Copper-based water repellent and antibacterial coatings by aerosol assisted chemical vapour deposition

Bioinspired superhydrophobic surfaces with silver and nitric oxide-releasing capabilities to prevent device-associated infections and thrombosis

Bacteria-associated infections and thrombus formation are the two major complications plaguing the application of blood-contacting medical devices. Therefore, functionalized surfaces and drug delivery for passive and active antifouling strategies have been employed. Herein, we report the novel integration of bio-inspired superhydrophobicity with nitric oxide release to obtain a functional polymeric material with anti-thrombogenic and antimicrobial characteristics. The nitric oxide release acts as an antimicrobial agent and platelet inhibitor, while the superhydrophobic components prevent non-specific biofouling. Widely used medical-grade silicone rubber (SR) substrates that are known to be susceptible to biofilm and thrombus formation were dip-coated with fluorinated silicon dioxide (SiO2) and silver (Ag) nanoparticles (NPs) using an adhesive polymer as a binder. Thereafter, the resulting superhydrophobic (SH) SR substrates were impregnated with S-nitroso-N-acetylpenicillamine (SNAP, an NO donor) to obtain a superhydrophobic, Ag-bound, NO-releasing (SH-SiAgNO) surface. The SH-SiAgNO surfaces had the lowest amount of viable adhered E. coli (> 99.9 % reduction), S. aureus (> 99.8 % reduction), and platelets (> 96.1 % reduction) as compared to controls while demonstrating no cytotoxic effects on fibroblast cells. Thus, this innovative approach is the first to combine SNAP with an antifouling SH polymer surface that possesses the immense potential to minimize medical device-associated complications without using conventional systemic anticoagulation and antibiotic treatments.

Recent Advances in Dual-Function Superhydrophobic Antibacterial Surfaces

Bacterial adhesion and subsequent biofilm formation on the surfaces of synthetic materials imposes a significant burden in various fields, which can lead to infections in patients or reduce the service life of industrial devices. Therefore, there is increasing interest in imbuing surfaces with antibacterial properties. Bioinspired superhydrophobic surfaces with high water contact angles (>150°) exhibit excellent surface repellency against contaminations, thereby preventing initial bacterial adhesion and inhibiting biofilm formation. However, conventional superhydrophobic surfaces typically lack long-term durability and are incapable of achieving persistent efficacy against bacterial adhesion. To overcome these limitations, in recent decades, dual-function superhydrophobic antibacterial surfaces with both bacteria-repelling and bacteria-killing properties have been developed by introducing bactericidal components. These surfaces have demonstrated improved long-term antibacterial performance in addressing the issues associated with surface-attached bacteria. This review summarizes the recent advancements of these dual-function superhydrophobic antibacterial surfaces. First, a brief overview of the fabrication strategies and bacteria-repelling mechanism of superhydrophobic surfaces is provided and then the dual-function superhydrophobic antibacterial surfaces are classified into three types based on the bacteria-killing mechanism: i) mechanotherapy, ii) chemotherapy, and iii) phototherapy. Finally, the limitations and challenges of current research are discussed and future perspectives in this promising area are proposed.

Superhydrophobic and Conductive Foams with Antifouling and Oil-Water Separation Properties

Hybrid organic-inorganic materials are attracting enormous interest in materials science due to the combination of multiple advantageous properties of both organic and inorganic components. Taking advantage of a simple, scalable, solvent-free hard-sacrificial method, we report the successful fabrication of three-dimensional hybrid porous foams by integrating two types of fillers into a poly(dimethylsiloxane) (PDMS) framework. These fillers consist of hydrophobic electrically conductive graphene (GR) nanoplatelets and hydrophobic bactericidal copper (Cu) microparticles. The fillers were utilized to create the hierarchical rough structure with low-surface-energy properties on the PDMS foam surfaces, leading to remarkable superhydrophobicity/superoleophilicity with contact angles of 158 and 0° for water and oil, respectively. The three-dimensional interconnected porous foam structures facilitated high oil adsorption capacity and excellent reusability as well as highly efficient oil/organic solvent-water separation in turbulent, corrosive, and saline environments. Moreover, the introduction of the fillers led to a significant improvement in the electrical conductivity and biofouling resistance (vs whole blood, fibrinogen, platelet cells, and Escherichia coli) of the foams. We envision that the developed composite strategy will pave a facile, scalable, and effective way for fabricating novel multifunctional hybrid materials with ideal properties that may find potential use in a broad range of biomedical, energy, and environmental applications.

The mechanism of metal-based antibacterial materials and the progress of food packaging applications: A review

Food packages have been detected carrying novel coronavirus in multi-locations since the outbreak of COVID-19, causing major concern in the field of food safety. Metal-based supported materials are widely used for sterilization due to their excellent antibacterial properties as well as low biological resistance. As the principal part of antibacterial materials, the active component, commonly referred to Ag, Cu, Zn, etc., plays the main role in inhibiting and killing pathogenic microorganisms by destroying the structure of cells. As another composition of metal-based antibacterial materials, the carrier could support and disperse the active component, which on one hand, could effectively decrease the usage amount of active component, on the other hand, could be processed into various forms to broaden the application range of antibacterial materials. Different from other metal-based antibacterial reviews, in order to highlight the detailed function of various carriers, we divided the carriers into biocompatible and adsorptable types and discussed their different antibacterial effects. Moreover, a novel substitution antibacterial mechanism was proposed. The coating and shaping techniques of metal-based antibacterial materials as well as their applications in food storage at ambient and low temperatures are also comprehensively summarized. This review aims to provide a theoretical basis and reference for researchers in this field to develop new metal-based antibacterial materials.

Highly Water-Repellent and Anti-Reflective Glass Based on a Hierarchical Nanoporous Layer

Optically anti-reflective and water-repellent glass is required for solar cell covers to improve power-generation efficiency due to transparency improvement and dirt removal. Research has been conducted in recent years on technologies that do not use fluorine materials. In this study, we focused on the anti-reflective properties and microstructure of hierarchical nanoporous layer (HNL) glass and used it as a substrate. As a result, we have achieved both strong anti-reflectivity and high water repellency on HNL glass by coating polydimethylsiloxane (PDMS) using baking and thermal chemical vapor deposition (CVD). The surfaces showed a significantly higher sliding velocity of water droplets than the PDMS-treated material on the flat glass plate. They also showed such water repellency that the droplets bounced off the surface.

Investigating the viability of sulfur polymers for the fabrication of photoactive, antimicrobial, water repellent coatings

Elemental sulfur (S₈), a by-product of the petroleum refining industries, possesses many favourable properties including photocatalytic activity and antibacterial activity, in addition to being intrinsically hydrophobic. Despite this, there is a relative lack of research employing elemental sulfur and/or sulfur copolymers within superhydrophobic materials design. In this work, we present the use of sulfur copolymers to produce superhydrophobic materials with advanced functionalities. Using inverse vulcanization and the use of a natural organic crosslinker, perillyl alcohol (PER), stable S₈-PER copolymers were synthesised and later combined with silica (SiO₂) nanoparticles, to achieve highly water repellent composites that displayed both antimicrobial and photocatalytic properties, in the absence of carcinogenic and/or expensive materials. Here, we investigated the antibacterial performance of coatings against the Staphylococcus aureus bacterial strain, where coatings displayed great promise for use in antifouling applications, as they were found to limit surface adhesion by more than 99%, when compared to uncoated glass samples. Furthermore, UV dye degradation tests were performed, utilizing the commercially available dye resazurin, and it was shown that coatings had the potential to simultaneously exhibit surface hydrophobicity and photoactivity, demonstrating a great advancement in the field of superhydrophobic materials.

Bioinspired ultra-low fouling coatings on medical devices to prevent device-associated infections and thrombosis

Addressing thrombosis and biofouling of indwelling medical devices within healthcare institutions is an ongoing problem. In this work, two types of ultra-low fouling surfaces (i.e., superhydrophobic and lubricant-infused slippery surfaces) were fabricated to enhance the biocompatibility of commercial medical grade silicone rubber (SR) tubes that are widely used in clinical care. The superhydrophobic (SH) coatings on the tubing substrates were successfully created by dip-coating in superhydrophobic paints consisting of polydimethylsiloxane (PDMS), perfluorosilane-coated hydrophobic zinc oxide (ZnO) and copper (Cu) nanoparticles (NPs) in tetrahydrofuran (THF). The SH surfaces were converted to lubricant-infused slippery (LIS) surfaces through the infusion of silicone oil. The anti-biofouling properties of the coatings were investigated by adsorption of platelets, whole blood coagulation, and biofilm formation in vitro. The results revealed that the LIS tubes possess superior resistance to clot formation and platelet adhesion than uncoated and SH tubes. In addition, bacterial adhesion was investigated over 7 days in a drip-flow bioreactor, where the SH-ZnO-Cu tube and its slippery counterpart significantly reduced bacterial adhesion and biofilm formation of Escherichia coli relative to control tubes (>5 log10 and >3 log10 reduction, respectively). The coatings also demonstrated good compatibility with fibroblast cells. Therefore, the proposed coatings may find potential applications in high-efficiency on-demand prevention of biofilm and thrombosis formation on medical devices to improve their biocompatibility and reduce the risk of complications from medical devices.

A Novel Strategy for Creating an Antibacterial Surface Using a Highly Efficient Electrospray-Based Method for Silica Deposition

Adhesion of bacteria on biomedical implant surfaces is a prerequisite for biofilm formation, which may increase the chances of infection and chronic inflammation. In this study, we employed a novel electrospray-based technique to develop an antibacterial surface by efficiently depositing silica homogeneously onto polyethylene terephthalate (PET) film to achieve hydrophobic and anti-adhesive properties. We evaluated its potential application in inhibiting bacterial adhesion using both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) bacteria. These silica-deposited PET surfaces could provide hydrophobic surfaces with a water contact angle greater than 120° as well as increased surface roughness (root mean square roughness value of 82.50 ± 16.22 nm and average roughness value of 65.15 ± 15.26 nm) that could significantly reduce bacterial adhesion by approximately 66.30% and 64.09% for E. coli and S. aureus, respectively, compared with those on plain PET surfaces. Furthermore, we observed that silica-deposited PET surfaces showed no detrimental effects on cell viability in human dermal fibroblasts, as confirmed by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide and live/dead assays. Taken together, such approaches that are easy to synthesize, cost effective, and efficient, and could provide innovative strategies for preventing bacterial adhesion on biomedical implant surfaces in the clinical setting.

Fluorinated Carbon Nanotube Superamphiphobic Coating for High-Efficiency and Long-Lasting Underwater Antibiofouling Surfaces

Biofilm formation on the surface of materials has brought great troubles to various industries. Designing surfaces with long-lasting antibiofouling properties can help restrain primary bacterial and protein attachment and subsequent biofilm formation for a long time, which is also of great significance for industrial applications. In this work, we successfully prepared fluorinated carbon nanotubes through a one-step fluorination method using fluorosilane and fabricated a superamphiphobic coating using a simple spray method. This coating with ultralow surface free energy and stable micro/nano structures achieved highly efficient and long-term underwater antibiofouling properties. Tea, milk, BSA, and bacterial solution can bounce highly on this surface without wetting the surface in air. The long-term existence of the underwater air-bubble layer on the surface of the superamphiphobic coating was observed. Thus, this surface can effectively resist BSA and bacterial attachment (E. coli), and the efficiency, respectively, reaches 97.5 and 98.2%. Even if it is fully soaked in BSA and BS solution for 120 h, the whole surface is still able to repel water, BSA, and BS solution very well. In addition, the coating possessed excellent wear resistance, the CAs of BSA and BS solution just decreased slightly (higher than 158°), and the sliding angles increased slightly (lower than 4°) after 50 tape abrasion cycles. Therefore, this superamphiphobic coating may have promising applications for marine devices, biomedical materials, protective clothing, and chemical shielding.

The challenges, achievements and applications of submersible superhydrophobic materials

Superhydrophobic materials have been widely reported throughout the scientific literature. Their properties originate from a highly rough morphology and inherently water repellent surface chemistry. Despite promising an array of functionalities, these materials have seen limited commercial development. This could be attributed to many factors, like material compatibility, low physical resilience, scaling-up complications, etc. In applications where persistent water contact is required, another limitation arises as a major concern, which is the stability of the air layer trapped at the surface when submerged or impacted by water. This review is aimed at examining the diverse array of research focused on monitoring/improving air layer stability, and highlighting the most successful approaches. The reported complexity of monitoring and enhancing air layer stability, in conjunction with the variety of approaches adopted, results in an assortment of suggested routes to achieving success. The review is addressing the challenge of finding a balance between maximising water repulsion and incorporating structures that protect air pockets from removal, along with challenges related to the variant approaches to testing air-layer stability across the research field, and the gap between the achieved progress and the required performance in real-life applications.

Superhydrophobic Nanocoatings as Intervention against Biofilm-Associated Bacterial Infections

Biofilm formation represents a significant cause of concern as it has been associated with increased morbidity and mortality, thereby imposing a huge burden on public healthcare system throughout the world. As biofilms are usually resistant to various conventional antimicrobial interventions, they may result in severe and persistent infections, which necessitates the development of novel therapeutic strategies to combat biofilm-based infections. Physicochemical modification of the biomaterials utilized in medical devices to mitigate initial microbial attachment has been proposed as a promising strategy in combating polymicrobial infections, as the adhesion of microorganisms is typically the first step for the formation of biofilms. For instance, superhydrophobic surfaces have been shown to possess substantial anti-biofilm properties attributed to the presence of nanostructures. In this article, we provide an insight into the mechanisms underlying biofilm formation and their composition, as well as the applications of nanomaterials as superhydrophobic nanocoatings for the development of novel anti-biofilm therapies.

Novel Copper Nanoparticles Intercalated Polyurethane Heparin/Poly-L-Lysine Chelates Coated Stents: Viability Study for Coronary Vascular Cells and Aneurysms Treatments

Continuous delayed endothelium regeneration and continues thrombosis development designate a task for coronary artery stent rehabilitation. To progress the direct vascular cell behavior, aneurysms treatments and compatibility of cardiovascular implants novel copper intercalated polyurethane heparin/poly-L-lysine chelates treated stent has established in this report. The functional group modifications, structural characteristics, and stability of the chelates have investigated for polyurethane heparin: poly-L-lysine, copper intercalated polyurethane heparin/poly-L-lysine coated stents. The FTIR results showed the copper intercalation at 446 cmr and the Cu 2s peak at 932 eV from XPS also indicated that the successful coating of copper, polyurethane heparin, poly-L-lysine. The relative surface geomorphology of the chelates displayed the uniform Cu coating consisting of multilayer poly-L-lysine on the substrate. The stability and biocompatibility studies indicated the significantly enhanced performance with clot the APTT and TT periods as clotting and cell proliferation assessments. This type of composite proposes a stage on a stent external area for discerning track of vascular cell performance and aneurysms treatments with low side effects.

Review of silicone surface modification techniques and coatings for antibacterial/antimicrobial applications to improve breast implant surfaces

Silicone implants are widely used in the medical field for plastic or reconstructive surgeries for the purpose of soft tissue issues. However, as with any implanted object, healthcare-associated infections are not completely avoidable. The material suffers from a lack of biocompatibility and is often subject to bacterial/microbial infections characterized by biofilm growth. Numerous strategies have been developed to either prevent, reduce, or fight bacterial adhesion by providing an antibacterial property. The present review summarizes the diverse approaches to deal with bacterial infections on silicone surfaces along with the different methods to activate/oxidize the surface before any surface modifications. It includes antibacterial coatings with antibiotics or nanoparticles, covalent attachment of active bacterial molecules like peptides or polymers. Regarding silicone surfaces, the activation step is essential to render the surface reactive for any further modifications using energy sources (plasma, UV, ozone) or chemicals (acid solutions, sol-gel strategies, chemical vapor deposition). Meanwhile, corresponding work on breast silicone prosthesis is discussed. The latter is currently in the line of sight for causing severe capsular contractures. Specifically, to that end, besides chemical modifications, the antibacterial effect can also be achieved by physical surface modifications by adjusting the surface roughness and topography for instance.

Fabrication of Bacteria- and Blood-Repellent Superhydrophobic Polyurethane Sponge Materials

Biofilm and thrombus formation on surfaces results in significant morbidity and mortality worldwide, which highlights the importance of the development of efficacious fouling-prevention approaches. In this work, novel highly robust and superhydrophobic coatings with outstanding multiliquid repellency, bactericidal performance, and extremely low bacterial and blood adhesion are fabricated by a simple two-step dip-coating method. The coatings are prepared combining 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS-17)-coated hydrophobic zinc oxide and copper nanoparticles to construct hierarchical micro/nanostructures on commercial polyurethane (PU) sponges followed by polydimethylsiloxane (PDMS) treatment that is used to improve the binding degree between the nanoparticles and the sponge surface. The micro/nanotextured samples can repel various liquids including water, milk, coffee, juice, and blood. Relative to the original PU, the superhydrophobic characteristics of the fabricated sponge cause a significant reduction in the adhesion of bacteria (Staphylococcus aureus) by up to 99.9% over a 4-day period in a continuous drip-flow bioreactor. The sponge is also highly resistant to the adhesion of fibrinogen and activated platelets with ∼76 and 64% reduction, respectively, hence reducing the risk of blood coagulation and thrombus formation. More importantly, the sponge can sustain its superhydrophobicity even after being subjected to different types of harsh mechanical damage such as finger-wiping, knife-scratching, tape-peeling, hand-kneading, hand-rubbing, bending, compress-release (1000 cycles) tests, and 1000 cm sandpaper abrasion under 250 g of loading. Hence, this novel hybrid surface with robustness and the ability to resist blood adhesion and bacterial contamination makes it an attractive candidate for use in diverse application areas.

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.

Effectiveness of Copper-Impregnated Solid Surfaces on Lowering Microbial Bio-Burden Levels in an Acute Care Hospital

Background

Microbial bio-burden on high-touch surfaces in patient rooms may lead to acquisition of health care-associated infections in acute care hospitals. This study examined the effect of a novel copper-impregnated solid material (16%-20% copper oxide in a polymer-based resin) on bacterial contamination on high-touch surfaces in patient rooms in an acute care hospital.

Methods

Five high-touch surfaces were sampled for aerobic bacterial colonies (ABCs) 3 times per day over a 3-day period in 16 rooms with copper installed and 16 rooms with standard noncopper laminate installed on high-touch surfaces. A Bayesian multilevel negative binomial regression model was used to compare ABC plate counts from copper-impregnated surfaces with standard hospital laminate surfaces.

Results

The mean and median (interquartile range [IQR]) ABC counts from copper-impregnated surfaces were 25.5 and 11 (4-27), and for standard hospital laminate surfaces they were 60.5 and 29 (10-74.3). The negative binomial regression model-estimated incidence rate for ABC counts on plates taken from copper-impregnated surfaces was 0.40 (0.21-0.70) times the incidence rate of ABC counts on plates taken from standard hospital laminate surfaces.

Conclusions

Copper-impregnated solid surfaces may reduce the level of microbial contamination on high-touch surfaces in patient rooms in the acute care environment, as our study demonstrated a decline in microbial bio-burden on samples taken from copper-impregnated compared with standard hospital laminate high-touch surfaces.

Silver-Polymethylhydrosiloxane Nanocomposite Coating on Anodized Aluminum with Superhydrophobic and Antibacterial Properties

Biofilm formation on both animate and inanimate surfaces serves as an ideal bacterial reservoir for the spread of nosocomial infections. Designing surfaces with both superhydrophobic and antibacterial properties can help reduce initial bacterial attachment and subsequent biofilm formation. In the present study, a two-step approach is deployed to fabricate silver-polymethylhydrosiloxane (Ag-PMHS) nanocomposites, followed by a simple dip-coating deposition on anodized Al. Ag-nanoparticles (Ag-NPs) are synthesized in situ within a PMHS polymeric matrix. Morphological features of Ag-PMHS coating observed by scanning electron microscopy shows heterogeneous micro-nano-structures. The chemical compositions of these coatings were characterized using X-ray diffraction and attenuated total reflection-Fourier transform infrared spectroscopy, which indicate the presence of a low-energy PMHS polymer. The as-synthesized Ag-PMHS nanocomposite demonstrated excellent antibacterial properties against clinically relevant planktonic bacteria with zone of inhibition values of 25.3 ± 0.5, 24.8 ± 0.5, and 23.3 ± 3.6 mm for Pseudomonas aeruginosa (P.A) (Gram -ve), Escherichia coli (E. coli) (Gram -ve), and Staphylococcus aureus (S.A) (Gram +ve), respectively. The Ag-PMHS nanocomposite coating on anodized Al provides an anti-biofouling property with an adhesion reduction of 99.0, 99.5, and 99.3% for Pseudomomas aeruginosa (P.A), E. coli, and S. aureus (S.A), respectively. Interestingly, the coating maintained a stable contact angle of 158° after 90 days of immersion in saline water (3.5 wt % NaCl, pH 7.4). The Ag-PMHS nanocomposite coating on anodized Al described herein demonstrates excellent antibacterial and anti-biofouling properties owing to its inherent superhydrophobic property.

Role of Trapped Air in the Attachment of Staphylococcus aureus on Superhydrophobic Silicone Elastomer Surfaces Textured by a Femtosecond Laser

Surface texturing is an easy way to control wettability as well as bacterial adhesion. Air trapped in the surface texture of an immersed sample was often proposed as the origin of the low adhesion of bacteria to surfaces showing superhydrophobic properties. In this work, we identified two sets of femtosecond laser processing parameters that led to extreme superhydrophobic textures on a silicone elastomer but showed opposite behavior against Staphylococcus aureus (S. aureus, ATCC 25923) over a short incubation times (6 h). The main difference from most of the previous studies was that the air trapping was not evaluated from the extrapolation of the results of the classical sessile drop technique but from the drop rebound and Wilhelmy plate method. Additionally, all wetting tests were performed with bacteria culture medium and at 37 °C in the case of the Wilhelmy plate method. Following this approach, we were able to study the formation of the liquid/silicone interface and the associated air trapping for immersed samples that is, by far, most representative of the cell culture conditions than those associated with the sessile drop technique. Finally, the conversion of these superhydrophobic coatings into superhydrophilic ones revealed that air trapping is not a necessary condition to avoid Staphylococcus aureus retention on one of these two textured surfaces at short incubation times.

Vapor-Deposited Biointerfaces and Bacteria: An Evolving Conversation

At the biointerface where materials and microorganisms meet, the organic and synthetic worlds merge into a new science that directs the design and safe use of synthetic materials for biological applications. Vapor deposition techniques provide an effective way to control the material properties of these biointerfaces with molecular-level precision that is important for biomaterials to interface with bacteria. In recent years, biointerface research that focuses on bacteria-surface interactions has been primarily driven by the goals of killing bacteria (antimicrobial) and fouling prevention (antifouling). Nevertheless, vapor deposition techniques have the potential to create biointerfaces with features that can manipulate and dictate the behavior of bacteria rather than killing or deterring them. In this review, we focus on recent advances in antimicrobial and antifouling biointerfaces produced through vapor deposition and provide an outlook on opportunities to capitalize on the features of these techniques to find unexplored connections between surface features and microbial behavior.

Optimization of Antibacterial Properties of “Hybrid” Metal-Sputtered Superhydrophobic Surfaces

Bacterial attachment and colonization to hygiene sensitive surfaces, both public and nosocomial, as well as in food industry areas, poses a serious problem to human healthcare. Several infection incidents are reported, while bacterial resistance to antibiotics is increasing. Recently, novel techniques for the design of antibacterial surfaces to limit bacterial spreading have emerged, including bifunctional antibacterial surfaces with antifouling and bactericidal action. In this context, we have recently developed smart, universal, metal-sputtered superhydrophobic surfaces, demonstrating both bacterial repulsion and killing efficacy. Herein, we present the optimization process that led to the realization of these “hybrid” antibacterial surfaces. To this end, two bactericidal agents, silver and copper, were tested for their efficiency against Gram-negative bacteria, with copper showing a stronger bactericidal action. In addition, between two low surface energy coatings, the fluorinated-alkyl self-assembled chlorosilane layer from perfluorinated octyltrichlorosilane (pFOTS) solution and the fluorocarbon layer from octafluorocyclobutane (C4F8) plasma were both approved for their anti-adhesive properties after immersion in bacterial solution. However, the latter was found to be more efficient when engrafted with the bactericidal agent in shielding its killing performance. Furthermore, the thickness of the plasma-deposited fluorocarbon layer was optimized, in order to simultaneously retain both the superhydrophobicity of the surface and its long-term bactericidal activity.

Bactericidal Activity of Superhydrophobic and Superhydrophilic Copper in Bacterial Dispersions

A method based on nanosecond laser processing was used to design superhydrophilic and superhydrophobic copper substrates. Three different protocols were used to analyze the evolution of the bactericidal activity of the copper substrates with different wettability. Scanning electron microscopy was used to study the variation of cell morphology after the attachment to superhydrophilic and superhydrophobic surfaces. The dispersions of Escherichia coli K12 C600 and Klebsiella pneumoniae 811 in Luria Bertani broth in contact with the superhydrophilic copper surface showed enhanced bacterial inactivation, associated with toxic action of both hierarchically textured copper surface and high content of Cu²⁺ ions in the dispersion medium. In contrast, the bacterial dispersions in contact with the superhydrophobic copper substrates demonstrated an increase in cell concentration with time until the development of corrosion processes. The resistance of bacterial cells to contact the copper substrates is discussed on the basis of surface forces, determining the primary adhesion and of the protective action of a superhydrophobic state of the surface against electrochemical and biological corrosion.

A rugged, self-sterilizing antimicrobial copper coating on ultra-high molecular weight polyethylene: a preliminary study on the feasibility of an antimicrobial prosthetic joint material

We report here for the first time how a copper coating bond to ultra-high molecular weight polyethylene (UHMWPE) via low temperature aerosol assisted chemical vapour deposition.

Radical Cation Initiated Surface Polymerization on Photothermal Rubber for Smart Antifouling Coatings

Biofouling on surfaces of various materials has attracted considerable attention in biomedical and marine industries. Surface grafting based on covalent surface-initiated polymerization offers a popular route to address this problem by providing diverse robust polymer coatings capable of preventing the biofouling in complex environments. However, the existing methods for synthesizing polymer coatings are complicated and rigorous, or require special catalysts, greatly limiting their practical applications. In this work, a radical-cation-based surface-initiated polymerization protocol to graft the surface of darkened trans-polyisoprene (TPI) rubber with a thermo-responsive smart polymer, poly(N-isopropylacrylamide) (PNIPAM), through a simple iodine doping process is reported. A series of characterizations were performed to provide adequate evidence to confirm the successful grafting. Combining the thermal sensitivity of PNIPAM with the photothermal conversion ability of the darkened rubber, efficient bacteria-killing and antifouling capabilities were successfully achieved as a result of temperature-controlled iodine release and switchable amphiphilicity of PNIPAM.

CuO Nanoparticles-Containing Highly Transparent and Superhydrophobic Coatings with Extremely Low Bacterial Adhesion and Excellent Bactericidal Property

Human health and industrial instruments have been suffering from bacterial colonization on the surface of materials for a long time. Recently, antibacterial coatings are regarded as the new strategy to resist bacterial pathogens. In this work, novel highly transparent and superhydrophobic coatings with extremely low bacterial adhesion and bactericidal performance were prepared by spray-coating hydrophobic silica sol and CuO nanoparticles. The coated glass showed high transmittance in 300-2500 nm with a maximum value of 96.6%. Compared with bare glass, its superhydrophobic characteristics resulted in a reduction in adhesion of bacteria ( Escherichia coli, E. coli) by up to 3.2 log cells/cm². Additionally, the live/dead staining test indicated that the as-prepared coating exhibited excellent bactericidal performance against E. coli. Moreover, the as-prepared coating could maintain their superhydrophobicity after the sand impact test. The proposed method to fabricate such coatings could be applied on various substrates. Therefore, this novel hybrid surface with the abilities to reduce bacterial adhesion and kill attached bacteria make it a promising candidate for biosensors, microfluidics, bio-optical devices, household facilities, lab-on-chips, and touchscreen devices.

The Anti-Biofouling Properties of Superhydrophobic Surfaces are Short-Lived

Superhydrophobic surfaces are present in nature on the leaves of many plant species. Water rolls on these surfaces, and the rolling motion picks up particles including bacteria and viruses. Man-made superhydrophobic surfaces have been made in an effort to reduce biofouling. We show here that the anti-biofouling property of a superhydrophobic surface is due to an entrapped air-bubble layer that reduces contact between the bacteria and the surface. Further, we showed that prolonged immersion of superhydrophobic surfaces in water led to loss of the bubble-layer and subsequent bacterial adhesion that unexpectedly exceeded that of the control materials. This behavior was not restricted to one particular type of material but was evident on different types of superhydrophobic surfaces. This work is important in that it suggests that superhydrophobic surfaces may actually encourage bacterial adhesion during longer term exposure.

Fabrication of Low-Cost Flexible Superhydrophobic Antibacterial Surface with Dual-Scale Roughness

In this work, we report a large-area fabrication of a flexible superhydrophobic bactericidal surface decorated with copper hydroxide nanowires. This involves a simple two-step method which involves growth followed by transfer of the nanowires onto the polydimethylsiloxane (PDMS) surface by mechanical peeling. Additional roughness in PDMS is obtained through incomplete wetting of the nanoscale gaps which leads to dual-scale roughness and superhydrophobicity with a contact angle of 169° and hysteresis of less than 2°. The simplicity of the process makes it low-cost and easily scalable. The process allows fabrication of nonplanar 3D surfaces. The surface shows blood repellence and antibacterial activity against Escherichia coli with more than 5 log reductions in bacterial colony. The surface also shows hemocompatible behavior, making it suitable for healthcare applications. The fabricated surface is found to be extremely robust against stretching, twisting, sandpaper abrasion, solid weight impact, and tape peel test. The surface is found to withstand human weight multiple times without losing its hydrophobicity, making it suitable for several practical scenarios in healthcare and household applications.

One-Pot Fabrication of Antireflective/Antibacterial Dual-Function Ag NP-Containing Mesoporous Silica Thin Films

Thin films that integrate antireflective and antibacterial dual functions are not only scientifically interesting but also highly desired in many practical applications. Unfortunately, very few studies have been devoted to the preparation of thin films with both antireflective and antibacterial properties. In this study, mesoporous silica (MSiO₂) thin films with uniformly dispersed Ag nanoparticles (Ag NPs) were prepared through a one-pot process, which simultaneously shows high transmittance, excellent antibacterial activity, and mechanical robustness. The optimal thin-film-coated glass substrate demonstrates a maximum transmittance of 98.8% and an average transmittance of 97.1%, respectively, in the spectral range of 400-800 nm. The growth and multiplication of typical bacteria, Escherichia coli ( E. coli), were effectively inhibited on the coated glass. Pencil hardness test, tape adhesion test, and sponge washing test showed favorable mechanical robustness with 5H pencil hardness, 5A grade adhesion, and functional durability of the coating, which promises great potential for applications in various touch screens, windows for hygiene environments, and optical apparatuses for medical uses such as endoscope, and so on.

White-Light-Activated Antibacterial Surfaces Generated by Synergy between Zinc Oxide Nanoparticles and Crystal Violet

The prevalence of hospital-acquired infections (HAIs) caused by multidrug-resistant bacteria is a growing public health concern worldwide. Herein, a facile, easily scalable technique is reported to fabricate white-light-activated bactericidal surfaces by incorporating zinc oxide (ZnO) nanoparticles and crystal violet (CV) dye into poly(dimethylsiloxane). The effect of ZnO concentration on photobactericidal activity of CV is investigated, and we show that there is synergy between ZnO and CV. These materials showed highly significant antibacterial activity when tested against Staphylococcus aureus and Escherichia coli under white light conditions. These surfaces have potential to be used in healthcare environments to decrease the impact of HAIs.

Facile Fabrication of Durable Copper-Based Superhydrophobic Surfaces via Electrodeposition

Superhydrophobic surfaces have myriad industrial applications, yet their practical utilization has been limited by their poor mechanical durability and longevity. We present a low-cost, facile process to develop superhydrophobic copper-based coatings via an electrodeposition route, that addresses this limitation. Through electrodeposition, a stable, multiscale, cauliflower shaped fractal morphology was obtained and upon modification by stearic acid, the prepared coatings show extreme water repellency with contact angle of 162 ± 2° and roll-off angle of about 3°. Systematic studies are presented on coatings fabricated under different processing conditions to demonstrate good durability, mechanical and underwater stability, corrosion resistance, and self-cleaning effect. The study also presents an approach for rejuvenation of slippery superhydrophobic nature (roll-off angle <10°) on the surfaces after long-term water immersion. The presented process can be scaled to larger, durable coatings with controllable wettability for diverse applications.

Enhancing the Bactericidal Efficacy of Nanostructured Multifunctional Surface Using an Ultrathin Metal Coating

Insects and plants exhibit bactericidal behavior through nanostructures, which leads to physical contact killing that does not require antibiotics or chemicals. Also, certain metallic ions (e.g., Ag⁺ and Cu²⁺) are well-known to kill bacteria by disrupting their cellular functionalities. The aim of this study is to explore the improvement in bactericidal activity by combining extreme physical structure with surface chemistry. We have fabricated tall (8-9 μm high) nanostructures on silicon surfaces (NSS) having sharp tips (35-110 nm) using a single-step, maskless deep reactive ion etching technique inspired by dragonfly wing. Bactericidal efficacy of the nanostructured surfaces coated with a thin layer of silver (NSS_Ag) or copper (NSS_Cu) was measured quantitatively using standard viability plate-count method and flow cytometry. NSS_Cu surfaces kill bacteria very efficiently (killing 97% within 30 min) when compared to the uncoated NSS. This can be attributed to the addition of a surface chemistry to the nanostructures. The antibacterial activity of NSS_Cu is further indicated by the morphological differences of the dying/dead bacteria observed in the SEM images. The nanostructured surfaces demonstrate excellent superhydrophobic behavior, even with an ultrathin layer of metal (Ag/Cu) coating. The nanostructured surfaces exhibit static contact angle greater than 150° and contact hysteresis less than 10°. Moreover, reflectance is found to be <1% (for NSS_Cu < 0.5%) for all the nanostructured surfaces in the wavelength range 250-800 nm. The results obtained suggest that the fabricated nanostructured surfaces are multifunctional and can be used in various practical applications.

Surface modification of valve metals using plasma electrolytic oxidation for antibacterial applications: A review

Plasma electrolytic oxidation (PEO) is an advance technique to develop porous oxidation layer on light metals, primarily to enhance corrosion and wear resistance. The oxidation layer can also offer a wide variety of mechanical, biomedical, tribological, and antibacterial properties through the incorporation of several ions and particles. Due to the increasing need of antimicrobial surfaces for biomedical implants, antibacterial PEO coatings have been developed through the incorporation of antibacterial agents. Metallic nanoparticles that have been employed most widely as antibacterial agents are reported to demonstrate serious health and environmental threats. To overcome the current limitations of these coatings, there is a significant need to develop antibacterial surfaces that are not harmful for patient's health and environment. Attention of the readers has been directed to utilize bioactive glasses as antibacterial agents for PEO coatings. Bioactive glasses are well known for their excellent bioactivity, biocompatibility, and antibacterial character. PEO coatings incorporated with bioactive glasses can provide environment-friendly antimicrobial surfaces with exceptional bioactivity, biocompatibility, and osseointegration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 590-605, 2018.

Natural and bioinspired nanostructured bactericidal surfaces

Bacterial antibiotic resistance is becoming more widespread due to excessive use of antibiotics in healthcare and agriculture. At the same time the development of new antibiotics has effectively ground to a hold. Chemical modifications of material surfaces have poor long-term performance in preventing bacterial build-up and hence approaches for realising bactericidal action through physical surface topography have become increasingly important in recent years. The complex nature of the bacteria cell wall interactions with nanostructured surfaces represents many challenges while the design of nanostructured bactericidal surfaces is considered. Here we present a brief overview of the bactericidal behaviour of naturally occurring and bio-inspired nanostructured surfaces against different bacteria through the physico-mechanical rupture of the cell wall. Many parameters affect this process including the size, shape, density, rigidity/flexibility and surface chemistry of the surface nanotextures as well as factors such as bacteria specificity (e.g. gram positive and gram negative) and motility. Different fabrication methods for such bactericidal nanostructured surfaces are summarised.

Transparent Copper-Loaded Chitosan/Silica Antibacterial Coatings with Long-Term Efficacy

Bacteria-contaminated inanimate surfaces within hospitals and clinics result in transmission of pathogens via direct or indirect contact, leading to increased risk of healthcare-associated infections (HAI). The use of antibacterial coatings is a potential way of reducing the bacterial burden, but many surfaces such as instrument panels and monitors necessitate the coatings to be transparent while being highly antibacterial. In this work, silica nanoparticles (SiO₂ NPs) were first grown over a layer of acrylated quaternized chitosan (AQCS) covalently immobilized on commercially available transparent poly(vinyl fluoride) (PVF) films. The SiO₂ NPs then served as nanoreservoirs for adsorption of copper ions. The coated PVF films were transparent and reduced viable bacterial count by ∼99% and 100%, when incubated with a bacteria-loaded droplet for 60 and 120 min, respectively. The killing efficacy of these coatings, after wiping 100 times, with a deionized water-wetted cloth was reduced slightly to 97-98%. The stability of these coatings can be further improved with the deposition of another layer of cationic quaternized chitosan (QCS) over the negatively charged SiO₂ NP layer, wherein the coatings maintained ∼99% killing efficacy even after 100 wipes. These coatings showed no significant toxicity to mammalian cells and, hence, can potentially be used in a clinical setting for reducing HAI.

Superhydrophobic and White Light-Activated Bactericidal Surface through a Simple Coating

Bacterial adhesion and proliferation on surfaces are a challenge in medical and industrial fields. Here, a simple one-step technique is reported to fabricate self-cleaning and bactericidal surfaces. White, blue, and violet paints were produced using titanium dioxide nanoparticles, 1H,1H,2H,2H-perfluorooctyltriethoxysilane, crystal violet, toluidine Blue O, and ethanol solution. All of the painted surfaces showed superhydrophobicity in air, and even after hexadecane oil contamination, they retained water repellency and self-cleaning properties. In an assay of bacterial adhesion, significant reductions (>99.8%) in the number of adherent bacteria were observed for all the painted surfaces. In bactericidal tests, the painted surfaces not only demonstrated bactericidal activity against Staphylococcus aureus and Escherichia coli in the dark but also induced very potent photosensitization (>4.4 log reduction in the number of viable bacteria on the violet painted surface) under white light illumination. The technique that we developed here is general and can be used on a wide range of substrates such as paper, glass, polymers, and others.

Surface-independent one-pot chelation of copper ions onto filtration membranes to provide antibacterial properties

Surface-independent one-pot chelation of copper ions onto filtration membranes to provide antibacterial properties.