The control of biofouling, which is the unwanted adsorption of biomolecules and organisms on solid surfaces, is a prerequisite for wider applicability of the functional materials that are currently being used in biomedical industries. One of the frequently used methods for controlling biofouling is the use of surface coatings with antifouling materials. Herein, fucoidan, which is a marine-derived polysaccharide, is reported as a new type of antifouling material that is safe and broadly applicable. Fucoidan is conjugated with catechols, which are known to act as adhesives for grafting functional molecules onto solid substrates. Fucoidan catechol (FD-C) is subsequently utilized for robust fucoidan coatings of solid substrates, and the FD-C-coated surfaces show excellent antifouling capability for fouling organisms, including platelets and bacteria. The FD-C coating is also confirmed to be nonirritating upon skin contact, demonstrating its potential use in public places for inhibiting contagions.
Curry stains on clothes and dishes in daily life inspired us to investigate the potential use of turmeric powder, the major ingredient in curry, as a universal coating material. After condition optimization, the coating solution was made by boiling and filtering a turmeric slurry, and the coating was formed at pH 3, leading to the formation of ultrathin, transparent films. Various inorganic and polymeric substrates were successfully coated with turmeric-based materials, including gold, TiO, SiO, glass, stainless steel, indium tin oxide, nylon, polyethylene, polycarbonate, polypropylene, acryl, and poly(ethylene terephthalate). The turmeric-based coating was also applied to poly(tetrafluoroethylene) (PTFE, Teflon) and cyclic olefin copolymer (COC), and after double dip-coating, the water contact angle was changed from 118.2° to 49.1° for PTFE and from 91.2° to 44.7° for COC. The water contact angles for the other substrates converged to 35° after coating, confirming the substrate-independent universal coating capability of turmeric. The X-ray photoelectron spectroscopic analysis indicated the presence of nitrogen in the film, and the possible involvement of amines in film formation was investigated with several amine compounds.
Catechols are prone to oxidative polymerization as well as complex formation with metal ions. These two features of catechols have played an important role in the construction of functional films on various surfaces. For example, marine antifouling films and antibacterial films were successfully prepared by oxidative polymerization and metal complexation of catechol-containing molecules, respectively. However, the effect of simultaneous metal complexation and oxidative polymerization on functional film formation has not yet been fully investigated. Herein, as a derivative of 3-(3,4dihydroxyphenyl)-L-alanine (DOPA), we synthesized an ethylene glycol-derivatized DOPA (OEG-DOPA) and formed OEG-DOPA thin films based on (1) oxidative polymerization and (2) the complexation between catechol groups of OEG-DOPA and iron(III) (Fe III ) ions. Either or both approaches were used for the film formation. OEG-DOPA film formation was characterized by ellipsometry, contact angle goniometry, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Among the conditions used, the formation of a uniform film was only achieved with the dual cross-linking system of Fe III complexation and oxidation-induced covalent bond formation. Compared to the uncoated substrate and other OEG-DOPA films prepared under different conditions, the uniform OEG-DOPA film strongly inhibited bacterial adhesion, showing excellent antibacterial capability. We think that our surface-coating strategy can be applied to medical devices, tools, and implants where bacterial adhesion and biofilm formation should be prevented. This work can also serve as a basis for the construction of functional thin films for other catechol-functionalized materials.
Catechol and/or pyrogallol groups are recognized as crucial for the formation of polyphenol coatings on various substrates. Meanwhile, studies on polyphenolic molecules that do not contain such groups are relatively rare.The key molecule in turmeric-based universal (i.e., substrate-independent) coatings is curcumin, which contains no catechol or pyrogallol groups. As chemically reactive hydroxyl groups would remain after curcumin coating, it is hypothesized that curcumin coating can serve as a reactive layer for controlling interfacial properties. In this study, a curcumin-based surface modification method is developed to graft polymer brushes from various substrates, including titanium dioxide, gold, glass, stainless steel, and nylon. 𝜶-Bromoisobutyryl bromide (BiBB), a polymerization initiator, is introduced to the curcumin-coated substrates via esterification; subsequently, poly(oligo(ethylene glycol) methacrylate) (poly(OEGMA)) is grafted from the surfaces. Compared to the control surfaces, poly(OEGMA)-grafted surfaces significantly suppress bacterial adhesion by up to 99.4%, demonstrating their antibacterial properties. Considering its facile and versatile surface modification, curcumin-based polymer grafting can be an efficient method for controlling the chemical/physical properties of surfaces in a substrate-independent manner.
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