Construction Of Phenolics Functional Coatings Through Spraying Layer-by-layer Assembly

The demand for biomedical materials, or biomaterials, has been growing rapidly with the development of the society. Surface functional coating of biomaterials plays an important role in improving the interactions between materials and the bodies. Bionic phenolics such as polydopamine and tannic acid have great application prospects in the field of functional surface coating of biomaterials due to their good biocompatibilities, wide-range adhesivity and secondary reaction activity. However, the conventional preparation methods of phenolics coatings such as the aerobic auto-oxidation polymerization method are less controllable and also time-consuming, which limits its use in preparing coatings rapidly and controllably. Based on its merits of mild preparing conditions, easy operation, adjustable components and properties and large area coating, spraying layer-by-layer assembly technique has unique superiority in the field of surface functional coating of biomaterials for promoting its rapid and controllable fabrication as well as its industrialization.In this paper, inspired by marine animals, a universal strategy of construction of composite coatings based on phenolics was provided. Taking advantage of the pH-dependent coordinating crosslinking interaction between phenolics and metal ions, (phenolics-Fe3+/polyelectrolyte) coatings were constructed with phenolics-Fe3+ complexes and an amino polyelectrolyte through a spraying layer-by-layer assembly technique and were functionalized afterward. Four core problems were studied including the impacts of driving force to the coating’s assembling behaviour, construction conditions to the coating’s performance, surface morphology and chemical components to presentation of the coating’s funtions and the coating’s application potential in the field of functional coatings of biomaterials. Two systems were studied as follows.Polydopamine, a synthetic polyphenol, was firstly studied in this paper. Polydopamine, with carbon nanotubes as carriers (CNTs@PDA), was coordinated with ferric ions (Fe3+) and assembled with amino polyethyleneimine (PEI) through a spraying layer-by-layer assembly technique constructing a (CNTs@PDA-Fe3+/PEI) coating rapidly. DLS size and Zeta potential experiments indicated that after coordinating with Fe3+, CNTs@PDA presented a pH responsive crosslinking ability. Ellipsometry and SEM showed that taking advantage of this ability, the coating was successfully constructed by pH-switched assembly method. The thickness and surface morphology of the coatings can be adjusted and controlled by the factors such as the concentration of Fe3+ and bilayer numbers. Contact angle measurements showed that by taking advantage of the micro-/nano-structures, the coating was turned to present a superhydrophobic property by modification with a fluorosilane. EDTA immersing stable experiment indicated that the superhydrophobic coating has good stability and has a potential in self-cleaning coating application.To verify the generality of this assembling strategy, a natural polyphenol, tannic acid (TA), was studied using as an assembling component. A (TA-Fe3+/PEI) functional coating was successfully and rapidly constructed by combining TA-Fe3+ complex and amino PEI through the spraying layer-by-layer assembly method. DLS size, TEM, UV-vis spectroscopy and contact angle (CA) measurements indicated that TA and Fe3+ formed stable complex particle suspensions and that their coordinating stoichiometric ratio was increased leading to a high crosslinking state during the assembly. The thickness, surface morphology and the wettability of the coatings were able to be controlled by adjusting assembly conditions such as concentration of Fe3+, rinsing step and bilayer numbers. In the aspect of functionalization, CA measurements showed that a self-cleaning superhydrophobic surface was prepared by modifying the coating with a fluorosilane. E. coli antibacterial assays, UV-vis spectroscopy and SEM proved that the (TA-Fe3+/PEI) coating had a certain ability of contact killing bacteria. The coating was further improved to present Ag+ releasing bactericidal ability after reducing Ag nanoparticles in situ by simply immersing the coating in AgNO3 aqueous solutions, showing a good potential in antibacterial coating applications. Moreover, the coating was easily coated on a commercial non-woven fabrics mask uniformly showing a great potential in anti-biofouling and anti-infective coatings of biomaterials.