Interfacial Properties of Mixed Polyethylene Glycol/Poly(<scp>d</scp>,<scp>l</scp>-lactide-<i>co</i>-glycolide) Films Spread at the Air/Water Interface

Abstract

The interfacial behavior and conformation of mixed films composed of poly(ethylene glycol) (PEG4000) and poly(d,l-lactide-co-glycolide) (PLGA) were studied. This was achieved by analyzing the isotherms and the dilatational rheological properties of the polymer films spread at the air/water interface and by performing atomic force microscopy (AFM) on the films after sampling on mica. The classical representation of molar fraction of mixtures against surface pressure deduced from the isotherms led us to conclude that PEG and PLGA were miscible in the mixed film at least in the range of pressure 0−7 mN/m. The viscoelastic properties of PEG were recovered in the mixed film with, however, a decrease of the relaxation time indicating the slower expulsion of PEG segments into the aqueous subphase. This was attributed to interpenetration of polymer segments in the plane of the interface. At higher surface coverage (12−15 mN/m), we demonstrated that PEG strongly influenced the behavior and the conformation of the PLGA. This was well supported by AFM images that indicated the presence of PEG segments between the PLGA ones. This led, for the mixed films, to large modification of the condensation properties of PLGA and gave rise to characteristic condensed patterns different from those observed in PLGA films. From the characterization of this simplified model, the anchoring of PEG in the PLGA film may constitute a suitable feature for the prevention of protein adsorption in the drug delivery systems formulated with those polymers.