Satoyuki Kawano

Piezoelectric materials mimic the function of the cochlear sensory epithelium

Cochlear hair cells convert sound vibration into electrical potential, and loss of these cells diminishes auditory function. In response to mechanical stimuli, piezoelectric materials generate electricity, suggesting that they could be used in place of hair cells to create an artificial cochlear epithelium. Here, we report that a piezoelectric membrane generated electrical potentials in response to sound stimuli that were able to induce auditory brainstem responses in deafened guinea pigs, indicating its capacity to mimic basilar membrane function. In addition, sound stimuli were transmitted through the external auditory canal to a piezoelectric membrane implanted in the cochlea, inducing it to vibrate. The application of sound to the middle ear ossicle induced voltage output from the implanted piezoelectric membrane. These findings establish the fundamental principles for the development of hearing devices using piezoelectric materials, although there are many problems to be overcome before practical application.

DNA Manipulation and Separation in Sublithographic-Scale Nanowire Array

Electrokinetic manipulations of biomolecules using artificial nanostructures within microchannels have proven capability for controlling the dynamics of biomolecules. Because there is an inherent spatial size limitation to lithographic technology, especially for nanostructures with a small diameter and high aspect ratio, manipulating a single small biomolecule such as in DNA elongation before nanopore sequencing is still troublesome. Here we show the feasibility for self-assembly of a nanowire array embedded in a microchannel on a fused silica substrate as a means to manipulate the dynamics of a single long T4-DNA molecule and also separate DNA molecules. High-resolution optical microscopy measurements are used to clarify the presence of fully elongated T4-DNA molecules in the nanowire array. The spatial controllability of sublithographic-scale nanowires within microchannels offers a flexible platform not only for manipulating and separating long DNA molecules but also for integrating with other nanostructures to detect biomolecules in methods such as nanopore sequencing.

Development of coarse-graining DNA models for single-nucleotide resolution analysis

Recently, analytical techniques have been developed for detecting single-nucleotide polymorphisms in DNA sequences. Improvements of the sequence identification techniques has attracted much attention in several fields. However, there are many things that have not been clarified about DNA. In the present study, we have developed a coarse-graining DNA model with single-nucleotide resolution, in which potential functions for hydrogen bonds and the π-stack effect are taken into account. Using Langevin-dynamics simulations, several characteristics of the coarse-grained DNA have been clarified. The validity of the present model has been confirmed, compared with other experimental and computational results. In particular, the melting temperature and persistence length are in good agreement with the experimental results for a wide range of salt concentrations.

Structure and stability of water chain in a carbon nanotube

Water molecules form a single-file chain structure in a (6, 6) carbon nanotube (CNT), and this stability is different from that of water molecules confined in CNTs with larger diameters, let alone the bulk. Using the molecular dynamics (MD) method and quantum mechanical (QM) calculations, we investigate the characteristics in the context of density dependence of the collective structure and hydrogen bond behavior. The results obtained from MD show that high water density leads to substantially longer hydrogen bond lifetimes. On the other hand, the hydrogen bond lifetime does not noticeably decrease with decreasing density but remains roughly the same when the density is lower than a certain critical value. The mean molecular orientation angle of the water molecule, defined by the angle that comprises the water dipole moment and the CNT axis, is smaller for higher densities, and asymptotically approaches 33° on the low density side. Such an asymptotic nature of the structure and stability stems from non-uniform distribution of water molecules. The mean orientation angle obtained from QM calculations using density functional theory coincides with the MD result. QM analysis also suggests that the charge distribution of water in the CNT originates from the molecular configuration due to spatial confinement rather than strong electronic interaction between water and the CNT.

Effects of fluid dynamic stress on fracturing of cell-aggregated tissue during purification for islets of Langerhans transplantation

Among clinical treatments for type 1 diabetes mellitus, the transplantation of islets of Langerhans to the portal vein of the hepar is a commonly used treatment for glucose homeostasis. Islet purification using the density gradient of a solution in a centrifuge separator is required for safety and efficiency. In the purification, the number of tissues to be transplanted is reduced by removing the acinar tissue and gathering the islet from the digest of pancreas. However, the mechanical effects on the fracture of islets in the centrifuge due to fluid dynamic stress are a serious problem in the purification process. In this study, a preliminary experiment using a cylindrical rotating viscometer with a simple geometry is conducted in order to systematically clarify the effect of fluid dynamic stress on the fracture of islets. The effects of fluid dynamic stress on the islet configuration is quantitatively measured for various flow conditions, and a predictive fracture model is developed based on the experimental results. Furthermore, in the practical purification process in the COBE (Gambro BCT), which is widely used in clinical applications, we perform a numerical analysis of the fluid dynamic stress based on Navier–Stokes equations to estimate the stress conditions for islets. Using the fracture model and numerical analysis, the islet fracture characteristics using the COBE are successfully investigated. The results obtained in this study provide crucial information for the purification of islets by centrifuge in practical and clinical applications.

Wide-range frequency selectivity in an acoustic sensor fabricated using a microbeam array with non-uniform thickness

In this study, we have demonstrated the fabrication of a microbeam array (MBA) with various thicknesses and investigated the suitability it for an acoustic sensor with wide-range frequency selectivity. For this, an MBA composed of 64 beams, with thicknesses varying from 2.99–142 µm, was fabricated by using single gray-scale lithography and a thick negative photoresist. The vibration of the beams in air was measured using a laser Doppler vibrometer; the resonant frequencies of the beams were measured to be from 11.5 to 290 kHz. Lastly, the frequency range of the MBA with non-uniform thickness was 10.9 times that of the MBA with uniform thickness.

Trapping and identifying single-nanoparticles using a low-aspect-ratio nanopore

Manipulation of particles and molecules in fluid is a fundamental technology in biosensors. Here, we report electrical trapping and identification of single-nanoparticles using a low-aspect-ratio nanopore. Particle trapping and detrapping are implemented through a control of the cross-membrane electrophoretic voltage. This electrical method is found to enable placing an individual nanoparticle in vicinity of a lithographically-defined nanopore by virtue of the balance between the two counteracting factors, electrostatic and electroosmotic forces. We also demonstrate identification of trapped nanoparticles by the ionic current through the particle-pore gap space. This technique may find applications in electrode-embedded nanopore sensors.

Single-molecule measurements and dynamical simulations of protein molecules near silicon substrates

Interactions between protein molecules and inorganic substrates were studied both experimentally and numerically to obtain fundamental insight into the assembly of biomacromolecules for engineering applications. We experimentally traced individual fluorescent-labelled lysozyme (F-lysozyme) molecules, diffusing in the vicinity of interfaces between a protein solution and oxidized Si(1?0?0) and glass plates. The results indicate that diffusion coefficients of F-lysozyme molecules on both substrates are more than three orders of magnitude smaller than those in a bulk solution. The molecular dynamics simulations reveal a drastically diminished diffusion coefficient of lysozyme on the substrates of pure Si(1?1?1) and oxidized Si(1?0?0) with a hydroxy-terminated surface compared with that in bulk solution due to molecular adsorption behaviour on the substrate, which is in good agreement with experimental results. Furthermore, full atomistic description of the behaviour provides detailed information of deformation due to the adsorption process. Lysozyme on pure Si(1?1?1) undergoes substantial deformation whereas that on oxidized Si(1?0?0) does not, which indicates the importance of substrate surface condition to preserve the structure, i.e. functionality of adsorbed biomolecules.

Separation of long DNA chains using a nonuniform electric field: A numerical study

In the present study, we investigate the migration of DNA molecules through a microchannel using a series of electric traps controlled by an ac electric field. We describe the motion of DNA based on Brownian dynamics simulations of a bead-spring chain. The DNA chain captured by an electric field escapes due to thermal fluctuation. The mobility of the DNA chain was determined to depend on the chain length, the mobility of which sharply increases when the length of the chain exceeds a critical value that is strongly affected by the amplitude of the applied ac field. Thus we can optimize the separation selectivity of the channel for DNA molecules that is to be separated, without changing the structure of the channel. In addition, we present a phenomenological description for the relationship between the critical chain length and the strength of binding electric field.

The antigen–antibody unbinding process through steered molecular dynamics of a complex of an Fv fragment and lysozyme

We have investigated the antigen–antibody unbinding process using steered molecular dynamics (SMD) simulations. We focus on a complex system consisting of an Fv fragment of an antibody molecule and a lysozyme as an antigen molecule. The Fv fragment consists of a VL and VH chain. The results show that the VH chain is unbound earlier than the VL chain, which is confirmed by the ensemble average of the distance profile obtained from 40 unbinding trajectories. The use of lysozyme as an antigen molecule instead of a small hapten molecule reveals the fact that the induced fit, estimated by the deformation accompanying the unbinding process, is more noticeable for the antigen molecule than for the antibody molecule. The SMD also reveals the non-Gaussian distribution of maximum force necessary for the unbinding process.