THE ADSORPTION OF POLY(VINYL ALCOHOL) TO BIODEGRADABLE MICROPARTICLESSTUDIED BY X-RAY PHOTOELECTRON-SPECTROSCOPY (XPS)

The design of biodegradable microparticle drug delivery systems with p recisely tailored surface properties requires surface analytical metho ds that can relate polymer chemistry and fabrication parameters to the final surface chemistry of the microparticles. We demonstrate using X -ray photoelectron spectroscopy (XPS) that it is possible to identify significant variations in the surface chemistry of microparticles comp osed of poly(lactic acid) (PLA), poly(lactide-co-glycolide) (PLGA), or block copolymers of PLA or PLGA with poly(ethylene glycol) (PEG). The se variations are related to the mechanism by which the microparticle/ water interface is stabilized. This, in turn, is controlled by the int erfacial surface tensions of the polymers within aqueous environments. For PEG containing block copolymers, adsorption of a surfactant, poly (vinyl alcohol) (PVA), from the aqueous medium onto the polymer is red uced compared with the PLA and PLGA polymers. This reduction is achiev ed because the PEG segments, within the copolymer structure, stabilize the polymer/water interface. Estimates of the relative amounts of lac tide, lactide-co-glycolide, vinyl alcohol, and ethylene glycol monomer units at the microparticle surfaces are presented based on curve-fitt ing analysis of the XPS data. (C) 1997 Academic Press