A Functional DNase I Coating to Prevent Adhesion of Bacteria and the Formation of Biofilm

Biofilms are detrimental in many industrial and biomedical applications and prevention of biofilm formation has been a prime challenge for decades. Biofilms consist of communities of adhering bacteria, supported and protected by extracellular‐polymeric‐substances (EPS), the so‐called “house of biofilm organisms”. EPS consists of water, proteins, polysaccharides and extracellular‐DNA (eDNA). eDNA, being the longest molecule in EPS, connects the different EPS components and therewith holds an adhering biofilm together. eDNA is associated with bacterial cell surfaces by specific and non‐specific mechanisms, mediating binding of other biopolymers in EPS. eDNA therewith assists in facilitating adhesion, aggregation and maintenance of biofilm structure. Here, a new method is described to prevent biofilm formation on surfaces by applying a DNase I enzyme coating to polymethylmethacrylate, using dopamine as an intermediate. The intermediate coupling layer and final DNase I coating are characterized by water‐contact‐angle measurements and X‐ray photoelectron‐spectroscopy. The DNase I coating strongly reduces adhesion of Staphylococcus aureus (95%) and Pseudomonas aeruginosa (99%) and prevents biofilm formation up to 14 h, without affecting mammalian cell adhesion and proliferation. Also agarose‐gel‐electrophoresis indicates loss of enzyme activity between 8 and 24 h. This duration however, is similar to many local antibiotic‐delivery devices, which makes it an ideal coating for biomaterial implants and devices, known to fail due to biofilm formation with disastrous consequences for patients and high costs to the healthcare system. With threatening increases in antibiotic resistance, the DNase I coating may provide a timely, potent new approach to biofilm prevention on biomaterial implants and devices.     

Surface‐Initiated Atom Transfer Radical Polymerization of Oligo(ethylene glycol) Methyl Methacrylate from a Mixed Self‐Assembled Monolayer on Gold

This paper describes the in‐situ synthesis of an oligo(ethylene glycol)‐functionalized polymer brush in which the oligo(ethylene glycol) chains are presented as side‐chains from a methacrylate backbone that is anchored to the surface. These polymer “bottlebrushes” have been synthesized by surface‐initiated atom transfer radical polymerization (SI‐ATRP) of oligo(ethylene glycol) methyl methacrylate (OEGMA) from a mixed self‐assembled monolayer (SAM) of an ATRP initiator‐functionalized alkanethiol and a diluent, methyl‐terminated thiol. The systematic control of the ATRP initiator surface density afforded by the mixed SAM on gold and the polymerization time enables the polymer chain length and surface density to be independently controlled. Surface plasmon resonance (SPR) spectroscopy of fibronectin (Fn) adsorption on poly(OEGMA) grown from the surface of the mixed SAMs on gold shows that above a threshold solution molar ratio of the ATRP‐initiator thiol to methyl‐terminated thiol of 0.2, and a dry film thickness of ～ 4 nm, Fn adsorption on the surface‐initiated poly(OEGMA) coatings was below the detection limit of SPR. The relatively low surface density of the ATRP initiator required to confer protein resistance to the surface suggests that SI‐ATRP may be a viable strategy to create protein resistant polymer brushes on real‐world materials.     

Self‐Assembled Monolayer Coatings on Nanostencils for the Reduction of Materials Adhesion

Nanostencils (shadow masks with submicrometer apertures in a thin silicon nitride membrane) are promising tools for the facile one‐step generation of nanopatterns of various materials by physical vapor deposition. Evaporation through a shadow mask is accompanied by gradual clogging of the apertures due to adhesion of evaporated material. In order to reduce this effect, nanostencils were coated with alkyl and perfluoroalkyl self‐assembled monolayers (SAMs). The formation and properties of SAMs on planar silicon nitride substrates were studied by contact angle goniometry, X‐ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The SAMs are stable under evaporation of gold at various angles. SAM‐coated nanostencils showed considerably less adhesion of gold compared to bare Si_xN_y stencils.     

Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers

An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO₂) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C₆₀) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO₂ dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec^?1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm² V^?1 s^?1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.     

An Engineered Mannoside Presenting Platform: Escherichia coli Adhesion under Static and Dynamic Conditions

The study of the adhesion mechanisms of pathogens to host tissues has gained increased interest as bacterial adhesion is involved in the early stages of surface colonization and infection. Here we describe a platform to study the specific binding of the bacterium Escherichia coli (E. coli) K‐12 strain to molecularly well‐defined surfaces mimicking cellular interfaces. This approach uses a poly(ethylene glycol) brush interface, which displays synthetic determinants of the high mannose N‐linked glycans in a range of densities (3.8 × 10⁴–1.6 × 10⁵ mannosides µm^?2) for the investigation of multivalent interactions with bacteria. The bacterial attachment is mediated by specific interactions between the adhesive protein FimH located on the tip of the bacterial type 1 pili and the mannosylated surfaces. With synthetically engineered mannoses, it is found that the number of strongly adhering bacteria is co‐regulated by many structural physical parameters. Beyond the dependency on carbohydrate density, higher numbers of E. coli attach to the branched trimannose Man(α1–3)(Man(α1–6))Man compared to the monomannose, while larger oligomannoses exposing Man(α1–2) Man at their non reducing end show low binding capacity. The linker used between the mannose moiety and PEG is also affecting the binding efficacy of E. coli. The (hydrophobic) propyl linker results in higher bacteria numbers in comparison to the (hydrophilic) tri(EG), likely a consequence of additional stabilization of the binding complex by hydrophobic interactions. Furthermore, differences are observed in bacteria attachment between stagnant and flow conditions that depend on the type of mannose ligand. Finally, a photolithographic resist lift‐off combined with site‐selective assembly of the glycopolymers is used to produce micropatterns with bacteria colonies confined to defined areas and at controlled colony numbers.     

Interaction of Zoospores of the Green Alga Ulva with Bioinspired Micro‐ and Nanostructured Surfaces Prepared by Polyelectrolyte Layer‐by‐Layer Self‐Assembly

The interaction of spores of Ulva with bioinspired structured surfaces in the nanometer–micrometer size range is investigated using a series of coatings with systematically varying morphology and chemistry, which allows separation of the contributions of morphology and surface chemistry to settlement (attachment) and adhesion strength. Structured surfaces are prepared by layer‐by‐layer spray‐coating deposition of polyelectrolytes. By changing the pH during application of oppositely charged poly(acrylic acid) and polyethylenimine polyelectrolytes, the surface structures are systematically varied, which allows the influence of morphology on the biological response to be determined. In order to discriminate morphological from chemical effects, surfaces are chemically modified with poly(ethylene glycol) and tridecafluoroctyltriethoxysilane. This chemical modification changes the water contact angles while the influence of the morphology is retained. The lowest level of settlement is observed for structures of the order 2 µm. All surfaces are characterized with respect to their wettability, chemical composition, and morphological properties by contact angle measurement, X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy.     

Organic Thin‐Film Transistors: Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers (Adv. Funct. Mater. 8/2011)

An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO₂) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C₆₀) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO₂ dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec^?1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm² V^?1 s^?1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.     

Electronic Structure of Self‐Assembled Monolayers on Au(111) Surfaces: The Impact of Backbone Polarizability

Modifying metal electrodes with self‐assembled monolayers (SAMs) has promising applications in organic and molecular electronics. The two key electronic parameters are the modification of the electrode work function because of SAM adsorption and the alignment of the SAM conducting states relative to the metal Fermi level. Through a comprehensive density‐functional‐theory study on a series of organic thiols self‐assembled on Au(111), relationships between the electronic structure of the individual molecules (especially the backbone polarizability and its response to donor/acceptor substitutions) and the properties of the corresponding SAMs are described. The molecular backbone is found to significantly impacts the level alignment; for molecules with small ionization potentials, even Fermi‐level pinning is observed. Nevertheless, independent of the backbone, polar head‐group substitutions have no effect on the level alignment. For the work‐function modification, the larger molecular dipole moments achieved when attaching donor/acceptor substituents to more polarizable backbones are largely compensated by increased depolarization in the SAMs. The main impact of the backbone on the work‐function modification thus arises from its influence on the molecular orientation on the surface. This study provides a solid theoretical basis for the fundamental understanding of SAMs and significantly advances the understanding of structure–property relationships needed for the future development of functional organic interfaces.     

Electropolymerized Self‐Assembled Monolayers of a 3,4‐Ethylenedioxythiophene‐Thiophene Hybrid System

Self‐assembled monolayers (SAMs) of a conjugated bithiophenic system connected to an alkanethiol chain have been deposited on gold surface. The electroactive bithiophenic system involves a 3,4‐ethylenedioxythiophene (EDOT) unit and a thiophene ring on which an alkanethiol is attached at the internal β‐position via a sulfide linkage. The analysis of the structure of the SAMs by IR spectroscopy, ellipsometry, contact angle measurement and X‐ray photoelectron spectroscopy (XPS) provides consistent results indicating compact monolayers in which the alkyl linkers are arranged in an almost vertical fashion while the bithiophenic‐conjugated systems are essentially parallel to the surface. Cyclic voltammetry shows that application of a few potential scans to SAMs immersed in a medium containing only a supporting electrolyte leads to the typical electropolymerization curves while the CV of the electrooxized monolayer exhibits a reversible cyclic voltammogram characteristic of a stable electroactive extended conjugated system. The characterization of the electropolymerized monolayers by IR spectroscopy, ellipsometry, contact angle measurement, and XPS indicates compact monolayers. The analysis of the current voltage characteristics of the monolayers by conducting AFM before and after electrooxidation shows that the enhancement of the effective conjugation resulting from electropolymerization leads to a significant increase of the transport properties.     

Normally Oriented Adhesion versus Friction Forces in Bacterial Adhesion to Polymer‐Brush Functionalized Surfaces Under Fluid Flow

Bacterial adhesion is problematic in many diverse applications. Coatings of hydrophilic polymer chains in a brush configuration reduce bacterial adhesion by orders of magnitude, but not to zero. Here, the mechanism by which polymer‐brush functionalized surfaces reduce bacterial adhesion from a flowing carrier fluid by relating bacterial adhesion with normally oriented adhesion and friction forces on polymer (PEG)‐brush coatings of different softness is studied. Softer brush coatings deform more than rigid ones, which yields extensive bond‐maturation and strong, normally oriented adhesion forces, accompanied by irreversible adhesion of bacteria. On rigid brushes, normally oriented adhesion forces remain small, allowing desorption and accordingly lower numbers of adhering bacteria result. Friction forces, generated by fluid flow and normally oriented adhesion forces, are required to oppose fluid shear forces and cause immobile adhesion. Summarizing, inclusion of friction forces and substratum softness provides a more complete mechanism of bacterial adhesion from flowing carrier fluids than available hitherto.     

Interface Immobilization Chemistry of cRGD‐based Peptides Regulates Integrin Mediated Cell Adhesion

The interaction of specific surface receptors of the integrin family with different extracellular matrix‐based ligands is of utmost importance for the cellular adhesion process. A ligand consists of an integrin‐binding group, here cyclic RGDfX, a spacer molecule that lifts the integrin‐binding group from the surface and a surface anchoring group. c(‐RGDfX‐) peptides are bound to gold nanoparticle structured surfaces via polyproline, polyethylene glycol or aminohexanoic acid containing spacers of different lengths. Although keeping the integrin‐binding c(‐RGDfX‐) peptides constant for all compounds, changes of the ligand's spacer chemistry and length reveal significant differences in cell adhesion activation and focal adhesion formation. Polyproline‐based peptides demonstrate improved cell adhesion kinetics and focal adhesion formation compared with common aminohexanoic acid or polyethylene glycol spacers. Binding activity can additionally be improved by applying ligands with two head groups, inducing a multimeric effect. This study gives insights into spacer‐based differences in integrin‐driven cell adhesion processes and remarkably highlights the polyproline‐based spacers as suitable ligand‐presenting templates for surface functionalization.     

A Coating that Combines Lotus‐Effect and Contact‐Active Antimicrobial Properties on Silicone

The antimicrobial equipment of materials is of great importance in medicine but also in daily life. A challenge is the antimicrobial modification of hydrophobic surfaces without increasing their low surface energy. This is particularly important for silicone‐based materials. Because most antimicrobial surface modifications render the materials more hydrophilic, methods are needed to achieve antimicrobial activity without changing the high water‐contact‐angle. This is achieved in the present work, where SiO₂ nanoparticles are prepared and functionalized with 3‐(trimethoxysilyl)‐propyldimethyloctadecyl ammonium chloride (QAS) in a one‐pot synthesis. The modified nanoparticles are applied onto a silicone surface from suspension with no need of elaborate pretreatment. The resulting surface exhibits a Lotus‐Effect combined with contact‐active antimicrobial properties. The particle surfaces show self‐organizing micro‐ and nanostructures that afford a water‐contact angle of 144° and a hysteresis below 10°. The particles are self‐adhering on the silicone after solvent evaporation and resistant against immersion into and washing with water for at least 5 d. Thereby, the adhesion of the bacterial strain Staphylococcus aureus to these surfaces is reduced and the remaining bacterial cells are killed within 16 h. This is the first example of a Lotus‐Effect surface with intrinsic contact‐active antimicrobial properties.     

Dual‐Mechanism Antimicrobial Polymer–ZnO Nanoparticle and Crystal Violet‐Encapsulated Silicone

The prevalence of healthcare‐associated infection caused by multidrug‐resistant bacteria is of critical concern worldwide. It is reported on the development of a bactericidal surface prepared by use of a simple, upscalable, two‐step dipping strategy to incorporate crystal violet and di(octyl)­phosphinic‐ acid‐capped zinc oxide nanoparticles into medical grade silicone, as a strategy to reduce the risk of infection. The material is characterized by UV–vis absorbance spectroscopy, X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma‐optical emission spectroscopy (ICP‐OES) and transmission electron microscopy (TEM) and confirmed the incorporation of the ZnO nanoparticles in the polymer. The novel system proves to be a highly versatile bactericidal material when tested against both Staphylococcus aureus and Escherichia coli, key causative micro‐organisms for hospital‐acquired infection (HAI). Potent antimicrobial activity is noted under dark conditions, with a significant enhancement exhibits when the surfaces are illuminated with a standard hospital light source. This polymer has the potential to decrease the risk of HAI, by killing bacteria in contact with the surface.     

Heat‐Assisted Photoacidic Oxidation Method for Tailoring the Surface Chemistry of Polymer Dielectrics for Low‐Power Organic Soft Electronics

The use in low‐power soft electronics of the appropriate insulating polymer materials with a high dielectric constant (k) is considered a practical alternative to that of inorganic dielectric materials, which are brittle and have high processing temperatures. However, the polar surfaces of typical high‐k polymer insulators are problematic. Further, it is a huge challenge to control their surface properties without damage because of their soft and chemically fragile nature. Here, a heat‐assisted photoacidic oxidation method that can be used to effectively oxidize the outermost surfaces of high‐k rubbery polymer films without degradation is presented. The oxidized surfaces prepared with the developed method contain large numbers of hydroxyl groups that enable the subsequent growth of dense and ordered self‐assembled monolayers (SAMs) consisting of organosilanes. The whole process modifies the surface characteristics of polymer dielectrics effectively. The mechanisms of the oxidation of polymer surfaces and the subsequent SAM growth process are investigated. The resulting surface‐tailored rubbery dielectrics exhibit superior electrical characteristics when used in organic transistors. These results demonstrate that this method can be used to realize practical soft organic electronics based on high‐k polymer dielectrics.     

Tunable Crystal Nanostructures of Pentacene Thin Films on Gate Dielectrics Possessing Surface‐Order Control

To enhance the electrical performance of pentacene‐based field‐effect transistors (FETs) by tuning the surface‐induced ordering of pentacene crystals, we controlled the physical interactions at the semiconductor/gate dielectric (SiO₂) interface by inserting a hydrophobic self‐assembled monolayer (SAM, CH₃‐terminal) of organoalkyl‐silanes with an alkyl chain length of C8, C12, C16, or C18, as a complementary interlayer. We found that, depending on the physical structure of the dielectric surfaces, which was found to depend on the alkyl chain length of the SAM (ordered for C18 and disordered for C8), the pentacene nano‐layers in contact with the SAM could adopt two competing crystalline phases—a “thin‐film phase” and “bulk phase” – which affected the π‐conjugated nanostructures in the ultrathin and subsequently thick films. The field‐effect mobilities of the FET devices varied by more than a factor of 3 depending on the alkyl chain length of the SAM, reaching values as high as 0.6 cm² V^?1 s^?1 for the disordered SAM‐treated SiO₂ gate‐dielectric. This remarkable change in device performance can be explained by the production of well π‐conjugated and large crystal grains in the pentacene nanolayers formed on a disordered SAM surface. The enhanced electrical properties observed for systems with disordered SAMs can be attributed to the surfaces of these SAMs having fewer nucleation sites and a higher lateral diffusion rate of the first seeding pentacene molecules on the dielectric surfaces, due to the disordered and more mobile surface state of the short alkyl SAM.     

Self‐assembled Electroactive Phosphonic Acids on ITO: Maximizing Hole‐Injection in Polymer Light‐Emitting Diodes

In order to fulfill the promise of organic electronic devices, performance‐limiting factors, such as the energetic discontinuity of the material interfaces, must be overcome. Here, improved performance of polymer light‐emitting diodes (PLEDs) is demonstrated using self‐assembled monolayers (SAMs) of triarylamine‐based hole‐transporting molecules with phosphonic acid‐binding groups to modify the surface of the indium tin oxide (ITO) anode. The modified ITO surfaces are used in multilayer PLEDs, in which a green‐emitting polymer, poly[2,7‐(9,9‐dihexylfluorene)‐co‐4,7‐(2,1,3‐benzothiadiazole)] (PFBT5), is sandwiched between a thermally crosslinked hole‐transporting layer (HTL) and an electron‐transporting layer (ETL). All tetraphenyl‐diamine (TPD)‐based SAMs show significantly improved hole‐injection between ITO and the HTL compared to oxygen plasma‐treated ITO and simple aromatic SAMs on ITO. The device performance is consistent with the hole‐transporting properties of triarylamine groups (measured by electrochemical measurements) and improved surface energy matching with the HTL. The turn‐on voltage of the devices using SAM‐modified anodes can be lowered by up to 3 V compared to bare ITO, yielding up to 18‐fold increases in current density and up to 17‐fold increases in brightness at 10 V. Variations in hole‐injection and turn‐on voltage between the different TPD‐based molecules are attributed to the position of alkyl‐spacers within the molecules.     

Length‐Scale Mediated Differential Adhesion of Mammalian Cells and Microbes

Surfaces of implantable biomedical devices are increasingly engineered to promote their interactions with tissue. However, surfaces that stimulate desirable mammalian cell adhesion, spreading, and proliferation also enable microbial colonization. The biomaterials‐associated infection that can result is now a critical clinical problem. We have identified an important mechanism to create a surface that can simultaneously promote healing while reducing the probability of infection. Surfaces are created with submicrometer‐sized, non‐adhesive microgels patterned on an otherwise cell‐adhesive surface. Quantitative force measurements between a staphylococcus and a patterned surface show that the adhesion strength decreases significantly at inter‐gel spacings comparable to bacterial dimensions. Time‐resolved flow‐chamber measurements show that the microbial deposition rate dramatically decreases at these same spacings. Importantly, the adhesion and spreading of osteoblast‐like cells is preserved despite the sub‐cellular non‐adhesive surface features. Since such length‐scale‐mediated differential interactions do not rely on antibiotics, this mechanism can be particularly significant in mitigating biomaterials‐associated infection by antibiotic‐resistant bacteria such as MRSA.     

Tuning Specific Biomolecular Interactions Using Electro‐Switchable Oligopeptide Surfaces

The ability to regulate biomolecular interactions on surfaces driven by an external stimuli is of great theoretical interest and practical impact in the biomedical and biotechnology fields. Herein, a new class of responsive surfaces that rely on electro‐switchable peptides to control biomolecular interactions on gold surfaces is presented. This system is based upon the conformational switching of positively charged oligolysine peptides that are tethered to a gold surface, such that bioactive molecular moieties (biotin) incorporated on the oligolysines can be reversibly exposed (bio‐active state) or concealed (bio‐inactive state) on demand, as a function of surface potential. The dynamics of switching the biological properties is studied by observing the binding events between biotin and fluorescently labeled NeutrAvidin. Fluorescence microscope images and surface plasmon resonance spectral data clearly reveal opposite binding behaviors when +0.3 V or ?0.4 V vs. SCE are applied to the surface. High fluorescence intensities are observed for an applied positive potential, while minimal fluorescence is detected for an applied negative potential. Surface plasmon resonance spectroscopy (SPR) results provided further evidence that NeutrAvidin binding to the surface is controlled by the applied potential. A large SPR response is observed when a positive potential is applied on the surface, while a negative applied potential induces over 90% reduction in NeutrAvidin binding.     

Controllable Anisotropic Dry Adhesion in Vacuum: Gecko Inspired Wedged Surface Fabricated with Ultraprecision Diamond Cutting

Gecko adhesion has inspired the fabrication of various dry adhesive surfaces, most of which are developed to be used under atmospheric conditions. However, applications of gecko‐inspired surfaces can be expanded to vacuum and even space environment due to the characteristics of van der Waals interactions, which are always present between materials regardless of the surrounding environment. In this paper, a controllable, anisotropic dry adhesion in vacuum is demonstrated with gecko‐inspired wedged dry adhesive surfaces fabricated using an ultraprecision diamond cutting mold. The adhesion and friction properties of the wedge‐structured surfaces are systematically characterized in loading–pulling mode and loading–dragging–pulling mode. The surfaces show significant anisotropic adhesion (P_ad ≈ 10.5 kPa vs P_ad ≈ 0.7 kPa) and friction (P_f ≈ 50 kPa vs P_f ≈ 30 kPa) when actuated in gripping and releasing direction, respectively. The wedge‐structured surfaces in vacuum show comparable properties as exposed in atmosphere. A three‐legged gripper is designed to pick up, hold, and release a patterned silicon wafer in vacuum. The study demonstrates a green, high‐yield, and low‐cost method to fabricate a reliable and durable mold for gecko inspired anisotropic dry adhesive surfaces and the potential application of dry adhesive surface in vacuum.     

A Shape‐Adaptive,Antibacterial‐Coating of Immobilized Quaternary‐Ammonium Compounds Tethered on Hyperbranched Polyurea and its Mechanism of Action

Quaternary‐ammonium‐compounds are potent cationic antimicrobials used in everyday consumer products. Surface‐immobilized, quaternary‐ammonium‐compounds create an antimicrobial contact‐killing coating. We describe the preparation of a shape‐adaptive, contact‐killing coating by tethering quaternary‐ammonium‐compounds onto hyperbranched polyurea coatings, able to kill adhering bacteria by partially enveloping them. Even after extensive washing, coatings caused high contact‐killing of Staphylococcus epidermidis, both in culture‐based assays and through confocal‐laser‐scanning‐microscopic examination of the membrane‐damage of adhering bacteria. In culture‐based assays, at a challenge of 1600 CFU/cm², contact‐killing was >99.99%. The working‐mechanism of dissolved quaternary‐ammonium‐compounds is based on their interdigitation in bacterial membranes, but it is difficult to envisage how immobilized quaternary‐ammonium‐molecules can exert such a mechanism of action. Staphylococcal adhesion forces to hyperbranched quaternary‐ammonium coatings were extremely high, indicating that quaternary‐ammonium‐molecules on hyperbranched polyurea partially envelope adhering bacteria upon contact. These lethally strong adhesion forces upon adhering bacteria then cause removal of membrane lipids and eventually lead to bacterial death.