AVS 53rd International Symposium
    Biomaterial Interfaces Wednesday Sessions
       Session BI-WeA

Paper BI-WeA8
Bridging Interactions beween Silica and Grafted PEO Surfaces

Wednesday, November 15, 2006, 4:20 pm, Room 2014

Session: Bio-Interfacial Modification and Bio-Immobilization II (Honoring Marcus Textor, ETH-Zürich for Substantial Contributions to the Field)
Presenter: L. Meagher, CSIRO Molecular and Health Technologies, Australia
Authors: L. Meagher, CSIRO Molecular and Health Technologies, Australia
P. Hamilton-Brown, CSIRO Molecular and Health Technologies, Australia
A. Tarasova, CSIRO Molecular and Health Technologies, Australia
H.J. Griesser, University of South Australia
Correspondent: Click to Email
Covalently grafted, functionalized polymer layers are of increasing technological interest, e.g. attaching molecules or proteins to the terminal functional group. One of the most widely studied is biotin terminated poly(ethylene oxide), which allows for specific attachment of biotin binding proteins. If densely grafted, these layers have the additional benefit of low non-specific interactions with proteins. One way of characterizing these layers is by direct interaction force measurements. Generally, it is assumed that the interactions between solid surfaces and such polymer layers are repulsive due to confinement of the polymer layer by the probe surface. In this study, we have used a combination of XPS and AFM interaction force measurements to characterize surfaces with covalently grafted PEO layers of different grafting density and functional end group. The surfaces were prepared using cloud point grafting of functionalised PEO molecules onto amine plasma polymers. Where the PEO coupling density was low, long ranged attractive polymer bridging forces were obtained between the PEO coated surfaces and AFM tips modified with silica particles in 0.15 M NaCl solutions. The range and magnitude of the forces were correlated with the grafting density of the PEO molecules, lower densities giving longer ranged, more attractive forces, and the molecular weight of the covalently attached PEO molecules. Long ranged attractive forces were also observed between silica and densely grafted layers with a small proportion of incorporated larger molecular weight chains, in an analogous fashion that those obtained for low grafting density, mono-dispersed layers. The origin of the attractive forces was related to the adsorption of PEO molecules onto the silica surface on approach, with more molecules adsorbing at smaller separation distances. This mechanism was verified by modification of the opposing surface and by specific coupling of NeutrAvidin to the grafted layer.