Influence Of Surface Charge Research Articles

Changing exposure media can reverse the cytotoxicity of ceria nanoparticles for Escherichia coli

Ceria nanoparticles have attracted a great deal of concern about their impact on human health and the environment due to their widespread applications. In the present work, different exposure media (normal saline and phosphate-buffered saline [PBS]) were used to adjust the surface charge density in order to investigate the influence of surface charge on the cytotoxicity of ceria nanoparticles for Escherichia coli. The results showed that the direct contact mediated by the electrostatic attraction between the cell wall and the positive-charged ceria nanoparticles in normal saline would result in outer membrane destabilization, increased reactive oxygen species (ROS) production and loss of viability. The situation in PBS was totally different, with significantly reduced contacts, so no outer membrane destabilization, no increased ROS production, and no cytotoxicity. The results suggested that surface charge density was closely involved in the cytotoxicity of ceria nanoparticles for E. coli. This work as a well designed comparison study contributes to a better understanding of the charge-associated biological effects of nanomaterials.

Liposome surface charge influence on skin penetration behaviour

Vesicular systems have shown their ability to increase dermal and transdermal drug delivery. Their mechanism of drug transport into and through the skin has been investigated but remains a much debated question. Several researchers have outlined that drug penetration can be influenced by modifying the surface charge of liposomes. In the present work we study the influence of particle surface charge on skin penetration. The final purpose is the development of a carrier system which is able to enhance the skin delivery of two model drugs, betamethasone and betamethasone dipropionate. Liposomes were characterised by their size, morphology, zeta potential, encapsulation efficiency and stability. Ex vivo diffusion studies using Franz diffusion cells were performed. Confocal microscopy was performed to visualise the penetration of fluorescently labelled liposomes into the skin. This study showed the potential of negatively charged liposomes to enhance the skin penetration of betamethasone and betamethasone dipropionate.

Influence of surface charge and textural properties of carbon electrodes on nitrate ion removal by electroadsorption

Influence of surface charge and textural properties of carbon electrodes on nitrate ion removal by electroadsorption

Influence of surface charge on the potential toxicity of PLGA nanoparticles towards Calu-3 cells

BackgroundBecause of the described hazards related to inhalation of manufactured nanoparticles, we investigated the lung toxicity of biodegradable poly (lactide-co-glycolide) (PLGA) nanoparticles displaying various surface properties on human bronchial Calu-3 cells.MethodsPositively and negatively charged as well as neutral nanoparticles were tailored by coating their surface with chitosan, Poloxamer, or poly (vinyl alcohol), respectively. Nanoparticles were characterized in terms of size, zeta potential, and surface chemical composition, confirming modifications provided by hydrophilic polymers.ResultsAlthough nanoparticle internalization by lung cells was clearly demonstrated, the cytotoxicity of the nanoparticles was very limited, with an absence of inflammatory response, regardless of the surface properties of the PLGA nanoparticles.ConclusionThese in vitro results highlight the safety of biodegradable PLGA nanoparticles in the bronchial epithelium and provide initial data on their potential effects and the risks associated with their use as nanomedicines.

Effects of Mutations Within Surface-Exposed Loops in the Pore-Forming Domain of the Cry9Ca Insecticidal Toxin of Bacillus thuringiensis

The pore-forming domain of Bacillus thuringiensis insecticidal Cry toxins is formed of seven amphipathic α-helices. Because pore formation is thought to involve conformational changes within this domain, the possible role of its interhelical loops in this crucial step was investigated with Cry9Ca double mutants, which all share the previously characterized R164A mutation, using a combination of homology modeling, bioassays and electrophysiological measurements. The mutations either introduced, neutralized or reversed an electrical charge carried by a single residue of one of the domain I loops. The ability of the 28 Cry9Ca double mutants to depolarize the apical membrane of freshly isolated Manduca sexta larval midguts was tested in the presence of either midgut juice or a cocktail of protease inhibitors because these conditions had been shown earlier to greatly enhance pore formation by Cry9Ca and its R164A single-site mutant. Most mutants retained toxicity toward neonate larvae and a pore-forming ability in the electrophysiological assay, which were comparable to those of their parental toxin. In contrast, mutants F130D, L186D and V189D were very poorly toxic and practically inactive in vitro. On the other hand, mutant E129A depolarized the midgut membrane efficiently despite a considerably reduced toxicity, and mutant Q192E displayed a reduced depolarizing ability while conserving a near wild-type toxicity. These results suggest that the conditions found in the insect midgut, including high ionic strength, contribute to minimizing the influence of surface charges on the ability of Cry9Ca and probably other B. thuringiensis toxins to form pores within their target membrane.

A discussion of the paper “Influence of surface charge on ingress of chloride ion in hardened pastes” by Y. Elakneswaran, T. Nawa, and K. Kurumisawa

The authors of Ref. [1] are to be congratulated on their interesting contribution regarding the permselective character of cement paste. By experiments and a theoretical model they reached the conclusion that pore walls are negatively charged and thus attract positive ions in the double layer. Ionic transport through the pores can thus be expected to be affected by double layer effects, viz. deceleration of cations with respect to anions. These conclusions are in agreement with the findings of other authors [2–5]. There are, however, a few points that need to be considered in more detail.

Influence of Surface Charge on Wetting Kinetics

The wettability of a titania surface, partially covered with octadecyltrihydrosilane, has been investigated as a function of solution pH. The results show that surface charge affects both static wettability and wetting kinetics. The static contact angle decreases above and below the point of zero charge of the titania surface in a Lippman-like manner as the pH is altered. The dependence of dynamic contact angle on velocity is also affected by pH. The molecular-kinetic theory (MKT) is used to interpret the dynamic contact angle data. The frequency of molecular displacement κ(0) strongly varies with surface charge, whereas the mean molecular displacement length λ is essentially unaffected. There is an exponential dependence of contact-line friction upon work of adhesion, which is varied simply by altering the pH.

Ion and pH Sensing with Colloidal Nanoparticles: Influence of Surface Charge on Sensing and Colloidal Properties

Ion sensors based on colloidal nanoparticles (NPs), either as actively ion-sensing NPs or as nanoscale carrier systems for organic ion-sensing fluorescent chelators typically require a charged surface in order to be colloidally stable. We demonstrate that this surface charge significantly impacts the ion binding and affects the read-out. Sensor read-out should be thus not determined by the bulk ion concentration, but by the local ion concentration in the nano-environment of the NP surface. We present a conclusive model corroborated by experimental data that reproduces the strong distance-dependence of the effect. The experimental data are based on the capability of tuning the distance of a pH-sensitive fluorophore to the surface of NPs in the nanometer (nm) range. This in turn allows for modification of the effective acid dissociation constant value (its logarithmic form, pK(a)) of analyte-sensitive fluorophores by tuning their distance to the underlying colloidal NPs.

Influence of surface charges on impulse flashover characteristics of alumina dielectrics in vacuum

For higher electrical insulator performance of vacuum circuit breakers (VCB), the surface flashover in vacuum should be improved. In particular, it is important to clarify how strongly surface charges influence the surface flashover mechanism. In this paper, we investigated the surface flashover characteristics based on the existence of surface charges on an alumina insulator in vacuum. We changed the location and magnitude of surface charges and measured surface flashover voltage. From our experimental results, an attempt was made to clarify the influence of charges on alumina dielectrics on impulse surface flashover characteristics in vacuum. From this, we concluded that (1) when surface charges were located near the cathode electrode, a positive charge made the surface flashover voltage lower and a negative charge made the surface flashover voltage higher; and, (2) when surface charges were located in the way of the discharge path, both positive and negative charges made the surface flashover voltage lower. We were able to explain these results by considering the influence of surface charges on the electric field at flashover and on the secondary electron emission avalanche.

In vitro translocation of quantum dots and influence of oxidative stress

In vivo, translocation of inhaled nanoparticles to the circulation has been demonstrated. However, the interaction of nanoparticles with the lung epithelium is not understood. In this study, we investigated, in vitro, the translocation of nano-sized quantum dots (QDs; 25 pmol/ml) through a tight monolayer of primary isolated rat alveolar epithelial cells. The influence of surface charge on translocation was examined using nonfunctionalized QDs, amine-QDs, and carboxyl-QDs. The interaction between nanoparticles and the lung epithelium was monitored by repeatedly measuring the transepithelial electrical resistance (TEER) and by examining the cell layer with confocal microscopy. The effect of oxidative stress was tested by incubating the cells with tert-butyl hydroperoxide (t-BOOH; 75 microM or 1 or 10 mM); the antioxidant N-acetyl-L-cysteine was also used to assess the role of particle-mediated oxidative stress. No translocation through a tight monolayer of primary rat alveolar epithelial cells was observed for any of the different types of QDs. In general, an increase in TEER was found after incubation with QDs. A condition of low oxidative stress did not enhance translocation. In contrast, conditions of high stress (1 or 10 mM t-BOOH or due to QDs toxicity) with disruption of the cell layer, as shown in a decreased TEER, resulted in substantial translocation. In conclusion, no translocation of QDs was found through a tight monolayer of primary rat alveolar epithelial cells, regardless of the QDs surface charge. QDs did not impair the barrier function of the epithelial cells. In conditions with disruption of the cell-cell barrier, translocation was demonstrated.

Electrically polarized HAp-coated Ti: In vitro bone cell–material interactions

Electrically polarized bulk sintered hydroxyapatite (HAp) compacts have been shown to accelerate mineralization and bone tissue ingrowth in vivo. In this work, a comprehensive study has been carried out to investigate the influence of surface charge and polarity on in vitro bone cell adhesion, proliferation and differentiation on electrically polarized HAp-coated Ti. Uniform and crack free sol–gel derived HAp coatings of 20 ± 1.38 μm thickness were polarized by application of an external d.c. field of 2.0 kV cm −1 at 400 °C for 1h. In vitro bioactivity of polarized HAp coatings was evaluated by soaking in simulated body fluid, and bone cell–material interactions were studied by culturing with human fetal osteoblast cells (hFOB) for a maximum period of 11 days. Scanning electron microscopic observation showed that accelerated mineralization on negatively charged surfaces favored rapid cell attachment and faster tissue ingrowth over non-polarized HAp coating surfaces, while positive charge on HAp coating surfaces restricted apatite nucleation with limited cellular response. Immunochemistry and confocal microscopy confirmed that the cell adhesion and early stage differentiation were more pronounced on negatively charged coating surfaces as hFOB cells expressed higher vinculin and alkaline phosphatase proteins on negatively charged surface compared to cells grown on all other surfaces. Our results in this study are process independent and potentially applicable to any other commercially available coating techniques.

Poly(amidoamine) dendrimers as skin penetration enhancers: Influence of charge, generation, and concentration

The study investigates the influence of surface charge, generation and concentration of poly(amidoamine) (PAMAM) dendrimers on skin permeation of a model hydrophilic drug, 5-fluorouracil (5FU). Permeation studies were performed using excised porcine skin in a Franz diffusion cell. Saturated concentration of 5FU in isopropyl myristate was applied on the skin after pretreatment with dendrimers and (14)C labeled 5FU was analyzed using a liquid scintillation counter. The influence of dendrimer surface charge (G4-NH(2), G3.5-COOH, and G4-OH), generations (G2-G6-NH(2)) and concentration (0.1-10 mM of G4-NH(2)) on skin permeation of 5FU were studied. The enhancement in drug permeability coefficient (K(p)) was in the following decreasing order G4-NH(2) > G4-OH > G3.5-COOH. Dendrimer increased the skin permeation by increasing the skin partitioning of 5FU. Transepidermal water loss, skin resistance measurements and ATR-FTIR studies revealed that cationic dendrimers act by interacting with the skin lipid bilayers. Increase in G4-NH(2) concentration did not proportionally increase the skin permeation of 5FU. The 5FU K(p) was inversely related to the molecular weight of the dendrimer. G2-NH(2) dendrimer reduced skin resistance to a greater extent than higher generation dendrimers. Overall, the study showed that lower generation cationic dendrimer is more effective in enhancing the skin permeation of hydrophilic drugs.

Influence of surface charge of PLGA particles of recombinant hepatitis B surface antigen in enhancing systemic and mucosal immune responses

This study investigates the efficacy of surface-modified microspheres of hepatitis B surface antigen (HBsAg) in eliciting systemic and mucosal immune responses. Positively charged poly( d, l-lactic- co-glycolic acid) microspheres were prepared by a double-emulsion solvent-evaporation method with cationic agents—stearylamine and polyethylenimine—in the external aqueous phase. Formulations were characterized for morphology, size, density, aerodynamic diameter, entrapment efficiency and in vitro drug-release profile. Immunization was performed after pulmonary administration of the formulations to female Sprague–Dawley rats and the immune response was monitored by measuring IgG levels in serum and secretory (sIgA) levels in salivary, vaginal and bronchoalveolar lavage fluids. The cell-mediated immune response was studied by measuring cytokine levels in spleen homogenates, and a cytotoxicity study was performed with Calu-3 cell line. The aerodynamic diameter of the particles was within the respirable range, with the exception of stearylamine-modified particles. Zeta potential values moved from negative (−6.76 mV) for unmodified formulations to positive (+0.515 mV) for polyethylenimine-modified particles. Compared to unmodified formulations, polyethylenimine-based formulations showed continuous release of antigen over a period of 28–42 days and increased levels of IgG in serum and sIgA in salivary, vaginal and bronchoalveolar lavage. Further, cytokine levels—interferon γ and interleukin-2—were increased in spleen homogenates. The viability of Calu-3 cells was not adversely affected by the microparticles. In summation, this study establishes that positive surface charges on poly( d, l-lactic- co-glycolic acid) particles containing HBsAg enhances both the systemic and mucosal immune response upon immunization via the respiratory route.

Influence of surface charges on the structure of a dielectric barrier discharge in air at atmospheric pressure: experiment and modeling

Dielectric barrier discharges (DBD) in air at atmospheric pressure and at low frequency are mainly constituted of thin transient plasma filaments (or microdischarges) with radii of a few hundreds of micrometers. In this work, we consider a point-to-plane geometry with the dielectric covering the plane electrode. Plasma filaments are initiated by streamers, starting from the high-field region close to the point electrode. The plasma filaments deposit charges on the dielectric plate which screen the electric field and lead to an extinction of the discharge filaments. In this work we experimentally demonstrate the synchronous start of several filaments in a time range of less than a few tens of nanoseconds and we show that the charges deposited on the dielectric have a strong impact on the discharge structure. This is validated using a simple electrostatic model. Then, the dynamics of the 2D streamer propagation in the gas gap and its interaction with the dielectric plane is calculated. The influence of space charges and surface charges on the discharge structure are discussed and compared with the experiment.

Surface hydrophilization of microporous polypropylene membrane by the interfacial crosslinking of polyethylenimine

To endow microporous polypropylene membrane (MPPM) with durable surface hydrophilicity, a facile interfacial crosslinking approach was developed, combined with a pretreatment by dielectric barrier discharge (DBD) plasma at atmospheric pressure. The commercially available polyethylenimine (PEI) was coated on MPPM firstly and was sequentially crosslinked with p-xylylene dichloride and quaternized with iodomethane to form a permanently positively charged layer. The physical and chemical changes of the membrane surface were characterized by tensile test, FT-IR/ATR, XPS, and FESEM. The surface hydrophilicity of the modified MPPMs was evaluated by water contact angle and pure water flux measurements. Besides, the influence of surface charge on protein filtration involving flux decline and protein transmission was also investigated in detail. It is found that the optimal time of DBD plasma treatment is ∼30 s. Mass gain for the MPPMs during the interfacial crosslinking can be controlled conveniently by adjusting the PEI concentration from 1.0 to 15 g/L. The surface hydrophilicity can be significantly enhanced and is durable, characterized by the sharp decrease of water contact angle, the double increase of pure water flux and the stability test. The results of protein filtration suggest that the obtained highly hydrophilic and charged membrane surface is resistant to protein fouling. Furthermore, almost 100% of protein transmission indicates that the microfiltration characteristic of MPPMs is unchanged.

Zeta potential of motile spores of the green alga Ulva linza and the influence of electrostatic interactions on spore settlement and adhesion strength

The zeta potential of the motile spores of the green alga (seaweed) Ulva linza was quantified by video microscopy in combination with optical tweezers and determined to be -19.3+/-1.1 mV. The electrostatic component involved in the settlement and adhesion of spores was studied using electret surfaces consisting of PTFE and bearing different net charges. As the surface chemistry remains the same for differently charged surfaces, the experimental results isolate the influence of surface charge and thus electrostatic interactions. Ulva spores were demonstrated to have a reduced tendency to settle on negatively charged surfaces and when they did settle the adhesion strength of settled spores was lower than with neutral or positively charged surfaces. These observations can be ascribed to electrostatic interactions.

Surface hydrophilization for polypropylene microporous membranes: A facile interfacial crosslinking approach

A hydrophilic surface is very important for hydrophobic separation membranes such as polypropylene microporous membranes (PPMMs). In this work a facile and effective method, interfacial crosslinking combined with pretreatment by dielectric barrier discharge plasma at atmospheric pressure, was developed for endowing PPMMs with a hydrophilic and charged surface. Poly( N, N-dimethylaminoethyl methacrylate) (PDMAEMA) and p-xylylene dichloride were selected for quaternization crosslinking to form a positively charged coating layer, which was characterized with FT-IR/ATR, XPS, and FESEM. Water contact angle and pure water flux measurements were conducted to evaluate the surface hydrophilicity. The influence of surface charges on protein filtration was also investigated. It is found that the mass gain of interfacial crosslinking increases almost linearly with increasing the PDMAEMA concentration from 0.5 to 10 g/L. The crosslinking degree is larger than 80% according to the XPS results, ensuring the stability of the crosslinking layer. The surface hydrophilicity is demonstrated by the sharp decrease of water contact angle from 145° to 20°. The pure water flux also increases 3 times under the optimized conditions. Furthermore, the results of protein filtration suggest that these highly hydrophilic and charged surfaces can effectively resist the fouling of proteins.

Removal of Oxide Nanoparticles in a Model Wastewater Treatment Plant: Influence of Agglomeration and Surfactants on Clearing Efficiency

The rapidly increasing production of engineered nanoparticles has created a demand for particle removal from industrial and communal wastewater streams. Efficient removal is particularly important in view of increasing long-term persistence and evidence for considerable ecotoxicity of specific nanoparticles. The present work investigates the use of a model wastewater treatment plant for removal of oxide nanoparticles. While a majority of the nanoparticles could be captured through adhesion to clearing sludge, a significant fraction of the engineered nanoparticles escaped the wastewater plant's clearing system, and up to 6 wt % of the model compound cerium oxide was found in the exit stream of the model plant. Our study demonstrates a significant influence of surface charge and the addition of dispersion stabilizing surfactants as routinely used in the preparation of nanoparticle derived products. A detailed investigation on the agglomeration of oxide nanoparticles in wastewater streams revealed a high stabilization of the particles against clearance (adsorption on the bacteria from the sludge). This unexpected finding suggests a need to investigate nanoparticle clearance in more detail and demonstrates the complex interactions between dissolved species and the nanoparticles within the continuously changing environment of the clearing sludge.

Influence of surface charge on ingress of chloride ion in hardened pastes

The amount of free chloride content in concrete is one of major factors in initiating the corrosion process. The material and environmental factors play a key role in diffusing the chloride ion through the cover concrete to reinforcement. Thus, the electrochemical study is indispensable to understand the mechanism of chloride ingress into concrete. Determination of surface charge and its influence on diffusion of chloride ion into cement matrix of concrete are researched for Ordinary Portland Cement (OPC) paste and cement paste containing Ground Granulated Blastfurnace Slag (GGBS). Different kinds of experiments such as measurement of membrane potential, determination of porosity and pore size distribution, determination of pore solution concentration, and steady state diffusion coefficient of chloride and sodium ions are employed to understand the mechanism of chloride ingress. The obtained results show that the positive surface charge on the pore walls of hardened paste regardless of GGBS’s presents. The surface charge of hardened paste mainly depends on pore solution concentration and cement composition. The physiochemical characteristics of the pores are affecting on transporting ions through it. Hardened paste has greater resistance to diffusing sodium ions than chloride ions. Moreover, there is a strong interaction between transport of chloride ion and surface charge in matured hardened paste.

The Link Between the Fiber Contact Zone and the Physical Properties of Paper: A Way to Control Paper Properties

Paper is a composite of fibers, air and additives where the fiber/fiber joints keep the network structure together. A study was undertaken to establish the link between the properties of the contact zone between fibers and paper performance under mechanical loading. The contact zone between fibers was investigated using light microscopy. A staining technique was developed for evaluating the influence of surface charge on fiber/fiber joint strength. The joint strength was linearly correlated with paper tensile strength and with the average amplitude of the acoustic events measured by acoustic emission testing. The fiber surface conformability was improved by changing the surface charge. This resulted in increased fiber/fiber joint strength as the relative contact area became larger. Increasing the molecular adhesion in the contact zone with the aid of strength additives also improved the fiber/fiber joint strength.