Microenvironment-Responsive Magnetic Nanocomposites Based on Silver Nanoparticles/Gentamicin for Enhanced Biofilm Disruption by Magnetic Field

Smart self-defensive coatings with bacteria-triggered antimicrobial response for medical devices

Bacterial colonization and biofilm formation on medical devices represent one of the most urgent and critical challenges in modern healthcare. These issues not only pose serious threats to patient health by increasing the risk of infections but also exert a considerable economic burden on national healthcare systems due to prolonged hospital stays and additional treatments. To address this challenge, there is a need for smart, customized biomaterials for medical device fabrication, particularly through the development of surface modification strategies that prevent bacterial adhesion and the growth of mature biofilms. This review explores three bioinspired approaches through which antibacterial and antiadhesive coatings can be engineered to exhibit smart, stimuli-responsive features. This responsiveness is greatly valuable as it provides the coatings with a controlled, on-demand antibacterial response that is activated only in the presence of bacteria, functioning as self-defensive coatings. Such coatings can be designed to release antibacterial agents or change their surface properties/conformation in response to specific stimuli, like changes in pH, temperature, or the presence of bacterial enzymes. This targeted approach minimizes the risk of developing antibiotic resistance and reduces the need for continuous, high-dose antibacterial treatments, thereby preserving the natural microbiome and further reducing healthcare costs. The final part of the review reports a critical analysis highlighting the potential improvements and future evolutions regarding antimicrobial self-defensive coatings and their validation.

Escaping the ESKAPE pathogens: A review on antibiofilm potential of nanoparticles

ESKAPE pathogens, a notorious consortium comprising Enterococcusfaecium, Staphylococcusaureus, Klebsiellapneumoniae, Acinetobacterbaumannii, Pseudomonasaeruginosa, and Enterobacter species, pose formidable challenges in healthcare settings due to their multidrug-resistant nature. The increasing global cases of antimicrobial-resistant ESKAPE pathogens are closely related to their remarkable ability to form biofilms. Thus, understanding the unique mechanisms of antimicrobial resistance of ESKAPE pathogens and the innate resilience of biofilms against traditional antimicrobial agents is important for developing innovative strategies to establish effective control methods against them. This review offers a thorough analysis of biofilm dynamics, with a focus on the general mechanisms of biofilm formation, the significant contribution of persister cells in the resistance mechanisms, and the recurrence of biofilms in comparison to planktonic cells. Additionally, this review highlights the potential strategies of nanoparticles for managing biofilms in the ESKAPE group of pathogens. Nanoparticles, with their unique physicochemical properties, provide promising opportunities for disrupting biofilm structures and improving antimicrobial effectiveness. The review has explored interactions between nanoparticles and biofilms, covering a range of nanoparticle types such as metal, metal-oxide, surface-modified, and functionalized nanoparticles, along with organic nanoparticles and nanomaterials. The additional focus of this review also encompasses green synthesis techniques of nanoparticles that involve plant extract and supernatants from bacterial and fungal cultures as reducing agents. Furthermore, the use of nanocomposites and nano emulsions in biofilm management of ESKAPE is also discussed. To conclude, the review addresses the current obstacles and future outlooks in nanoparticle-based biofilm management, stressing the necessity for further research and development to fully exploit the potential of nanoparticles in addressing biofilm-related challenges.

Iron Oxide Nanoparticles as Promising Antibacterial Agents of New Generation

Antimicrobial resistance (AMR) is growing into a major public health crisis worldwide. The reducing alternatives to conventional agents starve for novel antimicrobial agents. Due to their unique magnetic properties and excellent biocompatibility, iron oxide nanoparticles (IONPs) are the most preferable nanomaterials in biomedicine, including antibacterial therapy, primarily through reactive oxygen species (ROS) production. IONP characteristics, including their size, shape, surface charge, and superparamagnetism, influence their biodistribution and antibacterial activity. External magnetic fields, foreign metal doping, and surface, size, and shape modification improve the antibacterial effect of IONPs. Despite a few disadvantages, IONPs are expected to be promising antibacterial agents of a new generation.

Facile synthesis of magnetic intelligent sensors for the pH-sensitive controlled capture of Cr(vi)

In this work, intelligent pH-sensitive sensors (Fe3O4/RhB@PAM) for Cr(vi) detection were successfully synthesized based on polyacrylamide (PAM) and Rhodamine B (RhB) co-modified Fe3O4 nanocomposites. The characterization results indicated that the sensors had many favorable properties, including suitable size, stable crystal structure and excellent magnetic response performance (47.59 emu g-1). In addition, the fluorescence changes during the detection process indicated that Fe3O4/RhB@PAM were "ON-OFF" intelligent sensors. When the Fe3O4/RhB@PAM sensors were placed in acidic Cr(vi) solution (pH 4), PAM acted as a pH-responsive "gatekeeper" releasing RhB, and the fluorescence intensity of released RhB was weakened by the complexation of Cr(vi). Furthermore, the fluorescence changes of the magnetic sensors were remarkably specific for Cr(vi) even in the presence of other competitive cations, and the limit of detection (LOD) for Cr(vi) was lower (0.347 μM) than the value recommended by the World Health Organization (0.96 μM). All the results presented in this study showed that the Fe3O4/RhB@PAM sensors had significant potential for Cr(vi) detection in acidic environmental samples.

Antibiofilm activity of mesoporous silica nanoparticles against the biofilm associated infections

In pharmaceutical industries, various chemical carriers are present which are used for drug delivery to the correct target sites. The most popular and upcoming drug delivery carriers are mesoporous silica nanoparticles (MSN). The main reason for its popularity is its ability to be specific and optimize the drug delivery process in a controlled manner. Nowadays, MSNs are widely used to eradicate various microbial infections, especially the ones related to biofilms. Biofilms are sessile groups of cells that live by forming a consortium and exhibit antibacterial resistance (AMR). They exhibit AMR by extracellular polymeric substances (EPS) and various quorum sensing (QS) signaling molecules. Usually, bacterial and fungal cells are capable of forming biofilms. These biofilms are pathogenic. In the majority of the cases, biofilms cause nosocomial diseases. This review will focus on the antibiofilm activities of MSN, its mechanism of target-specific drug delivery, and its ability to disrupt the bacterial biofilms inhibiting the infection. The review will also discuss various mechanisms for the delivery of pharmaceutical molecules by the MSNs to inhibit the bacterial biofilms, and lastly, we will talk about the different types of MSNs and their antibiofilm activities.

Dynamic Antimicrobial Poly(disulfide) Coatings Exfoliate Biofilms On Demand Via Triggered Depolymerization

Bacterial biofilms are notoriously problematic in applications ranging from biomedical implants to ship hulls. Cationic, amphiphilic antibacterial surface coatings delay the onset of biofilm formation by killing microbes on contact, but they lose effectiveness over time due to non-specific binding of biomass and biofilm formation. Harsh treatment methods are required to forcibly expel the biomass and regenerate a clean surface. Here, a simple, dynamically reversible method of polymer surface coating that enables both chemical killing on contact, and on-demand mechanical delamination of surface-bound biofilms, by triggered depolymerization of the underlying antimicrobial coating layer, is developed. Antimicrobial polymer derivatives based on α-lipoic acid (LA) undergo dynamic and reversible polymerization into polydisulfides functionalized with biocidal quaternary ammonium salt groups. These coatings kill >99.9% of Staphylococcus aureus cells, repeatedly for 15 cycles without loss of activity, for moderate microbial challenges (≈105 colony-forming units (CFU) mL-1, 1 h), but they ultimately foul under intense challenges (≈107 CFU mL-1, 5 days). The attached biofilms are then exfoliated from the polymer surface by UV-triggered degradation in an aqueous solution at neutral pH. This work provides a simple strategy for antimicrobial coatings that can kill bacteria on contact for extended timescales, followed by triggered biofilm removal under mild conditions.

Strategies to Promote the Journey of Nanoparticles Against Biofilm-Associated Infections

Biofilm-associated infections are one of the most challenging healthcare threats for humans, accounting for 80% of bacterial infections, leading to persistent and chronic infections. The conventional antibiotics still face their dilemma of poor therapeutic effects due to the high tolerance and resistance led by bacterial biofilm barriers. Nanotechnology-based antimicrobials, nanoparticles (NPs), are paid attention extensively and considered as promising alternative. This review focuses on the whole journey of NPs against biofilm-associated infections, and to clarify it clearly, the journey is divided into four processes in sequence as 1) Targeting biofilms, 2) Penetrating biofilm barrier, 3) Attaching to bacterial cells, and 4) Translocating through bacterial cell envelope. Through outlining the compositions and properties of biofilms and bacteria cells, recent advances and present the strategies of each process are comprehensively discussed to combat biofilm-associated infections, as well as the combined strategies against these infections with drug resistance, aiming to guide the rational design and facilitate wide application of NPs in biofilm-associated infections.

Progress of stimulus responsive nanosystems for targeting treatment of bacterial infectious diseases

In recent decades, due to insufficient concentration at the lesion site, low bioavailability and increasingly serious resistance, antibiotics have become less and less dominant in the treatment of bacterial infectious diseases. It promotes the development of efficient drug delivery systems, and is expected to achieve high absorption, targeted drug release and satisfactory therapy effects. A variety of endogenous stimulation-responsive nanosystems have been constructed by using special infection microenvironments (pH, enzymes, temperature, etc.). In this review, we firstly provide an extensive review of the current research progress in antibiotic treatment dilemmas and drug delivery systems. Then, the mechanism of microenvironment characteristics of bacterial infected lesions was elucidated to provide a strong theoretical basis for bacteria-targeting nanosystems design. In particular, the discussion focuses on the design principles of single-stimulus and dual-stimulus responsive nanosystems, as well as the use of endogenous stimulus-responsive nanosystems to deliver antimicrobial agents to target locations for combating bacterial infectious diseases. Finally, the challenges and prospects of endogenous stimulus-responsive nanosystems were summarized.

Development and challenges of antimicrobial peptide delivery strategies in bacterial therapy: A review

The escalating global prevalence of antimicrobial resistance poses a critical threat, prompting concerns about its impact on public health. This predicament is exacerbated by the acute shortage of novel antimicrobial agents, a scarcity attributed to the rapid surge in bacterial resistance. This review delves into the realm of antimicrobial peptides, a diverse class of compounds ubiquitously present in plants and animals across various natural organisms. Renowned for their intrinsic antibacterial activity, these peptides provide a promising avenue to tackle the intricate challenge of bacterial resistance. However, the clinical utility of peptide-based drugs is hindered by limited bioavailability and susceptibility to rapid degradation, constraining efforts to enhance the efficacy of bacterial infection treatments. The emergence of nanocarriers marks a transformative approach poised to revolutionize peptide delivery strategies. This review elucidates a promising framework involving nanocarriers within the realm of antimicrobial peptides. This paradigm enables meticulous and controlled peptide release at infection sites by detecting dynamic shifts in microenvironmental factors, including pH, ROS, GSH, and reactive enzymes. Furthermore, a glimpse into the future reveals the potential of targeted delivery mechanisms, harnessing inflammatory responses and intricate signaling pathways, including adenosine triphosphate, macrophage receptors, and pathogenic nucleic acid entities. This approach holds promise in fortifying immunity, thereby amplifying the potency of peptide-based treatments. In summary, this review spotlights peptide nanosystems as prospective solutions for combating bacterial infections. By bridging antimicrobial peptides with advanced nanomedicine, a new therapeutic era emerges, poised to confront the formidable challenge of antimicrobial resistance head-on.

Moist Heat Synthesis of Magnetic EGCG-Cappedα-Fe2O3 Nanoparticles and Their In Vitro and In Silico Interactions with Pristine HSA- and NDM-1-Producing Bacteria

A simple, facile, moist-heating (e.g., autoclave), one-step procedure for EGCG-mediated biosynthesis of narrow-size magnetic iron oxide (α-Fe2O3) nanoparticles (EGCG-MINPs) was developed. The influence of pH of the reaction mixture over the size distribution of as-synthesized EGCG-MINPs was investigated systematically by employing UV-visible (UV-vis) spectroscopy and dynamic light scattering (DLS)-based hydrodynamic size, surface charge (zeta-potential), and polydispersity index (PDI). The FE-SEM, TEM, and XRD characterizations revealed that the EGCG-MINPs synthesized at pH 5.0 were in the size range of 6.20-16.7 nm and possess well-crystalline hexagonal shaped nanostructures of hematite (α-Fe2O3) crystal phase. The role of EGCG in Fe3+ ion reduction and EGCG-MINP formation was confirmed by FTIR analysis. The VSM analysis has revealed that EGCG-MINPs were highly magnetic nanostructures with the hysteretic feature of saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) as 33.64 emu/g, 12.18 emu/g, and 0.33 Oe, respectively. Besides, significant (p < 0.001) dose-dependent (250-1000 μg/mL) antibacterial and antibiofilm activities against the NDM-1-producing Gram-negative Escherichia coli (AK-33), Klebsiella pneumoniae (AK-65), Pseudomonas aeruginosa (AK-66), and Shigella boydii (AK-67) bacterial isolates warranted the as-synthesized EGCG-MINPs as a promising alternative for clinical management of chronic bacterial infections in biomedical settings. In addition, molecular docking experiments revealed that compared to free Fe3+ and EGCG alone, the EGCG-MINPs or Fe-EGCG complex possess significantly high binding affinity toward HSA and hence can be considered as promising biocompatible nanodrug carriers in in vivo drug delivery systems.

Zwitterionic silver nanoparticle based antibacterial eye drops for efficient therapy of bacterial keratitis

Inefficient biofilm clearance and the risk of drug resistance pose significant challenges for antibiotic eye drops in the treatment of bacterial keratitis (BK). Recently, silver nanoparticles (AgNPs) have emerged as promising alternatives to antibiotics due to their potent antibacterial activity and minimal drug resistance. However, concerns regarding the potential biotoxicity of aggregated AgNPs in tissues have limited their practical application. In this study, polyzwitterion-functionalized AgNPs with excellent dispersion stability in the ocular physiological environment were chosen to prepare antibacterial eye drops. Zwitterionic AgNPs were synthesized using a copolymer, poly(sulfobetaine methacrylate-co-dopamine methacrylamide) (PSBDA), as a stabilizer and a reducing agent. The resulting antibacterial eye drops, named ZP@Ag-drops, demonstrated outstanding biocompatibility in in vitro cytotoxicity tests and in vivo rabbit eye instillation experiments, attributed to the zwitterionic PSBDA surface. Furthermore, the ZP@Ag-drops exhibited strong antibacterial activity against multiple pathogenic bacteria, particularly in penetrating and eradicating biofilms, due to the synergistic bactericidal effect of the released Ag+ and reactive oxygen species (ROS). Importantly, in vivo BK rabbit models showed that the ZP@Ag-drops effectively inhibited corneal infection and prevented ocular tissue damage, surpassing the therapeutic effect of commercial levofloxacin eye drops (LEV-drops). Overall, this study presents a promising alternative option for the effective treatment of BK using antibacterial eye drops.

NIR-induced improvement of catalytic activity and antibacterial performance over AuAg nanorods in Rambutan-like Fe3O4@AgAu@PDA magnetic nanospheres

Pathogenic bacteria and difficult-to-degrade pollutants in water have been serious problems that always plague people. Therefore, finding a "one stone-two birds" method that can quickly catalyze the degradation of pollutants and show effective antibacterial behavior become an urgent requirement. This work reports a facile one-step strategy for fabricating a Rambutan-like Fe₃O₄@AgAu@PDA (Fe₃O₄@AgAu@Polydopamine) core/shell nanosphere with both catalytic and antibacterial activities which can be critically improved by externally applying an NIR laser irradiation (NIR, 808 nm) and a rotating magnetic field. Typically, the Rambutan-like Fe₃O₄@AgAu@PDA nanosphere have a rather rough surface due to the AuAg bimetallic nanorods sandwiched between the Fe₃O₄ core and the PDA shell. Owing to the penetrated PDA shell, AgAu nanorods show high and magnetically recyclable photothermal-enhanced catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol and they can also be applied to initiate TMB oxidation under the help of NIR heating condition. Moreover, Fe₃O₄@AgAu@PDA shows a moderate antibacterial activity due to the weak release of Ag⁺. Under applying a rotating external magnetic field, the rough-surface Fe₃O₄@AgAu@PDA nanospheres produce a controllable magnetolytic force on the bacterial due to their good affinity. As a result, the Fe₃O₄@AgAu@PDA nanospheres show a "magnetolytic-photothermal-Ag⁺" synergistic antibacterial behavior against E. coli and S. aureus.

Rational design of magnetoliposomes for enhanced interaction with bacterial membrane models

There is a growing need for alternatives to target and treat bacterial infection. Thus, the present work aims to develop and optimize the production of PEGylated magnetoliposomes (MLPs@PEG), by encapsulating superparamagnetic iron oxide nanoparticles (SPIONs) within fusogenic liposomes. A Box-Behnken design was applied to modulate size distribution variables, using lipid concentration, SPIONs amount and ultrasonication time as independent variables. As a result of the optimization, it was possible to obtain MLPs@PEG with a mean size of 182 nm, with polydispersity index (PDI) of 0.19, and SPIONs encapsulation efficiency (%EE) around 76%. Cytocompatibility assays showed that no toxicity was observed in fibroblasts, for iron concentrations up to 400μg/ml. Also, for safe lipid and iron concentrations, no hemolytic effect was detected. The fusogenicity of the nanosystems was first evaluated through lipid mixing assays, based on Förster resonance energy transfer (FRET), using liposomal membrane models, mimicking bacterial cytoplasmic membrane and eukaryotic plasma membrane. It was shown that the hybrid nanosystems preferentially interact with the bacterial membrane model. Confocal microscopy and fluorescence lifetime measurements, using giant unilamellar vesicles (GUVs), validated these results. Overall, the developed hybrid nanosystem may represent an efficient drug delivery system with improved targetability for bacterial membrane.

Smart delivery systems for microbial biofilm therapy: Dissecting design, drug release and toxicological features

Bacterial biofilms are highly protected surface attached communities of bacteria that typically cause chronic infections. To address their recalcitrance to antibiotics and minimise side effects of current therapies, smart drug carriers are being explored as promising platforms for antimicrobials. Herein, we briefly summarize recent efforts and considerations that have been applied in the design of these smart carriers. We guide readers on a journey on how they can leverage the inherent biofilm microenvironment, external stimuli, or combine both types of stimuli in a predictable manner. The specific carrier features that are responsible for their 'on-demand' properties are detailed and their impact on antibiofilm property are further discussed. Moreover, an analysis on the impact of such features on drug release profiles is provided. Since nanotechnology represents a significant slice of the drug delivery pie, some insights on the potential toxicity are also depicted. We hope that this review inspires researchers to use their knowledge and creativity to design responsive systems that can eradicate biofilm infections.

Dental plaque-inspired versatile nanosystem for caries prevention and tooth restoration

Dental caries is one of the most prevalent human diseases resulting from tooth demineralization caused by acid production of bacteria plaque. It remains challenges for current practice to specifically identify, intervene and interrupt the development of caries while restoring defects. In this study, inspired by natural dental plaque, a stimuli-responsive multidrug delivery system (PMs@NaF-SAP) has been developed to prevent tooth decay and promote enamel restoration. Classic spherical core-shell structures of micelles dual-loaded with antibacterial and restorative agents are self-assembled into bacteria-responsive multidrug delivery system based on the pH-cleavable boronate ester bond, followed by conjugation with salivary-acquired peptide (SAP) to endow the nanoparticle with strong adhesion to tooth enamel. The constructed PMs@NaF-SAP specifically adheres to tooth, identifies cariogenic conditions and intelligently releases drugs at acidic pH, thereby providing antibacterial adhesion and cariogenic biofilm resistance, and restoring the microarchitecture and mechanical properties of demineralized teeth. Topical treatment with PMs@NaF-SAP effectively diminishes the onset and severity of caries without impacting oral microbiota diversity or surrounding mucosal tissues. These findings demonstrate this novel nanotherapy has potential as a promising biomedical application for caries prevention and tooth defect restoration while resisting biofilm-associated diseases in a controlled manner activated by pathological bacteria.

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Nanomaterials can adhere to tooth and target acidic biofilms specifically.

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Application of caries prevention and tooth defect restoration.

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Guidance for the innovation of the existing post-defect restoration strategies.

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The multidrug delivery system exerts antibacterial and restorative abilities on demand.

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Bacteria-responsive system resists biofilm-associated diseases in a controlled manner.

Recent advances in responsive antibacterial materials: design and application scenarios

Bacterial infection is one of the leading causes of death globally, although modern medicine has made considerable strides in the past century. As traditional antibiotics are suffering from the emergence of drug resistance, new antibacterial strategies are of great interest. Responsive materials are appealing alternatives that have shown great potential in combating resistant bacteria and avoiding the side effects of traditional antibiotics. In this review, the responsive antibacterial materials are introduced in terms of stimulus signals including intrinsic (pH, enzyme, ROS, etc.) and extrinsic (light, temperature, magnetic fields, etc.) stimuli. Their biomedical applications in therapeutics and medical devices are then discussed. Finally, the author's perspective of the challenge and the future of such a system is provided.

Antibacterial intraosseous implant surface coating that responds to changes in the bacterial microenvironment

Bone implant-associated infection is one of the most challenging problems encountered by orthopedic surgeons. There is considerable interest in the development of drug-loaded antibacterial coatings for the surfaces of metal implants. However, it is difficult to achieve the stable local release of an effective drug dose for many antibacterial coatings. In the present study, analyses of the thickness and water contact angle of multiple layers confirmed the successful assembly of multilamellar membrane structures. Measurement of the zone of bacterial inhibition indicated gradual degradation of the (montmorillonite [MMT]/hyaluronic acid [HA])₁₀ multilamellar film structure with concentration-dependent degradation during incubation with hyaluronidase solution and Staphylococcus aureus. In vivo results resembled the in vitro results. Overall, the findings confirm that the (MMT/HA-rifampicin)₁₀ multilamellar film structure exhibits good antibacterial properties and excellent biocompatibility. Further studies of the clinical potential of the antibacterial coating prepared in this experiment are warranted.

Drug delivery approaches for enhanced antibiofilm therapy

Biofilms have attracted increasing attention in recent years. Many bacterial infections are associated with biofilm formation. A bacterial biofilm is an aggregated membrane-like substance that is composed of a large number of bacteria and their secreted extracellular polymeric substances. The traditional antibiofilm approaches, such as chemotherapy based on antibiotics, are often ineffective in eradicating biofilms owing to the limited diffusion ability of antibiotics within biofilms and inactivation of antibiotics by biofilms. Moreover, a larger dosage of antibiotics could be effective, but leads to an increased tolerance. Smart drug delivery systems that deliver antibiotics into the biofilm interior is a promising strategy to meet this challenge. In this review, we focus on the methods to improve drug delivery efficiency for enhanced chemotherapy of biofilms. Furthermore, we have summarized chemical approaches for enhanced drug delivery, such as chemical shields, charge reversal, and dual corona enhanced delivery strategies; these methods focus on physicochemical biofilm properties and specific biofilm features. Afterwards, physical approaches are discussed, such as magnetism-mediated drug delivery, electricity-mediated drug delivery, ultrasound-mediated drug delivery, and shock wave-mediated drug delivery. Finally, a perspective on the development of next-generation antibiofilm drug delivery systems is given.

Growth suppression of bacteria by biofilm deterioration using silver nanoparticles with magnetic doping

Decades of antibiotic use and misuse have generated selective pressure toward the rise of antibiotic-resistant bacteria, which now contaminate our environment and pose a major threat to humanity. According to the evolutionary "Red queen theory", developing new antimicrobial technologies is both urgent and mandatory. While new antibiotics and antibacterial technologies have been developed, most fail to penetrate the biofilm that protects bacteria against external antimicrobial attacks. Hence, new antimicrobial formulations should combine toxicity for bacteria, biofilm permeation ability, biofilm deterioration capability, and tolerability by the organism without renouncing compatibility with a sustainable, low-cost, and scalable production route as well as an acceptable ecological impact after the ineluctable release of the antibacterial compound in the environment. Here, we report on the use of silver nanoparticles (NPs) doped with magnetic elements (Co and Fe) that allow standard silver antibacterial agents to perforate bacterial biofilms through magnetophoretic migration upon the application of an external magnetic field. The method has been proved to be effective in opening micrometric channels and reducing the thicknesses of models of biofilms containing bacteria such as Enterococcus faecalis, Enterobacter cloacae, and Bacillus subtilis. Besides, the NPs increase the membrane lipid peroxidation biomarkers through the formation of reactive oxygen species in E. faecalis, E. cloacae, B. subtilis, and Pseudomonas putida colonies. The NPs are produced using a one-step, scalable, and environmentally low-cost procedure based on laser ablation in a liquid, allowing easy transfer to real-world applications. The antibacterial effectiveness of these magnetic silver NPs may be further optimized by engineering the external magnetic fields and surface conjugation with specific functionalities for biofilm disruption or bactericidal effectiveness.

Disrupting biofilm and eradicating bacteria by Ag-Fe3O4@MoS2 MNPs nanocomposite carrying enzyme and antibiotics

In this study, novel multilayered magnetic nanoparticles (ML-MNPs) loaded with DNase and/or vancomycin (Vanc) were fabricated for eliminating multispecies biofilms. Iron-oxide MNPs (IO-core) (500-800 nm) were synthesized via co-precipitation; further, the IO-core was coated with heavy-metal-based layers (Ag and MoS₂ NPs) using solvent evaporation. DNase and Vanc were loaded onto the outermost layer of the ML-MNP formed by nanoporous MoS₂ NPs through physical deposition and adsorption. The biofilms of S. mutans or E. faecalis (or both) were formed in a brain-heart-infusion broth (BHI) for 3 days, followed by treatment with ML-MNPs for 24 h. The results revealed that coatings of Ag (200 nm) and ultrasmall MoS₂ (20 nm) were assembled as outer layers of ML-MNPs successfully, and they formed Ag-Fe₃O₄@MoS₂ MNPs (3-5 μm). The DNase-Vanc-loaded MNPs caused nanochannels digging and resulted in the enhanced penetration of MNPs towards the bottom layers of biofilm, which resulted in a decrease in the thickness of the 72-h biofilm from 48 to 58 μm to 0-4 μm. The sustained release of Vanc caused a synergistic bacterial killing up to 96%-100%. The heavy-metal-based layers of MNPs act as nanozymes to interfere with bacterial metabolism and proliferation, which adversely affects biofilm integrity. Further, loading DNase/Vanc onto the nanoporous-MoS₂-layer of ML-MNPs promoted nanochannel creation through the biofilm. Therefore, DNase-and Vanc-loaded ML-MNPs exhibited potent effects on biofilm disruption and bacterial killing.

Enzyme-triggered smart antimicrobial drug release systems against bacterial infections

The rapid emergence and spread of drug-resistant bacteria, as one of the most pressing public health threats, are declining our arsenal of available antimicrobial drugs. Advanced antimicrobial drug delivery systems that can achieve precise and controlled release of antimicrobial agents in the microenvironment of bacterial infections will retard the development of antimicrobial resistance. A variety of extracellular enzymes are secreted by bacteria to destroy physical integrity of tissue during their invasion of host body, which can be utilized as stimuli to trigger "on-demand" release of antimicrobials. In the past decade, such bacterial enzyme responsive drug release systems have been intensively studied but few review has been released. Herein, we systematically summarize the recent progress of smart antimicrobial drug delivery systems triggered by bacteria secreted enzymes such as lipase, hyaluronidase, protease and antibiotic degrading enzymes. The perspectives and existing key issues of this field will also be discussed to fuel the innovative research and translational application in the future.

Layer-by-layer self-assembled emerging systems for nanosized drug delivery

New frontiers in the development of stimuli-responsive surfaces that offer switchable properties according to the end-use application have added a new dimension to the design of drug-delivery systems (DDS). In this respect, layer-by-layer (LbL) self-assembled technologies have attracted interest in nano-DDS (NDDS) design due to the advantage of encapsulating different drug types either individually or in multiple formulations as an easy-to-apply and cost-effective strategy. LbL-based microcapsules and core-shell structures in the form of polyelectrolyte multilayers (PEMs) have been proposed as versatile vehicles for NDDS over the last quarter. This review aims to provide a global view of LbL-PEMs used as templates in NDDS for the last 5 years with an emphasis on emerging drug loading and release strategies.

Nanocarriers for combating biofilms: advantages and challenges

Bacterial biofilms are highly resistant to antibiotics and pose a great threat to human and animal health. The control and removal of bacterial biofilms have become an important topic in the field of bacterial infectious diseases. Nanocarriers show great anti-biofilm potential because of their small particle size and strong permeability. In this review, the advantages of nanocarriers for combating biofilms are analyzed. Nanocarriers can act on all stages of bacterial biofilm formation and diffusion. They can improve the scavenging effect of biofilm by targeting biofilm, destroying extracellular polymeric substances, and enhancing the biofilm permeability of antimicrobial substances. Nanocarriers can also improve the antibacterial ability of antimicrobial drugs against bacteria in biofilm by protecting the loaded drugs and controlling the release of antimicrobial substances. Additionally, we emphasize the challenges faced in using nanocarrier formulations and translating them from a preclinical level to the clinical setting.

The effects of rotating magnetic field and antiseptic on in vitro pathogenic biofilm and its milieu

The application of various magnetic fields for boosting the efficacy of different antimicrobial molecules or in the character of a self-reliant antimicrobial agent is considered a promising approach to eradicating bacterial biofilm-related infections. The purpose of this study was to analyze the phenomenon of increased activity of octenidine dihydrochloride-based antiseptic (OCT) against Staphylococcus aureus and Pseudomonas aeruginosa biofilms in the presence of the rotating magnetic field (RMF) of two frequencies, 5 and 50 Hz, in the in vitro model consisting of stacked agar discs, placed in increasing distance from the source of the antiseptic solution. The biofilm-forming cells' viability and morphology as well as biofilm matrix structure and composition were analyzed. Also, octenidine dihydrochloride permeability through biofilm and porous agar obstacles was determined for the RMF-exposed versus unexposed settings. The exposure to RMF or OCT apart did not lead to biofilm destruction, contrary to the setting in which these two agents were used together. The performed analyses revealed the effect of RMF not only on biofilms (weakening of cell wall/membranes, disturbed morphology of cells, altered biofilm matrix porosity, and composition) but also on its milieu (altered penetrability of octenidine dihydrochloride through biofilm/agar obstacles). Our results suggest that the combination of RMF and OCT can be particularly promising in eradicating biofilms located in such areas as wound pockets, where physical obstacles limit antiseptic activity.

One-step coordination of metal-phenolic networks as antibacterial coatings with sustainable and controllable copper release for urinary catheter applications

Catheter-associated urinary tract infections (CAUTIs) draw great concern due to increased demand for urinary catheters in hospitalization. Encrustation caused by urinary pathogens, especially Proteus mirabilis, results in blocking of the catheter lumen and further infections. In this study, a facile and low-cost surface modification strategy of urinary catheters was developed using one-step coordination of tannic acid (TA) and copper ions. The copper content of the coating could be manipulated by the number of TA-Cu (TC) layers, and the coating released copper in a pH-responsive manner. The coating exhibited high antibacterial efficiency (killed >99% of planktonic bacteria, and reduced biofilm coverage to <1% after 24 h) due to the synergistic antimicrobial effect of TA and copper ions. In vivo study with a rabbit model indicated that with two TC layers, the coated catheter could effectively inhibit bacterial growth in urine and colonization on the surface, and reduce encrustation formation. In addition, the TC-coated catheter exhibited better tissue compatibility compared to the unmodified catheter, probably due to the antibacterial performance of the coating. Such a straightforward coating strategy with good in vitro and in vivo antibacterial properties and biocompatibility holds great promise for combating CAUTIs in clinical practice.

Polyethyleneimine Functionalized Mesoporous Magnetic Nanoparticles with Enhanced Antibacterial and Antibiofilm Activity in an Alternating Magnetic Field

Despite a lot of research on the antibacterial effect of Fe₃O₄ nanoparticles, their interactions with biofilm matrix have not been well understood. The surface charge of nanoparticles mainly determines their ability to adhere on the biofilm. In this work, negatively charged Fe₃O₄ nanoparticles were synthesized via a trisodium citrate-assisted solvothermal method and then the surfaces were functionalized using polyethyleneimine (PEI) to obtain positively charged Fe₃O₄ nanoparticles. The antibacterial and antibiofilm activities of both negatively and positively charged Fe₃O₄ nanoparticles in an alternating magnetic field were then systematically investigated. The positively charged Fe₃O₄ nanoparticles showed a strong self-adsorbed attachment ability to the planktonic and sessile cells, resulting in a better antibacterial activity and enhanced biofilm eradication performance compared to the conventional Fe₃O₄ nanoparticles with negative charges. Fe₃O₄@PEI nanoparticles produced physical stress and thermal damage in response to an alternating magnetic field, inducing the accumulation of intracellular reactive oxygen species into live bacterial cells, bacterial membrane damage, and biofilm dispersion. Utilizing an alternating magnetic field along with positively charged nanoparticles leads to a synergistic antibacterial approach to improve the antibiofilm performance of magnetic nanoparticles.

Nanophysical Antimicrobial Strategies: A Rational Deployment of Nanomaterials and Physical Stimulations in Combating Bacterial Infections

The emergence of bacterial resistance due to the evolution of microbes under antibiotic selection pressure, and their ability to form biofilm, has necessitated the development of alternative antimicrobial therapeutics. Physical stimulation, as a powerful antimicrobial method to disrupt microbial structure, has been widely used in food and industrial sterilization. With advances in nanotechnology, nanophysical antimicrobial strategies (NPAS) have provided unprecedented opportunities to treat antibiotic-resistant infections, via a combination of nanomaterials and physical stimulations. In this review, NPAS are categorized according to the modes of their physical stimulation, which include mechanical, optical, magnetic, acoustic, and electrical signals. The biomedical applications of NPAS in combating bacterial infections are systematically introduced, with a focus on their design and antimicrobial mechanisms. Current challenges and further perspectives of NPAS in the clinical treatment of bacterial infections are also summarized and discussed to highlight their potential use in clinical settings. The authors hope that this review will attract more researchers to further advance the promising field of NPAS, and provide new insights for designing powerful strategies to combat bacterial resistance.

Superparamagnetic Iron Oxide Nanoparticles Decorated Mesoporous Silica Nanosystem for Combined Antibiofilm Therapy

A crucial challenge to face in the treatment of biofilm-associated infection is the ability of bacteria to develop resistance to traditional antimicrobial therapies based on the administration of antibiotics alone. This study aims to apply magnetic hyperthermia together with controlled antibiotic delivery from a unique magnetic-responsive nanocarrier for a combination therapy against biofilm. The design of the nanosystem is based on antibiotic-loaded mesoporous silica nanoparticles (MSNs) externally functionalized with a thermo-responsive polymer capping layer, and decorated in the outermost surface with superparamagnetic iron oxide nanoparticles (SPIONs). The SPIONs are able to generate heat upon application of an alternating magnetic field (AMF), reaching the temperature needed to induce a change in the polymer conformation from linear to globular, therefore triggering pore uncapping and the antibiotic cargo release. The microbiological assays indicated that exposure of E. coli biofilms to 200 µg/mL of the nanosystem and the application of an AMF (202 kHz, 30 mT) decreased the number of viable bacteria by 4 log10 units compared with the control. The results of the present study show that combined hyperthermia and antibiotic treatment is a promising approach for the effective management of biofilm-associated infections.

A biofilm microenvironment-responsive one-for-all bactericidal nanoplatform for photothermal-augmented multimodal synergistic therapy of pathogenic bacterial biofilm infection

We rationally construct a biofilm microenvironment-responsive bactericidal nanoplatform (ZnPMp) consisting of ZnO core, a Fe3+-doped polydopamine coating and methylene blue (MB) payload for combined CT/CDT/PTT/PDT multi-mode antibacterial therapy.

Versatile polymer-based strategies for antibacterial drug delivery systems and antibacterial coatings

Human health damage and economic losses due to bacterial infections are very serious worldwide. Excessive use of antibiotics has caused an increase in bacterial resistance. Fortunately, various non-antibiotic antibacterial materials...

Bacteria-Responsive Biopolymer-Coated Nanoparticles for Biofilm Penetration and Eradication

Biofilm infections are common and can be extremely difficult to treat. Bacteria-responsive nanoparticles that respond to multiple bacterial stimuli have the potential to successfully prevent and eradicate biofilms. Here, we...

Infection microenvironment-related antibacterial nanotherapeutic strategies

The emergence and spread of antibiotic resistance is one of the biggest challenges in public health. There is an urgent need to discover novel agents against the occurrence of multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. The drug-resistant pathogens are able to grow and persist in infected sites, including biofilms, phagosomes, or phagolysosomes, which are more difficult to eradicate than planktonic ones and also foster the development of drug resistance. For years, various nano-antibacterial agents have been developed in the forms of antibiotic nanocarriers. Inorganic nanoparticles with intrinsic antibacterial activity and inert nanoparticles assisted by external stimuli, including heat, photon, magnetism, or sound, have also been discovered. Many of these strategies are designed to target the unique microenvironment of bacterial infections, which have shown potent antibacterial effects in vitro and in vivo. This review summarizes ongoing efforts on antibacterial nanotherapeutic strategies related to bacterial infection microenvironments, including targeted antibacterial therapy and responsive antibiotic delivery systems. Several grand challenges and future directions for the development and translation of effective nano-antibacterial agents are also discussed. The development of innovative nano-antibacterial agents could provide powerful weapons against drug-resistant bacteria in systemic or local bacterial infections in the foreseeable future.

Rotating Magnetic Field Increases β-Lactam Antibiotic Susceptibility of Methicillin-Resistant Staphylococcus aureus Strains

Methicillin-resistant strains of Staphylococcus aureus (MRSA) have developed resistance to most β-lactam antibiotics and have become a global health issue. In this work, we analyzed the impact of a rotating magnetic field (RMF) of well-defined and strictly controlled characteristics coupled with β-lactam antibiotics against a total of 28 methicillin-resistant and sensitive S. aureus strains. The results indicate that the application of RMF combined with β-lactam antibiotics correlated with favorable changes in growth inhibition zones or in minimal inhibitory concentrations of the antibiotics compared to controls unexposed to RMF. Fluorescence microscopy indicated a drop in the relative number of cells with intact cell walls after exposure to RMF. These findings were additionally supported by the use of SEM and TEM microscopy, which revealed morphological alterations of RMF-exposed cells manifested by change of shape, drop in cell wall density and cytoplasm condensation. The obtained results indicate that the originally limited impact of β-lactam antibiotics in MRSA is boosted by the disturbances caused by RMF in the bacterial cell walls. Taking into account the high clinical need for new therapeutic options, effective against MRSA, the data presented in this study have high developmental potential and could serve as a basis for new treatment options for MRSA infections.

The Effect of Rotating Magnetic Field on Susceptibility Profile of Methicillin-Resistant Staphylococcus aureus Strains Exposed to Activity of Different Groups of Antibiotics

Methicillin-resistant strains of Staphylococcus aureus (MRSA) have become a global issue for healthcare systems due to their resistance to most β-lactam antibiotics, frequently accompanied by resistance to other classes of antibiotics. In this work, we analyzed the impact of combined use of rotating magnetic field (RMF) with various classes of antibiotics (β-lactams, glycopeptides, macrolides, lincosamides, aminoglycosides, tetracyclines, and fluoroquinolones) against nine S. aureus strains (eight methicillin-resistant and one methicillin-sensitive). The results indicated that the application of RMF combined with antibiotics interfering with cell walls (particularly with the β-lactam antibiotics) translate into favorable changes in staphylococcal growth inhibition zones or in minimal inhibitory concentration values compared to the control settings, which were unexposed to RMF. As an example, the MIC value of cefoxitin was reduced in all MRSA strains by up to 42 times. Apart from the β-lactams, the reduced MIC values were also found for erythromycin, clindamycin, and tetracycline (three strains), ciprofloxacin (one strain), gentamicin (six strains), and teicoplanin (seven strains). The results obtained with the use of in vitro biofilm model confirm that the disturbances caused by RMF in the bacterial cell walls increase the effectiveness of the antibiotics towards MRSA. Because the clinical demand for new therapeutic options effective against MRSA is undisputable, the outcomes and conclusions drawn from the present study may be considered an important road into the application of magnetic fields to fight infections caused by methicillin-resistant staphylococci.

Stimuli-responsive nanocarriers for bacterial biofilm treatment

ABSTRACT

Bacterial biofilm infections have been threatening the human's life and health globally for a long time because they typically cause chronic and persistent infections. Traditional antibiotic therapies can hardly eradicate biofilms in many cases, as biofilms always form a robust fortress for pathogens inside, inhibiting the penetration of drugs. To address the issues, many novel drug carriers emerged as promising strategies for biofilm treatment. Among them, stimuli-responsive nanocarriers have attracted much attentions for their intriguing physicochemical properties, such as tunable size, shape and surface chemistry, especially smart drug release characteristic. Based on the microenvironmental difference between biofilm infection sites and normal tissue, many stimuli, such as bacterial products accumulating in biofilms (enzymes, glutathione, etc.), lower pH and higher H₂O₂ levels, have been employed and proved in favor of "on-demand" drug release for biofilm elimination. Additionally, external stimuli including light, heat, microwave and magnetic fields are also able to control the drug releasing behavior artificially. In this review, we summarized recent advances in stimuli-responsive nanocarriers for combating biofilm infections, and mainly, focusing on the different stimuli that trigger the drug release.

摘要

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FeCo nanoparticles as antibacterial agents with improved response in magnetic field: An insight into the associated toxicity mechanism

The emergence of multi-drug resistant bacterial infections has resulted in increased interest in the development of alternative systems which can sensitize bacteria to overcome resistance. In an attempt to contribute to the existing literature of potential antibacterial agents, we present here, a first report of the antibacterial potential of FeCo nanoparticles, both as stand-alone devices and in presence of magnetic field, against the bacterial strains of S. aureus and E. coli. A relatively simple polyol process was employed for nanoparticle synthesis. Formation of FeCo alloy in the desired BCC phase was confirmed by X-Ray Diffraction with a high saturation magnetization (Ms~180 Am2kg-1). Uniformly sized spherical structures with sharp edges were obtained. Solution stability was confirmed by the zeta potential value of -27.8 mV. Dose dependent bacterial growth inhibition was observed, the corresponding linear correlation coefficients being, R2 = 0.74 for S. aureus and R2 = 0.76 for E. coli. Minimum inhibitory concentration was accordingly ascertained to be >1024 μg/ml for both. Bacterial growth curves have been examined upon concomitant application of external magnetic field of varying intensities and revealed considerable enhancement in the antibacterial response upto 63% in a field of 100 mT. An effort has been made to understand the bacterial inhibitory mechanism by relating with the chemical and physical properties of the nanoparticles. The ease of field assisted targeting and retrieval of these highly magnetic, antibacterial nano-devices, with considerably improved response with magnetic fields, make them promising for several medical and environment remediation technologies.

Recent Innovations in Bacterial Infection Detection and Treatment

Bacterial infections are a major threat to human health, exacerbated by increasing antibiotic resistance. These infections can result in tremendous morbidity and mortality, emphasizing the need to identify and treat pathogenic bacteria quickly and effectively. Recent developments in detection methods have focused on electrochemical, optical, and mass-based biosensors. Advances in these systems include implementing multifunctional materials, microfluidic sampling, and portable data-processing to improve sensitivity, specificity, and ease of operation. Concurrently, advances in antibacterial treatment have largely focused on targeted and responsive delivery for both antibiotics and antibiotic alternatives. Antibiotic alternatives described here include repurposed drugs, antimicrobial peptides and polymers, nucleic acids, small molecules, living systems, and bacteriophages. Finally, closed-loop therapies are combining advances in the fields of both detection and treatment. This review provides a comprehensive summary of the current trends in detection and treatment systems for bacterial infections.

Recent advances in functionalized nanomaterials for the diagnosis and treatment of bacterial infections

The growing problem of resistant infections due to antibiotic misuse is a worldwide concern that poses a grave threat to healthcare systems. Thus, it is necessary to discover new strategies to combat infectious diseases. In this review, we provide a selective overview of recent advances in the use of nanocomposites as alternatives to antibiotics in antimicrobial treatments. Metals and metal oxide nanoparticles (NPs) have been associated with inorganic and organic supports to improve their antibacterial activity and stability as well as other properties. For successful antibiotic treatment, it is critical to achieve a high drug concentration at the infection site. In recent years, the development of stimuli-responsive systems has allowed the vectorization of antibiotics to the site of infection. These nanomaterials can be triggered by various mechanisms (such as changes in pH, light, magnetic fields, and the presence of bacterial enzymes); additionally, they can improve antibacterial efficacy and reduce side effects and microbial resistance. To this end, various types of modified polymers, lipids, and inorganic components (such as metals, silica, and graphene) have been developed. Applications of these nanocomposites in diverse fields ranging from food packaging, environment, and biomedical antimicrobial treatments to diagnosis and theranosis are discussed.

Targeted Stimuli-Responsive Mesoporous Silica Nanoparticles for Bacterial Infection Treatment

The rise of antibiotic resistance and the growing number of biofilm-related infections make bacterial infections a serious threat for global human health. Nanomedicine has entered into this scenario by bringing new alternatives to design and develop effective antimicrobial nanoweapons to fight against bacterial infection. Among them, mesoporous silica nanoparticles (MSNs) exhibit unique characteristics that make them ideal nanocarriers to load, protect and transport antimicrobial cargoes to the target bacteria and/or biofilm, and release them in response to certain stimuli. The combination of infection-targeting and stimuli-responsive drug delivery capabilities aims to increase the specificity and efficacy of antimicrobial treatment and prevent undesirable side effects, becoming a ground-breaking alternative to conventional antibiotic treatments. This review focuses on the scientific advances developed to date in MSNs for infection-targeted stimuli-responsive antimicrobials delivery. The targeting strategies for specific recognition of bacteria are detailed. Moreover, the possibility of incorporating anti-biofilm agents with MSNs aimed at promoting biofilm penetrability is overviewed. Finally, a comprehensive description of the different scientific approaches for the design and development of smart MSNs able to release the antimicrobial payloads at the infection site in response to internal or external stimuli is provided.

Self-Adaptive Antibacterial Coating for Universal Polymeric Substrates Based on a Micrometer-Scale Hierarchical Polymer Brush System

Surface-tethered hierarchical polymer brushes find wide applications in the development of antibacterial surfaces due to the well-defined spatial distribution and the separate but complementary properties of different blocks. Existing methods to achieve such polymer brushes mainly focused on inorganic material substrates, precluding their practical applications on common medical devices. In this work, a hierarchical polymer brush system is proposed and facilely constructed on polymeric substrates via light living graft polymerization. The polymer brush system with micrometer-scale thickness exhibits a unique hierarchical architecture consisting of a poly(hydroxyethyl methacrylate) (PHEMA) outer layer and an anionic inner layer loading with cationic antimicrobial peptide (AMP) via electrostatic attraction. The surface of this system inhibits the initial adhesion of bacteria by the PHEMA hydration outer layer under neutral pH conditions; when bacteria adhere and proliferate on this surface, the bacterially induced acidification triggers the cleavage of labile amide bonds within the inner layer to expose the positively charged amines and vigorously release melittin (MLT), allowing the surface to timely kill the adhering bacteria. The hierarchical surface employs multiple antibacterial mechanisms to combat bacterial infection and shows high sensitiveness and responsiveness to pathogens. A new paradigm is supplied by this modular hierarchical polymer brushes system for the progress of intelligent surfaces on universal polymer substrates, showing great potential to a promising strategy for preventing infection related to medical devices.

Bacteria responsive polyoxometalates nanocluster strategy to regulate biofilm microenvironments for enhanced synergetic antibiofilm activity and wound healing

Backgroud: Nowadays, biofilms that are generated as a result of antibiotic abuse cause serious threats to global public health. Such films are the primary factor that contributes to the failure of antimicrobial treatment. This is due to the fact that the films prevent antibiotic infiltration, escape from innate immune attacks by phagocytes and consequently generate bacterial resistance. Therefore, exploiting novel antibacterial agents or strategies is extremely urgent.

Methods: Herein, we report a rational construction of a novel biofilm microenvironment (BME)-responsive antibacterial platform that is based on tungsten (W)-polyoxometalate clusters (POMs) to achieve efficient bactericidal effects.

Results: On one hand, the acidity and reducibility of a BME could lead to the self-assembly of POMs to produce large aggregates, which favor biofilm accumulation and enhance photothermal conversion under near-infrared (NIR) light irradiation. On the other hand, reduced POM aggregates with BME-induced photothermal-enhanced efficiency also exhibit surprisingly high peroxidase-like activity in the catalysis of bacterial endogenous hydrogen peroxide (H₂O₂) to produce abundant reactive oxygen species (ROS). This enhances biofilm elimination and favors antibacterial effects. Most importantly, reduced POMs exhibit the optimal peroxidase-like activity in an acidic BME.

Conclusion: Therefore, in addition to providing a prospective antibacterial agent, intelligent acid/reductive dual-responsive POMs will establish a new representative paradigm for the areas of healthcare with minimal side effects.

Silver Nanoparticles for Water Pollution Monitoring and Treatments: Ecosafety Challenge and Cellulose-Based Hybrids Solution

Silver nanoparticles (AgNPs) are widely used as engineered nanomaterials (ENMs) in many advanced nanotechnologies, due to their versatile, easy and cheap preparations combined with peculiar chemical-physical properties. Their increased production and integration in environmental applications including water treatment raise concerns for their impact on humans and the environment. An eco-design strategy that makes it possible to combine the best material performances with no risk for the natural ecosystems and living beings has been recently proposed. This review envisages potential hybrid solutions of AgNPs for water pollution monitoring and remediation to satisfy their successful, environmentally safe (ecosafe) application. Being extremely efficient in pollutants sensing and degradation, their ecosafe application can be achieved in combination with polymeric-based materials, especially with cellulose, by following an eco-design approach. In fact, (AgNPs)-cellulose hybrids have the double advantage of being easily produced using recycled material, with low costs and possible reuse, and of being ecosafe, if properly designed. An updated view of the use and prospects of these advanced hybrids AgNP-based materials is provided, which will surely speed their environmental application with consequent significant economic and environmental impact.

Circumventing antimicrobial-resistance and preventing its development in novel, bacterial infection-control strategies

INTRODUCTION

Development of new antimicrobials with ever 'better' bacterial killing has long been considered the appropriate response to the growing threat of antimicrobial-resistant infections. However, the time-period between the introduction of a new antibiotic and the appearance of resistance amongst bacterial pathogens is getting shorter and shorter. This suggests that alternative pathways than making ever 'better' antimicrobials should be taken.

AREAS COVERED

This review aims to answer the questions (1) whether we have means to circumvent existing antibiotic-resistance mechanisms, (2) whether we can revert existing antibiotic-resistance, (3) how we can prevent the development of antimicrobial-resistance against novel infection-control strategies, including nano-antimicrobials.

EXPERT OPINION

Relying on relieving antibiotic-pressure and natural outcompeting of antimicrobial-resistant bacteria seems an uncertain way out of the antibiotic-crisis facing us. Novel, non-antibiotic, nanotechnology-based infection control-strategies are promising. At the same time, rapid development of new resistance mechanisms once novel strategies is taken into global clinical use, may not be ruled out and must be closely monitored. This suggests focusing research and development on designing suitable combinations of existing antibiotics with new nano-antimicrobials in a way that induction of new antimicrobial-resistance mechanisms is avoided. The latter suggestion, however, requires a change of focus in research and development.

Layer-by-Layer Biomaterials for Drug Delivery

Controlled drug delivery formulations have revolutionized treatments for a range of health conditions. Over decades of innovation, layer-by-layer (LbL) self-assembly has emerged as one of the most versatile fabrication methods used to develop multifunctional controlled drug release coatings. The numerous advantages of LbL include its ability to incorporate and preserve biological activity of therapeutic agents; coat multiple substrates of all scales (e.g., nanoparticles to implants); and exhibit tuned, targeted, and/or responsive drug release behavior. The functional behavior of LbL films can be related to their physicochemical properties. In this review, we highlight recent advances in the development of LbL-engineered biomaterials for drug delivery, demonstrating their potential in the fields of cancer therapy, microbial infection prevention and treatment, and directing cellular responses. We discuss the various advantages of LbL biomaterial design for a given application as demonstrated through in vitro and in vivo studies.

Supramolecular Assemblies of Heterogeneous Mesoporous Silica Nanoparticles to Co-deliver Antimicrobial Peptides and Antibiotics for Synergistic Eradication of Pathogenic Biofilms

Pathogenic biofilms protected by extracellular polymeric substances frequently compromise the efficiency of antibacterial drugs and severely threaten human health. In this study, we designed a multi-stimuli-responsive magnetic supramolecular nanoplatform to co-deliver large and low molecular weight drugs for synergistic eradication of pathogenic biofilms. This co-delivery platform was composed of mesoporous silica nanoparticles (MSNs) with large pores (MSNLP) capped by β-cyclodextrin (β-CD)-modified polyethylenimine (PEICD) and adamantane (ADA)-decorated MSNs containing a magnetic core (MagNP@MSNA) capped by cucurbit[6]uril (CB[6]). The host MSNs (H, MSNLP@PEICD) and the guest MSNs (G, MagNP@MSNA-CB[6]) spontaneously form coassemblies (H+G), based on the host-guest interactions between β-CD and ADA. Under the stimulus of pathogen cells together with heating by an alternating magnetic field (AMF), the supramolecular coassemblies released both the large molecular weight antimicrobial peptide melittin (MEL) and the low molecular weight antibiotic ofloxacin (OFL) with high efficiency. As compared to free drugs (MEL and OFL) or unattached MSNs (H or G), the drug-loading H+G coassemblies (H-MEL+G-OFL) exhibited much higher capacity for biofilm eradication, thoroughly removing biofilm biomass and killing the pathogenic cells, and displaying no obvious toxicity to mammalian cells. This strong antibiofilm capacity was severely decreased when the host and guest components were prevented from coassembling but administered simultaneously, revealing the critical role of the supramolecular assembly in biofilm removal. Moreover, an in vivo implantation model showed that the coassemblies eradicated the pathogenic biofilms from the implants, preventing host tissue damage and inflammation. Therefore, the co-delivering and multi-stimuli-responsive nanocarriers could overcome the anti-infection difficulties during treatment of infections because of protective biofilms.

Innovative Strategies Toward the Disassembly of the EPS Matrix in Bacterial Biofilms

Bacterial biofilms represent a major concern at a worldwide level due to the high demand for implantable medical devices and the rising numbers of bacterial resistance. The complex structure of the extracellular polymeric substances (EPS) matrix plays a major role in this phenomenon, since it protects bacteria from antibiotics, avoiding drug penetration at bactericidal concentrations. Besides, this structure promotes bacterial cells to adopt a dormant lifestyle, becoming less susceptible to antibacterial agents. Currently, the available treatment for biofilm-related infections consists in the administration of conventional antibiotics at high doses for a long-term period. However, this treatment lacks efficiency against mature biofilms and for implant-associated biofilms it may be necessary to remove the medical device. Thus, biofilm-related infections represent an economical burden for the healthcare systems. New strategies focusing on the matrix are being highlighted as alternative therapies to eradicate biofilms. Here, we outline reported matrix disruptive agents, nanocarriers, and technologies, such as application of magnetic fields, photodynamic therapy, and ultrasounds, that have been under investigation to disrupt the EPS matrix of clinically relevant bacterial biofilms. In an ideal therapy, a synergistic effect between antibiotics and the explored innovated strategies is aimed to completely eradicate biofilms and avoid antimicrobial resistance phenomena.

Silver Nanoparticles as Colorimetric Sensors for Water Pollutants

This review provides an up-to-date overview on silver nanoparticles-based materials suitable as optical sensors for water pollutants. The topic is really hot considering the implications for human health and environment due to water pollutants. In fact, the pollutants present in the water disturb the spontaneity of life-related mechanisms, such as the synthesis of cellular constituents and the transport of nutrients into cells, and this causes long / short-term diseases. For this reason, research continuously tends to develop always innovative, selective and efficient processes / technologies to remove pollutants from water. In this paper we will report on the silver nanoparticles synthesis, paying attention to the stabilizers and mostly used ligands, to the characterizations, to the properties and applications as colorimetric sensors for water pollutants. As water pollutants our attention will be focused on several heavy metals ions, such as Hg(II), Ni(II),Cu(II), Fe(III), Mn(II), Cr(III/V) Co(II) Cd(II), Pb(II), due to their dangerous effects on human health. In addition, several systems based on silver nanoparticles employed as pesticides colorimetric sensors in water will be also discussed. All of this with the aim to provide to readers a guide about recent advanced silver nanomaterials, used as colorimetric sensors in water.