title: Adsorption of poly(ethylene glycol)-modified ribonuclease A to a poly(lactide-co-glycolide) surface.
abstract: Protein adsorption is a source of variability in the release profiles of therapeutic proteins from biodegradable microspheres. We employ optical reflectometry and total internal reflection fluorescence to explore the extent and kinetics of ribonuclease A (RNase A) adsorption to spin-cast films of poly(lactide-co-glycolide) (PLG) and, in particular, to determine how covalent grafting of polyethylene glycol (PEG) to RNase A affects adsorption. Adsorption kinetics on PLG surfaces are surface-limited for RNase A but transport-limited for unconjugated PEG homopolymers and for PEG-modified RNase A, indicating that PEG anchors the conjugates to the surface during the transport-limited regime. PEG modification of RNase A decreases the total number of adsorbed molecules per unit area but increases the areal surface coverage because the grafted PEG chains exclude additional surface area. Total internal reflection fluorescence-based exchange measurements show that there is no exchange between adsorbed and solution-phase protein molecules. This indicates an unusually tenacious adsorption. Streaming current measurements indicate that the zeta potential of the PLG surface becomes increasingly negative as the film is exposed to water for several weeks, as expected. Aging of the PLG surface results in increased adsorption of unmodified RNase A but decreased adsorption of unconjugated PEG homopolymers and of PEG-RNase A conjugates, relative to the extent of adsorption on freshly prepared PLG surfaces. Adsorption results correlate well with an increase in the rate, total extent and preservation of bioactivity of RNase A released from PLG microspheres for the PEG-modified version of RNase A.
authors.affiliation: Departments of Chemical Engineering and Biomedical Engineering, Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Daly
authors.forename: Todd M
authors.initials: TM
authors.lastname: Przybycien
authors.forename: Robert D
authors.initials: RD
authors.lastname: Tilton
mesh_terms: D000327:Adsorption; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D004058:Diffusion; D004337:Drug Carriers / Q000737:chemistry; D004355:Drug Stability; D004789:Enzyme Activation; D007700:Kinetics; D019344:Lactic Acid / Q000737:chemistry*; D008422:Materials Testing; D011092:Polyethylene Glycols / Q000737:chemistry*; D011100:Polyglycolic Acid / Q000737:chemistry*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry*; D011485:Protein Binding; D012259:Ribonuclease, Pancreatic / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D020099:Coated Materials, Biocompatible; D004337:Drug Carriers; D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; D011092:Polyethylene Glycols; D012259:Ribonuclease, Pancreatic