Hiroyuki Shinto

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.

Wetting-induced interaction between rigid nanoparticle and plate: A Monte Carlo study

The interaction forces between a nanosphere and a flat plate in undersaturated vapors are examined. We perform grand canonical Monte Carlo simulations, where the surfaces of the sphere and the plate are treated as rigid smooth and the vapors are modeled as a Lennard-Jones fluid of nonpolar spherical molecules. The following results are obtained: (i) The force between the sphere and plate becomes attractive at the surface distances where capillary condensation takes place in the gap between the surfaces; (ii) the onset of the attractive force becomes farther as the relative vapor pressure increases; (iii) the curve of the pull-off force (or the adhesion force) as a function of the relative vapor pressure has a peak, where the peak position shifts to a higher relative pressure and the peak height becomes smaller with decreasing the attractive interaction of the surfaces with a fluid molecule; (iv) at the relative vapor pressure where the pull-off force becomes maximum, the coverage of the surface by fluid m...

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.

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.

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.

Lattice Boltzmann study of capillary forces between cylindrical particles

Abstract —In the present study, numerical simulations based on a two-dimensional two-phase lattice Boltzmann (LB) method have been performed to examine two types of capillary forces: (i) the lateral capillary force between two horizontal cylinders of wetting and/or non-wetting surfaces trapped at a liquid—vapor interface, and (ii) the capillary bridge force between the two wetting cylinders covered with liquid films in vapor. The force—distance profiles for these two systems agree well with those from the corresponding theoretical descriptions, indicating that the present LB simulation can reproduce the capillary forces between two bodies with various wettabilities.

Fragile structured layers on surfaces detected by dynamic atomic force microscopy in aqueous electrolyte solutions

Abstract In the present study, the detailed characteristics of the layers of water molecules, ions and hydrated ions adsorbed on surfaces in NaCl solutions were investigated by introducing the dynamic method in the use of atomic force microscopy (AFM). We found the following. (1) There exist two kinds of structured layers on solid surfaces in electrolyte solutions — one is a thin, but firm primary layer in which water molecules, cations and hydrated cations are adsorbed directly on the solid surface, and the other is a thick, but fragile secondary layer outside the primary layer. (2) The thickness of the primary layer varies from 0.35 to 1.0 nm with the concentration of NaCl solution. (3) The secondary structure is detectable by introducing the dynamic method in the use of AFM, and the maximum gap at which the fragile structure starts to interact between surfaces was found to be around 4.0 nm at the maximum sensitivity of the present study.

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.

Interactions between colloidal particles in NaCl aqueous solutions: molecular dynamics simulations with an implicit solvent model

Abstract An implicit solvent model based on the potentials of mean force (PMFs) has been applied to the molecular dynamics simulations of charged macroparticle(s) immersed in NaCl aqueous solutions, where the ion concentration profiles around the macroparticle(s) and the interaction forces between two macroparticles and among three macroparticles are investigated. As a consequence, it is found that (i) the ion concentration profiles of the smaller Na+ ions near the macroparticle are in good agreement with the theoretical predictions base on the Poisson–Boltzmann equation, whereas those of the larger Cl- ions slightly deviate from the theoretical profiles, (ii) the interaction force between the unlike-charged macroparticles is more attractive than expected from the theory at a lower NaCl concentration of 0.001 M, although the force at a higher NaCl concentration of 0.1 M or the forces between the like-charged macroparticles agree with the theoretical force curves, and (iii) the threebody force among the like-charged macroparticles is less repulsive than the pairwise approximation using the two-body force at a lower NaCl concentration of 0.001 M. The present simulations demonstrate that the interactions between colloidal particles in aqueous electrolyte solutions can be computed by the implicit solvent model based on the PMFs.