Natural bactericidal surfaces: mechanical rupture of Pseudomonas aeruginosa cells by cicada wings

Bioinspired bi-phasic 3D nanoflowers of MgO/Mg(OH)2 coated melamine sponge as a novel bactericidal agent

By roughly mimicking the surface architectural design of dragonfly wings, novel bi-phasic 3D nanoflowers of MgO/Mg(OH)2 were successfully synthesized via the electrospinning technique. The 3D nanoflowers were coated over a commercial melamine sponge and extensively characterized by SEM, XRD, FTIR, and EDS. The formation of distinct dense 3D nano petals was revealed by SEM images whereby the mean petal thickness and mean distance between the adjacent petals were found to be 36 nm and 121 nm, respectively. The bactericidal activities of synthesized 3D nano-flowers coated melamine sponges were assessed against five different bacteria (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa). This study demonstrated significant bactericidal activity of MgO/Mg(OH)2 3D nanoflowers coated MS against Gram-positive and Gram-negative bacteria. Plausible bactericidal mechanisms include envelope deformation, penetration, and induction of oxidative stress. This study introduces novel bioinspired biomaterial with the capacity to reduce the risk associated with pathogenic bacterial infections, especially in medical devices.

Study of Finite Element Simulation on the Mechano-Bactericidal Mechanism of Hierarchical Nanostructure Arrays

Biomimetic nanostructures with bactericidal performance have become the research focus in constructing sterilization surfaces, but the mechano-bactericidal mechanism is still not fully understood, especially for the hierarchical nanostructure arrays with different heights. Herein, the interaction between Escherichia coli cells and nanostructure arrays was simulated by finite element, and the initial rupture points, i.e., critical action sites, of bacterial cells and the effects of nanostructure geometries on the cell rupture speed were analyzed based on the mechano-response of Escherichia coli cells on flat (identical heights) and hierarchical nanostructure arrays. The critical action sites of bacterial cells on nanostructure arrays are all at the three-phase junction zone of cell-liquid-nanostructure, but they are slightly shifted by the height difference ΔH of nanostructures on hierarchical nanopillar (NP)/nanosheet (NS) arrays, where the NP is higher than the NS. When ΔH < 20 nm, the site nears the NS corners, and when ΔH ≥ 20 nm, the site is consistent with that of the NP/NP array, i.e., the site locates at the three-phase junction zone of cell-liquid-high NP. In addition, except for decreasing the NP diameter, the NS thickness/width, or properly increasing the nanostructure spacing, the cell rupture can be accelerated via increasing the ΔH of nanostructures. ΔH = 40 nm is distinguished as the boundary for the effect of nanostructure ΔH on the cell rupture speed. When ΔH < 40 nm, the cell rupture speed rapidly increases as the ΔH increases; when ΔH ≥ 40 nm, the cell rupture speed reaches the maximum value and remains stable. This study provides a new strategy on how to design high-efficiency bactericidal surfaces.

Research progress and future prospects of antimicrobial modified polyetheretherketone (PEEK) for the treatment of bone infections

Infection of the bone is a difficult problem in orthopedic diseases. The key and basis of the treatment of bone infection is the effective control of local infection, as well as the elimination of infection focus and dead cavities. The most commonly used approach utilized for the prevention and management of bone infection is the application of antibiotic bone cement. However, the incorporation of antibiotics into the cement matrix has been found to considerably compromise the mechanical characteristics of bone cement. Moreover, some investigations have indicated that the antibiotic release rate of antibiotic bone cement is relatively low. Polyetheretherketone (PEEK) and its composites have been considered to perfectly address the challenges above, according to its favorable biomechanical characteristics and diverse surface functionalizations. This article provides a comprehensive overview of the recent advancements in the antimicrobial modification of PEEK composites in the field of antibacterial therapy of bone infection. Furthermore, the potential application of PEEK-modified materials in clinical treatment was discussed and predicted.

Smart dental materials for antimicrobial applications

Smart biomaterials can sense and react to physiological or external environmental stimuli (e.g., mechanical, chemical, electrical, or magnetic signals). The last decades have seen exponential growth in the use and development of smart dental biomaterials for antimicrobial applications in dentistry. These biomaterial systems offer improved efficacy and controllable bio-functionalities to prevent infections and extend the longevity of dental devices. This review article presents the current state-of-the-art of design, evaluation, advantages, and limitations of bioactive and stimuli-responsive and autonomous dental materials for antimicrobial applications. First, the importance and classification of smart biomaterials are discussed. Second, the categories of bioresponsive antibacterial dental materials are systematically itemized based on different stimuli, including pH, enzymes, light, magnetic field, and vibrations. For each category, their antimicrobial mechanism, applications, and examples are discussed. Finally, we examined the limitations and obstacles required to develop clinically relevant applications of these appealing technologies.

Biomaterial engineering surface to control polymicrobial dental implant-related infections: focusing on disease modulating factors and coatings development

INTRODUCTION

Peri-implantitis is the leading cause of dental implant loss and is initiated by a polymicrobial dysbiotic biofilm formation on the implant surface. The destruction of peri-implant tissue by the host immune response and the low effectiveness of surgical or non-surgical treatments highlight the need for new strategies to prevent, modulate and/or eliminate biofilm formation on the implant surface. Currently, several surface modifications have been proposed using biomolecules, ions, antimicrobial agents, and topography alterations.

AREAS COVERED

Initially, this review provides an overview of the etiopathogenesis and host- and material-dependent modulating factors of peri-implant disease. In addition, a critical discussion about the antimicrobial surface modification mechanisms and techniques employed to modify the titanium implant material is provided. Finally, we also considered the future perspectives on the development of antimicrobial surfaces to narrow the bridge between idea and product and favor the clinical application possibility.

EXPERT OPINION

Antimicrobial surface modifications have demonstrated effective results; however, there is no consensus about the best modification strategy and in-depth information on the safety and longevity of the antimicrobial effect. Modified surfaces display recurring challenges such as short-term effectiveness, the burst release of drugs, cytotoxicity, and lack of reusability. Stimulus-responsive surfaces seem to be a promising strategy for a controlled and precise antimicrobial effect, and future research should focus on this technology and study it from models that better mimic clinical conditions.

Multi-functional approach in the design of smart surfaces to mitigate bacterial infections: a review

Advancements in biomedical devices are ingenious and indispensable in health care to save millions of lives. However, microbial contamination paves the way for biofilm colonisation on medical devices leading to device-associated infections with high morbidity and mortality. The biofilms elude antibiotics facilitating antimicrobial resistance (AMR) and the persistence of infections. This review explores nature-inspired concepts and multi-functional approaches for tuning in next-generation devices with antibacterial surfaces to mitigate resistant bacterial infections. Direct implementation of natural inspirations, like nanostructures on insect wings, shark skin, and lotus leaves, has proved promising in developing antibacterial, antiadhesive, and self-cleaning surfaces, including impressive SLIPS with broad-spectrum antibacterial properties. Effective antimicrobial touch surfaces, photocatalytic coatings on medical devices, and conventional self-polishing coatings are also reviewed to develop multi-functional antibacterial surfaces to mitigate healthcare-associated infections (HAIs).

Recent Advances in Superhydrophobic and Antibacterial Cellulose-Based Fibers and Fabrics: Bio-inspiration, Strategies, and Applications

Cellulose-based fabrics are ubiquitous in our daily lives. They are the preferred choice for bedding materials, active sportswear, and next-to-skin apparels. However, the hydrophilic and polysaccharide characteristics of cellulose materials make them vulnerable to bacterial attack and pathogen infection. The design of antibacterial cellulose fabrics has been a long-term and on-going effort. Fabrication strategies based on the construction of surface micro-/nanostructure, chemical modification, and the application of antibacterial agents have been extensively investigated by many research groups worldwide. This review systematically discusses recent research on super-hydrophobic and antibacterial cellulose fabrics, focusing on morphology construction and surface modification. First, natural surfaces showing liquid-repellent and antibacterial properties are introduced and the mechanisms behind are explained. Then, the strategies for fabricating super-hydrophobic cellulose fabrics are summarized, and the contribution of the liquid-repellent function to reducing the adhesion of live bacteria and removing dead bacteria is elucidated. Representative studies on cellulose fabrics functionalized with super-hydrophobic and antibacterial properties are discussed in detail, and their potential applications are also introduced. Finally, the challenges in achieving super-hydrophobic antibacterial cellulose fabrics are discussed, and the future research direction in this area is proposed.

Graphical Abstract

The figure summarizes the natural surfaces and the main fabrication strategies of superhydrophobic antibacterial cellulose fabrics and their potential applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42765-023-00297-1.

Automated Prediction of Bacterial Exclusion Areas on SEM Images of Graphene-Polymer Composites

To counter the rising threat of bacterial infections in the post-antibiotic age, intensive efforts are invested in engineering new materials with antibacterial properties. The key bottleneck in this initiative is the speed of evaluation of the antibacterial potential of new materials. To overcome this, we developed an automated pipeline for the prediction of antibacterial potential based on scanning electron microscopy images of engineered surfaces. We developed polymer composites containing graphite-oriented nanoplatelets (GNPs). The key property that the algorithm needs to consider is the density of sharp exposed edges of GNPs that kill bacteria on contact. The surface area of these sharp exposed edges of GNPs, accessible to bacteria, needs to be inferior to the diameter of a typical bacterial cell. To test this assumption, we prepared several composites with variable distribution of exposed edges of GNP. For each of them, the percentage of bacterial exclusion area was predicted by our algorithm and validated experimentally by measuring the loss of viability of the opportunistic pathogen Staphylococcus epidermidis. We observed a remarkable linear correlation between predicted bacterial exclusion area and measured loss of viability (R² = 0.95). The algorithm parameters we used are not generally applicable to any antibacterial surface. For each surface, key mechanistic parameters must be defined for successful prediction.

Designing Effective Antimicrobial Nanostructured Surfaces: Highlighting the Lack of Consensus in the Literature

Research into nanostructured materials, inspired by the topography of certain insect wings, has provided a potential pathway toward drug-free antibacterial surfaces, which may be vital in the ongoing battle against antimicrobial resistance. However, to produce viable antibacterial nanostructured surfaces, we must first understand the bactericidal mechanism of action and how to optimize them to kill the widest range of microorganisms. This review discusses the parameters of nanostructured surfaces that have been shown to influence their bactericidal efficiency and highlights the highly variable nature of many of the findings. A large-scale analysis of the literature is also presented, which further shows a lack of clarity in what is understood about the factors influencing bactericidal efficiency. The potential reasons for the ambiguity, including how the killing effect may be a result of multiple factors and issues with nonstandardized testing of the antibacterial properties of nanostructured surfaces, are then discussed. Finally, a standard method for testing of antimicrobial killing is proposed that will allow comparison between studies and enable a deeper understanding about nanostructured surfaces and how to optimize their bactericidal efficiency.

Quantifiable Relationship Between Antibacterial Efficacy and Electro-Mechanical Intervention on Nanowire Arrays

Physical disruption is an important antibacterial means as it is lethal to bacteria without spurring antimicrobial resistance. However, it is very challenging to establish a quantifiable relationship between antibacterial efficacy and physical interactions such as mechanical and electrical forces. Herein, titanium nitride (TN) nanowires with adjustable orientations and capacitances are prepared to exert gradient electro-mechanical forces on bacteria. While vertical nanowires show the strongest mechanical force resulting in an antibacterial efficiency of 0.62 log reduction (vs 0.22 for tiled and 0.36 for inclined nanowires, respectively), the addition of electrical charges maximizes the electro-mechanical interactions and elevates the antibacterial efficacy to more than 3 log reduction. Biophysical and biochemical analyses indicate that electrostatic attraction by electrical charge narrows the interface. The electro-mechanical intervention more easily stiffens and rips the bacteria membrane, disturbing the electron balance and generating intracellular oxidative stress. The antibacterial ability is maintained in vivo and bacteria-challenged rats are protected from serious infection. The physical bacteria-killing process demonstrated here can be controlled by adjusting the electro-mechanical interactions. Overall, these results revealed important principles for rationally designing high-performance antibacterial interfaces for clinical applications.

Review of Antimicrobial Nanocoatings in Medicine and Dentistry: Mechanisms of Action, Biocompatibility Performance, Safety, and Benefits Compared to Antibiotics

This review discusses topics relevant to the development of antimicrobial nanocoatings and nanoscale surface modifications for medical and dental applications. Nanomaterials have unique properties compared to their micro- and macro-scale counterparts and can be used to reduce or inhibit bacterial growth, surface colonization and biofilm development. Generally, nanocoatings exert their antimicrobial effects through biochemical reactions, production of reactive oxygen species or ionic release, while modified nanotopographies create a physically hostile surface for bacteria, killing cells via biomechanical damage. Nanocoatings may consist of metal nanoparticles including silver, copper, gold, zinc, titanium, and aluminum, while nonmetallic compounds used in nanocoatings may be carbon-based in the form of graphene or carbon nanotubes, or composed of silica or chitosan. Surface nanotopography can be modified by the inclusion of nanoprotrusions or black silicon. Two or more nanomaterials can be combined to form nanocomposites with distinct chemical or physical characteristics, allowing combination of different properties such as antimicrobial activity, biocompatibility, strength, and durability. Despite their wide range of applications in medical engineering, questions have been raised regarding potential toxicity and hazards. Current legal frameworks do not effectively regulate antimicrobial nanocoatings in matters of safety, with open questions remaining about risk analysis and occupational exposure limits not considering coating-based approaches. Bacterial resistance to nanomaterials is also a concern, especially where it may affect wider antimicrobial resistance. Nanocoatings have excellent potential for future use, but safe development of antimicrobials requires careful consideration of the "One Health" agenda, appropriate legislation, and risk assessment.

Bioinspired nanoflakes with antifouling and mechano-bactericidal capacity

Pathogenic bacteria contamination ubiquitously occurs on high-contact surfaces in hospitals and has long been a threat to public health, inducing severe nosocomial infections that cause multiple organ dysfunction and increased hospital mortality. Recently, nanostructured surfaces with mechano-bactericidal properties have shown potential for modifying material surfaces to fight against the spread of pathogenic microorganisms without the risk of triggering antibacterial resistance. Nevertheless, these surfaces are readily contaminated by bacterial attachment or inanimate pollutants like solid dust or common fluids, which has greatly weakened their antibacterial capabilities. In this work, we discovered that the nonwetting Amorpha fruticosa leaf surfaces are equipped with mechano-bactericidal capacity by means of their randomly-arranged nanoflakes. Inspired by this discovery, we reported an artificial superhydrophobic surface with similar nanofeatures and superior antibacterial abilities. Compared to conventional bactericidal surfaces, this bioinspired antibacterial surface was synergistically accompanied by antifouling performances, which significantly prevent either initial bacterial attachment or inanimate pollutants like dust covering and fluid contaminants. Overall, the bioinspired antifouling nanoflakes surface holds promise as the design of next-generation high-touch surface modification that effectively reduces the transmission of nosocomial infections.

Mechano-Bactericidal Surfaces: Mechanisms, Nanofabrication, and Prospects for Food Applications

Mechano-bactericidal (MB) nanopatterns have the ability to inactivate bacterial cells by rupturing cellular envelopes. Such biocide-free, physicomechanical mechanisms may confer lasting biofilm mitigation capability to various materials encountered in food processing, packaging, and food preparation environments. In this review, we first discuss recent progress on elucidating MB mechanisms, unraveling property-activity relationships, and developing cost-effective and scalable nanofabrication technologies. Next, we evaluate the potential challenges that MB surfaces may face in food-related applications and provide our perspective on the critical research needs and opportunities to facilitate their adoption in the food industry.

Modulation of MG-63 Osteogenic Response on Mechano-Bactericidal Micronanostructured Titanium Surfaces

Despite recent advances in the development of orthopedic devices, implant-related failures that occur as a result of poor osseointegration and nosocomial infection are frequent. In this study, we developed a multiscale titanium (Ti) surface topography that promotes both osteogenic and mechano-bactericidal activity using a simple two-step fabrication approach. The response of MG-63 osteoblast-like cells and antibacterial activity toward Pseudomonas aeruginosa and Staphylococcus aureus bacteria was compared for two distinct micronanoarchitectures of differing surface roughness created by acid etching, using either hydrochloric acid (HCl) or sulfuric acid (H₂SO₄), followed by hydrothermal treatment, henceforth referred to as either MN-HCl or MN-H₂SO₄. The MN-HCl surfaces were characterized by an average surface microroughness (S_a) of 0.8 ± 0.1 μm covered by blade-like nanosheets of 10 ± 2.1 nm thickness, whereas the MN-H₂SO₄ surfaces exhibited a greater S_a value of 5.8 ± 0.6 μm, with a network of nanosheets of 20 ± 2.6 nm thickness. Both micronanostructured surfaces promoted enhanced MG-63 attachment and differentiation; however, cell proliferation was only significantly increased on MN-HCl surfaces. In addition, the MN-HCl surface exhibited increased levels of bactericidal activity, with only 0.6% of the P. aeruginosa cells and approximately 5% S. aureus cells remaining viable after 24 h when compared to control surfaces. Thus, we propose the modulation of surface roughness and architecture on the micro- and nanoscale to achieve efficient manipulation of osteogenic cell response combined with mechanical antibacterial activity. The outcomes of this study provide significant insight into the further development of advanced multifunctional orthopedic implant surfaces.

All-perfluoropolymer, nonlinear stability-assisted monolithic surface combines topology-specific superwettability with ultradurability

Developing versatile and robust surfaces that mimic the skins of living beings to regulate air/liquid/solid matter is critical for many bioinspired applications. Despite notable achievements, such as in the case of developing robust superhydrophobic surfaces, it remains elusive to realize simultaneously topology-specific superwettability and multipronged durability owing to their inherent tradeoff and the lack of a scalable fabrication method. Here, we present a largely unexplored strategy of preparing an all-perfluoropolymer (Teflon), nonlinear stability-assisted monolithic surface for efficient regulating matters. The key to achieving topology-specific superwettability and multilevel durability is the geometric-material mechanics design coupling superwettability stability and mechanical strength. The versatility of the surface is evidenced by its manufacturing feasibility, multiple-use modes (coating, membrane, and adhesive tape), long-term air trapping in 9-m-deep water, low-fouling droplet transportation, and self-cleaning of nanodirt. We also demonstrate its multilevel durability, including strong substrate adhesion, mechanical robustness, and chemical stability, all of which are needed for real-world applications.

Bioinspired MoS2 Nanosheet-Modified Carbon Fibers for Synergetic Bacterial Elimination and Wound Disinfection

Bacterial infection is one of the most frequent wound complications and has become a major public health concern. Increasing resistance to antibiotics has been noted with these agents broadly used in wound management. It is an urgent demand to develop alternative antibacterial strategies with a reduced chance of resistance. Herein, a Nepenthes-mimicking nanosheet array of MoS₂ on carbon fibers (CF-MoS₂ ) is proposed to achieve dual bactericidal activities. First, the sharp edges of synthesized surfaces are capable of inducing physical disruption of cell membranes, demonstrating mechanical antibacterial activity like their natural counterparts. Second, in the presence of near-infrared light, bioinspired CF-MoS₂ nanosheets are able to cause the death of damaged bacteria owing to their inherent photothermal properties. Such dual-functional modes endow the surfaces with nearly 100% killing efficiency for highly concentrated Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Furthermore, their potential to be applied as wound dressings for photothermal treatment of infectious wounds is also investigated in vivo. Bioinspired CF-MoS₂ dressings show advantages of synergistic disinfection and efficient promotion of wound regeneration. It is foreseen that this high-performance and multifunctional CF-MoS₂ could afford a feasible broad-spectrum treatment for non-antibiotic disinfection.

Finite Element Modelling of a Gram-Negative Bacterial Cell and Nanospike Array for Cell Rupture Mechanism Study

Inspired by nature, it is envisaged that a nanorough surface exhibits bactericidal properties by rupturing bacterial cells. In order to study the interaction mechanism between the cell membrane of a bacteria and a nanospike at the contact point, a finite element model was developed using the ABAQUS software package. The model, which saw a quarter of a gram-negative bacteria (Escherichia coli) cell membrane adhered to a 3 × 6 array of nanospikes, was validated by the published results, which show a reasonably good agreement with the model. The stress and strain development in the cell membrane was modeled and were observed to be spatially linear and temporally nonlinear. From the study, it was observed that the bacterial cell wall was deformed around the location of the nanospike tips as full contact was generated. Around the contact point, the principal stress reached above the critical stress leading to a creep deformation that is expected to cause cell rupture by penetrating the nanospike, and the mechanism is envisaged to be somewhat similar to that of a paper punching machine. The obtained results in this project can provide an insight on how bacterial cells of a specific species are deformed when they adhere to nanospikes, and how it is ruptured using this mechanism.

Mechanobactericidal Nanotopography on Nitrile Surfaces toward Antimicrobial Protective Gear

We have much to learn from other living organisms when it comes to engineering strategies to combat bacterial infections. This study describes the fabrication of cicada wing-inspired nanotopography on commercially pure (CP) nitrile sheets and nitrile gloves for medical use using the reactive ion etching (RIE) technique. Antibacterial activity against P. aeruginosa was tested using two different surface morphologies. It was observed that the etched nitrile surfaces effectively minimized bacterial colonization by inducing membrane damage. Our findings demonstrate a single-step dry etching method for creating mechanobactericidal topographies on nitrile-based surfaces. These findings have utility in designing next-generation personal protective gear in the clinical setting and for many other important applications in the age of antimicrobial resistance.

Recent advances in targeted antibacterial therapy basing on nanomaterials

Bacterial infection has become one of the leading causes of death worldwide, particularly in low-income countries. Despite the fact that antibiotics have provided successful management in bacterial infections, the long-term overconsumption and abuse of antibiotics has contributed to the emergence of multidrug resistant bacteria. To address this challenge, nanomaterials with intrinsic antibacterial properties or that serve as drug carriers have been substantially developed as an alternative to fight against bacterial infection. Systematically and deeply understanding the antibacterial mechanisms of nanomaterials is extremely important for designing new therapeutics. Recently, nanomaterials-mediated targeted bacteria depletion in either a passive or active manner is one of the most promising approaches for antibacterial treatment by increasing local concentration around bacterial cells to enhance inhibitory activity and reduce side effects. Passive targeting approach is widely explored by searching nanomaterial-based alternatives to antibiotics, while active targeting strategy relies on biomimetic or biomolecular surface feature that can selectively recognize targeted bacteria. In this review article, we summarize the recent developments in the field of targeted antibacterial therapy based on nanomaterials, which will promote more innovative thinking focusing on the treatment of multidrug-resistant bacteria.

A hybrid and scalable nanofabrication approach for bio-inspired bactericidal silicon nanospike surfaces

Insects and plants exhibit bactericidal properties through surface nanostructures, such as nanospikes, which physically kill bacteria without antibiotics or chemicals. This is a promising new avenue for achieving antibacterial surfaces. However, the existing methods for fabricating nanospikes are incapable of producing uniform nanostructures on a large scale and in a cost-effective manner. In this paper, a scalable nanofabrication method involving the application of nanosphere lithography and reactive ion etching for constructing nanospike surfaces is demonstrated. Low-cost silicon nanospikes with uniform spacing that were sized similarly to biological nanospikes on cicada wings with a 4-inch wafer scale were fabricated. The spacing, tip radius, and base diameter of the silicon nanospikes were controlled precisely by adjusting the nanosphere diameters, etching conditions, and diameter reduction. The bactericidal properties of the silicon nanospikes with 300 nm spacing were measured quantitatively using the standard viability plate count method; they killed E. coli cells with 59 % efficiency within 30 h. The antibacterial ability of the nanospike surface was further indicated by the morphological differences between bacteria observed in the scanning electron microscopic images as well as the live/dead stains of fluorescence signals. The fabrication process combined the advantages of both top-down and bottom-up methods and was a significant step toward affordable bio-inspired antibacterial surfaces.

Glasswing-Butterfly-Inspired Multifunctional Scleral Lens and Smartphone Raman Spectrometer for Point-of-Care Tear Biomarker Analysis

Augmenting contact lenses with sensing capabilities requires incorporating multiple functionalities within a diminutive device. Inspired by multifunctional biophotonic nanostructures of glasswing butterflies, a nanostructured scleral lens with enhanced optical, bactericidal, and sensing capabilities is reported. When used in conjunction with a smartphone-integrated Raman spectrometer, the feasibility of point-of-care applications is demonstrated. The bioinspired nanostructures made on parylene films are mounted on the anterior and posterior side of a scleral lens to create a nanostructured lens. Compared to unstructured parylene, nanostructured parylene minimizes glare by 4.3-fold at large viewing angles up to 80^o . When mounted on a scleral lens, the nanostructures block 2.8-fold more ultraviolet (UVA) light while offering 1.1-fold improved transmission in the visible regime. Furthermore, the nanostructures exhibit potent bactericidal activity against Escherichia coli, killing 89% of tested bacteria within 4 h. The same nanostructures, when gold-coated, are used to perform rapid label-free multiplex detection of lysozyme and lactoferrin, the protein biomarkers of the chronic dry eye disease, in whole human tears using drop-coating deposition Raman spectroscopy. The detection of both proteins in whole human tear samples from different subjects using the nanostructured lens produced excellent correlation with commercial enzyme-based assays while simultaneously displaying a 1.5-fold lower standard deviation.

Structure-Based Design of Dual Bactericidal and Bacteria-Releasing Nanosurfaces

Here, we report synergistic nanostructured surfaces combining bactericidal and bacteria-releasing properties. A polystyrene-block-poly(methyl methacrylate) (PS-block-PMMA) diblock copolymer is used to fabricate vertically oriented cylindrical PS structures ("PS nanopillars") on silicon substrates. The results demonstrate that the PS nanopillars (with a height of about 10 nm, size of about 50 nm, and spacing of about 70 nm) exhibit highly effective bactericidal and bacteria-releasing properties ("dual properties") against Escherichia coli for at least 36 h of immersion in an E. coli solution. Interestingly, the PS nanopillars coated with a thin layer (≈3 nm thick) of titanium oxide (TiO₂) ("TiO₂ nanopillars") show much improved dual properties against E. coli (a Gram-negative bacterium) compared to the PS nanopillars. Moreover, the dual properties emerge against Listeria monocytogenes (a Gram-positive bacterium). To understand the mechanisms underlying the multifaceted property of the nanopillars, coarse-grained molecular dynamics (MD) simulations of a lipid bilayer (as a simplified model for E. coli) in contact with a substrate containing hexagonally packed hydrophilic nanopillars were performed. The MD results demonstrate that when the bacterium-substrate interaction is strong, the lipid heads adsorb onto the nanopillar surfaces, conforming the shape of a lipid bilayer to the structure/curvature of nanopillars and generating high stress concentrations within the membrane (i.e., the driving force for rupture) at the edge of the nanopillars. Membrane rupture begins with the formation of pores between nanopillars (i.e., bactericidal activity) and ultimately leads to the membrane withdrawal from the nanopillar surface (i.e., bacteria-releasing activity). In the case of Gram-positive bacteria, the adhesion area to the pillar surface is limited due to the inherent stiffness of the bacteria, creating higher stress concentrations within a bacterial cell wall. The present study provides insight into the mechanism underlying the "adhesion-mediated" multifaceted property of nanosurfaces, which is crucial for the development of next-generation antibacterial surface coatings for relevant medical applications.

Antibacterial Nanostructured Surfaces Modulate Protein Adsorption, Inflammatory Responses, and Fibrous Capsule Formation

The present study interrogates the interaction of highly efficient antibacterial surfaces containing sharp nanostructures with blood proteins and the subsequent immunological consequences, processes that are of key importance for the fate of every implantable biomaterial. Studies with human serum and plasma pointed to significant differences in the composition of the protein corona that formed on control and nanostructured surfaces. Quantitative analysis using liquid chromatography-mass spectrometry demonstrated that the nanostructured surface attracted more vitronectin and less complement proteins compared to the untreated control. In turn, the protein corona composition modulated the adhesion and cytokine expression by immune cells. Monocytes produced lower amounts of pro-inflammatory cytokines and expressed more anti-inflammatory factors on the nanostructured surface. Studies using an in vivo subcutaneous mouse model showed reduced fibrous capsule thickness which could be a consequence of the attenuated inflammatory response. The results from this work suggest that antibacterial surface modification with sharp spike-like nanostructures may not only lead to the reduction of inflammation but also more favorable foreign body response and enhanced healing, processes that are beneficial for most medical devices implanted in patients.

Superhydrophobic Mechano-Bactericidal Surface with Photodynamic Antibacterial Capability

Bacterial invasion and proliferation on various surfaces pose a serious threat to public health worldwide. Conventional antibacterial strategies that mainly rely on bactericides exhibit high bacteria-killing efficiency but might trigger the well-known risk of antibiotic resistance. Here, we report a superhydrophobic mechano-bactericidal surface with photodynamically enhanced antibacterial capability. First, bioinspired nanopillars with polycarbonate as the bulk material were replicated from anodized alumina oxide templates via a simple hot-pressing molding method. Subsequently, a facile bovine serum albumin phase-transition method was used to introduce chlorin e6 onto the nanopillar-patterned surface, which was then perfluorinated to render the surface superhydrophobic. Benefiting from its strong liquid super-repellency and photodynamically enhanced mechano-bactericidal properties, the superhydrophobic nanopillar-patterned surface exhibits 100% antibacterial efficiency after 30 min visible light irradiation (650 nm, 20 mW cm^-2). More strikingly, the surface exhibited impressive long-lasting antimicrobial performance, maintaining a very high bactericidal efficiency (≥99%) even after 10 cycles of bacterial contamination tests. Also, the superhydrophobic nanopillar-patterned surface displays good hemocompatibility with a much lower than the 5% hemolysis rate. Overall, this work offers a new method for significantly enhancing the antibacterial efficiency of structural antimicrobial surfaces without involving any bactericidal agents, and this functional surface shows great potential in the field of advanced medical materials and hospital 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.

Bio-inspired antimicrobial surfaces fabricated by glancing angle deposition

This paper describes the fabrication of cicada-wing-inspired antimicrobial surfaces using Glancing Angle Deposition (GLAD). From the study of an annual cicada (Neotibicen Canicularis, also known as dog-day cicada) in North America, it is found that the cicada wing surfaces are composed of unique three-dimensional (3D) nanofeature arrays, which grant them extraordinary properties including antimicrobial (antifouling) and antireflective. However, the morphology of these 3D nanostructures imposes challenges in artificially synthesizing the structures by utilizing and scaling up the template area from nature. From the perspective of circumventing the difficulties of creating 3D nanofeature arrays with top-down nanofabrication techniques, this paper introduces a nanofabrication process that combines bottom-up steps: self-assembled nanospheres are used as the bases of the features, while sub-100 nm pillars are grown on top of the bases by GLAD. Scanning electron micrographs show the resemblance of the synthesized cicada wing mimicry samples to the actual cicada wings, both quantitatively and qualitatively. The synthetic mimicry samples are hydrophobic with a water contact angle of 125˚. Finally, the antimicrobial properties of the mimicries are validated by showing flat growth curves of Escherichia coli (E. coli) and by direct observation under scanning electron microscopy (SEM). The process is potentially suitable for large-area antimicrobial applications in food and biomedical industries.

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.

Advances in Research on Titanium and Titanium Alloys with Antibacterial Functionality for Medical Use—A Review

Materials based on titanium and its alloys are widely used in the medical and dental fields because of their excellent physical properties such as hardness, ductility and elastic modulus, etc. However, because commonly used titanium alloy internal plants do not have antibacterial properties, when these implants are implanted into the human body, there is a certain risk of infection. Such infections are extremely painful for the patient and problematic for the attending physician. In the past, infections of implants were usually treated with systemic antibiotics in combination with thorough debridement or implant replacement. However, these are passive treatments and typically cause huge physical and economic burdens on the patient. Therefore, attempts towards the development of implants with antibacterial functionality have been increasing, with the combination of titanium alloys with antibiotics, antibacterialmetals, and antibacterial peptides being the main research direction. Therefore, this paper will discuss the latest research progress in the preparation of titanium alloys with antibacterial strategies such as combining antibiotics or antimicrobial peptides, adding antimicrobial metals, and the antibacterial properties and biocompatibility of proposed systems are summarised and discussed herein. This review should serve as a reference for further research on antibacterial titanium alloy implants.

Fabrication of Antibacterial TiO2 Nanostructured Surfaces Using the Hydrothermal Method

Implant-associated infections (IAI) are a common cause for implant failure, increased medical costs, and critical for patient healthcare. Infections are a result of bacterial colonization, which leads to biofilm formation on the implant surface. Nanostructured surfaces have been shown to have the potential to inhibit bacterial adhesion mainly due to antibacterial efficacy of their unique surface nanotopography. The change in topography affects the physicochemical properties of their surface such as surface chemistry, morphology, wettability, surface charge, and even electric field which influences the biological response. In this study, a conventional and cost-effective hydrothermal method was used to fabricate nanoscale protrusions of various dimensions on the surface of Ti, Ti₆Al₄V, and NiTi materials, commonly used in biomedical applications. The morphology, surface chemistry, and wettability were analyzed using scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), and water contact angle analysis. The antibacterial efficacy of the synthesized nanostructures was analyzed by the use of Escherichia coli bacterial strain. XPS analysis revealed that the concentration of oxygen and titanium increased on Ti and Ti₆Al₄V, which indicates that TiO₂ is formed on the surface. The concentration of oxygen and titanium however decreased on the NiTi surface after hydrothermal treatment, and also a small amount of Ni was detected. SEM analysis showed that by hydrothermal treatment alterations in the surface topography of the TiO₂ layer could be achieved. The oxide layer on the NiTi prepared by the hydrothermal method contains a low amount of Ni (2.8 atom %), which is especially important for implantable materials. The results revealed that nanostructured surfaces significantly reduced bacterial adhesion on the Ti, Ti₆Al₄V, and NiTi surface compared to the untreated surfaces used as a control. Furthermore, two sterilization techniques were also studied to evaluate the stability of the nanostructure and its influence on the antibacterial activity. Sterilization with UV light seems to more efficiently inhibit bacterial growth on the hydrothermally modified Ti₆Al₄V surface, which was further reduced for hydrothermally treated Ti and NiTi. The developed nanostructured surfaces of Ti and its alloys can pave a way for the fabrication of antibacterial surfaces that reduce the likelihood of IAI.

Strategies to Mitigate and Treat Orthopaedic Device-Associated Infections

Orthopaedic device implants play a crucial role in restoring functionality to patients suffering from debilitating musculoskeletal diseases or to those who have experienced traumatic injury. However, the surgical implantation of these devices carries a risk of infection, which represents a significant burden for patients and healthcare providers. This review delineates the pathogenesis of orthopaedic implant infections and the challenges that arise due to biofilm formation and the implications for treatment. It focuses on research advancements in the development of next-generation orthopaedic medical devices to mitigate against implant-related infections. Key considerations impacting the development of devices, which must often perform multiple biological and mechanical roles, are delineated. We review technologies designed to exert spatial and temporal control over antimicrobial presentation and the use of antimicrobial surfaces with intrinsic antibacterial activity. A range of measures to control bio-interfacial interactions including approaches that modify implant surface chemistry or topography to reduce the capacity of bacteria to colonise the surface, form biofilms and cause infections at the device interface and surrounding tissues are also reviewed.

The Development of Technology to Prevent, Diagnose, and Manage Antimicrobial Resistance in Healthcare-Associated Infections

There is a growing risk of antimicrobial resistance (AMR) having an adverse effect on the healthcare system, which results in higher healthcare costs, failed treatments and a higher death rate. A quick diagnostic test that can spot infections resistant to antibiotics is essential for antimicrobial stewardship so physicians and other healthcare professionals can begin treatment as soon as possible. Since the development of antibiotics in the last two decades, traditional, standard antimicrobial treatments have failed to treat healthcare-associated infections (HAIs). These results have led to the development of a variety of cutting-edge alternative methods to combat multidrug-resistant pathogens in healthcare settings. Here, we provide an overview of AMR as well as the technologies being developed to prevent, diagnose, and control healthcare-associated infections (HAIs). As a result of better cleaning and hygiene practices, resistance to bacteria can be reduced, and new, quick, and accurate instruments for diagnosing HAIs must be developed. In addition, we need to explore new therapeutic approaches to combat diseases caused by resistant bacteria. In conclusion, current infection control technologies will be crucial to managing multidrug-resistant infections effectively. As a result of vaccination, antibiotic usage will decrease and new resistance mechanisms will not develop.

Toward the Scalable Fabrication of Fully Bio-Based Antimicrobial and UVB-Blocking Transparent Polylactic Acid Films That Incorporate Natural Coatings and Nanopatterns

Microbial transmissions via membrane surface and single-use plastic-induced pollution are two urgent societal problems. This research introduces a scalable fabrication strategy for fully biobased antibacterial and ultraviolet-B block polylactic acid (PLA) films integrating natural coatings and nanopatterns via ultrasonic atomization spray coating and thermal nanoimprinting lithography (TNIL) techniques, respectively. Tannic acid (TA) and gallic acid (GA) were formulated prior to TNIL using anode aluminum oxide template. Results reveal that TA and GA inks display intense adsorption in the UVB region. Plasma increases the hydrophilicity of PLA films for fast spreading of ink droplets. Micron-sized pillars observed on film confirm the successful structural replication. TA-coated PLA films display higher transparency than GA-coated ones. Nanopatterned PLA films have a modest antibacterial resistance of c. 45% against Escherichia coli. TA/GA coatings, however, impart PLA films with a bacterial reduction rate of over 80%. The integration of a TA or GA coating with nanopatterns further promotes the antibacterial rate up to 98%. The cytocompatibility of TA and GA demonstrates that the engineered film can potentially be applied as food packaging. Finally, a continuous mass production strategy is proposed along with an outline of the associated challenges and costs. This study provides a scalable strategy to the sustainable development of eco-benign and functional films.

Surface Texturing and Combinatorial Approaches to Improve Biocompatibility of Implanted Biomaterials

Biomaterial associated microbial infection and blood thrombosis are two of the barriers that inhibit the successful use of implantable medical devices in modern healthcare. Modification of surface topography is a promising approach to combat microbial infection and thrombosis without altering bulk material properties necessary for device function and without contributing to bacterial antibiotic resistance. Similarly, the use of other antimicrobial techniques such as grafting poly(ethylene glycol) (PEG) and nitric oxide (NO) release also improve the biocompatibility of biomaterials. In this review, we discuss the development of surface texturing techniques utilizing ordered submicron-size pillars for controlling bacterial adhesion and biofilm formation, and we present combinatorial approaches utilizing surface texturing in combination with poly(ethylene glycol) (PEG) grafting and NO release to improve the biocompatibility of biomaterials. The manuscript also discusses efforts towards understanding the molecular mechanisms of bacterial adhesion responses to the surface texturing and NO releasing biomaterials, focusing on experimental aspects of the approach.

Bio-Inspired Self-Adaptive Nanocomposite Array: From Non-antibiotic Antibacterial Actions to Cell Proliferation

Pathogenic bacterial infection and poor native tissue integration are two major issues encountered by biomaterial implants and devices, which are extremely hard to overcome within a single surface, especially for those without involvement of antibiotics. Herein, a self-adaptive surface that can transform from non-antibiotic antibacterial actions to promotion of cell proliferation is developed by in situ assembly of bacteriostatic 3,3'-diaminodipropylamine (DADP)-doped zeolitic imidazolate framework-8 (ZIF-8) on bio-inspired nanopillars. Initially, the nanocomposite surface shows impressive antibacterial effects, even under severe bacterial infection, due to the combination of mechano-bactericidal activity from a nanopillar structure and bacteriostatic activity contributed by pH-responsive release of DADP. After the complete degradation of the ZIF-8 layer, the refurbished nanopillars not only can still physically rupture bacterial membrane but also facilitate mammalian cell proliferation, due to the obvious difference in cell size. More strikingly, the nanocomposite surface totally avoids the usage of antibiotics, eradicating the potential risk of antimicrobial resistance, and the surface exhibited excellent histocompatibility and lower inflammatory response properties as revealed by in vivo tests. This type of self-adaptive surface may provide a promising alternative for addressing the intractable implant-associated requirements, where antibiotic-free antibacterial activity and native tissue integration are both highly needed.

Biology and nature: Bionic superhydrophobic surface and principle

Nature is the source of human design inspiration. In order to adapt to the environment better, creatures in nature have formed various morphological structures during billions of years of evolution, among which the superhydrophobic characteristics of some animal and plant surface structures have attracted wide attention. At present, the preparation methods of bionic superhydrophobic surface based on the microstructure of animal and plant body surface include vapor deposition, etching modification, sol-gel method, template method, electrostatic spinning method and electrostatic spraying method, etc., which have been used in medical care, military industry, shipping, textile and other fields. Based on nature, this paper expounds the development history of superhydrophobic principle, summarizes the structure and wettability of superhydrophobic surfaces in nature, and introduces the characteristics differences and applications of different superhydrophobic surfaces in detail. Finally, the challenge of bionic superhydrophobic surface is discussed, and the future development direction of this field is prospected.

Preventing Peri-implantitis: The Quest for a Next Generation of Titanium Dental Implants

Titanium and its alloys are frequently the biomaterial of choice for dental implant applications. Although titanium dental implants have been utilized for decades, there are yet unresolved issues pertaining to implant failure. Dental implant failure can arise either through wear and fatigue of the implant itself or peri-implant disease and subsequent host inflammation. In the present report, we provide a comprehensive review of titanium and its alloys in the context of dental implant material, and how surface properties influence the rate of bacterial colonization and peri-implant disease. Details are provided on the various periodontal pathogens implicated in peri-implantitis, their adhesive behavior, and how this relationship is governed by the implant surface properties. Issues of osteointegration and immunomodulation are also discussed in relation to titanium dental implants. Some impediments in the commercial translation for a novel titanium-based dental implant from "bench to bedside" are discussed. Numerous in vitro studies on novel materials, processing techniques, and methodologies performed on dental implants have been highlighted. The present report review that comprehensively compares the in vitro, in vivo, and clinical studies of titanium and its alloys for dental implants.

Death at the interface: Nanotechnology’s challenging frontier against microbial surface colonization

The emergence of antimicrobial-resistant bacterial strains has led to novel approaches for combating bacterial infections and surface contamination. More specifically, efforts in combining nanotechnology and biomimetics have led to the development of next-generation antimicrobial/antifouling nanomaterials. While nature-inspired nanoscale topographies are known for minimizing bacterial attachment through surface energy and physicochemical features, few studies have investigated the combined inhibitory effects of such features in combination with chemical alterations of these surfaces. Studies describing surface alterations, such as quaternary ammonium compounds (QACs), have also gained attention due to their broad spectrum of inhibitory activity against bacterial cells. Similarly, antimicrobial peptides (AMPs) have exhibited their capacity to reduce bacterial viability. To maximize the functionality of modified surfaces, the integration of patterned surfaces and functionalized exteriors, achieved through physical and chemical surface alterations, have recently been explored as viable alternatives. Nonetheless, these modifications are prone to challenges that can reduce their efficacy considerably in the long term. Their effectiveness against a wider array of microbial cells is still a subject of investigation. This review article will explore and discuss the emerging trends in biomimetics and other antimicrobials while raising possible concerns about their limitations and discussing future implications regarding their potential combined applications.

Early Antimicrobial Evaluation of Nanostructured Surfaces Based on Bacterial Biological Properties

Nanostructured physical antibacterial surfaces are of great interest due to the increasing antibiotic resistance. In this work, the titania nanotube (TNT) array, a potential physical antibacterial surface, was used for antimicrobial evaluation. The early antibacterial properties of TNTs were assessed based on three growth phases of Staphylococcus aureus (S. aureus), and the physical factors influencing the antibacterial properties were comprehensively discussed. The results show apparent early antibacterial effects of TNTs, including the anti-initial attachment during the lag phase, the inhibition of proliferation and bactericidal effect during the logarithmic phase, and the inhibition of biofilm formation during the stationary phase. These antimicrobial effects are closely related to the combined influence of various physical properties of TNTs, such as diameter, hydrophilicity, roughness, and charge. The present work suggests that the evaluation of the early antimicrobial behavior of biomaterials should pay more attention on the biological characteristics of bacteria.

Mechanobactericidal, Gold Nanostar Hydrogel-Based Bandage for Bacteria-Infected Skin Wound Healing

The emergence of multidrug resistant (MDR) microorganisms has led to the development of alternative approaches for providing relief from microbial attacks. The mechano-bactericidal action as a substitute for antimicrobials has become the focus of intensive research. In this work, nanostructure-conjugated hydrogel are explored as a flexible dressing against Staphylococcus aureus (S. aureus)-infected skin wounds. Herein gold nanostars (AuNst) with spike lengths reaching 120 nm are probed for antibacterial action. The bacterial killing of >95% is observed for Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli), while up to 60% for Gram-positive S. aureus. AuNst conjugated hydrogel (AuNst₁₂₀@H) reduced >80% colonies of P. aeruginosa and E. coli. In comparison, around 35.4% reduction of colonies are obtained for S. aureus. The viability assay confirmed the presence of about 85% of living NIH-3T3 cells when grown with hydrogels. An animal wound model is also developed to assess the efficiency of AuNst₁₂₀@H. A significant reduction in wound size is observed on the 10th day in AuNst₁₂₀@H treated animals with fully formed epidermal layers, hair follicles, new blood vessels, and arrector muscles. These findings suggest that novel dressing materials can be developed with antimicrobial nanotextured surfaces.

Antibacterial Adhesion Strategy for Dental Titanium Implant Surfaces: From Mechanisms to Application

Dental implants are widely used to restore missing teeth because of their stability and comfort characteristics. Peri-implant infection may lead to implant failure and other profound consequences. It is believed that peri-implantitis is closely related to the formation of biofilms, which are difficult to remove once formed. Therefore, endowing titanium implants with anti-adhesion properties is an effective method to prevent peri-implant infection. Moreover, anti-adhesion strategies for titanium implant surfaces are critical steps for resisting bacterial adherence. This article reviews the process of bacterial adhesion, the material properties that may affect the process, and the anti-adhesion strategies that have been proven effective and promising in practice. This article intends to be a reference for further improvement of the antibacterial adhesion strategy in clinical application and for related research on titanium implant surfaces.

Bioselectivity of silk protein-based materials and their bio-inspired applications

Adhesion to material surfaces is crucial for almost all organisms regarding subsequent biological responses. Mammalian cell attachment to a surrounding biological matrix is essential for maintaining their survival and function concerning tissue formation. Conversely, the adhesion and presence of microbes interferes with important multicellular processes of tissue development. Therefore, tailoring bioselective, biologically active, and multifunctional materials for biomedical applications is a modern focus of biomaterial research. Engineering biomaterials that stimulate and interact with cell receptors to support binding and subsequent physiological responses of multicellular systems attracted much interest in the last years. Further to this, the increasing threat of multidrug resistance of pathogens against antibiotics to human health urgently requires new material concepts for preventing microbial infestation and biofilm formation. Thus, materials exhibiting microbial repellence or antimicrobial behaviour to reduce inflammation, while selectively enhancing regeneration in host tissues are of utmost interest. In this context, protein-based materials are interesting candidates due to their natural origin, biological activity, and structural properties. Silk materials, in particular those made of spider silk proteins and their recombinant counterparts, are characterized by extraordinary properties including excellent biocompatibility, slow biodegradation, low immunogenicity, and non-toxicity, making them ideally suited for tissue engineering and biomedical applications. Furthermore, recombinant production technologies allow for application-specific modification to develop adjustable, bioactive materials. The present review focusses on biological processes and surface interactions involved in the bioselective adhesion of mammalian cells and repellence of microbes on protein-based material surfaces. In addition, it highlights the importance of materials made of recombinant spider silk proteins, focussing on the progress regarding bioselectivity.

Surfaces Containing Sharp Nanostructures Enhance Antibiotic Efficacy

The ever-increasing rate of medical device implantations is met by a proportionately high burden of implant-associated infections. To mitigate this threat, much research has been directed toward the development of antibacterial surface modifications by various means. One recent approach involves surfaces containing sharp nanostructures capable of killing bacteria upon contact. Herein, we report that the mechanical interaction between Staphylococcus aureus and such surface nanostructures leads to a sensitization of the pathogen to the glycopeptide antibiotic vancomycin. We demonstrate that this is due to cell wall damage and impeded bacterial defenses against reactive oxygen species. The results of this study promise to be impactful in the clinic, as a combination of nanostructured antibacterial surfaces and antibiotics commonly used in hospitals may improve antimicrobial therapy strategies, helping clinicians to prevent and treat implant-associated infections using reduced antibiotic concentrations instead of relying on invasive revision surgeries with often poor outcomes.

Dual-action silver functionalized nanostructured titanium against drug resistant bacterial and fungal species

HYPOTHESIS

Titanium and its alloys are commonly used implant materials. Once inserted into the body, the interface of the biomaterials is the most likely site for the development of implant-associated infections. Imparting the titanium substrate with high-aspect-ratio nanostructures, which can be uniformly achieved using hydrothermal etching, enables a mechanical contact-killing (mechanoresponsive) mechanism of bacterial and fungal cells. Interaction between cells and the surface shows cellular inactivation via a physical mechanism meaning that careful engineering of the interface is needed to optimse the technology. This mechanism of action is only effective towards surface adsorbed microbes, thus any cells not directly in contact with the substrate will survive and limit the antimicrobial efficacy of the titanium nanostructures. Therefore, we propose that a dual-action mechanoresponsive and chemical-surface approach must be utilised to improve antimicrobial activity. The addition of antimicrobial silver nanoparticles will provide a secondary, chemical mechanism to escalate the microbial response in tandem with the physical puncture of the cells.

EXPERIMENTS

Hydrothermal etching is used as a facile method to impart variant nanostrucutres on the titanium substrate to increase the antimicrobial response. Increasing concentrations (0.25 M, 0.50 M, 1.0 M, 2.0 M) of sodium hydroxide etching solution were used to provide differing degrees of nanostructured morphology on the surface after 3 h of heating at 150 °C. This produced titanium nanospikes, nanoblades, and nanowires, respectively, as a function of etchant concentration. These substrates then provided an interface for the deposition of silver nanoparticles via a reduction pathway. Methicillin-resistant Staphylococcous aureus (MRSA) and Candida auris (C. auris) were used as model bacteria and fungi, respectively, to test the effectiveness of the nanostructured titanium with and without silver nanoparticles, and the bio-interactions at the interface.

FINDINGS

The presence of nanostructure increased the bactericidal response of titanium against MRSA from ∼ 10 % on commercially pure titanium to a maximum of ∼ 60 % and increased the fungicidal response from ∼ 10 % to ∼ 70 % in C. auris. Introducing silver nanoparticles increased the microbiocidal response to ∼ 99 % towards both bacteria and fungi. Importantly, this study highlights that nanostructure alone is not sufficient to develop a highly antimicrobial titanium substrate. A dual-action, physical and chemical antimicrobial approach is better suited to produce highly effective antibacterial and antifungal surface technologies.

Liquid-Repellent Surfaces

Surfaces are vibrant sites for various activities with environments, especially as the transfer station for mass and energy exchange. In nature, natural creatures exhibit special wetting and interfacial properties such as water repellency and water affinity to adapt to various environmental challenges by taking advantage of air or liquid infusion media. Inspired by natural surfaces, various engineered liquid-repellent surfaces have been developed with a wide range of applications in both open and closed underwater environments. In particular, underwater conditions are characterized by high viscosity, high pressure, and complex compositions, which pose more challenges for the design of robust and functional repellent surfaces. In this Perspective, we take a parallel approach to introduce two classical liquid-repellent surfaces: an air-infused repellent surface and a lubricated liquid-repellent surface. Then we highlight fundamental challenges and design configurations of robust liquid-repellent surfaces both in air and underwater. We summarize the advantages and drawbacks of two kinds of repellent surfaces and list several applications of liquid-repellent surfaces for use in the ocean, medical care, and energy harvesting. Finally, we provide an outlook of research directions for robust liquid-repellent surfaces.