Takashi Mineta

Three-axis capacitive accelerometer with uniform axial sensitivities

A three-axis capacitive accelerometer which has uniform sensitivities to three axes was developed using a micromachining technique. This sensor has a seismic mass whose center of gravity is raised above suspending beams so that longitudinal and lateral accelerations can be detected by parallel shift and tilt of a seismic mass, respectively. Uniform axial sensitivities without cross axis sensitivity could be realized by a three-dimensional sensor structure.

Small diameter hydraulic active bending catheter using laser processed super elastic alloy and silicone rubber tube

Small diameter active bending catheter which is actuated by hydraulic suction mechanism for intravascular minimally invasive diagnosis and therapy has been developed. The catheter is made of a Ti-Ni super elastic alloy (SEA) tube which is processed by laser micromachining and a silicone rubber tube which covers the outside of the SEA tube. The processed SEA tube consists of a line of rings connected with meandering beams. The active catheter is filled with water and its bending angle is controlled from outside the body by suction of the water. The tip of the silicone rubber tube functions as a valve and closes by initial suction of the water, and the catheter is bent by subsequent suction. External diameter of the fabricated bending active catheter is 0.94 mm and the internal diameter is 0.85 mm. Inner space of the catheter functions as a working channel for insertion medical tools and fluids. The active catheter is effective for insertion in branch of blood vessel which diverse in acute angle which is difficult to proceed, and selective embolization of arteries for treatments tumors. The bending mechanism can be used safely in blood vessel because of its simple structure and materials which is assessed for medical use.

Electrochemical etching of a shape memory alloy using new electrolyte solutions

In this paper we present the electrochemical etching characteristics of a shape memory alloy (SMA) using new electrolytes of inorganic salt in alcohol, in comparison with conventional H2SO4–methanol solution. It has become apparent that pattern etching of SMA sheets can be carried out in electrolyte solutions using LiCl and NH4Cl. Especially, in the case of 1 mol l−1 LiCl–ethanol, good etching properties such as a controllable low etch rate of about 3.5 µm min−1, high etch factor (etching depth/side etching width) of 1.5, uniform etching depth and smooth etched surface can be obtained. Throughout etching can be carried out by using a back-side dummy metal of Ni or Cu. This etching technique has been applied to the micromachining of SMA sheet for fabrication of microactuators.

Minimally invasive diagnostics and treatment using micro/nano machining

Several medical tools with various functions have been developed for minimally invasive diagnostics and treatment. Microfabrication techniques such as MEMS technology are useful for the realization of high‐performance multifunctional minimally invasive medical tools with small sizes. An ultra‐miniature pressure sensor and an intravascular ultrasonic forward‐viewing imager have been developed as microsensors for use in the human body. Active bending catheters have been developed for steering catheter tips without using traction of wires from outside the body. An ultrasonic therapeutic tool for sonodynamic therapy and sonoporation, and a micro scanner for precise laser treatment have been developed as therapeutic tools for use in the human body. High‐functionalized endoscopic tools and catheters will enable more precise and safe diagnostics and therapy, as well as novel diagnostics and treatment which have been impossible to date.

A wet abrasive blasting process for smooth micromachining of glass by ductile-mode removal

This paper describes the ductile removal behavior of a Pyrex glass substrate in a wet blasting process with an aqueous fine abrasive slurry of 4 µm Al2O3 particles in water. Glass was removed in a ductile cutting mode when the blasting was carried out with low applied pressure or with a long nozzle distance. Although the removal rate in the ductile mode was much lower than with brittle-mode blasting, a smooth surface within a roughness of 50 nm Ra was obtained. Using ductile-mode blasting, a micro groove with a smooth surface (roughness <50 nm Ra) was successfully obtained. The profile of the micro groove was U-shaped, in contrast to the V-shaped profile obtained with conventional brittle-mode blasting. Ductile-mode blasting was also used for surface finishing after a rough pre-blasting process. The roughness of the pre-blasted surface was reduced from 200 nm Ra to about 100 nm Ra by the finishing process.

Mechanical characterization and insertion performance of hollow microneedle array for cell surgery

In order to implement cell surgery on a chip-based system, we have been developing microneedle arrays capable of introducing desired biomolecules (nucleic acids, proteins, etc.) into living cells and the parallel extracting biomolecules expressed in the cells. An array of hollow silicon dioxide (SiO 2 ) microneedles with a sharp tip radius of less than 0.5 µm was successfully fabricated by using a micromachining technique. In order to investigate the mechanical stability of fabricated microneedle arrays, insertion tests with a gelatin as an artificial cell were performed. The results indicated that the microneedles are expected to be sufficiently stiff to insert into living cells without fracture. In addition, bending behavior was characterized by both finite element method (FEM) analysis and experimental fracture test. Needle insertion performance into gelatin was also evaluated. The displacement required for needle insertion increased linearly with an increase in surface area at the needle tip, resulting in the relative value of estimated insertion stresses being approximately constant. Moreover, the results showed that the mechanical oscillation with an amplitude of 0.6 µm was effective and that increasing oscillation frequency decreased remarkably the displacement probably due to an increase in the viscous resistance of a viscoelastic material.

Active catheter, active guide wire and related sensor systems

Active catheters and active guide wires which move like a snake utilizing distributed shape memory alloy actuators have been developed for catheter-based minimally invasive diagnosis and therapy. Active catheters and guide wires can have bending, torsional and extending mechanisms. Communication and control IC chips in the active catheter reduce the number of lead wires for control. An ultra miniature fiber-optic pressure sensor, a forward-looking ultrasonic probe and a magnetic position and orientation sensor have been developed for multifunctional catheters and multifunctional guide wires. These moving mechanisms and several sensors, which are equipped near the tip of the catheter and guide wire can provide detail information near the tip and enable doctors to perform delicate and effective catheter intervention.

Biochemical and atomic force microscopic characterization of salmon nasal cartilage proteoglycan

Biological activities of salmon nasal cartilage proteoglycan fractions are known, however, structural information is lacking. Recently, the major proteoglycan of this cartilage was identified as aggrecan. In this study, global molecular images and glycosaminoglycan structure of salmon nasal cartilage aggrecan purified from 4M guanidine hydrochloride extract were analyzed using HPLCs and atomic force microscopy with bovine tracheal cartilage aggrecan as a control. The estimated numbers of sulfates per disaccharide unit of chondroitin sulfate chains of salmon and bovine aggrecans were similar (approximately 0.85). However, the disaccharide composition showed a higher proportion of chondroitin 6-sulfate units in salmon aggrecan, 60%, compared to 40% in bovine. Gel filtration HPLC and monosaccharide analysis showed the salmon aggrecan had a lower number (approximately one-third), but 1.5-3.3 times longer chondroitin sulfate chains than the bovine aggrecan. Atomic force microscopic molecular images of aggrecan supported the images predicted by biochemical analyses.

Batch fabricated flat winding shape memory alloy actuator for active catheter

Batch fabrication process of a shape memory alloy (SMA) sheet based on electrochemical pulsed etching with a sacrificial dummy metal layer has been studied and flat winding S-shape SMA actuators have been developed. The actuators are 38 /spl mu/m in thickness and generated forces from 40 to 95 mN were obtained according to the width from 410 to 170 /spl mu/m. The flat winding SMA actuator could realize active catheter with small outer diameter and wide inner working channel. The batch fabrication process was also applied to micromachining of NiTi super elastic alloy (SEA) for biasing spring of the catheter.

Shape Memory Thin Film for Blood Vessel Holding Actuator of Thrombus Detector

For the purpose of an application for a blood vessel holding actuator of thrombus detector, evaporation technique and film properties of TiNiCu ternary shape memory alloy (SMA) thin film was studied. The SMA thin film was formed on a sacrificial Cu substrate by using a flash evaporation technique, with which very small TiNiCu alloy pellets were evaporated repeatedly. With this evaporation technique, phase transformation temperature of the deposited thin film can be controlled by deposition timing after the each pellet starts to vaporize. When the interval time before the deposition was 0s, the deposited thin film became a super elastic alloy (SEA), which starts to deform below the human body temperature of 37°C. On the other hand, when the interval time was 1s or longer, the deposited thin film shows a shape recovery temperature of about 60°C. Fracture strength of the thin film was obtained at least 170MPa, that corresponds to a fracture force of 570mN for holding actuator of 0.6mm in width and 6µm in thickness. Although the SEA film was fragile, the SMA film at the interval time of 5s was flexible enough to be bendable to small radius of 0.15mm.