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.     

Model Organic Surfaces to Probe Marine Bacterial Adhesion Kinetics by Surface Plasmon Resonance

Understanding how bacteria adhere to a surface is a critical step in the development of novel materials and coatings to prevent bacteria forming biofilms. Here, surface plasmon resonance (SPR) spectroscopy, in combination with self‐assembled monolayers (SAMs) that have different backbone structures and/or functional groups, is used for the first time to study the initial stages of bacterial adhesion to surfaces (i.e., initial interaction of cells with a surface, a process governed by van der Waals, electrostatic, and hydrophobic interactions). The work highlights SPR spectroscopy as a powerful and unique approach to probe bacterial adhesion in real time. SPR spectral data reveal different kinetics of adhesion for the interaction of two marine bacterial species (Marinobacter hydrocarbonoclasticus and Cobetia marina) to a range of organosulfur SAMs. Furthermore, the extent of adhesion is dependent on the backbone structures and functional groups of the SAMs. The role of extracellular polymeric substances (EPS) in bacterial adhesion is also investigated. Pre‐conditioning experiments with cell‐free culture supernatants, containing planktonic EPS, allow quantification of the amount adsorbed onto surfaces and directly account for the impact of EPS adsorption on bacterial adhesion in the assay. While the physicochemical characteristics of the surfaces play a significant role in determining bacterial cell adhesion for low levels of conditioning by planktonic EPS, greater levels of conditioning by EPS reduce the difference between surfaces.     

Silver Nanoparticles Deposited Layered Double Hydroxide Nanoporous Coatings with Excellent Antimicrobial Activities

Simple and facile processes to produce silver nanoparticles deposited layered double hydroxide (Ag‐LDH) coatings are reported. High quality nanoporous LDH coatings are obtained under hydrothermal conditions via an improved in situ growth method by immersing the substrates in LDH suspensions after removal of free electrolytes. Different types of substrates including metal, ceramics, and glass with planar and non‐planar surfaces can all be coated with the oriented LDH films with strong adhesion. The pore size can be easily tuned by changing the metal:NaOH ratio during the precipiation process of LDH precursors. In the presence of LDH coatings, silver ions can be readily reduced to metallic silver nanoparticles (Ag NPs) in aqueous solutions. The resulting Ag NPs are incorporated evenly on LDH surface. The Ag‐LDH coating exhibits excellent and durable antimicrobial activities against both Gram‐negative (E. Coli and P. Aeruginosa) and Gram‐positive (B. Subtilis and S. Aureus) bacteria. Even at the 4th recycled use, more than 99% of all types of bacteria can be killed. Moreover, the Ag‐LDH coating can also effectively inhibit the bacterial growth and prevent the biofilm formation in the nutrient solutions. These newly designed Ag‐LDH coatings may offer a promising antimicrobial solution for clinical and environmental applications.     

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.     

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.     

Taming Charge Transport in Semiconducting Polymers with Branched Alkyl Side Chains

The solid‐state packing and polymer orientation relative to the substrate are key properties to control in order to achieve high charge carrier mobilities in organic field effect transistors (OFET). Intuitively, shorter side chains are expected to yield higher charge carrier mobilities because of a denser solid state packing motif and a higher ratio of charge transport moieties. However our findings suggest that the polymer chain orientation plays a crucial role in high‐performing diketopyrrolopyrrole‐based polymers. By synthesizing a series of DPP‐based polymers with different branched alkyl side chain lengths, it is shown that the polymer orientation depends on the branched alkyl chain lengths and that the highest carrier mobilities are obtained only if the polymer adopts a mixed face‐on/edge‐on orientation, which allows the formation of 3D carrier channels in an otherwise edge‐on‐oriented polymer chain network. Time‐of‐flight measurements performed on the various polymer films support this hypothesis by showing higher out‐of‐plane carrier mobilities for the partially face‐on‐oriented polymers. Additionally, a favorable morphology is mimicked by blending a face‐on polymer into an exclusively edge‐on oriented polymer, resulting in higher charge carrier mobilities and opening up a new avenue for the fabrication of high performing OFET devices.     

Tuning Molecular Adhesion via Material Anisotropy

Cell adhesion with extracellular matrix depends on the collective behaviors of a large number of receptor‐ligand bonds at the compliant cell‐matrix interface. While most biological tissues and structures, including cells and extracellular matrices, exhibit strongly anisotropic material properties, existing studies on molecular adhesion via receptor‐ligand bonds have been largely limited to isotropic materials. Here the effects of transverse isotropy, a common form of material anisotropy in biological systems, in modulating the adhesion behavior of a cluster of receptor‐ligand bonds are investigated. The results provide a theoretical basis to understand cell adhesion on anisotropic extracellular matrices and to explore the possibility of controlling cell adhesion via anisotropy design in material properties. The combined analysis and simulations show that the orientation of material anisotropy strongly affects the apparent softness felt by the adhesive bonds, thereby altering their ensemble lifetime by several orders of magnitude. An implication of this study is that distinct cellular behaviors can be achieved through remodeling of material anisotropy in either extracellular matrix or cytoskeleton. Comparison between different loading conditions, together with the effects of material anisotropy, yields a rich array of out‐of‐equilibrium behaviors in the molecular interaction between reactant‐bearing soft surfaces, with important implications on the mechanosensitivity of cells.     

Highly Permeable Skin Patch with Conductive Hierarchical Architectures Inspired by Amphibians and Octopi for Omnidirectionally Enhanced Wet Adhesion

Amphibian adhesion systems can enhance adhesion forces on wet or rough surfaces via hexagonal architectures, enabling omnidirectional peel resistance and drainage against wet and rough surfaces, often under flowing water. In addition, an octopus has versatile suction cups with convex cup structures located inside the suction chambers for strong adhesion in various dry and wet conditions. Highly air‐permeable, water‐drainable, and reusable skin patches with enhanced pulling adhesion and omnidirectional peel resistance, inspired by the microchannel network in the toe pads of tree frogs and convex cups in the suckers of octopi, are presented. By investigating various geometric parameters of microchannels on the adhesive surface, a simple model to maximize peeling strength via a time‐dependent zig‐zag profile and an arresting effect against crack propagation is first developed. Octopus‐like convex cups are employed on the top surfaces of the hexagonal structures to improve adhesion on skin in sweaty and even flowing water conditions. The amount of reduced graphene oxide nanoplatelets coated on the frog and octopus‐inspired hierarchical architectures is controlled to utilize the patches as flexible electrodes which can monitor electrocardiography signals without delamination from wet skin under motion.     

Oriented Poly(dialkylstannane)s

The inorganic (or ‘organometallic’) polymers poly(dibutylstannane), poly(dioctylstannane), and poly(didodecylstannane) have been oriented by shear forces, the tensile drawing of blends with polyethylene, and deposition from solution onto glass slides coated with an oriented, friction‐deposited poly(tetrafluoroethylene) (PTFE) layer. Orientation of the polystannanes has been examined by polarization microscopy, UV‐vis spectroscopy with polarized light, and X‐ray diffraction and their direction is found to depend on the length of the alkyl side groups and the method of orientation. Remarkably, in some cases the polystannane backbones are oriented parallel and in other instances perpendicular to the direction of the external orientation stimuli. The latter structural arrangement is most conspicuous for polymers substituted with dodecyl side groups, which are found to align parallel to the applied orientation direction, which forces the polymer backbone into a perpendicular position. Finally, UV‐vis spectra indicate that changes in the backbone conformation of certain polystannanes might be induced by applying mechanical stress.     

Gecko‐Inspired Dry Adhesive for Robotic Applications

Most geckos can rapidly attach and detach from almost any kind of surface. This ability is attributed to the hierarchical structure of their feet (involving toe pads, setal arrays, and spatulae), and how they are moved (articulated) to generate strong adhesion and friction forces on gripping that rapidly relax on releasing. Inspired by the gecko's bioadhesive system, various structured surfaces have been fabricated suitable for robotic applications. In this study, x–y–z asymmetric, micrometer‐sized rectangular flaps composed of polydimethylsiloxane (PDMS) were fabricated using massively parallel micro‐electromechanical systems (MEMS) techniques with the intention of creating directionally responsive, high‐to‐low frictional‐adhesion toe pads exhibiting properties similar to those found in geckos. Using a surface forces apparatus (SFA), the friction and adhesion forces of both vertical (symmetric) and angled/tilted (x–y–z asymmetric) microflaps under various loading, unloading and shearing conditIons were investigated. It was found that the anisotropic structure of tilted microflaps gives very different adhesion and tribological forces when articulated along different x–y–z directions: high friction and adhesion forces when articulated in the y–z plane along the tilt (+y) direction, which is also the direction of motion, and weak friction and adhesion forces when articulated against the tilt (–y) direction. These results demonstrate that asymmetric angled structures, as occur in geckos, are required to enable the gecko to optimize the requirements of high friction and adhesion on gripping, and low frictional‐adhesion on releasing. These properties are intimately coupled to a (also optimum) articulation mechanism. We discuss how both of these features can be simultaneously optimized in the design of robotic systems that can mimic the gecko adhesive system.     

Tension Pistons: Amplifying Piston Force Using Fluid‐Induced Tension in Flexible Materials

Pistons are ubiquitous devices used for fluid‐mechanical energy conversion. However, despite this ubiquity and centuries of development, the forces and motions produced by conventional rigid pistons are limited by their design. The use of flexible materials and structures opens a door to the design of a piston with unconventional features. In this study, an architecture for pistons that utilizes a combination of flexible membrane materials and compressible rigid structures is proposed. In contrast to conventional pistons, the fluid‐pressure‐induced tension forces in the flexible membrane play a primary role in the system, rather than compressive forces on the internal surfaces of the piston. The compressive skeletal structures offer the opportunity for the production of tunable forces and motions in the “tension piston” system. The experimental results indicate that the tension piston concept is able to produce substantially greater force (more than three times), higher power, and higher energy efficiency (more than 40% improvement at low pressures) compared to a conventional piston, and these features enable myriad potential applications for the tension piston as a drop‐in replacement for existing pistons.     

Nonchemotherapic and Robust Dual‐Responsive Nanoagents with On‐Demand Bacterial Trapping,Ablation, and Release for Efficient Wound Disinfection

Recent emerged antibacterial agents provide enormous new possibilities to replace antibiotics in fighting bacterial infectious diseases. Although abundant types of nanoagents are developed for preventing pathogen colonization, however, rationally design of nonchemotherapic, robust, and clinical‐adaptable nanoagents with tunable bacterial trap and killing activities remains a major challenge. Here, a demonstration of controlling the trap, ablation, and release activities of pathogenic bacteria via stimulus‐responsive regulatory mechanism is reported. First, temperature‐sensitive polymer brush is chemically grown onto carbon nanotube–Fe₃O₄, whereby the synthesized nanoagents can transfer from hydrophilic dispersion to hydrophobic aggregation upon near‐infrared light irradiation, which thus controls the bacterial trap, killing, and detaching. In turn, the formed aggregations will serve as localized heating sources to enhance photothermal ablation of bacteria. Systematically antibacterial experiments and mouse wound disinfection demonstrate the ultrarobust and recyclable disinfection capability of nanoagents with nearly 100% killing ratio to Staphylococcus aureus. Overall, for the first time, we represent a pioneering study on designing nonchemotherapic and robust dual‐responsive nanoagents that can sensitively and reversibly trap, inactivate, and detach bacteria. We envision that such nanoagents will not only have potential applications in pathogenic bacteria prevention but also provide a new pathway for wound disinfection, implant sterilization, and also live bacteria transportation.     

A Universal Strategy for Tough Adhesion of Wet Soft Material

Achieving adhesion between hydrogels and diverse materials in a facile and universal way is challenging. Existing methods rely on special chemical or physical properties of the hydrogel and adherends, which lead to limited applicability and complicated pretreatments. A stitch‐bonding strategy is proposed here by introducing a polymer chain with versatile functional group and triggerable crosslinking property inspired by catechol chemistry. The polymer chain can stitch the hydrogel by forming a network in topological entanglement with the preexisting hydrogel network, and directly bond to the adherend surface by versatile chemical interactions. Through this, the polymer chain solution works as a universal glue for facile adhesion of hydrogels to diverse substrates like metals, glasses, elastomers, plastics, and living tissues, without requiring any chemical design or pretreatment for the hydrogel and adherends. The adhesion energy between polyacrylamide hydrogel and diverse substrates can reach 200–400 J m^?2, and it can reach ≈900 J m^?2 with a toughened polyacrylic acid polyacrylamide hydrogel. The mechanism of stitch‐bonding strategy is illustrated by studying various influence factors.     

Insights into the Adhesive Mechanisms of Tree Frogs using Artificial Mimics

Elastic, microstructured surfaces (hydrophobic and hydrophilic) mimicking the surface structure of tree‐frog toe‐pads are fabricated. Their adhesion and friction behaviour in the presence of a liquid layer is evaluated and compared to flat controls. Tree‐frog‐like patterns are beneficial for wet adhesion only if the liquid does not wet the surface. The situation is different in friction, where the surface structure lead to significantly higher friction forces only if the liquid does wet the surface. Taking into account that tree‐frog attachment pads are hydrophilic and that their secretion wets all kind of surfaces, our results indicate that the surface structure in tree‐frog toe‐pads has been developed for climbing, when shear (friction) forces are involved. These results evidence the benefits and limitations of the surface design (microstructure and hydrophilicity) for adhesion and friction under wet conditions.     

Versatile Nanocomposite Coatings with Tunable Cell Adhesion and Bactericidity

TiO₂‐Ag nanocomposites are known for their bactericidal effect during exposure to appropriate UV radiation. While involving hazardous radiation, and limited to accessible areas, the bactericidity of these coatings is not persistent in the absence of UV light, which impedes their commercial application. Herein it is shown that TiO₂‐Ag nanocomposites can be made highly bactericidal without the need of irradiation. Beyond this, bactericidity can even be mitigated in the presence of pre‐irradiated coatings. Biocompatibility and cell adhesion are also negligibly small for the as‐processed, non‐irradiated coatings, and become fairly high when the coatings are irradiated prior to testing. This opens the possibility to pattern the coatings into areas with high and low cell adhesion properties. Indeed by irradiating the coating through a mechanical mask it is shown that fibroblast cell adherence is sharply confined to the irradiated area. These properties are achieved using TiO₂‐Ag thin films with high silver loadings of 50 wt%. The films are processed on stainless steel substrates using solution deposition. Microstructural characterization by means of X‐ray diffraction, Raman, and X‐ray photoelectron spectroscopy, high‐resolution scanning electron microscopy, and atomic force microscopy show a highly amorphous TiO₂‐Ag_xO nanocomposite matrix with scattered silver nanoparticles. UV irradiation of the films results in the precipitation of a high density of silver nanoparticles at the film surface. Bactericidal properties of the films are tested on α‐haemolyzing streptococci and in‐vitro biocompatibility is assessed on primary human fibroblast cultures. The results mentioned above as to the tunable bactericidity and biocompatibility of the TiO₂‐Ag coatings developed herein, are amenable to silver ion release, to catalytic effects of silver nanoparticles, and to specific wettabilities of the surfaces.     

Microtribological and Nanomechanical Properties of Switchable Y‐Shaped Amphiphilic Polymer Brushes

We have characterized the morphology and nanomechanical properties of surface‐grafted nanoscale layers consisting of Y‐shaped binary molecules with one polystyrene (PS) arm and one poly(acrylic acid) (PAA) arm. We examined these amphiphilic brushes in fluids (in‐situ visualization), and measured their microtribological characteristics as a function of chemical composition. Atomic force microscopy (AFM)‐based nanomechanical testing has shown that nanoscale reorganization greatly influences the adhesion and elastic properties of the nanoscale brush layer. In water, a bimodal distribution of the elastic modulus, arising from the mixed chemical composition of the topmost layer, is observed. In contrast, the top layer is completely dominated by PS in toluene. As a result of this reorganization, the Y‐shaped‐brush layer exhibits a dramatic variation in the friction and wear properties after exposure to different solvents. Unexpectedly, the tribological properties are enhanced for the hydrophilic and polar, PAA‐dominated, surface, which shows a lower friction coefficient and higher wear stability, despite higher adhesion and heterogeneous surface composition. We suggest that this unusual behavior is caused by the combination of the presence of a thicker water layer on the PAA‐enriched surface that acts as a boundary lubricant and the glassy state of the PAA chains.     

Novel Brush Polymers with Phosphorylcholine Bristle Ends: Synthesis,Structure, Properties,and Biocompatibility

N ew brush polymers with various numbers of bristle ends incorporating phosphorylcholine (PC) moieties are synthesized. The polymers are thermally stable up to 175 °C and form good‐quality films with conventional spin‐, roll‐, and dip‐coating, and subsequent drying processes. Interestingly, all these brush polymers, as a PC‐containing polymer, demonstrate a stable molecular multi‐bilayer structure in thin films that arise due to the efficient self‐assembly of the bristles for temperatures <55 °C and PC‐rich surfaces, and therefore successfully mimic natural cell‐membrane surfaces. These brush‐polymer films exhibit excellent water wettability and water sorption whilst retaining the remarkable molecular multi‐bilayer structure, and thus have hydrophilic surfaces. These novel multi‐bilayer structured films repel fibrinogen molecules and platelets from their surfaces but also have bactericidal effects on bacteria. Moreover, the brush‐polymer films are found to provide comfortable surface environments for the successful anchoring and growth of HEp‐2 cells, and to exhibit excellent biocompatibility in mice. These newly developed brush polymers are suitable for use in biomedical applications including medical devices and biosensors that require biocompatibility and the reduced possibility of post‐operative infection.     

4D Printing of a Bioinspired Microneedle Array with Backward‐Facing Barbs for Enhanced Tissue Adhesion

Microneedle (MN), a miniaturized needle with a length‐scale of hundreds of micrometers, has received a great deal of attention because of its minimally invasive, pain‐free, and easy‐to‐use nature. However, a major challenge for controlled long‐term drug delivery or biosensing using MN is its low tissue adhesion. Although microscopic structures with high tissue adhesion are found from living creatures in nature (e.g., microhooks of parasites, barbed stingers of honeybees, quills of porcupines), creating MNs with such complex microscopic features is still challenging with traditional fabrication methods. Here, a MN with bioinspired backward‐facing curved barbs for enhanced tissue adhesion, manufactured by a digital light processing 3D printing technique, is presented. Backward‐facing barbs on a MN are created by desolvation‐induced deformation utilizing cross‐linking density gradient in a photocurable polymer. Barb thickness and bending curvature are controlled by printing parameters and material composition. It is demonstrated that tissue adhesion of a backward‐facing barbed MN is 18 times stronger than that of barbless MN. Also demonstrated is sustained drug release with barbed MNs in tissue. Improved tissue adhesion of the bioinspired MN allows for more stable and robust performance for drug delivery, biofluid collection, and biosensing.     

Design of Nanocomposite Low‐Friction Coatings

Friction and wear between moving surfaces is unavoidable and is an important reason for failure of mechanical components. A wear‐resistant and low‐friction coating can prolong the lifetime of an engineered component. Here we demonstrate a new concept for the design of low‐friction nanocomposite carbide coatings with an intrinsic driving force to form amorphous carbon (C–C bonds). Ti–Al–C has been chosen as a model system, but the idea is general and should be applicable to a wide class of materials. The ability to intrinsically form amorphous carbon is achieved by a substitutional solid solution of the weak‐carbide‐forming metal (Al) into the thermodynamically stable monocarbide (TiC). This creates, in a controllable manner, a driving force for phase separation of carbide particles embedded in a matrix of amorphous carbon. In a tribological contact the amorphous carbon can be further graphitized and thereby lower the friction coefficient. Consequently, the model system has a self‐lubricating mechanism but at the same time a tunable share of the two phases, which gives excellent possibilities to design wear resistance and toughness. In this paper we show that the friction coefficient can be lowered by more than 50 % for Al‐containing TiC coatings without severe loss in mechanical characteristics.     

Microtribology of Aqueous Carbon Nanotube Dispersions

The tribological behavior of carbon nanotubes (CNTs) in aqueous humic acid (HA) solutions was studied using a surface forces apparatus (SFA) and shows promising lubricant additive properties. Adding CNTs to the solution changes the friction forces between two mica surfaces from “adhesion controlled” to “load controlled” friction. The coefficient of friction with either single‐walled (SW) or multi‐walled (MW) CNT dispersions is in the range 0.30–0.55 and is independent of the load and sliding velocity. More importantly, lateral sliding promotes a redistribution or accumulation, rather than squeezing out, of nanotubes between the surfaces. This accumulation reduced the adhesion between the surfaces (which generally causes wear/damage of the surfaces), and no wear or damage was observed during continuous shearing experiments that lasted several hours even under high loads (pressures ～10 MPa). The frictional properties can be understood in terms of the Cobblestone Model where the friction force is related to the fraction of the adhesion energy dissipated during impacts of the nanoparticles. We also develop a simple generic model based on the van der Waals interactions between particles and surfaces to determine the relation between the dimensions of nanoparticles and their tribological properties when used as additives in oil‐ or water‐based lubricants.