Potent antibacterial activity of a novel silver nanoparticle-halloysite nanotube nanocomposite powder

Characterization of a pseudohemocyanin gene (PtPhc1) and its immunity function in response to Vibrio parahaemolyticus infection in the swimming crab Portunus trituberculatus

Pseudohemocyanin is a member of the hemocyanin superfamily, but little research is available on its function in immunology. In this study, a Portunus trituberculatus pseudohemocyanin gene, named PtPhc1, was obtained by gene cloning. The PtPhc1 cDNA was 2312 bp in length, encoding 684 amino acids while exhibiting a characteristic hemocyanin structural domain. Tissue expression analysis revealed ubiquitous expression of PtPhc1 across all tissues, with the highest level of expression observed in the hepatopancreas. The expression pattern of PtPhc1 in response to Vibrio parahaemolyticus infection was clarified using RT-qPCR in swimming crabs. Notably, the expression peaked at 24 h, and increased 1435-fold compared to the control group in the hepatopancreas. While the expression level reached the maximum value at 72 h, which was 3.24 times higher than that of the control group in hemocytes. Remarkably, the reduction in PtPhc1 expression led to a noteworthy 30% increase in the mortality rate of P. trituberculatus when exposed to V. parahaemolyticus. In addition, in vitro bacterial inhibition assays exhibited a dose-dependent suppression of bacterial proliferation by recombinant PtPhc1 protein, with a notable inhibition rate of 48.33% against V. parahaemolyticus at a concentration of 0.03 mg/mL. To the best of our knowledge, the results establish the function of pseudohaemocyanin in immunity for the first time, contributing to a deeper comprehension of innate immune regulatory mechanisms in aquatic organisms and advancing strategies for disease-resistant breeding.

Recent Advances of Halloysite Nanotubes in Biomedical Applications

Halloysite nanotubes (HNTs) have emerged as a highly regarded choice in biomedical research due to their exceptional attributes, including superior loading capacity, customizable surface characteristics, and excellent biocompatibility. HNTs feature tubular structures comprising alumina and silica layers, endowing them with a large surface area and versatile surface chemistries that facilitate selective modifications. Moreover, their substantial pore volume and wide range of pore sizes enable efficient entrapment of diverse functional molecules. This comprehensive review highlights the broad biomedical application spectrum of HNTs, shedding light on their potential as innovative and effective therapeutic agents across various diseases. It emphasizes the necessity of optimizing drug delivery techniques, developing targeted delivery systems, rigorously evaluating biocompatibility and safety through preclinical and clinical investigations, exploring combination therapies, and advancing scientific understanding. With further advancements, HNTs hold the promise to revolutionize the pharmaceutical industry, opening new avenues for the development of transformative treatments.

Synthesis and characterization of Ag@Cu-based MOFs as efficient adsorbents for iodine anions removal from aqueous solutions

Due to the critical importance of capturing radioiodine from aquatic environments for human health and ecosystems, developing highly efficient adsorbent materials with rapid kinetics for capturing iodide ions in aqueous solutions is urgently needed. Although extensive research has been conducted on iodine adsorption in gas and organic phases, limited research has been dedicated to adsorption in aqueous solutions. An effective technique for removing iodide was proposed using Ag@Cu-based MOFs synthesized by incorporating Ag into calcined HKUST-1 with varying mass ratios of Ag/Cu-C. Extensive characterization using SEM, XRD, XPS, and nitrogen adsorption-desorption analysis confirmed successful incorporation of Ag in Cu-C. Batch adsorption experiments were conducted, demonstrating that the 5% Ag@Cu-C material exhibited a high adsorption capacity of 247.1 mg g^-1 at pH 3. Mechanism investigations revealed that Cu⁰ and dissolved oxygen in water generate Cu₂O and H₂O₂, while Ag and a small amount of CuO generate Ag₂O and Cu₂O. Furthermore, iodide ions in the solution are captured by Cu⁺ and Ag⁺ adsorption sites. These findings highlighted the potential of Ag@Cu-based MOFs as highly effective adsorbents for iodine anions removal in radioactive wastewater.

XPS, structural and antimicrobial studies of novel functionalized halloysite nanotubes

A novel robust preparation method based on thermal salt decomposition has been elaborated for synthesis of halloysite nanotubes (HNTs) impregnated with silver and iron oxide nanoparticles. The developed method is simple, time-effective, and can be employed for large scale material fabrication. Different characterization techniques, including X-ray diffraction (XRD), scanning and transmission electron spectroscopy (SEM and TEM) and energy dispersive X-ray spectroscopy (EDS) have been used to characterize the functionalized HNTs composite materials. Surface elemental and chemical state analysis was conducted using X-ray photoelectron spectrometer (XPS). The functionalized HNTs exhibit enhanced total surface area (by 17.5%) and pore volume (by 11%) compare to the raw HNTs calculated by using the Brunauer-Emmett-Teller (BET) method. It was shown that functionalized HNTs possess high antimicrobial properties towards both gram- positive and gram-negative bacteria species. The enhanced surface area and bactericidal properties of functionalized HNTs could be beneficial for employing of the prepared material as low cost filtration media for water treatment applications. Molecular dynamics (FPMD) were performed to obtain insights about possible physiochemical mechanisms for chemical adsorption and on the HNT thermal stability.

Recent Advances of Silver-Based Coordination Polymers on Antibacterial Applications

With the continuous evolution of bacteria and the constant use of traditional antibiotics, the emergence of drug-resistant bacteria and super viruses has attracted worldwide attention. Antimicrobial therapy has become the most popular and important research field at present. Coordination Polymer (CP) and/or metal-organic framework (MOF) platforms have the advantages of a high biocompatibility, biodegradability, and non-toxicity, have a great antibacterial potential and have been widely used in antibacterial treatment. This paper reviewed the mechanism and antibacterial effect of three typical MOFs (pure Ag-MOFs, hybrid Ag-MOFs, and Ag-containing-polymer @MOFs) in silver-based coordination polymers. At the same time, the existing shortcomings and future views are briefly discussed. The study on the antibacterial efficacy and mechanism of Ag-MOFs can provide a better basis for its clinical application and, meanwhile, open up a novel strategy for the preparation of more advanced Ag-contained materials with antibacterial characteristics.

Nano-Clays for Cancer Therapy: State-of-the Art and Future Perspectives

To date, cancer continues to be one of the deadliest diseases. Current therapies are often ineffective, leading to the urgency to develop new therapeutic strategies to improve treatments. Conventional chemotherapeutics are characterized by a reduced therapeutic efficacy, as well as them being responsible for important undesirable side effects linked to their non-specific toxicity. In this context, natural nanomaterials such as clayey mineral nanostructures of various shapes (flat, tubular, spherical and fibrous) with adjustable physico-chemical and morphological characteristics are emerging as systems with extraordinary potential for the delivery of different therapeutic agents to tumor sites. Thanks to their submicron size, high specific surface area, high adsorption capacity, chemical inertia and multilayer organization of 0.7 to 1 nm-thick sheets, they have aroused considerable interest among the scientific community as nano systems that are highly biocompatible in cancer therapy. In oncology, the nano-clays usually studied are halloysite, bentonite, laponite, kaolinite, montmorillonite and sepiolite. These are multilayered minerals that can act as nanocarriers (with a drug load generally between 1 and 10% by weight) for improved stabilization, efficient transport and the sustained and controlled release of a wide variety of anticancer agents. In particular, halloysite, montmorillonite and kaolinite are used to improve the dissolution of therapeutic agents and to delay and/or direct their release. In this review, we will examine and expose to the scientific community the extraordinary potential of nano-clays as unique crystalline systems in the treatment of cancer.

Silver nanoparticle effect on Salmonella enterica isolated from Northern West Egypt food, poultry, and calves

A total no. of 65 Salmonella enterica isolates recovered from food samples, feces of diarrheic calves, poultry, and hospital patient in large five cities at Northern West Egypt were obtained from the Department of Microbiology, Faculty of Veterinary Medicine, Alexandria University, Alexandria, Egypt. The 65 Salmonella enterica isolates had the invA gene were grouped into 11 Salmonella enterica serovars with dominance of S. Enteritidis and S. Kentucky serovars. Their resistance pattern were characterized by using 18 antibiotics from different classes. Approximately 80% of the isolates were multidrug resistant (MDR). Enterobacterial repetitive intergenic consequences polymerase chain reaction (ERIC-PCR) typing of 7 strains of S. Enteritidis showed 5 clusters with dissimilarity 25%. S. Enteritidis clusters in 2 main groups A and B. Group A have 2 human strain (HE2 and HE3) and one food origin (FE7) with a similarity 99%. Group B divided into B1 (FE2) and B2 (FE3) with a similarity ratio ≥ 93%, while ERIC-PCR analysis of 5 strains of S. Kentucky revealed 4 ERIC types, clustered in 2 main groups A and B with similarity 75%. We studied the effect of silver nanoparticles (Ag-NPs) on 10 antibiotic resistant strains of S. Enteritidis and S. Kentucky. The broth microdilution minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were detected. Evaluation of the affection using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed different ratios of Ag-NPs and microorganism as well as at different contact time ended finally with morphological alteration of the bacteria. We submitted new method in vivo to explore the activity of nanosilver in chicken. KEY POINTS: • Importance of ERIC-PCR to determine the relatedness between Salmonella isolates. • Effect of silver nanoparticles to confront the antibacterial resistance. • Studying the effect of silver nanoparticles in vivo on infected chicken with Salmonella.

Silver nanoparticles nucleated in NaOH-treated halloysite: a potential antimicrobial material

Despite all recent advances in medical treatments, infectious diseases remain dangerous. This has led to intensive scientific research on materials with antimicrobial properties. Silver nanoparticles (Ag-NPs) are a well-established solution in this area. The present work studied the nucleation of silver on halloysite substrates modified by chemical treatment with NaOH. The resulting stabilized Ag-NPs were characterized by X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The nucleation was characterized by thermogravimetric analysis and differential scanning calorimetry. The antimicrobial properties of the Ag-NPs were investigated against E. coli and S. aureus. The potential of the Ag-NPs for industrial application was tested by dispersing them into low-density polyethylene. The importance of the chemical affinity between matrix and additive was tested through coating the Ag-NPs with dodecanethiol, a non-polar surfactant. The resulting composites were characterized by scanning electron microscopy and in terms of surface antimicrobial activity. The results demonstrate that the Ag-NPs synthesized in this work are indeed antimicrobial, and that it is possible to imbue a polymeric matrix with the antimicrobial properties of Ag-NPs.

Nitric oxide releasing halloysite nanotubes for biomedical applications

Halloysite nanotubes (HNTs) are natural aluminosilicate clay that have been extensivelyexplored fordelivery of bioactive agents in biomedical applications because of their desirable features including unique hollow tubular structure, good biocompatibility, high mechanical strength, and extensive functionality. For the first time, in this work, functionalized HNTs are developed as a delivery platform for nitric oxide (NO), a gaseous molecule, known for its important roles in the regulation of various physiological processes. HNTs were first hydroxylated and modified with an aminosilane crosslinker, (3-aminopropyl) trimethoxysilane (APTMS), to enable the covalent attachment of a NO donor precursor, N-acetyl-d-penicillamine (NAP). HNT-NAP particles were then converted to NO-releasing S-nitroso-N-acetyl-penicillamine HNT-SNAP by nitrosation. The total NO loading on the resulting nanotubes was 0.10 ± 0.07 μmol/mg which could be released using different stimuli such as heat and light. Qualitative (Fourier-transform infrared spectroscopy and Nuclear magnetic resonance) and quantitative (Ninhydrin and Ellman) analyses were performed to confirm successful functionalization of HNTs at each step. Field emission scanning electron microscopy (FE-SEM) showed that the hollow tubular morphology of the HNTs was preserved after modification. HNT-SNAP showed concentration-dependent antibacterial effects against Gram-positive Staphylococcus aureus (S. aureus), resulting in up to 99.6% killing efficiency at a concentration of 10 mg/mL as compared to the control. Moreover, no significant cytotoxicity toward 3T3 mouse fibroblast cells was observed at concentrations equal or below 2 mg/mL of HNT-SNAP according to a WST-8-based cytotoxicity assay. The SNAP-functionalized HNTs represent a novel and efficient NO delivery system that holds the potential to be used, either alone or in combination with polymers for different biomedical applications.

Antibody-Functionalized Halloysite Nanotubes for Targeting Bacterial Cells

Halloysite nanotubes (HNTs) are naturally occurring tubular clay particles which have emerged in recent years as a promising nanomaterial for numerous applications. Specifically, HNTs’ large pore volume and high specific surface area in combination with their biocompatibility make them ideal nanocarriers for bioactive compounds. This research aims to design and synthesize functionalized HNTs, which could selectively bind to target bacterial cells in suspension. Such a system can allow us to treat target cells within a challenging heterogeneous population, such as contaminated ecosystems or gut flora. HNTs functionalization is achieved by immobilizing specific antibodies onto the nanotube surface. The synthetic route is realized by the following subsequent steps: acidic etching of the HNTs, silanization of reactive surface hydroxyls, conjugation of protein A, and oriented immobilization of the antibody. HNT functionalization is studied by a set of analytical techniques including attenuated total reflectance Fourier-transform infrared spectroscopy, zeta potential measurements, thermal gravimetric analysis, scanning and transmission electron microscopy, as well as fluorescence microscopy. The selective binding of the functionalized HNTs to their target bacteria is observed upon incubation with live homogenous and heterogeneous cultures using fluorescence microscopy and high-throughput flow cytometry. Plate count and live/dead staining experiments demonstrate the biocompatibility of the antibody-HNT hybrid with its target bacteria. The suggested HNT-based smart carrier constitutes a generic platform for targeted delivery that could be selectively tailored against any microorganism by facile antibody adjustment.

Nanoclay-based drug delivery systems and their therapeutic potentials

Safe, therapeutically effective, and patient-compliant drug delivery systems are needed to design novel tools and strategies to combat the deadliest of diseases such as cancer, SARS, H7N9 avian influenza, and dengue infection. The major challenges in drug delivery are cytotoxicity, poor biodistribution, insufficient functionality, ineffective drug incorporation in delivery devices, and subsequent drug release. Clay minerals are a class of nanolayered silicates that have good biocompatibility, high specific surface area, chemical inertness, colloid, and thixotropy, and are attractive practical and potential nanomaterials in medicine. These properties enable the usage of nanoclays as drug carriers for the delivery of antibiotics, antihypertensive drugs, anti-psychotic, and anticancer drugs. The review examines the latest advances in nanoclay-based drug delivery systems and related applications in gene therapy and tissue engineering. Clay minerals, particularly montmorillonite, kaolinite, and halloysite are used to delay and/or target drug release or even improve drug dissolution due to their surface charge. Chemical modification of clay minerals such as intercalation of ions into the interlayer space of clay minerals or surface modification of clay minerals is a strategy to tune the properties of nanoclays for the loading and release of a drug. The modified nanoclay can take up drugs by encapsulation, immobilization, ion exchange reaction, or electrostatic interactions. Controlled drug release from the drug-clay originates from the incorporation and interactions between the drug and inorganic layers, including electrostatic interactions and hydrogen bonding. Montmorillonite has proven non-toxic through hematological, biochemical, and histopathological analyses in rat. Montmorillonite can also act as a potent detoxifier. Halloysite nanotubes can bind synthetic and biological components such as chitosan, gelatin, and alginate innate nanocarriers for the improved loading and controlled release of drugs, proteins, and DNA. The peculiar properties of clay nanoparticles lead to promising applications in drug delivery, gene delivery, tissue engineering, cancer and stem cell isolation, and bioimaging.

Characterization of polyvinyl alcohol/starch composite films incorporated with p-coumaric acid modified chitosan and chitosan nanoparticles: A comparative study

In this paper, polyvinyl alcohol/starch composite films with p-coumaric acid modified chitosan (P-CS) and chitosan nanoparticles (P-CSNPs) at different concentrations were successfully prepared. The films were compared for their mechanical, thermal, physical, antioxidant, antibacterial, cytotoxicity and optical barrier properties. The results suggested that P-CS could significantly increase the tensile strength (TS) of the film from 15.67 MPa to a maximum of 24.32 MPa. The compact structure of P-CSNPs film prevented water diffusion, reducing the water amount within. Both films showed a reduction in water solubility, the extent of swelling, and water vapor transmittance. Specifically, P-CSNPs films showed better thermal stability while P-CS films revealed higher antioxidant activity. Besides, the P-CS films exhibited excellent transparency and good ultraviolet-barrier at 200-280 nm. P-CSNPs films demonstrated higher antibacterial activity on both Gram-negative and Gram-positive bacteria. Additionally, P-CS films were less cytotoxic compared to P-CSNPs films.

Enhanced antimicrobial activity and physicochemical stability of rapid pyro-fabricated silver-kaolinite nanocomposite

The present research aims to enhance the antimicrobial activity of kaolinite surfaces by a one-step cost-effective and energy-efficient dry thermal reaction, producing an antibacterial and antifungal silver-kaolinite (Ag-Kao) nanocomposite agent. Pharmaceutical grade kaolin powder samples, with variable kaolinite structural order-disorder degree, were homogeneously mixed with silver nitrate in a proportion 1:4 AgNO₃:kaolin (w/w) and sintered at 400 °C for 30 min. The composition, microstructure, microtexture and surface characteristics of the pyro-fabricated nanocomposites were characterized by XRD/XRF diffractometry, differential scanning calorimetry DSC, FT-IR spectroscopy, TEM/EDX, zeta potential (mV) measured within the 2-12 pH range, and BET method. Physicochemical stability was evaluated by silver dissociation testing under close-neutral and acidic conditions with Ag content assay using ICP-OES. The resulting Ag-Kao nanocomposites exhibited bulk silver contents ranging from 9.29% to 13.32% with high physicochemical stability in both neutral and acidic mediums (Ag dissociation rate <0.5% in 5 days). Ag nanocrystals exhibited particle sizes ranging from 5 to 30 nm, which were embedded and reinforced within the kaolinite matrix. The sizes of the Ag nanocrystals and their distribution patterns on the edges and faces of kaolinite platelets were controlled by the structural order-disorder degree. Highly ordered kaolinites (Hinckley Index, HI > 1) produced platelet edge-clustered silver nanocrystals due to the abundance of the dangling hydroxyls on platelet edges, while the highly disordered kaolinite (HI < 1) provided homogeneous platelet basal-doped silver nanocrystals due to the presence of some residual charges by exposed basal hydroxyl groups with interplatelet silver diffusivity. At pH 2, the magnitude of the positive surface charge was influenced by the silver nanocrystal size. Nanocomposites with the smallest silver nanocrystals (10-5 nm) exhibited the highest positive zeta potential (+15.2 mV to +17.0 mV), while those with larger silver nanocrystals (up to 30 nm) indicated lower positive zeta potential values (+9.5 mV to +3.6 mV). Under the same testing conditions using the Mueller-Hinton broth microdilution method, the raw kaolin samples did not show any significant antimicrobial activity, while all the pyro-fabricated Ag-Kao nanocomposite samples showed potent antibacterial and antifungal activity at low doses (MIC range 0.1-0.0125 mg/mL). Therefore, modulation of the effective electrostatic surface charge of the kaolinite platelets, via thermal doping of silver within their basal planes and edges, was found to be strongly dependent on the pH as well as the size and microtexture of the silver nanocrystals (mainly controlled by the order-disorder degree HI). The resulting modified nanostructure, with physicochemical stability and the efficient surface properties of the designed pyro-fabricated nanocomposite, led to an enhanced synergistic biophysical antimicrobial activity.

Water-Stable Silver-Based Metal-Organic Frameworks of Quaternized Carboxylates and Their Antimicrobial Activity

Three-dimensional (3D) and two-dimensional (2D) Ag-based zwitterionic metal-organic frameworks (MOFs) [Ag₂(Cedcp)]_n (1, 3D, H₃CedcpBr denotes N-(carboxyethyl)-(3,5-dicarboxyl)-pyridinium bromide) and {[Ag₄(Cmdcp)₂(H₂O)₄]·4H₂O}_n (2, 2D, H₃CmdcpBr denotes N-(carboxymethyl)-(3,5-dicarboxyl)-pyridinium bromide) have been prepared and investigated for antimicrobial activity via minimal inhibition concentration (MIC) test and killing kinetic assay. Both MOFs 1 and 2 show good water stability and solubility ascribed to their characteristic aromatic rings and positively charged pyridinium of the ligands, as well as the presence of Ag⁺ on their surface, leading to strong antimicrobial activity and a wide antimicrobial spectrum toward Gram-negative and positive bacteria. The results indicated that MOF 2 possesses a faster antibacterial activity (60 min) than MOF 1 (120 min). Scanning electron microscopy analysis further suggests that the Ag-based MOFs are capable of rupturing the bacterial membrane, leading to cell death. Moreover, both MOFs exhibit little hemolytic activity against mouse erythrocytes and show good biocompatibility in vitro, rendering MOFs 1 and 2 potential therapeutic agents for diseases caused by bacteria.

Halloysite nanotubes - the nano-bio interface

The numerous biological applications of nanoparticles in general and nano-clays in particular are rooted in understanding and harnessing their dynamic nano-bio interface. Among clays, the intrinsically-mesoporous halloysite nanotubes (HNTs) have emerged in recent years as promising nanomaterials. The diverse interactions of these nanotubes with living cells, encompassing electrostatic, van der Waals, and ion exchange, along with cellular response, are crucial in determining the behaviour of HNTs in biological systems. Thus, rational engineering of the nanotube properties allows for vast applications ranging from bacteria encapsulation for bioremediation, through algae flocculation for aquaculture, to intracellular drug delivery. This review summarizes the many aspects of the nano-bio interface of HNTs with different cell types (bacteria, algae and fungi, and mammalian cells), highlighting biocompatibility/bio-adverse properties, interaction mechanisms, and the latest cutting-edge technologies.

Physicochemical and biological assessment of silver nanoparticles immobilized Halloysite nanotubes-based resin composite for dental applications

OBJECTIVE

The purpose of this study was to investigate the effect of Silver nanoparticle immobilized Halloysite Nanotubes (HNT/Ag) fillers on physicochemical, mechanical, and biological properties of novel experimental dental resin composite in order to compare with the properties of corresponding composites containing conventional glass fillers.

METHODS

Dental resin (Bis-GMA/TEGDMA with ratio 70/30) composites were prepared by incorporation of varied mass fraction of HNT/Ag. Experimental composites were divided into six groups, one control group and five experimental groups containing mass fraction 1 to 10.0 wt. % of HNT/Ag. Mechanical properties of the dental composites were recorded. Degree of conversion and depth of cure of the dental resin composites were assessed. Antimicrobial properties were assessed using agar diffusion test and evaluation of cytotoxicity were performed on NIH-3T3 cell line.

RESULTS

The inclusion of mass fractions (1-5 wt. %) of the HNT/Ag in dental resins composites, significantly improved mechanical properties. While, addition of larger mass fractions (7.5 and 10 wt. %) of the HNT/Ag did not show further improvement in the mechanical properties of dental resins composites. Theses composites also demonstrated satisfactory depth of cure and degree of conversion. A significant antibacterial activity was observed on S. mutans. No significant cytotoxicity was found on NIH-3T3 cell lines.

CONCLUSION

The incorporation of HNT/Ag in Bis-GMA/TEGDMA dental resins composites resulted in enhancement in mechanical as well as biological properties for dental applications.

CLINICAL SIGNIFICANCE

HNT/Ag containing dental composite is proposed to be highly valuable in the development of restorative dental material for patients with high risk of dental caries.

Design strategy of rGO–HNT–AgNPs based hybrid nanocomposite with enhanced performance for electrochemical detection of 4-nitrophenol

We report a highly precise and sensitive electrochemical sensor to detect 4-nitrophenol based on halloysite nanotubes with silver nanoparticles decorated on reduced graphene oxide.

Nano-interfacial decoration of Halloysite Nanotubes for the development of antimicrobial nanocomposites

In recent times, incorporation of Halloysite Nanotubes (HNTs) with various antimicrobial agents as interfacial materials between these nanotubes and pathogenic microorganisms, for the development of antimicrobial nanocomposites with enhanced antimicrobial activities has gained researcher's interest. The main benefits given by HNT to these nanocomposites include enhanced thermal and mechanical stability of the antimicrobial nanocomposites and also prolong durability and release of the antimicrobial agents in a sustained manner. The exceptional structure of these aluminosilicate minerals based nanotubes (hollow tubular lumen with huge surface area) and oppositely charged surface molecules assist in attaching various molecules on both, the internal surface as well as on the outer surface of these nanotubes. Other advantages of these clay-based minerals are their biocompatibility, non-toxicity, eco-friendly nature and their natural availability with affordable price, which also contribute in selecting them as supporting material for biological applications. Therefore, these clay-based nanotubes have been recently used for developing various antimicrobial nanocomposites. In this review, various antimicrobial nanocomposites developed through incorporation of HNT with myriad antimicrobial agents such as nanoparticles, metal ions, antibiotics, essential oils, biopolymers, phenolic compounds, surfactants and food preservatives as an interface between these nanotubes and microorganisms have been discussed. These antimicrobial nanocomposites could be synthesized in different forms (powder, film, nanocapsule and adhesive) which can be applicable in various fields such as food packaging, water decontamination, waste water management, healing of wounds, antimicrobial agents for surfaces, orthopedics and for the treatment of microbial infections.

Highly integrated nanocomposites of RGO/TiO2 nanotubes for enhanced removal of microbes from water

Highly integrated nanocomposite of Graphene oxide (GO) and its derivatives with metal oxides is essential for enhanced performance for various applications. Tuning the morphology is an important aspect during nanomaterials synthesis; this has an amplifying influence upon physicochemical properties of advanced functional materials. In this research work, GO/TiO₂ nanotube composites have been successfully synthesized via alkaline hydrothermal treatment method by augmenting GO layers with two different phases of TiO₂ (anatase and rutile) nanoparticles, followed by the hydrothermal treatment that also have caused reduction of GO to reduced GO (RGO). The morphology of the as-prepared samples appeared to be nanotubes with a large aspect ratio (length to diameter). The synthesized materials have been characterized using various techniques to determine their morphological and functional properties. Large surface area (158 m²/g) nanotube composites found accountable as effective disinfectant for water containing microorganisms. The antimicrobial activity of the synthesized composites was examined by disk diffusion method and optical density for bacterial growth using two different bacterial species; Escherichia Coli (E.coli, Gram-negative) and Staphylococcus Aureus (Methicillin-resistant Staphylococcus aureus, Gram-positive). The antibacterial study revealed that, the anatase phase RGO/TiO₂ nanotube composites manifested appreciable effect on both bacteria as compared to rutile phase RGO/TiO₂ nanotubecomposite.

Antimicrobial Applications of Clay Nanotube-Based Composites

Halloysite nanotubes with different outer surface/inner lumen chemistry (SiO₂/Al₂O₃) are natural objects with a 50 nm diameter hollow cylindrical structure, which are able to carry functional compounds both inside and outside. They are promising for biological applications where their drug loading capacity combined with a low toxicity ensures the safe interaction of these nanomaterials with living cells. In this paper, the antimicrobial properties of the clay nanotube-based composites are reviewed, including applications in microbe-resistant biocidal textile, paints, filters, and medical formulations (wound dressings, drug delivery systems, antiseptic sprays, and tissue engineering scaffolds). Though halloysite-based antimicrobial materials have been widely investigated, their application in medicine needs clinical studies. This review suggests the scalable antimicrobial nano/micro composites based on natural tubule clays and outlines research and development perspectives in the field.

The Effect of Nanofillers on the Functional Properties of Biopolymer-based Films: A Review

Waste from non-degradable plastics is becoming an increasingly serious problem. Therefore, more and more research focuses on the development of materials with biodegradable properties. Bio-polymers are excellent raw materials for the production of such materials. Bio-based biopolymer films reinforced with nanostructures have become an interesting area of research. Nanocomposite films are a group of materials that mainly consist of bio-based natural (e.g., chitosan, starch) and synthetic (e.g., poly(lactic acid)) polymers and nanofillers (clay, organic, inorganic, or carbon nanostructures), with different properties. The interaction between environmentally friendly biopolymers and nanofillers leads to the improved functionality of nanocomposite materials. Depending on the properties of nanofillers, new or improved properties of nanocomposites can be obtained such as: barrier properties, improved mechanical strength, antimicrobial, and antioxidant properties or thermal stability. This review compiles information about biopolymers used as the matrix for the films with nanofillers as the active agents. Particular emphasis has been placed on the influence of nanofillers on functional properties of biopolymer films and their possible use within the food industry and food packaging systems. The possible applications of those nanocomposite films within other industries (medicine, drug and chemical industry, tissue engineering) is also briefly summarized.

A facile one-step grafting of polyphosphonium onto halloysite nanotubes initiated by Ce(iv)

Polyphosphonium was facilely grafted onto HNTs in an aqueous phase by a one-step method initiated by Ce(iv) at a mild temperature.

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

Biofilms contribute to persistent bacterial infections as well as formidable resistances to conventional antibiotics. However, it is still a major challenge to establish an advanced antibacterial nanoplatform that can efficiently eradicate biofilms while overcoming bacterial resistances. Taking advantage of the stimuli-responsive technique and the magnetic guidance strategy, here we present a highly efficient nanoplatform for planktonic inactivation and biofilm disruption. The multilayer films consisting of antibiotic gentamicin (Gen), tannic acid, and silver nanoparticles (AgNPs) were fabricated and coated on magnetic nanoparticles via electrostatic interactions. To achieve controlled drug release and improved biocompatibility, biodegradable hyaluronic acid was capped on the outer surface as a responsive shell. In vitro release profiles suggested that the nanocomposites showed both enzyme and pH-responsive release properties. The nanoplatform could be employed as a powerful nanocarrier for small molecular Gen and AgNPs delivery and on-demand release in response to bacterial infection microenvironment. The nanocomposites also showed satisfying antibacterial capacities against planktonic Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Intriguingly, with magnetic field navigation (NdFeB, 2000 gauss), the nanocomposites could be guided to handily penetrate into S. aureus biofilm and performed dual-responsive release, showing significantly enhanced biofilm disruption. Moreover, excess reactive oxygen species production resulting from the nanocomposites contributed to the decomposition of biofilm matrix and ultimate biofilm eradication. As a consequence, the ingenious antibacterial nanoplatform could be promising for combating biofilm infections while overcoming bacterial resistances with extra environmental factors such as magnetic field.

Recent advances in hydrophilic modification and performance of polyethersulfone (PES) membrane via additive blending

The blending of additives in the polyethersulfone (PES) matrix is an important approach in the membrane industry to reduce membrane hydrophobicity and improve the performance (flux, solute rejection, and reduction of fouling). Several (hydrophilic) modifications of the PES membrane have been developed. Given the importance of the hydrophilic modification methods for PES membranes and their applications, we decided to dedicate this review solely to this topic. The types of additives embedded into the PES matrix can be divided into two main categories: (i) polymers and (ii) inorganic nanoparticles (NPs). The introduced polymers include polyvinylpyrrolidone, chitosan, polyamide, polyethylene oxide, and polyethylene glycol. The introduced nanoparticles discussed include titanium, iron, aluminum, silver, zirconium, silica, magnesium based NPs, carbon, and halloysite nanotubes. In addition, the applications of hydrophilic PES membranes are also reviewed. Reviewing the research progress in the hydrophilic modification of PES membranes is necessary and imperative to provide more insights for their future development and perhaps to open the door to extend their applications to other more challenging areas.

Halloysite nanotubes-induced Al accumulation and oxidative damage in liver of mice after 30-day repeated oral administration

Halloysite (Al₂ Si₂ O₅ (OH)₄ ·nH₂ O) nanotubes (HNTs) are natural clay materials and widely applied in many fields due to their natural hollow tubular structures. Many in vitro studies indicate that HNTs exhibit a high level of biocompatibility, however the in vivo toxicity of HNTs remains unclear. The objective of this study was to assess the hepatic toxicity of the purified HNTs in mice via oral route. The purified HNTs were orally administered to mice at 5, 50, and 300 mg/kg body weight (BW) every day for 30 days. Oral administration of HNTs stimulated the growth of the mice at the low dose (5 mg/kg BW) with no liver toxicity, but inhibited the growth of the mice at the middle (50 mg/kg BW) and high (300 mg/kg BW) doses. In addition, oral administration of HNTs at the high dose caused Al accumulation in the liver but had no marked effect on the Si content in the organ. The Al accumulation caused significant oxidative stress in the liver, which induced hepatic dysfunction and histopathologic changes. These findings demonstrated that Al accumulation-induced oxidative stress played an important role in the oral HNTs-caused liver injury.

Cytotoxic consequences of Halloysite nanotube/iron oxide nanocomposite and iron oxide nanoparticles upon interaction with bacterial, non-cancerous and cancerous cells

Cytotoxic effects of iron oxide (Fe₃O₄) nanoparticles and Halloysite nanotube/iron oxide (HNT/Fe₃O₄) nanocomposite are compared based on their interaction with Gram-negative bacteria Escherichia coli and Gram-positive bacteria Bacillus subtilis. Similarly, the action of these two nanomaterials on non-cancerous Vero cell lines and human lung cancerous (A-549) cell lines are compared. The cytotoxicity studies on Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite showed difference in the rate of killing of bacterial cells. This is reflected in differential cell growth, cell membrane integrity loss, lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) production. These factors are measured over a range of concentrations of Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite and at specified time intervals, to test if there is any statistically significant difference between the toxicity of the two nanomaterials. Between the two nanomaterials, HNT/Fe₃O₄ nanocomposite is found to be less toxic to bacterial cells than Fe₃O₄ nanoparticles. HNT, when attached to the Fe₃O₄ nanoparticles, changes their surface characteristics and suppresses their inherent toxicity on bacteria. In the study on the effect on cell lines, Fe₃O₄ nanoparticles and HNT/Fe₃O₄ nanocomposite are both seen to be biocompatible with Vero cell lines. However, HNT/Fe₃O₄ nanocomposite showed more cytotoxicity than Fe₃O₄ nanoparticles on A-549 cell lines.

Chemical modification of halloysite nanotubes for controlled loading and release

Clay minerals have been used for medical purposes from ancient times. Among them, the halloysite nanotube, an aluminosilicate of the kaolin group, is an emerging nanomaterial which possesses peculiar chemical characteristics. By means of suitable modifications, such as supramolecular functionalization or covalent modifications, it is possible to obtain novel nanomaterials with tunable properties for several applications. In this context the covalent grafting of suitable organic moieties on the external surface or in the halloysite lumen has been exploited to improve the loading and release of several biologically active molecules. The resulting hybrid nanomaterials have been applied as drug carrier and delivery systems, as fillers for hydrogels, in tissue regeneration and in the gene delivery field. Furthermore the loading and release of specific molecules have been also investigated for environmental purposes. This review summarizes the main developments in the halloysite modifications in the last 20 years with a particular attention to the development in the past two years.

Halloysite Nanotubes-Induced Al Accumulation and Fibrotic Response in Lung of Mice after 30-Day Repeated Oral Administration

Natural halloysite (Al₂Si₂O₅(OH)₄· nH₂O) nanotubes (HNT) are clay materials with hollow tubular structure and are widely applied in many fields. Many in vitro studies indicate that HNTs exhibit a high level of biocompatibility; however, the in vivo toxicity of HNTs remains unclear. In this study, the biodistribution and pulmonary toxicity of the purified HNTs in mice were investigated after intragastric administration for 30 days. HNTs have high stability in biological conditions. Oral administration of HNTs caused significant Al accumulation predominantly in the lung with relative slight effects on Si biodistribution. Oral administration of HNTs stimulated the growth of the mice at low dose (5 mg/kg BW) with no pulmonary toxicity but inhibited the mouse growth and resulted in oxidative stress and inflammation in lung at high dose (50 mg/kg BW). In addition, oral HNTs at high dose could be absorbed from the gastrointestinal tract and deposited in lung and could also induce pulmonary fibrosis.

Mussel inspired green synthesis of silver nanoparticles-decorated halloysite nanotube using dopamine: characterization and evaluation of its catalytic activity

Naturally occurring ceramic tubular clay, Halloysite nanotubes (HNTs), having a significant amount of surface hydroxyls has been coated by self-polymerized dopamine in this work. The polydopamine-coated HNTs acts as a self-reducing agent for Ag+ ion to Ag0 in nanometer abundance. Herein, nano size Ag0 deposited on solid support catalyst has been used to mitigate water pollution within 10 min. To establish the versatility of the catalyst, nitroaryl (4-nitrophenol) and synthetic dye (methylene blue) have been chosen as model pollutant. The degradation/reduction of the aforementioned pollutants was confirmed after taking UV–visible spectra of the respective compounds. All the study can make sure that the catalyst is green and the rate constant value for catalytic reduction of 4-nitrophenol and methylene blue was calculated to be 4.45 × 10−3 and 1.13 × 10−3 s−1, respectively, which is found to be more efficient in comparison to other nanostructure and commercial Pt/C nanocatalyst (1.00 × 10−3 s−1).

Antifouling membranes for sustainable water purification: strategies and mechanisms

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

Cytotoxicity, genotoxicity and antibacterial activity of poly(vinyl alcohol)-coated silver nanoparticles and farnesol as irrigating solutions

OBJECTIVE

To evaluate the cytotoxicity, genotoxicity and antibacterial activity of poly(vinyl alcohol)-coated silver nanoparticles (AgNPs-PVA) and farnesol (FAR).

DESIGN

The cytotoxicity (% of cell viability) was evaluated by MTT assay and the genotoxicity (% of DNA in the tail) was evaluated by Comet assay. Root canal disinfection with different irrigating protocols was evaluated ex vivo in human teeth contaminated with Enterococcus faecalis for 21days. Three microbiological samples were collected: initial (after contamination); post-irrigation (after irrigation); and final (after 7days). After each sample, the number of log 10 CFU mL^-1 was determined. Statistical analyses was performed using two-way ANOVA and Bonferroni post-hoc tests for MTT assay, Kruskal-Wallis and Dunn post-hoc tests for Cometa and antibacterial assays (α=0.05).

RESULTS

The MTT assay showed that AgNPs and FAR were less cytotoxic that sodium hypochlorite (NaOCl) and showed a lower% of DNA in the tail, in comparison with H₂O₂ (positive control - C+). In the post-irrigation microbiological sample, all the irrigating protocols were more effective than C+ (without irrigation). NaOCl/saline, NaOCl/saline/AgNPs-PVA and NaOCl/saline/FAR led to complete bacterial elimination (p >0.05). In comparison with the initial sample, both the post-irrigation and the final samples showed microbial reduction (p < 0.05).

CONCLUSIONS

AgNPs-PVA and FAR showed low cytotoxicity and genotoxicity, and exhibit potential for use as a final endodontic irrigation protocols.

Clay-based drug-delivery systems: what does the future hold?

Clays for drug delivery have been used from ancient time due to the large availability of clay minerals and their unprecedented properties. The empirical use of nanoclays from the past is converted in a stimulating scientific task aimed at building up nanoarchitectonic vehicles for drug delivery in a targeted and stimuli-responsive fashion. Here the historical aspects are discussed; next the modern examples of applications of different clay-based materials are discussed. A special focus is given to halloysite clay nanotubes, which are an emerging and very promising nanomaterial for drug-delivery purposes due to its special morphology and unique chemical properties. Advantages and limitations of these natural nanomaterials are critically discussed pointing out the future perspectives and directions for further research.

AgNP-coordinated glucosamine-grafted carbon nanotubes with enhanced antibacterial properties

After glucosamine is coated on MWCNTs, the bonding force between the AgNPs and MWCNT–glucosamine increases because the charge of the O atom changes.

Covalently modified halloysite clay nanotubes: synthesis, properties, biological and medical applications

Halloysite (HNT) is a promising natural nanosized tubular clay mineral that has many important uses in different industrial fields.

Ecotoxicity of halloysite nanotube-supported palladium nanoparticles in Raphanus sativus L

Halloysite nanotubes (HNTs) are natural nanomaterials that are biocompatible and available in large amounts at low prices. They are emerging nanomaterials with appealing properties for applications like support for metal nanoparticles (NPs). The potential environmental impacts of NPs can be understood in terms of phytotoxicity. Current research has been focusing on HNT applications in cell or animal models, while their use in plants is limited so their ecotoxicological impact is poorly documented. To date there are no studies on the phytotoxic effects of functionalized halloysites (functionalized-HNTs). To develop a quantitative risk assessment model for predicting the potential impact of HNT-supported palladium nanoparticles (HNT-PdNPs) on plant life, an investigation was undertaken to explore their effects on seed germination, seedling development, and mitotic division in root tip cells of 2 lots of Raphanus sativus L. with different vigor. The results showed that exposure to 1500 mg/L of HNTs, functionalized-HNTs, and HNT-PdNPs had no significant influence on germination, seedling development, xylem differentiation, or mitotic index in both lots. Cytogenetic analyses revealed that treatments with functionalized-HNT significantly increased the number of aberrations in low-vigor seeds. These results suggest that low-vigor seeds represent a model for a stress test that would be useful to monitor the effects of NPs. Moreover the present study offers scientific evidence for the use of halloysite for environmental purposes, supporting the biological safety of HNT-PdNPs. Environ Toxicol Chem 2016;35:2503-2510. © 2016 SETAC.

Poly(ε-caprolactone)/triclosan loaded polylactic acid nanoparticles composite: A long-term antibacterial bionanocomposite with sustained release

In this study, the antibacterial bionanocomposites of poly(ε-caprolactone) (PCL) with different concentrations of triclosan (TC) loaded polylactic acid (PLA) nanoparticles (30wt% triclosan) (LATC30) were fabricated via a melt mixing process in order to lower the burst release of PCL and to extend the antibacterial activity during its performance. Due to the PLA's higher glass transition temperature (Tg) and less flexibility compared with PCL; the PLA nanoparticles efficiently trapped the TC particles, reduced the burst release of TC from the bionanocomposites; and extended the antibacterial property of the samples up to two years. The melt mixing temperature was adjusted to a temperature lower than the melting point of LATC30 nanoparticles; therefore, these nanoparticles were dispersed in the PCL matrix without any chemical reaction and/or drug extraction. The sustained release behavior of TC from PCL remained unchanged since no significant changes occurred in the samples' crystallinity compared with that in the neat PCL. The elastic moduli of samples were enhanced once LATC30 is included. This is necessary since the elastic modulus is decreased with water absorption. The rheological behaviors of samples showed appropriate properties for melt electro-spinning. A stable process was established as the relaxation time of the bionanocomposites was increased. The hydrophilic properties of samples were increased with increasing LATC30. The proliferation rate of the fibroblast (L929) cells was enhanced as the content of nanoparticles was increased. A system similar to this could be implemented to prepare long-term antibacterial and drug delivery systems based on PCL and various low molecular weight drugs. The prepared bionanocomposites are considered as candidates for the soft connective tissue engineering and long-term drug delivery.

PdNP Decoration of Halloysite Lumen via Selective Grafting of Ionic Liquid onto the Aluminol Surfaces and Catalytic Application

The synthesis of selectively deposited palladium nanoparticles (PdNPs) inside tubular halloysite lumens is reported. This specific localization was directed by the selective modification of the aluminol surfaces of the clay mineral through stable Al-O-C bonds. An ionic liquid (1-(2-hydroxyethyl)-3-methylimidazolium) was grafted onto halloysite following the guest displacement method (generally used for kaolinite) using halloysite-DMSO preintercalate. The characterization of this clay nanohybrid material (XRD, NMR, TGA) showed characteristics reminiscent of similar materials synthesized from kaolinite. The grafting on halloysite lumens was also effective without using the DMSO preintercalate. The presence of these new functionalities in halloysite directs the synthesis of uniform PdNPs with size ranging between 3 and 6 nm located exclusively in the lumens. This results from the selective adsorption of PdNPs precursors in functionalized lumens through an anion exchange mechanism followed by in situ reduction. In contrast, the unmodified clay mineral displayed nanoparticles both inside and outside the tubes. These catalysts showed significant catalytic activity for the reduction of 4-nitrophenol (4-NP). The most efficient catalysts were recycled up to three times without reducing significantly the catalytic activities.

Synthesis of copper–silver bimetallic nanopowders for a biomedical approach; study of their antibacterial properties

Copper–silver nanopowders (NPs) are synthesized using a combination of sonoelectrodeposition for the inner core and galvanic replacement reaction for the outer shell.