Antibacterial effects of nanopillar surfaces are mediated by cell impedance, penetration and induction of oxidative stress

Magnetic field-driven nanospears for enhancing antibacterial strategy

Antimicrobial resistance poses a significant challenge to global health, necessitating innovative strategies to combat bacterial infections. This study introduces a novel approach that combines the mechanical effects of magnetically-driven nanospears with photothermal action to enhance bacterial eradication efficacy. The anisotropic Fe3O4@PDA nanorobots with controllable aspect ratios are synthesized by encapsulating strong magnetic Fe3O4 nanospears with polydopamine (PDA), which exhibits high near-infrared (NIR) photothermal efficiency. Because the sharp tips on the Fe3O4@PDA nanospears concentrate mechanical stress on bacterial membranes, they exhibit enhanced antibacterial activity when a rotating magnetic field (RMF) is applied to increase the mechanical damage. Notably, the combination of RMF and NIR irradiation markedly enhance biofilm removal and bacterial inactivation, especially against Staphylococcus aureus. The aspect ratio is found to have a high influence on the coupling effect, and the ellipsoidal nanoparticles without the sharp tips exhibit a significantly reduced effect compared to the nanospears. The piercing effect of nanospears on bacterial membranes and the synergistic impact of mechanical penetration and photothermal treatment are clearly observed via experimental analysis. Finite element analysis (FEA) and coarse-grained molecular dynamics (CGMD) simulations further confirm that the nanospears can effectively penetrate bacterial membranes and the elevated temperatures amplify membrane disruption. This photothermal-magnetomechanical synergistic effect offers a promising and function-tailored strategy to address antimicrobial resistance, positioning nanospears as a viable alternative to conventional antibacterial treatments.

Nanowire arrays with programmable geometries as a highly effective anti-biofilm surface

Biofilm-related microbial infections are the Achilles' heel of many implantable medical devices. Surface patterning with nanostructures in the form of vertically aligned silicon (Si) nanowires (VA-SiNWs) holds promise to prevent these often "incurable" infections. In this study, we fabricated arrays of highly ordered SiNWs varying in three geometric parameters, including height, pitch size, and tip diameter (sharpness). Anti-infective efficacies of fabricated SiNW arrays were assessed against representative laboratory reference bacterial strains, Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922, using a modified microwell biofilm assay representing microorganism-implant interactions at a liquid-solid interface. To further understand the role of individual geometric parameters to the SiNW-induced bacterial killing, SiNW arrays with stepwise changes in individual geometric parameters were compared. The force that NWs applied on bacterial cells was mathematically calculated. Our results suggested that NWs with specific geometries were able to kill adherent bacterial cells and prevent further biofilm formation on biomaterial surfaces. Tip diameter and pitch size appeared to be key factors of nanowires predetermining their anti-infectiveness. Mechanistic investigation found that tip diameter and pitch size co-determined the pressure that NWs put on the cell envelope. The most effective anti-infective NWs fabricated in our study (50 nm in tip diameter and 400 nm in pitch size for S. aureus and 50 nm in tip diameter and 800 nm in pitch size for E. coli) put pressures of approximately 2.79 Pa and 8.86 Pa to the cell envelop of S. aureus and E. coli, respectively, and induced cell lyses. In addition, these NWs retained their activities against clinical isolates of S. aureus and E. coli from patients with confirmed device-related infections and showed little toxicity against human fibroblast cells and red blood cells.

Antibacterial and bactericidal properties of resin nanostructures coated with SiO2 thin films

Nanotextures exhibit physical antibacterial and bactericidal properties; hence, they have great potential to prevent infection related to bacteria through contact. The surface characteristics of a nanostructure determine its antibacterial and bactericidal activities. In this study, an atomic layer deposition (ALD) was used to prepare nano-level, hard, thin SiO2 layers on resin nanostructures and their effects were demonstrated through antibacterial and bactericidal tests. The SiO2-layer-coated resin nanostructure exhibited a water contact angle of 7.2°, dramatically lower than that of the uncoated specimen (130.2°), as well as a three-fold higher local elastic modulus. Further, 10-nm-thin SiO2-layer-coated nanopillars showed antibacterial and bactericidal effects against E. coli. These results demonstrate that SiO2 thin layer coating has great potential for improving the antibacterial and bactericidal properties of polymeric nanopillar arrays.

A review of the advances in implant technology: accomplishments and challenges for the design of functionalized surface structures

Biomedical implants are extensively utilized to replace hard-tissue defects owing to their biocompatibility and remarkable tissue-affinity. The materials and functional design are selected based on the resultant osseointegration level and resistance to infection, and these considerations constitute the dominant research topic in this field. However, high rates of implantation failure and peri-implantitis have been reported. Current research on biomedical-implant design encompasses enhancement of the implant surface properties, such as the roughness, nano/micro topography, and hydrophilicity, along with the realization of advanced features including antibacterial properties and cell and immunomodulation regulation. This review considers the two achievements of contemporary implant manufacturing; namely, osseointegration and the realization of antibacterial properties. Present mainstream surface modifications and coatings are discussed, along with functional design technologies and achievements. The impacts of direct surface-treatment techniques and osteogenic functional coatings on osseointegration performance and antibacterial surface structures are elucidated, considering inorganic and organic coatings with antibacterial properties as well as antibiotic-releasing coatings. Furthermore, this review highlights recent advancements in physically driven antimicrobial strategies. Expanding upon existing research, future directions for implant studies are proposed, including the realization of comprehensive functionality that integrates osseointegration and antibacterial properties, as well as patient-specific design. Our study presents a comprehensive review and offers a novel perspective on the design of biomedical implants for enhanced versatility. An in-depth exploration of future research directions will also stimulate subsequent investigations.

Electrocapillary Plating-An Innovative Method of Creating Nanostructures Enhances the Working Performance of Implantable Bioelectrodes

The current optimization of implantable electrodes focuses on reducing impedance and improving anti-inflammatory properties. The fabrication of nanostructures on electrode surfaces is a promising strategy for reducing impedance while also minimizing interference from the array of immune cells that cause foreign body reactions. Electrochemical deposition is a common method for creating nanostructures. However, the generation of impurities that are difficult to remove during the preparation process is unavoidable. Herein, we develop a simple, economical, and stable method, namely, electrocapillary plating, to create nanostructures on the electrode surface based on the electrocapillary phenomenon and electrochemical deposition without introducing impurities. This technology enables the fabrication of various nanostructures at different current densities and pH values. The process and mechanism of structure formation are investigated through simulations, which show that the conductive droplets undergo droplet climbing and nanostructure deposition due to the electrocapillary phenomenon and electrochemical deposition. Compared to traditional plating and control groups, the Electrocapillary plating-modified electrode demonstrates reduced impedance, lower protein adhesion, and greater tolerance to changes in the physicochemical environment. The in vitro and in vivo biological experiments verify that the Electrocapillary plating modified electrode shows the properties of bactericidal, pro-tissue repair and inhibition of the inflammatory response. These results highlight the potential of Electrocapillary plating as a novel strategy to optimize electrode performance in the field of implantable bioelectrodes. In addition, Electrocapillary plating, as an innovative surface modification technology, can create nanostructures of different metals and even further modulate the surface morphology by means such as hydrogen reduction. It may have even wider applications in various fields such as electronics, medicine, energy, environment, and materials science.

Exploring Broad-Spectrum Antimicrobial Nanotopographies: Implications for Bactericidal, Antifungal, and Virucidal Surface Design

Inspired by the natural defense strategies of insect wings and plant leaves, nanostructured surfaces have emerged as a promising tool in various fields, including engineering, biomedical sciences, and materials science, to combat bacterial contamination and disrupt biofilm formation. However, the development of effective antimicrobial surfaces against fungal and viral pathogens presents distinct challenges, necessitating tailored approaches. Here, we aimed to review the recent advancements of the use of nanostructured surfaces to combat microbial contamination, particularly focusing on their mechano-bactericidal and antifungal properties, as well as their potential in mitigating viral transmission. We comparatively analyzed the diverse geometries and nanoarchitectures of these surfaces and discussed their application in various biomedical contexts, such as dental and orthopedic implants, drug delivery systems, and tissue engineering. Our review highlights the importance of preventing microbial attachment and biofilm formation, especially in the context of rising antimicrobial resistance and the economic impact of biofilms. We also discussed the latest progress in materials science, particularly nanostructured surface engineering, as a promising strategy for reducing viral transmission through surfaces. Overall, our findings underscore the significance of innovative strategies to mitigate microbial attachment and surface-mediated transmission, while also emphasizing the need for further interdisciplinary research in this area to optimize antimicrobial efficacy and address emerging challenges.

Electron-Withdrawing Effects for Tailoring Oxidative-Stress-Mediated Coating in Marine Antifouling

Oxidative stress derived from excess reactive oxygen radicals (ROS) induces cellular damage, apoptosis, and necrosis, thus effective biofouling control by directly inhibiting primary membrane formation. However, the oxidative stress produced that does not rely on additional energy still is a challenge. Herein, an oxidative-stress-mediated marine antifouling polyurea coating is prepared leveraging the strong electron absorption effect of C═N. Given the structure of the urethane bond, the reversible reaction energy barrier of the dynamic urethane bond can be reduced, thereby enabling the urethane bond to be broken without the need for additional energy. The alkyl radical (R·) originating from the oxime-urethane bond can mediate the induction of oxidative stress in cells and microbial death, thus preserving exceptional antifouling properties and resisting most of the organism to adhere on the substrates. Notably, the coating indicates satisfactory antibacterial and antialgae performance and exhibits 8 months of marine field antifouling performance. In addition, the electron structure is investigated by theoretical calculation, and the interface behavior is investigated by molecular dynamics simulation. This work presents a pioneering example of the construction of oxidative-stress-mediated coating, which might be a judicious design strategy for an environmentally friendly marine antifouling coating.

Carbon-Infiltrated Carbon Nanotube Topography Reduces the Growth of Staphylococcus aureus Biofilms

Orthopedic implant-associated infections are a growing problem. These infections are often associated with bacterial biofilms, such as those formed by Staphylococcus aureus. Nanotextured surfaces can reduce or prevent the development of bacterial biofilms and could help reduce infection rates and severity. Previous work has shown that a carbon-infiltrated carbon nanotube (CICNT) surface reduces the growth of S. aureus biofilms. This work expands on previous experiments, showing that the topography of the CICNT, rather than its surface chemistry, is responsible for the reduction in biofilm growth. Additionally, the CICNT surface does not reduce biofilm growth by killing the bacteria or by preventing their attachment. Rather it likely slows cell growth, resulting in fewer cells and reduced biofilm formation.

Interfering with proton and electron transfer enables antibacterial starvation therapy

Implant-associated infections are urgently addressed; however, existing materials are difficult to kill bacteria without damaging cells. Here, we propose an innovative concept of selective antibacterial starvation therapy based on interfering with proton and electron transfer on the bacterial membrane. As a proof-of-principle demonstration, a special Schottky heterojunction film composed of gold and alkaline magnesium-iron mixed metal oxides (Au/MgFe-MMO) was constructed on the titanium implant. Once bacteria contacted this implant, the Au/MgFe-MMO film continuously captured the proton and electron participated in respiratory chain of bacteria to impede their energy metabolism, leading to the deficit of adenosine 5'-triphosphate. Prolonged exposure to this starvation state inhibited numerous biosynthesis processes and triggered severe oxidative stress in bacteria, ultimately leading to their death due to DNA and membrane damage. In addition, this heterojunction film was comfortable for mammalian cells, without inhibiting mitochondrial function. This proposed starvation antibacterial therapy gives a notable perspective in designing biosafe smart antibacterial biomaterials.

Coating Nanowires with Straw Carbon Enhances Their Bactericidal Performance and Enables Efficient Water Disinfection

Bacterial contamination in water remains a significant public health threat, and it is crucial to develop disinfection methods that are both safe and effective. In this study, we developed straw carbon-coated nanowires (SC/NWs) as an effective bactericidal material for water disinfection. The thermal decomposition of rice straw produced an sp2-structured, amorphous carbon layer with oxygen-containing functional groups and hetero atoms on its surface. The SC coating enhanced the bactericidal performance of Cu(OH)2 NWs by more than 3-log, achieving >6-log inactivation of Escherichia coli at a flux of 2000 L m-2 h-1. The bacteria exposed to SC/NWs suffered extensive membrane disruption and lost cellular integrity. In contrast, the uncoated NWs caused limited damage to the bacteria. Molecular dynamics simulations revealed that the SC coating had strong van der Waals and electrostatic interactions with bacterial membranes, and these attractive forces led to efficient rupture of bacteria during water flow. The SC/NWs were used to disinfect real water samples, including tap water and reclaimed water, with >6-log reductions in bacterial counts during storage. Importantly, no bacterial reactivation was observed after 24 h of storage, which indicated that the SC/NWs caused irreversible membrane damage to the bacteria. This work presents a cost-effective, sustainable solution for developing mechano-bactericidal materials tailored to water disinfection.

The effect of the dual scale surface topography of a surface-modified titanium alloy on its bactericidal activity against Pseudomonas aeruginosa

The rapid advancement of antibacterial nanostructured surfaces indicates that they will soon be integrated into real-world applications. However, despite notable progress, a comprehensive understanding of the antibacterial properties of nanostructures remains elusive, posing a critical barrier to the translation of this in vitro technology into practical applications. Among the numerous antibacterial nanostructures developed, nanowire structures play an important role due to their enhanced efficacy against bacteria and viruses and their ease of fabrication. Antibacterial nanowire structures exhibit the dual capability of lysing bacteria upon surface adhesion and mitigating bacterial colonization. The interplay of surface energy significantly influences bacterial adhesion, and macro surface roughness appears to be a pivotal determining factor. Macro-scale surface roughness not only modulates surface energy but also results in micro-scale topographical features that impact the bactericidal efficacy of nanowire structures. The integration of nanofabrication techniques on surfaces with macro-scale roughness yields multi-hierarchical micro- and nanoscale features, thereby possibly amplifying the bactericidal effect. Pseudomonas aeruginosa is an opportunistic pathogen that can cause serious infections. Moreover, this species has a higher risk of developing antibiotic resistance, which makes treatments for infections extremely difficult. Nanowire structures have demonstrated higher efficacy against P. aeruginosa species, making it a good alternative for fighting P. aeruginosa infections. This study demonstrates that heightened surface roughness amplifies the bactericidal potency of nanowire structures against P. aeruginosa bacterial species. The bactericidal effect reaches its maximum when the average surface roughness value is close to the bacterial cell size. This is contrary to the conventional assumption that the substrate surface must be smooth for the nanostructures to work, as the nanowire structures exhibit robust bactericidal efficacy, even when fabricated on rough surfaces. Therefore, the applicability of bactericidal nanostructures is expanded beyond smooth substrates. Consequently, these nanostructures can be effectively deployed on rugged industrial surfaces, broadening their potential impact across a diverse array of sectors. The widespread adoption of this nanotechnology promises transformative benefits not only to the medical sector but also to various industries. Moreover, by curbing bacterial infections, nanostructured surfaces hold the potential to reduce mortality rates and yield more direct economic dividends through waste reduction and enhanced safety. Ultimately, the widespread implementation of antibacterial nanowire technology stands poised to improve societal well-being and quality of life.

Solid-State Precipitation of Silver Nanoparticles Nucleated during Al Anodizing: Mechanism and Antibacterial Properties

This study presents an innovative approach to creating antibacterial aluminum surfaces by combining the antibacterial properties of silver nanoparticles (Ag NPs) with the nanoarchitecture of anodized aluminum oxide in one step. An Al-Ag alloy containing 10 wt % Ag was synthesized and anodized in 0.3 M oxalic acid. Ag NPs precipitated in the solid state during anodization, resulting in a porous nanocomposite structure. Comprehensive characterization using SEM, TEM, and EDS revealed a 43 μm thick oxide layer with uniformly distributed nanopores of approximately 100 nm in diameter. Ag NPs with diameters ranging from 2 to 14 nm precipitated dispersed on the surface, inside pores, and within the Al2O3 matrix. Antibacterial properties were evaluated against Escherichia coli. The anodized Al-Ag surface demonstrated robust antibacterial activity after short incubation times (up to 1 × 108 CFU/ml after 3 h). The enhanced antibacterial properties are attributed to the optimal size and distribution of Ag NPs and the potential physical bactericidal effect of the nanoporous structure. This strategy for the precipitation of Ag NPs in the solid state could be used to fabricate high-touch surfaces in hospitals.

Graveyard effects of antimicrobial nanostructured titanium over prolonged exposure to drug resistant bacteria and fungi

Innovations in nanostructured surfaces have found a practical place in the medical area with use in implant materials for post-operative infection prevention. These textured surfaces should be dual purpose: (1) bactericidal on contact and (2) resistant to biofilm formation over prolonged periods. Here, hydrothermally etched titanium surfaces were tested against two highly antimicrobial resistant microbial species, methicillin-resistant Staphylococcus aureus and Candida albicans. Two surface types - unmodified titanium and nanostructured titanium - were incubated in a suspension of each microbial strain for 1 day and 7 days. Surface topography and cross-sectional information of the microbial cells adhered to the surfaces, along with biomass volume and live/dead rate, showed that while nanostructured titanium was able to kill microbes after 1 day of exposure, after 7 days, the rate of death becomes negligible when compared to the unmodified titanium. This suggests that as biofilms mature on a nanostructured surface, the cells that have lysed conceal the nanostructures and prime the surface for planktonic cells to adhere, decreasing the possibility of structure-induced lysis. Synchrotron macro-attenuated total reflection Fourier transform infrared (macro ATR-FTIR) micro-spectroscopy was used to elucidate the biochemical changes occurring following exposure to differing surface texture and incubation duration, providing further understanding into the effects of surface morphology on the biochemical molecules (lipids, proteins and polysaccharides) in an evolving and growing microbial colony.

Nanospiked Cellulose Gauze That Attracts Bacteria with Biomolecules for Reducing Bacterial Load in Burn Wounds

Nanostructuring surfaces is an emergent strategy to endow materials with abilities to combat pathogenic bacteria. Nevertheless, it remains challenging to create nanospike structures on the curved surfaces of polymer materials, including gauze and other microfibrous medical materials. Additionally, the effects of nanostructured surfaces on bacteria in the presence of proteins and in vivo remain largely unexplored. Herein, we demonstrated the decoration of gauze microfiber surfaces with nanospike structures via the self-assembly of cello-oligosaccharides and investigated the effects of the nanospiked gauze on bacteria in the presence of proteins. The nanospiked gauze had low bacterial adhesion properties in the absence of proteins, whereas in the presence of proteins, it promoted bacterial adhesion. Analyses suggested that the adsorbed protein layers on the nanospikes were involved in the promoted bacterial adhesion. Furthermore, the bacterial adhesion-promoting effects were exploited to remove pathogenic bacteria from burn wounds with exudate containing proteins using the nanospiked gauze.

The nanocellulose fiber scaffold to construct a hierarchical phenolic coating on cotton fiber surfaces for inactivating pathogens through an enhanced protein adsorption mechanism

Emerging pathogens present a significant societal threat, and biological protection textiles are expected to play a pivotal role in controlling their spread. However, incorporating highly effective pathogen transmission-blocking abilities into textiles while ensuring their large-scale production remains challenging. This work has successfully developed a hierarchically structured coating for cotton fibers, which exhibits enhanced antiviral and antibacterial functionalities compared to existing phenolic coating methods. The multilevel coating consisted of a cellulose nanofibers (CNFs) scaffold on cotton fibers, along with a phenolic layer constructed of 4,4-bis(4-hydroxyphenyl)valeric acid (DPA) on the CNF surfaces. The bioactive textile exhibited remarkable antiviral and antibacterial capabilities with exceptional durability, while demonstrating strong protein affinity for pathogen destruction. Especially, the CNFs with diameters below 10 nm show significant size effect in capturing phi6. This is primarily due to their complementary shape matching the spike proteins, resulting in an increased number of binding sites and improved inactivation effectiveness. Moreover, the modification process was demonstrated to be scalable in a pad-dry-cure line commonly employed by textile finishing factories, and the resultant coating ensured reliable safety for human skin without sacrificing wearing comfort. This approach opens up new possibilities for developing protective textiles that effectively block pathogen transmission.

Application of Light-Responsive Nanomaterials in Bone Tissue Engineering

The application of light-responsive nanomaterials (LRNs) in bone tissue engineering shows broad prospects, especially in promoting bone healing and regeneration. With a deeper understanding of the mechanisms of bone defects and healing disorders, LRNs are receiving increasing attention due to their non-invasive, controllable, and efficient properties. These materials can regulate cellular biological reactions and promote bone cell adhesion, proliferation, and differentiation by absorbing specific wavelengths of light and converting them into physical and chemical signals. In addition, the unique surface morphology and biocompatibility of LRNs enable them to effectively load drugs in bone tissue engineering, achieve precise release, and optimize the bone regeneration process. Through photothermal and photodynamic therapy, these materials also possess antibacterial properties and can play an important role in the repair of infectious bone defects. Although LRNs have shown significant advantages in bone tissue regeneration, a series of challenges still need to be overcome to achieve their widespread and effective clinical applications. This article summarizes the basic principles, classification, and potential applications of LRNs in bone tissue regeneration, aiming to provide reference for future research and clinical applications.

Antibacterial properties and biological activity of 3D-printed titanium alloy implants with a near-infrared photoresponsive surface

PURPOSE

SLM 3D printing technology is one of the most widely used implant-making technologies. However, the surfaces of the implants are relatively rough, and bacteria can easily adhere to them; increasing the risk of postoperative infection. Therefore, we prepared a near-infrared photoresponsive nano-TiO2 coating on the surface of an SLM 3D-printed titanium alloy sheet (Ti6Al4V) via a hydrothermal method to evaluate its antibacterial properties and biocompatibility.

METHODS

Using SLM technology, titanium alloy sheets were 3D printed, and a nano-TiO2 coating was prepared on its surface via a hydrothermal method to obtain Ti6Al4V@TiO2. The surface morphology, physicochemical properties, and photothermal response of the samples were observed. The Ti6Al4V groups and Ti6Al4V@TiO2 groups were cocultured with S. aureus and E. coli and exposed to 808 nm NIR light (0.8 W/cm2) and viable plate count experiments and live/dead bacterial staining were used to assess their in vitro antibacterial properties.

RESULTS

The hydrophilicity of the nano-TiO2 coating sample significantly improved and the sample exhibited an excellent photothermal response. The temperature reached 46.9± 0.32 °C after 15 min of irradiation with 808 nm NIR light (0.8 W/cm2). The Ti6Al4V group showed significant antibacterial properties after irradiation with 808 nm NIR light, and the Ti6Al4V@TiO2 group also had partial antibacterial ability without irradiation. After irradiation with 808 nm NIR light, the Ti6Al4V@TiO2 group showed the strongest antibacterial properties, reaching 90.11± 2.20% and 90.60± 1.08% against S. aureus and E. coli, respectively.

CONCLUSIONS

A nano-TiO2 coating prepared via a hydrothermal method produced synergistic antibacterial effects after NIR light irradiation.

Nanostructure-Mediated Photothermal Effect for Reinforcing Physical Killing Activity of Nanorod Arrays

The physical killing of bacteria based on surface topography has attracted much attention due to the sustainable and safe prevention of biofilm formation. However, the antibacterial efficiency of biomedical implants derived solely from nanostructures or microstructures is insufficient to combat bacteria against common infections, such as methicillin-resistant Staphylococcus aureus with thick cell walls. Herein, photothermal therapy is carried out in the presence of nanorod arrays to mitigate infection of biomedical implants. Different from traditional photothermal therapy relying on a photosensitizer, the photothermal effect is mediated by light traps rendered by the nanorod arrays, and consequently, the photosensitizer is not needed. Finite element simulations and experiments are performed to elucidate the light-to-thermal conversion mechanism. This photothermal platform, in conjunction with thermosensitive nitric oxide therapy, is applied to treat titanium implant infection. The nanostructure-mediated photothermal effect destroys bacterial cell walls by inhibiting peptidoglycan synthesis and increasing the membrane permeability by affecting fatty acid synthesis. Furthermore, the nanorods synergistically puncture the bacterial membrane easily as demonstrated by experiments and transcriptome analysis. The results provide insights into the development of efficient antibacterial treatment of implants by combining nanostructures and photothermal therapy.

Nitrided Ti-6Al-4V: A Catalyst for Increase Mineralization and Osteogenic Marker Expression

Plasma nitriding is one of the surface modifications that show more effectiveness than other methods. In this study, the plasma-based ion implantation (PBII) technique was performed on the surface of titanium alloy (Ti-6Al-4V, Ti64) using a mixture of nitrogen (N2) and argon (Ar), resulting in a plasma-nitrided surface (TiN-Ti64). The surface composition of the TiN-Ti64 was verified through X-ray photoelectron spectroscopy (XPS). TiN-Ti64 demonstrated superior hydrophilicity compared with Ti64. TiN-Ti64 exhibited higher surface hardness than the original surface. The biological responses of primary human alveolar bone cells (hAVs) were observed on the TiN-Ti64, revealing greater activation of cell adhesion and spreading compared with Ti64 and the control group (glass coverslip). Moreover, the TiN-Ti64 significantly promoted cell proliferation compared with Ti64 and tissue culture plates. The mineralization of hAVs on the TiN-Ti64 showed a significant increase, almost 20% greater than that of Ti64. Furthermore, a significant upregulation of mRNA expression for osteogenic differentiation marker genes, including BMP2, OCN, OPN, and RUNX2, was observed in TiN-Ti64 compared with other conditions. In addition, the TiN-Ti64 exhibited antibiofilm activity against Streptococcus aureus. In conclusion, the TiN-Ti64, modified with the PBII technique utilizing a mixture of N2 and Ar, emerges as a promising alternative for surface modification in dental implant applications.

How Much Force is Needed to Kill a Single Bacterium?

The interaction between bacteria and nanomaterials, particularly from a physical or mechanical perspective, has emerged as a topic of significant interest in both science and medicine. Mechanobactericidal nanomaterials, which exert antimicrobial effects through purely physical mechanisms, hold promise as alternative strategies to combat bacterial resistance to traditional antibiotics. High-aspect-ratio nanoparticles and surface topographies are being engineered to enhance their mechanobactericidal properties. However, progress in this field is hindered by an incomplete understanding of how these materials induce mechanical cell death in bacteria. This review examines the role of atomic force microscopy (AFM) nanoindentation in quantifying forces required to rupture the bacterial cell wall. The reported values range from nN to a few tens of nN, depending on the type of bacterium and the experimental conditions used. The potential effect of AFM tip properties, loading speed, bacterial immobilization strategy, or environmental conditions on the measured rupture values are discussed. This perspective also highlights the complexities of modeling bacterial cell rupture and the importance of pressure as a parameter for standardizing results across experiments. Furthermore, the implications of these quantitative insights to understand the mechanisms of action of mechanobactericidal nanomaterials are discussed.

Trends and Advances in Antimicrobial Surface Modification for Orthopedic Implants (2014-2024)

The failure of orthopedic implants can significantly impact patients physiologically, psychologically, and economically. A bibliometric study of the field of surface modification for antimicrobial purposes in orthopedic implants provides insights into its developmental trajectory and offers valuable predictions for future advancements, thus playing a pivotal role in guiding research in this domain. Relevant publications on surface modification for antimicrobial purposes in orthopedic implants published between 2014 and 2024 were selected from the Web of Science (Core Collection) dataset and analyzed using VOSviewer and Citespace. The analysis encompassed 725 articles. Over the past decade, there has been a steady increase in the number of publications related to surface modification for antimicrobial purposes in orthopedic implants, with China emerging as the primary contributor. Novel antimicrobial materials development, osteogenesis, and angiogenesis have become focal areas of research interest in this domain. Surface modification for antimicrobial purposes in orthopedic implants garners increasing attention. Research in this field is anticipated to expand, with future focus likely to revolve around novel material applications, repair outcomes, and underlying mechanisms.

Supramolecular Switching-Enabled Quorum Sensing Trap for Pathogen-Specific Recognition and Eradication to Treat Enteritis

Intestinal bacterial infections have become a significant threat to human health. However, the current typical antibiotic-based therapies not only contribute to drug resistance but also disrupt gut microbiota balance, resulting in additional adverse effects on life activities. There is an urgent need to develop new antibacterial materials that selectively eliminate pathogenic bacteria without disrupting beneficial bacterial communities or promoting drug resistance. Herein, we utilize bacterial quorum sensing (QS), a universal mechanism for regulating community behavior, to develop a supramolecular QS trap by encapsulating cucurbit[7]uril (CB[7]) on 1-vinyl-3-pentylimidazolium bromide ([VPIM]Br) to form a supramolecular switch ([VPIM]Br⊂CB[7]) through host-guest interactions followed by grafting it onto bacterial cell surfaces using atom transfer radical polymerization. Subsequently, the matched pathogens are recognized and aggregated through interbacterial QS signals. Furthermore, the addition of amantadine (AD) facilitates the release of [VPIM]Br by competitive binding of CB[7] on [VPIM]Br⊂CB[7] for sterilization. This QS trap specifically triggers the self-aggregation and efficient elimination of matched bacteria. The [VPIM]Br⊂CB[7]-based trap can increase the diversity and abundance of intestinal microorganisms in mice, effectively treating Escherichia coli K88-induced intestinal damage without perturbing gut microbiota balance. This supramolecular-switched QS trap opens up a promising avenue to specifically recognize and eradicate pathogens for the antibiotic-free treatment of intestinal bacterial infections and other inflammatory diseases.

Realizing Square-Ordered Nanopillars with a 0.1-Tera-Density through a Superimposed Masking Strategy for Advanced Surface-Enhanced Raman Spectroscopy

Despite widespread interest in nanoscale pillar structures for various optical devices, including solar cells, photonic crystal lasers, and sensors, the critical challenges for mass production are the high equipment costs and limited scalability of traditional manufacturing methods. To overcome these hurdles, this study develops a simple and highly scalable etch-mask superposition technique based on thermally assisted nanotransfer printing (T-nTP) of Cr line patterns. The orthogonal superposition of linear Cr mask patterns creates double-height cross-point arrays that effectively and selectively protect the underlying SiO2 during subsequent reactive ion etching. This process generates highly uniform nanoscale pillar arrays with an extremely high density of 0.1 tera-pillars per square inch, eliminating the need for high-cost patterning platforms. As an exemplary application, we demonstrate the use of these perfectly ordered nanopillar arrays as high-performance surface-enhanced Raman scattering (SERS) sensors through the deposition of noble metal films on the nanopillar surface. These nanopillars enable exceptionally uniform SERS intensity with spot variations of less than 7% in methylene blue (MB) measurements. Additionally, they exhibit sensitive detections and accurate quantification for thiabendazole (TBZ) at concentrations as low as 10-8 M, along with multicycle reusability without noticeable degradation, owing to the outstanding robustness of the SiO2 nanopillars.

Anti-Biofilm Performance of Resin Nanopillars Inspired from Cicada Wing Surface for Staphylococcus spp

The increase in infections derived from biofilms from Staphylococcal spp. prompted us to develop novel strategies to inhibit biofilm development. Nanoscale protrusion structures (nanopillars) observed on the wings of dragonflies and cicadas have recently gained notable attention owing to their physical, antimicrobial, and bactericidal properties. Thus, they are not only expected to reduce the damage caused by chemical antimicrobial agents to human health and the environment, but also to serve as a potential countermeasure against the emergence of antimicrobial-resistant bacteria (ARB). In this study, we evaluated the anti-biofilm effects of cyclo-olefin polymer (COP) nanopillars by changing the wettability of surfaces ranging in height from 100 to 500 nm against Staphylococcus spp., such as Staphylococcus aureus NBRC 100910 (MSSA), Staphylococcus aureus JCM 8702 methicillin-resistant S. aureus (MRSA), and Staphylococcus epidermidis ATCC 35984. The results clearly show that the fabricated nanopillar structures exhibited particularly strong biofilm inhibition against MRSA, with inhibition rates ranging from 51.2% to 62.5%. For MSSA, anti-biofilm effects were observed only at nanopillar heights of 100-300 nm, with relatively low hydrophobicity, with inhibition rates ranging from 23.9% to 40.8%. Conversely, no significant anti-biofilm effect was observed for S. epidermidis in any of the nanopillar structures. These findings suggest that the anti-biofilm properties of nanopillars vary among bacteria of the same species. In other words, by adjusting the height of the nanopillars, selective anti-biofilm effects against specific bacterial strains can be achieved.

A supervised machine learning tool to predict the bactericidal efficiency of nanostructured surface

The emergence and rapid spread of multidrug-resistant bacterial strains is a growing concern of public health. Inspired by the natural bactericidal surfaces of lotus leaves and shark skin, increasing attention has been focused on the use of mechano-bactericidal methods to create surfaces with antibacterial and/or bactericidal effects. There have been several studies exploring the bactericidal effect of nanostructured surfaces under various combinations of parameters. However, the correlation and synergies between these factors still need to be clarified. Recently machine learning (ML), which enables prediction or decision-making based on data, has been used in the field of biomaterials with promising results. In this study, we explored ML in nanotechnology to investigate the antimicrobial potential of nanostructured surfaces. A dataset of nanostructured surfaces and their antimicrobial properties was built by extracting the published literature. Based on the literature review and the distribution of our dataset, 70% bactericidal efficiency was selected as a practical benchmark for our classification model that balances stringent bactericidal performance with achievable targets in diverse conditions. Subsequently, we developed an ML classification model, which demonstrated an 81% accuracy in its predictive capability. A regression model was further developed to predict the value of bactericidal efficiency for nanostructured surfaces. Feature importance analysis of the ML models suggested that nanotopographical features have a greater influence on bactericidal properties than material properties, thus providing insight into the principles of the mechano-bactericidal effect of nanostructured surfaces. Overall, this ML model tool could help researchers to effectively select and design the parameters of the surface structure prior to experimentation, thereby improving the timeliness and reducing the number of experiments and the associated costs.

Anisotropic patterns of nanospikes induces anti-biofouling and mechano-bactericidal effects of titanium nanosurfaces with electrical cue

Anti-microbial nanopatterns have attracted considerable attention; however, its principle is not yet fully understood, particularly for inorganic nanopatterns. Titanium nanosurfaces with dense and anisotropically patterned nanospikes regulate biological functions with multiple physical stimulations, which may be because of the nanopattern-induced alternation of surface physical properties. This study aimed to determine the antimicrobial capability of titanium nanosurfaces and their mechanisms. Two types of alkali-etched titanium nanosurfaces with isotropically or anisotropically patterned nanospikes had markedly denser surface protrusions, greater superhydrophilicity, and greater negative charge than machined or micro-roughened titanium surfaces. The crystallographic properties of anisotropic titanium nanosurfaces were similar to those of isotropic nanosurfaces, but markedly higher in electric reactivity at nanoscale. The maximum value of the contact potential difference on titanium surfaces was significantly correlated with the product of the density and anisotropy in the distribution pattern of surface protrusions. Isotropic titanium nanosurfaces did not inhibit the attachment of gram-positive cocci, such as Staphylococcus aureus, whereas anisotropic titanium nanosurfaces substantially inhibited gram-positive cocci attachment. Most gram-negative bacilli, Escherichia coli, died via swelling of the cell body on anisotropic titanium nanosurfaces within 6 h of incubation, in contrast to other titanium surfaces where most of the cells did not lose viability or undergo morphological changes. The extent of cell swelling was positively correlated with the electric reactivity of the titanium surfaces. Titanium nanosurfaces with anisotropically patterned dense nanospikes exerted anti-biofouling or mechano-bactericidal effects on gram-positive or negative bacteria with electrical cue induced by the anisotropy of the nanospike patterns.

Platelet interaction and performance of antibacterial bioinspired nanostructures passivated with human plasma

The ever-increasing ageing of the world population is demanding superior orthopedic devices. Issues such as implant infection, poor osseointegration, or chronic inflammation remain problematic to the lifespan and long-term efficacy of implants. Fabrication of materials with bioinspired nanostructures is one emerging antibacterial strategy to prevent implant infection, however their interactions with blood components, and whether they retain their bactericidal properties in an environment displaying a complex protein corona, remains largely unexplored. In the present study, titanium alloy, commercially pure and plasma-sprayed titania were hydrothermally etched, passivated with human native plasma to develop a protein corona, and then incubated with either Staphylococcus aureus, Pseudomonas aeruginosa or human platelets. Surface analysis was first used to characterize the topography, chemical composition or crystallinity of each material. Fluorescence staining and SEM were performed to evaluate the nanostructure bactericidal properties, as well as to study platelet attachment and morphology. Composition of platelet supernatant was studied using ELISA and flow cytometry. Overall, our study showed that the bioinspired nanostructured surfaces displayed both impressive antibacterial properties in a complex environment, and a superior blood biocompatibility profile in terms of platelet activation (particularly for titanium alloy). Additionally, the amount of pro-inflammatory cytokines released by platelets was found to be no different to that found in native plasma (background levels) and, in some cases, presented a more pro-healing profile with an increased secretion of factors such as TGF-β, PDGF-BB or BMP-2. The nanostructured surfaces performed equally, or better, than hydroxyapatite-coated titanium which is one of the current gold standards in orthopedics. Although further in vivo studies are required to validate these results, such bioinspired nanostructured surfaces certainly show promise to be safely applied to medical device surfaces used in orthopedics and other areas.

Nanoengineering Spikey Surfaces: Investigation of Reversible Organizational Control of Surface-Tethered Polypeptide Brushes

Nature serves as an important source of inspiration for the innovation and development of micro- and nanostructures for advanced functional surfaces and substrates. One example used in nature is a spikey surface ranging from micrometer-sized spikes on pollen grains down to the nanometer-scale protein spikes found on viruses. This study explored the realization of such highly textured surfaces via the nanoengineering of self-assembled poly(γ-benzyl-l-glutamate) "nanospikes", exploiting solvent-induced chain organization, controlled surface chemical functionality, and enhanced stability in the form of polymer brushes. The reversible solvent-responsive behavior of these polymer chains and the aggregation behavior of the chain-ends were investigated via fluorescence characterization and studied through molecular simulations. Vapor-based solvent treatments were developed for orientation control with in situ analysis to understand film response and brush organizational behavior under different selected conditions. The effect of sub-100 nm nanopatterning on surface morphology and chain organization was examined via an integrated approach of experimental and computational studies. The methodologies established in this study present opportunities for engineering sophisticated nanoscale spikey surfaces with high customizability by means of nanolithography combined with solvent-assisted treatments.

Recent Advances in Antibacterial Strategies Based on TiO2 Biomimetic Micro/Nano-Structured Surfaces Fabricated Using the Hydrothermal Method

Ti and its alloys, widely utilized in orthopedic and dental implants, inherently lack antibacterial properties, posing significant infection risks, especially in the context of growing antibiotic resistance. This review critically evaluates non-antibiotic antibacterial strategies, with a particular focus on surface modifications and micro/nano-structured surfaces. Micro/nano-structured surfaces, inspired by natural topographies, utilize physical mechanisms to eradicate bacteria. Despite their potential, the antibacterial efficacy of these surfaces remains insufficient for clinical application. Titanium dioxide (TiO2), known for its excellent photocatalytic antibacterial activity and biocompatibility, is emerging as an ideal candidate for enhancing micro/nano-structured surfaces. By combining the photocatalytic antibacterial effects of TiO2 with the mechanical bactericidal properties of micro/nano-structured surfaces, superior antibacterial performance can be achieved. The hydrothermal method is frequently employed to fabricate TiO2 micro/nano-structured surfaces, and this area of research continues to thrive, particularly in the development of antibacterial strategies. With demonstrated efficacy, combined antibacterial strategies based on TiO2 micro/nano-structured surfaces have become a prominent focus in current research. Consequently, the integration of physical stimulation and chemical release mechanisms may represent the future direction for TiO2 micro/nano-structured surfaces. This review aims to advance the study of TiO2 micro/nano-structured surfaces in antibacterial applications and to inspire more effective non-antibiotic antibacterial solutions.

[Advances in nanostructured surfaces for enhanced mechano-bactericidal applications]

The issue of bacterial drug resistance has remained unresolved, and in recent years, biomimetic nanostructured surfaces inspired by nature have garnered significant attention due to their bactericidal properties demonstrated through mechanical mechanisms. This article reviewed the main research progress in the field of nanostructured mechanical bactericidal surfaces, including various preparation methods for nanostructured surfaces with mechanical bactericidal properties, as well as the basic mechanisms and related physical models of the interaction between bacteria and nanostructured surfaces. In addition, the application of nanostructured surfaces in biomedicine was introduced. Finally, the article proposed the major challenges faced by mechanical bactericidal research and the future development direction.

Bioinspired Zwitterionic Nanowires with Simultaneous Biofouling Reduction and Release

Marine biofouling is a complex and dynamic process that significantly increases the carbon emissions from the maritime industry by increasing drag losses. However, there are no existing non-toxic marine paints that can achieve both effective fouling reduction and efficient fouling release. Inspired by antifouling strategies in nature, herein, a superoleophobic zwitterionic nanowire coating with a nanostructured hydration layer is introduced, which exhibits simultaneous fouling reduction and release performance. The zwitterionic nanowires demonstrate >25% improvement in fouling reduction compared to state-of-the-art antifouling nanostructures, and four times higher fouling-release compared to conventional zwitterionic coatings. Fouling release is successfully achieved under a wall shear force that is four orders of magnitude lower than regular water jet cleaning. The mechanism of this simultaneous fouling reduction and release behavior is explored, and it is found that a combination of 1) a mechanical biocidal effect from the nanowire geometry, and 2) low interfacial adhesion resulting from the nanostructured hydration layer, are the major contributing factors. These findings provide insights into the design of nanostructured coatings with simultaneous fouling reduction and release. The newly established synthesis procedure for the zwitterionic nanowires opens new pathways for implementation as antifouling coatings in the maritime industry and biomedical devices.

Multifunctionally disordered TiO2 nanoneedles prevent periprosthetic infection and enhance osteointegration by killing bacteria and modulating the osteoimmune microenvironment

Rationale: Total hip arthroplasty (THA) and total knee arthroplasty (TKA) are effective interventions for end-stage osteoarthritis; however, periprosthetic infection is a devastating complication of arthroplasty. To safely prevent periprosthetic infection and enhance osteointegration, the surface modification strategy was utilized to kill bacteria, modulate the osteoimmune microenvironment, and improve new bone formation. Methods: We used the hydrothermal method to fabricate a bionic insect wing with the disordered titanium dioxide nanoneedle (TNN) coating. The mussel-inspired poly-dopamine (PDA) and antibacterial silver nanoparticles (AgNPs) were coated on TNN, named AgNPs-PDA@TNN, to improve the biocompatibility and long-lasting bactericidal capacity. The physicochemical properties of the engineered specimen were evaluated with SEM, AFM, XPS spectrum, and water contact assay. The biocompatibility, bactericidal ability, and the effects on macrophages and osteogenic differentiation were assessed with RT-qPCR, Western blotting, live/dead staining, immunofluorescent staining, etc. Results: The AgNPs-PDA@TNN were biocompatible with macrophages and exhibited immunomodulatory ability to promote M2 macrophage polarization. In addition, AgNPs-PDA@TNN ameliorated the cytotoxicity caused by AgNPs, promoted cell spreading, and increased osteogenesis and matrix deposition of BMSCs. Furthermore, AgNPs-PDA@TNN exhibited bactericidal ability against E. coli and S. aureus by the bionic nanostructure and coated AgNPs. Various imaging analyses indicated the enhanced bactericidal ability and improved new bone formation by AgNPs-PDA@TNN in vivo. H&E, Gram, and Masson staining, verified the improved bone formation, less inflammation, infection, and fibrosis encapsulation. The immunofluorescence staining confirmed the immunomodulatory ability of AgNPs-PDA@TNN in vivo. Conclusion: The bionic insect wing AgNPs-PDA@TNN coating exhibited bactericidal property, immunomodulatory ability, and enhanced osteointegration. Thus, this multidimensional bionic implant surface holds promise as a novel strategy to prevent periprosthetic infection.

Bioinspired oriented calcium phosphate nanocrystal arrays with bactericidal and osteogenic properties

The global diffusion of antibiotic resistance poses a severe threat to public health. Addressing antibiotic-resistant infections requires innovative approaches, such as antibacterial nanostructured surfaces (ANSs). These surfaces, featuring ordered arrays of nanostructures, exhibit the ability to kill bacteria upon contact. However, most currently developed ANSs utilize bioinert materials, lacking bioactivity crucial for promoting tissue regeneration, particularly in the context of bone infections. This study introduces ANSs composed of bioactive calcium phosphate nanocrystals. Two distinct ANSs were created through a biomineralization-inspired growth of amorphous calcium phosphate (ACP) precursors. The ANSs demonstrated efficient antibacterial properties against both Gram-negative (P. aeruginosa) and Gram-positive (S. aureus) antibiotic resistant bacteria, with up to 75 % mortality in adhered bacteria after only 4 h of contact. Notably, the ANS featuring thinner and less oriented nano-needles exhibited superior efficacy attributed to simultaneous membrane rupturing and oxidative stress induction. Moreover, the ANSs facilitate the proliferation of mammalian cells, enhancing adhesion, spreading, and reducing oxidative stress. The ANSs displayed also significant bioactivity towards human mesenchymal stem cells, promoting colonization and inducing osteogenic differentiation. Specifically, the ANS with thicker and more ordered nano-needles demonstrated heightened effects. In conclusion, ANSs introduced in this work have the potential to serve as foundation for developing bone graft materials capable of eradicate site infections while concurrently stimulating bone regeneration. STATEMENT OF SIGNIFICANCE: Nanostructured surfaces with antibacterial properties through a mechano-bactericidal mechanism have shown significant potential in fighting antibiotic resistance. However, these surfaces have not been fabricated with bioactive materials necessary for developing devices that are both antibacterial and able to stimulate tissue regeneration. This study demonstrates the feasibility of creating nanostructured surfaces of ordered calcium phosphate nano-needles through a biomineralization-inspired growth. These surfaces exhibit dual functionality, serving as effective bactericidal agents against Gram-negative and Gram-positive antibiotic-resistant bacteria while also promoting the proliferation of mammalian cells and inducing osteogenic differentiation of human mesenchymal stem cells. Consequently, this approach holds promise in the context of bone infections, introducing innovative nanostructured surfaces that could be utilized in the development of antimicrobial and osteogenic grafts.

Electrospun O-quaternary ammonium chitosan/polyvinyl alcohol nanofibrous film by application of Box-Behnken design response surface method for eliminating pathogenic bacteria

In this study, O-quaternary ammonium chitosan (O-HTCC) containing bicationic antibacterial active groups was synthesized to develop an O-HTCC/PVA porous nanofibrous film to enhance antibacterial activity, leveraging surface modification and nano-porous structure design. Uniform and smooth nanofibrous structures (average diameter: 72-294 nm) were successfully obtained using a simple and feasible electrospinning method. A response surface model via Box-Behnken design (BBD) was used to clarify the interaction relationship between O-HTCC fiber diameter and three critical electrospinning parameters (O-HTCC concentration, applied voltage, feed flow rate), predicting that the minimum O-HTCC fiber diameter (174 nm) could be achieved with 7 wt% of O-HTCC concentration, 14 kV of voltage, and 0.11 mL/h of feed flow rate. Linear regression (R2 = 0.9736, Radj2 = 0.9716) and the Anderson Darling test demonstrated the excellent fit of the RSM-BBD model. Compared to N-HTCC/PVA nanofibrous film, the O-HTCC/PVA version showed increased growth inhibition and more effective antibacterial efficacies against Escherichia coli (E. coli) (~;86.34 %) and Staphylococcus aureus (S. aureus) (~;99.99 %). DSC revealed improved thermal stability with an increased melting temperature (238 °C) and endothermic enthalpy (157.7 J/g). This study holds potential for further development of antibacterial packaging to extend food shelf-life to reduce bacterial infection.

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.

Advances in antimicrobial orthopaedic devices and FDA regulatory challenges

Implant-associated infections, caused by the formation of biofilms especially antibiotic resistant organisms, are among the leading causes of orthopaedic implant failure. Current strategies to combat infection and biofilm focus on either inhibiting bacterial growth or preventing bacterial adherence that could lead to biofilm creation. Despite research on developing numerous antimicrobial orthopaedic devices, to date, no robust solution has been translated to the clinic. One of the key bottlenecks is the disconnect between researchers and regulatory agencies. In this review, we outline recent strategies for minimizing orthopaedic implant-associated infections. In addition, we discuss the relevant Food and Drug Administration regulatory perspectives, challenges. We also highlight emerging technologies and the directions the field that is expected to expand. We discuss in depth challenges that include identifying strategies that render implants antibacterial permanently or for a long period of time without the use of antimicrobial compounds that could generate resistance in pathogens and negatively impact osseointegration.

Emerging trends and future challenges of advanced 2D nanomaterials for combating bacterial resistance

The number of multi-drug-resistant bacteria has increased over the last few decades, which has caused a detrimental impact on public health worldwide. In resolving antibiotic resistance development among different bacterial communities, new antimicrobial agents and nanoparticle-based strategies need to be designed foreseeing the slow discovery of new functioning antibiotics. Advanced research studies have revealed the significant disinfection potential of two-dimensional nanomaterials (2D NMs) to be severed as effective antibacterial agents due to their unique physicochemical properties. This review covers the current research progress of 2D NMs-based antibacterial strategies based on an inclusive explanation of 2D NMs' impact as antibacterial agents, including a detailed introduction to each possible well-known antibacterial mechanism. The impact of the physicochemical properties of 2D NMs on their antibacterial activities has been deliberated while explaining the toxic effects of 2D NMs and discussing their biomedical significance, dysbiosis, and cellular nanotoxicity. Adding to the challenges, we also discussed the major issues regarding the current quality and availability of nanotoxicity data. However, smart advancements are required to fabricate biocompatible 2D antibacterial NMs and exploit their potential to combat bacterial resistance clinically.

Bioinspired Hybrid Nanostructured PEEK Implant with Enhanced Antibacterial and Anti-inflammatory Synergy

Implant-associated infections and excessive immune responses are two major postsurgical issues for successful implantation. However, conventional strategies including antibiotic treatment and inflammatory regulation are always compromised due to the comodification of various biochemical agents and instances of functional interference. It is imperative to provide implant surfaces with satisfactory antibacterial and anti-inflammatory properties. Here, a dual-effect nanostructured polyetheretherketone (PEEK) surface (NP@PDA/Zn) with bionic mechano-bactericidal nanopillars and immobilized immunomodulatory Zn2+ is designed. The constructed hybrid nanopillars display remarkable antibacterial performance against Gram-negative and Gram-positive strains through the synergy of physical and chemical bactericidal effects imposed by nanopillars and Zn2+. Meanwhile, the immunoregulatory property is evaluated through the investigation of macrophage polarization both in vitro and in vivo, and the results reveal that NP@PDA/Zn could downregulate the expression of M1-related cytokines and decrease the M1 macrophage recruitment to lower the inflammatory response. Notably, the surface exhibited exceptional biocompatibility with discerning biocidal activity between bacterial and mammalian cells and antioxidant performance that effectively scavenges ROS, minimizing potential cytotoxicity. Taken together, NP@PDA/Zn presents a convenient and promising strategy of combining synergistic bactericidal activity and inflammatory regulation without any mutual interference, which can support the development of multifunctional implant-associated materials.

Insight into antibacterial effect of titanium nanotubular surfaces with focus on Staphylococcus aureus and Pseudomonas aeruginosa

Materials used for orthopedic implants should not only have physical properties close to those of bones, durability and biocompatibility, but should also exhibit a sufficient degree of antibacterial functionality. Due to its excellent properties, titanium is still a widely used material for production of orthopedic implants, but the unmodified material exhibits poor antibacterial activity. In this work, the physicochemical characteristics, such as chemical composition, crystallinity, wettability, roughness, and release of Ti ions of the titanium surface modified with nanotubular layers were analyzed and its antibacterial activity against two biofilm-forming bacterial strains responsible for prosthetic joint infection (Staphylococcus aureus and Pseudomonas aeruginosa) was investigated. Electrochemical anodization (anodic oxidation) was used to prepare two types of nanotubular arrays with nanotubes differing in dimensions (with diameters of 73 and 118 nm and lengths of 572 and 343 nm, respectively). These two surface types showed similar chemistry, crystallinity, and surface energy. The surface with smaller nanotube diameter (TNT-73) but larger values of roughness parameters was more effective against S. aureus. For P. aeruginosa the sample with a larger nanotube diameter (TNT-118) had better antibacterial effect with proven cell lysis. Antibacterial properties of titanium nanotubular surfaces with potential in implantology, which in our previous work demonstrated a positive effect on the behavior of human gingival fibroblasts, were investigated in terms of surface parameters. The interplay between nanotube diameter and roughness appeared critical for the bacterial fate on nanotubular surfaces. The relationship of nanotube diameter, values of roughness parameters, and other surface properties to bacterial behavior is discussed in detail. The study is believed to shed more light on how nanotubular surface parameters and their interplay affect antibacterial activity.

Mechanism of antibacterial property of micro scale rough surface formed by fine-particle bombarding

Fine-particle bombardment (FPB) is typically used to modify metal surfaces by bombarding them with fine particles at high speed. FPB is not a coating technique but is used for forming microscale concavities and convexities on a surface. Previously, we reported that an FPB-treated surface showed antibacterial effects; however, the underlying mechanisms remain unclear. We hypothesized that the pitch size of concavity and convexity, and irregular microscale pattern of FPB-treated surfaces might contribute to the antibacterial performance. In this study, we applied FPB to stainless-steel surfaces and evaluated the antibacterial effects of the FPB-treated surfaces based on ISO 22,196:2007. The FPB-treated surfaces exhibited antibacterial activity against Escherichia coli, with an antibacterial activity value (R) of two or more. Furthermore, our experiments suggest that the antibacterial mechanism of the FPB-treated surface can be attributed to increased oxidative stress in bacteria owing to physical stress from the rough surface. The antibacterial effect of FPB-treated surfaces offers an effective measure against drug-resistant bacteria.

Cell Wall Binding Strategies Based on Cu3SbS3 Nanoparticles for Selective Bacterial Elimination and Promotion of Infected Wound Healing

Utilizing nanomaterials as an alternative to antibiotics, with a focus on maintaining high biosafety, has emerged as a promising strategy to combat antibiotic resistance. Nevertheless, the challenge lies in the indiscriminate attack of nanomaterials on both bacterial and mammalian cells, which limits their practicality. Herein, Cu3SbS3 nanoparticles (NPs) capable of generating reactive oxygen species (ROS) are discovered to selectively adsorb and eliminate bacteria without causing obvious harm to mammalian cells, thanks to the interaction between O of N-acetylmuramic acid in bacterial cell walls and Cu of the NPs. Coupled with the short diffusion distance of ROS in the surrounding medium, a selective antibacterial effect is achieved. Additionally, the antibacterial mechanism is then identified: Cu3SbS3 NPs catalyze the generation of O2•-, which has subsequently been conversed by superoxide dismutase to H2O2. The latter is secondary catalyzed by the NPs to form •OH and 1O2, initiating an in situ attack on bacteria. This process depletes bacterial glutathione in conjunction with the disruption of the antioxidant defense system of bacteria. Notably, Cu3SbS3 NPs are demonstrated to efficiently impede biofilm formation; thus, a healing of MRSA-infected wounds was promoted. The bacterial cell wall-binding nanoantibacterial agents can be widely expanded through diversified design.

Microbiological interpretation of weak ultrasound enhanced biological wastewater treatment - using Escherichia coli degrading glucose as model system

The Escherichia coli (E.coli) degrading glucose irradiated by ultrasound irradiation (20 W, 14 min) was investigated as the model system, the glucose degradation increased by 13 % while the E.coli proliferation decreased by 10 % after culture for 18 h. It indicated a tradeoff effect between substrate degradation and cell proliferation, which drove the enhanced contaminants removal and excess sludge reduction in a weak ultrasound enhanced biological wastewater treatment. The enzymatic activities (catalase, superoxide dismutase, adenosine triphosphatases, lactic dehydrogenase, membrane permeability, intracellular reactive oxygen species and calcium ion of E. coli increased immediately by 12 %, 63 %, 124 %, 19 %, 15 %, 4-fold and 38-fold, respectively by ultrasound irradiation power of 20 W for 14 min. Furthermore, the membrane permeability of irradiated E. coli increased by 26 % even though the ultrasound stopped for 10 h. Additionally, pathways associated with glucose degradation and cell proliferation were continuously up-regulated and down-regulated, respectively.

Oxygen-Vacancy-Rich Monolayer BiO2- X Nanosheets for Bacterial Sepsis Management via Dual Physically Antibacterial and Chemically Anti-inflammatory Functions

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. Effective treatment of bacterial sepsis remains challenging due to the rapid progression of infection and the systemic inflammatory response. In this study, monolayer BiO2- X nanosheets (BiO2- X NSs) with oxygen-rich vacancies through sonication-assisted liquid-phase exfoliation are successfully synthesized. Herein, the BiO2- X NSs exhibit a novel nanozyme-enabled intervention strategy for the management of bacterial sepsis, based on its pH dependent dual antibacterial and anti-inflammatory functions. BiO2- X NSs exhibit effective antibacterial by utilizing oxidase (OXD)-like activity. Additionally, BiO2- X NSs can scavenge multiple reactive oxygen species (ROS) and mitigate systemic hyperinflammation by mimicking superoxide dismutase (SOD) and catalase (CAT). These dual capabilities of BiO2- X NSs allow them to address bacterial infection, proinflammatory cytokines secretion and ROS burst collaboratively, effectively reversing the progression of bacterial sepsis. In vivo experiments have demonstrated that BiO2- X NSs significantly reduce bacterial burden, attenuate systemic hyperinflammation, and rapidly rescued organ damage. Importantly, no obvious adverse effects are observed at the administered dose of BiO2- X NSs. This study presents a novel defect engineering strategy for the rational design of high-performance nanozymes and development of new nanomedicines for managing bacterial sepsis.

Versatile Ce(III)‐Terephthalic Acid@Au Metal Organic Frameworks for ROS Elimination and Photothermal Sterilization

Nanozymes have been widely used for treating reactive oxygen species (ROS) caused diseases. However, the ROS‐dependent antibacterial property is inevitably damaged during the process of scavenging ROS, which is unfavorable for the treatment of diseases related to both ROS accumulation and bacterial infections. To address the issues, biomedical materials with both ROS‐elimination ability and ROS‐independent antibacterial capacity are fabricated via in situ depositing spherical Au nanoparticles (Au NPs) on rough surface of metal organic frameworks composed of Ce(III) and terephthalic acid (Ce‐BDC@Au MOFs). The synthesized Ce‐BDC@Au MOFs show multi‐enzymatic activities owing to the reversible conversion between Ce3+ and Ce4+, and can significantly scavenge ROS in cells. The deposition of spherical Au NPs on surface of Ce‐BDC MOFs causes Au NPs to come close proximity for forming plasmon resonance coupling, inducing the resonance wavelength of Au NPs red shifted to NIR region. Based on this, Ce‐BDC@Au MOFs show good photothermal conversion efficiency under NIR laser (808 nm) irradiation. Benefitting from rough surface and photothermal conversion ability, Ce‐BDC@Au MOFs have high antibacterial efficiency against staphylococcus aureus through both mechanically damaging and photothermal destruction. This strategy is biosafety and effectiveness for treating diseases related to both ROS accumulation and bacterial infections.

In Situ Self-Growth of a ZnO Nanorod Array on Nonwoven Fabrics for Empowering Superhydrophobic and Antibacterial Features

ZnO nanorod nonwoven fabrics (ZNRN) were developed through hydrothermal synthesis to facilitate the prevention of the transmission of respiratory pathogens. The superhydrophobicity and antibacterial properties of ZNRN were improved through the response surface methodology. The synthesized material exhibited significant water repellency, indicated by a water contact angle of 163.9°, and thus demonstrated antibacterial rates of 91.8% for Escherichia coli (E. coli) and 79.75% for Staphylococcus aureus (S. aureus). This indicated that E. coli with thinner peptidoglycan may be more easily killed than S. aureus. This study identified significant effects of synthesis conditions on the antibacterial effectiveness, with comprehensive multivariate analyses elucidating the underlying correlations. In addition, the ZnO nanorod structure of ZNRN was characterized through SEM and XRD analyses. It endows the properties of superhydrophobicity (thus preventing bacteria from adhering to the ZNRN surface) and antibacterial capacity (thus damaging cells through the puncturing of these nanorods). Consequently, the alignment of two such features is desired to help support the development of personal protective equipment, which assists in avoiding the spread of respiratory infections.

Bacterial Surface Appendages Modulate the Antimicrobial Activity Induced by Nanoflake Surfaces on Titanium

Bioinspired nanotopography is a promising approach to generate antimicrobial surfaces to combat implant-associated infection. Despite efforts to develop bactericidal 1D structures, the antibacterial capacity of 2D structures and their mechanism of action remains uncertain. Here, hydrothermal synthesis is utilized to generate two 2D nanoflake surfaces on titanium (Ti) substrates and investigate the physiological effects of nanoflakes on bacteria. The nanoflakes impair the attachment and growth of Escherichia coli and trigger the accumulation of intracellular reactive oxygen species (ROS), potentially contributing to the killing of adherent bacteria. E. coli surface appendages type-1 fimbriae and flagella are not implicated in the nanoflake-mediated modulation of bacterial attachment but do influence the bactericidal effects of nanoflakes. An E. coli ΔfimA mutant lacking type-1 fimbriae is more susceptible to the bactericidal effects of nanoflakes than the parent strain, while E. coli cells lacking flagella (ΔfliC) are more resistant. The results suggest that type-1 fimbriae confer a cushioning effect that protects bacteria upon initial contact with the nanoflake surface, while flagella-mediated motility can lead to elevated membrane abrasion. This finding offers a better understanding of the antibacterial properties of nanoflake structures that can be applied to the design of antimicrobial surfaces for future medical applications.

Nano-ZnO-modified hydroxyapatite whiskers with enhanced osteoinductivity for bone defect repair

Hydroxyapatite (HA) whisker (HAw) represents a distinct form of HA characterized by its high aspect ratio, offering significant potential for enhancing the mechanical properties of bone tissue engineering scaffolds. However, the limited osteoinductivity of HAw hampers its widespread application. In this investigation, we observed HAw-punctured osteoblast membranes and infiltrated the cell body, resulting in mechanical damage to cells that adversely impacted osteoblast proliferation and differentiation. To address this challenge, we developed nano-zinc oxide particle-modified HAw (nano-ZnO/HAw). Acting as a reinforcing and toughening agent, nano-ZnO/HAw augmented the compressive strength and ductility of the matrix materials. At the same time, the surface modification with nano-ZnO particles improved osteoblast differentiation by reducing the mechanical damage from HAw to cells and releasing zinc ion, the two aspects collectively promoted the osteoinductivity of HAw. Encouragingly, the osteoinductive potential of 5% nano-ZnO/HAw and 10% nano-ZnO/HAw was validated in relevant rat models, demonstrating the efficacy of this approach in promoting new bone formation in vivo. Our findings underscore the role of nano-ZnO particle surface modification in enhancing the osteoinductivity of HAw from a physical standpoint, offering valuable insights into the development of bone substitutes with favorable osteoinductive properties while simultaneously bolstering matrix material strength and toughness.

Polydopamine-Coated Copper-Doped Co3O4 Nanosheets Rich in Oxygen Vacancy on Titanium and Multimodal Synergistic Antibacterial Study

Medical titanium-based (Ti-based) implants in the human body are prone to infection by pathogenic bacteria, leading to implantation failure. Constructing antibacterial nanocoatings on Ti-based implants is one of the most effective strategies to solve bacterial contamination. However, single antibacterial function was not sufficient to efficiently kill bacteria, and it is necessary to develop multifunctional antibacterial methods. This study modifies medical Ti foils with Cu-doped Co3O4 rich in oxygen vacancies, and improves their biocompatibility by polydopamine (PDA/Cu-Ov-Co3O4). Under near-infrared (NIR) irradiation, nanocoatings can generate •OH and 1O2 due to Cu+ Fenton-like activity and a photodynamic effect of Cu-Ov-Co3O4, and the total reactive oxygen species (ROS) content inside bacteria significantly increases, causing oxidative stress of bacteria. Further experiments prove that the photothermal process enhances the bacterial membrane permeability, allowing the invasion of ROS and metal ions, as well as the protein leakage. Moreover, PDA/Cu-Ov-Co3O4 can downregulate ATP levels and further reduce bacterial metabolic activity after irradiation. This coating exhibits sterilization ability against both Escherichia coli and Staphylococcus aureus with an antibacterial rate of ca. 100%, significantly higher than that of bare medical Ti foils (ca. 0%). Therefore, multifunctional synergistic antibacterial nanocoating will be a promising strategy for preventing bacterial contamination on medical Ti-based implants.

Anodization as a scalable nanofabrication method to engineer mechanobactericidal nanostructures on complex geometries

Bacterial contamination of implant surfaces is one of the primary causes of their failure, and this threat has been further exacerbated due to the emergence of drug-resistant bacteria. Nanostructured mechanobactericidal surfaces that neutralize bacteria via biophysical forces instead of traditional biochemical routes have emerged as a potential remedy against this issue. Here, we report on the bactericidal activity of titania nanotubes (TNTs) prepared by anodization, a well-established and scalable method. We investigate the differences in bacterial behavior between three different topographies and demonstrate the applicability of this technique on complex three-dimensional (3D) geometries. It was found that the metabolic activity of bacteria on such surfaces was lower, indicative of disturbed intracellular processes. The differences in deformations of the cell wall of Gram-negative and positive bacteria were investigated from electron micrographs Finally, nanoindentation experiments show that the nanotubular topography was durable enough against forces typically experienced in daily life and had minimal deformation under forces exerted by bacteria. Our observations highlight the potential of the anodization technique for fabricating mechanobactericidal surfaces for implants, devices, surgical instruments, and other surfaces in a healthcare setting in a cheap, scalable way.

Nanotextured titanium inhibits bacterial activity and supports cell growth on 2D and 3D substrate: A co-culture study

Medical implant-associated infections pose a significant challenge to modern medicine, with aseptic loosening and bacterial infiltration being the primary causes of implant failure. While nanostructured surfaces have demonstrated promising antibacterial properties, the translation of their efficacy from 2D to 3D substrates remains a challenge. Here, we used scalable alkaline etching to fabricate nanospike and nanonetwork topologies on 2D and laser powder-bed fusion printed 3D titanium. The fabricated surfaces were compared with regard to their antibacterial properties against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, and mesenchymal stromal cell responses with and without the presence of bacteria. Finite elemental analysis assessed the mechanical properties and permeability of the 3D substrate. Our findings suggest that 3D nanostructured surfaces have potential to both prevent implant infections and allow host cell integration. This work represents a significant step towards developing effective and scalable fabrication methods on 3D substrates with consistent and reproducible antibacterial activity, with important implications for the future of medical implant technology.