Lattice Boltzmann model for capillary interactions between particles at a liquid-vapor interface under gravity.

A computational technique based on the lattice Boltzmann method (LBM) is developed to simulate the wettable particles adsorbed to a liquid-vapor interface under gravity. The proposed technique combines the improved smoothed-profile LBM for the treatment of moving solid particles in a fluid and the free-energy LBM for the description of a liquid-vapor system. Five benchmark two-dimensional problems are examined: (A) a stationary liquid drop in the vapor phase; a wettable particle adsorbed to a liquid-vapor interface in (B) the absence and (C) the presence of gravity; (D) two freely moving particles at a liquid-vapor interface in the presence of gravity (i.e., capillary flotation forces); and (E) two vertically constrained particles at a liquid-vapor interface (i.e., capillary immersion forces). The simulation results are in good quantitative agreement with theoretical estimations, demonstrating that the proposed technique can reproduce the capillary interactions between wettable particles at a liquid-vapor interface under gravity.

Preparation and characterization of glycopolymers with biphenyl spacers via Suzuki coupling reaction.

Poly(vinylbiphenyl)s bearing glycoside ligands at the side chains were prepared using the Suzuku coupling reaction. Effects of glycoside reactant concentration, halide species, glycoside species, and catalyst species on the incorporation of glycoside ligand into the polymer were investigated. The obtained glycopolymers exhibited specific binding to proteins corresponding to the glycoside ligands. In addition, the biphenyl spacers formed by the Suzuki coupling reaction in the glycopolymer were fluorescent, whereas the polymer precursor was not.

Lattice Boltzmann method for simulation of wettable particles at a fluid-fluid interface under gravity.

A computational technique was developed to simulate wettable particles trapped at a fluid-fluid interface under gravity. The proposed technique combines the improved smoothed profile-lattice Boltzmann method (iSP-LBM) for the treatment of moving solid-fluid boundaries and the free-energy LBM for the description of isodensity immiscible two-phase flows. We considered five benchmark problems in two-dimensional systems, including a stationary drop, a wettable particle trapped at a fluid-fluid interface in the absence or presence of gravity, two freely moving particles at a fluid-fluid interface in the presence of gravity (i.e., capillary floatation forces), and two vertically constrained particles at a fluid-fluid interface (i.e., capillary immersion forces). The simulation results agreed well with theoretical estimations, demonstrating the efficacy of the proposed technique.

Formation of glyco-functionalized interfaces for protein binding using polyphenolic glycoside.

In this study, a polyphenolic glycoside (α-glucosyl rutin) was used to form glyco-functionalized interfaces for protein binding. α-Glucosyl rutin was coated onto precious metals, metal oxides, and synthetic polymers, including polyethylene and polytetrafluoroethylene with poor surface modifiability. The glyco-functionalized interfaces bound strongly and specifically to concanavalin A and Bauhinia purpurea lectin, which have different carbohydrate specificities. Competitive adsorption tests demonstrated that the binding sites for the abovementioned lectins were glucosyl and rhamnosyl residues, respectively. The glyco-functionalized interfaces maintained the protein binding ability after being stored in aqueous solution for 1 day and in air for 160 days. Once the glyco-functionalized interfaces were formed on gold, silicon dioxide, polystyrene, and polytetrafluoroethylene using α-glucosyl rutin, all the glyco-functionalized interfaces bound to concanavalin A rather than peanut agglutinin.

Decomposition of amyloid fibrils by NIR-active upconversion nanoparticles.

We demonstrate amyloid fibril (AF) decomposition induced by NIR-active upconversion nanoparticles complexed with photosensitisers. The process is triggered by upconversion, which initiates a photochemical reaction cascade that culminates in the generation of the highly reactive singlet-oxygen product 1O2 close to the amyloid superstructures, resulting in AF decomposition.

Effect of interfacial serum proteins on the cell membrane disruption induced by amorphous silica nanoparticles in erythrocytes, lymphocytes, malignant melanocytes, and macrophages.

It is very important to examine carefully the potential adverse effects of engineered nanoparticles (NPs) on human health and environments. In the present study, we have investigated the impact of interfacial serum proteins on the cell membrane disruption induced by silica NPs of primary diameter of 55-68 nm in four types of cells (erythrocytes, Jurkat, B16F10, and J774.1). The silica-induced membranolysis was repressed by addition of 1-2% serum into culture media, where the adhesion amount of the FBS-coated silica NPs onto a cell surface seemed comparable with that of the bare silica NPs. The nonspecific attraction between the bare silica and J774.1 cell membrane surfaces was masked by pretreatment of the silica surface with serum albumin, whereas the serum proteins-coated silica surface exhibited the attractive interactions with the cell membrane due to specific binding between some of adsorbed proteins thereon and the membrane receptors. The difference in silica-cell interaction between the nonspecific and specific attractions would explain the reason why interfacial serum proteins reduced the membranolysis without prevention of silica NPs adhering to cell surfaces.

Amplification of Sensor Signals from Metal Mesh Device with Fine Periodic Structure.

Two types of metal mesh devices with hole diameters of 1.7 and 0.3 µm were prepared by an electroforming method. The metal mesh devices with hole diameters of 1.7 and 0.3 µm transmitted electromagnetic waves with frequencies of approximately 100 and 285 THz, respectively. These spectral frequencies shifted depending on the adsorption amount of protein. The slope in the linear relationship between the adsorption amount and spectral shift (i.e. sensitivity) of the metal mesh device with a hole diameter of 0.3 µm was seven times as great as that of the device with a hole diameter of 1.7 µm. These results agreed with the theoretical concept of the sensitivity for the metal mesh device sensor being proportional to the square of the transmittance frequency. As biosensors, the structurally refined metal mesh devices amplified the output signals.

Effect of internal mass in the lattice Boltzmann simulation of moving solid bodies by the smoothed-profile method.

A computational method for the simulation of particulate flows that can efficiently treat the particle-fluid boundary in systems containing many particles was developed based on the smoothed-profile lattice Boltzmann method (SPLBM). In our proposed method, which we call the improved SPLBM (iSPLBM), for an accurate and stable simulation of particulate flows, the hydrodynamic force on a moving solid particle is exactly formulated with consideration of the effect of internal fluid mass. To validate the accuracy and stability of iSPLBM, we conducted numerical simulations of several particulate flow systems and compared our results with those of other simulations and some experiments. In addition, we performed simulations on flotation of many lightweight particles with a wide range of particle size distribution, the results of which demonstrated the effectiveness of iSPLBM. Our proposed model is a promising method to accurately and stably simulate extensive particulate flows.

Gadolinium-loaded chitosan nanoparticles for neutron-capture therapy: Influence of micrometric properties of the nanoparticles on tumor-killing effect.

As a nanoparticulate device for controlled delivery of Gd in NCT, the authors have developed gadolinium-loaded chitosan nanoparticles (Gd-nanoCPs). In the present study, influence of micrometric properties such as particle size, particle-surface charge and Gd content of Gd-nanoCPs on tumor-killing effect by Gd-NCT was investigated with Gd-nanoCPs. Two types of Gd-nanoCPs with different mean particle size, zeta potential and Gd-content (Gd-nanoCP-400; 391nm, 28mV, 9wt% and Gd-nanoCP-200; 214nm, 19mV, 24wt%) could be prepared by using chitosans with different molecular weights. Gd-nanoCPs incorporating 1.2mg of natural Gd were injected intratumorally once or twice to mice subcutaneously-bearing B16F10 melanoma. Eight hours after the last administration, thermal neutron was irradiated to tumor region of the mice. Remarkable tumor-growth was observed in both hot and cold control groups. In contrast, Gd-NCT groups showed significant tumor-growth suppression effect, though their efficacy was found to depend on the micrometric properties of Gd-nanoCPs. In particular, the Gd-nanoCP-200 exhibited stronger tumor-killing effect than the Gd-nanoCP-400 at the same Gd dose and it was still similar to Gd-nanoCP-400 in tumor-growth suppressing effect even at the half of Gd dose of Gd-nanoCP-400. This significance in tumor-killing effect would be ascribed from a higher Gd retention in the tumor tissue and an improved distribution of Gd with intratumorally administered Gd-nanoCP-200. Indeed, the Gd concentration in tumor tissue at the time corresponding to the onset of thermal neutron irradiation was determined to be significantly higher in Gd-nanoCP-200, compared with Gd-nanoCP-400. These results demonstrated that appropriate modification of Gd-nanoCPs in micrometric properties would be an effective way to improve the retention of Gd in the tumor tissue after intratumoral injection, leading to the enhanced tumor-killing effect in Gd-NCT.

Effect of interfacial serum proteins on melanoma cell adhesion to biodegradable poly(l-lactic acid) microspheres coated with hydroxyapatite.

We have measured the interaction forces between a murine melanoma cell and a poly(l-lactic acid) (PLLA) microsphere coated with/without hydroxyapatite (HAp) nanoparticles (i.e., an HAp/PLLA or a bare PLLA microsphere) in a serum-free culture medium, using atomic force microscopy (AFM) with colloid probe technique, in order to investigate how the HAp-nanoparticle coating as well as interfacial serum proteins influence the cell-microsphere adhesion. The cell adhesion force of the HAp/PLLA microspheres was 1.4-fold stronger than that of the bare PLLA microspheres. When the microspheres were pretreated with a culture medium supplemented with 10% fetal bovine serum, the cell adhesion force of the HAp/PLLA microspheres was increased by a factor of 2.1; in contrast, no change was observed in the cell adhesion force of the bare PLLA microspheres before/after the pretreatment. Indeed, the cell adhesion force of the HAp/PLLA was 2.8-fold larger than that of the bare PLLA after the pretreatment. Additionally, we have investigated the effect of interfacial serum proteins on the zeta potentials of these microspheres. On the basis of the obtained results, possible mechanism of cell adhesion to the HAp/PLLA and bare PLLA microspheres in the presence/absence of the interfacial serum proteins is discussed.

Adhesion of melanoma cells to the surfaces of microspheres studied by atomic force microscopy.

It is of fundamental importance to understand the mechanism of adhesion between a mammalian cell and a material surface. In the present study, we have used atomic force microscopy (AFM) to measure the interaction forces between the murine melanoma cells and the single polystyrene microspheres of different surface chemistries in serum-free culture media: the unmodified hydrophobic polystyrene (bare/PS) and the carboxyl-modified polystyrene (COOH/PS). The cell-microsphere interaction forces have been also measured in the culture media containing the free Arg-Gly-Asp (RGD) peptides as an integrin inhibitor. In the absence of free RGD peptides, the adhesion force for COOH/PS was larger than that for bare/PS. The adhesion force for COOH/PS decreased with increasing the concentration of free RGD peptides added in the culture media and then became almost constant at the RGD concentrations larger than 0.5 mg/mL, whereas that for bare/PS remained very small regardless of the RGD concentration. In addition, the effects of the microsphere diameter and the contact time on the adhesion forces were investigated. On the basis of the AFM results, possible mechanism of cell-microsphere adhesion will be discussed.

Implicit solvent model simulations of surfactant self-assembly in aqueous solutions.

The behaviors of the cationic surfactants of n-decyltrimethylammonium chloride (C(10)TAC) in water have been studied by the molecular dynamics (MD) simulations using the implicit solvent model proposed in our previous report (J. Chem. Theory Comput. 2007, 3, 1163). The MD simulations of 343 C(10)TAC surfactants in water at the surfactant concentrations of 5-100 mM have been performed for 25 ns, where the surfactant monomers at the initial configurations are uniformly dispersed. As a result, it was found that the C(10)TAC surfactants exist as monomers or oligomers at 5-15 mM, whereas they self-assemble to form surfactant aggregates at 30-100 mM. The growth and the breakup of these surfactant aggregates were repeatedly observed during the 25 ns simulations. The size distributions and the free monomer concentrations indicate that the critical micelle concentration of C(10)TAC surfactant in water represented by the ISM-3 lies between 15 and 30 mM, which fairly agrees with the experimental values of 50-65 mM.

Assembly of gold nanoparticles into microwire networks induced by drying liquid bridges.

Large interconnected gold wire structures ( approximately cm;{2}) of different topologies have been made by the drying of a gold nanoparticle suspension that has formed a connected network of liquid bridges in the interstices between a 2D crystalline layer of latex particles and a substrate. Slow evaporation of the suspending medium assembles the nanoparticles into a periodic or disordered conducting network of micrometer thick gold wires on the substrate. The presence of surfactants in the suspension is critical to maintaining the stability of the liquid bridge network during the evaporation process.

Revised Implicit Solvent Model for the Simulation of Surfactants in Aqueous Solutions. 2. Modeling of Charged Headgroups at Oil-Water Interface.

The revised implicit solvent model (ISM-2) for the simulation of cationic surfactants in water was proposed in the previous study (J. Phys. Chem. B 2005, 109, 11762): no water molecules of the solvent are explicitly treated, and their effects are incorporated using the solvent-averaged interactions between the surfactant segments in water, where the interactions between the hydrocarbon sites of the surfactants are allowed to vary depending on their surroundings. In the present study, the representation of a charged headgroup at the liquid-liquid interface between the hydrocarbon oil and the implicit water has been improved, where the free energy change due to the transfer of the charged headgroup across the interface is taken into account. The present model (ISM-3) has been applied to the molecular dynamics simulations of (i) the single preformed micelle of 30 n-decyltrimethylammonium chloride (C10TAC) cationic surfactants in water and (ii) 343 C10TAC surfactants uniformly dispersed in water, where the corresponding systems are also simulated using the ISM-2 for comparison. The first simulations showed that the ISM-3 as well as the ISM-2 is applicable to the simulation of the preformed micelle of the average aggregate size for C10TAC. The second simulations demonstrated that the ISM-3 can represent the surfactant self-assembling plausibly, while the ISM-2 fails to do so because of the rude treatment of the charged headgroups at the interface. The results will be compared with those from experiments and atomistic model simulations.

Lateral capillary forces between solid bodies on liquid surface: a lattice Boltzmann study.

When two solid bodies are placed on the surface of a dense liquid under gravitation, they deform the liquid surface to experience a lateral capillary force between themselves that can be attractive and repulsive, depending on the wettabilities and weights of the bodies. In the present study, the lateral capillary force between two square bodies at a liquid-vapor interface has been examined using numerical simulations based on a two-dimensional two-phase lattice Boltzmann (LB) method. The particular situations were simulated, where every body was vertically constrained and had the fixed triple points at its upper or lower corners. Here, the triple point indicates the place at which vapor, liquid, and solid phases meet. The interaction force between these two bodies was calculated as a function of the separation distance, the interfacial tension, and the gravitational acceleration. The simulation results agree well with the analytical expression of the lateral capillary interaction, indicating that our LB method can reproduce the interaction force between two bodies of various wettabilities at a liquid-vapor interface in mechanical equilibrium.

Effects of cleaning procedures of silica wafers on their friction characteristics.

Silicon wafers with thermal silicon oxide layers were cleaned and hydrophilized by three different methods: (1) the remote chemical analysis (RCA) wet cleaning by use of ammonia and hydrogen peroxide mixture solutions, (2) water-vapor plasma cleaning, and (3) UV/ozone combined cleaning. All procedures were found to remove effectively organic contaminations on wafers and gave identical characteristics of the contact angle, the surface roughness and the normal force interactions, measured by atomic force microscopy (AFM). However, it is found that wafers cleaned by the RCA method have several times larger friction coefficients than those cleaned by the plasma and UV/ozone methods. The difference was explained by the atomic-scale topological difference induced during the RCA cleaning. This study reveals the lateral force microscopy as a very sensitive method to detect the microstructure of surfaces.

Revised implicit solvent model for the simulation of surfactants in aqueous solutions.

The implicit solvent model (ISM) proposed previously for the simulation of surfactant aqueous solutions, in which no water molecules of the solvent are treated explicitly, but the effects are incorporated using the solvent-averaged interactions between the surfactant segments in water at infinite dilution, has been revised to represent the surfactant aggregates more appropriately. In the revised model (ISM-2), the interactions between the hydrophobic sites of the surfactants are varied depending on their surroundings, namely, the local hydrocarbon density. The ISM-2 has been applied to the molecular dynamics simulations of (i) the single n-hexane droplets of different sizes in water and (ii) the single micelle composed of 30 n-decyltrimethylammonium chloride (C10TAC) cationic surfactants. As a result, it was found that the ISM-2 can mimic the n-hexane/water interface and represent the fluidity of the hydrocarbon interior of the surfactant micelle that the original ISM fails to do. The results will be compared to those from experiments and atomistic model simulations.