Patterning cellular motility using an electrochemical technique and a geometrically confined environment

We describe herein a method for controlling the pattern of permissible cell migration and proliferation on a substrate in time and space. Using this method, a confluent monolayer of cells that is confined within a defined region is released into a neighboring region. Incorporated into the method is an electrochemical technique that uses a scanning microelectrode to draw regions on the surface of the system that thereafter can support cell migration and growth. The supporting glass substrate is patterned with regions of 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer that are not affected by the electrochemical treatment and also robustly resist cellular overgrowth as well as regions that can be individually switched when electrochemically treated from cell repellent to cell adhering. It is therefore possible to strictly define the areas into which cells can migrate. We found that HeLa cells migrate more rapidly as the width of cell-adhering lanes increases until a width of ca. 50 microm is reached, at which point the migration rate is roughly constant. We also designed a drug assay using our cell migration technique. The technique allows for cell migration only into defined region(s) and therefore may become an important tool for evaluating the biological activity of potential drugs because drug activity and cell motility often directly correlate.     

Immobilization and enzymatic activity of glucose oxidase on polystyrene surface modified with ozone aeration and UV irradiation in distilled water and/or aqueous ammonia solution

Adsorption condition and enzymatic activity of glucose oxidase (GOD) on polystyrene (PS) film surfaces modified with ozone aeration and UV irradiation (O3/UV) treatment were investigated. The total amount of GOD immobilized on the PS film modified with the O3/UV treatment in distilled water (PS-W film) was approximately twice as large as that on the film treated in an aqueous ammonia solution (PS-A film), whereas the specific activity of GOD on the PS-A film was four times higher than that on the PS-W film. In contrast, no enzymatic activity of GOD on the non-treated PS film was observed because of irreversible denaturation of the adsorbed GOD. We therefore conclude that the PS films modified by the O3/UV treatment in the aqueous media are effective in immobilizing GOD.     

Improving dispersion of nanometer-size diamond particles by acoustic cavitation

A novel acoustic-dispersion method for fine diamond particles was developed. Two samples of nanometer-sized diamond particles were used. They had primary particle sizes of 5 nm (ND5) and 150 nm (ND150). Disaggregation of agglomerated particles using ultrasound and surface modification of ND5 and ND150 were investigated. The ND5 and ND150 particles aggregated to secondary particles, having sizes on the order of micrometers. The surfaces of ND5 and ND150 particle were modified due to chemical reactions and the particles were disaggregated by acoustic cavitation. The ND5 particles were disaggregated to give an average particle size of about 100 nm by ultrasound exposure with average acoustic intensities higher than 800 W/m(2). The agglomerated ND150 particles with size of 15 microm were disaggregated to reach an average particle size of about 300 nm by ultrasound exposure with an average acoustic intensity higher than 2000 W/m(2). The surfaces of ND5 and ND150 particles were found to be modified with hydroxyl groups resulting from acoustic cavitation. This could lead to a well dispersed solution of nanometer-sized diamond particles in water.     

Nanoscale volcanoes: accretion of matter at ion-sculpted nanopores

We demonstrate the formation of nanoscale volcano-like structures induced by ion-beam irradiation of nanoscale pores in freestanding silicon nitride membranes. Accreted matter is delivered to the volcanoes from micrometer distances along the surface. Volcano formation accompanies nanopore shrinking and depends on geometrical factors and the presence of a conducting layer on the membrane's back surface. We argue that surface electric fields play an important role in accounting for the experimental observations.     

Experimental demonstration of the time reversal Aharonov-Casher effect

We demonstrate the time reversal Aharonov-Casher (AC) effect in small arrays of mesoscopic semiconductor rings. By using an electrostatic gate we can control the spin precession rate and follow the AC phase over several interference periods. We show that we control the precession rate in two different gate voltage ranges; in the lower range the gate voltage dependence is strong and linear and in the higher range the dependence in almost an order of magnitude weaker. We also see the second harmonic of the AC interference, oscillating with half the period. We finally map the AC phase to the spin-orbit interaction parameter alpha and find it is consistent with Shubnikov-de Haas analysis.     

Electrical properties and deep traps spectra in undoped M-plane GaN films prepared by standard MOCVD and by selective lateral overgrowth

Electrical properties, deep traps spectra and structural performance were studied for m-GaN films grown on m-SiC substrates by standard metalorganic chemical vapor deposition (MOCVD) and by MOCVD with lateral overgrowth (ELO) or sidewall lateral overgrowth (SELO). Standard MOCVD m-GaN films with a very high dislocation density over 10⁹ cm⁻² are semi-insulating n-type with the Fermi level pinned near E_c−0.7 eV when grown at high V/III ratio. For lower V/III they become more highly conducting, with the electrical properties still dominated by a high density (∼10¹⁶ cm⁻³) of E_c−0.6 eV electron traps. Lateral overgrowth that reduces the dislocation density by several orders of magnitude results in a marked increase in the uncompensated shallow donor density (∼10¹⁵ cm⁻³) and a substantial decrease of the density of major electron traps at E_c−0.25 and E_c−0.6 eV (down to about 10¹⁴ cm⁻³). Possible explanations are briefly discussed.     

A simulation-based study on longitudinal gust response of flexible flapping wings

Winged animals such as insects are capable of flying and surviving in an unsteady and unpredictable aerial environment. They generate and control aerodynamic forces by flapping their flexible wings. While the dynamic shape changes of their flapping wings are known to enhance the efficiency of their flight, they can also affect the stability of a flapping wing flyer under unpredictable disturbances by responding to the sudden changes of aerodynamic forces on the wing. In order to test the hypothesis, the gust response of flexible flapping wings is investigated numerically with a specific focus on the passive maintenance of aerodynamic forces by the wing flexibility. The computational model is based on a dynamic flight simulator that can incorporate the realistic morphology, the kinematics, the structural dynamics, the aerodynamics and the fluid–structure interactions of a hovering hawkmoth. The longitudinal gusts are imposed against the tethered model of a hovering hawkmoth with flexible flapping wings. It is found that the aerodynamic forces on the flapping wings are affected by the gust, because of the increase or decrease in relative wingtip velocity or kinematic angle of attack. The passive shape change of flexible wings can, however, reduce the changes in the magnitude and direction of aerodynamic forces by the gusts from various directions, except for the downward gust. Such adaptive response of the flexible structure to stabilise the attitude can be classified into the mechanical feedback, which works passively with minimal delay, and is of great importance to the design of bio-inspired flapping wings for micro-air vehicles.     

Sodium Ion Batteries using Ionic Liquids as Electrolytes

Sodium ion batteries have been developed using ionic liquids as electrolytes. Sodium is superior to lithium as a raw material for mass production of large‐scale batteries for energy storage due to its abundance and even distribution across the earth. Ionic liquids are non‐volatile and non‐flammable, which improved the safety of the batteries remarkably. In addition, operation temperatures were extended to higher values, improving the performance of the batteries by facilitating the reaction at the electrode and mass transfer. Binary systems of sodium and quaternary ammonium salts, such as 1‐ethyl‐3‐methylimidazolium and N‐methyl‐N‐propylpyrrolidinium bis(fluorosulfonyl)amide, were employed as electrolytes for sodium ion batteries. A series of positive and negative electrode materials were examined to be combined with these ionic liquid electrolytes. A 27 Ah full cell was fabricated employing sodium chromite (NaCrO₂) and hard carbon as positive and negative electrode materials, respectively. The gravimetric energy density obtained for the battery was 75 Wh kg^?1 and its volumetric energy density was 125 Wh L^?1. The capacity retention after 500 cycles was 87 %. Further improvement of the cell performance and energy density is expected on development of suitable electrode materials and optimization of the cell design.     

Substitution of Secondary Benzylic Phosphates with Diarylmethyl Anions

Substitution of diethyl and diphenyl benzylic phosphates, Alk-CH(Ar¹)OP(O)(OR)₂ (R = Et, Ph; Alk = Me, Et, i-Pr; Ar¹ = aryl), with the anions derived from Ar²CH₂ (Ph₂CH₂,9H-xanthene and fluorene) and n-BuLi at –15 °C was studied. For phosphates with Me as an Alk, diethyl phosphates produced Me-CH(Ar¹)CH(Ar²)₂ (Ar¹ = 4-halo-, 4-CN, 4-Me-, 2-Me, 2-Br-, 3-MeO-phenyl and 2-naphthyl). However, an unwanted substitution at the Et group competed with phosphates of Alk = Et- and i-Pr. Fortunately, the corresponding diphenyl phosphates cleanly underwent the desired substitution. Two enantioenriched phosphates, MeCH(Ph)OP(O)(OEt)₂ and EtCH(Ph)OP(O)(OPh)₂, proceeded with complete inversion of the stereochemistry.     

Preparation of spherical and uniform-sized ferrite nanoparticles with diameters between 50 and 150 nm for biomedical applications

Spherical uniform-sized iron ferrite nanoparticles were synthesized by adding a disaccharide and seed ferrite crystals into an aqueous reaction solution. The average size range 50-150 nm was controlled by choosing one out of five disaccharides and by changing the amount of the seed crystals. The particles had a saturation magnetization and a crystalline structure which are similar to those of intermediate Fe₃O₄-γ-Fe₂O₃. When coated with citrate, the particles with nearly 100 nm diameter were stably suspended in water for 2 days. These novel particles will be utilized as magnetic carriers in biomedical applications.