Water uptake and swelling of tablets are processes occurring during active pharmaceutical ingredient (API) release. Thereby, disintegration is promoted and the enhanced exposure of API surface area to the release medium facilitates API dissolution. An experimental set-up for the simultaneous and time-resolved determination of water uptake and swelling of tablets has been developed. Water uptake was determined with a balance and swelling was determined with a camera. To validate the gravimetrical analysis, real-time water uptake measurements with inert test specimens were performed. The standard deviation of these measurements was considered to depict precision. A complementary gravimetrical analysis was employed to determine accuracy. For both, precision and accuracy, a maximum deviation of 6% was found. An algorithm for the symmetry-based 3D volume reconstruction was applied to obtain volumes of the tablets from 2D images. X-ray micro computed tomography was used to validate the accuracy and the determined volumes were in good accordance within 6% deviation. A case study with binary formulations of a filler and disintegrants confirmed reproducibility and demonstrated the ability of the method to discriminate formulation characteristics, such as disintegrant type, composition and porosity for water uptake and swelling with the necessary temporal resolution.
Keywords: Gravimetric analysis; Optical imaging; Swelling; Tablet characterisation; Water uptake.
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