Optical Coherence Tomography: A New PAT-Tool for Fast and Non-Destructive Analysis of Tablet Coating Quality

Optical coherence tomography (OCT) is a non-invasive imaging technique allowing fast and high-quality cross-sectional imaging of semi-transparent and turbid media. Biomedical research and diagnostics have been up to now the main driving forces for the reported applications and progress in OCT. The characteristics of OCT are the ability to provide high-resolution images and depth-resolved information also in strongly scattering media in a contact-free way. Hence OCT is well suited to image layered structures like retina, skin or multi-layered foils in the packaging industry. However, the application of OCT for the analysis and characterization of tablet coatings in the pharmaceutical sciences is still relatively new [1]. The image contrast is due to inhomogeneities in the refractive index of the sample material, and thus, OCT provides complementary information to other high resolution imaging techniques like terahertz imaging, X-ray computed tomography (CT) and magnetic resonance imaging (MRI).

In this work, high-speed spectral domain OCT was demonstrated as a new Process Analytical Process (PAT) tool for the characterization of pharmaceutical tablet coatings [2]. A Design of Experiments (DoE) was created to produce tablet batches with three coating process parameters. The coating thickness was determined via conventional testings with a µm-caliper or weight gain measurements and compared with OCT measurments. In addition, the results were related to investigations carried out with already established PAT tools like Near-Infrared (NIR) and Raman spectroscopy combined with qualitative and quantitative Multivariate Data Analysis (MVDA).

Finally, the influence of process parameters on the dissolution behavior as a critical quality attribute for the tablets was related to the disintegration times of the tablets for response surface modelling.