[
    {
        "id": 1,
        "chunk": "# Material-Independent Surface Chemistry beyond Polydopamine Coating  \n\nHaesung A. Lee,† Yanfei Ma,‡,§ Feng Zhou,\\*,‡,∥ Seonki Hong, $\\ast,\\bot\\textcircled{\\dag}$ and Haeshin Lee\\*,†  \n\n†Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), 291 University Road, Daejeon 34141,   \nSouth Korea   \n‡State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000,   \nChina   \n§University of Chinese Academy of Sciences, Beijing 100049, China   \n∥State Key Laboratory of Solidification Processing, College of Materials Science and Technology, Northwestern Polytechnical   \nUniversity, 127 YouyiXi Road, Xi’an 710072, China   \n⊥Department of Emerging Materials Science, Daegu Gyeongbuk Institute of Science and Technology (DGIST), 333 Techno   \nJungang-daero, Daegu 42988, South Korea  \n\n![](images/5a5cdf2b531f44cb5c329e92a716cdbfe07351cdc688a6f1e34dc8459672d9fd.jpg)  \n\nCONSPECTUS: Various methods have been developed in surface chemistry to control interface properties of a solid material. A selection rule among surface chemistries is compatibility between a surface functionalization tool and a target material. For example, alkanethiol deposition on noble metal surfaces, widely known as the formation of a self-assembled monolayer (SAM), cannot be performed on oxide material surfaces. One must choose organosilane molecules to functionalize oxide surfaces. Thus, the surface chemistry strictly depends on the properties of the surface. Polydopamine coating is now generally accepted as the first toolbox for functionalization of virtually any material surface. Layer-by-layer (LbL) assembly is a widely used method to modify properties of versatile surfaces, including organic materials, metal oxides, and noble metals, along with polydopamine coating. On flat solid substrates, the two chemistries of polydopamine coating and LbL assembly provide similar levels of surface modifications. However, there are additional distinct features in polydopamine. First, polydopamine coating is effective for two- or three-dimensional porous materials such as metal−organic frameworks (MOFs), synthetic polyolefin membranes, and others because small-sized dopamine $\\mathrm{'MW}=153.18~\\mathrm{u},$ ) and its oxidized oligomers are readily attached onto narrow-spaced surfaces without exhibiting steric hindrance. In contrast, polymers used in LbL assembly are slow in diffusion because of steric hindrance due to their high molecular weight. Second, it is applicable to structurally nonflat surfaces showing special wettability such as superhydrophobicity or superoleophobicity. Third, a nonconducting, insulating polydopamine layer can be converted to be a conducting layer by pyrolysis. The product after pyrolysis is a N-doped graphene-like material that is useful for graphene or carbon nanotube-containing composites. Fourth, it is a suitable method for engineering the surface properties of various composite materials. The surface properties of participating components in composite materials can be unified by polydopamine coating with a simple one-step process. Fifth, a polydopamine layer exhibits intrinsic chemical reactivity by the presence of catecholquinone moieties and catechol radical species on surfaces. Nucleophiles such as amine and thiolate spontaneously react with the functionalized layer.  \n\nApplications of polydopamine coating are exponentially growing and include cell culture/patterning, microfluidics, antimicrobial surfaces, tissue engineering, drug delivery systems, photothermal therapy, immobilization of photocatalysts, Li-ion battery membranes, Li−sulfur battery cathode materials, oil/water separation, water detoxification, organocatalysts, membrane separation technologies, carbonization, and others. In this Account, we describe various polydopamine coating methods and then introduce a number of chemical derivatives of dopamine that will open further development of material-independent surface chemistry.",
        "category": " Abstract"
    },
    {
        "id": 2,
        "chunk": "# 1. ADVANCES IN POLYDOPAMINE COATING TECHNIQUES",
        "category": " Introduction"
    },
    {
        "id": 3,
        "chunk": "# 1.1. Understanding the Formation of Polydopamine  \n\nUnderstanding the chemistry of polydopamine formation is a challenging subject despite the extensive studies over a decade because of its chemical diversity and heterogeneity. A consensus in polydopamine chemistry begins with spontaneous oxidation of dopamine to dopamine quinone followed by further oxidative conversion to 3,4-dihydroxyindole (DHI), which is considered as an acceptable pathway for a polydopamine monomer since 2007.1 However, recent studies have proposed the existence of other intermediates in polydopamine formation: (1) there is always found to be a detectable level of uncyclized dopamine monomer (i.e., the presence of $\\mathrm{-NH}_{2,}^{\\cdot}$ ) in polydopamine chains,2,3 which indicates that the conversion yield from dopamine to DHI is not $100\\%$ (various reactions are discussed in sections 1.2 and 1.3); (2) DHI alone is insufficient for coating;4 (3) degradation of a catechol ring generates pyrroles with carboxylic acid in polydopamine;5,6 (4) DHI−dopamine oligomer intermediates participate in diverse non-covalent interactions (details are provided in section 1.1.2).2,7 Therefore, supramolecular assembly of various combinations of DHI-, dopamine-, and pyrrole-containing oligomers is a current structural insight for polydopamine. Thus, further understanding of the chemical diversity of oligomers that constitute polydopamine is critical in the future. Questions related to the topic include identifications of major repeating units in oligomers and molecular weight distributions. Finally, mechanisms to drive assembly of the oligomers should be address. In sections 1.1.1 and 1.1.2 we introduce a few very recent studies that address these questions related to polydopamine formation.  \n\n![](images/d123b7019d1fa30fddb109295106bea2d16266eb3c9a0a40aae59f423c0097e4.jpg)  \nFigure 1. Programmable disassembly and reassembly of polydopamine coatings by alternating non-covalent and cation $-\\pi$ interactions between oligomers. Adapted from ref 7.  \n\n1.1.1. Synergistic Effect of Amine and Catechol in Material Independence. Polydopamine coating is the first reported material-independent surface chemistry that can be applicable to virtually all kinds of substrates, regardless of surface properties.1 Catechol can interact with substrates via various types of molecular interactions: coordination bonding to metals,8 Michael-type addition and Schiff base formation with amine groups,8 hydrogen bonding on metal oxides,9 and so on. However, this dynamic bonding to various substrates is insufficient to explain the material independence shown in polydopamine coating because amine-free catechol analogues often fail to show such versatile surface modifications.10 A recent study performed using a surface force apparatus subsequently emphasized the synergistic effect of amine and catechol. Amine groups play an important role in displacing hydrated salts on the surface and then bring catechols near the surface to form strong molecular bonds.11  \n\n1.1.2. Non-covalent Interactions in Polydopamine. The identification of a physical trimer, (dopamine) $_{2}/\\mathrm{DHI}$ , in polydopamine suggested that non-covalent interactions between low-molecular-weight intermediates could be strong enough to generate a three-dimensional molecular assembly. Subsequent studies have suggested various types of noncovalent interactions, such as $\\pi$ effects, electrostatic forces, and van der Waals forces.12,13 Recently, Hong and co-workers7 suggested a new type of non-covalent interactions, cation $-\\pi$ interactions, upon revealing the important role of protonated amine groups in polydopamine. It was found that polydopamine disassembled from the surface under strongly basic conditions $\\mathrm{\\langlepH>10\\rangle}$ as a result of loss of cation−π interactions because the amine cationic species of dopamine became deprotonated. However, under the same $\\mathrm{\\tt{pH}}$ conditions in the presence of additional cations, it can mediate strong non-covalent interactions. For the first time, the authors demonstrated the pH-sensitive disassembly and subsequent reassembly of a polydopamine coating by re-establishing cation− $\\pi$ interactions using additional cations (Figure 1). Because catechol in DHI is not a strongly $\\pi$ -conjugated system, the coexistence of protonated uncyclized amines is a critical factor in the formation of polydopamine. However, recent studies have raised new questions about the origin of the material-independent coating properties of polydopamine, as systems of catecholic compounds and diamines have also succeeded in generating material-independent coating capabilities similar to those of polydopamine even though DHI is not generated during the process.14,15  \n\n![](images/01eb60f478bac53f90b70aa04c4c504f56e0a4dc37d8e5727ab71081af918374.jpg)  \nFigure 2. Nature-derived catechol/gallol families. $\\left({\\mathfrak{a}}{-}{\\mathfrak{g}}\\right)$ Representative plant-derived polyphenol molecules (section 2.1): (a) tannic acid; (b) catechin; (c) epigallocatechin (EGC); (d) epicatechin gallate (ECG); (e) epigallocatechin gallate (EGCG); (f) hydroxyhydroquinol; (g) morin. $\\left(\\mathrm{h-}\\right.$ j) Polymerization pathway of norepinephrine, a catecholic neurotransmitter (section 2.2): (h) norepinephrine; (i) dihydroxybenzaldehyde (DHBA); (j) norepinephrine−DHBA conjugate.",
        "category": " Introduction"
    },
    {
        "id": 4,
        "chunk": "# 1.2. Importance of Oxygen in Polydopamine Growth",
        "category": " Introduction"
    },
    {
        "id": 5,
        "chunk": "# 1.2.1. Thin-Film Formation at the Air−Water Interface  \n\nBall and co-workers observed that the growth of a polydopamine film at the air−water interface was twice as fast as that in solution and that the film was able to be transferred to a solid support.16 Independently, Hong et al.17 showed that amine-rich polymers such as polyethylenimine (PEI) dramatically enhanced interfacial film growth, allowing the film to be free-standable. Whereas the air-exposed side of the film was composed largely of nonswellable nonporous catechols resulting from oxidation, the solution side exhibited micropillar-rich water-swellable porous structures that displayed a Janus-type morphology.17 Interfacial free-standing films can also be produced by phenolic compounds called pyrogallols.18 The formation of films containing pyrogallol and PEI was rapid and occurred in a few minutes. In addition, the damaged area in the film was rapidly resealed by film regeneration because of re-exposure of the solution to the air−water interface.18  \n\n1.2.2. Gradient Polydopamine Coating. Limited oxygen diffusion naturally generates an oxygen gradient from the top air−water interface to the deep bulk solution. Xu and co-workers utilized the natural oxygen gradient to achieve a polydopamine coating showing gradients in thickness and hydrophilicity simply by tilting the surface in the solution during the coating process.19 Repeated draining and replenishing of the surface by cyclic tilting in the solution resulted in a similarly graded polydopamine coating that possessed gradient antibacterial properties.",
        "category": " Results and discussion"
    },
    {
        "id": 6,
        "chunk": "# 1.3. Various Polydopamine Coating Methods",
        "category": " Materials and methods"
    },
    {
        "id": 7,
        "chunk": "# 1.3.1. Polydopamine Coating at Acidic/Neutral pH.  \n\nThe $\\mathrm{p}K_{\\mathrm{al}}$ of the catechol group in dopamine is approximately 9; at this $\\mathrm{\\tt{pH}}_{\\mathrm{\\tt{f}}}$ , dissolved oxygen can uptake an electron from the deprotonated catechol anion, producing an oxidized species called catechol quinone. However, a decrease in $\\mathrm{\\ttpH}$ to neutral or acidic does not produce deprotonated catechol anions. Thus, chemical oxidants can be an option for oxidants to trigger polydopamine coating at acidic $\\mathrm{\\tt{pH}}$ The chemical structure of polydopamine can be altered depending on the oxidant used: it is noteworthy that the DHI subunits were partially degraded by the action of the oxidants during the oxidant coating, causing the surface to become more hydrophilic.21 A hydrothermal process in an autoclave can trigger polydopamine synthesis without oxidants.22 Also, plasma-activated water can initiate dopamine polymerization even in the absence of oxygen.23  \n\n1.3.2. Polydopamine Coating with Rapid Kinetics. The combination of basic $\\mathrm{\\tt{pH}}$ and chemical oxidants provides a dramatic increase in coating rate. The addition of 2 molar equiv of sodium periodate to dopamine at $\\mathrm{\\pH\\}9.5$ resulted in an approximately 200-fold increase in the coating rate.24 The coating could be applied to a large surface via a simple spray approach.24 Microwaves are another emerging trigger for catechol oxidation. Lee et al.25 reported that microwaves successfully reduced the coating time from $6\\mathrm{~h~}$ to $15\\ \\mathrm{min}$ They suggested that microwave-assisted rapid polydopamine coating can be achieved by the synergistic action of thermal acceleration followed by radical generation.25  \n\n1.3.3. Polydopamine Coating in Organic Solvents. Poor access of water molecules to hydrophobic surfaces is a major drawback of aqueous-based polydopamine coating methods despite the unique material-independent applicability. However, it has been reported that polydopamine coating of hydrophobic surfaces can be performed in the presence of watermiscible solvents such as alcohols.26 Furthermore, by the addition of an organic base such as piperidine, organic solvents that cannot be mixed with water can also be used as solvents for hydrophobic surface coating.27  \n\n1.3.4. Phototriggered Polydopamine Coating. Photoillumination followed by photoreaction is a facile method that can be turned on and off in a spatiotemporally controllable manner. This approach has been useful in the fabrication of twodimensional patterns on surfaces. Levkin’s group reported the photo-cross-linking reaction of catechol and gallol derivatives. UV irradiation at $260\\ \\mathrm{nm}$ triggered the oxidation of both dopamine28 and plant polyphenols29 and generated a coating in a few hours.  \n\n1.3.5. Dopamine One-Pot Coating with Desired Molecules. Polydopamine-coated surfaces can be further functionalized via various chemical modes of surface-decorated catechols. However, this two-step process is time-consuming and labor-intensive. In 2012, Kang and co-workers developed a single-step surface functionalization method, denoted as “onepot” coating, which introduces the desired molecule to the surface during polydopamine coating. It was found that biopolymers inserted in the one-pot polydopamine coating retained their biological activity.30",
        "category": " Results and discussion"
    },
    {
        "id": 8,
        "chunk": "# 2. NATURE-DERIVED CATECHOL/GALLOL FAMILIES",
        "category": " Introduction"
    },
    {
        "id": 9,
        "chunk": "# 2.1. Plant Polyphenol Family  \n\n2.1.1. Tannic Acid. In nature there exist a number of catechol/gallol chemical derivatives in addition to dopamine. Gallol is trihydroxyphenol, which is biochemically synthesized by hydroxylation of catechol. Gallol-containing molecules are generally superior in intermolecular binding, particularly for proteins. A representative gallol-containing small molecule is tannic acid (Figure 2a). In 1969 it was reported that tannic acid binds to proteins, producing complexes instantaneously.31 At neutral $\\mathrm{\\tt{pH}}_{\\mathrm{\\tt{f}}}$ , the gallol moieties in tannic acid are not fully protonated, and parts of the hydroxyl groups are deprotonated to form galloquinone. The hydrogen-bond configuration of the gallol moieties in complexes shows the alternating presence of hydrogen-bond donors and acceptors. The coexistence of donors and acceptors is closely related to cytosine base pairing in DNA as well as $\\alpha$ -helix and $\\beta$ -sheet formation in proteins. In this developing hypothesis, tannic acid is superior in the formation of protein/tannic acid complexes. A recently published study in 2018 demonstrated that proteins and peptides are complexed with tannic acid to form soluble nanoparticles in particular stoichiometric ranges. For example, nanoparticles are stably formed in aqueous solutions with a [tannic acid]/[green fluorescent protein] stoichiometry between 70 and 140. Surprisingly, when the nanocomplexes are injected via an intravenous route, they effectively target the myocardium. In addition to the extracellular matrix (ECM) proteins in the myocardium, mucin, found in the oral cavity as well as the gastrointestinal tract, is readily complexed with tannic acid.32 Although the exact binding sites in mucin are not known, the abundant hydroxyl groups of tannic acid could interact with surface-exposed oligo/polysaccharides via hydrogen bonds. The consumption of hydroxyl groups of tannic acid to anchor and mask the lubricating oligo/polysaccharides of mucin results in exposure of the phenolic moieties of tannic acid to the outermost layer. Thus, an increased feeling of friction is produced within the oral cavity, and this phenomenon is described as the unique taste called “astringency”.33 In addition to interactions with proteins, tannic acid is able to bind with a zwitterionic polymer, poly(sulfobetaine methacrylate) (PSBMA). This zwitterionic hydrophilic surface exhibits protein adsorption resistance (i.e., antifouling) properties.34 Similar to the material-independent surface chemistry of polydopamine, tannic acid also shows versatility in surface modifications. Surfaces of metal oxides and even hydrophobic polymers have been functionalized with a thickness of $\\overline{{20}}\\ \\mathrm{nm}$ .35 The surface wettability is controlled by tannic acid. Dense coating onto a polypropylene membrane with tannic acid-functionalized carbon nanotubes generates superoleophobicity upon vacuum filtration of the carbon nanotube solution.36 An additional important ability of tannic acid is the formation of metal−gallol coordination bonds, which are the basis of a second materialindependent surface chemistry.37,38 Metal ion/tannic acid coordination complexes result in the formation of thin adherent films on virtually any type of substrate. This surface chemistry is known as a metal−phenolic network (MPN). Beyond the thinfilm form adhered on surfaces, MPNs can be combined with polymer scaffolds such as polysaccharides to make freestandable hydrogel or fiber forms.39,40 Compared with polydopamine coating, an advantage of MPN surface chemistry is its rapid kinetics. Thus, MPN is suitable to functionalize “living” cell surfaces. Choi and co-workers reported the single-cell encapsulation of individual Saccharomyces cerevisiae by artificial shells (or spores).41 The yeast surfaces protected by MPN layers showed resistance to external stimuli such as UV radiation, lytic enzymes, and toxic silver nanoparticles.  \n\n2.1.2. Catechin Derivatives. Catechin (Figure 2b) is a nondegradable phenolic molecule that is a plant secondary metabolite. Similar to tannic acid, catechin also exhibits surface modification and intermolecular interaction capabilities. Catechin does functionalize various surfaces, such as polycarbonate (PC), nylon, poly(dimethylsiloxane) (PDMS), poly(tetrafluoroethylene) (PTFE), polystyrene (PS), Au, and $\\mathrm{SiO}_{2}$ .42 Interestingly, functionalized surfaces triggered the photografting of polymer brushes of PSBMA and poly(2- ((methacryloyloxy)ethyl)trimethylammonium chloride).43 The antioxidative and calcium-binding properties of surface-coated catechin resulted in the osteogenic differentiation of human adipose-derived stem cells (hADSCs).44 This was the first study to demonstrate the effectiveness of a polyphenol coating in stem cell culture. Catechin is poorly water-soluble. However, it can form complexes with poly(ethylene glycol) (PEG) by lyophilization processes. After freeze-drying, catechin/PEG complexes became highly water-soluble, demonstrating therapeutic effects for dry eye.45  \n\n2.1.3. Urushiol and Alkanecatechol. Beginning prior to the fifth century B.C., a series of catechol derivatives with unsaturated hydrocarbons, collectively called “urushiols”, have been used. Urushiols form protective and polishing coating layers on the surfaces of various wooden furniture. Oxidative cross-linking between catechol in urushiol coatings has similar aspects to polydopamine and other aforementioned polyphenol coatings. However, this cross-linking is largely mediated by the enzyme copper-containing laccase.46 Recently, saturated (i.e., hydrogenated) urushiol (h-urushiol) was prepared in a synthetic manner to investigate the physicochemical contributions of the saturated hydrocarbon in natural urushiols.47 Curing with hurushiol takes a long time $(\\sim12\\ \\mathrm{h})$ compared with the time required for natural urushiol $(<1\\mathrm{~h~})$ . Strain-induced elastic buckling occurs easily in $\\mathbf{h}$ -urushiol, indicating that the double bonds in natural urushiol form abundant cross-links between molecules. Further systematic molecular engineering studies performed by changing the hydrocarbon length were reported by the Ruiz-Molina group.48 The key purpose of the study was to provide hydrophobicity on polyester fabric surfaces. Applications include oil-absorbent and water-repellent materials after the formation of alkanecatechol coatings.  \n\n![](images/abae4057295553a2fc069f86d372f05c08660a52aa5fb1f32924958040a8bd6c.jpg)  \nFigure 3. Small-molecule dopamine conjugates. $(\\mathsf{a},\\mathsf{b})$ Catecholic derivatives. (c) Catechol-containing acrylate. (d) Diels−Alder (DA) reaction. (e) Cycloaddition reactions for click chemistry. (f) Catecholic liquid lubricant. $\\mathbf{\\eta}(\\mathbf{g})$ Zwitterionic polymers in biosurface formation and resistance to fouling. (h) Polydopamine gradient.",
        "category": " Introduction"
    },
    {
        "id": 10,
        "chunk": "# 2.2. Neurotransmitters: Norepinephrine  \n\nThe oxidative polymerization of norepinephrine was the first use of a small catecholamine derivative for material-independent coating and was reported shortly after polydopamine.49 In the process of polydopamine coating, oligo-DHI undergoes uncontrolled intermolecular interactions with other intermediates, producing massive aggregation. In contrast, the poly(norepinephrine) coating shows extremely smooth surface functionalization.50 As a result of the presence of additional alkyl hydroxyl groups in norepinephrine, tautomerization occurs, producing catechol aldehyde, which subsequently reacts with the amine group of norepinephrine, resulting in the formation of 3,4-dihydroxybenzaldehyde (DHBA) (Figure $\\mathrm{2h,i}^{\\cdot}$ . DHBA acts as the key molecule in reducing surface roughness by preventing the intermolecular aggregation of norepinephrine intermediates. The smooth poly(norepinephrine) nanolayer allows the functionalization of surfaces with micro/nanoscale structures without increasing surface roughness. Furthermore, the secondary alkylamine in DHBA provides a suitable platform for NONO-ate surface immobilization as a nitric oxide (NO) depot. The alkyl hydroxyl group of norepinephrine is effective in initiating surface-initiated ring-opening metathesis polymerization (SI-ROMP) on surfaces.49 In the cited study, the authors demonstrated the surfaceinitiated polymerization of $\\beta$ -caprolactone in a materialindependent manner. Later, the same group also showed surface-initiated atomic transfer radical polymerization (SIATRP) by a catechol-conjugated bromine initiator.51 As the redox activity of polydopamine layers originates from catechol oxidation and reduction, poly(norepinephrine) layers also show redox-active properties. Graphene oxide (GO) spontaneously receives electrons from poly(norepinephrine) layers to create reduced GO (rGO) by simple mixing.52 The advantage of using poly(norepinephrine) reduction is that the surfaces of rGO are simultaneously functionalized and used in additional metal ion doping or SI-ROMP. Biomedical applications of poly(norepinephrine) coatings have been published. Compared with polydopamine, surfaces coated by poly(norepinephrine) show increased hydrophilicity and provide versatile platforms for material-independent mammalian cell cultures. In particular, such coating is effective in neural stem cell cultures, even for lowsurface-energy materials such as PDMS and PTFE.53 By the coimmobilization of biomolecules and other molecules during poly(norepinephrine) layer formation (see section 1.3.5), researchers have demonstrated controlled cell adhesion and proliferation.54",
        "category": " Results and discussion"
    },
    {
        "id": 11,
        "chunk": "# 3. SMALL-MOLECULE DOPAMINE CONJUGATES FOR APPLICATIONS",
        "category": " Results and discussion"
    },
    {
        "id": 12,
        "chunk": "# 3.1. Surface-Initiated Polymerization  \n\n3.1.1. SI-ATRP. In 2005, a mussel-inspired SI-ATRP initiator was first reported (Figure 3a). The phenolic hydroxyl in the initiator can work as an anchor site for attachment on various surfaces.55 This biomimetic surface-grafting strategy is a highly versatile tool for functionalizing various substrates, such as Au, Ti, stainless steel, Si, quartz, glass, polypropylene, PDMS, PS, and nylon.56−58 By means of this strategy, researchers successfully brush-grafted poly(3-sulfopropyl methacrylate potassium salt) (PSPMA) onto very inert diamond-like carbon (DLC) films. The as-prepared functionalized DLC film surface showed good superhydrophilicity and excellent water lubrication properties.59 Moreover, this biomimetic surface-grafting strategy is applicable to rough surfaces such as fibrils and particles.60,61 Kuang and Messersmith56 synthesized a biomimetic tripeptide bromide (BrYKY). BrYKY was successfully assembled onto the substrate surface, and then PSBMA was grafted to form a high-density polymer brush layer. This method is a water-based reaction, which can avoid erosion from solvent to substrate. In addition, macromolecules functionalized with catechol groups have also been directly synthesized to realize the one-step modification of substrates. For example, zwitterionic sulfobetaine polymers with catechol groups (DOPA-PSB) were prepared to decorate a hydrophobic substrate surface.58  \n\n3.1.2. SI-ROMP. SI-ROMP based on catechol-functionalized initiators has also been reported. Perfluoroalkyl-substituted polymer brushes can be successfully grafted onto the surface of various metals and metal oxides. The grafted polymer brushes have good adhesion strength and thermal stability under ambient conditions (Figure 3b).62 By means of microcontact printing $\\left(\\mu\\mathrm{CP}\\right)$ and the combination of SI-ROMP with SIATRP, patterned microstructures have been fabricated, providing potential applications in hybrid surfaces, biochips, and biosensors.57 A multi-initiator coating was achieved by coadsorption, which can anchor hydroxyl and bromide moieties on the substrate to initiate ROMP and ATRP, respectively.51 Another step of research progress in the universal surfaceinitiated polymerization method was to initiate the free radical polymerization from a polydopamine layer under UV radiation or sunlight.63 Because polydopamine can be deposited on any substrate, it can also be brush-grafted from anywhere.  \n\n3.1.3. Catecholic Polyacrylates. To prepare coatings with long-term adhesion stability, researchers introduced catechols into the polymer chain. It was found that when a catechol group was incorporated into a perfluoropolymer, the polymer could adsorb onto a variety of substrates with high stability and render them superhydrophobic and superoleophobic.64 Zhang and coworkers reported terpolymer coatings containing pendant catechol, oligo(ethylene glycol) (OEG), and perfluoroalkyl functional groups (Figure 3c). The coatings exhibited robust adhesion ability and low biofouling.65 In addition, a highly stable catechol acrylate adhesive in wet environments was demonstrated by the Yoshie group.66 This study is informative in that two phenolic adhesion functional groups, catechol acrylate and gallol acrylate monomers, were radical-polymerized with $n$ -butyl acrylate. It was demonstrated that the gallol-incorporated copolymer showed about 7 times higher adhesive strength than the one with the catechol-incorporated adhesive. This comparative study is meaningful because both adhesives showed improved performance compared with an isocyanate-based commercial adhesive. Antioxidant and adsorption properties were also presented with the catecholic polyacrylates by the same group.67 Similar catecholic acrylates coordinate with seawater-rich cations such as ${\\mathrm{Ca}}^{2+}$ and $\\mathrm{\\dot{M}g^{2+}}$ , exhibiting a selfhealing property against external damage through reformation of metal−catechol coordination and hydrogen bonds.68",
        "category": " Results and discussion"
    },
    {
        "id": 13,
        "chunk": "# 3.2. Surface Anchoring for Chemoselective Bio-orthogonal Chemistry  \n\n3.2.1. Diels−Alder Reaction. The Diels−Alder reaction is a temperature-dependent coupling process. Upon assembly of catechol-based biomimetic anchors (Figure 3d), the Diels− Alder cycloaddition reaction can be easily performed to immobilize different macromolecules onto Ti substrates, resulting in changes in their surface properties.69  \n\n3.2.2. Click Chemistry. Similarly, a straightforward strategy based on dopamine derivatives has been reported for titanium surface modification by the use of click chemistry (Figure 3e).70 A similar strategy can also be applied to modify nanoparticles, which can endow new functionalities, such as good water dispersibility and thermal responsiveness.71 In addition, with azide-terminated dopamine, this method was able to functionalize graphene oxide (GO), wherein the reduction of GO and decoration with catechol occurred at the same time.72 By means of this strategy, micro/nanopatterns have successfully been prepared using photolithography and $\\mu\\mathrm{CP}$ techniques.  \n\n3.2.3. Ni-NTA. Xu et al.74 first demonstrated the surface modification of the iron oxide shells of magnetic nanoparticles with nitrilotriacetic acid (NTA). Upon chelation to $\\bar{\\bf N i}^{2+}$ , the functionalized $\\mathrm{Fe}_{2}\\mathrm{O}_{3}$ system could efficiently separate histidinetagged proteins from a cell lysate. This modification strategy broadens the possibility for the application of nanoparticles in biomedicine.  \n\n3.2.4. LbL Method. Longo et al.75 developed a new method for enzyme immobilization on surfaces by combining the catechol chemistry with the layer-by-layer (LbL) method. Alkaline phosphatase (ALP), an enzyme that aids hydrolysis of phosphoryl bonds, has its isoelectric point at $\\mathrm{pH}7.$ As a result, ALP allows the formation of multilayer films with highly negatively charged catechol-conjugated alginate in an LbL manner at $\\mathrm{pH}5.0$ . By subsequent oxidant treatment after LbL film formation, oxidative catechol chemistry successfully turned the multilayer film into a firmly cross-linked architecture without loss of enzyme activity. By means of this combination method, biomolecules can be easily and stably displayed while maintaining their functionalities.",
        "category": " Results and discussion"
    },
    {
        "id": 14,
        "chunk": "# 3.3. Antibiofouling  \n\n3.3.1. Zwitterionic Antifouling. Hydration plays a significant role in mitigating surface biofouling. Grafting of hydrophilic polymers on surfaces can create a high degree of surface hydration and prevent direct contact from foulants. Jiang and co-workers brush-grafted PSBMA onto a substrate based on the catechol initiator via ATRP.76 The grafted surface was highly resistant to bacterial adhesion. Higher-molecular-weight brushes showed better antifouling properties.58 In addition, a zwitterionic sulfobetaine dopamine (SB-DA) can be easily assembled on the substrate surface to form one layer of stable hydration film for effectively resisting protein and bacterial adsorption (Figure $3\\mathbf{g}{\\dot{}}$ ).77 To simplify the process for preparation of zwitterionic coatings, Emrick and co-workers reported a one-step surface modification strategy by the codeposition of polydopamine and poly(methacryloyloxyethyl phosphorylcholine), making the surface less prone to bacterial fouling. 78  \n\n3.3.2. PEGylation. Hwang, Hawker and co-workers found a removable and recoverable self-assembled monolayer by exploiting strong and reversible catechol−metal coordinative interactions.79 The recyclable surface coating successfully realized excellent antifouling properties as well as controllable wettability.",
        "category": " Results and discussion"
    },
    {
        "id": 15,
        "chunk": "# 3.4. Friction and Wetting Control  \n\n3.4.1. Friction Control. Micro/nanoelectromechanical systems play an important role in many areas of research, but serious adhesive and frictional behavior in miniaturized devices restricts their operational lifetime and durability. Zhou and coworkers combined ionic liquids, which possess good lubrication and antiwear properties, with dopamine derivatives to realize the successful self-assembly of compounds with significantly improved lubrication and antiwear properties (Figure 3f).80  \n\n3.4.2. Wetting Control. A perfluorinated dopamine derivative and polyacrylate were prepared and then assembled on a substrate to achieve superhydrophobic properties.62,81 Haag and co-workers achieved a surface with special wettability properties by coating with mussel-inspired dendritic polyglycerol (MI-dPG), which can adhere to the substrate to control the roughness by adjustment of the coating time. By this method, superhydrophobic/superhydrophilic surfaces were obtained by combining nano/micrometer-sized MI-dPG particles modified with perfluorinated acid chloride.82 Engineered surfaces with gradient features are important for diverse applications, such as mimicking biological systems,83 determining minimal drug inhibition concentrations, and constructing various superwetting systems.82 Perfluoroalkyl catechols and nitrodopamine were used in self-assembly to generate a surface hydrophobicity gradient.84 Furthermore, it can be realized on a hydrophobic surface using a microfluidic device, which can create protein or cell gradients for tissue engineering applications.83 In addition, a general technology of cyclic draining and replenishing (CDR) was used to generate a polydopamine gradient on hydrophobic surfaces (Figure 3h).20",
        "category": " Results and discussion"
    },
    {
        "id": 16,
        "chunk": "# 4. CONCLUSION  \n\nCatecholamine molecules such as dopamine, norepinephrine, and others have been studied primarily by neurobiologists. Also, their protective roles in forms of catecholamine polymers known as melanins have been studied. Surface chemistry to control properties at interfaces using catecholamine molecules is a recent research direction that began with the invention of polydopamine surface chemistry.1,85 Surface functionalizations utilizing catecholamines are the simplest and most versatile approaches for material-independent surface functionalization. This Account has introduced a variety of catecholamine derivatives for applications in many fields. However, there is still room for catecholamine derivatives to provide interface functions that have not yet been explored.",
        "category": " Conclusions"
    },
    {
        "id": 17,
        "chunk": "# AUTHOR INFORMATION",
        "category": " References"
    },
    {
        "id": 18,
        "chunk": "# Corresponding Authors  \n\n$^{*}\\mathrm{E}$ -mail: haeshin@kaist.ac.kr (H.L.). $^{*}\\mathrm{E}$ -mail: seonkihong@dgist.ac.kr (S.H.). \\*E-mail: zhouf@licp.cas.cn (F.Z.). ORCID  \n\nHaesung A. Lee: 0000-0002-1035-8036   \nFeng Zhou: 0000-0001-7136-9233   \nSeonki Hong: 0000-0003-1440-5167   \nHaeshin Lee: 0000-0003-3961-9727",
        "category": " References"
    },
    {
        "id": 19,
        "chunk": "# Notes  \n\nThe authors declare no competing financial interest.",
        "category": " Conclusions"
    },
    {
        "id": 20,
        "chunk": "# Biographies  \n\nHaesung A. Lee obtained his B.S. in Chemistry and Biological Sciences from KAIST in 2015 and is a Ph.D. candidate in the group of Prof. Haeshin Lee. His research interests include polyphenol-conjugated biopolymers and their applications.  \n\nYanfei Ma received his B.S. in chemistry from Northwest Normal University in China in 2015. He is currently a Ph.D. candidate in the group of Prof. Feng Zhou at the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences. His research interests include wet friction/adhesion control of soft matter and bionic adhesion.  \n\nFeng Zhou is a Professor at the State Key Laboratory of Solid Lubrication at the Lanzhou Institute of Chemical Physics and an adjunct professor at Northwestern Polytechnical University. He got his Ph.D. in 2004 from the Lanzhou Institute of Chemical Physics. He spent three years (2005−2008) in the Department of Chemistry at the University of Cambridge as a research associate. His research interests include surfaces and interfaces of soft matter, drag reduction and antifouling, and biolubrication.  \n\nSeonki Hong is an Assistant Professor in the Department of Emerging Materials Science at DGIST. She pursued her Ph.D. studies in the Department of Chemistry at KAIST and worked as a postdoctoral research fellow at Massachusetts General Hospital and Harvard Medical School. Her research interests have been focused on the design of innovative molecular glues/adhesives by mimicking the chemical structures of unique natural polyphenolic materials and the development of point-of-care bioassays for the precise detection of circulating biomarkers by utilizing these molecular glues.  \n\nHaeshin Lee is Professor in the Department of Chemistry at KAIST. He obtained his Ph.D. in Biomedical Engineering from Northwestern University in 2008. He invented polydopamine coating in 2007 with P. B. Messersmith. His research interests include bioinspired chemistry of catechol and gallol derivatives, adhesive hydrogels and sols, and drug delivery systems. Currently he is an associate editor of Biomaterials Science.",
        "category": " References"
    },
    {
        "id": 21,
        "chunk": "# ACKNOWLEDGMENTS  \n\nThis research was supported by National Research Foundation of Korea (NRF) grants funded by the Government of Korea (MSIT): Basic Science Research Program (NRF2018R1D1A1B07045249 to S.H.), Midcareer Researcher Program (NRF-2017R1A2A1A05001047 to H.L.), and Center for Multiscale Chiral Architectures, Science Research Center (SRC) Program (2018R1A5A1025208 to H.L.). This work was also supported by the KIST Institutional Program (Project 2V06630 to H.L.). This work was carried out with the support of the Cooperative Research Program for Agriculture Science and  \n\nTechnology Development (Project PJ01323201 to S.H.) from the Rural Development Administration of the Republic of Korea. This work was also supported by the National Key R e s e a r c h a n d D e v e l o p m e n t P r o g r a m o f C h i n a (2016YFC1100401 to F.Z.) and the National Natural Science Foundation of China (21434009 to F.Z.)",
        "category": " References"
    },
    {
        "id": 22,
        "chunk": "# REFERENCES  \n\n(1) Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Mussel-Inspired Surface Chemistry for Multifunctional coatings. Science 2007, 318, 426−430.   \n(2) Hong, S.; Na, Y. S.; Choi, S.; Song, I. T.; Kim, W. Y.; Lee, H. NonCovalent Self-Assembly and Covalent Polymerization Co-Contribute to Polydopamine Formation. Adv. Funct. Mater. 2012, 22, 4711−4717. (3) Liebscher, J.; Mrówczyński, R.; Scheidt, H. A.; Filip, C.; Hădade, N. D.; Turcu, R.; Bende, A.; Beck, S. Structure of Polydopamine: A Never-Ending Story? Langmuir 2013, 29, 10539−10548.   \n(4) Alfieri, M. L.; Micillo, R.; Panzella, L.; Crescenzi, O.; Oscurato, S. L.; Maddalena, P.; Napolitano, A.; Ball, V.; d’Ischia, M. Structural Basis of Polydopamine Film Formation: Probing 5,6-Dihydroxyindole-Based Eumelanin Type Units and the Porphyrin Issue. ACS Appl. Mater. Interfaces 2018, 10, 7670−7680.   \n(5) Della Vecchia, N. F.; Avolio, R.; Alfè, M.; Errico, M. E.; Napolitano, A.; d’Ischia, M. Building-Block Diversity in Polydopamine Underpins a Multifunctional Eumelanin-Type Platform Tunable Through a Quinone Control Point. Adv. Funct. Mater. 2013, 23, 1331−1340.   \n(6) Ding, Y.; Weng, L.-T.; Yang, M.; Yang, Z.; Lu, X.; Huang, N.; Leng, Y. Insight into the Aggregation/Deposition and Structure of a Polydopamine Film. Langmuir 2014, 30, 12258−12269.   \n(7) Hong, S.; Wang, Y.; Park, S. Y.; Lee, H. Progressive fuzzy cation−π assembly of biological catecholamines. Sci. Adv. 2018, 4, No. eaat7457. (8) Lee, H.; Scherer, N. F.; Messersmith, P. B. Single-molecule mechanics of mussel adhesion. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 12999−13003.   \n(9) Anderson, T. H.; Yu, J.; Estrada, A.; Hammer, M. U.; Waite, J. H.; Israelachvili, J. N. The Contribution of DOPA to Substrate-Peptide Adhesion and Internal Cohesion of Mussel-Inspired Synthetic Peptide Film. Adv. Funct. Mater. 2010, 20, 4196−4205.   \n(10) Hong, S.; Yeom, J.; Song, I. T.; Kang, S. M.; Lee, H.; Lee, H. Pyrogallol 2-Aminoethane: A Plant Flavonoid-Inspired Molecule for Material-Independent Surface Chemistry. Adv. Mater. Interfaces 2014, 1, 1400113.   \n(11) Maier, G. P.; Rapp, M. V.; Waite, J. H.; Israelachvili, J. N.; Butler, A. Adaptive synergy between catechol and lysine promotes wet adhesion by surface salt displacement. Science 2015, 349, 628−632. (12) Chen, C.-T.; Martin-Martinez, F. J.; Jung, G. S.; Buehler, M. J. Polydopamine and eumelanin molecular structures investigated with ab initio calculations. Chem. Sci. 2017, 8, 1631−1641.   \n(13) Micillo, R.; Panzella, L.; Iacomino, M.; Prampolini, G.; Cacelli, I.; Ferretti, A.; Crescenzi, O.; Koike, K.; Napolitano, A.; d’Ischia, M. Eumelanin broadband absorption develops from aggregation-modulated chromophore interactions under structural and redox control. Sci. Rep. 2017, 7, 41532.   \n(14) Suárez-García, S.; Sedó, J.; Saiz-Poseu, J.; Ruiz-Molina, D. Copolymerization of a Catechol and a Diamine as a Versatile Polydopamine-Like Platform for Surface Functionalization: The Case of a Hydrophobic Coating. Biomimetics 2017, 2, 22.   \n(15) Iacomino, M.; Paez, J. I.; Avolio, R.; Carpentieri, A.; Panzella, L.; Falco, G.; Pizzo, E.; Errico, M. E.; Napolitano, A.; del Campo, A.; d’Ischia, M. Multifunctional Thin Film and Coatings from Caffeic Acid and a Cross-Linking Diamine. Langmuir 2017, 33, 2096−2102. (16) Ponzio, F.; Payamyar, P.; Schneider, A.; Winterhalter, M.; Bour, J.; Addiego, F.; Krafft, M.-P.; Hemmerle, J.; Ball, V. Polydopamine Films from the Forgotten Air/Water Interface. J. Phys. Chem. Lett. 2014, 5, 3436−3440.   \n(17) Hong, S.; Schaber, C. F.; Dening, K.; Appel, E.; Gorb, S. N.; Lee, H. Air/Water Interfacial Formation of Freestanding, StimuliAdv. Mater. 201 587   \n(18) Wang, Y.; Park, J. P.; Hong, S. H.; Lee, H. Biologically Inspired Materials Exhibiting Repeatable Regeneration with Self-Sealing Capabilities without External Stimuli or Catalysts. Adv. Mater. 2016, 28, 9961−9968.   \n(19) Yang, H.-C.; Wu, Q.-Y.; Wan, L.-S.; Xu, Z.-K. Polydopamine gradients by oxygen diffusion controlled autoxidation. Chem. Commun. 2013, 49, 10522−10524.   \n(20) Zhao, M.-X.; Li, J.; Gao, X. Gradient Coating of Polydopamine via CDR. Langmuir 2017, 33, 6727−6731.   \n(21) Ponzio, F.; Barthès, J.; Bour, J.; Michel, $|\\mathrm{\\mathbf{M}}.\\mathrm{\\mathbf{;}}$ Bertani, P.; Hemmerlé, J.; d’Ischia, M.; Ball, V. Oxidant Control of Polydopamine Surface Chemistry in Acids: A Mechanism-Based Entry to Superhydrophilic-Superoleophobic Coatings. Chem. Mater. 2016, 28, 4697− 4705.   \n(22) Zheng, W.; Fan, H.; Wang, L.; Jin, Z. Oxidative SelfPolymerization of Dopamine in an Acidic Environment. Langmuir 2015, 31, 11671−11677.   \n(23) Chen, T.-P.; Liu, T.; Su, T.-L.; Liang, J. Self-Polymerization of Dopamine in Acidic Environments without Oxygen. Langmuir 2017, 33, 5863−5871.   \n(24) Hong, S. H.; Hong, S.; Ryou, M.-H.; Choi, J.-W.; Kang, S. M.; Lee, H. Sprayable Ultrafast Polydopamine Surface Modifications. Adv. Mater. Interfaces 2016, 3, 1500857.   \n(25) Lee, M.; Lee, S.-H.; Oh, I.-K.; Lee, H. Microwave-Accelerated Rapid, Chemical Oxidant-Free, Material-Independent Surface Chemistry of Poly(dopamine). Small 2017, 13, 1600443.   \n(26) Jiang, X.; Wang, Y.; Li, M. Selecting water−alcohol mixed solvent for synthesis of polydopamine nano-spheres using solubility parameter. Sci. Rep. 2015, 4, 6070.   \n(27) You, I.; Jeon, H.; Lee, K.; Do, M.; Seo, Y. C.; Lee, H. A.; Lee, H. Polydopamine coating in organic solvent for material-independent immobilization of water-insoluble molecules and avoidance of substrate hydrolysis. J. Ind. Eng. Chem. 2017, 46, 379−385.   \n(28) Du, X.; Li, L.; Li, J.; Yang, C.; Frenkel, N.; Welle, A.; Heissler, S.; Nefedov, A.; Grunze, M.; Levkin, P. A. UV-Triggered Dopamine Polymerization: Control of Polymerization, Surface Coating, and Photopatterning. Adv. Mater. 2014, 26, 8029−8033.   \n(29) Behboodi-Sadabad, F.; Zhang, H.; Trouillet, V.; Welle, A.; Plumeré, N.; Levkin, P. A. UV-Triggered Polymerization, Deposition, and Patterning of Plant Phenolic Compounds. Adv. Funct. Mater. 2017, 27, 1700127.   \n(30) Kang, S. M.; Hwang, N. S.; Yeom, J.; Park, S. Y.; Messersmith, P. B.; Choi, I. S.; Langer, R.; Anderson, D. G.; Lee, H. One-Step Multipurpose Surface Functionalization by Adhesive Catecholamine. Adv. Funct. Mater. 2012, 22, 2949−2955.   \n(31) Van Buren, J. P.; Robinson, W. B. Formation of Complexes between Protein and Tannic Acid. J. Agric. Food Chem. 1969, 17, 772− 777.   \n(32) Shin, M.; Lee, H.-A.; Lee, M.; Shin, Y.; Song, J.-J.; Kang, S.-W.; Nam, D.-H.; Jeon, E. J.; Cho, M.; Do, M.; Park, S.; Lee, M. S.; Jang, J.- H.; Cho, S.-W.; Kim, K.-S.; Lee, H. Targeting protein and peptide therapeutics to the heart via tannic acid modification. Nature Biomed. Eng. 2018, 2, 304−317.   \n(33) Ma, S.; Lee, H.; Liang, Y.; Zhou, F. Astringent Mouthfeel as a Consequence of Lubrication Failure. Angew. Chem., Int. Ed. 2016, 55, 5793−5797.   \n(34) Ren, P.-F.; Yang, H.-C.; Liang, H.-Q.; Xu, X.-L.; Wan, L.-S.; Xu, Z.-K. Highly Stable, Protein-Resistant Surfaces via the Layer-by-Layer Assembly of Poly(sulfobetaine methacrylate) and Tannic Acid. Langmuir 2015, 31, 5851−5858.   \n(35) Sileika, T. S.; Barrett, D. G.; Zhang, R.; Lau, K. H. A.; Messersmith, P. B. Colorless Multifunctional Coatings Inspired by Polyphenols Found in Tea, Chocolate, and Wine. Angew. Chem., Int. Ed. 2013, 52, 10766−10770.   \n(36) Jin, Y.-N.; Yang, H.-C.; Huang, H.; Xu, Z.-K. Underwater superoleophobic coatings fabricated from tannic acid-decorated carbon nanotubes. RSC Adv. 2015, 5, 16112−16115.  \n\n(37) Ejima, H.; Richardson, J. J.; Liang, K.; Best, J. P.; Van Koeverden, M. P.; Such, G. ${\\mathrm{K}}.{\\mathrm{}}$ Cui, J.; Caruso, F. One-Step Assembly of Coordination Complexes for Versatile Film and Particle Engineering. Science 2013, 341, 154−157. (38) Guo, J.; Ping, Y.; Ejima, H.; Alt, K.; Meissner, M.; Richardson, J. J.; Yan, Y.; Peter, ${\\mathrm{K}}.{\\mathrm{}}$ von Elverfeldt, D.; Hagemeyer, C. E.; Caruso, F. Engineering Multifunctional Capsules through the Assembly of MetalPhenolic Network. Angew. Chem., Int. Ed. 2014, 53, 5546−5551. (39) Krogsgaard, M.; Andersen, A.; Birkedal, H. Gels and threads: mussel-inspired one-pot route to advanced responsive materials. Chem. Commun. 2014, 50, 13278−13281. (40) Andersen, A.; Krogsgaard, M.; Birkedal, H. Mussel-Inspired SelfHealing Double-Cross-Linked Hydrogels by Controlled Combination of Metal Coordination and Covalent Cross-Linking. Biomacromolecules 2018, 19, 1402−1409. (41) Park, J. H.; Kim, K.; Lee, J.; Choi, J. Y.; Hong, D.; Yang, S. H.; Caruso, F.; Lee, Y.; Choi, I. S. A Cytoprotective and Degradable Metal− Polyphenol Nanoshell for Single-Cell Encapsulation. Angew. Chem., Int. Ed. 2014, 53, 12420−12425. (42) Barrett, D. G.; Sileika, T. S.; Messersmith, P. B. Molecular diversity in phenolic and polyphenolic precursors of tannin-inspired nanocoatings. Chem. Commun. 2014, 50, 7265−7268. (43) Bai, G.; Ma, S.; Qie, R.; Liu, Z.; Shi, Y.; Li, C.; Wang, R.; Guo, X.; Zhou, F.; Jia, X. UV-Triggered Surface-Initiated Polymerization from Colorless Green Tea Polyphenol-Coated Srufaces. Macromol. Rapid Commun. 2016, 37, 1256−1261. (44) Lee, J. S.; Lee, J. S.; Lee, M. S.; An, S.; Yang, K.; Lee, K.; Yang, H. S.; Lee, H.; Cho, S.-W. Plant Flavonoid-Mediated Multifunctional Surface Modification Chemistry: Catechin Coating for Enhanced Osteogenesis of Human Stem Cells. Chem. Mater. 2017, 29, 4375− 4384. (45) Lee, H.; Shim, W.; Kim, C. E.; Choi, S. Y.; Lee, H.; Yang, J. Therapeutic Efficacy of Nanocomplex of Poly(Ethylene Glycol) and Catechin for Dry Eye Disease in a Mouse Model. Invest. Ophthalmol. Visual Sci. 2017, 58, 1682−1691. (46) Kobayashi, S.; Uyama, H.; Ikeda, R. Artificial Urushi. Chem. - Eur. J. 2001, 7, 4754−4760. (47) Watanabe, H.; Fujimoto, A.; Nishida, J.; Ohishi, T.; Takahara, A. Biobased Polymer Coating Using Catechol Derivative Urushiol. Langmuir 2016, 32, 4619−4623. (48) García, B.; Saiz-Poseu, J.; Gras-Charles, R.; Hernando, J.; Alibés, R.; Novio, F.; Sédo, J.; Busqué, F.; Ruiz-Molina, D. Mussel-Inspired Hydrophobic Coatings for Water-Repellent Textiles and Oil Removal. ACS Appl. Mater. Interfaces 2014, 6, 17616−17625. (49) Kang, S. M.; Rho, J.; Choi, I. S.; Messersmith, P. B.; Lee, H. Norepinephrine: Material-Independent, Multifunctional Surface Modification Reagent. J. Am. Chem. Soc. 2009, 131, 13224−13225. (50) Hong, S.; Kim, J.; Na, Y. S.; Park, J.; Kim, S.; Singha, K.; Im, G.-I.; Han, D.-K.; Kim, W. J.; Lee, H. Poly(norepinephrine): Ultrasmooth Material-Independent Surface Chemistry and Nanodepot for Nitric Oxide. Angew. Chem., Int. Ed. 2013, 52, 9187−9191. (51) Kang, S. M.; Lee, H. One-Step Immobilization of Initiators for Surface-Initiated Ring Opening Polymerization and Atom Transfer Radical Polymerization by Poly(norepinephrine) Coating. J. Nanosci. Nanotechnol. 2015, 15, 1597−1600. (52) Kang, S. M.; Park, S.; Kim, D.; Park, S. Y.; Ruoff, R. S.; Lee, H. Simultaneous Reduction and Surface Functionalization of Graphene Oxide by Mussel-Inspired Chemistry. Adv. Funct. Mater. 2011, 21, 108−112. (53) Park, M.; Shin, M.; Kim, E.; Lee, S.; Park, K. I.; Lee, H.; Jang, J.-H. The Promotion of Human Neural Stem Cells Adhesion Using Bioinspired Poly(norepinephrine) Nanoscale Coating. J. Nanomater. 2014, 2014, 793052. (54) Kim, E.; Lee, S.; Hong, S.; Jin, G.; Kim, M.; Park, K. I.; Lee, H.; Jang, J.-H. Sticky “Delivering-From” Strategies Using Viral Vectors for Efficient Human Neural Stem Cell Infection by Bioinspired Catecholamines. ACS Appl. Mater. Interfaces 2014, 6, 8288−8294.  \n\n(55) Fan, X.; Lin, L.; Dalsin, J. L.; Messersmith, P. B. Biomimetic Anchor for Surface-Initiated Polymerization from Metal Substrates. J. Am. Chem. Soc. 2005, 127, 15843−15847.   \n(56) Kuang, J.; Messersmith, P. B. Universal Surface-Initiated Polymerization of Antifouling Zwitterionic Brushes Using a MusselMimetic Peptide Initiator. Langmuir 2012, 28, 7258−7266.   \n(57) Liu, J.; Ye, $\\mathrm{Q.;}$ Yu, B.; Wang, X.; Zhou, F. Contact printing a biomimetic catecholic monolayer on a variety of surfaces and derivation reaction. Chem. Commun. 2012, 48, 398−400.   \n(58) Sundaram, H. S.; Han, X.; Nowinski, A. K.; Ella-Menye, J.-R.; Wimbish, C.; Marek, P.; Senecal, K.; Jiang, S. One-Step Dip Coating of Zwitterionic Sulfobetaine Polymers on Hydrophobic and Hydrophilic Surfaces. ACS Appl. Mater. Interfaces 2014, 6, 6664−6671.   \n(59) Wei, $\\mathrm{Q.;}$ Pei, X.; Hao, J.; Cai, M.; Zhou, F.; Liu, W. Surface Modification of Diamond-Like Carbon Film with Polymer Brushes Using a Bio-Inspired Catechol Anchor for Excellent Biological Lubrication. Adv. Mater. Interfaces 2014, 1, 1400035.   \n(60) Ma, S.; Ye, $\\mathrm{Q.;}$ Pei, X.; Wang, D.; Zhou, F. Antifouling on Gecko’s Feet Inspired Fibrillar Surfaces: Evolving form Land to Marine and from Liquid Repellency to Algae Resistance. Adv. Mater. Interfaces 2015, 2, 1500257.   \n(61) Jia, L.; Zhou, F.; Liu, W. Janus nanoparticle magic: selective asymmetric modification of Au-Ni nanoparticles for its controllable assembly onto attapulgite nanorods. Chem. Commun. 2012, 48, 12112− 12114.   \n(62) Ye, $\\mathrm{Q.j}$ Wang, X.; Li, S.; Zhou, F. Surface-Initiated Ring-Opening Metathesis Polymerization of Pentadecafluorooctyl-5-norbornene-2- carboxylate from Variable Substrates Modified with Sticky Biomimetic Initiator. Macromolecules 2010, 43, 5554−5560.   \n(63) Sheng, W.; Li, B.; Wang, X.; Dai, B.; Yu, B.; Jia, X.; Zhou, F. Brushing up from “anywhere” under sunlight: a universal surfaceinitiated polymerization from polydopamine-coated surfaces. Chem. Sci. 2015, 6, 2068−2073.   \n(64) Wang, X.; Ye, $\\mathrm{Q.;}$ Liu, J.; Liu, X.; Zhou, F. Low surface energy surfaces from self-assembly of perfluoropolymer with sticky functional groups. J. Colloid Interface Sci. 2010, 351, 261−266.   \n(65) Zhong, J.; Ji, H.; Duan, J.; Tu, H.; Zhang, A. Coating morphology and surface composition of acrylic terpolymers with pendant catechol, OEG and perfluoroalkyl groups in varying ratio and the effect on protein adsorption. Colloids Surf., B 2016, 140, 254−261.   \n(66) Zhan, K.; Kim, C.; Sung, K.; Ejima, H.; Yoshie, N. TunicateInspired Gallol Polymers for Underwater Adhesive: Comparative Study of Catechol and Gallol. Biomacromolecules 2017, 18, 2959−2966. (67) Zhan, K.; Ejima, H.; Yoshie, N. Antioxidant and Adsorption Properties of Bioinspired Phenolic Polymers: A Comparative Study of Catechol and Gallol. ACS Sustainable Chem. Eng. 2016, 4, 3857−3863. (68) Li, J.; Ejima, H.; Yoshie, N. Seawater-Assisted Self-Healing of Catechol Polymers via Hydrogen Bonding and Coordination Interactions. ACS Appl. Mater. Interfaces 2016, 8, 19047−19053. (69) Laure, W.; Woisel, P.; Lyskawa, J. Switching the Wettability of Titanium Surfaces through Diels−Alder Chemistry. Chem. Mater. 2014, 26, 3771−3780.   \n(70) Watson, M. A.; Lyskawa, J.; Zobrist, C.; Fournier, D.; Jimenez, M.; Traisnel, M.; Gengembre, L.; Woisel, P. A “Clickable” Titanium Surface Platform. Langmuir 2010, 26, 15920−15924.   \n(71) Goldmann, A. S.; Schödel, C.; Walther, A.; Yuan, J.; Loos, K.; Müller, A. H. E. Biomimetic Mussel Adhesive Inspired Clickable Anchors Applied to the Functionalization of $\\mathrm{Fe}_{3}\\mathrm{O}_{4}$ Nanoparticles. Macromol. Rapid Commun. 2010, 31, 1608−1615.   \n(72) Kaminska, I.; Das, M. R.; Coffinier, Y.; Niedziolka-Jonsson, J.; Sobczak, J.; Woisel, P.; Lyskawa, J.; Opallo, M.; Boukherroub, R.; Szunerits, S. Reduction and Functionalization of Graphene Oxide Sheets Using Biomimetic Derivatives in One Step. ACS Appl. Mater. Interfaces 2012, 4, 1016−1020.   \n(73) Zheng, J.; Chen, Y.; Karim, A.; Becker, M. L. Dopamine-Based Copper-Free Click Kit for Efficient Surface Functionalization. ACS Macro Lett. 2014, 3, 1084−1087.   \n(74) Xu, C.; Xu, K.; Gu, H.; Zheng, R.; Liu, H.; Zhang, X.; Guo, Z.; Xu, B. Dopamine as A Robust Anchor to Immobilize Functional Molecules on the Iron Oxide Shell of Magnetic Nanoparticles. J. Am. Chem. Soc. 2004, 126, 9938−9939.   \n(75) Longo, J.; Garnier, T.; Mateescu, M.; Ponzio, F.; Schaaf, P.; Jierry, L.; Ball, V. Stable Bioactive Enzyme-Containing Multilayer Films Based on Covalent Cross-Linking from Mussel-Inspired Adhesives. Langmuir 2015, 31, 12447−12454.   \n(76) Li, G.; Cheng, G.; Xue, H.; Chen, S.; Zhang, F.; Jiang, S. Ultra low fouling zwitterionic polymers with a biomimetic adhesive group. Biomaterials 2008, 29, 4592−4597.   \n(77) Huang, C.-J.; Wang, L.-C.; Shyue, J.-J.; Chang, Y.-C. Developing Antifouling Biointerfaces Based on Bioinspired Zwitterionic Dopamine through pH-Modulated Assembly. Langmuir 2014, 30, 12638−12646. (78) Chang, C.-C.; Kolewe, K. W.; Li, Y.; Kosif, I.; Freeman, B. D.; Carter, K. R.; Schiffman, J. D.; Emrick, T. Underwater Superoleophobic Surfaces Prepared from Polymer Zwitterion/Dopamine Composite Coatings. Adv. Mater. Interfaces 2016, 3, 1500521.   \n(79) Kang, T.; Oh, D. X.; Heo, J.; Lee, H.-K.; Choy, S.; Hawker, C. J.; Hwang, D. S. Formation, Removal, and Reformation of Surface Coatings on Various Metal Oxide Surfaces Inspired by Mussel Adhesives. ACS Appl. Mater. Interfaces 2015, 7, 24656−24662.   \n(80) Liu, J.; Li, J.; Yu, B.; Ma, B.; Zhu, Y.; Song, X.; Cao, X.; Yang, W.; Zhou, F. Tribological Properties of Self-Assembled Monolayers of Catecholic Imidazolium and the Spin-Coated Films of Ionic Liquids. Langmuir 2011, 27, 11324−11331.   \n(81) Hong, D.; Bae, K.; Hong, S.-P.; Park, J. H.; Choi, I. S.; Cho, W. K. Mussel-inspired, perfluorinated polydopamine for self-cleaning coating on various substrates. Chem. Commun. 2014, 50, 11649−11652. (82) Schlaich, $\\mathrm{C.j}$ Wei, $\\mathrm{Q.;}$ Haag, R. Mussel-Inspired Polyglycerol Coatings with Controlled Wettability: From Superhydrophilic to Superhydrophobic Surface Coatings. Langmuir 2017, 33, 9508−9520. (83) Shi, X.; Ostrovidov, S.; Shu, Y.; Liang, X.; Nakajima, K.; Wu, H.; Khademhosseini, A. Microfluidic Generation of Polydopamine Gradients on Hydrophobic Surfaces. Langmuir 2014, 30, 832−838. (84) Rodenstein, M.; Zürcher, S.; Tosatti, S. G. P.; Spencer, N. D. Fabricating Chemical Gradients on Oxide Surfaces by Means of Fluorinated, Catechol-Based, Self-Assembled Monolayers. Langmuir 2010, 26, 16211−16220.   \n(85) Ryu, J. H.; Messersmith, P. B.; Lee, H. Polydopamine Surface Chemistry − A Decade of Discovery. ACS Appl. Mater. Interfaces 2018, 10, 7523−7540.",
        "category": " References"
    }
]