App116 Dynamic Vapor Sorption as a PAT Tool to Assess Tablet Coating
This application note from Surface Measurement Systems and Solvay Advanced Polymers demonstrates how Dynamic Vapor Sorption (DVS) can be employed as a Process Analytical Technology (PAT) to evaluate the moisture‑barrier performance of pharmaceutical tablet film coatings. The study focuses on two commercially used PVA‑based coatings, Opadry AMB and Opadry II, and investigates how formulation composition, coating thickness, and processing conditions affect moisture uptake. Four coating trials were conducted at Colorcon, varying wet vs. dry coating, atomizing air pressure, pattern air pressure, pan speed, and airflow, with and without sub‑coats. Tablets were characterized using DVS (sorption isotherms, kinetics, diffusion coefficients), Karl Fischer titration, videoscope imaging, and cross‑sectional microscopy. Results show that Opadry II provides a superior moisture barrier, reflected in lower equilibrium mass gains, smaller diffusion coefficients, and reduced weight gain after accelerated storage (40 °C/75 % RH). Thinner coatings and incomplete coverage lead to higher moisture uptake, underscoring the importance of coating thickness and uniformity. The note concludes that DVS offers rapid, sensitive, quantitative insight into coating integrity, enabling definition of design space, identification of critical process parameters, and optimization of coating systems during drug development.
Topics
Moisture‑Sensitive Tablet Coatings: Functional Role and Quality Impact
Explains why film coatings are critical for protecting moisture‑sensitive APIs, influencing product safety, efficacy, and regulatory compliance.
Opadry AMB vs. Opadry II: Formulation Chemistry and Expected Barrier Mechanisms
Compares the two PVA‑based coating systems, highlighting Opadry II’s PEG‑free formulation and anticipated superior water‑vapor resistance.
Limitations of Conventional Moisture Assessment and Rationale for DVS as a PAT Tool
Critiques long‑term weight gain and Karl Fischer methods, introducing DVS as a rapid gravimetric technique that captures sorption isotherms, kinetics, and diffusion.
Experimental Design: Coating Trials, Process Variables, and Complementary Analytical Techniques
Details the four coating trials (wet/dry, sub‑coat presence, atomizing air pressure, pattern air pressure, pan speed, airflow) and the suite of measurements (DVS, Karl Fischer, videoscope imaging, cross‑sectional microscopy).
DVS Sorption Isotherms and Kinetic Profiles: Quantitative Comparison of Coating Systems
Presents the mass‑change curves and equilibrium plateaus at 60 % RH, showing higher moisture uptake for Opadry AMB‑based tablets versus Opadry II‑based tablets.
Coating Thickness and Process Conditions as Determinants of Moisture Uptake
Links measured coating thickness (via cross‑sectional videoscope) to observed mass gains, demonstrating that thinner or partially covered coatings increase water ingress.
Diffusion Coefficient Calculation from Early‑Time DVS Data and Comparative Results
Explains the use of the Crank‑Park equation to derive D from early‑time sorption, reporting values (10⁻¹⁰–10⁻¹¹ cm²/s) that consistently favor Opadry II over Opadry AMB.
Concluding Evidence: Opadry II Superior Moisture Barrier and DVS Value as a PAT Tool
Synthesizes all data (isotherms, diffusion, thickness, accelerated storage) to assert Opadry II’s advantage and the utility of DVS for design‑space definition and CPP identification.