate on the surface roughness of the film coated extrudates has been evaluated. The film coating was performed in a typical lab system coater equipped with a Wurster insert by using a mixed full factorial design resulting in 16 batches. The surface roughness was measured with Flashsizer 3D which applies a photometric imaging technique [1]. This technique uses two white light sources that allow the reconstruction of a 3D image of the extrudates surface. The light source has been placed 180°C from each other in a horizontal plane. The extrudates batches were presented to the instrument in a continuous feed and were imaged through a glass window. Approximately 270 extrudates were measured per one feeding-cycle and each batch was measured on average 15 times resulting in measurement of roughly 4000 extrudates per batch. Different surface roughness values were calculated from the digital image information and are based on change in grey scale values in the surface images. An increased coating amount decreased the surface roughness described by R_a which is the arithmetic average of the roughness profile. The same effect was observed by increasing the spray rate of coating solution whereas an increased fluidising air flow rate increased the R_a surface roughness. No effect of R_a surface roughness was observed by increasing the ethyl cellulose concentration in the coating solution. The suggested approach is a promising tool for evaluating surface roughness of film coated extrudates in a continuous manner. References: 1. Sandler, N., Photometric imaging in particle size measurement and surface visualization. Int. J. Pharm. (2010)