Lubricant‐Infused Anisotropic Porous Surface Design of Reduced Graphene Oxide Toward Electrically Driven Smart Control of Conductive Droplets' Motion

The study of Nepenthes pitcher plants‐bioinspired anisotropic slippery liquid‐infused porous surfaces (SLIPS) is currently in its infancy. The factors that influence their anisotropic self‐cleaning and electric response of a drop's motion and the mechanism have not been fully elucidated. In order to address these problems, two new types of anisotropic slippery surfaces have been designed by using directional, porous, conductive reduced graphene oxide (rGO) films, and different lubricating fluids (conductive and nonconductive), which are used to study the influencing factors and the mechanism of anisotropic self‐cleaning and electric‐responsive control of a drop's motion. The results demonstrate the anisotropic self‐cleaning property of these two types of SLIPS is closely related to the interaction between liquid drops, lubricating fluids and dirt, and the conductive lubricating fluids filling the rGO porous film can reduce the response voltage of the electrically driven reversible control of a drop's slide. The uniqueness of this research lies in the use of two different lubricating fluids and graphene materials to prepare anisotropic SLIPS, identify the key factors to achieve an electrically driven system. These studies are essential for advancing the application of electronically responsive SLIPS in the fields of liquid directional transportation, microfluidics, microchips, and other related research.     

Omniphobic ZIF‐8@Hydrogel Membrane by Microfluidic‐Emulsion‐Templating Method for Wound Healing

Bacterial adhesion and colonization can result in chronic non‐healing wounds. Current hydrophilic wound dressings can release antibacterial agents into the wound exudate, but may result in overhydrated wounds, bacterial overgrowth, and even tissue maceration. Hydrophobic dressings are anti‐fouling, though ineffective to encapsulate and release bactericidal agents. Combining the advantages of hydrophilic and hydrophobic dressings seems difficult, until the development of superwettability surfaces offers an opportunity for omniphobic dressings from intrinsic hydrophilic polymers. Herein, omniphobic porous hydrogel wound dressings loaded with a zinc imidazolate framework 8 (ZIF‐8) are fabricated by a microfluidic‐emulsion‐templating method. The fabricated porous hydrogel membrane with its reentrant architecture is repellent to blood and body fluids, though intrinsically hydrophilic. This unique combination not only reduces the adhesion of harmful microbes, but also enables the encapsulation and release of antibacterial ingredients to wounded sites from hydrophilic polymer networks. As such, the omniphobic metal‐organic frameworks (MOFs)@hydrogel porous wound dressing can inhibit bacteria invasion and enable the controlled release of the bactericidal, anti‐inflammatory, and nontoxic zinc ions. Furthermore, in vivo study of infected full‐thickness skin defect models demonstrates that the dressing also accelerates wound closure by promoting angiogenesis and collagen deposition. Therefore, the omniphobic MOFs@hydrogel porous wound dressings are potentially useful for clinical application.     

Remote Photothermal Actuation of Underwater Bubble toward Arbitrary Direction on Planar Slippery Fe3O4‐Doped Surfaces

Unidirectional underwater gas bubble (UGB) transport on a surface is realized by buoyant force or wettability gradient force (F_wet‐grad) derived from a tailored geography. Unfortunately, intentional control of the UGB over transport speed, direction, and routes on horizontal planar surfaces is rarely explored. Herein reported is a light‐responsive slippery lubricant‐infused porous surface (SLIPS) composed of selective lubricants and super‐hydrophobic micropillar‐arrayed Fe₃O₄/polydimethylsiloxane film. Upon this SLIPS, the UGB can be horizontally actuated along arbitrary directions by remotely loading/discharging unilateral near‐infrared (NIR) stimuli. The underlying mechanism is that F_wet‐grad can be generated within 1 s in the presence of a NIR‐trigger due to the photothermal effect of Fe₃O₄. Once the NIR‐stimuli are discharged, F_wet‐grad vanishes to break the UGB on the SLIPS. Moreover, performed are systematic parameter studies to investigate the influence of bubble volume, lubricant rheology, and F_wet‐grad on the UGB steering performance. Fundamental physics renders the achievement of antibuoyancy manipulation of the UGBs on an inclined SLIPS. Significantly, steering UGBs by horizontal SLIPS to configurate diverse patterns, as well as facilitating light‐control‐light optical shutter, is deployed. Compared with the previous slippery surfaces, light‐responsive SLIPS is more competent for manipulating UGBs with controllable transport speed, direction, and routes independent of buoyancy or geography derivative force.     

Controlled Release of LL‐37‐Derived Synthetic Antimicrobial and Anti‐Biofilm Peptides SAAP‐145 and SAAP‐276 Prevents Experimental Biomaterial‐Associated Staphylococcus aureus Infection

The present study aims to develop an implant coating releasing novel antimicrobial agents to prevent biomaterial‐associated infections. The LL‐37‐derived synthetic antimicrobial and anti‐biofilm peptides (SAAP)‐145 and SAAP‐276 exhibit potent bactericidal and anti‐biofilm activities against clinical and multidrug‐resistant Staphylococcus aureus strains by rapid membrane permeabilization, without inducing resistance. Injection of SAAP‐145, but not SAAP‐276, along subcutaneous implants in mice reduces S. aureus implant colonization by approximately 2 log, but does not reduce bacterial numbers in surrounding tissue. To improve their efficacy, SAAP‐145 and SAAP‐276 are incorporated in a polymer–lipid encapsulation matrix (PLEX) coating, providing a constant release of 0.6% daily up to 30 d after an initial burst release of >50%. In a murine model for biomaterial‐associated infection, SAAP‐145‐PLEX and SAAP‐276‐PLEX coatings significantly reduce the number of culture positive implants and show ≥3.5 and ≥1.5 log lower S. aureus implant and tissue colonization, respectively. Interestingly, these peptide coatings are also highly effective against multidrug‐resistant S. aureus, both reducing implant colonization by ≥2 log. SAAP‐276‐PLEX additionally reduces tissue colonization by 1 log. Together, the peptide‐releasing PLEX coatings hold promise for further development as an alternative to coatings releasing conventional antibiotics to prevent biomaterial‐associated infections.     

Omniphobic “RF Paper” Produced by Silanization of Paper with Fluoroalkyltrichlorosilanes

The fabrication and properties of “fluoroalkylated paper” (“R^F paper”) by vapor‐phase silanization of paper with fluoroalkyl trichlorosilanes is reported. R^F paper is both hydrophobic and oleophobic: it repels water (θ_app^H2^O>140°), organic liquids with surface tensions as low as 28 mN m^‐1, aqueous solutions containing ionic and non‐ionic surfactants, and complex liquids such as blood (which contains salts, surfactants, and biological material such as cells, proteins, and lipids). The propensity of the paper to resist wetting by liquids with a wide range of surface tensions correlates with the length and degree of fluorination of the organosilane (with a few exceptions in the case of methyl trichlorosilane‐treated paper), and with the roughness of the paper. R^F paper maintains the high permeability to gases and mechanical flexibility of the untreated paper, and can be folded into functional shapes (e.g., microtiter plates and liquid‐filled gas sensors). When impregnated with a perfluorinated oil, R^F paper forms a “slippery” surface (paper slippery liquid‐infused porous surface, or “paper SLIPS“) capable of repelling liquids with surface tensions as low as 15 mN m^‐1. The foldability of the paper SLIPS allows the fabrication of channels and flow switches to guide the transport of liquid droplets.     

Synthetic Surfaces with Robust and Tunable Underwater Superoleophobicity

Surfaces with extreme wetting properties are useful for the collection, manipulation, transport, and avoidance of aqueous and organic fluids of commercial and strategic importance. Two major obstacles to the deployment of synthetic non‐wetting materials in practical scenarios are their lack of mechanical durability and their susceptibility to fouling in contaminated or chemically complex media. Here, crosslinked and nanoporous polymer multilayers are reported that overcome these limitations and exhibit robust and tunable “underwater superoleophobicity”, or the ability to almost completely prevent contact with oils and other organic fluids when submerged in water. These entirely organic coatings mimic key chemical and structural features found on the scales of fish and other natural anti‐oil‐fouling surfaces, and are remarkably tolerant to physical, chemical, and environmental insults commonly encountered in natural and synthetic aqueous environments. This approach also permits facile manipulation and patterning of surface chemistry and, thus, tunable spatial control over other important aspects of interfacial behavior, such as underwater oil adhesiveness, that extend and expand the potential utility of synthetic anti‐oil‐fouling surfaces in aqueous, aquatic, and marine environments.     

Tunable Structural Color Surfaces with Visually Self‐Reporting Wettability

Functional materials with wettability of specific surfaces are important for many areas. Here, a new lubricant‐infused elastic inverse opal is presented with tunable and visually “self‐reporting” surface wettability. The elastic inverse opal films are used to lock in the infused lubricating fluid and construct slippery surfaces to repel droplets of various liquids. The films are stretchable, and the lubricating fluid can penetrate the pores under stretching, leaving the surface layer free of lubrication; the resultant undulating morphology of the inverse opal scaffold topography can reversibly pin droplets on the fluidic film rather than the solid substrate. This mechanical stimulation process provides an effective means of dynamically tuning the surface wettability and the optical transparency of the inverse opal films. In particular, as the adjustments are accompanied by simultaneous deformation of the periodic macroporous structure, the inverse opal films can self‐report on their surface status through visible structural color changes. These features make such slippery structural color materials highly versatile for use in diverse applications.     

Self‐Defensive Biomaterial Coating Against Bacteria and Yeasts: Polysaccharide Multilayer Film with Embedded Antimicrobial Peptide

Prevention of pathogen colonization of medical implants is a major medical and financial issue since infection by microorganisms constitutes one of the most serious complications after surgery or critical care. Immobilization of antimicrobial molecules on biomaterials surfaces is an efficient approach to prevent biofilm formation. Herein, the first self‐defensive coating against both bacteria and yeasts is reported, where the release of the antimicrobial peptide is triggered by enzymatic degradation of the film due to the pathogens themselves. Biocompatible and biodegradable polysaccharide multilayer films based on functionalized hyaluronic acid by cateslytin (CTL), an endogenous host‐defensive antimicrobial peptide, and chitosan (HA‐CTL‐C/CHI) are deposited on a planar surface with the aim of designing both antibacterial and antifungal coating. After 24 h of incubation, HA‐CTL‐C/CHI films fully inhibit the development of Gram‐positive Staphylococcus aureus bacteria and Candida albicans yeasts, which are common and virulent pathogens agents encountered in care‐associated diseases. Hyaluronidase, secreted by the pathogens, leads to the film degradation and the antimicrobial action of the peptide. Furthermore, the limited fibroblasts adhesion, without cytotoxicity, on HA‐CTL‐C/CHI films highlights a medically relevant application to prevent infections on catheters or tracheal tubes where fibrous tissue encapsulation is undesirable.     

Engineering a Robust,Versatile Amphiphilic Membrane Surface Through Forced Surface Segregation for Ultralow Flux‐Decline

Unlike biofoulants/pollutants, oil foulants/pollutants are prone to coalesce, spread and migrate to form continuous fouling layer covering on the surfaces. Therefore, such kind of fouling can not be simply alleviated by hydrophilic modification with currently extensively used antifouling materials such as poly(ethylene glycol) (PEG)‐based or zwitterionic polymers etc. In the present study, an amphiphilic porous membrane surface, comprising hydrophilic fouling resistant domains and hydrophobic fouling release microdomains, is explored via a "forced surface segregation" approach. The resultant membranes exhibit both superior oil‐fouling and bio‐fouling resistant property: membrane fouling is exquisitely suppressed and the permeation flux‐decline is decreased to an ultralow level. It can be envisaged that the present study may open a novel avenue to the design and construction of robust, versatile antifouling surfaces.     

Slippery Lubricant‐Infused Surfaces: Properties and Emerging Applications

Bioinspired lubricant‐infused surfaces exhibit various unique properties attributed to their liquid‐like and molecularly smooth nature. Excellent liquid repellency and “slippery” properties, self‐healing, antiicing, anticorrosion characteristics, enhanced heat transfer, antibiofouling, and cell‐repellent properties have been already demonstrated. This progress report highlights some of the recent developments in this rapidly growing area, focusing on properties of lubricant‐infused surfaces, and their emerging applications as well as some future challenges.     

Metal‐Based Nanomaterials in Biomedical Applications: Antimicrobial Activity and Cytotoxicity Aspects

Microbial colonization on material surfaces is ubiquitous. Biofilms derived from surface‐colonized microbes pose serious problems to the society from both an economical perspective and a health concern. Incorporation of antimicrobial nanocompounds within or on the surface of materials, or by coatings, to prevent microbial adhesion or kill the microorganisms after their attachment to biofilms, represents an important strategy in an increasingly challenging field. Over the last decade, many studies have been devoted to preparing meta‐based nanomaterials that possess antibacterial, antiviral, and antifungal activities to combat pathogen‐related diseases. Herein, an overview on the state‐of‐the‐art antimicrobial nanosized metal‐based compounds is provided, including metal and metal oxide nanoparticles as well as transition metal nanosheets. The antimicrobial mechanism of these nanostructures and their biomedical applications such as catheters, implants, medical delivery systems, tissue engineering, and dentistry are discussed. Their properties as well as potential caveats such as cytotoxicity, diminishing efficacy, and induction of antimicrobial resistance of materials incorporating these nanostructures are reviewed to provide a backdrop for future research.     

pH‐Responsive Polymer–Drug Conjugate: An Effective Strategy to Combat the Antimicrobial Resistance

An urgent need for developing new antimicrobial approaches has emerged due to the imminent threat of antimicrobial‐resistant (AMR) pathogens. Bacterial infection can induce a unique microenvironment with low pH, which can be employed to trigger drug release and activation. Here, a pH‐responsive polymer–drug conjugate (PDC) capable of combating severe infectious diseases and overcoming AMR is reported. The PDC is made of a unique biodegradable and biocompatible cationic polymer Hex‐Cys‐DET and streptomycin, a model antibiotic. The two components show strong antimicrobial synergy since the polymer can induce pores on the bacterial wall/membrane, thus significantly enhancing the transport of antibiotics into the bacteria and bypassing the efflux pump. The PDC is neutralized for enhanced biocompatibility under physiological conditions but becomes positively charged while releasing the antibiotic in infected tissues due to the low pH. Additionally, the polymer contains disulfide bonds in its main chain, which makes it biodegradable in mammalian cells and thus reducing the cytotoxicity. The PDC can effectively penetrate bacterial biofilms and be taken up by mammalian cells, thereby minimizing biofilm‐induced AMR and intracellular infections. The PDC exhibits remarkable antimicrobial activity in three in vivo infection models, demonstrating its broad‐spectrum antimicrobial capability and great potency in eliminating AMR infections.     

Self‐Replenishing Dual Structured Superhydrophobic Coatings Prepared by Drop‐Casting of an All‐In‐One Dispersion

Robust dual structured superhydrophobic coatings which replenish spontaneously their surface chemical composition on new multi‐scale structured surfaces, recreated upon damage, are described. The surface repair occurs at room temperature, via intrinsic elements of the coatings, all covalently bonded. These coatings can be prepared from all‐in‐one dispersions by a simple drop‐cast method, with different thicknesses and on various substrates. The critical factors to optimize the self‐replenishment are described and three main design principles are postulated. The superhydrofobicity of the coatings is maintained even after 500 abrasion cycles. The principles reported can be extended towards self‐healing other surface‐dependent functionalities, that is, anti‐bacteria, anti‐fouling, or drag‐reduction, which will maintain high performance levels all through their life‐cycle with low cost and energy demand for maintenance and surface repair.     

Hybrid Materials from Ultrahigh‐Inorganic‐Content Mineral Plastic Hydrogels: Arbitrarily Shapeable,Strong, and Tough

Natural mineralized structural materials such as nacre and bone possess a unique hierarchical structure comprising both hard and soft phases, which can achieve the perfect balance between mechanical strength and shape controllability. Nevertheless, it remains a great challenge to control the complex and predesigned shapes of artificial organic–inorganic hybrid materials at ambient conditions. Inspired by the plasticity of polymer‐induced liquid precursor phases that can penetrate and solidify in porous organic frameworks for biomineral formation, here a mineral plastic hydrogel is shown with ultrahigh silica content (≈95 wt%) that can be similarly hybridized into a porous delignified wood scaffold, and the resultant composite hydrogels can be manually made into arbitrary shapes. Subsequent air drying well preserves the designed shapes and produces fire‐retardant, ultrastrong, and tough structural organic–inorganic hybrids. The proposed mineral plastic hydrogel strategy opens an easy and eco‐friendly way for fabricating bioinspired structural materials that compromise both precise shape control and high mechanical strength.     

Antibacterial Surface Coatings from Zinc Oxide Nanoparticles Embedded in Poly(N‐isopropylacrylamide) Hydrogel Surface Layers

Despite multiple research approaches to prevent bacterial colonization on surfaces, device‐associated infections are currently responsible for about 50% of nosocomial infections in Europe and significantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin‐coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite film morphology reveals a homogeneous distribution of the ZnO NP throughout the film for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confirmed by UV‐vis spectroscopy. The nanocomposite films exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈0.74 μg cm^?2 (1.33 mmol cm^?3), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non‐cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin films between bacterial and cellular species qualifies them as promising candidates for novel biomedical device coatings.     

Microskeleton‐Nanofiller Composite with Mechanical Super‐Robust Superhydrophobicity against Abrasion and Impact

Superhydrophobic surfaces have promised tremendous applications in living and industrial areas for the past two decades. Real applications, however, meet challenges, with the central concern being the robustness to resist mechanical abrasions and impacts. Here, a revolutionary strategy is proposed to create a microskeleton‐nanofiller (MSNF) film with exceptionally mechanical superstable superhydrophobicity. The strategy is conceptually different from the traditional superhydrophobic 3D microskeleton, because a 3D microskeleton is used to completely fill in the infused superhydrophobic medium. The resulting MSNF film can reserve superhydrophobicity under not only continuous abrasion before the complete wearing off the film, but also Taber abrasion, knife‐scratch, and cyclic tape peels. In addition, the MSNF film enables damage resistance to heavy impact at least up to a kinetic energy of ≈40.2 J. Furthermore, the MSNF film is also superamphiphobic to prevent oil contamination and can reserve the superhydrophobicity under large bending or torsion. Together with robustness and scalability, the MSNF film will be useful in automobiles, ships, aircraft, and houses in harsh environments and the strategy can extend to various inexpensive structured materials (such as porous iron).     

Poly(N‐isopropylacrylamide) Interfaces with Dissimilar Thermo‐responsive Behavior for Controlling Ion Permeation and Immobilization

Stimuli‐responsive polymer interfaces with tethered poly(N‐isopropylacrylamide) (PNIPAm) chains and its cross‐linked porous hydrogel as sensitive phases were fabricated by cycling an electronic potential in aqueous solution. Surface morphological analysis and electrochemical measurements revealed that, owing to their different novel structures, the PNIPAm chain‐modified interface showed ON/OFF switch behavior, whereas the PNIPAm gel‐modified interface exhibited a ‘breathing in' process. The results suggest that the interfacial physicochemical properties, which are greatly affected by the graft conformations and topologies of PNIPAm on the substrates, could be effectively modulated by easily varying the synthesis conditions and are investigated by simple electrochemical methods. The results also demonstrate that the ON/OFF switch behavior of the PNIPAm chain‐modified interface has potential applications in controlled ion/molecule permeation, and the ‘breathing in' mechanism of the gel‐modified interface might be applied to immobilize ions or nanoparticles. These thermo‐sensitive interfaces might be used to design adaptive/responsive biocompatible surfaces in a variety of areas.     

Imaging Surface Immobilization Chemistry: Correlation with Cell Patterning on Non‐Adhesive Hydrogel Thin Films

High‐fidelity surface functional group (e.g., N‐hydroxysuccinimide (NHS) reactive ester) patterning is readily and reliably achieved on commercial poly(ethylene glycol) (PEG)‐based polymer films already known to exhibit high performance non‐fouling properties in full serum and in cell culture conditions. NHS coupling chemistry co‐patterned with methoxy‐capped PEG using photolithographic methods is directly spatially imaged using imaging time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and principal components statistical analysis. Patterned NHS surface reactive zones are clearly resolved at high sensitivity despite the complexity of the polymer matrix chemistry. ToF‐SIMS imaging also reveals the presence of photo‐resist residue remaining from typical photolithography processing methods. High cross‐correlation between various ion‐derived ToF‐SIMS images is observed, providing sensitive chemical corroboration of pattern chemistry and biological reactivity in complex milieu. Surface‐specific protein coupling is observed first by site‐selective reaction of streptavidin with NHS patterns, followed by identical patterns of biotinylated Alexa‐labeled albumin coupling. This suggests that streptavidin immobilized on the patterns remains bioactive. Fluorescently labeled full serum is shown to react selectively with NHS‐reactive regions, with minimal signal from methoxy‐capped regions. Insufficient serum is adsorbed under any conditions to these surfaces to support cell attachment in serum‐containing media. This reflects the high intrinsic non‐adsorptive nature of this chemistry. Fibroblasts attach and proliferate in serum culture only when a cell adhesion peptide (RGD) is first grafted to NHS regions on the PEG‐based surfaces. Longer‐term serum‐based cell culture retains high cell‐pattern fidelity that correlates with chemical imaging of both the NHS and RGD patterns and also lack of cell adhesion to methoxy‐capped regions. Cell staining shows orientation of adherent cells within the narrow patterned areas. Cell patterns are consistently retained beyond 15 days in serum media.     

Vesicular Structures Self‐Assembled from Oligonucleotide‐Polymer Hybrids: Mechanical Prevention of Bacterial Colonization Upon their Surface Tethering Through Hybridization

In order to design soft coatings, surface tethering of vesicular structures self‐assembled from oligonucleotide‐polymer hybrids is achieved through hybridization. Watson‐Crick base‐pairing occurs between the nucleotide sequences involved in the self‐assembly and their surface‐tethered complementary sequences. Combining the quartz crystal microbalance and in situ observations using confocal laser scanning microscopy, it is evidenced that the vesicles retain their morphology even under flow stress. Surprisingly, these soft surfaces prevent bacterial colonization.     

Magnetocontrollable Droplet and Bubble Manipulation on a Stable Amphibious Slippery Gel Surface

Smart manipulation of liquid/bubble transport has garnered widespread attention due to its potential applications in many fields. Designing a responsive surface has emerged as an effective strategy for achieving controllable transport of liquids/bubbles. However, it is still challenging to fabricate stable amphibious responsive surfaces that can be used for the smart manipulation of liquid in air and bubbles underwater. Here, amphibious slippery surfaces are fabricated using magnetically responsive soft poly(dimethylsiloxane) doped with iron powder and silicone oil. The slippery gel surface retains its magnetic responsiveness and demonstrates strong affinity for bubbles underwater but shows small and switching resistance forces with the water droplets in air and bubbles underwater, which is the key factor for achieving the controllable transport of liquids/bubbles. On the slippery gel surface, the sliding behaviors of water droplets and bubbles can be reversibly controlled by alternately applying/removing an external magnetic field. Notably, compared with slippery liquid‐infused porous surfaces, the slippery gel surface demonstrates outstanding stability, whether in air or underwater, even after 100 cycles of alternately applying/removing the magnetic field. This surface shows potential applications in gas/liquid microreactors, gas–liquid mixed fluid transportation, bubble/droplet manipulation, etc.