Development of surface-attached thin film of non-fouling hydrogel from poly(2-oxazoline)

Abstract

In this study poly(2-ethyl-2-oxazoline) (PEOXA) chains that contains 11 mol% of benzophenone molecules was synthesized and coated on either 3-ethoxybenzophenonesilane-modified inorganic or bare organic substrates. Upon irradiation under UV light, the photo-active benzophenone molecules enabled the formation of polymer network as well as attachment of the polymer network onto the substrates. Important variables for the generation of hydrogel film with high gel content and stability, such as the heat treatment for solvent removal, the UV wavelength (that determines the irradiation energy), and the input of energy dose were varied and their influence to the gel content and stability of the hydrogel film was studied. The thickness, lifetime of benzophenone, and chemical composition of the film were determined using ellipsometry, UV/Vis spectroscopy, and XPS methods, respectively. On a film that has been exposed to physiological buffer for 14 days, XPS results indicated that chemical degradation of the copolymer did not take place. Ellipsometry results, however, indicated that some portion of the film detached and the remaining thickness was dependent on the input of energy dose during the hydrogel preparation. It was shown that when suitable conditions are applied during preparation, a stable surface-attached PEOXA-based hydrogel, i.e. approximately 78% gel content and 75–90% stability after 30 days of incubation in physiological buffer, could be generated on the surface. Dry and swollen thicknesses of the stable surface-attached film measured from AFM experiments revealed a swelling factor of 1.7. Furthermore, the AFM morphology image showed a homogenous polymer film with an average roughness of 30 nm. Protein adsorption test revealed that the resulting surface-attached PEOXA-based hydrogel film on PMMA substrate hinders BSA adsorption to the same extent as the reference system generated from benzophenone-bearing poly(dimethylacrylamide) (PDMAA).

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