Characterization of Protein Adsorption at the Phosphorylcholine Incorporated Polymer−Water Interface

We have studied the adsorption of a number of model proteins onto the surface of a cross-linkable hydrogel polymer incorporated with phosphorylcholine (PC) groups and dodecyl chains (PC 100B). The structure of the coated thin polymer film was determined by neutron reflection combined with spectroscopic ellipsometry. No measurable change in the thickness of the polymer film was detected within the experimental time scale of minutes when immersed in water, showing a fast water solubilization process. The polymer film at the solid−water interface was modeled using a single layer of 51 ± 3 Å with 40 ± 5% water, suggesting a uniform distribution of water across the polymer film. This film structure is in sharp contrast with the uneven swelling of the film formed from a different hydrogel polymer (PC 100A) which had a similar molar ratio of dodecyl chains and PC groups but did not contain any silyl groups as cross-linkers. The results hence suggest that the uniform structure of the PC 100B film is rendered by the formation of the silyl cross-linking network. The effectiveness of the PC 100B film at reducing protein adsorption under different solution conditions was subsequently characterized. Both neutron reflection and spectroscopic ellipsometry showed substantial reduction in protein adsorption on PC 100B. At the bulk protein concentration around 1 g dm-3 the surface excess was found to be less than 1 mg m-2 for lysozyme and fibrinogen at pH 7 and BSA at pH 5, while under the same solution conditions, the surface excess at the hydrophilic silicon oxide−water interface was 3.6 ± 0.3 mg m-2 for lysozyme, 6.0 ± 0.3 mg m-2 for fibrinogen, and 2.5 ± 0.3 mg m-2 for BSA. Despite the structural difference between the two coated polymer films, the residual level of protein adsorption was found to be comparable between the two PC polymer surfaces. The insensitivity of spectroscopic ellipsometry to the presence of a diffuse protein layer on the surface of the coated polymer films is also discussed.