Quantitative evaluation of interaction force of fibrinogen at well-defined surfaces with various structures

The effects of functional groups and structures at the surface of biomaterials on protein adsorption were examined using direct interaction force measurements. Three kinds of surface structures were evaluated: polymer brushes, self-assembled monolayers with low molecular weight compounds, and surfaces with conventional polymer coatings. These surfaces had various functional groups including phosphorylcholine (PC) group. The surface characterization demonstrated that surface wettability and flexibility depended on both the structure of the surface and the functional groups at the surface. The interactions of protein with these surfaces were evaluated by a force vs. distance curve using an atomic force microscope (AFM). We used fibrinogen as the protein, and the fibrinogen was immobilized on the surface of the AFM cantilever by a conventional technique. It was observed that the interaction force of fibrinogen was strongly related to surface hydrophobic nature and flexibility. That is, the interaction force increased with the increasing hydrophobic nature of the surface. The relationship between the amount of fibrinogen adsorbed on the surface and the interaction force showed good correlation in the range of fibrinogen adsorption from 0 to 250 ng/cm(2), that is, in a monolayered adsorption region. The interaction force decreased with increasing surface viscoelasticity. The most effective surface for preventing fibrinogen adsorption was the polymer brush surface with phosphorylcholine (PC) groups, that is, poly(2-methacryloyloxyethyl phosphorylcholine) brush. The interaction force of this sample was less than 0.1 nN and the amount of fibrinogen adsorbed on the surface was minimal. It was found that the evaluation of protein adsorption based on the interaction force measurement is useful for low-protein adsorption surfaces. It was demonstrated that an extremely hydrophilic and flexible surface could weaken the protein interactions at the surface, resulting in greater resistance to protein adsorption.