HYDROPHOBICITY OF PROTEIN-COATED POLYMERS: QUANTITATION BY MEANS OF THE ADVANCING SOLIDIFICATION FRONT TECHNIQUE

ABSTRACT

The focus of this study was to establish whether the advancing solidification front technique could be used to quantitate the surface hydrophoblcity of protein-coated polymer materials. The method has the advantage that it allows a study of this question without having to expose the protein-coated particle to an air interface which would denature the adsorbed protein layer. We have also used the technique to establish whether substrates with different surface tensions would induce a different extent of conformational change in the adsorbed protein molecules. Such changes are reflected by differences in the surface tension of different substrate materials coated by one and the same protein. The results with a low bulk protein concentration (< 0.1%) show a decreasing surface tension of the adsorbed protein layer with increasing substrate hydrophoblcity, suggesting more extensive conformational changes on the more hydrophobic surfaces. At high bulk protein concentrations (0.5% and above) the surface tension of the adsorbed protein layer is independent of the substrate material. Advancing solidification front measurements with different proteins adsorbed onto one and the same substrate material, octylsepharose beads, indicate that the hydrophobicity of the protein coated sepharose increases in the following order:

Bovine albumin < Human albumin < IgG < Fibrinogen. These results are in good agreement with the relative hydrophobicity of these proteins determined by other techniques such as hydrophobic interaction chromatography, protein adsorption, two phase partition and contact angle determinations.