Microorganism including bacteria can strongly adhere to solid surfaces and form biofilm. Biofilm can serve as a reservoir to release harmful microorganisms and can cause chronic inflammation upon contact. There has been many medical cases to report that biofilm is one of main causes to bring about health care associated infections. To deal with biofilm-related infections, in the first study, we synthesized a zwitterionic 3,4-dihydroxy-L-phenylalanine (L-DOPA) derivative (ZW-DOPA) as a sulfobetaine form containing both catechol and amine groups. Various substrates such as gold, stainless steel, and nylon were coated with ZW-DOPA. The surface coatings were characterized by ellipsometer, contact angle goniometry, and X-ray photoelectron spectroscopy, demonstrating the successful ZW-DOPA coatings. Interestingly, the static water contact angles of ZW-DOPA coated substrates converged to 11°, regardless of the initial values of uncoated substrates, clearly showing the substrate-independent coating capability of ZW-DOPA. Compared to the control (i.e., uncoated substrates), the ZW-DOPA-coated substrates showed antibacterial effects by inhibiting more than 90% of bacterial adsorption on the surface.
In the second study, we further employed sulfebetaine zwitterionic polymers to develop antiplatelet coatings. It has been known that platelet adhesion and its excessive accumulation can cause blood coagulation. However, the unnecessary blood coagulation has been a critical issue for blood-contact medical devices. For example, unnecessary blood coagulation on vascular stents can lead to blockage of blood flow and blood vessel destruction. In addition, medical devices inserted into the body may lose their function. To solve this problem, we aim to develop the functional coatings for preventing platelet adhesion/aggregation by grafting zwitterionic sulfobetaine polymer, poly((3-methacryloylamino)propyl-dimethyl(3-sulfopropyl)ammonium hydroxide) (Poly(MPDSAH)) onto titanium (Ti/TiO2) substrate that is a common material for biomedical applications. The polymerization was carried out by activators regenerated by electron transfer for atom transfer radical polymerization. The polymer grafting process was developed as a substrate-independent manner by using polyphenol chemistry. The polymer grafting was characterized by ellipsometry, contact angle goniometry, atomic force microscopy and X-ray photoelectron spectroscopy. After poly(MPDSAH) grafting from Ti/TiO2 substrate, the substrate became very hydrophilic, allowing the formation of strong hydration layer onto the surface. The poly(MPDSAH)-grafted substrate showed the strong resistance to nonspecific adsorption of fibrinogen, a main responsible protein for thrombus formation. Compared to bare and polyphenol-coated substrates, poly(MPDSAH)-grafted substrate suppressed more than 70% of fibrinogen adsorption. Furthermore, the polymer-coated substrate could prevent platelet adhesion/cohesiveness, showing more than 99% inhibition, compared to the controls.