Determination of compartment properties of press-coated tablets by non-destructive terahertz technology

Compared to conventional film coating, press-coated tablets (PCTs) excel in their suitability for heat- and moisture-sensitive drugs and in their ability to produce thicker functional coats with higher drug loading. Previous work has demonstrated the importance of porosity to the mechanical properties of PCTs, but determining the porosities of the press coating separately from the tablet cores in the finished tablets remains challenging. Terahertz time-domain spectroscopy (THz-TDS) overcomes this challenge and non-destructively interrogates the PCT's compartment properties, including porosity, mass, height and thickness. The THz-TDS results align with reported literature values, are more physically consistent, and more closely reflect PCT compartments than the conventional method, which is affected by elastic recovery and material loss during physical separation of compartments. The robust THz-TDS approach is demonstrated with a range of PCT geometries, and its sensitivity to defective PCTs is confirmed. Its non-destructiveness permits the systematic determination of the material, process, and structural properties of each PCT, enabling more comprehensive analysis. With a thorough mechanical understanding of PCTs enabled by THz-TDS, predictive models can be developed to support Quality by Design (QbD) or Quality by Digital Design (QbDD) of PCTs.