The design of biodegradable microparticle drug delivery systems croparticle surface and it has been proposed that the reducwith precisely tailored surface properties requires surface analytition of this adsorption or the alteration of the composition cal methods that can relate polymer chemistry and fabrication of the adsorbed protein layer may provide a general method parameters to the final surface chemistry of the microparticles.
of avoiding phagocytosis by the RES. Attention has, there-We demonstrate using X-ray photoelectron spectroscopy (XPS) fore, been directed towards methods of engineering microthat it is possible to identify significant variations in the surface particle surfaces with the aim of controlling protein adsorpchemistry of microparticles composed of poly(lactic acid) (PLA), tion events. A highly successful approach to achieve this poly(lactide-co-glycolide) (PLGA), or block copolymers of PLA or PLGA with poly(ethylene glycol) (PEG). These variations are surface engineering is the adsorption of a hydrophilic materelated to the mechanism by which the microparticle/water interrial to the microparticle surface (6-9). Early studies in this face is stabilized. This, in turn, is controlled by the interfacial field concentrated on the use of poly(ethylene glycol) surface tensions of the polymers within aqueous environments. (PEG)-poly(propylene oxide) (PPO) block copolymers to For PEG containing block copolymers, adsorption of a surfactant, coat polystyrene particles (6, 7). For example, Illum et al. poly(vinyl alcohol) (PVA), from the aqueous medium onto the demonstrated the reduction of RES uptake of poloxamine polymer is reduced compared with the PLA and PLGA polymers. coated microparticles and, hence, extended residence times This reduction is achieved because the PEG segments, within the in the vascular compartment (6). Recently, block copolymers copolymer structure, stabilize the polymer/water interface. Estiof PEG and poly(lactic acid) (PLA) have been physically mates of the relative amounts of lactide, lactide-co-glycolide, vinyl alcohol, and ethylene glycol monomer units at the microparticle entrapped in poly(lactide-co-glycolide) (PLGA) microparsurfaces are presented based on curve-fitting analysis of the XPS ticle surfaces giving these biodegradable microparticles the data. แญง 1997 Academic Press same ability to avoid the RES (8, 9). Adsorption of proteins, Key Words: Poly(lactic acid) (PLA); poly(lactide-co-glycolide) such as albumin, to PLGA microparticles also significantly (PLGA); poly(ethylene glycol) (PEG); poly(vinyl alcohol) (PVA); decreases phagocytosis (10, 11). X-ray photoelectron spectroscopy (XPS); microparticles.
An alternative approach to polymer adsorption is the incorporation of hydrophilic block segments into the backbone structure of the biodegradable polymer used for micropar-