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Adsorption of poly(ethylene glycol)‐modified ribonuclease A to a poly(lactide‐ co ‐glycolide) surface
Author(s) -
Daly Susan M.,
Przybycien Todd M.,
Tilton Robert D.
Publication year - 2005
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.20481
Subject(s) - adsorption , rnase p , peg ratio , chemistry , ethylene glycol , protein adsorption , polyethylene glycol , ribonuclease , pegylation , polymer chemistry , total internal reflection fluorescence microscope , organic chemistry , biochemistry , rna , finance , economics , gene , membrane
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 ζ 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. © 2005 Wiley Periodicals, Inc.