Surface characterization of polylactide/ polyglycolide copolymers

Abstract

The wettability and the surface composition of biodegradable polymers used as drug delivery particles were determined and compared. Films of poly(lactic acid), poly(glycolic acid), and their copolymers with four different lactide/ glycolide ratios of 85/15, 75/25, 65/35 and 50/50 were formed by solvent-casting on polar (silicon wafer, glass and mica) substrates. Advancing and receding water contact angles were measured goniometrically and also by using the automated axisymmetric drop shape analysis method. Both the advancing and the receding water contact angles of the copolymers were higher than was expected from the values obtained for the two homopolymers considering the increasing glycolide content of the copolymers. Surface analysis of the polyester films was performed by X-ray photoelectron spectroscopy at various takeoff angles to get information on the depth distribution of the components. Surface enrichment of the nonpolar (lactide) component in the outermost layer of the copolymer films was detected. The wettability behavior was in accordance with the surface composition results, suggesting a surface activity effect resulting in the orientation of the nonpolar segments of the copolymer chains towards the surface of the film and hence producing more hydrophobic character for the copolymer films than should be due to their bulk composition.