Impact of Bioinspired Nanotopography on the Antibacterial and Antibiofilm Efficacy of Chitosan

Nanotopology-Enabled On-Site Pathogen Detection for Managing Atopic Dermatitis

Atopic dermatitis (AD), a prevalent skin condition often complicated by microbial infection, poses a significant challenge in identifying the responsible pathogen for its effective management. However, a reliable, safe tool for pinpointing the source of these infections remains elusive. In this study, a novel on-site pathogen detection that combines chemically functionalized nanotopology with genetic analysis is proposed to capture and analyze pathogens closely associated with severe atopic dermatitis. The chemically functionalized nanotopology features a 3D hierarchical nanopillar array (HNA) with a functional polymer coating, tailored to isolate target pathogens from infected skin. This innovative nanotopology demonstrates superior pathogenic capture efficiency, favorable entrapment patterns, and non-cytotoxicity. An HNA-assembled stick is utilized to directly retrieve bacteria from infected skin samples, followed by extraction-free quantitative loop-mediated isothermal amplification (direct qLAMP) for validation. To mimic human skin conditions, porcine skin is employed to successfully capture Staphylococcus aureus, a common bacterium exacerbating AD cases. The on-site detection method exhibits an impressive detection limit of 103 cells mL-1. The HNA-assembled stick represents a promising tool for on-site detection of bacteria associated with atopic dermatitis. This innovative approach enables to deepen the understanding of AD pathogenesis and open avenues for more effective management strategies for chronic skin conditions.

Polysaccharide-based antibacterial coating technologies

To tackle antimicrobial resistance, a global threat identified by the United Nations, is a common cause of healthcare-associated infections (HAI) and is responsible for significant costs on healthcare systems, a substantial amount of research has been devoted to developing polysaccharide-based strategies that prevent bacterial attachment and biofilm formation on surfaces. Polysaccharides are essential building blocks for life and an abundant renewable resource that have attracted much attention due to their intrinsic remarkable biological potential antibacterial activities. If converted into efficient antibacterial coatings that could be applied to a broad range of surfaces and applications, polysaccharide-based coatings could have a significant potential global impact. However, the ultimate success of polysaccharide-based antibacterial materials will be determined by their potential for use in manufacturing processes that are scalable, versatile, and affordable. Therefore, in this review we focus on recent advances in polysaccharide-based antibacterial coatings from the perspective of fabrication methods. We first provide an overview of strategies for designing polysaccharide-based antimicrobial formulations and methods to assess the antibacterial properties of coatings. Recent advances on manufacturing polysaccharide-based coatings using some of the most common polysaccharides and fabrication methods are then detailed, followed by a critical comparative overview of associated challenges and opportunities for future developments. STATEMENT OF SIGNIFICANCE: Our review presents a timely perspective by being the first review in the field to focus on advances on polysaccharide-based antibacterial coatings from the perspective of fabrication methods along with an overview of strategies for designing polysaccharide-based antimicrobial formulations, methods to assess the antibacterial properties of coatings as well as a critical comparative overview of associated challenges and opportunities for future developments. Meanwhile this work is specifically targeted at an audience focused on featuring critical information and guidelines for developing polysaccharide-based coatings. Including such a complementary work in the journal could lead to further developments on polysaccharide antibacterial applications.

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.

Thermoresponsive Nanostructures: From Mechano-Bactericidal Action to Bacteria Release

Overuse of antibiotics can increase the risk of notorious antibiotic resistance in bacteria, which has become a growing public health concern worldwide. Featured with the merit of mechanical rupture of bacterial cells, the bioinspired nanopillars are promising alternatives to antibiotics for combating bacterial infections while avoiding antibacterial resistance. However, the resident dead bacterial cells on nanopillars may greatly impair their bactericidal capability and ultimately impede their translational potential toward long-term applications. Here, we show that the functions of bactericidal nanopillars can be significantly broadened by developing a hybrid thermoresponsive polymer@nanopillar-structured surface, which retains all of the attributes of pristine nanopillars and adds one more: releasing dead bacteria. We fabricate this surface through coaxially decorating mechano-bactericidal ZnO nanopillars with thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) brushes. Combining the benefits of ZnO nanopillars and PNIPAAm chains, the antibacterial performances can be controllably regulated between ultrarobust mechano-bactericidal action (∼99%) and remarkable bacteria-releasing efficiency (∼98%). Notably, both the mechanical sterilization against the live bacteria and the controllable release for the pinned dead bacteria solely stem from physical actions, stimulating the exploration of intelligent structure-based bactericidal surfaces with persistent antibacterial properties without the risk of triggering drug resistance.

Antifungal Carvacrol Loaded Chitosan Nanoparticles

The increased prevalence and incidence of fungal infections, of which Candida albicans represents one of the most life-threatening organisms, is prompting the scientific community to develop novel antifungal molecules. Many essential oils components are attracting attention for their interesting antifungal activities. Given the chemical and physical characteristics of these compounds, the use of appropriate nanodelivery systems is becoming increasingly widespread. In this study, chitosan nanoparticles were prepared using an ionic gelation procedure and loaded with the phenolic monoterpene carvacrol. After a bioassay guided optimization, the best nanoparticle formulation was structurally characterized by means of different spectroscopic (UV, FTIR and DLS) and microscopy techniques (SEM) and described for their functional features (encapsulation efficiency, loading capacity and release kinetics). The antifungal activity of this formulation was assayed with different Candida spp., both in planktonic and biofilm forms. From these studies, it emerged that the carvacrol loaded nanoparticles were particularly active against planktonic forms and that the antibiofilm activity was highly dependent on the species tested, with the C. tropicalis and C. krusei strains resulting as the most susceptible.

3D Hierarchical Polyaniline-Metal Hybrid Nanopillars: Morphological Control and Its Antibacterial Application

Effective and reliable antibacterial surfaces are in high demand in modern society. Although recent works have shown excellent antibacterial performance by combining unique hierarchical nanotopological structures with functional polymer coating, determining the antibacterial performance arising from morphological changes is necessary. In this work, three-dimensional (3D) hierarchical polyaniline–gold (PANI/Au) hybrid nanopillars were successfully fabricated via chemical polymerization (i.e., dilute method). The morphology and structures of the PANI/Au nanopillars were controlled by the reaction time (10 min to 60 h) and the molar concentrations of the monomer (0.01, 0.1, and 1 M aniline), oxidant (0.002, 0.0067, 0.01, and 0.02 M ammonium persulfate), and acid (0.01, 0.1, 1, and 2 M perchloric acid). These complex combinations allow controlling the hierarchical micro- to nanostructure of PANI on a nanopillar array (NPA). Furthermore, the surface of the 3D PANI/Au hierarchical nanostructure can be chemically treated while maintaining the structure using initiated chemical vapor deposition. Moreover, the excellent antibacterial performance of the 3D PANI/Au hierarchical nanostructure (HNS) exceeds 99% after functional polymer coating. The excellent antibacterial performance of the obtained 3D PANI/Au HNS is mainly because of the complex topological and physicochemical surface modification. Thus, these 3D PANI/Au hierarchical nanostructures are promising high-performance antibacterial materials.

Antibiofilm Activity of Gallium(III) Complexed Anionic Polymers in Combination with Antibiotics

Pseudomonas aeruginosa (P. aeruginosa) is a life-threatening pathogen associated with multiantibiotic resistance, which is largely caused by its strong ability to form biofilms. Recent research has revealed that gallium (III) shows an activity against the biofilm of P. aeruginosa by interfering with Fe metabolism. The antibacterial activity of the combination of Ga³⁺ ion and antibiotic rifampicin (RMP) against P. aeruginosa PAO1 is investigated. An anionic polymer poly{{2-[(2-methylprop-2-enoyl)oxy]ethyl}phosphonic acid} (PDMPOH) is exploited to form complexes (GaPD) with Ga³⁺ . The GaPD complexes act as a carrier of Ga³⁺ and release Ga³⁺ via enzymatic degradation by bacterial lipases. GaPD is found to damage the outer membrane, leading to enhanced cellular uptake of RMP and Ga³⁺ due to increased outer membrane permeability, which inhibits the RNA polymerase and interferes with Fe metabolism. The antibiofilm activity and biocompatibility of the GaPD system offer a promising treatment option for P. aeruginosa biofilm-related infections.

Antimicrobial Hybrid Coatings Combining Enhanced Biocidal Activity under Visible-Light Irradiation with Stimuli-Renewable Properties

Hybrid, organic-inorganic, biocidal films exhibiting polishing properties were developed as effective long-lasting antimicrobial surface coatings. The films were prepared using cationically modified chitosan, synthesized by the reaction with 3-bromo-N,N,N-trimethylpropan-1-aminium bromide, to introduce permanent biocidal quaternary ammonium salt (QAS) groups along the polymer backbone and were cross-linked by a novel, pH-cleavable acetal cross-linker, which allowed polishing the hybrid coatings with the solution pH. TiO₂ nanoparticles, modified with reduced graphene oxide (rGO) sheets, to narrow their band gap energy value and shift their photocatalytic activity in the visible light regime, were introduced within the polymer film to enhance its antibacterial activity. The hybrid coatings exhibited an effective biocidal activity in the dark (∼2 Log and ∼3 Log reduction for Gram-negative and Gram-positive bacteria, respectively), when only the QAS sites interacted with the bacteria membrane, and an excellent biocidal action upon visible-light irradiation (∼5 Log and ∼6 Log reduction for Gram-negative and Gram-positive bacteria, respectively) due to the synergistic antimicrobial effect of the QAS moieties and the rGO-modified TiO₂ nanoparticles. The gradual decrease in the film thickness, upon immersion of the coatings in mildly basic (pH 8), neutral (pH 7), and acidic (pH 6) media, reaching 10, 20, and 70% reduction, respectively, after 60 days of immersion time, confirmed the polishing behavior of the films, whereas their effective antimicrobial action was retained. The biocompatibility of the hybrid films was verified in human cell culture studies. The proposed approach enables the facile development of highly functional coatings, combining biocompatibility and bactericidal action with a "kill and self-clean" mechanism that allows the regeneration of the outer surface of the coating leading to a strong and prolonged antimicrobial action.

Ultrafast physical bacterial inactivation and photocatalytic self-cleaning of ZnO nanoarrays for rapid and sustainable bactericidal applications

Various nanostructured surfaces have been developed recently to physically inactivate bacteria, for reducing the rapidly spreading threat of pathogenic bacteria. However, it generally takes several hours for these surfaces to inactivate most of the bacteria, which greatly limits their application in the fields favoring rapid bactericidal performance. Besides, the accumulated bacteria debris left on these surfaces is rarely discussed in the previous reports. Herein we report the nanotip-engineered ZnO nanoarrays (NAs) with ultrafast physical bactericidal rate and the ability to photocatalytically remove the bacteria debris. Neither chemical (Zn²⁺ or reactive oxygen species) nor photocatalytic effect leads to the ultrafast bactericidal rate, where 97.5% of E. coli and 94.9% of S. aureus are inactivated within only 1 min. The simulation analysis further supported our proposed mechanism attributing the ultrafast bactericidal activity to the great stress enabled by the uneven topography. Moreover, the re-exposure of the ZnO NAs nanotips can be achieved in only 10 min under a mild UV light source. This study not only presents an ultrafast physical bactericidal activity, but also demonstrates the potential of the recyclable and photocatalytic self-cleaning functions of theses surfaces for applications that desire rapid and sustainable bactericidal performance.

Hydrophilic Mechano-Bactericidal Nanopillars Require External Forces to Rapidly Kill Bacteria

Nanopillars have been shown to mechanically damage bacteria, suggesting a promising strategy for future antibacterial surfaces. However, the mechanisms underlying this phenomena remain unclear, which ultimately limits translational potential toward real-world applications. Using real-time and end-point analysis techniques, we demonstrate that in contrast to initial expectations, bacteria on multiple hydrophilic "mechano-bactericidal" surfaces remained viable unless exposed to a moving air-liquid interface, which caused considerable cell death. Reasoning that normal forces arising from surface tension may underlie this mechano-bactericidal activity, we developed computational and experimental models to estimate, manipulate, and recreate the impact of these forces. Our experiments together demonstrate that a critical level of external force acting on cells attached to nanopillar surfaces can rapidly deform and rupture bacteria. These studies provide fundamental physical insight into how nanopillar surfaces can serve as effective antibacterial materials and suggest use-conditions under which such nanotechnology approaches may provide practical value.

Water-Based Scalable Methods for Self-Cleaning Antibacterial ZnO-Nanostructured Surfaces

Bacterial colonization poses significant health risks, such as infestation of surfaces in biomedical applications and clean water unavailability. If maintaining the surrounding water clean is a target, developing surfaces with strong bactericidal action, which is facilitated by bacterial access to the surface and mixing, can be a solution. On the other hand, if sustenance of a surface free of bacteria is the goal, developing surfaces with ultralow bacterial adhesion often suffices. Here we report a facile, scalable, and environmentally benign strategy that delivers customized surfaces for these challenges. For bactericidal action, nanostructures of inherently antibacterial ZnO, through simple immersion of zinc in hot water, are fabricated. The resulting nanostructured surface exhibits extreme bactericidal effectiveness (9250 cells cm^–2 h^–1) that eliminates bacteria in direct contact and also remotely through the action of reactive oxygen species. Remarkably, the remote bactericidal action is achieved without the need for any illumination, otherwise required in conventional approaches. As a result, ZnO nanostructures yield outstanding water disinfection of >99.98%, in the dark, by inactivating the bacteria within 3 h. Moreover, Zn²⁺ released to the aqueous medium from the nanostructured ZnO surface have a concentration of 0.73 ± 0.15 ppm, markedly below the legal limit for safe drinking water (5–6 ppm). The same nanostructures, when hydrophobized (through a water-based or fluorine-free spray process), exhibit strong bacterial repulsion, thus substantially reducing bacterial adhesion. Such environmentally benign and scalable methods showcase pathways toward inhibiting surface bacterial colonization.

Nanostructured Gold Coating for Prevention of Biofilm Development in Medical Devices

Bacterial biofilms on medical devices (MDs) can cause deadly infections due to their resistance to antibiotics. Technology to prevent this kind of complication is urgently needed because they impact not only patients' lives but also hospital budgets. In this article, the creation and testing of an easy-to-produce antibiofilm (more precisely antibiofouling) coating are described for the first time. This coating can be applied to catheters, prostheses, and other plastic pieces, even after they have been manufactured. Rapid and ecofriendly synthesis of nanostructured gold coating was done in situ in just 15 minutes. Complete characterization and microbiological analysis of its antibiofouling capacity are presented. The coating prevents biofilm formation of pathogenic clinical isolates and ATCC strains on MDs, possibly due to its complex nanostructured gold surface. If the next generation of MDs is coated with this kind of antibiofouling technology, biofilm-related infections could be dramatically reduced. Graphical Abstract [Figure: see text].

Adhesion and bactericidal properties of nanostructured surfaces dependent on bacterial motility

Different nanostructured surfaces have bactericidal properties that arise from the interaction between the bacteria and the nanostructured surface. In this study, we focused on the relationship between bacterial motility and bactericidal properties. The motility of Escherichia coli (E. coli) was tuned by genetic engineering, and four types of E. coli (wild type (WT), lacking flagella, and flagellated with deficient motility or deficient chemotaxis) were used to evaluate the adhesion and bactericidal properties of nanostructured surfaces. Cicada (Cryptotympana facialis) wings and Si nano-pillar array substrates were used as natural and artificial nanostructured surfaces, respectively. Differences in motility and chemotaxis strongly influenced the adhesion behavior and to some extent, the damage to the cell membrane. These results suggest that the bactericidal properties of nanostructured surfaces depend on bacterial motility.

Bactericidal effect derived from nanostructured surface was evaluated in the point of view of the motility of E. coli. The results suggest that the properties strongly depend on bacterial motility.

Mussel-Inspired Surface Functionalization of PET with Zwitterions and Silver Nanoparticles for the Dual-Enhanced Antifouling and Antibacterial Properties

Herein, we designed and constructed a dual functional surface with antimicrobial and antifouling abilities to prevent protein and bacterial attachment that are significant challenges in biomedical devices. Primary amino-group-capped sulfobetaine of DMMSA was synthesized and then grafted onto polydopamine pretreated PET sheets via click chemistry. The sheets were subsequently immersed into silver ion solution, in which the absorbed silver ions were reduced to silver nanoparticles (AgNPs) in situ by a polydopamine layer. The antifouling assays demonstrated that the resultant PET/DMMSA/AgNPs sheets exhibited great antifouling performances against bovine serum albumin (BSA), bovine fibrinogen (BFG), platelets, and bacteria, the critical proteins/microorganisms leading to implant failure. The antibacterial data suggested that the sheets had dual functions as inhibitors of bacterial growth and bactericide and could efficiently delay the biofilm formation. This repelling and killing approach is green and simple, with potential biomedical applications.

Ornamental morphology of ionic liquid functionalized ternary doped N, P, F and N, B, F-reduced graphene oxide and their prevention activities of bacterial biofilm-associated with orthopedic implantation

The multifunctional biological active material design for bone tissue engineering is essential to induce osteoblast cell proliferation and attachment. Adhesion of bacteria on biomaterials to produce biofilms can be major contributors to the pathogenesis of implant material associated infections. This research work focuses on NPF& NBF elemental doping and functionalization of reduced graphene oxide using an imidazolium-based ionic liquid such as BMIM PF₆ and BMIM BF₄ by hydrothermal method. The resulting tri doped reduced graphene oxide (NPF-rGO and NBF-rGO) composite was further used as a scaffold for bone tissue engineering and anti-biofilm activities. The observation of the effect of NPF-rGO and NBF-rGO on the morphology, adhesion and cell proliferation of HOS cell was investigated. Moreover, the tri doped composite tested its antibiofilm properties against B. subtilis, E. coli, K. pneumoniae, and P. aeruginosa pathogenic bacteria. In-vitro studies clearly show the effectiveness of N, P, B, and F doping promoting the rGO mineralization, biocompatibility, and destruction of bacterial biofilm formation. The result of this study suggests that NPF-rGO and NBF-rGO hybrid material will be a promising scaffold for bone reaeration and implantation with a minimal bacterial infection.

Facile Fabrication of Multifunctional ZnO Urchins on Surfaces

Functional ZnO nanostructured surfaces are important in a wide range of applications. Here we report the simple fabrication of ZnO surface structures at near room temperature with morphology resembling that of sea urchins, with densely packed, μm-long, tapered nanoneedles radiating from the urchin center. The ZnO urchin structures were successfully formed on several different substrates with high surface density and coverage, including silicon (Si), glass, polydimethylsiloxane (PDMS), and copper (Cu) sheets, as well as Si seeded with ZnO nanocrystals. Time-resolved SEM revealed growth kinetics of the ZnO nanostructures on Si, capturing the emergence of “infant” urchins at the early growth stage and subsequent progressive increases in the urchin nanoneedle length and density, whilst the spiky nanoneedle morphology was retained throughout the growth. ε-Zn(OH)2 orthorhombic crystals were also observed alongside the urchins. The crystal structures of the nanostructures at different growth times were confirmed by synchrotron X-ray diffraction measurements. On seeded Si substrates, a two-stage growth mechanism was identified, with a primary growth step of vertically aligned ZnO nanoneedle arrays preceding the secondary growth of the urchins atop the nanoneedle array. The antibacterial, anti-reflective, and wetting functionality of the ZnO urchins—with spiky nanoneedles and at high surface density—on Si substrates was demonstrated. First, bacteria colonization was found to be suppressed on the surface after 24 h incubation in gram-negative Escherichia coli (E. coli) culture, in contrast to control substrates (bare Si and Si sputtered with a 20 nm ZnO thin film). Secondly, the ZnO urchin surface, exhibiting superhydrophilic property with a water contact angle ~ 0°, could be rendered superhydrophobic with a simple silanization step, characterized by an apparent water contact angle θ of 159° ± 1.4° and contact angle hysteresis ∆θ < 7°. The dynamic superhydrophobicity of the surface was demonstrated by the bouncing-off of a falling 10 μL water droplet, with a contact time of 15.3 milliseconds (ms), captured using a high-speed camera. Thirdly, it was shown that the presence of dense spiky ZnO nanoneedles and urchins on the seeded Si substrate exhibited a reflectance R < 1% over the wavelength range λ = 200–800 nm. The ZnO urchins with a unique morphology fabricated via a simple route at room temperature, and readily implementable on different substrates, may be further exploited for multifunctional surfaces and product formulations.

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

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