Preparation and characterisation of controlled release co-spray dried drug–polymer microparticles for inhalation 1: Influence of polymer concentration on physical and in vitro characteristics

A series of co-spray dried microparticles containing di-sodium cromoglycate (DSCG) and polyvinyl alcohol (PVA – 0%, 30%, 50%, 70% and 90% w/w, respectively), were prepared as potential controlled release (CR) viscous/gelling vehicles for drug delivery to the respiratory tract. The microparticles were characterised in terms of particle size, crystal structure, density, surface morphology, moisture sorption, surface energy and in vitro aerosolisation efficiency. The co-spray dried particles were amorphous in nature and had spherical geometry. High-resolution atomic force microscopy analysis of the surfaces of the DSCG/PVA suggested no significant differences in roughness between microparticles containing 30–90% w/w PVA (ANOVA, p < 0.05), while no specific trend in either size or density was observed with respect to PVA concentration. In comparison, a linear decrease in the relative moisture sorption (R2 = 0.997) and concurrent increase in total surface free energy (R2 = 0.870) were observed as PVA concentration was increased. Furthermore a linear increase in the aerosolisation efficiency, measured by inertial impaction, was observed as PVA concentration was increased (R2 = 0.993). In addition, the increase in aerosolisation efficiency showed good correlation with equilibrium moisture content (R2 = 0.974) and surface energy measurement (R2 = 0.905). These relationships can be attributed to the complex interplay of particle forces at the contiguous interfaces in this particulate system.