COMPARISON OF TETHERED STAR AND LINEAR POLY(ETHYLENE OXIDE) FOR CONTROL OF BIOMATERIALS SURFACE-PROPERTIES

Four different poly(ethylene oxide) [PEO] molecules were compared as g rafted polymer layers for biomaterials' substrates: two linear polymer s and two star polymers. Conditions maximizing surface coverage for ea ch molecule were employed with the aim of inhibiting protein adsorptio n and increasing the density of end groups. Neutron reflectivities of the grafted layers immersed in deuterium oxide (heavy water) were meas ured and used to calculate volume fraction profiles of the polymer as a function of distance from the surface. These density profiles were c ombined with protein adsorption data on the grafted layers to compare with recent theoretical and experimental studies of protein resistance by PEO at surfaces. We found that the grafting density is maximized b y coupling the linear PEO from a K2SO4 salt buffer, which is a poor so lvent for PEO. However, the grafting density of star PEO was maximized when no K2SO4 was used and the stars were dissolved near the overlap concentration. Concentration profiles obtained from the reflectivity d ata show that the hydrated polymers swell to similar to 10 times the d ried layer thickness and exhibit a low density (maximum volume fractio ns < 0.4 PEO) throughout the layer. The PEO surfaces obtained with bot h the star and linear polymers resisted adsorption of cytochrome-c and albumin except for a small amount of cytochrome-c adsorption on the s hort, many-armed star polymer surface. A hypothesis of adsorption on t he star polymer layer is presented and criteria for controlling recept or-mediated cell-substrate interactions by ligand-modified chain ends are discussed. (C) 1998 John Wiley & Sons, Inc.