Release Of AgNPs Research Articles

Silver nanoparticles adsorption by the synthetic and natural adsorbent materials: an exclusive review

Silver nanoparticles (AgNPs) have been used in a wide range of industrial products. The release of AgNPs as antimicrobial agent into the river or lake can raise the ecological concern because they have been proven to be associated with toxicity of the aquatic animals. An exclusive review of AgNPs adsorbed by the various synthetic and natural adsorbent materials is important to understand the behaviour of AgNPs in the complex environmental conditions. The transformation of AgNPs into various forms in an aquatic environment depends on the physical, chemical, and biological characteristics of water. Many types of natural materials can be used to fabricate the adsorbents because pore structure, surface area, and active sites of functional groups of the adsorbent can be developed during the carbonisation and activation stages. The mass transfer factor and modified mass transfer factor models would be considered tools that can be used to describe the mechanism and kinetics of AgNPs adsorption onto the natural adsorbents influenced by the electrostatic and van der Waals forces. This exclusive review provides the valuable insights into future challenges of AgNPs adsorption to contribute to sustainable improvement in the management of aquatic ecosystems.

Safer-by-design biocides made of tri-thiol bridged silver nanoparticle assemblies.

Silver nanoparticles (AgNPs) are efficient biocides increasingly used in consumer products and medical devices. Their activity is due to their capacity to release bioavailable Ag(i) ions making them long-lasting biocides but AgNPs themselves are usually easily released from the product. Besides, AgNPs are highly sensitive to various chemical environments that triggers their transformation, decreasing their activity. Altogether, widespread use of AgNPs leads to bacterial resistance and safety concerns for humans and the environment. There is thus a crucial need for improvement. Herein, a proof of concept for a novel biocide based on AgNP assemblies bridged together by a tri-thiol bioinspired ligand is presented. The final nanomaterial is stable and less sensitive to chemical environments with AgNPs completely covered by organic molecules tightly bound via their thiol functions. Therefore, these AgNP assemblies can be considered as safer-by-design and innovative biocides, since they deliver a sufficient amount of Ag(i) for biocidal activity with no release of AgNPs, which are insensitive to transformations in the nanomaterial.

Preparation, Characterization and Antifungal Activity Studies of AgNPs Loaded Silk Fibroin Hydrogels

Silk fibroin hydrogels are promising materials for controlled drug delivery device due to their aqueous process ability, biocompatibility, and biodegradability. The research work is aimed to prepare silk fibroin (SF) hydrogels loaded with Ag nanoparticles and to evaluate its antifungal activities. The Silk fibroin hydrogels were formulated at 37°C using 2% (w/v) silk fibroin aqueous solution either by treating 50% (v/v) of ethanol, or 50% (v/v) of propanol, or 50% (v/v) of glycerol, respectively. Above these, the rate of gelation was sufficiently accelerated by addition of glycerol. The silk fibroin hydrogels and prepared silver nanoparticles (AgNPs) were characterized by using Scanning Electron Microscopy (SEM), Thermo Gravimetrical Analysis (TGA). The encapsulation efficiency and release profile of AgNPs were studied by UV-vis spectrometry. The particle size of AgNPs was measured by Malvern Zetasizer Nano and found 93±5 nm. The encapsulation efficiency and morphology of the hydrogels was affected by the formulation conditions. The in vitro release profile showed an initial burst release of AgNPs followed by controlled release for next 20 hours. The antifungal activity of AgNPs loaded SF hydrogels showed a positive response to Aspergillus Niger pathogen. Therefore, silk fibroin hydrogels might be an effective biopolymeric matrix for antifungal applications.

Evidence for the critical role of nanoscale surface roughness on the retention and release of silver nanoparticles in porous media

Although nanoscale surface roughness has been theoretically demonstrated to be a crucial factor in the interaction of colloids and surfaces, little experimental research has investigated the influence of roughness on colloid or silver nanoparticle (AgNP) retention and release in porous media. This study experimentally examined AgNP retention and release using two sands with very different surface roughness properties over a range of solution pH and/or ionic strength (IS). AgNP transport was greatly enhanced on the relatively smooth sand in comparison to the rougher sand, at higher pH, and lower IS and fitted model parameters showed systematic changes with these physicochemical factors. Complete release of the retained AgNPs was observed from the relatively smooth sand when the solution IS was decreased from 40 mM NaCl to deionized (DI) water and then the solution pH was increased from 6.5 to 10. Conversely, less than 40% of the retained AgNPs was released in similar processes from the rougher sand. These observations were explained by differences in the surface roughness of the two sands which altered the energy barrier height and the depth of the primary minimum with solution chemistry. Limited numbers of AgNPs apparently interacted in reversible, shallow primary minima on the smoother sand, which is consistent with the predicted influence of a small roughness fraction (e.g., pillar) on interaction energies. Conversely, larger numbers of AgNPs interacted in deeper primary minima on the rougher sand, which is consistent with the predicted influence at concave locations. These findings highlight the importance of surface roughness and indicate that variations in sand surface roughness can greatly change the sensitivity of nanoparticle transport to physicochemical factors such as IS and pH due to the alteration of interaction energy and thus can strongly influence nanoparticle mobility in the environment.

Coal Fly Ash-based Geopolymer Spheres Coated with Amoxicillin and Nanosilver for Potential Antibacterial Applications

Geopolymers are emerging “green” materials for its low embodied energy and carbon footprint, and its potential to valorize wastes, such as coal fly ash. It is an inorganic cementitious material formed from the polymerization of aluminosilicates in an activating solution such as that of alkali hydroxides or silicates. Their superior mechanical properties, including heat and fire resistance make them an excellent material for diverse applications. Recent studies have also exploited the tunable open porosity and adsorbing properties of geopolymers. Our work thus explores the potential of porous geopolymer spheres for antibacterial applications. These spheres were synthesized using coal fly ash as the geopolymer precursor and the porous surface is coated with either amoxicillin or silver nanoparticles (AgNPs) adsorbed in the matrix. For the AgNP geopolymer spheres, SEM images show spherical nanostructures when using ascorbic acid as a reducing agent, while spherical, cubical, and wire structures were observed when reduced using NaBH4. Indication from UV-Vis results also suggests the gradual release of both amoxicillin and AgNPs in the solution from the functionalized geopolymer spheres. Using E. Coli as the test organism for a modified disk diffusion assay, both showed zones of inhibition against the bacteria. Further tests on antibacterial application of AgNP geopolymer spheres show their effectiveness to kill at least 95% of the E. coli in a water sample initially containing 105 cfu/mL in just 30 minutes.

Polycaprolactone nanofiber mats decorated with photoresponsive nanogels and silver nanoparticles: Slow release for antibacterial control.

Smart nanomaterials activated by light is one of the most exciting strategies to control the release of substances in varied environments. Here we developed a smart nanomaterial composed by a photoresponsive nanogel containing silver nanoparticles (AgNps) immobilized on the surface of biodegradable and biocompatible polycaprolactone (PCL) nanofibers mats produced by electrospinning. The AgNps are released from the nanogel and dispersed inside the nanofiber mats when this system is irradiated by light at 405 nm. This light excites the plasmonic band of the AgNps, which breaks the nanogel and, as a consequence, releases the AgNps on the nanofibers. Consequently, this AgNps release mechanism controls the propagation of silver ions by the application of light. Different configurations of antibacterial nanofibers mats, including neat PCL nanofibers and PCL nanofibers modified with AgNps-Nanogels and AgNps, excited by laser light at 405 nm, were investigated regarding antibacterial properties. The best result was achieved using PCL nanofiber mats functionalized with AgNps and AgNps-Nanogels after light exposure, which generated inhibition diameters of 2.6 ± 0.3 mm and 1.8 ± 0.5 mm for S. aureus and E. coli, respectively. The smart nanomaterial developed here is a promising material for clinical application as wound dressing activated by light.

Hydroxyapatite/silver electrospun fibers for anti-infection and osteoinduction

Bone implant materials cause the most common complication of bone infections in orthopedic surgery, resulting in implant failure. Antibiotic treatment of bone infections leads to problems such as bacterial resistance and reduced osteogenic capacity. In this study, dopamine (DA) was self-polymerized on the surface of Polylactic acid (PLLA)/Hydroxyapatite (HA) nanowire composite fibers to form an adhesive polydopamine (PDA) membrane, and a stable silver-nanoparticles (Ag-NPs) coating layer was constructed on it by electrochemically driven Ag+ coordination and chelation through Polypyrrole (PPy) mediation, achieving steady and slow release of Ag-NPs. With optimized DA soaking time of 24 h and soaking concentration of 0.5 g·L−1, nanoparticles were uniformly distributed on PLLA/HA/PDA/PPy/Ag composite fibers and the hydrophilicity of the composite fibers was well-behaved. Besides, the composite fibers possessed good physiological stability and 100% antibacterial rate against Escherichia coli (E. coli) as well as Staphylococcus aureus (S. aureus). In addition, the composite fibers had promoted apatite nucleation and growth on surface and good cytocompatibility with osteoblasts, indicating ability of inducing osteogenic differentiation. In summary, a multi-functional PLLA/HA/PDA/PPy/Ag composite fiber with long-term antibacterial property, bioactivity and osteoinductivity was successfully constructed by electrospinning and electrochemical deposition.

Soil chloride content influences the response of bacterial but not fungal diversity to silver nanoparticles entering soil via wastewater treatment processing

Silver nanoparticles (NPs) are among the most widely used nanomaterials and are entering soil ecosystems, mainly via biosolids in agriculture. When added directly to soils, metallic Ag-NPs have been shown to affect microbial communities, which underpin important ecosystem functions. During wastewater treatment processing, metallic Ag-NPs are rapidly converted to Ag2S, which is relatively insoluble and less toxic. Furthermore, recent evidence indicates that silver bioavailability is influenced by soil chloride content. Hence there is a need to understand how Ag2S, which forms from Ag-NPs during wastewater treatment, influences soil microbial diversity at varying salinity. In this study, after adding Ag-NPs to sludge (with most converted to Ag2S), we then applied the sludge to soil and examined how salinity influences the effects of 0 mg, 1 mg and 10 mg kg−1 Ag on bacterial and fungal diversity over time. Using high-throughput phylogenetic marker gene sequencing of 16S rRNA gene and ITS2 amplicons, we demonstrate that, despite being theoretically less toxic, wastewater treatment processed Ag-NPs can affect the composition of soil bacterial and fungal communities, and influence bacterial alpha diversity. In addition, we found that silver-associated changes in bacterial community composition were affected by soil chloride content, with more acute responses to silver being observed in more saline soils. This work highlights that the release of Ag-NPs and their conversion into Ag2S prior to addition to soils via realistic exposure pathways can alter microbial diversity and that these effects may be influenced by soil chloride content.

Simultaneous green synthesis and in-situ impregnation of silver nanoparticles into organic nanofibers by Lythrum salicaria extract: Morphological, thermal, antimicrobial and release properties.

This research has revealed the promising, green and one-pot approach for fabrication of antimicrobial nanohybrids based on organic nanofibers including cellulose (CNF), chitosan (CHNF), and lignocellulose (LCNF) nanofibers impregnated with silver nanoparticles (AgNPs). Lythrum salicaria extract was used as a reducing agent as well as a capping agent. Formation of the spherical AgNPs ranging between 45 and 65 nm was proved by UV-Vis spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). Biomaterials supported AgNPs were characterized and compared for their morphological, thermal, release, and antimicrobial properties. The considerable influence of the phenolic compounds of L.salicaria extract on the synthesis and uniform distribution of AgNPs on nanofibers was confirmed by field emission electron microscopy (FE-SEM). Energy dispersive X-ray spectroscopy (EDX) and ICP-OES analysis of nanohybrids, reflected a high loading capacity for LCNF and also CHNF in contrast to CNF. The release of AgNPs from LCNF substrate was lower than other nanofibers but the order of antimicrobial activity of nanohybrids against E.coli and S.aureus was as this: CHNF ˃ LCNF ˃ CNF. Generally, this research suggested that the efficiency of CHNF and LCNF as immobilizing support of AgNPs is higher than CNF and L.salicaria extract was proposed as a high potential reducing and capping agent.

On the transformation mechanism of polyethylene glycol- and citrate-coated silver nanocolloids under sunlight exposure

As the use of nanomaterials continues to increase, their release into the environment is also expected to increase. During the use phase of nano-enhanced products containing silver nanoparticles (Ag NPs) or after the release of Ag NPs in the environment, the latter are likely to be altered by the conditions they will encounter, such as sunlight irradiation. In this work, suspensions of citrate-stabilized and PEG-stabilized Ag NPs of around 20 nm in diameter were synthesized and aged for a week in a climatic chamber under controlled temperature (40 °C) and sunlight irradiation. The suspensions were analyzed by UV/visible spectroscopy, asymmetric flow field flow fractionation—inductively coupled plasma mass spectrometry (AF4-ICP-MS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). We found that the electrostatic-stabilizing citrate promoted particle morphology changes with the emergence of a transient and minor secondary population of truncated 2D prisms (110–120 nm in size) but postponed the final sedimentation step. Conversely, the initial protecting role of the steric-stabilizing PEG was reduced by the photodegradation of the polymer chains and eventually favored inter-particle bridging resulting in aggregation and sedimentation. It is hypothesized that the bridging process proceeds via PEG chain interpenetration between two adjacent particles and reduction by the polymer photodegradation products of the Ag+ ions generated by oxidative dissolution.

Long-term effects of environmentally relevant concentration of Ag nanoparticles on the pollutant removal and spatial distribution of silver in constructed wetlands with Cyperus alternifolius and Arundo donax

The widely usage of silver nanoparticles in a range of consumer products inevitably results in its being released to the wastewater. As a result, the potential negative effects associated with AgNPs on wastewater treatment systems need to be assessed to develop the regulatory guidelines. In this paper, the exposure experiment at environmentally relevant concentration (100 μg L−1) were conducted to demonstrate the effects of AgNPs on the pollutant removals in constructed wetlands (CWs) with different plants and the spatial distribution of silver. Before adding AgNPs, the system with Arundo donax (VF2) had the better nitrogen removal than Cyperus alternifolius (VF1). After exposure for about 94 d, the average removal efficiencies of NH4+-N significantly reduced by 32.43% and 23.92%, TN of 15.82% and 17.18% and TP of 22.74% and 20.46% in VF1 and VF2, respectively, while the COD removal had no difference. However, presence of 100 μg L−1 AgNPs for about 450 d showed no inhibition effects on nutrient removals in two experimental CWs. Two wetlands showed high removal efficiencies of about 98% on AgNPs, indicating CWs could play a crucial role to control the AgNPs release to environment. It was found that AgNPs mainly accumulated in the soil layer with the Ag content of 0.45–5.96 μg g−1 dry weight in lower soil and 2.84–11.37 μg g−1 dry weight in upper soil. The roots of Cyperus alternifolius absorbed more AgNPs, with higher bioconcentration factors (1.32–1.44) than that of 0.59 in Arundo donax. The differences of translocation factors on leaves and stems in two test plants showed that AgNPs assimilated by roots in Cyperus alternifolius were more easily transferred to the leaves. The obtained results showed that the macrophyte Cyperus alternifolius could be better choice for immobilization of AgNPs.

Exposure to a nanosilver-enabled consumer product results in similar accumulation and toxicity of silver nanoparticles in the marine mussel Mytilus galloprovincialis

The incorporation of silver nanoparticles (AgNPs) in commercial products is increasing rapidly. The consequent release of AgNPs into domestic and industrial wastewater raises environmental concerns due to their anti-microbial properties and toxicity to non-target aquatic organisms. The aim of the present study was to investigate the effects of nanArgen™ (Nanotek S.A.), a AgNP-enabled consumer product, in the marine bivalve Mytilus galloprovincialis. Two environmentally relevant concentrations of nanArgen™ (1 and 10 μg/L) were tested in vivo for 96 h, and Ag was quantified in mussel soft tissue and natural seawater (NSW). nanArgen™ suspensions were characterized via TEM, SEM, EDS, DLS, and UV–vis optical analysis. Several molecular and biochemical responses were investigated in exposed mussels: lysosomal membrane stability by Neutral Red Retention Time (NRRT) assay; micronucleus (MN) frequency in hemocytes; metallothionein (MT) protein content and gene expression (mt10 and mt20); catalase (CAT) and glutathione-S-transferase (GST) activities; malondialdehyde (MDA) accumulation in digestive glands; and efflux activity of ATP-binding cassette transport proteins (ABC) in gill biopsies. SEM, TEM and DLS analyses confirmed the presence of well-defined AgNPs in nanArgen™ which were roughly spherical with an average particle size of approx. 30 ± 10 nm. DLS analysis revealed the formation of AgNP aggregates in nanArgen™ suspension in NSW (Z-average of 547.80 ± 90.23 nm; PDI of 0.044). A significant concentration-dependent accumulation of Ag was found in mussels’ whole soft tissue in agreement with a concentration-dependent decrease in NRRT and an increase of MN frequency in hemocytes and GST activities in digestive glands. A significant increase in MDA levels and MT via both molecular and biochemical tests, were also observed but only at the highest nanArgen™ concentration (10 μg/L). No changes were observed in CAT activities. ABC efflux activities in gill biopsies showed a significant decrease (p < 0.05) only at the lowest concentration (1 μg/L). On such basis, nanArgen™ is shown to be able to induce toxicity and Ag accumulation in marine mussels similarly to AgNPs and in short-term exposure conditions at environmentally relevant concentrations. AgNP-enabled products, instead of pristine AgNPs, should be the focus of future ecotoxicity studies in order to address any risks associated to their widespread use, disposal and uncontrolled release into the aquatic environment for non target species.

Antimicrobial and physicomechanical natures of silver nanoparticles incorporated into silicone-hydrogel films

PurposeThe effects of silver nanoparticles (AgNPs) incorporated in silicone-hydrogel films on their physicochemical properties and microbial activity were investigated. MethodsSilicone-hydrogel composite films (SiHCFs) were prepared by in-situ chemical reduction of silver ions added in different concentrations (0, 10, 20, 30, 40, 60, and 80 ppm) followed by ultraviolet (UV) casting. The reduction of silver ions into AgNPs was confirmed by transmission electron microscopy (TEM) and absorption spectroscopy over ultraviolet and visible (UV–vis) wavelengths. Incorporation of AgNPs into SiHCFs was confirmed by UV–vis absorption spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopic mapping. The physico- mechanical properties of the SiHCFs were evaluated. Antimicrobial activity and biofilm formation of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were assessed. ResultsTEM, UV–vis absorption, SEM, and EDX mapping showed that silver ions were reduced in the mixture of co-polymerizing monomers and incorporation of AgNPs into SiHCFs was achieved. Mechanical properties of the SiHCFs were enhanced with increasing AgNPs concentration without affecting their chemical and thermal properties. SiHCFs exhibited transmittance greater than 90% at a wavelength 600 nm. Bacterial growths in the solutions bathing the SiHCFs with increasing silver concentration were 95, 78, 4, 2, 0, 0, 0% respectively, for Escherichia coli; 95, 82, 4, 0.6, 0, 0, 0% for Pseudomonas aeruginosa; and 93, 79, 4, 0.5, 0, 0, 0% for Staphylococcus aureus. ConclusionsIncorporation of AgNPs into SiHCFs demonstrated sufficient release of AgNPs to inhibit bacterial growth and reduce biofilm formation, with collateral enhancement of some mechanical properties of SiHCFs.

Differential transformation and antibacterial effects of silver nanoparticles in aerobic and anaerobic environment

Silver nanoparticles (AgNP) undergo various transformations into different Ag species in the environment, which determines their toxicity in microorganisms. In aerobic condition, AgNPs release Ag+ that causes cell inactivation. Limited information is known about the AgNP-cell interaction in oxygen-free environment. Here we compared the transformation and antibacterial effects of AgNPs in aerobic and anaerobic environment. The bacterium Pseudomonas aeruginosa was relatively not susceptible to Ag+ or AgNP in anaerobic environment, indicated by near two orders of magnitude greater of anaerobic minimum inhibitory concentration (MIC) than the aerobic counterpart. In anaerobic environment, the dissolved Ag concentration decreased due to the reduction of Ag+. Electron microscopy images showed the formation of new AgNPs and aggregates, preferably on cell surface or associated with extracellular polymer substances (EPS) matrix. Accumulating AgNPs onto the cells could cause membrane damage, cytoplasm release or bacterial death. Meanwhile, EPS and cell lysate were very likely to bind AgNPs, facilitating the extensively assembling of AgNPs into large aggregates. This reduced the effective Ag exposure to cells and might contribute to the detoxification in anaerobic environment. Further, flow cytometry analysis quantified that bacterial membrane was largely intact under the treatment of AgNPs in anaerobic condition compared to the dose–response manner in aerobic condition.

Physicochemical and functional properties of chitosan-based nano-composite films incorporated with biogenic silver nanoparticles

In this study, biogenic AgNPs were synthesize using Nigella sativa extract (NSE) with potential antioxidant activity. The transmission electron microscopy (TEM) image showed spherical AgNPs with biphasic nature and an average particle size 8 nm. AgNPs was then evaluated for their effect on sustained release and film-forming capacity of chitosan. Characterization of the films was done to analyze their physical, mechanical as well as antibacterial properties. The structural change in the films was indicated by FTIR spectra which showed the shift of characteristics peak and modification of the absorbance intensity. Scanning electron micrographs (SEM) showed an uneven distribution of AgNPs all over the CS polymer matrix. Moreover, the mechanical and barrier properties of CS/ Ag nanocomposite films were influenced by the intercalation of AgNPs. The tensile strength and elongation of the films were improved by 8.4–22.5% and 4.4–9.2%, whereas water vapor permeability reduced by 15.23% depending on the concentration of AgNPs. Further, the films showed a pH-dependent sustained release of AgNPs and Ag+ ions and significant antibacterial activity. Largely, the excellent antibacterial activity and biocompatibility mark CS-AgNPs composite films a promising material for packaging of food, pharmaceutical, and allied products.

Silver nanoparticle impregnated chitosan-PEG hydrogel enhances wound healing in diabetes induced rabbits

Non-healing wounds are among the serious complications of type-2-diabetes around the globe, associated with high incidence of bacterial infection, chronic nerve and blood vessel damage, and eventually repeated amputation of limbs and organs. Silver nanoparticles offer strong wound healing potential due to their well-known antibacterial activities. The present study reports the development of silver nanoparticle impregnated chitosan-poly ethylene glycol (PEG) hydrogel to accelerate wound healing in diabetic patients. The aim of the study was to formulate a sustained and slow release of silver nanoparticle using chitosan-PEG-Silver Nitrate based hydrogel for the treatment of chronic diabetic wounds. The silver nanoparticle containing chitosan-PEG pre-polymer solution was synthesized by reducing silver nitrate with PEG and chitosan solution, thereby, transforming the silver ions into silver nanoparticles. The resulted pre-polymer solution was then crosslinked using glutaraldehyde to form the desired hydrogel. The developed silver nanoparticle impregnated chitosan hydrogel was characterized using ultra-violet (UV) visible spectrophotometry, Fourier Transform-infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) followed by the determination of porosity, and swelling properties. The release of AgNPs from hydrogel was determined by UV-vis spectroscopy followed by antimicrobial and antioxidant assays. The wound healing efficacy of the synthesized hydrogel was evaluated in diabetic rabbits. The results demonstrated a higher porosity, higher degree of swelling and higher water vapor transition rate (WVTR) for silver nanoparticle impregnated hydrogel compared to bare chitosan-PEG hydrogel as well as improved antimicrobial and antioxidant properties in-vitro and enhanced wound healing capability in-vivo in diabetic rabbits. The hydrogel showed a slow and sustained release of AgNPs over a period of at least seven days manifesting the slow biodegradation of developed hydrogels. The improved antimicrobial, antioxidant and wound healing results indicate that the silver nanoparticle impregnated chitosan-PEG hydrogel can be a promising material for wound healing dressing for chronic diabetic wounds.

Functional bioreactor characterization to assess potentials of nanocomposites based on different alginate types and silver nanoparticles for use as cartilage tissue implants.

In this work, functional characterization of biomaterials concerning potential application as articular cartilage implants was performed by using a biomimetic bioreactor with dynamic compression in the physiological regime (10% strain, 0.84 Hz frequency, 1 h on/1 h off). Specifically, two alginate types with low (LG) and high (HG) guluronic/mannuronic residue ratios with electrochemically synthesized silver nanoparticles (AgNPs) were evaluated. HG Ag/alginate hydrogels were clearly indicated as potential candidates due to better initial mechanical properties as compared to LG hydrogels (dynamic compression modulus of ~60 vs. ~40 kPa) as well as the mechanical stability displayed during 7 days of dynamic compression. Cytotoxicity studies in 3D bovine cartilage explant cultures under dynamic compression have shown negligible effects as compared to standard 2D monolayers of bovine chondrocytes where moderate cytotoxicity was observed. Finally, experimental and mathematical modeling studies revealed different mechanisms of AgNP release under physiological-like bioreactor conditions as compared to static conditions. Overall, the results clearly demonstrate bioreactor advantages in characterization and selection of candidate biomaterials as well as potentials to bridge the in vitro-in vivo gap. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 755-768, 2019.

Interactions between silver nanoparticles and other metal nanoparticles under environmentally relevant conditions: A review

Global production of engineered nanoparticles (ENPs) continues to increase due to the demand of enabling properties in consumer products and industrial applications. Release of individual or aggregates of ENPs have been shown to interact with one another subsequently resulting in adverse biological effects. This review focuses on silver nanoparticles (AgNPs), which are currently used in numerous applications, including but not limited to antibacterial action. Consequently, the release of AgNPs into the aquatic environment, the dissociation into ions, the binding to organic matter, reactions with other metal-based materials, and disruption of normal biological and ecological processes at the cellular level are all potential negative effects of AgNPs usage. The potential sources of AgNPs includes leaching of intact particles from consumer products, disposal of waste from industrial processes, intentional release into contaminated waters, and the natural formation of AgNPs in surface and ground water. Formation of natural AgNPs is greatly influenced by different chemical parameters including: pH, oxygen levels, and the presence of organic matter, which results in AgNPs that are stable for several months. Both engineered and natural AgNPs can interact with metal and metal oxide particles/nanoparticles. However, information on the chemical and toxicological interactions between AgNPs and other nanoparticles is limited. We have presented current knowledge on the interactions of AgNPs with gold nanoparticles (AuNPs) and titanium dioxide nanoparticles (TiO2 NPs). The interaction between AgNPs and AuNPs result in stable bimetallic Ag-Au alloy NPs. Whereas the interaction of AgNPs with TiO2 NPs under dark and light conditions results in the release of Ag+ ions, which may be subsequently converted back into AgNPs and adsorb on TiO2 NPs. The potential chemical mechanisms and toxic effects of AgNPs with AuNPs and TiO2 NPs are discussed within this review and show that further investigation is warranted.

Toxicity of silver nanoparticles to green algae M. aeruginosa and alleviation by organic matter.

Silver nanoparticles (AgNPs) have been increasingly used in a wide range of consumer products over the last decade. The release of AgNPs into aquatic ecosystems raises concerns about their safety and environmental toxicity, which have been the subject of recent studies. Herein, we assess the toxicity of AgNPs to the common algae Microcystis. aeruginosa. A toxicological response by M. aeruginosa was exhibited at an early stage of exposure to AgNPs, which were also toxic to its growth, photosynthetic, and membrane systems. The attachment of AgNPs to microalgae is likely the main mechanism by which it damages cell membranes. Dissolved Ag ions, originating from internalized AgNPs, seem to directly target the photosynthetic system. We also found that several humus-related indicators of water quality (HIX and β/α) were related to reduced AgNPs toxicity. Graphical abstract.

Ag nanoparticles inhibit the growth of the bryophyte, Physcomitrella patens

The wide use of Ag nanoparticles (Ag NPs) as antimicrobial agents has resulted in a massive release of Ag NPs into environment, such as water and soil. As bryophytes live ubiquitously in water and soil, their tolerance and response to Ag NPs could be employed as an indicator for the harm of Ag NPs to the environment. Herein, we report the study on the physiological and biochemical responses of bryophytes to Ag NPs with different surface coatings at the gametophyte stages: protonema and leafy gametophyte, by using Physcomitrella patens as a model system. We found that Ag NPs, including AgNPs-B (Ag NPs without surface coating), AgNPs-PVP (Ag NPs coated with poly (N-vinyl-2-pyrrolidone)) and AgNPs-Cit (Ag NPs coated with citrate), were toxic to P. patens in terms of growth and development of the gametophyte. The toxicity was closely related to the concentration and surface coating of Ag NPs, and the growth stage of P. patens. The protonema was more sensitive to Ag NPs than the leafy gametophyte. Ag NPs inhibited the growth of the protonema following the trend of AgNPs-B > AgNPs-Cit > AgNPs-PVP. Ag NPs changed the thylakoid and chlorophyll contents, but did not affect the contents of essential elements in the protonema. At the leafy gametophyte stage, Ag NPs inhibited the growth of P. patens following a different order: AgNPs-Cit > AgNPs-B ≈ AgNPs-PVP. Ag NPs decreased the chlorophyll b content and disturbed the balance of some important essential elements in the leafy gametophytes. Both the dissolved fraction of Ag NPs and Ag NPs per se contributed to the toxicity. This study for the first time reveals the effects of Ag NPs on bryophytes at different growth stages, which calls for more attention to the nanoecotoxicology of Ag NPs.