Mussel-Inspired Polyglycerol Coatings with Controlled Wettability

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Mussel-Inspired Polyglycerol Coatings with Controlled Wettability: From Superhydrophilic towards Superhydrophobic Surface Coatings Christoph Schlaich, Qiang Wei, and Rainer Haag Langmuir, Just Accepted Manuscript • Publication Date (Web): 12 Jun 2017 Downloaded from http://pubs.acs.org on June 13, 2017

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Mussel-Inspired Polyglycerol Coatings with Controlled Wettability: From Superhydrophilic towards Superhydrophobic Surface Coatings Christoph Schlaich,† Qiang Wei,†,‡,§ and Rainer Haag*,†,§ †

Institut für Chemie und Biochemie, Freie Universität Berlin, Takustrasse 3, 14195, Berlin, Germany

‡

Department of Cellular Biophysics, Max-Planck Institute for Medical Research, Heisenbergstr. 3, 70569, Stuttgart, Germany §

Helmholtz Virtual Institute, Multifunctional Biomaterials for Medicine, Kantstraße 55, 14513, Teltow-Seehof, Germany

ABSTRACT: Facile approaches for substrate-independent surface coatings with special wettability properties, such as superhydrophobicity, superhydrophilicity, and superamphiphobicity have been limited. To address this problem, we combined two separate and biomimetic concepts of mussel-inspired adhesion and highly hierarchical lotus-like surface structures to develop a universal fabrication method for various superwetting systems on any kind of material. In this feature article, we would like to summarize our work on mussel-inspired polyglycerol (MI-dPG) and its application in the area of superwetting interfacial materials. The MI-dPG not only mimics the functional groups of the mfp-5 but also their molecular weight and molecular structure, which results in strong and rapid adhesion to the substrate. Furthermore, the MI-dPG coating process provides a precise roughness control. The construction of highly hierarchical and superhydrophilic structures was achieved either directly by pH-controlled aggregation or in combination with nanoparticles. Subsequent post-modification of these highly hierarchical structures with different fluorinated or non-fluorinated hydrophobic molecules yielded a surface with superhydrophobic and even superamphiphobic properties.

INTRODUCTION In the last decade, the development and the fabrication of interfacial material systems with superwettability have become some of the most important aspects of surface chemistry. In 1997 Barthlott et al. first described the lotus effect and set the foundation for more than 20 years of research in the area of superwetting and super-repellent materials.1 They pointed out that superhydrophobicity is the result of a combination of a micro-/nanostructured surface and a hydrophobic material with a low surface free energy. This new understanding of the basic principles underlying the construction of superwetting materials triggered a scientific boom. Many studies pointed out the importance of hierarchical structures with two-tier roughness on both the micro- and the nano-level for superhydrophobic surfaces with extremely low contact angle hysteresis (CAH) and the associated self-cleaning effect.2-5 The principle behind the interplay between surface roughness and surface energy was expanded to other superwetting states (e.g., superhydrophilic), and theoretical descriptions have provided a better understanding of extreme wetting conditions.6-8 To date, more than a thousand different strategies for the fabrication of superhydrophobic surfaces have been reported based on different chemical and physical methods including lithography, chemical vapor deposition, plasma etching techniques, chemically modified monolayers, electrochemical methods, sol-gel processes.9-16 Besides the fabrication protocols, numerous studies have shown many potential applications for superhydrophobic or superhydrophilic surfaces in various areas, such as self-cleaning surfaces, oil/water separation, non-sticky, or anti-fouling surfaces.17-19

Although there are several ways to fabricate superwetting surfaces, most of the published fabrications protocols have two disadvantages. First, fabricating coatings with special roughness often requires a tedious protocol and/or specialized equipment. Second, most of these surface coatings have been prepared on certain substrates and rely heavily on the underlying material’s properties. Therefore, our group focused on developing novel and substrate-independent methods for constructing superwetting surfaces on any kind of substrate by facile approaches. To achieve this goal, we linked two separate biomimetic approaches together. We combined the remarkable adhesive ability of mussel-inspired adhesives with a lotus-like hierarchical structure to develop a universal method to construct various superwetting systems on any kind of material. In several attempts, polydopamine (PDA), which is a well-known mussel-inspired polymer for substrate-independent surface coatings,20 was employed to prepare superhydrophobic surfaces.21-24 Recently, PDA was combined with silica nanoparticles to construct a microscale porous superamphiphobic surface coating via a combination of ice templation and chemical vapor deposition.25 Nevertheless, due to the narrow size range of the aggregate and the limited coating thickness, PDA could not be directly used to produce the right roughness for superhydrophobic or superamphiphobic coatings. In all these examples, the lack of a roughness control in the PDA-based coatings had to be overcome by combining PDA with various particles, templates, or meshes. For this reason, we developed a 2nd generation mussel-inspired adhesive based on a dendritic polymer that allowed one to build up roughness on any kind of

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material via a simple dip coating approach under extremely mild conditions. We will summarize here our recent work on mussel-inspired polyglycerols and their application as superwetting coatings. First, we will introduce the concept of superwetting and then we will discuss the area of mussel-inspired coatings with the focus on mussel-inspired dendritic polyglycerol. After that, we will present our approach for constructing highly hierarchical structures with extreme wetting properties using MI-dPG. The concepts for mussel-inspired adhesives/coatings and superwettability are very comprehensive, which makes it impossible to cover all the aspects in one article. Therefore, we will mainly focus on areas that were relevant for our research. For more detailed studies on specific aspects, we would like to refer the reader to several excellent reviews in these areas.19, 26-30

SUPERWETTABILITY The concept of superwettability is relatively new and combines various extreme wetting states of materials / surfaces under different media.18, 31 These extreme wetting states include, in particular, drops on superhydrophobic (SHP), superhydrophilic (SHL), superolephilic (SOL), and superoleophobic (SOP) surfaces (Figure 2).32-33 Only the substrate-to-air interface is considered in classical wetting. With the ongoing development of surface science, superwetting interfacial materials have been described for different media, such as oil or water. However, to cover all aspects of superwetting would go beyond the scope of this article and we will only focus on the substrate-to-air interphase. The basis for all wetting states is the Young equation (Eq. 1 and Figure 1a), which describes the static contact angle (CA, θ) for homogeneous and flat surfaces.34 (Eq. 1) Young's equation describes a thermodynamic equilibrium, where the terms γSV, γSL, and γLV refer to the interfacial surface tensions of the solid-vapor, solid-liquid, and the liquid-vapor phase. From a classical point of view, any surface with a CA < 90° is hydrophilic and any surface with a CA > 90° is hydrophobic. According to current knowledge, the limit should be regarded as the theoretical value of the mathematical model. Recent empirical studies and investigations have shown that a CA of 65° rather than 90° from the theoretical model determines whether a solid material is hydrophilic or hydrophobic.3536 This threshold is also called the intrinsic CA.

Figure 1. (a) A) Definition of contact angle (CA, θ) according to Young’s equation. (b) Droplet in Cassie-Baxter Mode on top on a rough surface. (c) Droplet in Wenzel Mode on top on a rough surface. (d) Advancing CA (CAAdv, θAdv) and receding CA (CARec, θRec) of a moving droplet. (e) Super-repellent surface as characterized by a CA over 150° and ultra-low contact angle hysteresis (CAH) between CAAdv and CARec. (f) A superhydrophobic but sticky surface, which is characterized by both very high CA and CAH. In reality most surfaces are not flat and show a certain surface roughness and heterogeneity. Roughness plays an especially key role in surfaces with superwettability. This means a water droplet can then either penetrate or be suspended above the asperities, because most surfaces are usually covered with micro- and/or nanoscale roughness grooves (Figure 1b and 1c). Wenzel, Cassie, and Baxter extensively studied the wettability effect on surface roughness, which resulted in two models (Figure 1).37-38 In the Wenzel state, a water droplet fully penetrates into the rough grooves of a textured surface. As a consequence, the effective contact area of a droplet with the surface increases and a roughness factor has to be considered (Eq. 2). cos θW = r cos θ

(Eq. 2)

In Equation 2, θw corresponds to the apparent contact angle and r represents the roughness factor. Wenzel's model predicts that the wetting of hydrophobic surfaces is enhanced by roughness and lessened by roughness for the hydrophilic case. In the second case, the Cassie-Baxter (CB) state, the air pockets trapped inside textured surfaces support the water droplet. (Eq. 3) In Equation 3, θCB corresponds to the apparent contact angle, θ refers to the CA from Eq. 1, and the surface fraction s corresponds to the ratio of the surface on top of the roughness grooves (in contact with the liquid) and the apparent surface of the substrate. Two main points be-


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come apparent from the Equation 3: (a) the fraction of the solid part should be as small as possible for superhydrophobic surfaces and (b) a hydrophobic material should be selected, which has a high water contact angle (WCA) in the ideally flat case. For the characterization of superhydrophobic surfaces, the CAH and the related dynamic CAs are important parameters.39 Dynamic contact angles are non-equilibrium CAs and can be observed in a moving droplet. The CAH is given by the difference of the CA at the front of the moving droplet (advancing CA) and the CA at the back of the moving droplet (receding CA). The actual contact mode of the droplet on the surface is crucial in the design of a superhydrophobic surface and is what determines its wetting properties. In the case of surface with a WCA over 150 ° in the Wenzel mode, the surface is still considered as superhydrophobic, although the CAH is significantly higher than in Cassie mode. As a result, the surface typically shows a relatively high adhesion and the droplet strongly pins to the surface (Figure 1f). Differently in the Cassie-Baxter state, the air entrapped inside the rough grooves supports the water droplets on top and pins the three-phase contact line on the topside of the surface structure. Therefore, the surface normally exhibits a low CAH and its adhesion can be reduced dramatically, which enables the droplet to roll off easily upon tilting (Figure 1e). It should be emphasized that both models, the Wenzel state and Cassie-Baxter state, are two extremes and, in reality, the air can only be entrapped to a certain degree, indicating a transition state between Wenzel and Cassie-Baxter state.40

Figure 2. (a) Different wetting states as examples of superwettability: superhydrophobic (SHP) superhydrophilic (SHL) superamphiphilic (SAL), superoleophilic (SOL), superolephobic (SOP), and superamphiphobic (SAP). (b) and (c) Rice and Lotus leaves as examples for superhydrophobic surfaces.41-42 (d) Rose petal structure is superhydrophobic but has a strongly adhesive surface.43 (e) Sharkskin as an example for an underwater superoleophobic surface.44 Modified reprint from ref. 41, 42, 43, and 44 with kind permission of the American Chemical Society, Beilstein Institute, Royal Societey of Chemistry, and the Material Research Society. Superhydrophobic surfaces are still the most analyzed superwetting systems, although most superhydrophobic surfaces in daily life are exposed to a surfactant containing solutions or oil than pure water. Because the surface tension of a surfactant containing solutions and oils (< 60 mN·m–1) is smaller than that of water (∼72 mN·m–1), the superhydrophobic materials are usually wetted in air. Therefore, superamphiphobic surfaces, which can repel both water and oil, have received a great deal of interest in the last decade, because they open the door for a much broader range of applications such as solvent-free synthesis of polymeric microspheres on a surface or handling of biologically sensitive liquids.45-46 However, for the fabrication of superamphiphobic surfaces, the established ways to fabricate superhydrophobic surfaces are no longer sufficient and an even more precise design of micro- to nano-scaled hybrid structures is required.47 In general, a surface is considered superamphiphobic when the organic solvents such as hexadecane (27.5 mN/m) contacting the surface show a contact angle over 150° and the rolling off angle is less than 10°.48-49 In the last decade, there have been several reports of attempts to engineer superamphiphobic surfaces by precisely designing surface topographies, in which the importance of hierarchical surface roughness and re-entrant structures has been described.50-54 However, most of the superamphiphobic attempts are limited and repel liquids only down to a certain surface tension. In some examples in the literature, it was possible to successfully repel liquids with surface tensions down to 20 mN/m (e.g., octane or heptane) by electrospinning microbeads of fluoropolymers on stainless steel meshes.55-56 Only a specific double-reentrant structure, which enables a very low liquid-solid contact fraction, repels liquids with the lowest known value of 10 mN/m (i.e., FC-72).57 Superhydrophilic surfaces that represent the opposite extreme of wettability have received less attention compared to the numerous publications on superhydrophobic surfaces.58-60 However, superhydrophilic surfaces have their own advantages and are extremely promising candidates regarding oil/water separation, anti-fogging, or water harvesting.61-63 A general guideline to construct superhydrophilic surfaces is to create rough structures with a hydrophilic component according to Wenzel’s theory.64-65 An alternative approach is to irradiate semiconductors (e.g., TiO2) with UV, which leads to a photo-


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induced hydrophilic (PIH) effect that generates a SHL surface even without a microstructure.66 The Nepenthes pitcher plant is an example of a natural SHL surface that is always lubricated, which is due to the extreme hydrophilicity. As a result, the liquid-infused surface becomes highly slippery and insects can easily fall into the pitchershaped leaves. Inspired by the Nepenthes pitcher plant, the slippery liquid-infused porous surfaces (SLIPS) have turned out to be a good alternative to classical superrepellent systems.67 The concept of SLIPS was derived from the Nepenthes pitcher plant and is based on the infiltration of a low-surface-energy porous surface texture with lubricating liquids. The method represents a straightforward solution for liquid repellency and resistance to fouling combined with an extremely simple fabrication process.68-72 MUSSEL-INSPIRED COATINGS Marine mussels adhere rapidly under extremely harsh environmental conditions onto practically any kind of material.73-74 The reason for these unique, outstanding adhesion properties is a really complex protein mixture containing 25-30 different mussel foot proteins (mfp) that are expressed and excreted by the mussel to form the socalled adhesive byssus.29 In 1981 White and et al. first identified 3,4-dihydroxyphenyl-l-alanine (DOPA) and claimed its key role in the adhesion mechanism.75 This important discovery was the starting point for a deeper understanding of the exact structure of proteins responsible for the adhesion. The mfp 3 and mfp 5 are considered the most adhesive proteins located in the byssal-substrate interface.76 Both show a conspicuously high amount of catechol (in the form of DOPA) and amine groups. Inspired by these two functional groups, Messersmith et al. reported PDA as the ideal strategy for substrateindependent coatings.20 In general, PDA is formed by pHinduced, oxidative polymerization of dopamine in alkaline solutions. The simple immersion of a substrate into an aqueous solution of dopamine buffered to alkaline pH results in the spontaneous deposition of a thin PDA film. Although the preparation is relatively simple, the molecular mechanism of the coating formation has not been completely understood yet. It is widely agreed that the first steps include the oxidation of dopamine to the dopamine-quinone, the intramolecular cyclization to the dopamine chrome, and formation of 5,6-dihydroxyindole (DHI) and 5,6-indolequinone (IDQ).77-79 The IDQ molecules then undergo further crosslinking reactions with each other to oligomers, which then aggregate via a combination of hydrogen bonds and π-stacking interactions to form a stable coating. Various interactions of the catechol moiety, including hydrogen bonding, metal–catechol coordination, electrostatic interaction, cation–π interaction, and π–π aromatic interactions, are responsible for the strong adhesion to different substrates (Figure 3a).76, 80 Strong non-covalent interactions (hydrogen bonds or π–π stacking interactions) can be found between catechol groups and inorganic substrates such as glass or mica.81-82 In the case of metal oxides (e.g., TiO2), catechol groups have been assumed to form strong metal–catechol coor-

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dination bonds.83 In the case of more hydrophobic substrates or even inert polymer materials, hydrophobic interaction, π-stacking, and van der Waals’ forces between catechol and the substrate are believed to contribute to the strong interaction.84-85 Moreover, the covalent and non-covalent cross-linking of the DA oligomers extend the monovalent interaction with substrates to polyvalent anchoring, which results final stable coating.86 Since 2007, the versatility of PDA has been demonstrated in many examples in the literature.87-92 Hence, PDA has opened a new door for surface modification and has become one of the most popular strategies for the fabrication of functional surfaces and materials.93 Among the various strategies, the so called one-pot PDA functionalization is the most widely used approach, because of the outstanding simplicity to immobilize a molecule of interest onto the substrate by co-dissolving it in the coating mixture.94

Figure 3. (a) Catechol-mediated adhesion to different substrates such as mica, polystyrene (PS), TiO2 via hydrogen bonding, π-π stacking interactions, and metal coordination. (b) Schematic illustration of different musselinspired polymer architectures. Besides PDA, several other dopamine derivatives have been found to show similar adhesive and crosslinking properties. The most commented derivate reported in the literature is amino acid DOPA.95-96 Compared to PDA, polyDOPA has the advantage that further functionalization can take place via an additional COOH group.97 As a result, functional surfaces can be produced directly in one step by the appropriate choice of the side chains. Alternatively, regarding low molecular weight precursors for universal coatings, the direct attachment of catechol derivatives to polymer architectures has been demonstrated to offer various strategies for fabricating novel functional polymer coatings (Figure 3b).98-102 In these polymeric architectures, the catechol normally serves as an anchor


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and crosslinking group at the same time, whereby the amount of catechol functionalization has to be adjusted depending on the substrate.103 In the case of metal oxide surfaces (e.g., TiO2), one functional group might be enough for the initial adhesion because the adhesion of the catechol is quite strong. However, due to oxidative detachment, multiple catechol groups are required to stably anchor the to the surface.104-105 In contrast, the interaction between the catechol and the substrate is really too weak for chemical inert surfaces like Teflon or polystyrene (PS).106 As a result, an even higher amount of catechol units or hydrophobic residues are necessary to form a stable coating.102 While in nature the adhesion and solidification of a mussel byssus only requires 3-10 min, a PDA coating takes several hours to form a thick and dense film.20, 107 The reason for the enormous divergence can be explained by the difference of the precursors for the coating. Dopamine mimics the chemical functionality of mfps, but neither the molecular weight nor the molecular structure is taken into account. To overcome these inherent drawbacks of PDA, we recently introduced mussel-inspired dendritic polyglycerol (MI-dPG) that not only mimics the functional groups of mfp-1 and mfp-5 but also their molecular weight and molecular structure (Figure 4).108 Similar to the natural protein, the combination of both the catechol and amine moieties is responsible for the strong adhesion to the substrate. Furthermore, the multivalent character of the dendritic polyglycerol scaffold not only exposes most of its functional groups to periphery (similar to folded proteins), but also significantly accelerates the crosslinking of the polymers during the coating. As a result, the MI-dPG can serve as a remarkable surface coating and can form stable coatings on virtually all types of material surfaces within 10 min or a micrometer-scale coating within hours. The MI-dPG was synthesized in a four-step synthesis starting from dendritic polyglycerol (dPG) as reported in our optimized procedure.109 In brief, the hydroxyl groups of the dPG scaffold (Mn = 12,000 g·mol-1, PDI = 1.5) were converted to amine groups. 40% of the terminal amine groups of the scaffold were functionalized with catechol moieties using 3,4dihydroxyhydrocinnamic (CHHA) via an EDC coupling strategy under slightly acidic conditions. It should be noted that we have used mainly two molecular weights in our studies (Mn = 6,000 and Mn = 12,000 of the initial dPG scaffold). Interestingly, both showed nearly identical coating properties. Under basic conditions, the MI-dPG can undergo covalent crosslinking and form a chemically and mechanically stable coating on virtually all types of materials (Figure 4). Amines can couple with catechols under oxidizing conditions via Michael addition or Schiff base reactions to enhance the crosslinking of the coatings.110

Figure 4. Top left: Structure of the mussel-foot protein mfp-5 showing the peptide sequence that contains amine (blue) and catechol (red) units in their side chains. Top right: the chemical structure of mussel-inspired dendritic polyglycerol (MI-dPG). Bottom: the covalent postulated crosslinks of the universal surface coatings and postmodification possibilities. Modified reprint from ref. 108 with kind permission of Wiley. In PDA or DOPA coatings, the coating time has a strong influence on the resulting layer thickness. However, regardless of the time in most of the coatings, a flat and smooth polymeric film is obtained. In the case of MI-dPG, two possible coating formations have to be considered. First, the MI-dPG directly adsorbs and anchors onto the substrate and forms a film that constantly increases with time (similar to PDA coatings). Second, the MI-dPG starts to crosslink in the solutions and forms partially insoluble particles that will sediment to the bottom and crosslink with the pre-adsorbed MI-dPG film on the substrate. The second mechanism has a strong influence on the resulting surface roughness and morphology of the coating. The increase in surface roughness over time has a large influence on the wetting properties of the coating and makes characterization via contact angle measurements difficult. The static water contact angles of the MI-dPG-coated silica wafers decreased with the incubation time. In the case of the covalently crosslinked MI-dPG coatings, the increase in roughness with coating time, will automatically lead to a further decrease in the contact angle. Figure 5 demonstrates some representative WCAs on different substrates after 15 min, 3 h, and 16 h of MI-dPG coating. The WCA for all these substrates reached 55°-60° and 20°– 30° after 15 min and 3 h, respectively, even for hydrophobic substrates such as Teflon and polypropylene (PP). This indicates that the original wetting property of these substrates was completely changed after the MI-dPG coatings. The MI-dPG coatings are still chemically active surfaces due to numerous catechols and amine groups on top. Different amines, thiols, or carboxylic acids can be attached to the surface to generate a variety of functional


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surfaces. Furthermore, the physical characteristics of the coatings can be tuned by adjusting surface roughness and morphology of the coatings. Combining all these properties creates an interesting polymer that can serve as universal, modifiable, and multifunctional surface for various purposes.108

Figure 6. (a) General coating concept of the superhydrophilic (SHL) and superhydrophobic (SHP) MI-dPG. (b) The surface morphology of the bare glass and the superhydrophilic and superhydrophobic coatings on glass. (c) The related static water contact angle of the bare substrate, SHL, and SHP MI-dPG.

Figure 5. (a) Water contact angle (WCA) on the MI-dPGcoated slides after 15 min, 3 h, and 16 h. (b) Timedependent thickness of the covalently crosslinked MIdPG coatings on silica surfaces. SUBSTRATE-INDEPENDENT SUPERWETTABILITY Based on MI-dPG’s large influence on surface roughness and morphology during coating, MI-dPG is an exceedingly promising polymer for various materials with superwettability. A micrometer-scaled surface roughness that shows extreme wetting properties is obtained after a coating time of 16 h (see Figure 6b). This micrometer scale roughness highly affected the surface wetting. A superhydrophilic surface with WCA close to zero was thus obtained. Even on rather hydrophobic substrates like PP or Teflon, the coated surface was completely wetted by the droplet. After perfluoroalkyl-modification of the SHL substrate, the wetting properties completely changed to the other extreme, which yielded a SHP surface with a water contact angle higher than 150° (see Figure 6a and 6c). As a result, a droplet that hits the SHP MI-dPG surface with an inclination of 10° directly easily rolls off. This self-cleaning effect is further represented in the relatively low contact angle hysteresis of 6.6°. It is worth mentioning that the post-modification did not affect the morphology and surface structure of the MI-dPG coating.

By introducing hierarchical structures into the MI-dPGcoated surface, roughness can be further increased, which makes even more hydrophobic surfaces accessible.111 Depending on coating parameters, such as the pH value, concentration of polymer, and/or coating time, the crosslinking of the MI-dPG polymer precursor could be accelerated or decelerated. As a result, the aggregate size could be precisely adjusted from micro- to nanoscale, and control over surface roughness and morphology could be obtained. When the crosslinking of a solution MI-dPG in MeOH (1 mg/mL) was triggered by adding 3-(Nmorpholino)propanesulfonic acid (MOPS) to buffer solution with a pH-value of 8.5 (3v/1v) within 16 h, aggregates with a size of 0.5 - 2 µm were obtained, which resulted in a uniform micro-roughened surface (Figure 7a). When the pH-value of the MOPS buffer was reduced to 7.5 and the concentration of MI-dPG was 0.5 mg/mL, much smaller nanometer sized aggregates were obtained. In a two-layer approach combining the micrometer- and the nanometer-sized coatings, “lotus-like” hierarchical structures were achieved (Figure 7b). In the first step, a microroughened surface was prepared that then served as the initial layer for the second layer with the nanometer-sized particles. As a result, a highly hierarchical MI-dPG-coated surface (hMI-dPG) was obtained. Alternatively, nanoparticles (NP) were used as a second layer to obtain hierarchical micro and nanometer-sized coatings. Microroughened MI-dPG slides were immersed in an AuCl3 (0.1 g/mL) solution for 16 h to deposit gold NPs (AuNPs). In the case of the silver NPs (AgNPs) as a 2nd layer, the slides with the initial layer were immersed in an aqueous AgNO3 for 5 h. Due to the reducing effect of the catechol groups, no additional reducing agent was necessary and the NPs were uniformly distributed over the whole surface. The formation of the hierarchical surface structures was confirmed by scanning electron microscopy (SEM).


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The highly porous aggregated polymeric cluster with twotier roughness for both hMI-dPG and the MI-dPG NPs coatings are clearly shown in Figure 7c and d.

Figure 7. Top: general coating approach for the highly hierarchical MI-dPG (hMI-dPG) surfaces. SEM images of (a) micro-roughened MI-dPG-coated surface, (b) hierarchical MI-dPG-coated surface (hMI-dPG), (c) MI-dPG AuNP-coated surface, and (d) MI-dPG AgNP-coated surface. Insets: images of 3 μL water droplets on these surfaces and the results of the contact angle (CA) measurements. Modified reprint from ref. 111 with kind permission of American Chemical Society.

The hMI-dPG and MI-dPG Au/Ag NP structures with optimized roughness highly affected the wetting of the surface. In all cases, the surface turned completely superhydrophilic and showed a WCA close to zero. After post-modification with a perfluorinated acid chloride, the WCA dramatically increased and showed an even higher WCA than for the SHP MI-dPG. It was hard to deposit the water droplets on the coating, because they easily rolled off due to the extremely low adhesion to the coating. These extremely repellent properties are further enhanced by an extremely low rolling off angle and CAH of less than 1°. Changing the solvent from water to different organic solvents or surfactant containing solutions, the droplets deposited on the hMI-dPG coating showed contact angles ranging from 148° ± 4° for hexadecane up to 163° ± 3° for diiodomethane (Table 1). As shown in Figure 8a the CA for droplets for various solvents on top of the MI-dPG Au/Ag NP-coated surfaces were lower compared to the SAP hMI-dPG, but still significantly better than for the SHP MI-dPG with only microroughness. While a droplet of surfactant-containing solutions like sodium dodecyl sulfate (SDS 4% w/w) easily rolls down the hMI-dPG coated slides, it stayed strongly pinned on the MI-dPG NPs coated surfaces upon tilting, although the CA was close to 150°. The superamphiphobicity systematically increased with the ratios of the nanometer- to micrometersized aggregates from 1/50 for the MI-dPG Au/Ag NPs to 1/10 for the hMI-dPG, which was in accordance with previous studies in the literature.112 For this reason, we exclusively used hMI-dPG for all further experiments. In contrast to SHP surfaces, the nomenclature for SAP systems was not exactly defined. Compared to state-of-the-art reentrant structure-based superamphiphobic surfaces, our substrate-independent approach certainly repels fewer solvents and superamphiphobicity is slightly limited. However, since there is no exact term for such surfaces, which are significantly better than SHP surfaces but do not reach the state of the art regarding liquid repellency, we have designated our SAP hMI-dPG surfaces as quasi-superamphiphobic surface coating.


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Figure 8. (a) Contact angles of various solvents on different types of MI-dPG coatings and on flat PTFE. Pictures on the right: CA of serum (top) and hexadecane (bottom) on the hMI-dPG surface. (b) Time-sequence images representing the repellency of the hMI-dPG surface against water, water with high pressure, SDS (4%), and a torrent of SDS (4%) (from left to right). Reprint from ref. 111 with kind permission of American Chemical Society.

Table 1. Static CA and roll off angle of the superamphiphobic hMI-dPG coating. Liquid Surface Tension CA Water 72.1 mN/m 173° ± 3° Serum 56.9 mN/m 166° ± 3° Diodomethane 50.9 mN/m 163° ± 3° Ethylene glycol 34.5 mN/m 157° ± 3° SDS (4%) 34.2 mN/m 156° ± 3° Hexadecane 27.5 mN/m 148° ± 4° Dodecane 23.4 mN/m 95° ± 4° Hexane 18.4 mN/m < 10°

quasiRA < 2° 5° 7.5° 10° 10° -

In addition to the coating time and the pH value, the depth of the coating solution is another factor that highly affects the resulting structure and morphology. The coating produces aggregates that settle as a sediment and crosslink with the base layer. Adjusting the coating depth controls the number of final particles stacked on each other. The deeper the coating depth, the more aggregates form in the solution above and settle down to the substrate, which in the end leads to a higher roughness. Consequently, a coating with a gradient layer thickness can be obtained by simply tilting the substrate during coating. Post-modification of this gradient coating yielded a quasisuperamphiphobic surface with anisotropic wettability, and the liquid repellency constantly decreased along the gradient from high to low thickness (Figure 9). For instance, a droplet of SDS (4%) decreased from 154° for maximum height to 73° for minimum height. The difference in the layer thickness was confirmed by AFM and SEM measurements. The AFM and SEM pictures showed an increase in layer thickness, aggregate density, surface roughness, and the maximum peak height (Figure 9). Superamphiphobic surfaces are considered highly promising candidates for perfect anti-fouling surfaces. Most approaches prevent the adhesion of proteins or microorganisms by using hydrophilic coatings and a hydration shell. A new approach has been presented with hardly any contact with the surface and a really low adhesion due to the nearly contact-free, solid-liquid interface of the droplet with the superamphiphobic surface. The antifouling properties of the fluorinated hMI-dPG coating were tested using the BCA™ protein assay reagent kit (PIERCE) and quantitated by quartz crystal microbalance (QCM). Figure 10a shows the protein adsorption of a hMI-dPGcoated glass in comparison to a polystyrene (PS) and a glass reference from undiluted blood serum. The adsorbed amounts of protein for the PS and glass reference were 2.4 and 1.7 μg / cm2, respectively. In contrast, the hMI-dPG-coated glass has a protein adsorption close to zero (lower than the limit of detection) and the contact area in the serum-coating interface is minimized (Figure

10a). Cell adhesion studies were performed with GFPmodified Hela cells fibroblasts. In the case of the noncoated glass surfaces, the cells spread regularly over the whole surface after 3 days of cultivation, whereas no cells were detected on the hMI-dPG modified surface (Figure 10b). Such low fouling properties for highly complex protein mixtures such as serum are very impressive, since completely non-fouling coatings are still a major challenge in surface science. However, an accurate analysis of the protein adsorption and the handling of biological fluids on top of superamphiphobic surfaces are very difficult, since many conventional methods for investigation (e.g., QCM and/or SPR) cannot be used due to the greater layer thickness, non-transparency, and pressure dependency of these highly hierarchical structures.

Figure 9. (a) Photo of the gradient hMI-dPG coating with dye-colored SDS (4%) on top. SEM images of the gradient hMI-dPG coating for (b) low thickness and (c) high thickness. 100 x 100 μm AFM images of a scratched gradient hMI-dPG surfaces and corresponding cross-section profile (d, f) for low thickness with Rq = 360 nm, Ra = 454 nm, and Rmax = 2.91 μm, (e, g) for high thickness with Rq = 639 nm, Ra = 764 nm, and Rmax = 3.64 μm. The listed R-values are the mean of three different cross sections. Modified reprint from ref. 111 with kind permission of American Chemical Society.


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Figure 10. (a) Protein adsorption of the fluorinated hMIdPG surface in comparison to glass and polystyrene (PS). The adsorbed amount of proteins on both hMI-dPGcoated PS and glass was close to zero (lower than the limit of detection). (b) The adhesion of Hela cells that express green fluorescent protein (GFP) on the bare and hMI-dPG-modified glass after 3 days of cultivation. Modified reprint from ref. 111 with kind permission of American Chemical Society. Although the bioaccumulation and dramatic ecological impact of perfluorinated building blocks is obvious, perfluorination of surfaces is still the most used method for lowering the surface energy. Therefore, we recently proposed a fluorine-free alternative based on the hMI-dPG. Instead of perfluorination, the highly hierarchical structures were transferred into superhydrophobic surfaces by post-functionalization with different fatty acids (e.g., stearic acid).113 Similar to nature, highly water repellent surfaces were obtained by combining optimized roughness and a precise morphology with stearic acid as the hydrophobic component. To achieve these alkylated hMIdPG surfaces, the slides were simply immersed in a slightly basic solution of stearic acid chloride for 5 h. As shown in Table 2, the WCA on top of the fluorinated and nonfluorinated hierarchical structures were all in the same range. Even the CAH and the rolling angle (RA) hardly differed from their fluorinated analog. The limitations of the fluorine-free coatings became obvious when the solvent was changed from water to hexadecane. The SAP hMI-dPG and MI-dPG Au/Ag NP coatings still showed values close to 150°, whereas the alkylated surfaces were completely wetted and showed a CA of 0°. Table 2. Comparison of WCA and Hexadecane CA of the fluorinated and alkylated hMI-dPG coating. Coating MI-dPG

Post-Mod CF8

WCA 158 ± 4

CA (C16) 110 ± 3

hMI-dPG

CF8

172 ± 3

148 ± 5

MI-dPG

C18

155 ± 5

< 10°

hMI-dPG

C18

169 ± 3

< 10°

The superhydrophobic and superoleophilic properties shown in Table 2 clearly indicate that the alkylated hMIdPG surfaces are an ideal substrate for a lubricant-infused

slippery surface. The porous polymeric structure of the alkylated hMI dPG coating can be infused by a lipophilic solvent such as hexadecane. The cheap and daily used sunflower oil from the supermarket surprisingly qualified as a lubricant just as well as pure chemicals. Once the oil penetrated the porous texture, a smooth, defect-free lubricating layer was obtained over the entire surface. Because we completely avoided the fluorinated building block and lubricating oils, we have defined this surface a more environmentally friendly slippery surface (eSLIPS). A water droplet on top of the eSLIPS showed a CA of 27° ± 1° and the CAH was 10°. This is sufficiently slippery for a water drop to smoothly roll off at a tilting angle of α = 10° (Figure 11). It should be mentioned that droplets placed on slippery surfaces cannot be directly compared to droplets on a superhydrophobic surface, because they exhibit fundamentally different behavior. The apparent contact angles on slippery surfaces are caused by the formation of an annular ridge of the lubricant, which is cloaked around the water drop in order to keep the balance of the fourphase system. Besides the change in the wetting properties, the eSLIPS exhibited improved transparency in comparison to the dry superhydrophobic hMI-dPG coating (Figure 11). In contrast to established fluorinated SLIPSs, the repellency regarding more lipophilic solvents such as hexane, silicon oil, and crude oil is certainly limited, since these liquids tend to directly act as the lubricant itself.67, 114

Figure 11. (a) Droplet sliding down the environmentalfriendly slippery surface (eSLIPS). (b)-(e) Oil contamination on top of the eSLIPS act as a new lubricant after short incubation time. (f) Water repellency after oil contamination. (g) The adhesion of Hela cells that express green fluorescent protein (GFP) on the bare and hMI-dPG modified glass after 2 days of cultivation. (h) Comparison of the transparency of the SHP hMI-dPG and the eSLIPS surfaces. Reprint from ref. 113 with kind permission of Royal Society of Chemistry.

CONCLUSION AND FUTURE PERSPECTIVE In this feature article, we summarized our work on mussel-inspired dendritic polyglycerol (MI-dPG), which effectively mimic mussel-foot proteins not only with regard to their functional groups but also their molecular weight and molecular structure. MI-dPG can rapidly adhere on


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virtually any material surface and form a polymeric film in a nanometer range within 10 min or a rough coating in micrometer range in several hours. By a precise control over the surface roughness and morphology, highly hierarchical structures were accessible. Based on the hMIdPG structure, we proposed a straightforward method for the construction of substrate-independent superhydrophobic, superamphiphobic, superhydrophilic, and slippery surfaces. Furthermore, we presented an entirely fluorine-free approach as an alternative to the conventional method of perfluoration to achieve more environmental friendly coatings with special wettability. Therefore, the MI-dPG can be used as a highly efficient, universal, and easy-to-use platform for constructing various superwetting systems on various substrates that are based on the same material. For this reason, MI-dPG can serve as an ideal model system to test the influence of different wetting properties of a surface regarding various processes such as release properties of a material. In general, the progress in the area of superwetting surfaces rapidly improved in the last decade and has great potential for the future. However, for an implementation in daily life, some rather basic problems of superwetting systems, such as durability, cost effectivity, and complexity of the process, have to be addressed. ACKNOWLEDGMENT This work was supported by the FU Berlin Graduate School “Fluorine as a Key Element” (GRK 1582) funded by the German Science Foundation (DFG) and the Helmholtz Virtual Institute (HVI). The authors thank, the core facility BioSupraMol and Anke Schindler for their support with the SEM measurements, and Dr. Pamela Winchester for language polishing this manuscript.

REFERENCES

1. Barthlott, W.; Neinhuis, C., Purity of the Sacred Lotus, or Escape from Contamination in Biological Surfaces. Planta 1997, 202 (1), 1-8. 2. Koch, K.; Bhushan, B.; Jung, Y. C.; Barthlott, W., Fabrication of Artificial Lotus Leaves and Significance of Hierarchical Structure for Superhydrophobicity and Low Adhesion. Soft Matter 2009, 5 (7), 1386-1393. 3. Bharat, B.; Yong Chae, J., Micro- and Nanoscale Characterization of Hydrophobic and Hydrophilic Leaf Surfaces. Nanotechnology 2006, 17 (11), 2758. 4. Feng, L.; Li, S.; Li, Y.; Li, H.; Zhang, L.; Zhai, J.; Song, Y.; Liu, B.; Jiang, L.; Zhu, D., Super-Hydrophobic Surfaces: From Natural to Artificial. Adv. Mater. 2002, 14 (24), 1857-1860. 5. Michael, N.; Bhushan, B., Hierarchical Roughness Makes Superhydrophobic States Stable. Microelectron. Eng. 2007, 84 (3), 382-386. 6. Bhushan, B.; Jung, Y. C.; Koch, K., Micro-, Nano- and Hierarchical Structures for Superhydrophobicity, SelfCleaning and Low Adhesion. Phil. Trans. R. Soc. A 2009, 367 (1894), 1631-1672.

Page 10 of 16

7. Feng, X. J.; Jiang, L., Design and Creation of Superwetting/Antiwetting Surfaces. Adv. Mater. 2006, 18 (23), 3063-3078. 8. Lau, K. K. S.; Bico, J.; Teo, K. B. K.; Chhowalla, M.; Amaratunga, G. A. J.; Milne, W. I.; McKinley, G. H.; Gleason, K. K., Superhydrophobic Carbon Nanotube Forests. Nano Lett. 2003, 3 (12), 1701-1705. 9. Qu, M.; Zhang, B.; Song, S.; Chen, L.; Zhang, J.; Cao, X., Fabrication of Superhydrophobic Surfaces on Engineering Materials by a Solution-Immersion Process. Adv. Funct. Mater. 2007, 17 (4), 593-596. 10. Tsai, H.-J.; Lee, Y.-L., Facile Method to Fabricate Raspberry-Like Particulate Films for Superhydrophobic Surfaces. Langmuir 2007, 23 (25), 12687-12692. 11. Larmour, I. A.; Bell, S. E. J.; Saunders, G. C., Remarkably Simple Fabrication of Superhydrophobic Surfaces Using Electroless Galvanic Deposition. Angew. Chem., Int. Ed. 2007, 46 (10), 1710-1712. 12. Zhao, N.; Shi, F.; Wang, Z.; Zhang, X., Combining Layer-by-Layer Assembly with Electrodeposition of Silver Aggregates for Fabricating Superhydrophobic Surfaces. Langmuir 2005, 21 (10), 4713-4716. 13. Qian, B.; Shen, Z., Fabrication of Superhydrophobic Surfaces by Dislocation-Selective Chemical Etching on Aluminum, Copper, and Zinc Substrates. Langmuir 2005, 21 (20), 9007-9009. 14. Shiu, J.-Y.; Kuo, C.-W.; Chen, P.; Mou, C.-Y., Fabrication of Tunable Superhydrophobic Surfaces by Nanosphere Lithography. Chem. Mater. 2004, 16 (4), 561564. 15. Jiang, L.; Zhao, Y.; Zhai, J., A Lotus-Leaf-Like Superhydrophobic Surface: A Porous Microsphere/Nanofiber Composite Film Prepared by Electrohydrodynamics. Angew. Chem. 2004, 116 (33), 4438-4441. 16. Wei, Q.; Schlaich, C.; Prevost, S.; Schulz, A.; Bottcher, C.; Gradzielski, M.; Qi, Z.; Haag, R.; Schalley, C. A., Supramolecular Polymers as Surface Coatings: Rapid Fabrication of Healable Superhydrophobic and Slippery Surfaces. Adv. Mater. 2014, 26 (43), 7358-7364. 17. Hao, C.; Liu, Y.; Chen, X.; Li, J.; Zhang, M.; Zhao, Y.; Wang, Z., Bioinspired Interfacial Materials with Enhanced Drop Mobility: From Fundamentals to Multifunctional Applications. Small 2016, 12 (14), 1825-1839. 18. Wen, L.; Tian, Y.; Jiang, L., Bioinspired SuperWettability from Fundamental Research to Practical Applications. Angew. Chem., Int. Ed. 2015, 54 (11), 33873399. 19. Wang, Z.; Elimelech, M.; Lin, S., Environmental Applications of Interfacial Materials with Special Wettability. Environ. Sci. Technol. 2016, 50 (5), 21322150. 20. Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B., Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science 2007, 318 (5849), 426430. 21. 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 (79), 11649-11652.


Page 11 of 16

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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22. Zhang, L.; Wu, J.; Wang, Y.; Long, Y.; Zhao, N.; Xu, J., Combination of Bioinspiration: A General Route to Superhydrophobic Particles. J. Am. Chem. Soc. 2012, 134 (24), 9879-9881. 23. Wang, Z.; Xu, Y.; Liu, Y.; Shao, L., A Novel MusselInspired Strategy toward Superhydrophobic Surfaces for Self-Driven Crude Oil Spill Cleanup. J. Mater. Chem. A 2015, 3 (23), 12171-12178. 24. You, I.; Chang Seo, Y.; Lee, H., Material-Independent Fabrication of Superhydrophobic Surfaces by MusselInspired Polydopamine. RSC Advances 2014, 4 (20), 10330-10333. 25. Li, F.; Du, M.; Zheng, Q., Dopamine/Silica Nanoparticle Assembled, Microscale Porous Structure for Versatile Superamphiphobic Coating. ACS Nano 2016, 10 (2), 2910-2921. 26. Tian, Y.; Jiang, L., Design of Bioinspired, Smart, Multiscale Interfacial Materials with Superwettability. MRS Bull. 2015, 40 (02), 155-165. 27. Zhang, X.; Shi, F.; Niu, J.; Jiang, Y.; Wang, Z., Superhydrophobic Surfaces: From Structural Control to Functional Application. J. Mater. Chem. 2008, 18 (6), 621633. 28. Li, X.-M.; Reinhoudt, D.; Crego-Calama, M., What Do We Need for a Superhydrophobic Surface? A Review on the Recent Progress in the Preparation of Superhydrophobic Surfaces. Chem. Soc. Rev. 2007, 36 (8), 1350-1368. 29. Lee, B. P.; Messersmith, P. B.; Israelachvili, J. N.; Waite, J. H., Mussel-Inspired Adhesives and Coatings. Annu. Rev. Mater. Res. 2011, 41, 99-132. 30. Silverman, H. G.; Roberto, F. F., Understanding Marine Mussel Adhesion. Mar. Biotechnol. 2007, 9 (6), 661-681. 31. Su, B.; Tian, Y.; Jiang, L., Bioinspired Interfaces with Superwettability: From Materials to Chemistry. J. Am. Chem. Soc. 2015. 32. Liu, M.; Wang, S.; Wei, Z.; Song, Y.; Jiang, L., Bioinspired Design of a Superoleophobic and Low Adhesive Water/Solid Interface. Adv. Mater. 2009, 21 (6), 665-669. 33. Wang, J.; Zheng, Y.; Nie, F.-Q.; Zhai, J.; Jiang, L., Air Bubble Bursting Effect of Lotus Leaf. Langmuir 2009, 25 (24), 14129-14134. 34. Young, T., An Essay on the Cohesion of Fluids. Phil. Trans. R. Soc. Lond. 1805, 95, 65-87. 35. Vogler, E. A., Structure and Reactivity of Water at Biomaterial Surfaces. Adv. Colloid Interface Sci. 1998, 74 (1–3), 69-117. 36. Guo, C.; Wang, S.; Liu, H.; Feng, L.; Song, Y.; Jiang, L., Wettability Alteration of Polymer Surfaces Produced by Scraping. J. Adhes. Sci. Technol. 2008, 22 (3-4), 395-402. 37. Cassie, A. B. D.; Baxter, S., Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40 (0), 546-551. 38. Wenzel, R. N., Resisctance of Solid Surfaces to Wetting by Water. Ind. Eng. Chem. 1936, 28 (8), 988-994. 39. Bharat, B.; Yong Chae, J., Wetting, Adhesion and Friction of Superhydrophobic and Hydrophilic Leaves and Fabricated Micro/Nanopatterned Surfaces. J. Phys.: Condens. Matter 2008, 20 (22), 225010.

40. Wang, S.; Jiang, L., Definition of Superhydrophobic States. Adv. Mater. 2007, 19 (21), 3423-3424. 41. Bixler, G. D.; Bhushan, B., Rice- and Butterfly-Wing Effect Inspired Self-Cleaning and Low Drag Micro/Nanopatterned Surfaces in Water, Oil, and Air Flow. Nanoscale 2014, 6 (1), 76-96. 42. Ensikat, H. J.; Ditsche-Kuru, P.; Neinhuis, C.; Barthlott, W., Superhydrophobicity in Perfection: The Outstanding Properties of the Lotus Leaf. Beilstein Journal of Nanotechnology 2011, 2, 152-161. 43. Bhushan, B.; Her, E. K., Fabrication of Superhydrophobic Surfaces with High and Low Adhesion Inspired from Rose Petal. Langmuir 2010, 26 (11), 82078217. 44. Liu, M. J.; Wang, S. T.; Jiang, L., Bioinspired Multiscale Surfaces with Special Wettability. MRS Bull. 2013, 38 (5), 375-382. 45. Paven, M.; Papadopoulos, P.; Schöttler, S.; Deng, X.; Mailänder, V.; Vollmer, D.; Butt, H.-J., Super LiquidRepellent Gas Membranes for Carbon Dioxide Capture and Heart–Lung Machines. Nat. Commun. 2013, 4, 2512. 46. Deng, X.; Paven, M.; Papadopoulos, P.; Ye, M.; Wu, S.; Schuster, T.; Klapper, M.; Vollmer, D.; Butt, H. J., Solvent-Free Synthesis of Microparticles on Superamphiphobic Surfaces. Angew. Chem., Int. Ed. 2013, 52 (43), 11286-11289. 47. Butt, H.-J.; Semprebon, C.; Papadopoulos, P.; Vollmer, D.; Brinkmann, M.; Ciccotti, M., Design Principles for Superamphiphobic Surfaces. Soft Matter 2013, 9 (2), 418428. 48. Brown, P. S.; Bhushan, B., Designing Bioinspired Superoleophobic Surfaces. Apl Mater. 2016, 4 (1), 015703. 49. Kota, A. K.; Choi, W.; Tuteja, A., Superomniphobic Surfaces: Design and Durability. MRS Bull. 2013, 38 (05), 383-390. 50. Wang, Y.; Bhushan, B., Wear-Resistant and Antismudge Superoleophobic Coating on Polyethylene Terephthalate Substrate Using Sio2 Nanoparticles. ACS Appl. Mater. Interfaces 2015, 7 (1), 743-755. 51. Lu, Y.; Sathasivam, S.; Song, J.; Crick, C. R.; Carmalt, C. J.; Parkin, I. P., Robust Self-Cleaning Surfaces That Function When Exposed to Either Air or Oil. Science 2015, 347 (6226), 1132-1135. 52. Chen, F.; Song, J.; Lu, Y.; Huang, S.; Liu, X.; Sun, J.; Carmalt, C. J.; Parkin, I. P.; Xu, W., Creating Robust Superamphiphobic Coatings for Both Hard and Soft Materials. J. Mater. Chem. A 2015, 3 (42), 20999-21008. 53. Deng, X.; Mammen, L.; Butt, H.-J.; Vollmer, D., Candle Soot as a Template for a Transparent Robust Superamphiphobic Coating. Science 2012, 335 (6064), 6770. 54. Tuteja, A.; Choi, W.; Mabry, J. M.; McKinley, G. H.; Cohen, R. E., Robust Omniphobic Surfaces. Proc. Natl. Acad. Sci. 2008, 105 (47), 18200-18205. 55. Kota, A. K.; Li, Y.; Mabry, J. M.; Tuteja, A., Hierarchically Structured Superoleophobic Surfaces with Ultralow Contact Angle Hysteresis. Adv. Mater. 2012, 24 (43), 5838-5843.


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

56. Pan, S.; Kota, A. K.; Mabry, J. M.; Tuteja, A., Superomniphobic Surfaces for Effective Chemical Shielding. J. Am. Chem. Soc. 2013, 135 (2), 578-581. 57. Liu, T. L.; Kim, C.-J. C., Turning a Surface Superrepellent Even to Completely Wetting Liquids. Science 2014, 346 (6213), 1096-1100. 58. Zhang, L.; Zhao, N.; Xu, J., Fabrication and Application of Superhydrophilic Surfaces: A Review. J. Adhes. Sci. Technol. 2014, 28 (8-9), 769-790. 59. Drelich, J.; Chibowski, E.; Meng, D. D.; Terpilowski, K., Hydrophilic and Superhydrophilic Surfaces and Materials. Soft Matter 2011, 7 (21), 9804-9828. 60. Drelich, J.; Chibowski, E., Superhydrophilic and Superwetting Surfaces: Definition and Mechanisms of Control. Langmuir 2010, 26 (24), 18621-18623. 61. Nishimoto, S.; Bhushan, B., Bioinspired Self-Cleaning Surfaces with Superhydrophobicity, Superoleophobicity, and Superhydrophilicity. RSC Advances 2013, 3 (3), 671690. 62. Guo, T.; Heng, L.; Wang, M.; Wang, J.; Jiang, L., Robust Underwater Oil-Repellent Material Inspired by Columnar Nacre. Adv. Mater. 2016, 28 (38), 8505-8510. 63. Xue, Z.; Wang, S.; Lin, L.; Chen, L.; Liu, M.; Feng, L.; Jiang, L., A Novel Superhydrophilic and Underwater Superoleophobic Hydrogel-Coated Mesh for Oil/Water Separation. Adv. Mater. 2011, 23 (37), 4270-4273. 64. Bhushan, B.; Jung, Y. C., Natural and Biomimetic Artificial Surfaces for Superhydrophobicity, Self-Cleaning, Low Adhesion, and Drag Reduction. Progress in Materials Science 2011, 56 (1), 1-108. 65. Liu, M.; Jiang, L., Switchable Adhesion on Liquid/Solid Interfaces. Adv. Funct. Mater. 2010, 20 (21), 3753-3764. 66. Wang, R.; Hashimoto, K.; Fujishima, A.; Chikuni, M.; Kojima, E.; Kitamura, A.; Shimohigoshi, M.; Watanabe, T., Light-Induced Amphiphilic Surfaces. Nature 1997, 388 (6641), 431-432. 67. Wong, T.-S.; Kang, S. H.; Tang, S. K. Y.; Smythe, E. J.; Hatton, B. D.; Grinthal, A.; Aizenberg, J., Bioinspired Self-Repairing Slippery Surfaces with Pressure-Stable Omniphobicity. Nature 2011, 477 (7365), 443-447. 68. Kim, P.; Wong, T.-S.; Alvarenga, J.; Kreder, M. J.; Adorno-Martinez, W. E.; Aizenberg, J., Liquid-Infused Nanostructured Surfaces with Extreme Anti-Ice and AntiFrost Performance. ACS Nano 2012, 6 (8), 6569-6577. 69. Xiao, L.; Li, J.; Mieszkin, S.; Di Fino, A.; Clare, A. S.; Callow, M. E.; Callow, J. A.; Grunze, M.; Rosenhahn, A.; Levkin, P. A., Slippery Liquid-Infused Porous Surfaces Showing Marine Antibiofouling Properties. ACS Appl. Mater. Interfaces 2013, 5 (20), 10074-10080. 70. Leslie, D. C.; Waterhouse, A.; Berthet, J. B.; Valentin, T. M.; Watters, A. L.; Jain, A.; Kim, P.; Hatton, B. D.; Nedder, A.; Donovan, K.; Super, E. H.; Howell, C.; Johnson, C. P.; Vu, T. L.; Bolgen, D. E.; Rifai, S.; Hansen, A. R.; Aizenberg, M.; Super, M.; Aizenberg, J.; Ingber, D. E., A Bioinspired Omniphobic Surface Coating on Medical Devices Prevents Thrombosis and Biofouling. Nat. Biotechnol. 2014, 32 (11), 1134-1140. 71. Hou, X.; Hu, Y.; Grinthal, A.; Khan, M.; Aizenberg, J., Liquid-Based Gating Mechanism with Tunable Multiphase

Page 12 of 16

Selectivity and Antifouling Behaviour. Nature 2015, 519 (7541), 70-73. 72. Wang, J.; Kato, K.; Blois, A. P.; Wong, T.-S., Bioinspired Omniphobic Coatings with a Thermal SelfRepair Function on Industrial Materials. ACS Appl. Mater. Interfaces 2016, 8 (12), 8265-8271. 73. Ding, Y. H.; Floren, M.; Tan, W., Mussel-Inspired Polydopamine for Bio-Surface Functionalization. Biosurface and Biotribology 2016, 2 (4), 121-136. 74. Lee, H.; Scherer, N. F.; Messersmith, P. B., SingleMolecule Mechanics of Mussel Adhesion. Proc. Natl. Acad. Sci. 2006, 103 (35), 12999-13003. 75. Waite, J. H.; Tanzer, M. L., Polyphenolic Substance of Mytilus Edulis: Novel Adhesive Containing L-Dopa and Hydroxyproline. Science 1981, 212 (4498), 1038-1040. 76. Kord Forooshani, P.; Lee, B. P., Recent Approaches in Designing Bioadhesive Materials Inspired by Mussel Adhesive Protein. J. Polym. Sci. A Polym. Chem. 2017, 55 (1), 9-33. 77. Yang, J.; Cohen Stuart, M. A.; Kamperman, M., Jack of All Trades: Versatile Catechol Crosslinking Mechanisms. Chem. Soc. Rev. 2014, 43 (24), 8271-8298. 78. d’Ischia, M.; Napolitano, A.; Ball, V.; Chen, C.-T.; Buehler, M. J., Polydopamine and Eumelanin: From Structure–Property Relationships to a Unified Tailoring Strategy. Acc. Chem. Res. 2014, 47 (12), 3541-3550. 79. Hong, S.; Na, Y. S.; Choi, S.; Song, I. T.; Kim, W. Y.; Lee, H., Non-Covalent Self-Assembly and Covalent Polymerization Co-Contribute to Polydopamine Formation. Adv. Funct. Mater. 2012, 22 (22), 4711-4717. 80. Gebbie, M. A.; Wei, W.; Schrader, A. M.; Cristiani, T. R.; Dobbs, H. A.; Idso, M.; Chmelka, B. F.; Waite, J. H.; Israelachvili, J. N., Tuning Underwater Adhesion with Cation–Π Interactions. Nature Chem. 2017. 81. Mian, S. A.; Yang, L.-M.; Saha, L. C.; Ahmed, E.; Ajmal, M.; Ganz, E., A Fundamental Understanding of Catechol and Water Adsorption on a Hydrophilic Silica Surface: Exploring the Underwater Adhesion Mechanism of Mussels on an Atomic Scale. Langmuir 2014, 30 (23), 6906-6914. 82. 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 Films. Adv. Funct. Mater. 2010, 20 (23), 4196-4205. 83. Rodrı́guez, R.; Blesa, M. A.; Regazzoni, A. E., Surface Complexation at the Tio2(Anatase)/Aqueous Solution Interface: Chemisorption of Catechol. J. Colloid Interface Sci. 1996, 177 (1), 122-131. 84. Li, Y.; Qin, M.; Li, Y.; Cao, Y.; Wang, W., Single Molecule Evidence for the Adaptive Binding of Dopa to Different Wet Surfaces. Langmuir 2014, 30 (15), 43584366. 85. Yu, J.; Kan, Y.; Rapp, M.; Danner, E.; Wei, W.; Das, S.; Miller, D. R.; Chen, Y.; Waite, J. H.; Israelachvili, J. N., Adaptive Hydrophobic and Hydrophilic Interactions of Mussel Foot Proteins with Organic Thin Films. Proc. Natl. Acad. Sci. 2013, 110 (39), 15680-15685.


Page 13 of 16

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Langmuir

86. Wei, Q.; Haag, R., Universal Polymer Coatings and Their Representative Biomedical Applications. Mater. Horiz. 2015, 2 (6), 567-577. 87. Liu, Y.; Ai, K.; Lu, L., Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields. Chem. Rev. 2014, 114 (9), 5057-5115. 88. 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. 89. Zhang, C.; Ou, Y.; Lei, W. X.; Wan, L. S.; Ji, J.; Xu, Z. K., Cuso4/H2o2-Induced Rapid Deposition of Polydopamine Coatings with High Uniformity and Enhanced Stability. Angew. Chem., Int. Ed. 2016, 55 (9), 3054-7. 90. Lee, M.; Lee, S. H.; Oh, I. K.; Lee, H., MicrowaveAccelerated Rapid, Chemical Oxidant-Free, MaterialIndependent Surface Chemistry of Poly(Dopamine). Small 2017, 13 (4), 1600443. 91. Hong, S. H.; Hong, S.; Ryou, M. H.; Choi, J. W.; Kang, S. M.; Lee, H., Sprayable Ultrafast Polydopamine Surface Modifications. Adv. Mater. Interf. 2016, 3 (11), 1500857n/a. 92. Du, X.; Li, L.; Li, J.; Yang, C.; Frenkel, N.; Welle, A.; Heissler, S.; Nefedov, A.; Grunze, M.; Levkin, P. A., UvTriggered Dopamine Polymerization: Control of Polymerization, Surface Coating, and Photopatterning. Adv. Mater. 2014, 26 (47), 8029-33. 93. Liu, M.; Zeng, G.; Wang, K.; Wan, Q.; Tao, L.; Zhang, X.; Wei, Y., Recent Developments in Polydopamine: An Emerging Soft Matter for Surface Modification and Biomedical Applications. Nanoscale 2016, 8 (38), 1681916840. 94. 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 (14), 2949-2955. 95. Nardo, T.; Chiono, V.; Ciardelli, G.; Tabrizian, M., Polydopa Mussel-Inspired Coating as a Means for Hydroxyapatite Entrapment on Polytetrafluoroethylene Surface for Application in Periodontal Diseases. Macromol. Biosci. 2016, 16 (2), 288-298. 96. Wei, H.; Ren, J.; Han, B.; Xu, L.; Han, L.; Jia, L., Stability of Polydopamine and Poly(Dopa) Melanin-Like Films on the Surface of Polymer Membranes under Strongly Acidic and Alkaline Conditions. Colloids Surf., B 2013, 110, 22-28. 97. Faure, E.; Falentin-Daudré, C.; Jérôme, C.; Lyskawa, J.; Fournier, D.; Woisel, P.; Detrembleur, C., Catechols as Versatile Platforms in Polymer Chemistry. Prog. Polym. Sci. 2013, 38 (1), 236-270. 98. Moulay, S., Dopa/Catechol-Tethered Polymers: Bioadhesives and Biomimetic Adhesive Materials. Polym. Rev. 2014, 54 (3), 436-513. 99. Lee, H.; Lee, K. D.; Pyo, K. B.; Park, S. Y.; Lee, H., Catechol-Grafted Poly(Ethylene Glycol) for Pegylation on Versatile Substrates. Langmuir 2010, 26 (6), 3790-3793.

100. Zhang, F.; Liu, S.; Zhang, Y.; Chi, Z.; Xu, J.; Wei, Y., A Facile Approach to Surface Modification on Versatile Substrates for Biological Applications. J. Mater. Chem. 2012, 22 (33), 17159-17166. 101. Wei, Q.; Becherer, T.; Noeske, P.-L. M.; Grunwald, I.; Haag, R., A Universal Approach to Crosslinked Hierarchical Polymer Multilayers as Stable and Highly Effective Antifouling Coatings. Adv. Mater. 2014, 26 (17), 2688-2693. 102. Yu, L.; Cheng, C.; Ran, Q.; Schlaich, C.; Noeske, P.L. M.; Li, W.; Wei, Q.; Haag, R., Bioinspired Universal Monolayer Coatings by Combining Concepts from Blood Protein Adsorption and Mussel Adhesion. ACS Appl. Mater. Interfaces 2017. 103. Gong, Y.-K.; Liu, L.-P.; Messersmith, P. B., Doubly Biomimetic Catecholic Phosphorylcholine Copolymer: A Platform Strategy for Fabricating Antifouling Surfaces. Macromol. Biosci. 2012, 12 (7), 979-985. 104. Dalsin, J. L.; Lin, L.; Tosatti, S.; Vörös, J.; Textor, M.; Messersmith, P. B., Protein Resistance of Titanium Oxide Surfaces Modified by Biologically Inspired Mpeg−Dopa. Langmuir 2005, 21 (2), 640-646. 105. Wei, Q.; Krysiak, S.; Achazi, K.; Becherer, T.; Noeske, P.-L. M.; Paulus, F.; Liebe, H.; Grunwald, I.; Dernedde, J.; Hartwig, A.; Hugel, T.; Haag, R., Multivalent Anchored and Crosslinked Hyperbranched Polyglycerol Monolayers as Antifouling Coating for Titanium Oxide Surfaces. Colloids Surf., B 2014, 122, 684-692. 106. Lu, Q.; Danner, E.; Waite, J. H.; Israelachvili, J. N.; Zeng, H.; Hwang, D. S., Adhesion of Mussel Foot Proteins to Different Substrate Surfaces. J. R. Soc. Interface 2013, 10 (79). 107. Waite, J. H., The Formation of Mussel Byssus: Anatomy of a Natural Manufacturing Process. In Structure, Cellular Synthesis and Assembly of Biopolymers, Case, S. T., Ed. Springer Berlin Heidelberg: Berlin, Heidelberg, 1992; pp 27-54. 108. Wei, Q.; Achazi, K.; Liebe, H.; Schulz, A.; Noeske, P. L.; Grunwald, I.; Haag, R., Mussel-Inspired Dendritic Polymers as Universal Multifunctional Coatings. Angew. Chem., Int. Ed. 2014, 53 (43), 11650-11655. 109. Roller, S.; Zhou, H.; Haag, R., High-Loading Polyglycerol Supported Reagents for Mitsunobu- and Acylation-Reactions and Other Useful Polyglycerol Derivatives. Mol. Diversity 2005, 9 (4), 305-316. 110. Della Vecchia, N. F.; Avolio, R.; Alfè, M.; Errico, M. E.; Napolitano, A.; d'Ischia, M., Building-Block Diversity in Polydopamine Underpins a Multifunctional EumelaninType Platform Tunable through a Quinone Control Point. Adv. Funct. Mater. 2013, 23 (10), 1331-1340. 111. Schlaich, C.; Cuellar Camacho, L.; Yu, L.; Achazi, K.; Wei, Q.; Haag, R., Surface-Independent Hierarchical Coatings with Superamphiphobic Properties. ACS Appl. Mater. Interfaces 2016, 8 (42), 29117-29127. 112. Yong Chae, J.; Bharat, B., Contact Angle, Adhesion and Friction Properties of Micro-and Nanopatterned Polymers for Superhydrophobicity. Nanotechnology 2006, 17 (19), 4970. 113. Schlaich, C.; Yu, L. X.; Camacho, L. C.; Wei, Q.; Haag, R., Fluorine-Free Superwetting Systems:


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Construction of Environmentally Friendly Superhydrophilic, Superhydrophobic, and Slippery Surfaces on Various Substrates. Polym. Chem. 2016, 7 (48), 7446-7454. 114. You, I.; Lee, T. G.; Nam, Y. S.; Lee, H., Fabrication of a Micro-Omnifluidic Device by Omniphilic/Omniphobic Patterning on Nanostructured Surfaces. ACS Nano 2014, 8 (9), 9016-9024.

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Qiang Wei

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Christoph Schlaich

Dr. Qiang Wei received his Bachelor's and Master's degrees in 2008 and 2011, respectively, from Sichuan University, China. He completed his PhD with Prof. Dr Rainer Haag at Freie Universität Berlin in 2014. His PhD thesis focused on the design of mussel-inspired polymers and the development of multifunctional polymer coatings. He then joined Max-Planck Institute for Medical Research as postdoctoral researcher in the research area of cell and tissue engineering. Rainer Haag

Christoph Schlaich received his B.Sc. and M.Sc. degree in Chemistry from the Freie Universität Berlin, Germany. He is currently working with Prof. Rainer Haag on his PhD in polymer chemistry. His research interest is mainly focused on fabrication of novel polymeric functional surface coatings with special wettability.

Prof. Dr Rainer Haag obtained his PhD with A. de Meijere at the University of Göttingen in 1995. After postdoctoral work with S. V. Ley, University of Cambridge (UK), and G. M. Whitesides, Harvard University, Cambridge (USA), he completed his habilitation at the University of Freiburg in 2002. He then became associate professor at the Universi-


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ty of Dortmund and in 2004 was appointed full Professor of organic and macromolecular chemistry at the Freie Universität Berlin. His main research interests are the mimicry of biological systems by functional dendritic polymers, with particular focus on applications in nanomedicine and multivalent systems.


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Mussel-Inspired Polyglycerol Coatings with Controlled Wettability

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