Cicada-inspired cell-instructive nanopatterned arrays

Photocatalytic and antibacterial activity properties of Ti surface treated by femtosecond laser-a prospective solution to peri-implant disease

Laser texturing seems to be a promising technique for reducing bacterial adhesion on titanium implant surfaces. This work aims to demonstrate the possibility of obtaining a functionally orientated surface of titanium implant elements with a specific architecture with specific bacteriological and photocatalytic properties. Femtosecond laser-generated surface structures, such as laser-induced periodic surface structures (LIPSS, wrinkles), grooves, and spikes on titanium, have been characterised by XRD, Raman spectroscopy, and scanning electron microscopy (SEM). The photocatalytic activity of the titanium surfaces produced was tested based on the degradation effect of methylene blue (MB). The correlation between the photocatalytic activity of TiO2 coatings and their morphology and structure has been analysed. Features related to the size, shape, and distribution of the roughness patterns were found to influence the adhesion of the bacterial strain on different surfaces. On the laser-structurised surface, the adhesion of Escherichia coli bacteria were reduced by 80% compared to an untreated reference surface.

Biofilm formation of Staphylococcus aureus on various implants used for surgical treatment of destructive spondylodiscitis

The incidence of spondylodiscitis has witnessed a significant increase in recent decades. Surgical intervention becomes necessary in case of bone destruction to remove infected tissue and restore spinal stability, often involving the implantation of a cage. Despite appropriate treatment, relapses occur in up to 20 percent of cases, resulting in substantial economic and social burdens. The formation of biofilm has been identified as a major contributor to relapse development. Currently, there is no consensus among German-speaking spinal surgeons or in the existing literature regarding the preferred choice of material to minimize relapse rates. Thus, the objective of this study is to investigate whether certain materials used in spinal implants exhibit varying degrees of susceptibility to bacterial attachment, thereby providing valuable insights for improving treatment outcomes.Eight cages of each PEEK, titanium-coated PEEK (Ti-PEEK), titanium (Ti), polyetherketoneketone (PEKK), tantalum (Ta) and antibiotic-loaded bone cement were incubated with 20% human plasma for 24 h. Subsequently, four implants were incubated with S. aureus for 24 h or 48 h each. The biofilm was then removed by sonication and the attained solution plated for Colony Forming Units (CFU) counting. Scanning electron microscopy was used to confirm bacterial attachment. The CFUs have been compared directly and in relation to the cages surface area. The surface area of the implants was PEEK 557 mm2, Ti-PEEK 472 mm2, Ti 985 mm2, PEKK 594 mm2, Ta 706 mm2, bone cement 123 mm2. The mean CFU count per implant and per mm2 surface area after 24 h and after 48 h was calculated. Bone cement was found to have significantly more CFUs per mm2 surface area than the other materials tested. When comparing the CFU count per implant, bone cement was statistically significantly more prone to biofilm formation than PEEK after 48 h. There was no statistical significance between the other materials when comparing both CFU count per mm2 surface area and CFU count per implant. The electron microscopic analysis showed the attachment of the bacteria, as well as production of extracellular polymeric substances (EPS) as a sign for beginning biofilm formation. Antibiotic-loaded bone cement has shown statistically significantly more bacterial attachment than the other examined materials. No difference was found between the other materials regarding bacterial attachment after 24 h and 48 h. Proposed hypotheses for further studies include testing whether differences become apparent after longer incubation or with different pathogens involved in the pathogenesis of pyogenic spondylodiscitis.

Nanotopography Influences Host-Pathogen Quorum Sensing and Facilitates Selection of Bioactive Metabolites in Mesenchymal Stromal Cells and Pseudomonas aeruginosa Co-Cultures

Orthopedic implant-related bacterial infections and resultant antibiotic-resistant biofilms hinder implant-tissue integration and failure. Biofilm quorum sensing (QS) communication determines the pathogen colonization success. However, it remains unclear how implant modifications and host cells are influenced by, or influence, QS. High aspect ratio nanotopographies have shown to reduce biofilm formation of Pseudomonas aeruginosa, a sepsis causing pathogen with well-defined QS molecules. Producing such nanotopographies in relevant orthopedic materials (i.e., titanium) allows for probing QS using mass spectrometry-based metabolomics. However, nanotopographies can reduce host cell adhesion and regeneration. Therefore, we developed a polymer (poly(ethyl acrylate), PEA) coating that organizes extracellular matrix proteins, promoting bioactivity to host cells such as human mesenchymal stromal cells (hMSCs), maintaining biofilm reduction. This allowed us to investigate how hMSCs, after winning the race for the surface against pathogenic cells, interact with the biofilm. Our approach revealed that nanotopographies reduced major virulence pathways, such as LasR. The enhanced hMSCs support provided by the coated nanotopographies was shown to suppress virulence pathways and biofilm formation. Finally, we selected bioactive metabolites and demonstrated that these could be used as adjuncts to the nanostructured surfaces to reduce biofilm formation and enhance hMSC activity. These surfaces make excellent models to study hMSC-pathogen interactions and could be envisaged for use in novel orthopedic implants.

Optimizing alkaline hydrothermal treatment for biomimetic smart metallic orthopedic and dental implants

Orthopedic and dental implant failure continues to be a significant concern due to localized bacterial infections. Previous studies have attempted to improve implant surfaces by modifying their texture and roughness or coating them with antibiotics to enhance antibacterial properties for implant longevity. However, these approaches have demonstrated limited effectiveness. In this study, we attempted to engineer the titanium (Ti) alloy surface biomimetically at the nanometer scale, inspired by the cicada wing nanostructure using alkaline hydrothermal treatment (AHT) to simultaneously confer antibacterial properties and support the adhesion and proliferation of mammalian cells. The two modified Ti surfaces were developed using a 4 h and 8 h AHT process in 1 N NaOH at 230 °C, followed by a 2-hour post-calcination at 600 °C. We found that the control plates showed a relatively smooth surface, while the treatment groups (4 h & 8 h AHT) displayed nanoflower structures containing randomly distributed nano-spikes. The results demonstrated a statistically significant decrease in the contact angle of the treatment groups, which increased wettability characteristics. The 8 h AHT group exhibited the highest wettability and significant increase in roughness 0.72 ± 0.08 µm (P < 0.05), leading to more osteoblast cell attachment, reduced cytotoxicity effects, and enhanced relative survivability. The alkaline phosphatase activity measured in all different groups indicated that the 8 h AHT group exhibited the highest activity, suggesting that the surface roughness and wettability of the treatment groups may have facilitated cell adhesion and attachment and subsequently increased secretion of extracellular matrix. Overall, the findings indicate that biomimetic nanotextured surfaces created by the AHT process have the potential to be translated as implant coatings to enhance bone regeneration and implant integration.

A Multifunctional Scaffold for Bone Infection Treatment by Delivery of microRNA Therapeutics Combined With Antimicrobial Nanoparticles

Treating bone infections and ensuring bone repair is one of the greatest global challenges of modern orthopedics, made complex by antimicrobial resistance (AMR) risks due to long-term antibiotic treatment and debilitating large bone defects following infected tissue removal. An ideal multi-faceted solution would will eradicate bacterial infection without long-term antibiotic use, simultaneously stimulating osteogenesis and angiogenesis. Here, a multifunctional collagen-based scaffold that addresses these needs by leveraging the potential of antibiotic-free antimicrobial nanoparticles (copper-doped bioactive glass, CuBG) to combat infection without contributing to AMR in conjunction with microRNA-based gene therapy (utilizing an inhibitor of microRNA-138) to stimulate both osteogenesis and angiogenesis, is developed. CuBG scaffolds reduce the attachment of gram-positive bacteria by over 80%, showcasing antimicrobial functionality. The antagomiR-138 nanoparticles induce osteogenesis of human mesenchymal stem cells in vitro and heal a large load-bearing defect in a rat femur when delivered on the scaffold. Combining both promising technologies results in a multifunctional antagomiR-138-activated CuBG scaffold inducing hMSC-mediated osteogenesis and stimulating vasculogenesis in an in vivo chick chorioallantoic membrane model. Overall, this multifunctional scaffold catalyzes killing mechanisms in bacteria while inducing bone repair through osteogenic and angiogenic coupling, making this platform a promising multi-functional strategy for treating and repairing complex bone infections.

Reusable mechano-bactericidal surface with echinoid-shaped hierarchical micro/nano-structure

Biofilms formed owing to the attachment of bacteria to surfaces have caused various problems in industries such as marine transportation/logistics and medicine. In response, many studies have been conducted on bactericidal surfaces, and nanostructured surfaces mimicking cicada and dragonfly wings are emerging as candidates for mechano-bactericidal surfaces. In specific circumstances involving mechano-bactericidal activity, certain nanostructured surfaces could exhibit their bactericidal effects by directly deforming the membranes of bacteria that adhere to these nanostructures. Additionally, in most cases, debris of bacterial cells may accumulate on these nanostructured surfaces. Such accumulation poses a significant challenge: it diminishes the mechano-bactericidal effectiveness of the surface, as it hinders the direct interaction between the nanostructures and any new bacteria that attach subsequently. In specific circumstances involving mechano-bactericidal activity, certain nanostructured surfaces could exhibit their bactericidal effects by directly deforming the membranes of bacteria that adhere to these nanostructures. Additionally, in most cases, debris of bacterial cells may accumulate on these nanostructured surfaces. Such accumulation poses a significant challenge: it diminishes the mechano-bactericidal effectiveness of the surface, as it hinders the direct interaction between the nanostructures and any new bacteria that attach subsequently.In other words, there is a need for strategies to remove the accumulated bacterial debris in order to sustain the mechano-bactericidal effect of the nanostructured surface. In this study, hierarchical micro/nano-structured surface (echinoid-shaped nanotextures were formed on Al micro-particle's surfaces) was fabricated using a simple pressure-less sintering method, and effective bactericidal efficiency was shown against E. coli (97 ± 3.81%) and S. aureus (80 ± 9.34%). In addition, thermal cleaning at 500 °C effectively eliminated accumulated dead bacterial debris while maintaining the intact Al2O3 nanostructure, resulting in significant mechano-bactericidal activity (E. coli: 89 ± 6.86%, S. aureus: 75 ± 8.31%). As a result, thermal cleaning maintains the intact nanostructure and allows the continuance of the mechano-bactericidal effect. This effect was consistently maintained even after five repetitive use (E. coli: 80 ± 16.26%, S. aureus: 76 ± 12.67%).

Preferential adhesion of bacterial cells onto top- and bottom-mounted nanostructured surfaces under flow conditions

The bactericidal effect of biomimetic nanostructured surfaces has been known for a long time, with recent data suggesting an enhanced efficiency of the nanostructured surfaces under fluid shear. While some of the influential factors on the bactericidal effect of nanostructured surfaces under fluid shear are understood, there are numerous important factors yet to be studied, which is essential for the successful implementation of this technology in industrial applications. Among those influential factors, the orientation of the nanostructured surface can play an important role in bacterial cell adhesion onto surfaces. Gravitational effects can become dominant under low flow velocities, making the diffusive transport of bacterial cells more prominent than the advective transport. However, the role of nanostructure orientation in determining its bactericidal efficiency under flow conditions is still not clear. In this study, we analysed the effect of surface orientation of nanostructured surfaces, along with bacterial cell concentration, fluid flow rate, and the duration of time which the surface is exposed to flow, on bacterial adhesion and viability on these surfaces. Two surface orientations, with one on the top and the other on the bottom of a flow channel, were studied. Under flow conditions, the bactericidal efficacy of the nanostructured surface is both orientation and bacterial species dependent. The effects of cell concentration, fluid flow rate, and exposure time on cell adhesion are independent of the nanostructured surface orientation. Fluid shear showed a species-dependent effect on bacterial adhesion, while the effects of concentration and exposure time on bacterial cell adhesion are independent of the bacterial species. Moreover, bacterial cells demonstrate preferential adhesion onto surfaces based on the surface orientation, and these effects are species dependent. These results outline the capabilities and limitations of nanostructures under flow conditions. This provides valuable insights into the applications of nanostructures in medical or industrial sectors, which are associated with overlaying fluid flow.

Surface antibacterial properties enhanced through engineered textures and surface roughness: A review

The spread of bacteria through contaminated surfaces is a major issue in healthcare, food industry, and other economic sectors. The widespread use of antibiotics is not a sustainable solution in the long term due to the development of antibiotic resistance. Therefore, surfaces with antibacterial properties have the potential to be a disruptive approach to combat microbial contamination. Different methods and approaches have been studied to impart or enhance antibacterial properties on surfaces. The surface roughness and texture are inherent parameters that significantly impact the antibacterial properties of a surface. They are also directly related to the previously employed machining and treatment methods. This review article discusses the correlation between surface roughness and antibacterial properties is presented and discussed. It begins with an introduction to the concepts of surface roughness and texture, followed by a description of the most commonly utilized machining methods and surface. A thorough analysis of bacterial adhesion and growth is then presented. Finally, the most recent studies in this research area are comprehensively reviewed. The studies are sorted and classified based on the utilized machining and treatment methods, which are divided into mechanical processes, surface treatments and coatings. Through the systematic review and record of the recent advances, the authors aim to assist and promote further research in this very promising and extremely important direction, by providing a systematic review of recent advances.

Black silicon spacing effect on bactericidal efficacy against gram-positive bacteria

The morphology of regular and uniform arrays of black silicon structures was evaluated for bactericidal efficacy against gram-positive, non-motileStaphylococcusepidermidis(S.epidermidis). In this study, uniform and regular arrays of black silicon structures were fabricated using nanosphere lithography and deep reactive ion etching. The effects of nanomorphology on bacterial killing were systematically evaluated using silicon nanostructures with pitches ranging from 300 to 1400 nm pitch on spherical cocci approximately 500 to 1000 nm in diameter. Our results show that nanostructure morphology factors such as height and roughness do not directly determine bactericidal efficacy. Instead, the spacing between nanostructures plays a crucial role in determining how bacteria are stretched and lysed. Nanostructures with smaller pitches are more effective at killing bacteria, and an 82 ± 3% enhancement in bactericidal efficacy was observed for 300 nm pitch nanoneedles surface compared to the flat control substrates.

Progress in Nanostructured Mechano-Bactericidal Polymeric Surfaces for Biomedical Applications

Bacterial infections and antibiotic resistance remain significant contributors to morbidity and mortality worldwide. Despite recent advances in biomedical research, a substantial number of medical devices and implants continue to be plagued by bacterial colonisation, resulting in severe consequences, including fatalities. The development of nanostructured surfaces with mechano-bactericidal properties has emerged as a promising solution to this problem. These surfaces employ a mechanical rupturing mechanism to lyse bacterial cells, effectively halting subsequent biofilm formation on various materials and, ultimately, thwarting bacterial infections. This review delves into the prevailing research progress within the realm of nanostructured mechano-bactericidal polymeric surfaces. It also investigates the diverse fabrication methods for developing nanostructured polymeric surfaces with mechano-bactericidal properties. We then discuss the significant challenges associated with each approach and identify research gaps that warrant exploration in future studies, emphasizing the potential for polymeric implants to leverage their distinct physical, chemical, and mechanical properties over traditional materials like metals.

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.

A High-Performance Antibacterial Nanostructured ZnO Microfluidic Device for Controlled Bacterial Lysis and DNA Release

In this work, the antibacterial properties of nanostructured zinc oxide (ZnO) surfaces are explored by incorporating them as walls in a simple-to-fabricate microchannel device. Bacterial cell lysis is demonstrated and quantified in such a device, which functions due to the action of its nanostructured ZnO surfaces in contact with the working fluid. To shed light on the mechanism responsible for lysis, E. coli bacteria were incubated in zinc and nanostructured ZnO substrates, as well as the here-investigated ZnO-based microfluidic devices. The unprecedented killing efficiency of E. coli in nanostructured ZnO microchannels, effective after a 15 min incubation, paves the way for the implementation of such microfluidic chips in the disinfection of bacteria-containing solutions. In addition, the DNA release was confirmed by off-chip PCR and UV absorption measurements. The results indicate that the present nanostructured ZnO-based microfluidic chip can, under light, achieve partial inactivation of the released bacterial DNA via reactive oxygen species-mediated oxidative damage. The present device concept can find broader applications in cases where the presence of DNA in a sample is not desirable. Furthermore, the present microchannel device enables, in the dark, efficient release of bacterial DNA for downstream genomic DNA analysis. The demonstrated potential of this antibacterial device for tailored dual functionality in light/dark conditions is the main novel contribution of the present work.

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.

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.

Enhanced and Stem-Cell-Compatible Effects of Nature-Inspired Antimicrobial Nanotopography and Antimicrobial Peptides to Combat Implant-Associated Infection

Nature-inspired antimicrobial surfaces and antimicrobial peptides (AMPs) have emerged as promising strategies to combat implant-associated infections. In this study, a bioinspired antimicrobial peptide was functionalized onto a nanospike (NS) surface by physical adsorption with the aim that its gradual release into the local environment would enhance inhibition of bacterial growth. Peptide adsorbed on a control flat surface exhibited different release kinetics compared to the nanotopography, but both surfaces showed excellent antibacterial properties. Functionalization with peptide at micromolar concentrations inhibited Escherichia coli growth on the flat surface, Staphylococcus aureus growth on the NS surface, and Staphylococcus epidermidis growth on both the flat and NS surfaces. Based on these data, we propose an enhanced antibacterial mechanism whereby AMPs can render bacterial cell membranes more susceptible to nanospikes, and the membrane deformation induced by nanospikes can increase the surface area for AMPs membrane insertion. Combined, these effects enhance bactericidal activity. Since functionalized nanostructures are highly biocompatible with stem cells, they make promising candidates for next generation antibacterial implant 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.

Atmospheric Pressure Plasma Polymerisation of D-Limonene and Its Antimicrobial Activity

Antibacterial coating is necessary to prevent biofilm-forming bacteria from colonising medical tools causing infection and sepsis in patients. The recent coating strategies such as immobilisation of antimicrobial materials and low-pressure plasma polymerisation may require multiple processing steps involving a high-vacuum system and time-consuming process. Some of those have limited efficacy and durability. Here, we report a rapid and one-step atmospheric pressure plasma polymerisation (APPP) of D-limonene to produce nano-thin films with hydrophobic-like properties for antibacterial applications. The influence of plasma polymerisation time on the thickness, surface characteristic, and chemical composition of the plasma-polymerised films was systematically investigated. Results showed that the nano-thin films deposited at 1 min on glass substrate are optically transparent and homogenous, with a thickness of 44.3 ± 4.8 nm, a smooth surface with an average roughness of 0.23 ± 0.02 nm. For its antimicrobial activity, the biofilm assay evaluation revealed a significant 94% decrease in the number of Escherichia coli (E. coli) compared to the control sample. More importantly, the resultant nano-thin films exhibited a potent bactericidal effect that can distort and rupture the membrane of the treated bacteria. These findings provide important insights into the development of bacteria-resistant and biocompatible coatings on the arbitrary substrate in a straightforward and cost-effective route at atmospheric pressure.

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.

Bactericidal Efficacy of Nanostructured Surfaces Increases under Flow Conditions

Bacterial colonization on solid surfaces creates enormous problems across various industries causing billions of dollars' worth of economic damages and costing human lives. Biomimicking nanostructured surfaces have demonstrated a promising future in mitigating bacterial colonization and related issues. The importance of this non-chemical method has been elevated due to bacterial evolvement into antibiotic and antiseptic-resistant strains. However, bacterial attachment and viability on nanostructured surfaces under fluid flow conditions has not been investigated thoroughly. In this study, attachment and viability of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) on a model nanostructured surface were studied under fluid flow conditions. A wide range of flow rates resulting in a broad spectrum of fluid wall shear stress on a nanostructured surface representing various application conditions were experimentally investigated. The bacterial suspension was pumped through a custom-designed microfluidic device (MFD) that contains a sterile Ti-6Al-4V substrate. The surface of the titanium substrate was modified using a hydrothermal synthesis process to fabricate the nanowire structure on the surface. The results of the current study show that the fluid flow significantly reduces bacterial adhesion onto nanostructured surfaces and significantly reduces the viability of adherent cells. Interestingly, the bactericidal efficacy of the nanostructured surface was increased under the flow by ∼1.5-fold against P. aeruginosa and ∼3-fold against S. aureus under static conditions. The bactericidal efficacy had no dependency on the fluid wall shear stress level. However, trends in the dead-cell count with the fluid wall shear were slightly different between the two species. These findings will be highly useful in developing and optimizing nanostructures in the laboratory as well as translating them into successful industrial applications. These findings may be used to develop antibacterial surfaces on biomedical equipment such as catheters and vascular stents or industrial applications such as ship hulls and pipelines where bacterial colonization is a great challenge.

Antibacterial nanopatterned coatings for dental implants

Dental implants, usually made of titanium, are exposed to hostile oral microflora that facilitate bacterial infections and subsequent inflammation. To mitigate these processes, we coated titanium substrates with block copolymer nanopatterns and investigated the bactericidal effect of these coatings against Gram-positive and Gram-negative bacteria. We found that the bactericidal efficacy of the coatings depends on their morphology and surface chemistry as well as on the bacterial strain: an optimal combination can lead to significant bacterial death for a short time, i.e. 90% for 90 min. Human gingival fibroblasts in contact with the nanopatterned coatings showed similar cell attachment and morphology as on bare Ti. Immunostaining assays showed similar levels of CCR7 and CD206 in macrophages cultured over the nanopatterns and bare Ti, demonstrating adequate properties for tissue integration. The nanopatterns induced a small increase in macrophage aspect ratio, which might indicate early states of M2 polarization, given the absence of CD206.

Microbial Response to Micrometer-Scale Multiaxial Wrinkled Surfaces

We investigate the effect of micrometer-scale surface wrinkling on the attachment and proliferation of model bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli K12) and fungi (Candida albicans). Specifically, sinusoidal (1D), checkerboard (C), and herringbone (H) patterns were fabricated by mechanical wrinkling of plasma-oxidized polydimethylsiloxane (PDMS) bilayers and contrasted with flat (F) surfaces. Microbial deformation and orientation were found to correlate with the aspect ratio and commensurably with surface pattern dimensions and local pattern order. Significantly, the proliferation of P. aeruginosa could be described by a linear scaling between bacterial area coverage and available surface area, defined as a fraction of the line integral along each profile with negative curvature. However, in the early stages of proliferation (up to 6 h examined), that C and H patterns disrupt the spatial arrangement of bacteria, impeding proliferation for several hours and reducing it (by ∼50%) thereafter. Our findings suggest a simple framework to rationalize the impact of micrometer-scale topography on microbial action and demonstrate that multiaxial patterning order provides an effective strategy to delay and frustrate the early stages of bacterial proliferation.

Carbonized lotus leaf/ZnO/Au for enhanced synergistic mechanical and photocatalytic bactericidal activity under visible light irradiation

Nowadays, bacterial resistance has continued to be a troublesome issue caused by the abuse of antibiotics, and it is the paramount difficulty in resolving the bacterial proliferation and infection. In this study, fresh lotus leaf was treated with Zn²⁺ followed by sintered and modification with gold nanoparticles through the photoreduction process sequentially, and thus a composite of micro/nanostructured carbonized lotus leaf/ZnO/Au (C-LL/ZnO/Au) was obtained to explore its bactericidal properties. C-LL/ZnO/Au retained the papillary structure of fresh lotus leaf and showed great mechanical bactericidal performance and photocatalytic sterilization. The antibacterial rate of mechanical sterilization for C-LL/ZnO/Au amount to 79.5% in 30 min, 4.7 times of fresh lotus leaf's figure under the same conditions. Furthermore, in C-LL/ZnO/Au, the introduction of gold nanoparticles heightened light absorbance through localized surface plasmon resonance (LSPR) effect and separation efficiency of photogenerated electron-hole pairs, which showed improved photocatalytic sterilization than that of carbonized lotus leaf/ZnO (C-LL/ZnO). Carbonized lotus leaf/ZnO/Au exhibited prominent photocatalytic and mechanical synergistic antibacterial performance against E. coli: all the bacteria were inactivated within 30 min under visible light. The approach presented here could be applied to a variety of biomass materials, which holds a promising application potential in biomedical, public health and other fields.

Advances and Perspective on Antimicrobial Nanomaterials for Biomedical Applications

Microbial infection and antibiotic resistance is recognized as a serious problem to society from both an economical perspective and a health concern. To tackle this problem, “nanotechnology,” a multidisciplinary field of research, has provided a plethora of nanomaterials for potential applications in the antimicrobial sector. This letter discusses how antimicrobial nanomaterials are shaping this challenging field and being evaluated as therapeutic and medication delivery agents. The recently designed smart antimicrobial surfaces with switchable features that displayed synergistic antibacterial action were also highlighted. To end, we provide the current scenario and future perspectives with regards to emerging antimicrobial nano-engineered materials and nanotechnology.

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

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

Role of Implantable Drug Delivery Devices with Dual Platform Capabilities in the Prevention and Treatment of Bacterial Osteomyelitis

As medicine advances and physicians are able to provide patients with innovative solutions, including placement of temporary or permanent medical devices that drastically improve quality of life of the patient, there is the persistent, recurring problem of chronic bacterial infection, including osteomyelitis. Osteomyelitis can manifest as a result of traumatic or contaminated wounds or implant-associated infections. This bacterial infection can persist as a result of inadequate treatment regimens or the presence of biofilm on implanted medical devices. One strategy to mitigate these concerns is the use of implantable medical devices that simultaneously act as local drug delivery devices (DDDs). This classification of device has the potential to prevent or aid in clearing chronic bacterial infection by delivering effective doses of antibiotics to the area of interest and can be engineered to simultaneously aid in tissue regeneration. This review will provide a background on bacterial infection and current therapies as well as current and prospective implantable DDDs, with a particular emphasis on local DDDs to combat bacterial osteomyelitis.

Recent Advances in Metal-Based Antimicrobial Coatings for High-Touch Surfaces

International interest in metal-based antimicrobial coatings to control the spread of bacteria, fungi, and viruses via high contact human touch surfaces are growing at an exponential rate. This interest recently reached an all-time high with the outbreak of the deadly COVID-19 disease, which has already claimed the lives of more than 5 million people worldwide. This global pandemic has highlighted the major role that antimicrobial coatings can play in controlling the spread of deadly viruses such as SARS-CoV-2 and scientists and engineers are now working harder than ever to develop the next generation of antimicrobial materials. This article begins with a review of three discrete microorganism-killing phenomena of contact-killing surfaces, nanoprotrusions, and superhydrophobic surfaces. The antimicrobial properties of metals such as copper (Cu), silver (Ag), and zinc (Zn) are reviewed along with the effects of combining them with titanium dioxide (TiO2) to create a binary or ternary contact-killing surface coatings. The self-cleaning and bacterial resistance of purely structural superhydrophobic surfaces and the potential of physical surface nanoprotrusions to damage microbial cells are then considered. The article then gives a detailed discussion on recent advances in attempting to combine these individual phenomena to create super-antimicrobial metal-based coatings with binary or ternary killing potential against a broad range of microorganisms, including SARS-CoV-2, for high-touch surface applications such as hand rails, door plates, and water fittings on public transport and in healthcare, care home and leisure settings as well as personal protective equipment commonly used in hospitals and in the current COVID-19 pandemic.

Mechano-bactericidal anisotropic particles for oral biofilm treatment

Bacterial biofilms stand for the main etiological factor of dental diseases worldwide. At present, toothpaste with bactericidal chemicals as well as abrasive materials are used as preventive care. However, chemicals...

In Vivo Antibacterial Efficacy of Nanopatterns on Titanium Implant Surface: A Systematic Review of the Literature

Background: Bionic surface nanopatterns of titanium (Ti) materials have excellent antibacterial effects in vitro for infection prevention. To date, there is a lack of knowledge about the in vivo bactericidal outcomes of the nanostructures on the Ti implant surfaces. Methods: A systematic review was performed using the PubMed, Embase, and Cochrane databases to better understand surface nanoscale patterns’ in vivo antibacterial efficacy. The inclusion criteria were preclinical studies (in vivo) reporting the antibacterial activity of nanopatterns on Ti implant surface. Ex vivo studies, studies not evaluating the antibacterial activity of nanopatterns or surfaces not modified with nanopatterns were excluded. Results: A total of five peer-reviewed articles met the inclusion criteria. The included studies suggest that the in vivo antibacterial efficacy of the nanopatterns on Ti implants’ surfaces seems poor. Conclusions: Given the small number of literature results, the variability in experimental designs, and the lack of reporting across studies, concluding the in vivo antibacterial effectiveness of nanopatterns on Ti substrates’ surfaces remains a big challenge. Surface coatings using metallic or antibiotic elements are still practical approaches for this purpose. High-quality preclinical data are still needed to investigate the in vivo antibacterial effects of the nanopatterns on the implant surface.

Effect of a Nanostructured Titanium Surface on Gingival Cell Adhesion, Viability and Properties against P. gingivalis

OBJECTIVES

The transgingival part of titanium implants is either machined or polished. Cell-surface interactions as a result of nano-modified surfaces could help gingival fibroblast adhesion and support antibacterial properties by means of the physico-mechanical aspects of the surfaces. The aim of the present study was to determine how a nanocavity titanium surface affects the viability and adhesion of human gingival fibroblasts (HGF-1). Additionally, its properties against Porphyromonas gingivalis were tested.

MATERIAL AND METHODS

Two different specimens were evaluated: commercially available machined titanium discs (MD) and nanostructured discs (ND). To obtain ND, machined titanium discs with a diameter of 15 mm were etched with a 1:1 mixture of 98% H₂SO₄ and 30% H₂O₂ (piranha etching) for 5 h at room temperature. Surface topography characterization was performed via scanning electron microscopy (SEM) and atomic force microscopy (AFM). Samples were exposed to HGF-1 to assess the effect on cell viability and adhesion, which were compared between the two groups by means of MTT assay, immunofluorescence and flow cytometry. After incubation with P. gingivalis, antibacterial properties of MD and ND were determined by conventional culturing, live/dead staining and SEM. Results: The present study successfully created a nanostructured surface on commercially available machined titanium discs. The etching process created cavities with a 10-20 nm edge-to-edge diameter. MD and ND show similar adhesion forces equal to about 10-30 nN. The achieved nanostructuration reduced the cell alignment along machining structures and did not negatively affect the proliferation of gingival fibroblasts when compared to MD. No differences in the expression levels of both actin and vinculin proteins, after incubation on MD or ND, were observed. However, the novel ND surface failed to show antibacterial effects against P. gingivalis.

CONCLUSION

Antibacterial effects against P. gingivalis cannot be achieved with nanocavities within a range of 10-20 nm and based on the piranha etching procedure. The proliferation of HGF-1 and the expression levels and localization of the structural proteins actin and vinculin were not influenced by the surface nanostructuration. Further studies on the strength of the gingival cell adhesion should be performed in the future.

CLINICAL RELEVANCE

Since osseointegration is well investigated, mucointegration is an important part of future research and developments. Little is known about how nanostructures on the machined transgingival part of an implant could possibly influence the surrounding tissue. Targeting titanium surfaces with improved antimicrobial properties requires extensive preclinical basic research to gain clinical relevance.

Recent advances in the local antibiotics delivery systems for management of osteomyelitis

Chronic osteomyelitis is a challenging disease due to its serious rates of mortality and morbidity while the currently available treatment strategies are suboptimal. In contrast to the adopted systemic treatment approaches after surgical debridement in chronic osteomyelitis, local drug delivery systems are receiving great attention in the recent decades. Local drug delivery systems using special carriers have the pros of enhancing the feasibility of penetration of antimicrobial agents to bone tissues, providing sustained release and localized concentrations of the antimicrobial agents in the infected area while avoiding the systemic side effects and toxicity. Most important, the incorporation of osteoinductive and osteoconductive materials in these systems assists bones proliferation and differentiation, hence the generation of new bone materials is enhanced. Some of these systems can also provide mechanical support for the long bones during the healing process. Most important, if the local systems are designed to be injectable to the affected site and biodegradable, they will reduce the level of invasion required for implantation and can win the patients’ compliance and reduce the healing period. They will also allow multiple injections during the course of therapy to guard against the side effect of the long-term systemic therapy. The current review presents different available approaches for delivering antimicrobial agents for the treatment of osteomyelitis focusing on the recent advances in researches for local delivery of antibiotics.

HIGHLIGHTS

Chronic osteomyelitis is a challenging disease due to its serious mortality and morbidity rates and limited effective treatment options.

Local drug delivery systems are receiving great attention in the recent decades.

Osteoinductive and osteoconductive materials in the local systems assists bones proliferation and differentiation

Local systems can be designed to provide mechanical support for the long bones during the healing process.

Designing the local system to be injectable to the affected site and biodegradable will reduces the level of invasion and win the patients’ compliance.

Spatial Period of Laser-Induced Surface Nanoripples on PET Determines Escherichia coli Repellence

Bacterial adhesion and biofilm formation on surfaces are associated with persistent microbial contamination, biofouling, and the emergence of resistance, thus, calling for new strategies to impede bacterial surface colonization. Using ns-UV laser treatment (wavelength 248 nm and a pulse duration of 20 ns), laser-induced periodic surface structures (LIPSS) featuring different sub-micrometric periods ranging from ~210 to ~610 nm were processed on commercial poly(ethylene terephthalate) (PET) foils. Bacterial adhesion tests revealed that these nanorippled surfaces exhibit a repellence for E. coli that decisively depends on the spatial periods of the LIPSS with the strongest reduction (~91%) in cell adhesion observed for LIPSS periods of 214 nm. Although chemical and structural analyses indicated a moderate laser-induced surface oxidation, a significant influence on the bacterial adhesion was ruled out. Scanning electron microscopy and additional biofilm studies using a pili-deficient E. coli TG1 strain revealed the role of extracellular appendages in the bacterial repellence observed here.

Carbon Nanomaterials Modified Biomimetic Dental Implants for Diabetic Patients

Dental implants are used broadly in dental clinics as the most natural-looking restoration option for replacing missing or highly diseased teeth. However, dental implant failure is a crucial issue for diabetic patients in need of dentition restoration, particularly when a lack of osseointegration and immunoregulatory incompetency occur during the healing phase, resulting in infection and fibrous encapsulation. Bio-inspired or biomimetic materials, which can mimic the characteristics of natural elements, are being investigated for use in the implant industry. This review discusses different biomimetic dental implants in terms of structural changes that enable antibacterial properties, drug delivery, immunomodulation, and osseointegration. We subsequently summarize the modification of dental implants for diabetes patients utilizing carbon nanomaterials, which have been recently found to improve the characteristics of biomimetic dental implants, including through antibacterial and anti-inflammatory capabilities, and by offering drug delivery properties that are essential for the success of dental implants.

Antimicrobial properties of nanostructured surfaces - demonstrating the need for a standard testing methodology

Bioinspired nanostructured materials that exhibit antimicrobial properties are being synthesized and tested at increasing rates for use in healthcare, manufacturing processes, and diagnostics. Although progress has been made in improving and understanding their bactericidal activity, arguably, the biggest problem currently in the field is the lack of a standard testing methodology that allows for optimal characterization and better comparison of emerging nanostructures. Here, we examine two forms of nanostructured silicon that vary in their ability to kill certain bacterial species due to different physical mechanisms and derive guidelines for the comparative testing. We perform a comprehensive evaluation of methodologies used extensively in the field (e.g., colony counting and live dead analysis) and the novel application of high-throughput flow cytometry. The data reveal how the techniques are complementary but not always directly equivalent or correlative. Therefore, comparison of results obtained using different methodologies on different materials can be grossly misleading. We report significant variations in bactericidal efficiencies depending on experimental environments (medium type, etc.) and methodologies employed. In addition, we demonstrate how cytometry is yet another powerful complementary tool that can aid the mechanistic understanding of antimicrobial activities of rough surfaces. Besides standardization for comparison, ultimately, evaluation methods need to consider anticipated applications. Then and only then can the true potential (or limitation) of a novel material be determined for its suitability for advancement in a particular field of use.

Trends in Bactericidal Nanostructured Surfaces: An Analytical Perspective

Since the discovery of the bactericidal properties of cicada wing surfaces, there has been a surge in the number of studies involving antibacterial nanostructured surfaces (NSS). Studies show that there are many parameters (and thus, thousands of parameter combinations) that influence the bactericidal efficiency (BE) of these surfaces. Researchers attempted to correlate these parameters to BE but have so far been unsuccessful. This paper presents a meta-analysis and perspective on bactericidal NSS, aiming to identify trends and gaps in the literature and to provide insights for future research. We have attempted to synthesize data from a wide range of published studies and establish trends in the literature on bactericidal NSS. Numerous research gaps and findings based on correlations of various parameters are presented here, which will assist in the design of efficient bactericidal NSS and shape future research. Traditionally, it is accepted that BE of NSS depends on the bacterial Gram-stain type. However, this review found that factors beyond Gram-stain type are also influential. Furthermore, it is found that despite their higher BE, hydrophobic NSS are less commonly studied for their bactericidal effect. Interestingly, the impacts of surface hydrophobicity and roughness on the bactericidal effect were found to be influenced by a Gram-stain type of the tested bacteria. In addition, cell motility and shape influence BE, but research attention into these factors is lacking. It was found that hydrophobic NSS demonstrate more promising results than their hydrophilic counterparts; however, these surfaces have been overlooked. Confirming the common belief of the influence of nanofeature diameter on bactericidal property, this analysis shows the feature aspect ratio is also decisive. NSS fabricated on silicon substrates perform better than their titanium counterparts, and the success of these silicon structures maybe attributed to the fabrication processes. These insights benefit engineers and scientists alike in developing next-generation NSS.

Strategies toward development of antimicrobial biomaterials for dental healthcare applications

Several approaches for elimination of oral pathogens are being explored at the present time since oral diseases remain prevalent affecting approximately 3.5 billion people worldwide. Need for antimicrobial biomaterials in dental healthcare include but is not restricted to designing resin composites and adhesives for prevention of dental caries. Constant efforts are also being made to develop antimicrobial strategies for clearance of endodontic space prior root canal treatment and for treatment of periimplantitis and periodontitis. This article discusses various conventional and nanotechnology-based strategies to achieve antimicrobial efficacy in dental biomaterials. Recent developments in the design and synthesis of antimicrobial peptides and antifouling zwitterionic polymers to effectively lessen the risks of antimicrobial drug resistance are also outlined in this review. Further, the role of contemporary strategies such as use of smart biomaterials, ionic solvent-based biomaterials and quorum quenchers incorporated biomaterials in the elimination of dental pathogens are described in detail. Lastly, we mentioned the approach of using polymers to print custom-made three-dimensional antibacterial dental products via additive manufacturing technologies. This review provides a critical perspective on the chemical, biomimetic, and engineering strategies intended for developing antimicrobial biomaterials that have the potential to substantially improve the dental health.

Behavior of Pseudomonas aeruginosa strains on the nanopillar topography of dragonfly (Pantala flavescens) wing under flow conditions

Bacterial associated infection is a threat in the medical field. Pseudomonas aeruginosa, one of the major causative agents for nosocomial infection, has developed resistance to almost all the classes of antibiotics. Recently, nanopillar-like structures were identified on the wings of insects such as cicada and dragonfly. Nanopillars both on natural surfaces and those mimicked on artificial surfaces were reported to possess bactericidal activity against a wide range of bacteria. An earlier study reported strain specific variation in the viability of P. aeruginosa on the nanopillar topography of a dragonfly wing under static condition. Here, we report the behavior of P. aeruginosa strains on a dragonfly wing under hydrodynamic conditions. The results of the study indicated that, under hydrodynamic conditions, P. aeruginosa PAO1 was attached in higher numbers to the wing surface than P. aeruginosa ATCC 9027 but killed in lower numbers. The plausible reason was identified to be the masking of nanopillars by the secreted extracellular polysaccharide. The shear rate of 1.0 s^-1 showed a relatively higher bactericidal effect among the three tested shear rates.

Effects of Nanopillar Size and Spacing on Mechanical Perturbation and Bactericidal Killing Efficiency

Nanopatterned surfaces administer antibacterial activity through contact-induced mechanical stresses and strains, which can be modulated by changing the nanopattern's radius, spacing and height. However, due to conflicting recommendations throughout the theoretical literature with poor agreement to reported experimental trends, it remains unclear whether these key dimensions-particularly radius and spacing-should be increased or decreased to maximize bactericidal efficiency. It is shown here that a potential failure of biophysical models lies in neglecting any out-of-plane effects of nanopattern contact. To highlight this, stresses induced by a nanopattern were studied via an analytical model based on minimization of strain and adhesion energy. The in-plane (areal) and out-of-plane (contact pressure) stresses at equilibrium were derived, as well as a combined stress (von Mises), which comprises both. Contour plots were produced to illustrate which nanopatterns elicited the highest stresses over all combinations of tip radius between 0 and 100 nm and center spacing between 0 and 200 nm. Considering both the in-plane and out-of-plane stresses drastically transformed the contour plots from those when only in-plane stress was evaluated, clearly favoring small tipped, tightly packed nanopatterns. In addition, the effect of changes to radius and spacing in terms of the combined stress showed the best qualitative agreement with previous reported trends in killing efficiency. Together, the results affirm that the killing efficiency of a nanopattern can be maximized by simultaneous reduction in tip radius and increase in nanopattern packing ratio (i.e., radius/spacing). These findings provide a guide for the design of highly bactericidal nanopatterned surfaces.

Nanostructured Copper Surface Kills ESKAPE Pathogens and Viruses in Minutes

In the search for a fast contact-killing antimicrobial surface to break the transmission pathway of lethal pathogens, nanostructured copper surfaces were found to exhibit the desired antimicrobial properties. Compared with plain copper, these nanostructured copper surfaces with Cu(OH)₂ nano-sword or CuO nano-foam were found to completely eliminate pathogens at a fast rate, including clinically isolated drug resistant species. Additionally these nanostructured copper surfaces demonstrated potential antiviral properties when assessed against bacteriophages, as a viral surrogate, and murine hepatitis virus, a surrogate for SARS-CoV-2. The multiple modes of killing, physical killing and copper ion mediated killing contribute to the superior and fast kinetics of antimicrobial action against common microbes, and ESKAPE pathogens. Prototypes for air and water cleaning with current nanostructured copper surface have also been demonstrated.

Resolving physical interactions between bacteria and nanotopographies with focused ion beam scanning electron microscopy

To robustly assess the antibacterial mechanisms of nanotopographies, it is critical to analyze the bacteria-nanotopography adhesion interface. Here, we utilize focused ion beam milling combined with scanning electron microscopy to generate three-dimensional reconstructions of Staphylococcus aureus or Escherichia coli interacting with nanotopographies. For the first time, 3D morphometric analysis has been exploited to quantify the intrinsic contact area between each nanostructure and the bacterial envelope, providing an objective framework from which to derive the possible antibacterial mechanisms of synthetic nanotopographies. Surfaces with nanostructure densities between 36 and 58 per μm² and tip diameters between 27 and 50 nm mediated envelope deformation and penetration, while surfaces with higher nanostructure densities (137 per μm²) induced envelope penetration and mechanical rupture, leading to marked reductions in cell volume due to cytosolic leakage. On nanotopographies with densities of 8 per μm² and tip diameters greater than 100 nm, bacteria predominantly adhered between nanostructures, resulting in cell impedance.

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Bacteria-nanotopography interactions can be quantified using FIB-SEM

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Envelope penetration and cell impedance are influenced by nanotopography density

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Low density nanotopographies (8 per μm²) mediate cell impedance

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High-density nanotopographies (36–137 per μm²) mediate deformation and penetration

Biomaterials for human space exploration: A review of their untapped potential

As biomaterial advances make headway into lightweight radiation protection, wound healing dressings, and microbe resistant surfaces, a relevance to human space exploration manifests itself. To address the needs of the human in space, a knowledge of the space environment becomes necessary. Both an understanding of the environment itself and an understanding of the physiological adaptations to that environment must inform design parameters. The space environment permits the fabrication of novel biomaterials that cannot be produced on Earth, but benefit Earth. Similarly, designing a biomaterial to address a space-based challenge may lead to novel biomaterials that will ultimately benefit Earth. This review describes several persistent challenges to human space exploration, a variety of biomaterials that might mitigate those challenges, and considers a special category of space biomaterial. STATEMENT OF SIGNIFICANCE: This work is a review of the major human and environmental challenges facing human spaceflight, and where biomaterials may mitigate some of those challenges. The work is significant because a broad range of biomaterials are applicable to the human space program, but the overlap is not widely known amongst biomaterials researchers who are unfamiliar with the challenges to human spaceflight. Additionaly, there are adaptations to microgravity that mimic the pathology of certain disease states ("terrestrial analogs") where treatments that help the overwhelmingly healthy astronauts can be applied to help those with the desease. Advances in space technology have furthered the technology in that field on Earth. By outlining ways that biomaterials can promote human space exploration, space-driven advances in biomaterials will further biomaterials technology.

Low-Temperature Hydrothermal Synthesis of Novel 3D Hybrid Nanostructures on Titanium Surface with Mechano-bactericidal Performance

Titanium is extensively employed in modern medicines as orthopedic and dental implants, but implant failures frequently occur because of bacterial infections. Herein, three types of 3D nanostructured titanium surfaces with nanowire clusters (NWC), nanowire/sheet clusters (NW/SC) and nanosheet clusters (NSC), were fabricated using the low-temperature hydrothermal synthesis under normal pressure, and assessed for the sterilization against two common human pathogens. The results show that the NWC and NSC surfaces merely display good bactericidal activity against Escherichia coli, whereas the NW/SC surface represents optimal bactericidal efficiency against both Escherichia coli (98.6 ± 1.23%) and Staphylococcus aureus (69.82 ± 2.79%). That is attributed to the hybrid geometric nanostructure of NW/SC, i.e., the pyramidal structures of ∼23 nm in tip diameter formed with tall clustered wires, and the sharper sheets of ∼8 nm in thickness in-between these nanopyramids. This nanostructure displays a unique mechano-bactericidal performance via the synergistic effect of capturing the bacteria cells and penetrating the cell membrane. This study proves that the low-temperature hydrothermal synthesized hybrid mechano-bactericidal titanium surfaces provide a promising solution for the construction of bactericidal biomedical implants.

Tuning surface topographies on biomaterials to control bacterial infection

Microbial contamination and subsequent formation of biofilms frequently cause failure of surgical implants and a good understanding of the bacteria-surface interactions is vital to the design and safety of biomaterials. In this review, the physical and chemical factors that are involved in the various stages of implant-associated bacterial infection are described. In particular, topographical modification strategies that have been employed to mitigate bacterial adhesion via topographical mechanisms are summarized and discussed comprehensively. Recent advances have improved our understanding about bacteria-surface interactions and have enabled biomedical engineers and researchers to develop better and more effective antibacterial surfaces. The related interdisciplinary efforts are expected to continue in the quest for next-generation medical devices to attain the ultimate goal of improved clinical outcomes and reduced number of revision surgeries.

A call for action to the biomaterial community to tackle antimicrobial resistance

The global surge of antimicrobial resistance (AMR) is a major concern for public health and proving to be a key challenge in modern disease treatment, requiring action plans at all levels. Microorganisms regularly and rapidly acquire resistance to antibiotic treatments and new drugs are continuously required. However, the inherent cost and risk to develop such molecules has resulted in a drying of the pipeline with very few compounds currently in development. Over the last two decades, efforts have been made to tackle the main sources of AMR. Nevertheless, these require the involvement of large governmental bodies, further increasing the complexity of the problem. As a group with a long innovation history, the biomaterials community is perfectly situated to push forward novel antimicrobial technologies to combat AMR. Although this involvement has been felt, it is necessary to ensure that the field offers a united front with special focus in areas that will facilitate the development and implementation of such systems. This paper reviews state of the art biomaterials strategies striving to limit AMR. Promising broad-spectrum antimicrobials and device modifications are showcased through two case studies for different applications, namely topical and implantables, demonstrating the potential for a highly efficacious physical and chemical approach. Finally, a critical review on barriers and limitations of these methods has been developed to provide a list of short and long-term focus areas in order to ensure the full potential of the biomaterials community is directed to helping tackle the AMR pandemic.

Anti-Periprosthetic Infection Strategies: From Implant Surface Topographical Engineering to Smart Drug-Releasing Coatings

Despite advanced implant sterilization and aseptic surgical techniques, periprosthetic bacterial infection remains a major challenge for orthopedic and dental implants. Bacterial colonization/biofilm formation around implants and their invasion into the dense skeletal tissue matrices are difficult to treat and could lead to implant failure and osteomyelitis. These complications require major revision surgeries and extended antibiotic therapies that are associated with high treatment cost, morbidity, and even mortality. Effective preventative measures mitigating risks for implant-related infections are thus in dire need. This review focuses on recent developments of anti-periprosthetic infection strategies aimed at either reducing bacterial adhesion, colonization, and biofilm formation or killing bacteria directly in contact with and/or in the vicinity of implants. These goals are accomplished through antifouling, quorum-sensing interfering, or bactericidal implant surface topographical engineering or surface coatings through chemical modifications. Surface topographical engineering of lotus leaf mimicking super-hydrophobic antifouling features and cicada wing-mimicking, bacterium-piercing nanopillars are both presented. Conventional physical coating/passive release of bactericidal agents is contrasted with their covalent tethering to implant surfaces through either stable linkages or linkages labile to bacterial enzyme cleavage or environmental perturbations. Pros and cons of these emerging anti-periprosthetic infection approaches are discussed in terms of their safety, efficacy, and translational potentials.

Advancing of Additive-Manufactured Titanium Implants with Bioinspired Micro- to Nanotopographies

There is an increasing demand for low-cost and more efficient titanium (Ti) medical implants that will provide improved osseointegration and at the same time reduce the likelihood of infection. In the past decade, additive manufacturing (AM) using metal selective laser melting (SLM) or three-dimensional (3D) printing techniques has emerged to enable novel implant geometries or properties to overcome such potential challenges. This study presents a new surface engineering approach to create bioinspired multistructured surfaces on SLM-printed Ti alloy (Ti6Al4V) implants by combining SLM technology, electrochemical anodization, and hydrothermal (HT) processes. The resulting implants display unique surfaces with a distinctive dual micro- to nano-topography composed of micron-sized spherical features, fabricated by SLM and vertically aligned nanoscale pillar structures as a result of combining anodization and HT treatment. The fabricated implants enhanced hydroxyapatite-like mineral deposition from simulated body fluid (SBF) compared to control. In addition, normal human osteoblast-like cells (NHBCs) showed strong adhesion to the nano-/microstructures and displayed greater propensity to mineralize compared to control surfaces. This engineering approach and the resulting nature-inspired multiscale-structured surface offers desired features for improving osseointegration and antibacterial performance toward the development of next-generation orthopedic and dental implants.