(605d) Characterization of Tablet Core and Coating Roughness By Means of Optical Coherence Tomography

Although tablet coating is a well-established unit operation in pharmaceutical industry, the achievable quality of coating is still limited by the fact that it is a highly complex process depending on many parameters. Specifically for functional coatings slight changes of the coating equipment and process parameters may impact the physicochemical properties of the film and may consequently affect the coating quality. There are significant gaps remaining in the full scientific understanding of the process, which makes it a difficult task to produce tablets with an exact thickness and density and with only small tablet-to-tablet variations between batches or even within one single batch. The use of advanced quality control tools facilitates the understanding of physico-chemical changes of the film.

Such a quality control tool is optical coherence tomography (OCT) showing not only high potential for off-line quality control of film-coatings but also for in-line monitoring of coating processes. OCT is a high resolution imaging methodology to produce cross-sectional and three-dimensional (3D) images of film coatings in a non-destructive and contactless manner. This modality allows the direct measurement of the coating thickness under consideration of the refractive index of the coating. Beside the analysis of the coating thickness, it additionally facilitates the characterization of the tablet core and coating roughness.

An automated data evaluation algorithm extracts information about coating thickness as well as tablet core and coating roughness. This analysis can be carried out either on the basis of cross-sectional images or by using 3D data of samples. The focus in this study is on the analysis of 3D images of samples removed periodically from a pan coating process. A thickness map and profile maps of the tablet core and coating is computed from about 480,000 depth measurements per sample. This data enables among others the calculation of the arithmetical mean deviation, the root mean square deviation, the skewness and the kurtosis of the assessed profiles. Moreover, the impact of the tablet core roughness on the coating thickness is analyzed by correlating the tablet core profile and the coating thickness map. This analysis is further transferred to in-line OCT measurements allowing the investigation of core and coating roughness during the production. Such detailed information specifically emphasizes the high capability of the OCT technology to improve process understanding.