Non-destructive detection and quantification of moisture ingress evolution in film-coated compressed tablets using ultrasonic techniques.

Trapped moisture in film-coated tablets can redistribute over time, altering interparticle bonding, microstructure, viscoelasticity, and disintegrant functionality. In this proof-of-concept study, it is shown that ultrasonic wave propagation can be used to detect and monitor these time-dependent changes under sealed conditions. Tablets with identical formulations, compacted at 5-25 kN, were conditioned to 5-7 % moisture uptake, then sealed to prevent further external moisture exchange with the environment. Sealed-state responses were evaluated over short-term (8 h) and long-term (7 days) time scales using temporal, spectral, and dispersion-domain analyses, together with extracted micro-viscoelastic parameters. The results indicate that, despite a nearly constant overall moisture content, trapped moisture continues to redistribute from moisture-rich outer regions into the tablet core through the interconnected pore network, producing measurable changes in wave-transmission characteristics, bulk stiffness, and microstructural and micro-viscoelastic properties. Within the selected tablet set, the most pronounced responses occurred at intermediate compaction forces (15-20 kN), whereas the 5- and 25-kN tablets showed smaller changes. This pattern reflects differences in granular packing: low compaction allows rapid moisture diffusion, whereas high compaction restricts penetration. Intermediate compaction leaves micropore networks neither fully open nor highly restricted to moisture redistribution. Overall, the results demonstrate that ultrasonic techniques provide a sensitive, rapid, and non-destructive means of quantifying hidden moisture-driven microstructural and micro-viscoelastic changes in film-coated tablets, their impact on the functionality of superdisintegrants responsible for programmable disintegration, and the effects on key quality attributes.