Slippery Liquid-Infused Porous Surfaces that Prevent Bacterial Surface Fouling and Inhibit Virulence Phenotypes in Surrounding Planktonic Cells

Recent Developments in Slippery Liquid-Infused Porous Surface Coatings for Biomedical Applications

Slippery liquid-infused porous surface (SLIPS), inspired by the Nepenthes pitcher plant, exhibits excellent performances as it has a smooth surface and extremely low contact angle hysteresis. Biomimetic SLIPS attracts considerable attention from the researchers for different applications in self-cleaning, anti-icing, anticorrosion, antibacteria, antithrombotic, and other fields. Hence, SLIPS has shown promise for applications across both the biomedical and industrial fields. However, the manufacturing of SLIPS with strong bonding ability to different substrates and powerful liquid locking performance remains highly challenging. In this review, a comprehensive overview of research on SLIPS for medical applications is conducted, and the design parameters and common fabrication methods of such surfaces are summarized. The discussion extends to the mechanisms of interaction between microbes, cells, proteins, and the liquid layer, highlighting the typical antifouling applications of SLIPS. Furthermore, it identifies the potential of utilizing the controllable factors provided by SLIPS to develop innovative materials and devices aimed at enhancing human health.

Removal of Free Liquid Layer from Liquid-Infused Catheters Reduces Silicone Loss into the Environment while Maintaining Adhesion Resistance

Silicone urinary catheters infused with silicone liquid offer an effective alternative to antibiotic coatings, reducing microbial adhesion while decreasing bladder colonization and systemic dissemination. However, loss of free silicone liquid from the surface into the host system is undesirable. To reduce the potential for liquid loss, free silicone liquid was removed from the surface of liquid-infused catheters by either removing excess liquid from fully infused samples or by partial infusion. The effect on bacterial and host protein adhesion was then assessed. Removing the free liquid from fully infused samples resulted in a ~64% decrease in liquid loss into the environment compared to controls, with no significant increase in deposition of the host protein fibrinogen or the adhesion of the common uropathogen Enterococcus faecalis. Partially infusing samples decreased liquid loss as total liquid content decreased, with samples infused to 70-80% of their maximum capacity showing a ~85% reduction in liquid loss compared to fully infused controls. Furthermore, samples above 70% infusion showed no significant increase in fibrinogen or E. faecalis adhesion. Together, the results suggest that eliminating free liquid layer, mechanically or through partial infusion, can reduce liquid loss from liquid-infused catheters while preserving functionality.

Anti-Fouling Properties of Phosphonium Ionic Liquid Coatings in the Marine Environment

Biofouling is the buildup of marine organisms on a submerged material. This research tests the efficacy of phosphonium ion gels comprising phosphonium monomers ([P444VB][AOT] and [P888VB][AOT]) and free ionic liquid ([P4448][AOT], [P88814][AOT]) (10 to 50 wt%), varying copper(II) oxide biocide concentrations (0 to 2 wt%), and the docusate anion [AOT]- for added hydrophobicity. The efficacy of these formulations was tested using a seachest simulator protected from light and tidal currents in New Zealand coastal waters over the summer and autumn periods. Anti-fouling performance was correlated with the hydrophobicity of the surface (water contact angle: 14-131°) and biocide concentration. Formulations with higher hydrophobicity (i.e., less free ionic liquid and longer alkyl chain substituents) displayed superior anti-fouling performance. The presence of the copper(II) biocide negatively affected anti-fouling performance via significant increases to hydrophilicity. No correlation was observed between antimicrobial activity and anti-fouling performance. Overall, phosphonium ion gels show potential for combining anti-fouling and foul release properties.

Bio-inspired microfluidics: A review

Biomicrofluidics, a subdomain of microfluidics, has been inspired by several ideas from nature. However, while the basic inspiration for the same may be drawn from the living world, the translation of all relevant essential functionalities to an artificially engineered framework does not remain trivial. Here, we review the recent progress in bio-inspired microfluidic systems via harnessing the integration of experimental and simulation tools delving into the interface of engineering and biology. Development of "on-chip" technologies as well as their multifarious applications is subsequently discussed, accompanying the relevant advancements in materials and fabrication technology. Pointers toward new directions in research, including an amalgamated fusion of data-driven modeling (such as artificial intelligence and machine learning) and physics-based paradigm, to come up with a human physiological replica on a synthetic bio-chip with due accounting of personalized features, are suggested. These are likely to facilitate physiologically replicating disease modeling on an artificially engineered biochip as well as advance drug development and screening in an expedited route with the minimization of animal and human trials.

Reactive Multilayer Coating As Versatile Nanoarchitectonics for Customizing Various Bioinspired Liquid Wettabilities

In last few decades, multilayer coatings have achieved enormous attention owing to their unique ability to tune thickness, topography, and chemical composition for developing various functional materials. Such multilayer coatings were mostly and conventionally derived by following a simple layer-by-layer (LbL) deposition process through the strategic use of electrostatic interactions, hydrogen bonding, host-guest interactions, covalent bonding, etc. In the conventional design of multilayer coatings, the chemical composition and morphology of coatings are modulated during the process of multilayer constructions. In such an approach, the postmodulations of the porous multilayers with different and desired chemistries are challenging to achieve due to the lack of availability of readily and selectively reactive moieties. Recently, the design of readily and selectively reactive multilayer coatings (RMLCs) provided a facile basis for postmodulating the prepared coating with various desired chemistries. In fact, by taking advantage of the inherent ability of co-optimizing the topography and various chemistries in porous RMLCs, different durable bioinspired liquid wettabilities (i.e., superhydrophobicity, underwater superoleophobicity, underwater superoleophilicity, slippery property, etc.) were successfully derived. Such interfaces have enormous potential in various prospective applications. In this review, we intend to give an overview of the evolution of LbL multilayer coatings and their synthetic strategies and discuss the key advantages of porous RMLCs in terms of achieving and controlling wettability properties. Recent attempts toward various applications of such multilayer coatings that are strategically embedded with different desired liquid wettabilities will be emphasized.

A Bifunctional Spray Coating Reduces Contamination on Surfaces by Repelling and Killing Pathogens

Surface-mediated transmission of pathogens is a major concern with regard to the spread of infectious diseases. Current pathogen prevention methods on surfaces rely on the use of biocides, which aggravate the emergence of antimicrobial resistance and pose harmful health effects. In response, a bifunctional and substrate-independent spray coating is presented herein. The bifunctional coating relies on wrinkled polydimethylsiloxane microparticles, decorated with biocidal gold nanoparticles to induce a "repel and kill" effect against pathogens. Pathogen repellency is provided by the structural hierarchy of the microparticles and their surface chemistry, whereas the kill mechanism is achieved using functionalized gold nanoparticles embedded on the microparticles. Bacterial tests with methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa reveal a 99.9% reduction in bacterial load on spray-coated surfaces, while antiviral tests with Phi6─a bacterial virus often used as a surrogate to SARS-CoV-2─demonstrate a 98% reduction in virus load on coated surfaces. The newly developed spray coating is versatile, easily applicable to various surfaces, and effective against various pathogens, making it suitable for reducing surface contamination in frequently touched, heavy traffic, and high-risk surfaces.

Nature-Inspired Surface Structures Design for Antimicrobial Applications

Surface contamination by microorganisms such as viruses and bacteria may simultaneously aggravate the biofouling of surfaces and infection of wounds and promote cross-species transmission and the rapid evolution of microbes in emerging diseases. In addition, natural surface structures with unique anti-biofouling properties may be used as guide templates for the development of functional antimicrobial surfaces. Further, these structure-related antimicrobial surfaces can be categorized into microbicidal and anti-biofouling surfaces. This review introduces the recent advances in the development of microbicidal and anti-biofouling surfaces inspired by natural structures and discusses the related antimicrobial mechanisms, surface topography design, material application, manufacturing techniques, and antimicrobial efficiencies.

Antibacterial features of material surface: strong enough to serve as antibiotics?

Bacteria are small but need big efforts to control. The use of antibiotics not only produces superbugs that are increasingly difficult to inactivate, but also raises environmental concerns with the growing consumption. It is now believed that the antibacterial task can count on some physiochemical features of material surfaces, which can be anti-adhesive or bactericidal without releasing toxicants. It is necessary to evaluate to what extent can we rely on the surface design since the actual application scenarios will need the antibacterial performance to be sharp, robust, environmentally friendly, and long-lasting. Herein, we review the recent laboratory advances that have been classified based on the specific surface features, including hydrophobicity, charge potential, micromorphology, stiffness and viscosity, and photoactivity, and the antibacterial mechanisms of each feature are included to provide a basic rationale for future design. The significance of anti-biofilms is also introduced, given the big role of biofilms in bacteria-caused damage. A perspective on the potential wide application of antibacterial surface features as a substitute or supplement to antibiotics is then discussed. Surface design is no doubt a solution worthy to explore, and future success will be a result of further progress in multiple directions, including mechanism study and material preparation.

Slippery lubricant-infused silica nanoparticulate film processing for anti-biofouling applications

Microbial biofilm build-up in water distribution systems can pose a risk to human health and pipe material integrity. The impact is more devastating in space stations and to astronauts due to the isolation from necessary replacement parts and medical resources. As a result, there is a need for coatings to be implemented onto the inner region of the pipe to minimize the adherence and growth of biofilms. Lubricant-infused surfaces has been one such interesting material for anti-biofouling applications in which their slippery property promotes repellence to many liquids and thus prevents bacterial adherence. Textured and porous films are suitable substrate candidates to infuse and contain the lubricant. However, there is little investigation in utilizing a nanoparticulate thin film as the substrate material for lubricant infusion. A nanoparticulate film has high porosity within the structure which can promote greater lubricant infusion and retention. The implementation as a thin film structure aids to reduce material consumption and cost. In our study, we utilized a well-studied nanoporous thin film fabricated via layer-by-layer assembly of polycations and colloid silica and then calcination for greater stability. The film was further functionalized to promote fluorinated groups and improve affinity with a fluorinated lubricant. The pristine nanoporous film was characterized to determine its morphology, thickness, wettability, and porosity. The lubricant-infused film was then tested for its lubricant layer stability upon various washing conditions and its performance against bacterial biofilm adherence as a result of its slippery property. Overall, the modified silica nanoparticulate thin film demonstrated potential as a base substrate for lubricant-infused surface fabrication that repelled against ambient aqueous solvents and as an anti-biofouling coating that demonstrated low biofilm coverage and colony forming unit values. Further optimization to improve lubricant retention or incorporation of a secondary function can aid in developing better coatings for biofilm mitigation.

Bio-inspired hemocompatible surface modifications for biomedical applications

When blood first encounters the artificial surface of a medical device, a complex series of biochemical reactions is triggered, potentially resulting in clinical complications such as embolism/occlusion, inflammation, or device failure. Preventing thrombus formation on the surface of blood-contacting devices is crucial for maintaining device functionality and patient safety. As the number of patients reliant on blood-contacting devices continues to grow, minimizing the risk associated with these devices is vital towards lowering healthcare-associated morbidity and mortality. The current standard clinical practice primarily requires the systemic administration of anticoagulants such as heparin, which can result in serious complications such as post-operative bleeding and heparin-induced thrombocytopenia (HIT). Due to these complications, the administration of antithrombotic agents remains one of the leading causes of clinical drug-related deaths. To reduce the side effects spurred by systemic anticoagulation, researchers have been inspired by the hemocompatibility exhibited by natural phenomena, and thus have begun developing medical-grade surfaces which aim to exhibit total hemocompatibility via biomimicry. This review paper aims to address different bio-inspired surface modifications that increase hemocompatibility, discuss the limitations of each method, and explore the future direction for hemocompatible surface research.

Bioinspired liquid-infused surface for biomedical and biosensing applications

Nature always inspires us to develop advanced materials for diverse applications. The liquid-infused surface (LIS) inspired by Nepenthes pitcher plants has aroused broad interest in fabricating anti-biofouling materials over the past decade. The infused liquid layer on the solid substrate repels immiscible fluids and displays ultralow adhesion to various biomolecules. Due to these fascinating features, bioinspired LIS has been applied in biomedical-related fields. Here, we review the recent progress of LIS in bioengineering, medical devices, and biosensing, and highlight how the infused liquid layer affects the performance of medical materials. The prospects for the future trend of LIS are also presented.

Patterned Liquid-Infused Nanocoating Integrating a Sensitive Bacterial Sensing Ability to an Antibacterial Surface

The slippery liquid-infused surfaces show a great antibacterial property. However, most liquid-infused surfaces cannot detect whether or not the unknown aqueous samples contain microorganisms. Therefore, it is highly necessary but a challenge to integrate bacterial sensing capability into antibacterial surface. In this work, we prepared a slippery patterned liquid-infused nanocoating on the glass substrate for integrating bacterial sensing capability into the bacterial repellence surface. Dendritic mesoporous silica nanoparticles (DMSNs) with a suitable particle size of ca. 128 nm were employed as a building block to fabricate the multifunctional nanocoating with a superhydrophilic microwell and hydrophobic periphery by a dip-coating strategy, hydrophobic treatment, photomask-mediated plasma etching, and liquid infusion. Dendritic porous silica nanoparticles (DPSNs) with a larger particle size of ca. 260 nm were uniformly loaded with Au nanoparticles (NPs), providing large surface area for the modification of Raman reporter (4-mercaptobenzoic acid (4-MBA)) and aptamer. Thus, as a Raman tag, the formed DPSNs-Au-MBA-aptamer could achieve sensitive surface-enhanced Raman spectroscopy (SERS) detection of target bacteria. Combined with the Raman tag, the patterned liquid-infused nanocoating not only completely repelled bacteria on the hydrophobic area but also enabled sensitive SERS detection of Staphylococcus aureus in a very low sample volume (1 μL) with a low detection limit of 2.6 colony formation units (CFU)/mL on the antibody-modified superhydrophilic microwell. This research provided a novel and reliable strategy to construct a multifunctional nanocoating with microbial repellence and sensing capabilities.

Long-Term Reduction of Bacterial Adhesion on Polyurethane by an Ultra-Thin Surface Modifier

Indwelling urinary catheters are employed widely to relieve urinary retention in patients. A common side effect of the use of these catheters is the formation of urinary tract infections (UTIs), which can lead not only to severe medical complications, but even to death. A number of approaches have been used to attempt reduction in the rate of UTI development in catheterized patients, which include the application of antibiotics and modification of the device surface by coatings. Many of these coatings have not seen use on catheters in medical settings due to either the high cost of their implementation, their long-term stability, or their safety. In previous work, it has been established that the simple, stable, and easily applicable sterilization surface coating 2-(3-trichlorosilylpropyloxy)-ethyl hydroxide (MEG-OH) can be applied to polyurethane plastic, where it greatly reduces microbial fouling from a variety of species for a 1-day time period. In the present work, we establish that this coating is able to remain stable and provide a similarly large reduction in fouling against Escherichia coli and Staphylococcus aureus for time periods in an excess of 30 days. This non-specific coating functioned against both Gram-positive and Gram-negative bacteria, providing a log 1.1 to log 1.9 reduction, depending on the species and day. This stability and continued efficacy greatly suggest that MEG-OH may be capable of providing a solution to the UTI issue which occurs with urinary catheters.

Slippery Antifouling Polymer Coatings Fabricated Entirely from Biodegradable and Biocompatible Components

We report the design of slippery liquid-infused porous surfaces (SLIPS) fabricated from building blocks that are biodegradable, edible, or generally regarded to be biocompatible. Our approach involves infusion of lubricating oils, including food oils, into nanofiber-based mats fabricated by electrospinning or blow spinning of poly(ε-caprolactone), a hydrophobic biodegradable polymer used widely in medical implants and drug delivery devices. This approach leads to durable and biodegradable SLIPS that prevent fouling by liquids and other materials, including microbial pathogens, on objects of arbitrary shape, size, and topography. This degradable polymer approach also provides practical means to design "controlled-release" SLIPS that release molecular cargo at rates that can be manipulated by the properties of the infused oils (e.g., viscosity or chemical structure). Together, our results provide new designs and introduce useful properties and behaviors to antifouling SLIPS, address important issues related to biocompatibility and environmental persistence, and thus advance new potential applications, including the use of slippery materials for food packaging, industrial and marine coatings, and biomedical implants.

Slippery 3-dimensional porous bioabsorbable membranes with anti-adhesion and bactericidal properties as substitute for vaseline gauze

Vaseline gauze is a common type of wound dressing that consist of absorbent gauze impregnated with white petrolatum. It has excellent anti-adhesive property which can reduce trauma during dressing changes. However, this kind of wound dressing doesn't have bacterial killing property. Thus, a new kind of wound dressing that has anti-adhesive and bactericidal properties is needed urgently. Creating slippery liquid-impregnated porous surfaces (SLIPS) that insensitive to the structure of porous solid are generally viewed as a new anti-adhesion strategy. To expand the potential utility of SLIPS as substitute for vaseline gauze, dual-functional slippery membranes with anti-adhesion and bactericidal properties by using triclosan, vegetable oils and polylactic acid (PLA) were prepared. It's demonstrated that the triclosan-loaded/vegetable oils-infused PLA membranes (T/V-PM) has good cytocompatibility in vitro. Notably, the T/V-PM can gradually release biocide molecule into surrounding aqueous media. Moreover, the T/V-PM can kill planktonic bacterial cells without loss of their antifouling property. The in vivo study revealed that the T/V-PM can prevent the secondary injuries during wound dressing changes. This simple and low-cost strategy can be applied to inhibit blood and bacterial adhesion, and prevent tissue adhesion at the wound site. It's confirmed that the T/V-PM have great potential as substitute for vaseline gauze.

Bioactive Poly(4-hydroxybutyrate)/Poly(ethylene glycol) Fibrous Dressings Incorporated with Zinc Oxide Nanoparticles for Efficient Antibacterial Therapy and Rapid Clotting

Antibacterial and hemostatic. This article is protected by copyright. All rights reserved.

Slippery Liquid-Like Solid Surfaces with Promising Antibiofilm Performance under Both Static and Flow Conditions

Biofilms are central to some of the most urgent global challenges across diverse fields of application, from medicine to industries to the environment, and exert considerable economic and social impact. A fundamental assumption in anti-biofilms has been that the coating on a substrate surface is solid. The invention of slippery liquid-infused porous surfaces─a continuously wet lubricating coating retained on a solid surface by capillary forces─has led to this being challenged. However, in situations where flow occurs, shear stress may deplete the lubricant and affect the anti-biofilm performance. Here, we report on the use of slippery omniphobic covalently attached liquid (SOCAL) surfaces, which provide a surface coating with short (ca. 4 nm) non-cross-linked polydimethylsiloxane (PDMS) chains retaining liquid-surface properties, as an antibiofilm strategy stable under shear stress from flow. This surface reduced biofilm formation of the key biofilm-forming pathogens Staphylococcus epidermidis and Pseudomonas aeruginosa by three-four orders of magnitude compared to the widely used medical implant material PDMS after 7 days under static and dynamic culture conditions. Throughout the entire dynamic culture period of P. aeruginosa, SOCAL significantly outperformed a typical antibiofilm slippery surface [i.e., swollen PDMS in silicone oil (S-PDMS)]. We have revealed that significant oil loss occurred after 2-7 day flow for S-PDMS, which correlated to increased contact angle hysteresis (CAH), indicating a degradation of the slippery surface properties, and biofilm formation, while SOCAL has stable CAH and sustainable antibiofilm performance after 7 day flow. The significance of this correlation is to provide a useful easy-to-measure physical parameter as an indicator for long-term antibiofilm performance. This biofilm-resistant liquid-like solid surface offers a new antibiofilm strategy for applications in medical devices and other areas where biofilm development is problematic.

Slippery nanoemulsion-infused porous surfaces (SNIPS): anti-fouling coatings that can host and sustain the release of water-soluble agents

We report the design of 'slippery' nanoemulsion-infused porous surfaces (SNIPS). These materials are strongly anti-fouling to a broad range of substances, including microorganisms. Infusion with water-in-oil nanoemulsions also endows these slippery coatings with the ability to host and control or sustain the release of water-soluble agents, including polymers, peptides, and nucleic acids, opening the door to new applications of liquid-infused materials.

Programmable droplet manipulation and wetting with soft magnetic carpets

A set of magnetically responsive, soft hairs, which form a soft magnetic carpet, can be infused with a liquid to achieve switchable wetting. Applying a pattern of magnetic field results in a reconfigurable wetting pattern on the soft magnetic carpet. Combining this switchable wetting with a travelling magnetic field wave can allow us to spatially manipulate droplets. The efficiency of the droplet manipulation depends on the size and the contact angle of the droplet, which allows a pathway to sort and separate different droplets. Temporal and spatial control over multiple droplets allows us to conduct droplet reactions, which has a potential to be used for automated analytical testing and screening.

The ability to regulate interfacial and wetting properties is highly demanded in anti-icing, anti-biofouling, and medical and energy applications. Recent work on liquid-infused systems achieved switching wetting properties, which allow us to turn between slip and pin states. However, patterning the wetting of surfaces in a dynamic fashion still remains a challenge. In this work, we use programmable wetting to activate and propel droplets over large distances. We achieve this with liquid-infused soft magnetic carpets (SMCs) that consist of pillars that are responsive to external magnetic stimuli. Liquid-infused SMCs, which are sticky for a water droplet, become slippery upon application of a magnetic field. Application of a patterned magnetic field results in a patterned wetting on the SMC. A traveling magnetic field wave translates the patterned wetting on the substrate, which allows droplet manipulation. The droplet speed increases with an increased contact angle and with the droplet size, which offers a potential method to sort and separate droplets with respect to their contact angle or size. Furthermore, programmable control of the droplet allows us to conduct reactions by combining droplets loaded with reagents. Such an ability of conducting small-scale reactions on SMCs has the potential to be used for automated analytical testing, diagnostics, and screening, with a potential to reduce the chemical waste.

Reduction in Foreign Body Response and Improved Antimicrobial Efficacy via Silicone-Oil-Infused Nitric-Oxide-Releasing Medical-Grade Cannulas

Foreign body response and infection are two universal complications that occur with indwelling medical devices. In response, researchers have developed different antimicrobial and antifouling surface strategies to minimize bacterial colonization and fibrous encapsulation. In this study, the nitric oxide (NO) donor S-nitroso-N-acetylpenicillamine (SNAP) and silicone oil were impregnated into silicone rubber cannulas (SR-SNAP-Si) using a solvent swelling method to improve the antimicrobial properties and decrease the foreign body response. The fabricated SR-SNAP-Si cannulas demonstrated a stable, prolonged NO release, exhibited minimal SNAP leaching, and maintained sliding angles < 15° for 21 days. SR-SNAP-Si cannulas displayed enhanced antimicrobial efficacy against Staphylococcus aureus in a 7-day biofilm bioreactor study, reducing the viability of adhered bacteria by 99.2 ± 0.2% compared to unmodified cannulas while remaining noncytotoxic toward human fibroblast cells. Finally, SR-SNAP-Si cannulas were evaluated for the first time in a 14- and 21-day subcutaneous mouse model, showing significantly enhanced biocompatibility compared to control cannulas by reducing the thickness of fibrous encapsulation by 60.9 ± 6.1 and a 60.8 ± 10.5% reduction in cell density around the implant site after 3 weeks. Thus, this work demonstrates that antifouling, NO-releasing surfaces can improve the lifetime and safety of indwelling medical devices.

Liquid Crystal-Infused Porous Polymer Surfaces: A "Slippery" Soft Material Platform for the Naked-Eye Detection and Discrimination of Amphiphilic Species

We report the design and characterization of liquid crystal (LC)-infused porous polymer membranes that can detect and report on the presence of natural and synthetic amphiphiles in aqueous solution. We demonstrate that thermotropic LCs can be infused into nanoporous polymer membranes to yield LC-infused surfaces that exhibit slippery behaviors in contact with a range of aqueous fluids. In contrast to conventional liquid-infused surfaces (LIS) or slippery liquid-infused porous surfaces (SLIPS) prepared using isotropic oils, aqueous solutions slide over the surfaces of these LC-infused materials at speeds that depend strongly upon the composition of the fluid, including the presence, concentration, or structure of a dissolved surfactant. In general, the sliding times of aqueous droplets on these LC-infused surfaces increase significantly (e.g., from times on the order of seconds to times on the order of minutes) with increasing amphiphile concentration, allowing sliding times to be used to estimate the concentration of the amphiphile. Additional experiments revealed other intrinsic and extrinsic variables or parameters that can be used to further manipulate droplet sliding times and discriminate among amphiphiles of similar structure. Our results are consistent with a physical picture that involves reversible changes in the interfacial orientation of anisotropic LCs mediated by the interfacial adsorption of amphiphiles. These materials thus permit facile "naked-eye" detection and discrimination of amphiphiles in aqueous samples using equipment no more sophisticated than a stopwatch. We demonstrate the potential utility of these LC-infused surfaces for the unaided, naked-eye detection and monitoring of amphiphilic biotoxins in small droplets of fluid extracted directly from cultures of two common bacterial pathogens (Pseudomonas aeruginosa and Staphylococcus aureus). The ability to translate molecular interactions at aqueous/LC interfaces into large and readily observed changes in the sliding times of small aqueous droplets on surfaces could open the door to new applications for antifouling, liquid-infused materials in the context of environmental sensing and other fundamental and applied areas.

Antibiotic-Impregnated Liquid-Infused Coatings Suppress the Formation of Methicillin-Resistant Staphylococcus aureus Biofilms

Medical device-associated infections are an ongoing problem. Once an implant is infected, bacteria create a complex community on the surface known as a biofilm, protecting the bacterial cells against antibiotics and the immune system. To prevent biofilm formation, several coatings have been engineered to hinder bacterial adhesion or viability. In recent years, liquid-infused surfaces (LISs) have been shown to be effective in repelling bacteria due to the presence of a tethered liquid interface. However, local lubricant loss or temporary local displacement can lead to bacteria penetrating the lubrication layer, which can then attach to the surface, proliferate, and form a biofilm. Biofilm formation on biomedical devices can subsequently disrupt the chemistry tethering the slippery liquid interface, causing the LIS coating to fail completely. To address this concern, we developed a "fail-proof" multifunctional coating through the combination of a LIS with tethered antibiotics. The coatings were tested on a medical-grade stainless steel using contact angle, sliding angle, and Fourier transform infrared spectroscopy. The results confirm the presence of antibiotics while maintaining a stable and slippery liquid interface. The antibiotic liquid-infused surface significantly reduced biofilm formation (97% reduction compared to the control) and was tested against two strains of Staphylococcus aureus, including a methicillin-resistant strain. We also demonstrated that antibiotics remain active and reduce bacteria proliferation after subsequent coating modifications. This multifunctional approach can be applied to other biomaterials and provide not only a fail-safe but a fail-proof strategy for preventing bacteria-associated infections.

Facile deposition of biogenic silver nanoparticles on porous alumina discs, an efficient antimicrobial, antibiofilm, and antifouling strategy for functional contact surfaces

Surface modification is an emerging strategy for the design of contact materials. Fabricated alumina discs were functionalized by deposition of biogenic silver nanoparticles. The surfaces were characterized for physico-chemical, antibacterial and antibiofilm properties against microbial pathogens. The surface demonstrated improved hydrophobicity and a surface silver nanoparticle content of 6.4 w%. A reduction of more than 99.9% in CFU mL^-i was observed against the Gram-positive and Gram-negative bacteria tested, with >90% reduction of the fungal isolate. After 4 h, microbial adhesion was reduced by >99.9 and 90% for Escherichia coli and Staphylococcus aureus, respectively. Scanning electron micrographs further revealed a biofilm reduction. Cell viability tests indicated a bioincompatibility higher than 80% with Caco-2 and HaCaT cell lines after 48 h contact. The results suggest that deposition of biogenic silver nanoparticles on the surface of contact materials could be employed as a strategy to prevent biofilm formation.

Recent Innovations in Bacterial Infection Detection and Treatment

Bacterial infections are a major threat to human health, exacerbated by increasing antibiotic resistance. These infections can result in tremendous morbidity and mortality, emphasizing the need to identify and treat pathogenic bacteria quickly and effectively. Recent developments in detection methods have focused on electrochemical, optical, and mass-based biosensors. Advances in these systems include implementing multifunctional materials, microfluidic sampling, and portable data-processing to improve sensitivity, specificity, and ease of operation. Concurrently, advances in antibacterial treatment have largely focused on targeted and responsive delivery for both antibiotics and antibiotic alternatives. Antibiotic alternatives described here include repurposed drugs, antimicrobial peptides and polymers, nucleic acids, small molecules, living systems, and bacteriophages. Finally, closed-loop therapies are combining advances in the fields of both detection and treatment. This review provides a comprehensive summary of the current trends in detection and treatment systems for bacterial infections.

Polysiloxane Nanofilaments Infused with Silicone Oil Prevent Bacterial Adhesion and Suppress Thrombosis on Intranasal Splints

Like all biofluid-contacting medical devices, intranasal splints are highly prone to bacterial adhesion and clot formation. Despite their widespread use and the numerous complications associated with infected splints, limited success has been achieved in advancing their safety and surface biocompatibility, and, to date, no surface-coating strategy has been proposed to simultaneously enhance the antithrombogenicity and bacterial repellency of intranasal splints. Herein, we report an efficient, highly stable lubricant-infused coating for intranasal splints to render their surfaces antithrombogenic and repellent toward bacterial cells. Lubricant-infused intranasal splints were prepared by creating superhydrophobic polysiloxane nanofilament (PSnF) coatings using surface-initiated polymerization of n-propyltrichlorosilane (n-PTCS) and further infiltrating them with a silicone oil lubricant. Compared with commercially available intranasal splints, lubricant-infused, PSnF-coated splints significantly attenuated plasma and blood clot formation and prevented bacterial adhesion and biofilm formation for up to 7 days, the typical duration for which intranasal splints are kept. We further demonstrated that the performance of our engineered biointerface is independent of the underlying substrate and could be used to enhance the hemocompatibility and repellency properties of other medical implants such as medical-grade catheters.

Reduction of microbial adhesion on polyurethane by a sub-nanometer covalently-attached surface modifier

Indwelling urinary catheters are a common medical device used to relieve urinary retention. Many patients who undergo urinary catheterization develop urinary tract infections (UTIs), which can lead to severe medical complications and high cost of subsequent treatment. Recent years have seen a number of attempts at reducing the rate of UTIs in catheterized patients via catheter surface modifications. In this work, a low cost, robust anti-thrombogenic, and sterilizable anti-fouling layer based on a covalently-bound monoethylene glycol hydroxide (MEG-OH) was attached to polyurethane, a polymeric material commonly used to fabricate catheters. Modified polyurethane tubing was compared to bare tubing after exposure to a wide spectrum of pathogens including Gram-negative bacteria (Pesudomonas aeruginosa, Escherichia coli), Gram-positive bacteria (Staphylococcus aureus) and a fungus (Candida albicans). It has been demonstrated that the MEG-OH monolayer was able to significantly reduce the amount of adhesion of pathogens present on the material surface, with between 85 and 96 % reduction after 24 h of exposure. Additionally, similar reductions in surface fouling were observed following autoclave sterilization, long term storage of samples in air, and longer exposure up to 3 days.

Bioinspired surfaces with wettability: biomolecule adhesion behaviors

Surface wettability plays an important role in regulating biomolecule adhesion behaviors. The biomolecule adhesion behaviors of superwettable surfaces have become an important topic as an important part of the interactions between materials and organisms. In addition to general research on the moderate wettability of surfaces, the studies of biomolecule adhesion behaviors extend to extreme wettability ranges such as superhydrophobic, superhydrophilic and slippery surfaces and attract both fundamental and practical interest. In this review, we summarize the recent studies on biomolecule adhesion behaviors on superwettable surfaces, especially superhydrophobic, superhydrophilic and slippery surfaces. The first part will focus on the influence of extreme wettability on cell adhesion behaviors. The second part will concentrate on the adhesion behaviors of biomacromolecules on superwettable surfaces including proteins and nucleic acids. Finally, the influences of wettability on small molecule adhesion behaviors on material surfaces have also been investigated. The mechanism of superwettable surfaces and their influences on biomolecule adhesion behaviors have been studied and highlighted.

Single and multi-functional coating strategies for enhancing the biocompatibility and tissue integration of blood-contacting medical implants

Device-associated clot formation and poor tissue integration are ongoing problems with permanent and temporary implantable medical devices. These complications lead to increased rates of mortality and morbidity and impose a burden on healthcare systems. In this review, we outline the current approaches for developing single and multi-functional surface coating techniques that aim to circumvent the limitations associated with existing blood-contacting medical devices. We focus on surface coatings that possess dual hemocompatibility and biofunctionality features and discuss their advantages and shortcomings to providing a biocompatible and biodynamic interface between the medical implant and blood. Lastly, we outline the newly developed surface modification techniques that use lubricant-infused coatings and discuss their unique potential and limitations in mitigating medical device-associated complications.

Dynamic Self-Repairing Hybrid Liquid-in-Solid Protective Barrier for Cementitious Materials

Corrosion and surface fouling of structural materials, such as concrete, are persistent problems accelerating undesirable material degradation for many industries and infrastructures. To counteract these detrimental effects, protective coatings are frequently applied, but these solid-based coatings can degrade or become mechanically damaged over time. Such irreversible and irreparable damage on solid-based protective coatings expose underlying surfaces and bulk materials to adverse environmental stresses leading to subsequent fouling and degradation. We introduce a new concept of a hybrid liquid-in-solid protective barrier (LIB) to overcome the limitations of traditional protective coatings with broad applicability to structural materials. Through optimization of capillary forces and reduction of the interfacial energy between an upper mobile liquid and a lower immobile solid phase, a stable liquid-based protective layer is created. This provides a persistent self-repairing barrier against the infiltration of moisture and salt, in addition to omniphobic surface properties. As a model experimental test bed, we applied this concept to cementitious materials, which are commonly used as binders in concrete, and investigated how the mobile liquid phase embedded within a porous solid support contributes to the material's barrier protection and antifouling properties. Using industry standard test methods for acid resistance, chloride-ion penetrability, freeze-thaw cyclability, and mechanical durability, we demonstrate that LIBs exhibit significantly reduced water absorption and ion penetrability, improved repellency against various nonaqueous liquids, and resistance to corrosion while maintaining their required mechanical performance as structural materials.

Liquid Crystal Emulsions That Intercept and Report on Bacterial Quorum Sensing

We report aqueous emulsions of thermotropic liquid crystals (LCs) that can intercept and report on the presence of N-acyl-l-homoserine lactones (AHLs), a class of amphiphiles used by pathogenic bacteria to regulate quorum sensing (QS), monitor population densities, and initiate group activities, including biofilm formation and virulence factor production. The concentration of AHL required to promote "bipolar" to "radial" transitions in micrometer-scale droplets of the nematic LC 4'-pentyl-cyanobiphenyl (5CB) decreases with increasing carbon number in the acyl tail, reaching a threshold concentration of 7.1 μM for 3-oxo-C12-AHL, a native QS signal in the pathogen Pseudomonas aeruginosa. The LC droplets in these emulsions also respond to biologically relevant concentrations of the biosurfactant rhamnolipid, a virulence factor produced by communities of P. aeruginosa under the control of QS. Systematic studies using bacterial mutants support the conclusion that these emulsions respond selectively to the production of rhamnolipid and AHLs and not to other products produced by bacteria at lower (subquorate) population densities. Finally, these emulsions remain configurationally stable in growth media, enabling them to be deployed either in bacterial supernatants or in situ in bacterial cultures to eavesdrop on QS and report on changes in bacterial group behavior that can be detected in real time using polarized light. Our results provide new tools to detect and report on bacterial QS and virulence and a materials platform for the rapid and in situ monitoring of bacterial communication and resulting group behaviors in bacterial communities.

Antiadhesive Properties of Oil-Infused Gels against the Universal Adhesiveness of Polydopamine

Polydopamine (PDA) is well-known as the first material-independent adhesive, which firmly attaches to various substances, even hydrophobic materials, through strong coordinative interactions between the phenolic hydroxyl groups of PDA and the substances. In contrast, oil-infused materials such as self-lubricating gels (SLUGs) exhibit excellent antiadhesive properties against viscous liquids, ice/snow, (bio)fouling, and so on. In this study, we simply questioned: "What will happen when these two materials with contrary nature meet"? To answer this, we formed a PDA layer on a SLUG surface that exhibits thermoresponsive syneretic properties (release of liquid from the gel matrix to the outer surface) and investigated its interfacial behavior. The oil layer caused by syneresis from the SLUGs at -20 °C was found to show resistance to adhesion of universally adhesive PDA.

High Temperature Durability of Oleoplaned Slippery Copper Surfaces

Slippery surfaces, inspired by the functionality of trapping interfaces of specialized leaves of pitcher plants, have been widely used in self-cleaning, anti-icing, antifrost, and self-healing surfaces. They can be fabricated on metallic surfaces as well, presenting a more durable and low-maintenance anticorrosive surface on metals. However, the lack of studies on the durability of these slippery surfaces at high temperature prohibits their practical deployment in real industrial applications where thermal effects are critical and high temperature conditions are inevitable. We present here a unique fabrication technique of a copper-based oleoplaned slippery surface that has been tested for high temperature durability under repeated thermal cycles. Their slipperiness at high temperatures has also been tested in the absence of the Leidenfrost effect. Our findings suggest that these new substrates can be used for fabricating low maintenance surfaces for high temperature applications or even where the surface undergoes repeated thermal cycles like heat exchanger pipes, utensils, engine casings, and outdoor metallic structures.

Mucus-Inspired Supramolecular Adhesives with Oil-Regulated Molecular Configurations and Long-Lasting Antibacterial Properties

Inspired by mucus, which provides an ideal supramolecular model and whose fluid-like (viscous) and solid-like (elastic) behaviors can be adjusted to meet different physiological requirements, we report oil-regulated supramolecular adhesives by the co-assembly of polyurea oligomers and carvacrol oils. The adhesive is crosslinked by weak but abundant hydrogen bonds, which can be regulated by the incorporated carvacrol oils through the competition of intermolecular hydrogen bonds, presenting a unique set of mucus-mimicking features including oil-regulated mechanics, processability, reusable adhesivity, and extreme longevity in both air and water. Owing to the intrinsic bactericidal effect of the carvacrol oils, the developed adhesives can serve as potent antibacterial coatings with both rapid contact killing (99.9% killing within 15 min) and long-term controlled release abilities (up to 70 days), enabling versatile antibacterial applications in diverse conditions. We envision that these adhesives will be useful in buildings and architectures, community and public facilities, food storage and packaging technologies, functional textiles, and practical biomedical fields.

How Does Chemistry Influence Liquid Wettability on Liquid-Infused Porous Surface?

Design of Nepenthes pitcher-inspired slippery liquid-infused porous surface (SLIPS) appeared as an important avenue for various potential and practically relevant applications. In general, hydrophobic base layers were infused with selected liquid lubricants for developing chemically inert SLIPS. Here, in this current study, an inherently hydrophilic (soaked beaded water droplet with ∼20° within a couple of minutes), porous and thick (above 200 μm) polymeric coating, loaded with readily chemically reactive acrylate moieties yielded a chemically reactive SLIPS, where residual acrylate groups in the synthesized hydrophilic and porous interface rendered stability to the infused lubricants. The chemically reactive SLIPS is capable of reacting with the solution of primary amine-containing nucleophiles in organic solvent through 1,4-conjugate addition reaction, both in the presence (referred as "in situ" modification) and absence (denoted as pre-modification) of lubricated phase in the porous polymeric coating. Such amine reactive SLIPS was further extended to (1) examining the impact of different chemical modifications on the performance of SLIPS and (2) developing a spatially selective and "in situ" postmodification with primary amine-containing nucleophiles through 1,4-conjugate addition reaction. Moreover, the chemically reactive SLIPS was capable of sustaining various physical abrasions and prolonged (minimum 10 days) exposure to complex and harsh aqueous phases, where infused lubricants protect the residual acrylate groups from harsh aqueous exposures. Such, principle will be certainly useful for spatially selective covalent immobilization of water-insoluble functional molecules/polymers directly from organic solvents, which would be of potential interest for various applied and fundamental contexts.

Preparation of Polymeric Films of PVDMA-PEI Functionalized with Fatty Acids for Studying the Adherence and Proliferation of Langerhans β-Cells

This study reports the synthesis of thin polymeric films by the layer-by-layer deposition and covalent cross-linking of polyvinyl dimethylazlactone and polyethylene imine, which were functionalized with lauric (12-C), myristic (14-C), and palmitic (16-C) saturated fatty acids, whose high levels in the bloodstream are correlated with insulin resistance and the potential development of type 2 diabetes mellitus. Aiming to assess the effect of the fatty acids on the adhesion and proliferation of Langerhans β-cells, all prepared films (35 and 35.5 bilayers with and without functionalization with the fatty acids) were characterized in terms of their physical, chemical, and biological properties by a battery of experimental techniques including 1H and 13C NMR, mass spectrometry, attenuated total reflectance-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, atomic force microscopy, cell staining, and confocal laser scanning microscopy among others. In general, the developed films were found to be nanometric, transparent, resistant against manipulation, chemically reactive, and highly cytocompatible. On the other hand, in what the effect of the fatty acids is concerned, palmitic acid was found to impair the proliferation of the cultured β-cells, contrary to its homologues which did not alter this biological process. In our opinion, the multidisciplinary study presented here might be of interest for the research community working on the development of cytocompatible 2D model substrates for the safe and reproducible characterization of cell responses.

Life and death of liquid-infused surfaces: a review on the choice, analysis and fate of the infused liquid layer

We review the rational choice, the analysis, the depletion and the properties imparted by the liquid layer in liquid-infused surfaces – a new class of low-adhesion surface.

Bioinspired surfaces with wettability for antifouling application

Wettability is a special character found in nature, including the superhydrophobicity of lotus leaves, the underwater superoleophobicity of fish scales and the slipperiness of pitcher plants. These surfaces exhibit unique properties such as resistance to icing, corrosion, and the like. The antifouling properties of the material surface have important applications in a variety of areas, such as in hulls, in medical equipment, in water pipes and underwater equipment. However, the traditional anti-fouling surface is usually combined with toxic substances or its manufacturing process is complicated and expensive, which cannot meet the current antifouling demand. These wettable surfaces have always exhibited good anti-biofouling and self-cleaning properties, and their use as antifouling surfaces can well solve the problems of the above-mentioned traditional antifouling surfaces. Here, we divided the wettable surfaces into superhydrophobic surfaces, underwater superoleophobic surfaces and slippery surfaces, respectively, summarizing their development in the field of antifouling. Their research progress in antibacterial, antibiotic flocculation and antiplatelet adhesion is highlighted. Furthermore, we provide our own insights into the shortcomings and development prospects of wettable surface applications in the field of antifouling.

Role of trapped air and lubricant in the interactions between fouling and SiO2 nanoparticle surfaces

Both biomimetic superhydrophobic surfaces and biomimetic slippery liquid-infused porous surfaces (SLIPSs) have been developed as potential alternatives for solving the problem of biofouling. Herein, a facile method was used to construct superhydrophobic surfaces and liquid infused porous surfaces on stainless steels for antifouling applications. The nano-structures were formed by electrostatic attraction between polycations and negatively charged SiO₂ nanoparticles, providing a structural basis for superhydrophobic surfaces and liquid infused surfaces. Biofouling testing suggested excellent antifouling performances of the liquid infused porous surfaces by decreasing the adhesion of Chlorella pyrenoidosa by 93% and of Phaeodactylum tricornutum by 71%. The thermodynamic interpretation further indicated that the air layer captured by the superhydrophobic surfaces and the lubricant layer entrapped by the liquid infused porous surfaces played the dominant role in their antifouling performances. The inspiring results might show great potential for liquid infused porous surfaces in antifouling applications.

Liquid-Infused Surfaces: A Review of Theory, Design, and Applications

Due to inspiration from the Nepenthes pitcher plant, a frontier of devices has emerged with unmatched capabilities. Liquid-infused surfaces (LISs), particularly known for their liquid-repelling behavior under low tilting angles (<5°), have demonstrated a plethora of applications in medical, marine, energy, industrial, and environmental materials. This review presents recent developments of LIS technology and its prospective to define the future direction of this technology in solving tomorrow's real-life challenges. First, an introduction to the different models explaining the physical phenomena of these surfaces, their wettability, and viscous-dependent frictional forces is discussed. Then, an outline of different emerging strategies required to fabricate a stable liquid-infused interface is presented, including different substrates, lubricants, surface chemistries, and design parameters which can be tuned depending on the application. Furthermore, applications of LIS coatings in the areas of anticorrosion, antifouling, anti-icing, self-healing, droplet manipulation, and biomedical devices will be presented followed by the limitations and future direction of this technology.

Suppression of Biofouling on a Permeable Membrane for Dissolved Oxygen Sensing Using a Lubricant-Infused Coating

Specific ranges of dissolved oxygen (DO) concentrations must be maintained in a waterbody for it to be hospitable for aquatic animals. DO sensor designs can employ selectively permeable membranes to isolate DO from untargeted compounds or organisms in waterbodies. Hence, the DO concentration can be monitored and the health of the water can be evaluated over time. However, the presence of bacteria in natural waterbodies can lead to the formation of biofilms that can block pores and prevent analyte from permeating the membrane, resulting in inaccurate readings. In this work, we demonstrate the implementation of a fluorosilane-based omniphobic lubricant-infused (OLI) coating on a selectively permeable membrane and investigate the rate of biofilm formation for a commercially available DO sensor. Coated and unmodified membranes were incubated in an environment undergoing accelerated bacterial growth, and the change in sensitivity was evaluated after 40, 100, 250, and 500 h. Our findings show that the OLI membranes attenuate biofouling by 70% and maintain sensitivity after 3 weeks of incubation, further demonstrating that oxygen transfer through the OLI coating is achievable. Meanwhile, unmodified membranes exhibit significant biofouling that results in a 3.35 higher rate of decay in oxygen measurement sensitivity and an over 70% decrease in static contact angle. These results show that the OLI coating can be applied on commercially available membranes to prevent biofouling. Therefore, OLI coatings are a suitable candidate to suppress biofilm formation in the widespread use of selectively permeable membranes for environmental, medical, and fluid separation applications.

Development of Multimodal Antibacterial Surfaces Using Porous Amine-Reactive Films Incorporating Lubricant and Silver Nanoparticles

Anti-biofouling has been improved by passive or active ways. Passive antifouling strategies aim to prevent the initial adsorption of foulants, while active strategies aim to eliminate proliferative fouling by destruction of the chemical structure and inactivation of the cells. However, neither passive antifouling strategies nor active antifouling strategies can solely resist biofouling due to their inherent limitations. Herein, we successfully developed multimodal antibacterial surfaces for waterborne and airborne bacteria with the benefit of a combination of antiadhesion (passive) and bactericidal (active) properties of the surfaces. We elaborated multifunctionalizable porous amine-reactive (PAR) polymer films from poly(pentafluorophenyl acrylate) (PPFPA). Pentafluorophenyl ester groups in the PAR films facilitate creation of multiple functionalities through a simple postmodification under mild condition, based on their high reactivity toward various primary amines. We introduced amine-containing poly(dimethylsiloxane) (amine-PDMS) and dopamine into the PAR films, resulting in infusion of antifouling silicone oil lubricants and formation of bactericidal silver nanoparticles (AgNPs), respectively. As a result, the PAR film-based lubricant-infused AgNPs-incorporated surfaces demonstrate outstanding antibacterial effects toward both waterborne and airborne Escherichia coli, suggesting a new door for development of an effective multimodal anti-biofouling surface.

Nepenthes-inspired multifunctional nanoblades with mechanical bactericidal, self-cleaning and insect anti-adhesive characteristics

In order to reduce the widespread threat of bacterial pathogen diseases, mechanical bactericidal surfaces have been widely reported. However, few of these nanostructured surfaces were investigated from a sustainable perspective. In this study, we have prepared, inspired by the slippery zone of Nepenthes, a multifunctional nanostructured surface with mechanical bactericidal, self-cleaning and insect anti-adhesive characteristics. First, a nanoblade-like surface made of Zn–Al layered double hydroxides was prepared for achieving faster bactericidal rate and wider bactericidal spectrum (2.10 × 10⁴ CFU cm⁻² min⁻¹ against Escherichia coli and 1.78 × 10³ CFU cm⁻² min⁻¹ against Staphylococcus aureus). Then the self-cleaning and insect anti-adhesive properties were tested on the fluorosilane-modified nanoblades, leaving little cell debris remaining on the surface even after 4 continuous bactericidal experiments, and showing a slippery surface for ants to slide down in 3 s. This study not only discovers a new nature-inspired mechanical bactericidal nanotopography, but also provides a facile approach to incorporate multiple functions into the nanostructured surface for practical antibacterial applications.

Inspired by the slippery zone of Nepenthes, we fabricated a multifunctional blade like nanostructured surface with the same mechanical bactericidal, self-cleaning and insect anti-adhesive characteristics.