Bioinspired and Green Synthesis of Silver Nanoparticles for Medical Applications: A Green Perspective

Silver nanoparticles (AgNPs) possess unmatched chemical, biological, and physical properties that make them unique compounds as antimicrobial, antifungal, antiviral, and anticancer agents. With the increasing drug resistance, AgNPs serve as promising entities for targeted drug therapy against several bacterial, fungal, and viral components. In addition, AgNPs also serve as successful anticancer agents against several cancers, including breast, prostate, and lung cancers. Several works in recent years have been done towards the development of AgNPs by using plant extracts like flowers, leaves, bark, root, stem, and whole plant parts. The green method of AgNP synthesis thus has several advantages over chemical and physical methods, especially the low cost of synthesis, no toxic byproducts, eco-friendly production pathways, can be easily regenerated, and the bio-reducing potential of plant derived nanoparticles. Furthermore, AgNPs are biocompatible and do not harm normally functioning human or host cells. This review provides an exhaustive overview and potential of green synthesized AgNPs that can be used as antimicrobial, antifungal, antiviral, and anticancer agents. After a brief introduction, we discussed the recent studies on the development of AgNPs from different plant extracts, including leaf parts, seeds, flowers, stems, bark, root, and whole plants. In the following section, we highlighted the different therapeutic actions of AgNPs against various bacteria, fungi, viruses, and cancers, including breast, prostate, and lung cancers. We then highlighted the general mechanism of action of AgNPs. The advantages of the green synthesis method over chemical and physical methods were then discussed in the article. Finally, we concluded the review by providing future perspectives on this promising field in nanotechnology.

Eco-Friendly CuO/Fe3O4 Nanocomposite synthesis, characterization, and cytotoxicity study

The current study report a convenient, simple, and low cost approach for the biogenic synthesis of CuO/Fe3O4 nanocomposites (NCs) from pumpkin seeds extract and their vitro cytotoxicity. The characterization of finally obtained CuO/Fe3O4 nanocomposites (NCs) performed using UV-Visible, FT-IR, XRD, XPS, GC-MS, SEM-EDX and TEM analysis. The formation and elemental analysis were determined using the energy-dispersive X-ray (EDX) microanalysis technique. The formation of rod-like monoclinic and spherical, having size range 5 nm-20 nm confirmed by scanning electron microscope (SEM) and transmission electron microscopy (TEM) respectively. Finally, the MTT assay of the synthesized composites was evaluated for toxicity against cancerous cell lines HCT-116 (Colon cancer cell) and A549 (human lung adenocarcinoma cell). The synthesized composite material showed moderate (IC50 = 199 μg/mL) to low (IC50 = 445 μg/mL) activity against HCT-116 and A549 cell lines, respectively.

Recent Approaches for Downplaying Antibiotic Resistance: Molecular Mechanisms

Antimicrobial resistance (AMR) is a ubiquitous public health menace. AMR emergence causes complications in treating infections contributing to an upsurge in the mortality rate. The epidemic of AMR in sync with a high utilization rate of antimicrobial drugs signifies an alarming situation for the fleet recovery of both animals and humans. The emergence of resistant species calls for new treatments and therapeutics. Current records propose that health drug dependency, veterinary medicine, agricultural application, and vaccination reluctance are the primary etymology of AMR gene emergence and spread. Recently, several encouraging avenues have been presented to contest resistance, such as antivirulent therapy, passive immunization, antimicrobial peptides, vaccines, phage therapy, and botanical and liposomal nanoparticles. Most of these therapies are used as cutting-edge methodologies to downplay antibacterial drugs to subdue the resistance pressure, which is a featured motive of discussion in this review article. AMR can fade away through the potential use of current cutting-edge therapeutics, advancement in antimicrobial susceptibility testing, new diagnostic testing, prompt clinical response, and probing of new pharmacodynamic properties of antimicrobials. It also needs to promote future research on contemporary methods to maintain host homeostasis after infections caused by AMR. Referable to the microbial ability to break resistance, there is a great ultimatum for using not only appropriate and advanced antimicrobial drugs but also other neoteric diverse cutting-edge therapeutics.

Preparation of Laser-Ablated Ag Nanoparticle-MMT Clay-Based Beeswax Antibiofilm Coating

Unlike other antimicrobial agents, Ag-based composites are stable and currently widely used as broad spectral additives, fighting microbial biofilms and other biological threats. The goal of the present study is to develop a green, multifunctional, and robust antibiofilm water-insoluble coating, inhibiting histamine-producing Lentilactobacillus parabuchneri biofilms. Herein, laser-ablated Ag NPs (L-Ag NPs) were incorporated into and onto a montmorillonite (MMT) surface layer with a simple wet chemical method, provided that the electrostatic interaction between L-Ag NPs and MMT clay led to the formation of L-Ag/MMT nanoantimicrobials (NAMs). The use of MMT support can facilitate handling Ag NPs in industrial applications. The Ag/MMT composite was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), which confirmed the entrapment of L-Ag NPs into MMT clay. The surface chemical composition was assessed with X-ray photoelectron spectroscopy, proving that Ag NPs were in contact with and deposited onto the surface of MMT. The characteristic L-Ag/MMT band was investigated with UV-vis spectroscopy. Following that, the L-Ag/MMT composite was embedded into a biosafe water-insoluble beeswax agent with a spin coating technique. The antimicrobial ion release kinetic profile of the L-Ag/MMT/beeswax coating through an electrothermal atomic absorption spectroscopy (ETAAS) study supported the controlled release of Ag ions, reaching a plateau at 420 ± 80 nM, which is safe from the point of view of Ag toxicity. Microbial biofilm growth inhibition was assessed with real-time in situ Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) in a flow cell assembly over 32 h. The study was further supported by optical density (OD) measurements and SEM on bacteria incubated in the presence of the L-Ag/MMT/beeswax coating.

Metal Oxide Nanoparticles: Review of Synthesis, Characterization and Biological Effects

In the last few years, the progress made in the field of nanotechnology has allowed researchers to develop and synthesize nanosized materials with unique physicochemical characteristics, suitable for various biomedical applications. Amongst these nanomaterials, metal oxide nanoparticles (MONPs) have gained increasing interest due to their excellent properties, which to a great extent differ from their bulk counterpart. However, despite such positive advantages, a substantial body of literature reports on their cytotoxic effects, which are directly correlated to the nanoparticles' physicochemical properties, therefore, better control over the synthetic parameters will not only lead to favorable surface characteristics but may also increase biocompatibility and consequently lower cytotoxicity. Taking into consideration the enormous biomedical potential of MONPs, the present review will discuss the most recent developments in this field referring mainly to synthesis methods, physical and chemical characterization and biological effects, including the pro-regenerative and antitumor potentials as well as antibacterial activity. Moreover, the last section of the review will tackle the pressing issue of the toxic effects of MONPs on various tissues/organs and cell lines.

Enhanced Antibacterial Activity through Silver Nanoparticles Deposited onto Carboxylated Graphene Oxide Surface

The strong bactericidal action of silver nanoparticles (AgNPs) is usually limited by their degree of aggregation. Deposition of AgNPs onto a graphene oxide (GO) surface to generate GO-Ag hybrids has been shown to be an effective method of controlling these aggregation problems. In this sense, a novel carboxylated graphene oxide–silver nanoparticle (GOCOOH-Ag) material has been synthesized, and their antibacterial and biofilm formation inhibitions have been studied. AgNPs decorating the GOCOOH surface achieved an average size of 6.74 ± 0.25 nm, which was smaller than that of AgNPs deposited onto the GO surface. In addition, better distribution of AgNPs was achieved using carboxylated material. It is important to highlight the main role of the carboxylic groups in the nucleation and growth of the AgNPs that decorate the GO-based material surface. In vitro antibacterial activity and antibiofilm-forming action were tested against Gram-positive (Staphylococcus aureus and Staphylococcus epidermidis) and Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli). Both GO-Ag and GOCOOH-Ag reduced bacterial growth, analyzed by time–kill curves. However, the minimum inhibitory concentration and the minimum bactericidal concentration of GOCOOH-Ag were lower than those of GO-Ag for all strains studied, indicating that GOCOOH-Ag has better antibacterial activity. In addition, both nanomaterials prevent biofilm formation, with a higher reduction of biofilm mass and cell viability in the presence of GOCOOH-Ag. The carboxylation functionalization in GO-based materials can be applied to improve the bactericidal and antibiofilm-forming action of the AgNPs.

Antibacterial Activities of Prenylated Isoflavones from Maclura tricuspidata against Fish Pathogenic Streptococcus: Their Structure-Activity Relationships and Extraction Optimization

Streptococcus zoonotic bacteria cause serious problems in aquaculture with clinical effects on humans. A structure-antibacterial activity relationships analysis of 22 isoflavones isolated from M. tricuspidata (leaves, ripe fruits, and unripe fruits) against S. iniae revealed that prenylation of the isoflavone skeleton was an important key for their antibacterial activities (minimum inhibitory concentrations: 1.95–500 μg/mL). Through principal component analysis, characteristic prenylated isoflavones such as 6,8-diprenlygenistein (4) were identified as pivotal compounds that largely determine each part’s antibacterial activities. M. tiricuspidata ripe fruits (MTF), which showed the highest antibacterial activity among the parts tested, were optimized for high antibacterial activity and low cytotoxicity on fathead minnow cells using Box–Behnken design. Optimized extraction conditions were deduced to be 50%/80 °C/7.5 h for ethanol concentration/extraction temperature/time, and OE-MTF showed contents of 6,8-diprenlygenistein (4), 2.09% with a MIC of 40 µg/mL. These results suggest that OE-MTF and its active isoflavones have promising potential as eco-friendly antibacterial agents against streptococcosis in aquaculture.

Mechanistic insight into the binding of graphene oxide with human serum albumin: Multispectroscopic and molecular docking approach

Increasing manufacturing and use of nanoparticles in industrial and biomedical applications creates the necessity to understand the impact of the interaction of nanoparticles with biomacromolecules. In the present study, graphene oxide nanosheets (GONS) were synthesized using modified Hummer's method and further characterized employing X-ray diffraction (XRD), UV, FTIR, and Raman spectroscopy. After characterization, the interaction of GONS with human serum albumin (HSA) was investigated to delineate the binding mechanism employing different kinds of spectroscopic techniques. Intrinsic fluorescence spectroscopy revealed that complex formation is taking place between HSA and GONS. Fluorescence-based binding studies suggested that GONS binds to HSA with a significant binding affinity, and the interaction is governed by dynamic quenching. The evaluation of enthalpy change (ΔH) and entropy change (ΔS) suggested that the HSA-GONS complex formation is driven by hydrogen bonding and van der Waals interaction and hence complexation process is seemingly specific. Structural transition in the microenvironment of HSA was monitored using synchronous fluorescence spectroscopy and three-dimensional fluorescence spectroscopy, which showed that GONS binding to HSA influences the microenvironment around tyrosine and tryptophan residues. Secondary structural alterations in HSA upon binding to GONS were measured using circular dichroism (CD) spectroscopy. Additionally, molecular docking provided an insight into the critical residues involved in HSA-GONS interaction and further validated our in vitro observations affirming interaction between GONS and HSA. The significance of this study is attributable to the fact that HSA and GONS can be used as nanocarriers in drug delivery systems.

An Overview of Antimicrobial Properties of Carbon Nanotubes-Based Nanocomposites

The development of carbon-based nanomaterials has extensively facilitated new discoveries in various fields. Carbon nanotube-based nanocomposites (CNT-based nanocomposites) have lately recognized as promising biomaterials for a wide range of biomedical applications due to their unique electronic, mechanical, and biological properties. Nanocomposite materials such as silver nanoparticles (AgNPs), polymers, biomolecules, enzymes, and peptides have been reported in many studies, possess a broad range of antibacterial activity when incorporated with carbon nanotubes (CNTs). It is crucial to understand the mechanism which governs the antimicrobial activity of these CNT-based nanocomposite materials, including the decoupling individual and synergistic effects on the cells. In this review, the interaction behavior between microorganisms and different types of CNT-based nanocomposites is summarized to understand the respective antimicrobial performance in different conditions. Besides, the current development stage of CNT-based nanocomposite materials, the technical challenges faced, and the exceptional prospect of implementing potential antimicrobial CNT-based nanocomposite materials are also discussed.

ZIF-8@s-EPS as a novel hydrophilic multifunctional biomaterial for efficient scale inhibition, antibacterial and antifouling in water treatment

The hydrophilic biomaterial was constructed based on the soluble extracellular polysaccharides (s-EPS) secreted by Bacillus megaterium and zeolitic imidazolate framework-8 (ZIF-8), namely ZIF-8@s-EPS, wrapped in s-EPS shell with ZIF-8 as the core. ZIF-8@s-EPS was used as a novel multifunctional biomaterial in water treatment for the first time. Unexpectedly, results showed ZIF-8@s-EPS with strong synergistic effect presented multifunctional performances including descaling, antifouling and antibacterial. Scale inhibition efficiency reached 98.63% for CaCO₃ and as high as 99.40% for CaSO₄ at concentration 20.00 mg/L. The synergy of s-EPS and ZIF-8 demonstrated effective antibacterial activity against Pseudomonas aeruginosa and inhibitory effect on biofilms, and result presented that ZIF-8@s-EPS could inhibit the growth of nearly 89.4% P. aeruginosa. Therefore, the obtained insights will shed light on the development of s-EPS modified biomaterials in water treatment.

In vivo toxicity and antitumor activity of newly green synthesized reduced graphene oxide/silver nanocomposites

A novel biosynthesis of dual reduced graphene oxide/silver nanocomposites (rGO/AgNC) using the crude metabolite of Escherichia coli D8 (MF06257) strain and sunlight is introduced in this work. Physicochemical analysis of these rGO/AgNC revealed that they are sheet-like structures having spherically shaped silver nanoparticles (AgNPs) with an average particle size of 8 to 17 nm, and their absorption peak ranged from 350 to 450 nm. The biosynthesized rGO/AgNC were characterized by UV-vis and FT-IR spectra, X-ray diffraction, Zeta potential and transmission electron microscopy. After the injection of these nanocomposites to mice, their uptake by the kidney and liver has been proven by the ultrastructural observation and estimation of the hepatic and renal silver content. These nanocomposites caused a moderate toxicity for both organs. Changes in the liver and kidney functions and histopathological effects had been observed. The rGO/AgNC revealed a remarkable antitumor effect. They showed a dose-dependent cytotoxic effect on Ehrlich ascites carcinoma (EAC) cells in vitro. Treatment of mice bearing EAC tumors intraperitoneally with 10 mg/kg rGO/AgNC showed an antiproliferative effect on EAC cells, reduced ascites volume, and maintained mice survival. The results indicate that this green synergy of silver nanoparticles with reduced graphene oxide may have a promising potential in cancer therapy.

Microbial and quality improvement of boiled gansi dish using carbon dots combined with radio frequency treatment

Use of carbon dots (CDs) combined with radio frequency (RF) was applied to pasteurize and reduce the microorganism population in order to improve the quality of boiled gansi dish. CDs were prepared from banana using hydrothermal method, and characterized by using TEM, XRD and FTIR. The minimal inhibitory concentration (MIC) test showed CDs can efficiently inactivate Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis). This study also evaluated the effectiveness of five treatments, including CDs alone, CDs combined RF (CDRF) heating for different time (8 min, 12 min, and 16 min), and high pressure steam (HPS) sterilization of boiled gansi dish inoculated with B. subtilis. After CDRF treated for 8 min, 12 min, and 16 min, the center temperature of samples reached to 78.92, 87.77 and 93.82 °C, and the colony forming units (CFU) of B. subtilis reduced by 2.13, 3.62, and 4.63 log, respectively. Samples with CDRF12 treatment, exhibited better product quality as evidenced by reduced loss of texture, flavor, and sensory as compared with HPS sample. The results indicated that CDRF treatment has a great potential to produce packaged boiled gansi dish with high product quality.

Graphene Oxide-Polypyrrole Coating for Functional Ceramics

Ceramic substrates were metallized with a Ni-Mo-P electroless coating and further modified with a polypyrrole (PPy) coating by the electrodeposition method. The properties of the polypyrrole coating were studied with the addition of a graphene oxide (GO) nanomaterial prior to the electrodeposition and its reduction degree. Fourier Transform Infrared Spectroscopy, Field-Emission Scanning Electron Microscopy, Raman spectroscopy and cyclic voltammetry were employed to characterize the properties of the coatings. The results indicated the successful synthesis of conductive electrodes by the proposed approach. The electrodeposition of PPy and its charge storage properties are improved by chemically reduced GO. The surface capacitive contribution to the total stored charge was found to be dominant and increased 2–3 fold with the reduction of GO. The chemically reduced GO-modified PPy exhibits the highest capacitance of 660 F g⁻¹ at 2 mV s⁻¹, and shows a good cyclability of 94% after 500 charge/discharge cycles. The enclosed results indicate the use of an NiMoP electroless coating, and modification with a carbon nanomaterial and conducting polymer is a viable approach for achieving functional ceramics.

Synthesis, characterization and investigation of synergistic antibacterial activity and cell viability of silver-sulfur doped graphene quantum dot (Ag@S-GQDs) nanocomposites

The excessive use of traditional antibiotic and antibacterial agents has globally increased the growth of antibiotic-resistant bacteria that poses serious health risks. Therefore, the development of new generation antibacterial or antimicrobial agents for effective inhibition of bacterial growth is highly desired. In this study, we report a facile one-step synthesis approach for the preparation of a nanocomposite composed of silver nanoparticles (AgNPs) decorated with sulfur-doped graphene quantum dots (S-GQDs). The nanocomposite was comprehensively characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis absorption spectra, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The characterization results demonstrated that the AgNPs were closely and uniformly surrounded by the S-GQDs, and consequently, this ensured the dispersion and stability of the so formed nanocomposite (Ag@S-GQDs). Further, the antibacterial activity of the Ag@S-GQDs nanocomposite was investigated and compared with bare S-GQDs and AgNPs against Gram-positive S. aureus (MTCC 737) and Gram-negative P. aeruginosa (MTCC 424) bacteria using macrodilution and agar well diffusion methods. Minimum inhibitory concentration (MIC) values of 70 and 35 μg mL^-1 of the Ag@S-GQDs nanocomposite were found to be sufficient to hinder the growth of P. aeruginosa and S. aureus. A fractional inhibition concentration (FIC) index below 0.5 confirmed the existence of a synergistic effect between AgNPs and S-GQDs in the Ag@S-GQDs nanocomposite. In addition, the cytotoxicity of the Ag@S-GQDs nanocomposite, AgNPs and S-GQDs was also investigated using HEK 293 cell lines. Interestingly, the Ag@S-GQDs nanocomposite exhibited superior cell viability as compared to AgNPs and S-GQDs. These improved antibacterial and biocompatibility data demonstrate that the Ag@S-GQDs nanocomposite can serve as a promising antibacterial agent for industry to fabricate next-generation self-sterile textiles, antibacterial coatings and useful health care products supporting cell viability.

Improving Electrochemical Properties of Polypyrrole Coatings by Graphene Oxide and Carbon Nanotubes

Nanostructured polypyrrole coating was applied on carbon paper via simple dip-coating and electrochemical approach. Hybridization with nanocarbon materials (graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs)) and their effect as an anchoring hybrid layer for the growth of polypyrrole towards improving electrochemical properties are studied. The loading of each component and their w/w ratio were evaluated. Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and Raman spectroscopy were employed to characterize the properties of the coatings. The electrochemical properties were investigated by cyclic voltammetry. The results indicated the electrodeposition of polypyrrole is enhanced by the addition of MWCNTs to the GO layer due to the formation of a hierarchical network. The electrochemical performance of the modified electrode was shown to be highly dependent on the employed w/w ratio, reaching a capacitance value of about 40 mF cm⁻² for a carbon paper substrate modified with GO:MWCNT in a w/w ratio of 1:2.5 and PPy layer deposited by cyclic voltammetry for 30 cycles. The contribution to total stored charge was found to be primary from the inner capacitance component of about 95.5% contribution.

Effect of Deposition Parameters on Electrochemical Properties of Polypyrrole-Graphene Oxide Films

Graphene oxide (GO)-modified polypyrrole (PPy) coatings were obtained by electrochemical methods in the presence of the anionic surfactant, sodium dodecyl sulfate (SDS). The structure, morphology, and electrochemical properties of the coatings were assessed by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM) and cyclic voltammetry at varying scan rates, respectively. The properties of the obtained coatings were analyzed with the GO and PPy loadings and electrodeposition mode. The hybrid coatings obtained galvanostatically showed a coarser appearance than those deposited by cyclic voltammetry CV mode and improved performance, respectively, which was further enhanced by GO and PPy loading. The capacitance enhancement can be attributed to the SDS surfactant that well dispersed the GO sheets, thus allowing the use of lower GO content for improved contribution, while the choice of suitable electrodeposition parameters is highly important for improving the applicability of GO-modified PPy coatings in energy storage applications.

A review of the antimicrobial potential of precious metal derived nanoparticle constructs

The field of nanotechnology is rapidly growing. The promise of pharmacotherapeutics emerging from this vast field has drawn the attention of many researchers. However, with the increase in the prevalence of antibiotic resistant microorganisms, the manifestations of these promises are needed now more than ever. Many have postulated the antimicrobial potential of nanoparticle constructs derived from precious metals/noble metals nanoparticles (NMNPs), such as silver nanoparticles that show activity against multidrug resistant bacteria. In this review we will evaluate the current studies and explore the data to obtain a clear picture of the potential of these particles and the validity of the claims of drug resistant treatments with NMNPs.

Rapid synthesis of multifunctional carbon nanodots as effective antioxidants, antibacterial agents, and quercetin nanoprobes

A facile and rapid synthesis of multifunctional carbon nanodots (CNDs) was developed by using the acid-base neutralization spontaneous heat with glucose as precursor, 1,2-ethylenediamine (EDA) and concentrated nitric acid as dual N-dopants. The CND has a tremendous antioxidant potency, which represents effective inhibitory concentrations of reactive oxygen species that are significantly lower than ascorbic acid. Furthermore, minimum inhibitory concentration (MIC) assay revealed CNDs possessed significant antimicrobial activity for Gram-positive S. aureus and Gram-negative E. coli. Moreover, the CNDs are endowed with favorable fluorescence (FL) behaviors including the quantum yield (QY) of 14.2% and stable FL within a wide range of pH and high tolerance to external ionic strength, rendering them applicable in quercetin (QCT) detection as a FL nanoprobe. The CNDs were effectively quenched by QCT due to static quenching which takes place by the electrostatic interaction between basic groups of CNDs and QCT of 3-hydroxyl. This nanoprobe had profitable selectivity and sensitivity towards QCT with a linearity ranging from 1 μM to 47 μM and a low detection limit of 172.4 nM and were successfully performed for QCT detection in human serum and urine samples.

Optimizing the nanostructure of graphene oxide/silver/arginine for effective wound healing

In this study, we introduce a novel graphene oxide/silver/arginine (GO/Ag/Arg) nanohybrid structure, which can act as an angiogenesis promoter and provide antibacterial nanostructure for improving the wound healing process. GO/Ag nanostructure has been optimized in terms of the GO/Ag mass ratio and pH values using central composite design and the response surface method to increase the Ag loading efficiency. Then, Arg was chemically introduced to the surface of GO/Ag nanostructure. Electrospun polycaprolactone (PCL)-GO/Ag/Arg nanocomposite was successfully fabricated and characterized. The synthesized nanocomposite demonstrated not only a great antibacterial effect on both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacterial species, but appropriate biocompatibility against L929 fibroblastic cell lines. The results demonstrated that the preparation of the PCL-GO/Ag/Arg nanocomposite at a concentration of 1.0 wt% GO/Ag/Arg possessed the best biological and mechanical features. In vivo experiments also revealed that the use of optimized PCL-GO/Ag/Arg nanocomposite, after 12 d of treatment, led to significant increase in the healing process and also regeneration of the wound via reconstruction of a thickened epidermis layer on the wound surface, which was confirmed by histological analysis. In conclusion, the proposed approach can introduce a novel notion for preparing antibacterial material that significantly promotes angiogenesis.

'Green' synthesis of metals and their oxide nanoparticles: applications for environmental remediation

In materials science, “green” synthesis has gained extensive attention as a reliable, sustainable, and eco-friendly protocol for synthesizing a wide range of materials/nanomaterials including metal/metal oxides nanomaterials, hybrid materials, and bioinspired materials. As such, green synthesis is regarded as an important tool to reduce the destructive effects associated with the traditional methods of synthesis for nanoparticles commonly utilized in laboratory and industry. In this review, we summarized the fundamental processes and mechanisms of “green” synthesis approaches, especially for metal and metal oxide [e.g., gold (Au), silver (Ag), copper oxide (CuO), and zinc oxide (ZnO)] nanoparticles using natural extracts. Importantly, we explored the role of biological components, essential phytochemicals (e.g., flavonoids, alkaloids, terpenoids, amides, and aldehydes) as reducing agents and solvent systems. The stability/toxicity of nanoparticles and the associated surface engineering techniques for achieving biocompatibility are also discussed. Finally, we covered applications of such synthesized products to environmental remediation in terms of antimicrobial activity, catalytic activity, removal of pollutants dyes, and heavy metal ion sensing.

Graphene oxide/silver nanohybrid: Optimization, antibacterial activity and its impregnation on bacterial cellulose as a potential wound dressing based on GO-Ag nanocomposite-coated BC

Recently, bacterial cellulose (BC) based wound dressing have raised significant interests in medical fields. However, to our best knowledge, it is apparent that the BC itself has no antibacterial activity. In this study, we optimized graphene oxide-silver (GO-Ag) nanohybrid synthesis using Response Surface Methodology and impregnate it to BC and carefully investigate their antibacterial activities against both the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus aureus. We discover that, compared to silver nanoparticles, GO-Ag nanohybrid with an optimal GO suspension's pH and [ G O ] [ A g N O 3 ] ratio is much more effective and shows synergistically enhanced, strong antibacterial activities at rather low dose. The GO-Ag nanohybrid is more toxic to E. coli than that to S. aureus. The antibacterial and mechanical properties of BC/GO-Ag composite are further investigated.

Multifunctional HA/Cu nano-coatings on titanium using PPy coordination and doping via pulse electrochemical polymerization

An anti-wear and antibacterial hydroxyapatite nanoparticle bioactive coating on a titanium matrix is fabricated through hydroxyapatite/copper nanoparticle co-deposition.

Recent Advances in Antimicrobial Hydrogels Containing Metal Ions and Metals/Metal Oxide Nanoparticles

Recently, the rapid emergence of antibiotic-resistant pathogens has caused a serious health problem. Scientists respond to the threat by developing new antimicrobial materials to prevent or control infections caused by these pathogens. Polymer-based nanocomposite hydrogels are versatile materials as an alternative to conventional antimicrobial agents. Cross-linking of polymeric materials by metal ions or the combination of polymeric hydrogels with nanoparticles (metals and metal oxide) is a simple and effective approach for obtaining a multicomponent system with diverse functionalities. Several metals and metal oxides such as silver (Ag), gold (Au), zinc oxide (ZnO), copper oxide (CuO), titanium dioxide (TiO₂) and magnesium oxide (MgO) have been loaded into hydrogels for antimicrobial applications. The incorporation of metals and metal oxide nanoparticles into hydrogels not only enhances the antimicrobial activity of hydrogels, but also improve their mechanical characteristics. Herein, we summarize recent advances in hydrogels containing metal ions, metals and metal oxide nanoparticles with potential antimicrobial properties.

Colloid particle formulations for antimicrobial applications

Colloidal particles are being extensively studied in various antimicrobial applications due to their small size to volume ratio and ability to exhibit a wide spectrum of antibacterial, antifungal, antialgal and antiviral action. The present review focuses on various nanoparticles (NPs) of inorganic, organic and hybrid materials, and discusses some of the methods for their preparation as well as mechanisms of their antimicrobial action. We consider the antimicrobial applications of metal oxide nanoparticles (ZnO, MgO, CuO, Cu₂O, Al₂O₃, TiO₂, CeO₂ and Y₂O₃), metal nanoparticles (NPs), such as copper, silver and gold, metal hydroxide NPs such as Mg(OH)₂ as well as hybrid NPs made from biodegradable materials, such as chitosan, lignin and dextran, loaded with other antimicrobial agents. Recent developments for targeted delivery of antimicrobials by using colloid antibodies for microbial cell shape and surface recognition are also discussed. We also consider recent advances in the functionalization of nanoparticles and their potential antimicrobial applications as a viable alternative of conventional antibiotics and antiseptic agents which can help to tackle antimicrobial resistance. The review also covers the recently developed environmentally benign NPs (EbNPs) as a "safer-by-design" green chemistry solution of the post use fate of antimicrobial nanomaterials.

Fabrication of Antibacterial and Antiwear Hydroxyapatite Coatings via In Situ Chitosan-Mediated Pulse Electrochemical Deposition

Although bioinert titanium has been widely applied in orthopedics and related fields, its usage is limited by its unsatisfying osteoinductivity, anti-infection capability, and wear-resistance. Osteoinductive apatite coating can be fabricated on a titanium surface by electrochemical methods, but this causes bacterial adhesion and poor wear-resistance. On the basis of pulse electrochemical technology, a wear-resistance and antibacterial osteoinductive coating was fabricated through codeposition of hydroxyapatite (HA) and nano-Ag effectuated by the cohybridization ofchitosan (CS) with Ag⁺ and Ca²⁺. A composite coating formed with uniformly dispersed spherical nanoparticles was obtained at optimized deposition potential, Ag concentration, and apatite concentration. The nanocomposite coating shows excellent bioinductive activity; it promotes preferential growth on the (002) face, and needle-like ordered arrangement of apatite. Due to the mediation of CS hybridization, a compact structure is achieved in the HA/Ag composite coating which significantly enhances the wear-resistance of the coating and reduces the release of Ca²⁺ and Ag⁺. The antibacterial rate of the coating on Escherichia coli and Staphylococcus aureus is up to 99% according to the antibacterial test. In conclusion, a wear-resistant and long-term antibacterial bioactive nanocomposite coating is successfully fabricated on titanium surface through the strategy established in this study.

Recent Nanotechnology Approaches for Prevention and Treatment of Biofilm-Associated Infections on Medical Devices

Bacterial colonization in the form of biofilms on surfaces causes persistent infections and is an issue of considerable concern to healthcare providers. There is an urgent need for novel antimicrobial or antibiofilm surfaces and biomedical devices that provide protection against biofilm formation and planktonic pathogens, including antibiotic resistant strains. In this context, recent developments in the material science and engineering fields and steady progress in the nanotechnology field have created opportunities to design new biomaterials and surfaces with anti-infective, antifouling, bactericidal, and antibiofilm properties. Here we review a number of the recently developed nanotechnology-based biomaterials and explain underlying strategies used to make antibiofilm surfaces.

A nanotechnology based new approach for chemotherapy of Cutaneous Leishmaniasis: TIO2@AG nanoparticles - Nigella sativa oil combinations

Since toxicity and resistance are the major drawbacks of current antileishmanial drugs, studies have been recently focused on combination therapy in fight against leishmaniasis. Combination therapy generally provides opportunity to decrease toxicity of applied agents and enhance their antimicrobial performance. Moreover, this method can be effective in preventing drug resistance. Highly antileishmanial effects of silver doped titanium dioxide nanoparticles (TiAgNps) and Nigella sativa oil were demonstrated in previous studies. However, toxicity is still an important factor preventing use of these molecules in clinic. By considering high antileishmanial potential of each agent and basic principles of combination therapy, we propose that use of combinations including non-toxic concentrations of TiAgNps and N. sativa oil may compose more effective and safer formulations against Leishmania parasites. Therefore, the main goal of the present study was to investigate antileishmanial effects of non-toxic concentrations of TiAgNps and Nigella sativa oil combinations on promastigote and amastigote-macrophage culture systems and also to develop nanotechnology based new antileishmanial strategies against Cutaneous Leishmaniasis. Numerous parameters such as proliferation, metabolic activity, apoptosis, amastigote-promastigote conversion, infection index analysis and nitric oxide production were used to detect antileishmanial efficacies of combinations. Investigated all parameters demonstrated that TiAgNps-N. sativa oil combinations had significant antileishmanial effect on each life forms of parasites. Tested combinations were found to decrease proliferation rates of Leishmania tropica promastigotes in a range between 1,5-25 folds and metabolic activity values between 2 and 4 folds indicating that combination applications lead to virtually inhibition of promastigotes and elimination of parasites were directly related to apoptosis manner. TiAgNps-N. sativa combinations also demonstrated killing effects on L. tropica amastigotes by decreasing infection index values of macrophages 5-20 folds, inhibiting their metabolic activities up to 5 fold, preventing amastigote-promastigote conversion and producing high amounts of nitric oxide. All these results emphasize high potential of TiAgNps-N. sativa oil combinations as new, safer and effective antileishmanial formulations against Cutaneous Leishmaniasis.

Changes in soil bacterial communities and diversity in response to long-term silver exposure

Silver-induced selective pressure is becoming increasingly important due to the growing use of silver (Ag) as an antimicrobial agent in biomedical and commercial products. With demonstrated links between environmental resistomes and clinical pathogens, it is important to identify microbial profiles related to silver tolerance/resistance. We investigated the effects of ionic Ag stress on soil bacterial communities and identified resistant/persistent bacterial populations. Silver treatments of 50-400 mg Ag kg(-1) soil were established in five soils. Chemical lability measurements using diffusive gradients in thin-film devices confirmed that significant (albeit decreasing) labile Ag concentrations were present throughout the 9-month incubation period. Synchrotron X-ray absorption near edge structure spectroscopy demonstrated that this decreasing lability was due to changes in the Ag speciation to less soluble forms such as Ag(0) and Ag2S. Real-time PCR and Illumina MiSeq screening of 16S rRNA bacterial genes showed β-diversity changes, increasing α-diversity in response to Ag pressure, and immediate and significant reductions in 16S rRNA gene counts with varying degrees of recovery. These effects were more strongly influenced by exposure time than by Ag dose at these rates. Ag-selected dominant OTUs principally resided in known persister taxa (mainly Gram positive), including metal-tolerant bacteria and slow-growing Mycobacteria.

Nanoparticles for antimicrobial purposes in Endodontics: A systematic review of in vitro studies

INTRODUCTION

Antimicrobial nanoparticles with enhanced physiochemical properties have attracted attention as modern antimicrobials, especially in the complicated oral cavity environment. The goal of the present article is to review the current state of nanoparticles used for antimicrobial purposes in root canal infections.

METHODS

A review was conducted in electronic databases using MeSH keywords to identify relevant published literature in English. The analysis and eligibility criteria were documented according to the Preferred Reporting Items for Systematic Reviews and Meta Analysis (PRISMA-guidelines). No restrictions on publication date were imposed. Data regarding root canal disinfections, general antimicrobial mechanisms of nanoparticles, type of nanoparticles as antimicrobial agent and antimicrobial effect of nanoparticles in endodontics were collected and subjected to descriptive data analysis.

RESULTS

The literature search in electronic databases according to the inclusion criteria provided 83 titles and abstracts. Among them 15 papers were related to antimicrobial effect of nanoparticles in Endodontics. Silver nanoparticles with sustainable activity were the most studied agent for its antimicrobial behavior in root canal infection. Aided polymeric nanoparticles with photo or ultrasound, glass bioactive nanoparticles as well as Calcium derivative based nanoparticles, with improved activity in comparison with the non-nano counterparts, are of importance in infection control of dental root canal. Bioactive Non-organic nanoparticles with structural capabilities present enhanced antimicrobial activity in root canal infections.

DISCUSSION

All included studies showed an enhanced or at least equal effect of nanoparticulate systems to combat dental root canal infections compared to conventional antimicrobial procedures. However, it is crucial to understand their shortcomings and their probable cellular effects and toxicity as well as environmental effects.