Digital Pulsed Force Mode AFM and Confocal Raman Microscopy in Drug-Eluting Coatings Research

Abstract

Controlled release of amorphous drug from a polymer matrix depends intimately upon the degree of mixing of drug and polymer, the susceptibility of the drug to crystallization, and the ability of the drug to dissolve and diffuse through water-swollen polymer. Characterization methods ideally would follow these processes on the molecular level in situ and in real time. We move closer to this ideal state of characterization through application of two imaging methods: digital pulsed force mode atomic force microscopy (D-PFM AFM) and confocal Raman microscopy (CRM). We examine model spin-coated films ~1 μm thick containing the drug dexamethasone dispersed in poly(n-alkyl methacrylate) homopolymer and blend coatings. We report aqueous-immersion studies of surface and subsurface structural changes due to drug elution over time frames ranging from very fast (a few minutes) to slow (tens of hours).