Yuta Sunami

Mini Review: Nanosheet Technology towards Biomedical Application

The fabrication technique of ultrathin film (commonly known as nanosheets) has been significantly developed over the years. Due to the mechanical properties of nanosheets, such as high levels of adhesion and flexibility, this made nanosheets the ideal candidate in biomedical applications. In this review, innovative biomedical applications of nanosheets are discussed, which include, drug delivery, wound treatment, and functional nanosheets towards flexible biodevices, etc. Finally, the future outlook of nanosheet technology towards a biomedical application is discussed.

Optimum Design of Oil Lubricated Thrust Bearing for Hard Disk Drive with High Speed Spindle Motor

This paper presents the application of optimization method developed by Hashimoto to design oil lubricated thrust bearings for 2.5 inch form factor hard disk drives (HDD). The designing involves optimization of groove geometry and dimensions. Calculations are carried out to maximize the dynamic stiffness of the thrust bearing spindle motor. Static and dynamic characteristics of the modeled thrust bearing are calculated using the divergence formulation method. Results show that, by using the proposed optimization method, dynamic stiffness values can be well improved with the bearing geometries not being fixed to conventional grooves.

Vibro-Perception of Optical Bio-Inspired Fiber-Skin

In this research, based on the principle of optical interferometry, the Mach-Zehnder and Optical Phase-locked Loop (OPLL) vibro-perception systems of bio-inspired fiber-skin are designed to mimic the tactile perception of human skin. The fiber-skin is made of the optical fiber embedded in the silicone elastomer. The optical fiber is an instinctive and alternative sensor for tactile perception with high sensitivity and reliability, also low cost and susceptibility to the magnetic interference. The silicone elastomer serves as a substrate with high flexibility and biocompatibility, and the optical fiber core serves as the vibro-perception sensor to detect physical motions like tapping and sliding. According to the experimental results, the designed optical fiber-skin demonstrates the ability to detect the physical motions like tapping and sliding in both the Mach-Zehnder and OPLL vibro-perception systems. For direct contact condition, the OPLL vibro-perception system shows better performance compared with the Mach-Zehnder vibro-perception system. However, the Mach-Zehnder vibro-perception system is preferable to the OPLL system in the indirect contact experiment. In summary, the fiber-skin is validated to have light touch character and excellent repeatability, which is highly-suitable for skin-mimic sensing.

Deformation behavior of dragonfly-inspired nodus structured wing in gliding flight through experimental visualization approach

Dragonfly has excellent flight performance and maneuverability due to the complex vein structure of wing. In this research, nodus as an important structural element of the dragonfly wing is investigated through an experimental visualization approach. Three vein structures were fabricated as, open-nodus structure, closed-nodus structure (with a flex-limiter) and rigid wing. The samples were conducted in a wind tunnel with a high speed camera to visualize the deformation of wing structure in order to study the function of nodus structured wing in gliding flight. According to the experimental results, nodus has a great influence on the flexibility of the wing structure. Moreover, the closed-nodus wing (with a flex-limiter) enables the vein structure to be flexible without losing the strength and rigidity of the joint. These findings enhance the knowledge of insect-inspired nodus structured wing and facilitate the application of Micro Air Vehicle (MAV) in gliding flight.

Applications of Nanosheets in Frontier Cellular Research

Several types of nanosheets, such as graphene oxide (GO) nanosheet, molybdenum disulfide (MoS2) and poly(l-lactic acid) (PLLA) nanosheets, have been developed and applied in vitro in cellular research over the past decade. Scientists have used nanosheet properties, such as ease of modification and flexibility, to develop new cell/protein sensing/imaging techniques and achieve regulation of specific cell functions. This review is divided into three main parts based on the application being examined: nanosheets as a substrate, nanosheets as a sensitive surface, and nanosheets in regenerative medicine. Furthermore, the applications of nanosheets are discussed, with two subsections in each section, based on their effects on cells and molecules. Finally, the application prospects of nanosheets in cellular research are summarized.

Tactile Sliding Behavior of R2R Mass-Produced PLLA Nanosheet towards Biomedical Device in Skin Applications

In this research, sliding friction was measured between the fingertip and nanosheet on a silicon substrate under two conditions: dry and wet. By using a force transducer, the tactile friction force and applied load were measured. According to the experimental results, the relationship of friction force and applied load exhibits a positive correlation under both dry and wet conditions. In addition, the nanosheets are able to reduce the friction force and coefficient of friction (COF) compared to the reference sample, especially under the wet condition. Under the assumption of a full contact condition, the estimated contact area increases with larger applied loads. Furthermore, based on the wear observation, the skin sliding performance caused slight abrasions to the surface of the nanosheet samples with a mild wear track along the sliding direction. Overall, the sliding behavior between the skin and nanosheet was investigated in terms of friction force, COF, applied load, contact area, and wear. These findings can contribute to the nanosheet-related research towards biomedical devices in skin applications.

Perceptual Surgical Knife with Wavelet Denoising

Robotic surgery is a new technology in medical applications and has been undergoing rapid development. The surgical knife, essential for robotic surgery, has the ability to determine the success of an operation. In this paper, on the basis of the principle of field-effect transistors (FETs), a perceptual surgical knife is proposed to detect the electrons or electric field of the human body with distinguishable signals. In addition, it is difficult to discriminate between the motions of surgical knives from the perceptual signals that are disturbed by high-frequency Gaussian white noise. Therefore, the wavelet denoising approach is chosen to reduce the high-frequency noise. The proposed perceptual surgical knife with the wavelet denoising method has the characteristics of high sensitivity, low cost, and good repeatability.

Blood-mimicking delivery in polygonal structure of inner quadrupletip microneedle with valveless micro-pump

This paper presents a titanium quadrupletip micro-needle integrated with a micropump with different inner designs, length and diameter of the micro-channels to measure and maximize the velocity flow in the micro-needle as blood delivered into human body. Titanium is used as the material of the micro-needle which are also the common material in manufacturing of micro-needle. The advancement of micro-needle technologies is improved in penetrating human outermost skin, stratum corneum and further to human blood vessels. The micro-needles with channel inner design of circular, square, hexagon, and dodecagon with quadruple tip designs are drawn with inner diameter parameter of 150μm and 100μm with two different channel length which are 10mm and 25mm. The characteristics of blood delivery in geometrically changed inner designs affect the output velocity in microneedle when the micropump is operating. The results showed that, when it is pumped at 0.04m/s, the blood velocity improved by 5.6% than when the pump is increased by 30% of its capacity. This is due to the backflow generated in the micropump.

Effect of static electricity on static friction force between plastic film and steel roller

To establish the new technology named Roll-to-Roll Printed Electronics, which can be applied to manufacture the high functional thin film based devices such as flexible displays, batteries, and electric skins, it is needed to combine the roll-to-roll transportation system and coating technology effectively. For that purpose, one of important factors to be considered is the effect of electrostatic force on the friction characteristics between the film and roller surface. In this paper, the static friction between the plastic film (polyethylene terephthalate film) and steel roller was measured to clarify the effect of electrostatic force on the friction characteristics. The static friction was measured by pulley method while changing the film thickness, web tension, and relative humidity of ambient air. In the process it was found that both the decrease in the film thickness and increase in relative humidity of the air have an effect of an increase in the static friction coefficient in the system. Moreover, the tendency can be pronounced with the decrease in the web tension.

Study on angular displacement characteristics on topological optimum design problem of hydrodynamic thrust air bearing

The purpose of this research is to find the optimum groove geometry to enhance the stiffness against the axial and angular direction of thrust bearing simultaneously. In order to fulfill the requirement of miniaturization and thinning of many devices, the topological optimization is conducted to maximize the axial and angular stiffness of thrust air bearing. Applying the boundary fitted coordinate system and spline interpolation function make it possible to change the shape of bearing groove freely, and then the static and dynamic characteristics of the bearings are calculated numerically by using the divergence formulation method. The spring and damping coefficients against the axial and angular fluctuations are obtained by applying the assumption of the micro vibration of bearing clearance and pressure to the numerical method. Based on the numerical calculation method, topological optimization is conducted. As a result, a new groove shape having two curved portions is obtained. In case of the optimized bearing, positive pressure in the outer circumference on the bearing surface and negative pressure in the inner circumference are simultaneously generated. Comparing the maximum pressure, it was found that the optimized bearing is superior to spiral-grooved bearing. Moreover, drastically improvements in the axial and angular stiffness of the optimized bearing are shown.