Investigations into the structure and composition of beta-cyclodextrin/poly(acrylic acid) microspheres

Microspheres composed of the hydrophilic polymer poly(acrylic acid) (PAA), with and without beta-cyclodextrin (beta-CD), were prepared by a water-in-oil (w/o) solvent evaporation technique. Microspheres were characterised for particle size, beta-CD and residual oil content. The type of matrix formed during microsphere synthesis was investigated by solid state carbon 13C NMR, in vitro release of beta-CD and swelling measurements. A high encapsulation efficiency of the beta-CD was observed (?90%). The in vitro release of beta-CD in water over 24 h was initially rapid ( approximately 70% in 3 h) with no further loss thereafter, suggesting potential covalent binding of the residual beta-CD. NMR indicated that in the presence of beta-CD, two concomitant chemical processes occur during microsphere synthesis: (i) esterification of the hydroxyl group(s) of the beta-CD with the carboxylic acid groups of the PAA; and (ii) the formation of intra-/inter-polymer acid anhydrides.