Formulation of salicylate-based poly(anhydride-ester) microspheres for short- and long-term salicylic acid delivery

The formulation of salicylate-based poly(anhydride-ester) (PAE) microspheres was optimized by altering polymer concentration and homogenization speed to improve the overall morphology. The microspheres were prepared using three salicylate-based PAEs with different chemical compositions comprised of either a heteroatomic, linear aliphatic, or branched aliphatic moiety. These PAEs broadened the range of complete salicylic acid release to now include days, weeks and months. The molecular weight (M(w)), polydispersity index (PDI) and glass transition temperature (T(g)) of the formulated polymers were compared to the unformulated polymers. In general, the M(w) and PDI exhibited decreased and increased values, respectively, after formulation, whereas the T(g) changes did not follow a specific trend. Microsphere size and morphology were determined using scanning electron microscopy. These microspheres exhibited smooth surfaces, no aggregation, and size distributions ranging from 2-34 m in diameter. In vitro release studies of the chemically incorporated salicylic acid displayed widely tunable release profiles.