The uptake of nanoparticles (NPs) into biological cells with rigid cell walls is poorly understood. Interestingly, the authors demonstrated that positively charged polystyrene NPs were taken into yeast cells in the physiological saline. However, the polystyrene NPs are not suitable for carrier NPs due to their low biodegradability. In this study, we evaluated the uptake of biodegradable poly(lactic-co-glycolic) acids (PLGA) NPs into the yeast cells. As a result, PLGA NPs were taken into yeast cells regardless of their surface potentials. The yeast cells were alive after the uptake of negatively charged NPs, whereas the cell viability for the positively charged NPs was low. In addition, the experiments using endocytosis inhibitors suggested that the uptake of PLGA NPs was different from the conventional endocytosis. These experimental results strongly suggested that the negatively charged PLGA NPs are suitable for the delivery of useful substances to eukaryotic cells with cell walls.

Monolayer films composed of ordered particle arrays exhibit unique optical properties, which lead to various potential applications like sensors and antireflective coatings. In this study, we investigated particle deposition processes by using a drag coating technique based on convective self-assembly. Unlike micron-sized particles, 300-nm particles formed submonolayers instead of monolayers. Hence, we modified the technique and demonstrated that reversed dragging, introduction of a film blade, and periodic change in deposition speed dramatically improved the particle deposition process to cover the entire substrate surface uniformly with a monolayer of ordered particle arrays. Furthermore, our modified drag coating process produced monolayers of particles with different sizes of 570, 120, 45, and 27 nm. Thus, our technique is simple and versatile, and is applicable to a wide particle size ranging from microns to tens of nanometers.

Computational fluid dynamics has been increasingly adopted as a promising tool to understand the essential dynamics of particulate flow. The present review gives a brief description of numerical methods to describe the boundary condition of moving solid surface at lattice Boltzmann method (LBM), including bounce-back (BB) method (and improved BB method), immersed boundary (IB) method, and smoothed profile (SP) method. It is essential to choose an appropriate numerical method according to the target system. Among these methods, the author and coworkers have used the SP method to efficiently simulate flows including a number of particles. Here, typical results obtained by the SP-LBM simulations are presented.

Preparation of boehmite-silica composite particles using heterocoagulation was studied to improve the packing ratio and flowability of the particles used as fillers and flame retardants in resins. By measuring the zeta potential of each particle, silica showed a negative charge at pH > 2, and boehmite showed a positive charge at pH < 9. Therefore, mixing of each suspension of silica and boehmite prepared at pH 4 successfully produced boehmite-silica composite particles by heterocoagulation. We used two different silica particle sizes. Using smaller silica particles, composite particles uniformly coated with silica were obtained. The composite particles showed excellent fluidity in liquid paraffin, which suggested improved packing ratio.

Magnetorheological Fluids (MRF) whose apparent viscosity is controllable by applying magnetic fields are known as a kind of functional fluids. It is generally considered that such viscosity changes are caused by the formation of chain-like clusters of magnetic particles dispersed in the fluid. Many researches have been conducted to understand the mechanism of the viscosity change of MRF but there are few report which directly indicate the relation between the cluster formation and the viscosity change because of the difficulty of the observation such phenomena simultaneously. In this study, the relation between particle clustering and viscosity change has been investigated using DEM-DNS simulation. The simulations are conducted just a few chain-like clusters of magnetic particles in simple shear flow and the simulation results indicate that the apparent viscosity corresponds to both of the chain length and the angle between magnetic field direction and chain axis which depend on the Mason number.