(641e) Modelling the Stress Distribution in Tablet Coatings Exposed to Rapid Environmental Changes

Non-functional film coatings are applied to core tablets to improve product appearance, impart taste-masking properties, improve handling and stability of the dosage form, and reduce exposure to active drug substance for caregivers. The coatings protect tablets from negative effects of environment such as humidity, oxidation, and light. The mechanical stability and integrity of tablet coatings are therefore important to maintain drug product quality attributes such as appearance and stability. Therefore, environmental conditions under which these coatings may crack are important to understand so as to prevent their occurrence. In this work, we present a novel computational framework to assess the mechanical integrity of tablet coatings exposed to rapid variations in environmental conditions. We perform detailed stress and strain analysis of tablet coatings on tablet surfaces with debossed regions and identify conditions for cracking for both elastic and viscoelastic coatings. Rapid changes in environmental temperature and humidity can cause differential expansion/contraction of coating and tablet core resulting in stresses that are many times more than those experienced during the drying process in a coater. Debossed regions on the tablet surface with sharp surface curvatures act as stress concentrators that may lead to coating cracks. Small changes in the design of the debossed regions lead to modest reductions in the peak stress. Stress calculations suggest that coating crack is much more likely when the coating delaminates from the surface of the tablet core.

The attached figure presents the stress distribution for a bi-convex tablet with the letter `0' debossed on the top surface of the tablet. (a) Maximum in-plane principal stress in the coating of the tablet with 0.24mm debossed depth and 0.2mm corner radius in the debossed letter. (b) Coating stresses after reducing the debossing depth to 0.14mm, while keeping the corner radius constant. (c) Coating stresses after increasing the corner radius to 0.4mm keeping the debossing depth at 0.24mm. (d) Coating stresses in the tablets with more rounded letter (or oval ‘0’) with a debossing depth of 0.24mm.