Abstract
Antifouling technique has been developed for over two decades and used in many biomedical and engineering applications ranging from contact lenses to marine coating. Among so many different antifouling materials, zwitterionic antifouling materials attract growing attentions around the world because their prefect protein-resistance and hemocompatibility. The structure of zwitterionic materials, bio-inspired from cell membranes, is similar to phosphatidylcholine, which contains positive and negative charges and thus can strongly bind with water molecules and form a hydration layer by electrostatically induced interaction, resulting in highly resistant to protein adsorption. Yet, a zwitterionic-polymer modified surface will become too hydrophilic and promote dirt adhesion or surface contamination much easier in air; herein, there appears a great demand on developing an air-stable zwitterionic material. On the other hand, to develop such zwitterionic material should achieve super-low fouling level as well. To approach these two requirements, in this work, we successfully synthesize and characterize a new zwitterionic material, zwitterionic 4-vinylpyridine carboxybetaine (z4VP) and then grafted zwitterionic poly(4-vinylpyridine carboxybetaine) (zP4VP) brushes from a gold surface via surface-initiated atom transfer radical polymerization (SI-ATRP) to reduce nonspecific protein adsorption and blood cell attachment. Besides, by changing different parameters of SI-ATRP such as a monomer concentration and ionic strength of a solvent, we obtained the optimized conditions for antifouling performance of the zP4VP system. In addition, to measure protein adsorption, we employ surface plasmon resonance (SPR) and the results suggest that the zP4VP surface can indeed reduce protein adsorption down to 7.5 ng/cm2, a super-low fouling level. The consistent results of platelets and blood cell attachment on the zP4VP surface observed by a confocal laser scanning microscopy (CLSM) are also provided to further confirm the antifouling performance of the zP4VP surface. Further, an oil contact angle of both the zP4VP surface and well-known poly(sulfobetaine methacrylate) (PSBMA) surface in the water is around 130 degrees which reveals a low interfacial energy in the water and explains their high hydrophilicity to resist protein adsorption. On the other hand, the zP4VP surface with a water contact angle (CA) around 80 degrees indicates the surface energy of the zP4VP surface is lower than the PSBMA surface (~6 degree) in the air. As a result, we claim that the zP4VP surface indeed exhibits the air-stable property. With the abovementioned properties of the z4VP, we summarize that the zP4VP surface not only exhibits a similar antifouling capability compared to the PSBMA surface in the water but also possesses relatively higher air-stable characterization than the PSBMA surface evidenced by both SPR and CA measurement.