Parameters affecting the adhesion strength between a living cell and a colloid probe when measured by the atomic force microscope

In this study, we used the colloid probe atomic force microscopy (AFM) technique to investigate the adhesion force between a living cell and a silica colloid particle in a Leibovitz's L-15 medium (L-15). The L-15 liquid maintained the pharmaceutical conditions necessary to keep the cells alive in the outside environment during the AFM experiment. The force curves in such a system showed a steric repulsion in the compression force curve, due to the compression of the cells by the colloid probe, and an adhesion force in the decompression force curve, due to binding events between the cell and the probe. We also investigated for the first time how the position on the cell surface, the strength of the pushing force, and the residence time of the probe at the cell surface individually affected the adhesion force between a living cell and a 6.84 μm diameter silica colloid particle in L-15. The position of measuring the force on the cell surface was seen not to affect the value of the maximum adhesion force. The loading force was also seen not to notably affect the value of the maximum adhesion force, if it was small enough not to pierce and damage the cell. The residence time of the probe at the cell surface, however, clearly affected the adhesion force, where a longer residence time gave a larger maximum force. From these results, we could conclude that the AFM force measurements should be made using a loading force small enough not to damage the cell and a fixed residence time, when comparing results of different systems.     

Force measurements of bacterial adhesion on metals using a cell probe atomic force microscope

The adhesion of microbial cells to metal surfaces in aqueous media is an important phenomenon in both the natural environment and engineering systems. The adhesion of two anaerobic sulfate-reducing bacteria (Desulfovibrio desulfuricans and a local marine isolate) and an aerobe (Pseudomonas sp.) to four polished metal surfaces (i.e., stainless steel 316, mild steel, aluminum, and copper) was examined using a force spectroscopy technique with an atomic force microscope (AFM). Using a modified bacterial tip, the attraction and repulsion forces (in the nano-Newton range) between the bacterial cell and the metal surface in aqueous media were quantified. Results show that the bacterial adhesion force to aluminum is the highest among the metals investigated, whereas the one to copper is the lowest. The bacterial adhesion forces to metals are influenced by both the electrostatic force and metal surface hydrophobicity. It is also found that the physiological properties of the bacterium, namely the bacterial surface charges and hydrophobicity, also have influence on the bacteria-metal interaction. The adhesion to the metals by Pseudomonas sp. and D. desulfuricans was greater than by the marine SRB isolate. The cell-cell interactions show that there are strong electrostatic repulsion forces between bacterial cells. Cell probe atomic force microscopy has provided some useful insight into the interactions of bacterial cells with the metal surfaces.     

Green synthesis of Copper oxide nanoparticles decorated with graphene oxide for anticancer activity and catalytic applications

Nanotechnology is an embryonic field that grips countless impacts on the drug delivery system. Nanoparticles as haulers increase the capability of target-specific drug delivery to many folds hence are used in the treatment of dreadful diseases such as cancer, diabetes, etc. This boom has aimed at, to synthesize Copper oxide nanoparticles (CuO-NPs) using Acalypha Indica leaf extract and then incorporated with graphene oxide (GO) to form GO-CuO nanocomposites. Secondly, to sightsee the photocatalytic activity of CuO-NPs and GO-CuO nanocomposites towards the decolorization of methylene blue-dye and to test its activity against HCT-116 Human colon cancer cell lines. Synthesized nanocomposites were characterized using FTIR, UV–vis, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray Photoelectron Spectroscopy (XPS) and transmission electron microscopy (TEM) analysis. The photocatalytic studies revealed that synthesized nanocomposites have the efficiency to degrade methylene blue dye by 83.20% and cytotoxic activity was found to be 70% against HCT-116 Human colon cancer cell lines at 100 μg/ml. GO-CuO nanocomposites have appreciable activity towards cancer cell lines and photocatalytic activity when compared to nanoparticles as such.     

A new technique for membrane characterisation: direct measurement of the force of adhesion of a single particle using an atomic force microscope

An Atomic Force Microscope (AFM) has been used to quantify directly the adhesive force between a colloid probe and two polymeric ultrafiltration membranes of similar MWCO (4000 Da) but different materials (ES 404 and XP 117, PCI Membrane Systems (UK)). The colloid probe was made from a polystyrene sphere (diameter 11 μm) glued to a V shaped AFM cantilever. Measurements were made in 10⁻² M NaCl solution at pH 8. It was found that the adhesive force at the ES 404 membrane was more than five times greater than that at the XP 117 membrane. As it allows direct quantification of particle/membrane interactions, this technique should be invaluable in the development of new membrane materials and in the elucidation of process behaviour.     

Latex film formation studied with the atomic force microscope: Influence of aging and annealing

The surface structure of latex dispersion films was examined with an atomic force microscope. All measurements were done in air on latex films having a minimum film formation temperature of 12°C and a glass transition temperature of 18°C. One aim of this study was to follow structural changes during film formation. Three minutes after spreading the film, its surface layer dried. Afterwards, the structure of the film did not change anymore. Only after 4 months could structural changes be observed: Though individual latex particles could be identified, the particles partly melted into one another.After annealing films at 50° or 60°C for 4 h, the latex particles partly melted into one another, but individual particles could still be identified. When annealing at or above 80°C, no individual latex particles were visible anymore. With increasing temperature the film roughness decreased from 3 nm without annealing to 0.8 nm at 100°C annealing temperature. In addition, islands of 2–4 nm thickness appeared on the film surface. These islands could be scraped off the film by increasing the force between tip and sample, indicating that they are composed of surfactant which was squeezed out of the film.     

Study of uptake and loss of silica nanoparticles in living human lung epithelial cells at single cell level

The toxicology of nanomaterials is a blooming field of study, yet it is difficult to keep pace with the innovations in new materials and material applications. Those applications are quickly being introduced in research, industrial, and consumer settings. Even though the cytotoxicity of many types of nanoparticles has been demonstrated, the behavior of those particles in a biological environment is not yet fully known. This work characterized the following over time: protein adsorption on silica particle surfaces, the internalization of particles in human lung carcinoma (A549) cells when coated with different specific proteins or no proteins at all, and the cellular loss of particles following the removal of extracellular particles. Proteins were shown to quickly saturate the particle surface, followed by a competitive process of particle agglomeration and protein adsorption. Uptake of particles peaked at 8–10 h, and it was determined that, in this system, the charge of the protein-coated particles changed the rate of uptake if the charge difference was great enough. Cells internalized particles lacking any adsorbed proteins with approximately 3 times the rate of protein-coated particles with the same charge. Although particles exited cells over time, the process was slower than uptake and did not near completion within 24 h. Finally, analysis at the single cell level afforded observations of particle agglomerates loosely associated with cell membranes when serum was present in the culture medium, but in the absence of serum, particles adhered to the dish floor and formed smaller agglomerates on cell surfaces. Although data trends were easily distinguished, all samples showed considerable variation from cell to cell. Figure Silica-capped fluorescent semiconductor nanoparticles as internalized by human lung epithelial cells and adsorbed to a glass substrate in protein-free culture medium.     

Effect of ampere force on electrolyte flow and current passing due to EMF generation in electrochemical cell rotating in magnetic field

An Ampere force acts in the rotating electrochemical cell, which is located in the magnetic field. This force causes an electrolyte flow directed oppositely to the direction of cell rotation. The effect of Ampere force on the distribution of hydrodynamic velocity in the gap between two cylindrical electrodes of rotating cell is theoretically analyzed. Under certain simplifying assumptions, an equation is obtained for calculating the current passing in the cell by action of potential difference, which arises in the cell due to the Lorentz force taking into account the Ampere force.     

Effect of roughness on particle adhesion in aqueous solutions: a study of Saccharomyces cerevisiae and a silica particle

An atomic force microscope (AFM) has been used to quantify the adhesion of living cells Saccharomyces cerevisiae on three different silica surfaces with defined roughness. The effects of support roughness on the adhesion forces of a smooth silica particle were studied in addition. A living single cell was immobilized at the apex of a tipless AFM cantilever using a key-lock mechanism. Adhesion was quantified from the force-distance data measured on a smooth silica substrate and two substrates coated with hydrophilic monodisperse silica particles with 110 and 240 nm in diameter to study the effect of roughness on particle adhesion. The AFM technique gives unique insight into the primary colonization event of biofilm formation. The new knowledge helps substantially to design surface coatings relevant for biotechnology, medicine and dentistry.     

Elasticity of cardiac cells on the polymer substrates with different stiffness: an atomic force microscopy study

Influences of substrate stiffness on mechanical properties of cardiac myocytes and fibroblasts were investigated by cell elasticity measurement with atomic force microscopy. The cells were cultured on collagen-coated polyacrylamide substrates with gradient rigidity. While cardiac myocytes showed no evident change in cell elasticity on different substrates, cardiac fibroblasts displayed the non-monotonic dependence on substrate stiffness with a maximum elastic modulus. Moreover, the elasticity change of cardiac fibroblasts with substrates stiffness was found to be regulated by actin filaments. Study of the effect of substrate stiffness on cell elasticity for different cardiac cells provides new information for the better understanding of cardiac physiology and pathology.     

化学反应过程中分子中1个电子所受到的作用势与力常数的理论研究

通过典型的双分子亲核取代和烯烃亲电加成反应,讨论了反应过程中,化学键伸缩振动力常数和分子中1个电子所受到的作用势(D_(pb))之间的关联.研究表明分子中1个电子所受到的作用势能够很好地描述反应中键形成和断裂时的化学键强度.     

Construction of a pH-responsive drug delivery platform based on the hybrid of mesoporous silica and chitosan

Mesoporous silica nanoparticles (MSN) have been widely used for drug delivery due to their large specific surface area and excellent biocompatibility. However, the mesoporous structure of MSN would lead to the inevitable “premature release” of the drugs, and therefore the modification of MSN for controlled delivery seems to be a necessary step. Herein, chitosan (CS) was used for the surface functionalization of MSN via amidation reaction, and the introduced CS could function as a “gatekeeper” and the drug of methotrexate (MTX) might be encapsulated in the mesopores of MSN. As a result, the “premature release” of the encapsulated MTX could be effectively circumvented with the aid of the CS cap. More importantly, the drug delivery from the hybrid of MSN and CS (MSN/CS) can be endowed with pH-sensitivity by the introduction of CS because the amide bonding between CS and MSN is highly pH-sensitive. The cumulative release of MTX from the MSN/CS is more pronounced at pH 5.0 (80.86%) than those at pH 6.8 (40.46%) and pH 7.4 (18.25%).     

An experimental study of the drag force on a sphere exposed to an argon thermal plasma flow

Experimental data are presented concerning the drag force on a stationary phere exposed to an argon plasma flow with temperatures about 10⁴ K and velocities about 10² m/s. A novel probe construction has been employed in the drag measurements in order to exclude the effect of the supporting wire on the sphere drag data. By using the new probe construction with a compensating wire, drag forces on an individual steel sphere in the plasma flow have been measured and compared with those obtained by using the probe construction ernployed by a few previous authors. Experimental results show that the measured drag forces are always less than their counterparts obtained from the standard sphere-drag curve under isothermal flow conditions with the same Reynolds numbers based on the oncoming plasma properties. The drag force on a sphere increases only slightly with the increasing surface temperature of the sphere before it melts. Appreciable diference was found between the experimental data and the predicted results of the available expressions for drag on a sphere exposed to a thermal plasma flow. Further research effort is required to build a more suitable drag correlation.     

In situ determination of the thermodynamic surface properties of chemically modified surfaces on a local scale: an attempt with the atomic force microscope

We have monitored deflection-distance curves with an atomic force microscope (AFM) in contact mode, with a silicon nitride tip, on chemically modified silicon wafers, in the air. The wafers were modified on their surface by grafting self-assembled monolayers (SAMs) of different functional groups such as methyl, ester, amine, or methyl fluoride. A chemically modified surface with a functionalized hydroxyl group was also considered. Qualitative analysis allowed us to compare adhesive forces versus chemical features and surface energy. The systematic calibration procedure of the AFM measurements was performed to produce quantitative data. Our results show that the experimentally determined adhesive force or thermodynamic work of adhesion increases linearly with the total surface energy determined with contact angles measured with different liquids. The influence of capillary condensation of atmospheric water vapor at the tip-sample interface on the measured forces is discussed. Quantitative assessment values were used to determine in situ the SAM-tip thermodynamic work of adhesion on a local scale, which have been found to be in good agreement with quoted values. Finally, the determination of the surface energy of the silicon wafer deduced from the thermodynamic work of adhesion is also proposed and compared with the theoretical value.     

Physicochemical characterization of an anatase TiO2 surface and the adsorption of a nonionic surfactant: an atomic force microscopy study

Atomic force microscopy was used to characterize an anatase TiO2 surface, prepared by the helical vapor preparation method. The forces between two bare TiO2 surfaces were measured in the presence of water at various pH values. This TiO2 isoelectric point (iep) was characterized by the presence of only a van der Waals attraction and was measured at pH 5.8; this value is similar to that for a rutile TiO2 surface. The adsorption mechanism of a nonionic surfactant molecule to this anatase TiO2 surface was investigated by measuring the forces between two such TiO2 surfaces at their iep pH in the presence of linear dodecanol tetraethoxylate (C12E4), a poly(ethoxylene oxide) n-alkyl ether. C12E4 was seen by the presence of steric forces to adsorb to the uncharged TiO2 surface. For low surfactant concentrations, C12E4 adsorbed with its hydrophobic tail facing the TiO2 substrate, to reduce its entropically unfavorable contacts with water. Additional surfactant adsorption occurred at higher surfactant concentrations by the hydrophobic and hydrophilic interactions between the surfactant tails and heads, respectively, and gave sub-bilayers. A two-step adsorption isotherm was subsequently proposed with four regions: (1) submonolayer, (2) complete monolayer, (3) sub-bilayer, and (4) bilayer. The absence of a long-range repulsive force between the two TiO2 surfaces in the presence of the C12E4 surface aggregates indicated that a C12E4 nonionic surfactant aggregate did not possess charge.     

Computer simulation study of the binding of an antiviral agent to a sensitive and a resistant human rhinovirus

Summary Molecular dynamics simulations have been used to study the free energy of binding of an antiviral agent to the human rhinovirus HRV-14 and to a mutant in which a valine residue in the antiviral binding pocket is replaced by leucine. The simulations predict that the antiviral should bind to the two viruses with similar affinity, in apparent disagreement with experimental results. Possible origins of this discrepancy are outlined. Of particular importance is the apparent need for methods to systematically sample all significant conformations of the leucine side chain.     

Urea: an ab initio and force field study of the gas and solid phases

We have studied the gaseous and solid phases of urea using both quantum mechanics calculation and force field simulation methods. Our ab initio calculations confirmed experimental observations that urea structure is planar in the crystal, but nonplanar in the gas phase. Based on electron structure analysis, we suggest that the significant difference between these two structures in different environments can be qualitatively explained by two resonance structures. The planar structure is more polarized than the nonplanar one, and the former is stabilized in the solid phases due to strong electrostatic interactions. We found classical force field method is incapable to represent such strong polarization effect. Using molecular dynamics simulations with a force field optimized for condensed phases, we calculated the crystalline structures of urea in the temperature range of 12 to 293 K. The densities as well as cell parameters are within 2% deviation from the experimental data in the temperature range.     

Dynamic drag force based on iterative density mapping: A new numerical tool for three‐dimensional analysis of particle trajectories in a dielectrophoretic system

Dielectrophoresis is a widely used means of manipulating suspended particles within microfluidic systems. In order to efficiently design such systems for a desired application, various numerical methods exist that enable particle trajectory plotting in two or three dimensions based on the interplay of hydrodynamic and dielectrophoretic forces. While various models are described in the literature, few are capable of modeling interactions between particles as well as their surrounding environment as these interactions are complex, multifaceted, and computationally expensive to the point of being prohibitive when considering a large number of particles. In this paper, we present a numerical model designed to enable spatial analysis of the physical effects exerted upon particles within microfluidic systems employing dielectrophoresis. The model presents a means of approximating the effects of the presence of large numbers of particles through dynamically adjusting hydrodynamic drag force based on particle density, thereby introducing a measure of emulated particle–particle and particle–liquid interactions. This model is referred to as “dynamic drag force based on iterative density mapping.” The resultant numerical model is used to simulate and predict particle trajectory and velocity profiles within a microfluidic system incorporating curved dielectrophoretic microelectrodes. The simulated data are compared favorably with experimental data gathered using microparticle image velocimetry, and is contrasted against simulated data generated using traditional “effective moment Stokes‐drag method,” showing more accurate particle velocity profiles for areas of high particle density.     

Effect of thermal annealing on a bilayer polyvinyl alcohol/polyacrylic acid electrospun hydrogel nanofibres loaded with doxorubicin and clarithromycin for a synergism effect against osteosarcoma cells

Polyvinyl alcohol/polyacrylic acid (PVA/PAA) bilayer hydrogel nanofibres were successfully fabricated by electrospinning and physically crosslinked via heat treatment. The effects of the thermal annealing process on the structure, morphology, swelling, thermal properties and hydrophilicity of electrospun nanofibres were investigated. In addition, these membranes were also used to incorporate doxorubicin and clarithromycin for osteosarcoma treatment, one in each layer. These drugs were used because it is hypothesized in this work that a synergism occurs between both drugs. So, these membranes were analyzed towards their dual-drug release and potential cytotoxicity towards the U2OS human osteosarcoma cell line. Moreover, the water contact angle, disintegration, swelling and weight loss studies confirmed the rapid swelling and improved water stability of the annealed PVA/PAA bilayer nanofibres. The annealed bilayer nanofibres exhibited an increase in the average diameter and degree of crystallinity. In addition, the results revealed that a variation occurred in the degree of hydrophilicity of annealed PVA/PAA bilayer nanofibres. The PAA nanofibres surface exhibited higher hydrophilicity than the PVA nanofibres surface. Drug delivery presented to be as fast rate release for clarithromycin and slow-rate release for doxorubicin, which may be advantageous because both drugs exhibited to be synergetic for certain dosages presenting the combination of the drugs higher than 50% of cell inhibition, while these membranes had higher inhibition values (up to 90%), which was attributed to the PAA but also the drugs. These unique properties are of potential interest in drug delivery applications for dual drug delivery where the tunability of surfaces is desirable.     

Introducing a new pharmaceutical agent: Facile synthesis of CuFe12O19@HAp-APTES magnetic nanocomposites and its cytotoxic effect on HEK-293 cell as an efficient in vitro drug delivery system for atenolol

In this study, novel CuFe₁₂O₁₉@hydroxyapatite magnetic nanocomposites (CuFe₁₂O₁₉@HAp MNCs) as controlled target drug delivery were synthesized by ultrasound-assisted precipitation method for the first time. Then, the magnetic substrate was functionalized with APTES (CuFe₁₂O₁₉@HAp-APTES MNCs) to increase the efficiency of the drug delivery system. The crystallinity, size, morphology, and composition of the products were determined by FESEM, DLS, BET, TEM, XRD, EDS, and VSM. In order to investigate the drug loading ability of prepared nanocomposites, we chose antihypertensive drug (atenolol) as the model drug. After that, the release behavior of magnetic nanocomposites modified atenolol was investigated under stomach (pH value of 1.5–2) and intestine (pH value of 5.8–6.7) conditions. The results revealed that the highest entrapment efficiency was achieved by CuFe₁₂O₁₉@HAp-APTES MNCs (63.1%). Furthermore, the controlled-release potential for CuFe₁₂O₁₉@HAp-APTES MNCs was the highest compared with the pure CuFe₁₂O₁₉@HAp MNCs. Increased efficiency can be due to the binding of the amine group in APTES with the atenolol drug. The cytotoxicity of the ATL-loaded magnetic nanocomposites (ATL-CuFe₁₂O₁₉@HAp-APTES MNCs) was investigated on the HEK-293 cell line using MTT assay. Based on the results, we concluded that the synthesized magnetic nanocomposites could be effective vehicles for the sustained delivery of atenolol as an antihypertensive drug.     

Flexible matching of test ligands to a 3D pharmacophore using a molecular superposition force field: Comparison of predicted and experimental conformations of inhibitors of three enzymes

Summary A computer procedure TFIT, which uses a molecular superposition force field to flexibly match test compounds to a 3D pharmacophore, was evaluated to find out whether it could reliably predict the bioactive conformations of flexible ligands. The program superposition force field optimizes the overlap of those atoms of the test ligand and template that are of similar chemical type, by applying an attractive force between atoms of the test ligand and template which are close together and of similar type (hydrogen bonding, charge, hydrophobicity). A procedure involving Monte Carlo torsion perturbations, followed by torsional energy minimization, is used to find conformations of the test ligand which cominimize the internal energy of the ligand and the superposition energy of ligand and template. The procedure was tested by applying it to a series of flexible ligands for which the bioactive conformation was known experimentally. The 15 molecules tested were inhibitors of thermolysin, HIV-1 protease or endothiapepsin for which X-ray structures of the bioactive conformation were available. For each enzyme, one of the molecules served as a template and the others, after being conformationally randomized, were fitted. The fitted conformation was then compared to the known binding geometry. The matching procedure was successful in predicting the bioactive conformations of many of the structures tested. Significant deviation from experimental results was found only for parts of molecules where it was readily apparent that the template did not contain sufficient information to accurately determine the bioactive conformation.