A Review on Montmorillonite-Based Nanoantimicrobials: State of the Art

Development of super nanoantimicrobials combining AgCl, tetracycline and benzalkonium chloride

In this work, we demonstrate that a simple argentometric titration is a scalable, fast, green and robust approach for producing AgCl/antibiotic hybrid antimicrobial materials. We titrated AgNO3 into tetracycline hydrochloride (TCH) aqueous solution, thus forming AgCl/TCH in a one-step procedure. Furthermore, we investigated the one-pot synthesis of triply synergistic super-nanoantimicrobials, combining an inorganic source of Ag+ ions (AgCl), a disinfecting agent (benzyl-dimethyl-hexadecyl-ammonium chloride, BAC) and a molecular antibiotic (tetracycline hydrochloride, TCH). Conventional antimicrobial tests, industrial biofilm detection protocols, and in situ IR-ATR microbial biofilm monitoring, have been adapted to understand the performance of the synthesized super-nanoantimicrobial. The resulting hybrid AgCl/BAC/TCH nanoantimicrobials are found to be synergistically active in eradicating Salmonella enterica and Lentilactobacillus parabuchneri bacteria and biofilms. This study paves the way for the development of a new class of super-efficient nanoantimicrobials that combine relatively low amounts of multiple active species into a single (nano)formulation, thus preventing the development of antimicrobial resistance towards a single active principle.

Formation mechanism of a novel core-shell with tetradecyl dimethyl benzyl ammonium-modified montmorillonite interlayer nanofibrous membrane and its antimicrobial properties

A novel core-shell with a tetradecyl dimethyl benzyl ammonium chloride-modified montmorillonite (TDMBA/MMT) interlayer silk fibroin (SF)/poly(lactic acid) (PLLA) nanofibrous membrane was fabricated using a simple conventional electrospinning method. Scanning electron microscopy and pore size analyses revealed that this core-shell with TDMBA/MMT interlayer maintained its nanofibrous morphology and larger pore structure more successfully than SF/PLLA nanofibrous membranes after treatment with 75% ethanol vapor. Transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses testified that the SF/PLLA-TDMBA/MMT nanofibers exhibited a core-shell with an interlayer structure, with SF/PLLA in the core-shell layer and TDMBA/MMT in the interlayer. The formation of a core-shell with interlayer nanofibers was primarily attributed to the uniform dispersion of TDMBA/MMT nanosheets in a solution owing to its exfoliation using hexafluoroisopropanol and then preparing a stable spinning solution similar to an emulsion. Compared to SF/PLLA nanofibrous membranes, the core-shell structure with TDMBA/MMT interlayers of SF/PLLA nanofibrous membranes exhibited enhanced hydrophilicity, thermal stability, mechanical properties as well as improved and long-lasting antimicrobial performance against Escherichia coli and Staphylococcus aureus without cytotoxicity.

Fabrication and Characterization of Montmorillonite Clay/Agar-Based Magnetic Composite and Its Biological and Electrical Conductivity Evaluation

Montmorillonite clay and agar are naturally occurring materials of significant importance in designing biocompatible materials tailored for applications in biotechnology and medicine. The introduction of magnetic properties has the potential to significantly boost their characteristics and expand their applications. In this study, we have successfully synthesized highly intercalated magnetic composites, incorporating magnetic iron oxide nanoparticles (MNPs), montmorillonite clay (MMT), and agar (AG), through a thermo-physicomechanical method. Three samples of MMT-AG with 2, 1.5, and 0.5% MNPs and three sample composites of MNPs-AG with 2, 1, and 0.5% MMT clay are prepared. The synthesized composites were characterized by SEM, XRD, TGA, DTA, and FTIR. SEM analysis revealed a uniform dispersion of MNPs and MMT in the composite. The XRD pattern confirmed the presence of MNPs in the composite site. The TGA and DTA results demonstrated improved thermal stability due to the MNP incorporation. FTIR spectra showed all of the constituents of agar, MNPs, and MMT clay. The swelling ratio was observed to range from 835% to 1739%. The swelling study indicated an increased hydrophobicity with the addition of MNPs to the composite. Antibacterial activities revealed a significant inhibition of Escherichia coli (E. coli) growth by ranging from 10 to 19 nm in the composite. The composite also exhibited a considerable antioxidant action, with IC50 values of 7.96, 46.55, and 57.58 μg/mL, and electrical properties just like conductors.

Biosynthesis of Bt-Ag2O nanoparticles using Bacillus thuringiensis and their pesticidal and antimicrobial activities

Nanosilver oxide exhibits strong antibacterial and photocatalytic properties and has shown great application potential in food packaging, biochemical fields, and other fields involving diseases and pest control. In this study, Ag2O nanoparticles were synthesized using Bacillus thuringiensis (Bt-Ag2O NPs). The physicochemical characteristics of the Bt-Ag2O NPs were analyzed by UV‒vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), inductively coupled plasma emission spectrometry (ICP), high-resolution transmission electron microscopy (HR-TEM), and zeta potential. The phis-chemical characterization revealed that the Bt-Ag2O NPs are in spherical shape with the small particle size (18.24 nm), high crystallinity, well dispersity, and stability. The biopesticidal and antifungal effects of Bt-Ag2O NPs were tested against Tribolium castaneum, Aspergillus flavus, and Penicillium chrysogenum. The survival, growth, and reproduction of tested pests and molds were significantly inhibited by Bt-Ag2O NPs in a dose-dependent manner. Bt-Ag2O NPs showed higher pesticidal activities against T. castaneum than Bt and commercial Ag2O NPs. The LC50 values of Bt, Ag2O NPs, and Bt-Ag2O NPs were 0.139%, 0.072%, and 0.06% on day 14, respectively. The Bt-Ag2O NPs also showed well antifungal activities against A. flavus and P. chrysogenum, while it resulted a small inhibition zone than commercial Ag2O NPs did. In addition, A. flavus showed much more sensitive to Bt-Ag2O NP treatments, compared to P. chrysogenum. Our results revealed that Bt-Ag2O NPs synthesized using B. thuringiensis could act as pesticides and antifungal agents in stored-product fields. KEY POINTS: • Bt-Ag2O NPs could be synthesized using Bacillus thuringiensis (Bt). • The NPs showed a high degree of crystallinity, spherical shape, and small particle size. • The NPs also showed excellent insecticidal and antifungal activity.

Antibacterial and Antifungal Properties of Polyester, Polylactide, and Cotton Nonwovens and Fabrics, by Means of Stable Aqueous Dispersions Containing Copper Silicate and Some Metal Oxides

Literature reviews have described the applications of silver, copper, and zinc ions and metallic particles of Cu, Ti, and Zn oxides, which have been found to be useful antimicrobial reagents for the biofunctionalization of various materials and their surfaces. For this purpose, compositions of water dispersions containing emulsions of synthetic copolymers based on acrylic and vinyl monomers, polysaccharides (hydroxyethyl cellulose and starch), and various additives with wetting and stabilizing properties were used. Many stable water dispersions of different chemical compositions containing bioactive chemical compounds (copper silicate hydrate, titanium dioxide, and zinc oxide (and other auxiliary substances)) were developed. They were used for the preparation of thin hybrid coatings having good antimicrobial properties against Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcus aureus), and yeast fungus (Candida albicans). Polyester (PES) and polylactide (PLA) nonwovens were modified using the dip-coating method, while PES and cotton fabrics were biofunctionalized by means of dip-coating and coating methods. The antimicrobial (antibacterial and antifungal) properties of the textile materials (nonwovens and fabrics) biofunctionalized with the above-mentioned bioactive agents exhibiting antimicrobial properties (CuSiO3, TiO2, ZnO, or ZnO∙SiO2) were strongly dependent on the agents' content in the water dispersions. The PES and PLA nonwovens, modified on the surface with water compositions containing copper silicate hydrate, showed good antibacterial properties against the Gram-negative bacteria Escherichia coli, even at a content of 1 wt.% CuSiO3∙xH2O, and against the Gram-positive bacteria Staphylococcus aureus, at the content of at least 5 wt.% CuSiO3∙xH2O. The bacterial growth reduction factor (R) was greater than 99% for most of the samples tested. Good antifungal properties against the fungus Candida albicans were found for the PES and PLA nonwoven fabrics modified with dispersions containing 5-7 wt.% CuSiO3∙xH2O and 4.2-5.0 wt.% TiO2. The addition of TiO2 led to a significant improvement in the antifungal properties of the PES and PLA nonwovens modified in this way. For the samples of PES WIFP-270 and FS F-5 nonwovens, modified with water dispersions containing 5.0 wt.% CuSiO3∙xH2O and 4.2-5.0 wt.% TiO2, the growth reduction factor for the fungus Candida albicans (R) reached values in the range of 80.9-98.0%. These new biofunctionalized polymeric nonwoven textile materials can find practical applications in the manufacture of filters for hospital air-conditioning systems and for the automotive industry, as well as in air purification devices. Moreover, similar antimicrobial modification of fabrics with the dip-coating or coating methods can be applied, for example, in the fabrication of fungi- and mold-resistant garden furniture.

Recent Advances in Sustainable Antimicrobial Food Packaging: Insights into Release Mechanisms, Design Strategies, and Applications in the Food Industry

In response to the issues of foodborne microbial contamination and carbon neutrality goals, sustainable antimicrobial food packaging (SAFP) composed of renewable or biodegradable biopolymer matrices with ecofriendly antimicrobial agents has emerged. SAFP offers longer effectiveness, wider coverage, more controllability, and better environmental performance. Analyzing SAFP information, including the release profile of each antimicrobial agent for each food, the interaction of each biomass matrix with each food, the material size, form, and preparation methods, and its service quality in real foods, is crucial. While encouraging reports exist, a comprehensive review summarizing these developments is lacking. Therefore, this review critically examines recent release-antimicrobial mechanisms, kinetics models, preparation methods, and key regulatory parameters for SAFPs based on slow- or controlled-release theory. Furthermore, it discusses fundamental physicochemical characteristics, effective concentrations, advantages, release approaches, and antimicrobial and preservative effects of various materials in food simulants or actual food. Lastly, inadequacies and future trends are explored, providing practical references to regulate the movement of active substances in different media, reduce the reliance on petrochemical-based materials, and advance food packaging and preservation technologies.

Improvements of thermal and mechanical properties of achira starch/chitosan/clay nanocomposite films

Thermoplastic biofilms were developed from achira starch, chitosan and nanoclays using the solvent-casting method. To obtain the filmogenic solutions, different sonication times (0, 10, 20 and 30 min) were considered in order to evaluate the incidence of this parameter on the chemical and physico-mechanical properties of the bionanocomposite films. The chemical analysis using FTIR spectroscopy showed strong intermolecular interactions between the components with increasing sonication times. The results for tensile strength and elongation were satisfactory for films with 20 min of sonication with increases of 154% and 161%, respectively. Morphological analysis showed greater homogeneity, while thermal analysis showed that sonication favoured the plasticization process and thus, the production of homogeneous materials. The water absorption and wettability tests showed less hydrophilic materials allowing these new materials to be considered for use as coatings or packaging for the food sector.