Atomic Force Microscopy to Identify Dehydration Temperatures for Small Volumes of Active Pharmaceutical Ingredients

The environmental conditions associated with changing the hydration state of active pharmaceutical ingredients (API) are crucial to understanding their stability, bioperformance, and manufacturability. Identifying the dehydration event using < 1μg of material is an increasingly important challenge. Atomic Force Microscopy indentation mapping is implemented at controlled temperatures between 25-100°C, for nanoscale volumes of hydrated APIs exhibiting distinct dehydration behavior and anhydrous APIs as controls. For caffeine hydrate and azithromycin dihydrate, the relative mechanical modulus increases ~10-fold at dehydration temperatures. These are confirmed by conventional macroscopic measurements including Variable Temperature Powder X-ray Diffraction, Thermogravimetric Analysis, and Differential Scanning Calorimetry. Conversely, no such mechanical transition is observed for anhydrous ibuprofen or a proprietary anhydrous compound. AFM-based mechanical mapping is therefore demonstrated for small-volume determination of temperature-induced solid-state dehydration events, which may enable spatially or temporally mapping for future studies of dehydration mechanisms and kinetics, as a function of commercially relevant nanoscale heterogeneities.