Mussel-inspired superhydrophobic surfaces with enhanced corrosion resistance and dual-action antibacterial properties

Harnessing active biofilm for microbial corrosion protection of carbon steel against Geobacter sulfurreducens

Microbiologically influenced corrosion (MIC) caused by corrosive microorganisms poses significant economic losses and safety hazards. Conventional corrosion prevention methods have limitations, so it is necessary to develop the eco-friendly and long-term effective strategies to mitigate MIC. This study investigated the inhibition of Vibrio sp. EF187016 biofilm on Geobacter sulfurreducens on carbon steel. Vibrio sp. EF187016 biofilm reduced the corrosion current density and impeded pitting corrosion. A thick and uniform Vibrio sp. EF187016 biofilm formed on the coupon surfaces, acting as a protective layer against corrosive ions and electron acquisition by G. sulfurreducens. The pre-grown mature Vibrio sp. EF187016 biofilms, provided enhanced protection against G. sulfurreducens corrosion. Additionally, the extracellular polymeric substances from Vibrio sp. EF187016 was confirmed to act as a green corrosion inhibitor to mitigate microbial corrosion. This study highlights the potential of active biofilms for eco-friendly corrosion protection, offering a novel perspective on material preservation against microbial corrosion.

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.

Silver-Containing Biomaterials for Biomedical Hard Tissue Implants

Bacterial infection caused by biomaterials is a very serious problem in the clinical treatment of implants. The emergence of antibiotic resistance has prompted other antibacterial agents to replace traditional antibiotics. Silver is rapidly developing as an antibacterial candidate material to inhibit bone infections due to its significant advantages such as high antibacterial timeliness, high antibacterial efficiency, and less susceptibility to bacterial resistance. However, silver has strong cytotoxicity, which can cause inflammatory reactions and oxidative stress, thereby destroying tissue regeneration, making the application of silver-containing biomaterials extremely challenging. In this paper, the application of silver in biomaterials is reviewed, focusing on the following three issues: 1) how to ensure the excellent antibacterial properties of silver, and not easy to cause bacterial resistance; 2) how to choose the appropriate method to combine silver with biomaterials; 3) how to make silver-containing biomaterials in hard tissue implants have further research. Following a brief introduction, the discussion focuses on the application of silver-containing biomaterials, with an emphasis on the effects of silver on the physicochemical properties, structural properties, and biological properties of biomaterials. Finally, the review concludes with the authors' perspectives on the challenges and future directions of silver in commercialization and in-depth research.

Can Superhydrophobic PET Surfaces Prevent Bacterial Adhesion?

Prevention of bacterial adhesion is a way to reduce and/or avoid biofilm formation, thus restraining its associated infections. The development of repellent anti-adhesive surfaces, such as superhydrophobic surfaces, can be a strategy to avoid bacterial adhesion. In this study, a polyethylene terephthalate (PET) film was modified by in situ growth of silica nanoparticles (NPs) to create a rough surface. The surface was further modified with fluorinated carbon chains to increase its hydrophobicity. The modified PET surfaces presented a pronounced superhydrophobic character, showing a water contact angle of 156° and a roughness of 104 nm (a considerable increase comparing with the 69° and 4.8 nm obtained for the untreated PET). Scanning Electron Microscopy was used to evaluate the modified surfaces morphology, further confirming its successful modification with nanoparticles. Additionally, a bacterial adhesion assay using an Escherichia coli expressing YadA, an adhesive protein from Yersinia so-called Yersinia adhesin A, was used to assess the anti-adhesive potential of the modified PET. Contrarily to what was expected, adhesion of E. coli YadA was found to increase on the modified PET surfaces, exhibiting a clear preference for the crevices. This study highlights the role of material micro topography as an important attribute when considering bacterial adhesion.

Substrate-independent and widely applicable deposition of antibacterial coatings

Antibacterial coatings are regarded as a necessary tool to prevent implant-related infections. Substrate-independent and widely applicable coating techniques are gaining significant interest to synthesize different types of antibacterial films, which can be relevant from a fundamental and application-oriented perspective. Plasma polymer- and polydopamine-based antibacterial coatings represent the most widely studied and versatile approaches among these coating techniques. Both single- and dual-functional antibacterial coatings can be fabricated with these approaches and a variety of dual-functional antibacterial coating strategies can still be explored in future work. These coatings can potentially be used for a wide range of different implants (material, shape, and size). However, for most implants, significantly more fundamental knowledge needs to be gained before these coatings can find real-life use.

Enhancing the antibacterial property of chitosan through synergistic alkylation and chlorination

Chitosan exhibits moderate antimicrobial properties. Here, we enhanced the antimicrobial properties of chitosan through alkylation and chlorination and evaluated the effect of alkylation on chitosan's hydrophobicity, bacterial attachment, chlorination, biocidal property, and stability. First, chitosan films were prepared through casting and were then immersed in a hexanal solution of different concentrations. The aldehyde groups of hexanal reacted with the amino group in chitosan through a Schiff base reaction. Next, the hexanal-modified chitosan films were soaked in 10 % bleach to form N-halamine. The results demonstrated that the surface became more hydrophobic, and chitosan films with increased hexanal-grafting concentrations exhibited less bacterial attachment. However, the degree of chlorination decreased as the degree of alkylation increased, further reducing the diameter of the zone of inhibition. Nevertheless, all chlorinated samples could kill ~5 log of Staphylococcus aureus and Escherichia coli within 30 min. Unlike previous results for chlorinated chitosan, in this study, alkylation before chlorination enhanced antibacterial properties and bactericidal ability and decelerated the degradation of chlorinated samples. The results of a systematic evaluation indicated that a hexanal-grafting concentration of approximately 80 mM maintains the equilibrium of the various properties of chitosan. Alkylated and chlorinated chitosan has considerable potential application as mask filter layers.

Conformation-dominated surface antifouling and aqueous lubrication

Antifouling and aqueous lubrication are important properties for biomaterials, especially for those with implantation purposes. In order to better understand the polymer conformation dependence of the surface antifouling and lubrication properties, poly(ethylene glycol) (PEG) polymers with mono-functional and difunctional catechol anchors were designed and anchored on surface to adopt tail and loop conformations. Diblock and triblock copolymers with poly(dopamine methacrylamide) (PDMA) block as anchors and PEG block as the main body were synthesized and anchored on silicon surfaces by a "grafting to" strategy. The chemical composition, film thickness, and surface roughness of both coatings were controlled to be similar to give a direct comparison of looped brushes and tailed analogues. Then, the antifouling and surface friction behaviors were detected to verify the topological conformation effect of PEG polymer brushes. Results showed that PEG triblock copolymer modified surface exhibited an obviously better antifouling property and a lower friction coefficient of ∼0.011 than that of PEG diblock copolymer modified surface. Additionally, calculation and simulation results demonstrated that triblock copolymer had higher adsorption energy and anchored on surface with looped conformation. It is indicated that the strongly anchored PEG loops are effective for excellent antifouling and lubricating properties due to its strong hydration and steric hindrance. The conformation-dominated enhanced antifouling and reduced interfacial friction is an effective method for the development of excellent antifouling surfaces.

Bioinspired micro/nano structured aluminum with multifaceted applications

Inspired by many biological systems such as lotus leaves, insect wings and rose petals, great attention has been devoted to the study and fabrication of artificial superhydrophobic surfaces with multiple functionalities. In the present study, a simple and ecological synthesis route has been employed for large scale fabrication of self-assembled, sustainable nanostructures on unprocessed and micro imprinted aluminum surfaces named 'Nano' and 'Hierarchy'. The processed samples show extreme wettability ranging from superhydrophilicity to superhydrophobicity depending on post-processing conditions. The densely packed ellipsoidal nanostructures exhibited superhydrophobicity with excellent water, bacterial and dust repellency when modified by low surface energy material 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FOTES), characterized by a static contact angle of 163 ± 1° and contact angle hysteresis (CAH) ~3°. These coated surfaces show significant corrosion resistance with current density of 6 nA/cm² which is 40 times lower than unprocessed counterpart and retain chemical stability after prolonged immersion in corrosive media. These surfaces show excellent self-cleaning ability with significantly low water consumption (< 0.1 µl/mm²-mg) and prevent biofouling which ensures its applicability in biological environment and marine components. The nanostructured superhydrophilic aluminum shows maximum antibacterial activity due to disruption of cell membrane. This work can offer a simple strategy to large scale fabrication of multifunctional biomimetic metallic surfaces.

Marine Biofilms with Significant Corrosion Inhibition Performance by Secreting Extracellular Polymeric Substances

The development of environmentally friendly and sustainable corrosion protection technologies is a longstanding yet difficult problem, especially for the marine environment. The utilization of living biofilms isolated from local environments is an effective strategy for infrastructure protection. In this study, three aerobic marine bacteria, Tenacibaculum mesophilum D-6, Tenacibaculum litoreum W-4, and Bacillus sp. Y-6, with strong biofilm-forming abilities were isolated and evaluated for the corrosion protection of X80 carbon steel. The corrosion inhibitory effect of the bacteria was found to be closely related to their biofilm-forming abilities. This conclusion was corroborated by biofilm characterization, electrochemical tests, weight loss analysis, and corrosion product analysis. Moreover, secreted extracellular polymeric substances were identified to play significant roles in corrosion inhibition. Herein, we proposed a novel, eco-friendly, and cost-effective method for corrosion protection of carbon steels in the marine environment, providing guiding principles for identifying corrosion inhibitory bacteria from the local marine environment.

A transparent hydrophilic anti-biofouling coating for intraocular lens materials prepared by "bridging" of the intermediate adhesive layer

The attachment of bio-foulants, including unwanted cells, proteins, and bacteria, to a medical device such as an intraocular lens can lead to implantation failure. Hydrophilic polymers are often used as surface modifiers in the fabrication of anti-biofouling coatings, but a hydrophilic coating can easily become swollen and peel off the substrate. In this study, we chose polymethyl methacrylate (PMMA) as the representative material of intraocular lenses because PMMA has better biocompatibility, a higher refractive index, better optical clarity, lighter weight, more stable performance, and lower cost than other intraocular lens materials. We fabricated polyvinyl alcohol (PVA) coatings with or without a "bridge", that is, an intermediate adhesive layer (AL), to increase the adhesion bonding effect between the anti-biofouling coating and the substrate. The results indicated that the prepared coatings were transparent and noncytotoxic. Moreover, the anti-adhesion properties of the cells and the resistance properties to nonspecific protein adsorption of PMMA modified by both AL and PVA coatings were better and more durable compared with the sample only modified with a physically dipped PVA coating. The coating prepared by AL "bridging" provides a new strategy for the preparation of a transparent hydrophilic anti-biofouling coating suitable for PMMA intraocular lens materials.

Fluorine-Free Superhydrophobic Coating with Antibiofilm Properties Based on Pickering Emulsion Templating

This study presents antibiofilm coating formulations based on Pickering emulsion templating. The coating contains no bioactive material because its antibiofilm properties stem from passive mechanisms that derive solely from the superhydrophobic nature of the coating. Moreover, unlike most of the superhydrophobic formulations, our system is fluorine-free, thus making the method eminently suitable for food and medical applications. The coating formulation is based on water in toluene or xylene emulsions that are stabilized using commercial hydrophobic silica, with polydimethylsiloxane (PDMS) dissolved in toluene or xylene. The structure of the emulsions and their stability was characterized by confocal microscopy and cryogenic-scanning electron microscopy (cryo-SEM). The most stable emulsions are applied on polypropylene (PP) surfaces and dried in an oven to form PDMS/silica coatings in a process called emulsion templating. The structure of the resulting coatings was investigated by atomic force microscopy (AFM) and SEM. The surface of the coatings shows a honeycomb-like structure that exhibits a combination of micron-scale and nanoscale roughness, which endows it with its superhydrophobic properties. After tuning, the superhydrophobic properties of the coatings demonstrated highly efficient passive antibiofilm activity. In vitro antibiofilm trials with E. coli indicate that the coatings reduced the biofilm accumulation by 83% in the xylene-water-based surfaces and by 59% in the case of toluene-water-based surfaces.

Multi-scale hybrid modified coatings on titanium implants for non-cytotoxicity and antibacterial properties

Titanium and its alloys are among the widely used materials in the biomedical field, but they have poor wear resistance and antibacterial properties. In the present study, anodization, photo-reduction, and spin-coating technologies were integrated to prepare a hybrid modified coating for bio-inert titanium implants, having excellent comprehensive performance. The surface roughness of Ti-35Nb-2Ta-3Zr was specifically optimized by surface modification leading to improved wear resistance. Ag ions are still detectable after 28 days of submersion in saline. The antibacterial rate of the composite coating group reaches 100% by plate counting due to the antibacterial mechanism of direct and indirect contact. Both bacteria morphology and fluorescence staining experiments confirm these results. Besides, no cytotoxicity was detected in our fabricated implants during the CCK-8 assay. Accordingly, fabrication of hybrid modified coatings on Ti-35Nb-2Ta-3Zr is an effective strategy for infection and cytotoxicity prevention. These hybrid modified coatings can be regarded as promising multifunctional biomaterials.

Implication of Surface Properties, Bacterial Motility, and Hydrodynamic Conditions on Bacterial Surface Sensing and Their Initial Adhesion

Biofilms are structured microbial communities attached to surfaces, which play a significant role in the persistence of biofoulings in both medical and industrial settings. Bacteria in biofilms are mostly embedded in a complex matrix comprised of extracellular polymeric substances that provide mechanical stability and protection against environmental adversities. Once the biofilm is matured, it becomes extremely difficult to kill bacteria or mechanically remove biofilms from solid surfaces. Therefore, interrupting the bacterial surface sensing mechanism and subsequent initial binding process of bacteria to surfaces is essential to effectively prevent biofilm-associated problems. Noting that the process of bacterial adhesion is influenced by many factors, including material surface properties, this review summarizes recent works dedicated to understanding the influences of surface charge, surface wettability, roughness, topography, stiffness, and combination of properties on bacterial adhesion. This review also highlights other factors that are often neglected in bacterial adhesion studies such as bacterial motility and the effect of hydrodynamic flow. Lastly, the present review features recent innovations in nanotechnology-based antifouling systems to engineer new concepts of antibiofilm surfaces.

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.

Controlling the wettability of stainless steel from highly-hydrophilic to super-hydrophobic by femtosecond laser-induced ripples and nanospikes

Results on the manipulation of the wetting properties of stainless steel alloy surface by ultrashort pulse laser texturing are presented. The wide range of water droplet contact angles from highly-hydrophilic to super-hydrophobic was achieved by generation of laser-induced periodic surface structures (LIPSS) and nanospikes. In particular, the wetting state was controlled by accumulated laser fluence, which determines the carbon/oxygen content and nano-texture type of the surface after laser treatment. A super-hydrophobic water-repelling surface was generated. The simple, single-step laser processing technology was demonstrated as a promising tool for the large-scale industrial production of self-cleaning stainless steel.

Results on the manipulation of the wetting properties of stainless steel alloy surface by ultrashort pulse laser texturing are presented.

Robust Biomimetic Hierarchical Diamond Architecture with a Self-Cleaning, Antibacterial, and Antibiofouling Surface

Biofouling is a worldwide problem from healthcare to marine exploration. Aggressive biofouling, wear, and corrosion lead to severe deterioration in function and durability. Here, micro- and nanostructured hierarchical diamond films mimicking the morphology of plant leaves were developed to simultaneously achieve superhydrophobicity, antibacterial efficacy, and marine antibiofouling, combined with mechanical and chemical robustness. These coatings were designed and successfully constructed on various commercial substrates, such as titanium alloys, silicon, and quartz glass via a chemical vapor deposition process. The unique surface structure of diamond films reduced bacteria attachment by 90-99%. In the marine environment, these biomimetic diamond films significantly reduced more than 95% adhesion of green algae. The structured diamond films retained mechanical robustness, superhydrophobicity, and antibacterial efficacy under high abrasion and corrosive conditions, exhibiting at least 20 times enhanced wear resistance than the bare commercial substrates even after long-term immersion in seawater.

Facile One-Step Method to Fabricate a Slippery Lubricant-Infused Surface (LIS) with Self-Replenishment Properties for Anti-Icing Applications

In this work, a slippery lubricant-infused surface (LIS) was prepared by simple one-step mixing of polydimethylsiloxane (PDMS) resin and dimethyl silicone oil (PMX-200) directly. Silicone oil showed good compatibility with PDMS resin, and the added amount of silicone oil had no significant effect on the surface morphology of LIS. According to the results of surface observations, once the silicone oil film anchored on the LIS was removed, the silicone oil inside the PDMS polymer automatically diffused to the surface and formed a new silicone oil film again in a short time. Furthermore, with the increase of silicone oil content, the oil self-replenishment speed and amount of the LIS were enhanced, which also promoted a decrease of the surface water sliding angle and the improvement of the lubrication ability of the LIS. In the icing/deicing cycle tests, the slippery LIS still maintained very low ice adhesion strength after 24 cycles, showing excellent anti-icing performance.

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.

Polymer Microfibers Incorporated with Silver Nanoparticles: a New Platform for Optical Sensing

The enhanced sensitivity of up-conversion luminescence is imperative for the application of up-conversion nanoparticles (UCNPs). In this study, microfibers were fabricated after co-doping UCNPs with polymethylmethacrylate (PMMA) and silver (Ag) solutions. Transmission losses and sensitivities of UCNPs (tetrogonal-LiYF4:Yb3+/Er3+) in the presence and absence of Ag were investigated. Sensitivity of up-conversion luminescence with Ag (LiYF4:Yb3+/Er3+/Ag) is 0.0095 K-1 and reduced to (LiYF4:Yb3+/Er3+) 0.0065 K-1 without Ag at 303 K under laser source (980 nm). The UCNP microfibers with Ag showed lower transmission losses and higher sensitivity than without Ag and could serve as promising candidate for optical applications. This is the first observation of Ag-doped microfiber via facile method.

Effect of Dissolved Oxygen Concentration on the Microbiologically Influenced Corrosion of Q235 Carbon Steel by Halophilic Archaeon Natronorubrum tibetense

The influence of dissolved oxygen concentration (DOC) on the microbiologically influenced corrosion (MIC) of Q235 carbon steel in the culture medium of halophilic archaeon Natronorubrum tibetense was investigated. The increase of DOC from 0.0 to 3.0 ppm was found to strengthen the oxygen concentration cell by promoting cathodic reaction. Meanwhile, the increased DOC also promoted archaeal cell growth, which could consume more metallic iron as energy source and aggravated the localized corrosion. When the DOC further increased to 5.0 ppm, the uniform corrosion was dominant as the biofilms became uniformly presented on the steel surface. Combined with the stronger inhibition effect of oxygen diffusion by the increased biofilm coverage, the MIC of carbon steel in the 5.0 ppm medium was weaker than that in the 3.0 ppm medium. From weight loss and electrochemical tests, the results all demonstrated that the carbon steel in the 3.0 ppm medium had the largest corrosion rate.

Mussel-inspired coatings with tunable wettability, for enhanced antibacterial efficiency and reduced bacterial adhesion

The mussel-inspired coatings with tunable wettability were designed, showing enhanced antibacterial efficiency and reduced bacterial adhesion.

Facile fabrication of multifunctional fabrics: use of copper and silver nanoparticles for antibacterial, superhydrophobic, conductive fabrics

This study aims to develop a multifunctional fabric for antibacterial, superhydrophobic and conductive performance using a facile fabrication method. Conductive metal particles, copper and silver, were used as antibacterial agents as well as a means to create nanoscale roughness on the fabric surface. Subsequent hydrophobic coating with 1-dodecanethiol produced a superhydrophobic surface. The single metal treatment with Cu or Ag, and the combined metal treatment of Cu/Ag were compared for the multifunctionality. The Cu/Ag treated fabric and the Cu treated fabric showed a bacteriostatic rate ≥ 99% and a sterilization rate ≥ 99% against S. aureus, suggesting a higher antibacterial activity against the Gram-positive bacteria. In contrast, the Ag treated fabric showed a lower antibacterial effect regardless of the bacteria type. With regards to conductivity, the single metal treated fabric did not exhibit conductivity; however the Cu/Ag treated fabric showed a high level conductivity with a surface resistivity of 25.17 ± 8.18 Ω sq-1 and 184.38 ± 85.42 Ω sq-1 before and after hydrophobic coating, respectively. Fabrics treated with Cu and Cu/Ag particles (with hydrophobic coating) displayed superhydrophobic characteristics with the contact angle of 161-162° and the shedding angle of 7.0-7.8°. The air permeability decreased after the particle treatment as the particles blocked the pores in the fabric. However, the water vapor permeability and tensile strength were not significantly affected by the particle treatment. This study is significant in that a multifunctionality of antibacterial effect, superhydrophobicity, and conductivity was achieved through the facile processes for metal nanoparticle attachment and hydrophobic coating. The multifunctional fabrics produced in this study can be practically applied to self-cleaning smart clothing, which has reduced laundering need, without hygiene concerns.

TC4/Ag Metal Matrix Nanocomposites Modified by Friction Stir Processing: Surface Characterization, Antibacterial Property, and Cytotoxicity in Vitro

Numerous antibacterial biomaterials have been developed, but a majority of them suffer from poor biocompatibility. With the purpose of reducing biomaterial-related infection and cytotoxicity, friction stir processing (FSP) was employed to embed silver nanoparticles (Ag NPs) in a Ti-6Al-4V (TC4) substrate. Characterization using scanning electron microscopy, transmission electron microscopy, and three-dimensional atom probe tomography illustrates that NPs are distributed more homogeneously on the surface of TC4 as the groove depth increases, and silver-rich NPs with a size from 10 to 20 nm exist as metallic silver diffused into the substrate, where the silver content is 4.3-5.6%. Electrochemical impedance spectroscopy shows that both FSP and the addition of silver have positive effects on corrosion resistance. The modified samples effectively inhibit both Staphylococcus aureus and Escherichia coli strains and slightly reduce their adhesion while not displaying any cytotoxicity to bone mesenchymal stem cells in vitro. The antibacterial effect is independent of Ag-ion release and is likely due to the number of embedded silver NPs on the surface, which directly contact and subsequently destroy the cell membrane. Our study shows that the TC4/Ag metal matrix nanocomposite is a potential infection-related biomaterial and that embedding Ag NPs tightly on a biomaterial surface is an effective strategy for striking a balance between the antibacterial effect and biocompatibility, providing an innovative approach for accurately controlling the cytotoxicity of infection-related biomaterials.

Recent Advances in Scanning Electrochemical Microscopy for Biological Applications

Scanning electrochemical microscopy (SECM) is a chemical microscopy technique with high spatial resolution for imaging sample topography and mapping specific chemical species in liquid environments. With the development of smaller, more sensitive ultramicroelectrodes (UMEs) and more precise computer-controlled measurements, SECM has been widely used to study biological systems over the past three decades. Recent methodological breakthroughs have popularized SECM as a tool for investigating molecular-level chemical reactions. The most common applications include monitoring and analyzing the biological processes associated with enzymatic activity and DNA, and the physiological activity of living cells and other microorganisms. The present article first introduces the basic principles of SECM, followed by an updated review of the applications of SECM in biological studies on enzymes, DNA, proteins, and living cells. Particularly, the potential of SECM for investigating bacterial and biofilm activities is discussed.