AVS 47th International Symposium
    Biomaterial Interfaces Wednesday Sessions
       Session BI+SS-WeM

Paper BI+SS-WeM3
Neutron Reflectivity Studies on the Interaction of Water with Biocompatible Monolayer Films

Wednesday, October 4, 2000, 9:00 am, Room 202

Session: Water at Biointerfaces
Presenter: D. Schwendel, University of Heidelberg, Germany
Authors: D. Schwendel, University of Heidelberg, Germany
R. Steitz, Hahn-Meitner Institute, Germany
J. Pipper, University of Heidelberg, Germany
R. Dahint, University of Heidelberg, Germany
M. Grunze, University of Heidelberg, Germany
Correspondent: Click to Email
Since the early 1990s protein resistance has been obtained for surfaces coated with poly- or oligo(ethylene glycol) (PEG or OEG) derivatives ((CH@sub2@-CH@sub2@-O)@subn@). While the inertness of PEG has been explained by the steric repulsion theory associating the inertness of the polymer brushes with the high conformational freedom of PEG chains in the near surface region, FT-IRRAS studies related the protein resistance of OEG to its molecular conformation. Whereas the helical and amorphous conformers on Au are inert towards protein adsorption, the planar all-trans conformer on Ag does adsorb protein. In Small Angle Neutron Scattering (SANS) studies we found experimental evidence for a strongly bound water layer on helical OEG-terminated alkanethiolate self assembling monolayers (SAMs). The experimental observations have been predicted by ab initio calculations simulating the adsorption of water molecules on methoxy terminated OEG with 3 EG units (EG3-OMe) and Monte Carlo simulations of water close to the SAM surfaces. Both theoretical studies postulate easy accommodation of water at helical OEG strands and a lower density of water near the SAM surface. This strongly bound water film is identified as the physical cause that these surfaces are inert against protein adsorption and cell attachment. SANS studies showed that the data for a hydroxy terminated helical OEG-SAM with 6 EG units (EG6-OH) on Au correlate satisfactorily with the model assuming a boundary water layer of 56 Å at the solid/liquid interface with a density of 92 % of that of bulk water. Also for the investigation of amorphous EG3-OMe immobilized on Au the assumption of a 36 Å water layer with a density of 78 % compared to bulk D@sub2@O yielded a much lower @chi@@super2@ deviation between the experimental data and the fit than the assumption of no interphase water.