Kenta Kuwana

Probing the mechanical architecture of the vertebrate meiotic spindle

Accurate chromosome segregation during meiosis depends on the assembly of a microtubule-based spindle of proper shape and size. Current models for spindle-size control focus on reaction diffusion–based chemical regulation and balance in activities of motor proteins. Although several molecular perturbations have been used to test these models, controlled mechanical perturbations have not been possible. Here we report a piezoresistive dual cantilever–based system to test models for spindle-size control and examine the mechanical features, such as deformability and stiffness, of the vertebrate meiotic spindle. We found that meiotic spindles prepared in Xenopus laevis egg extracts were viscoelastic and recovered their original shape in response to small compression. Larger compression resulted in plastic deformation, but the spindle adapted to this change, establishing a stable mechanical architecture at different sizes. The technique we describe here may also be useful for examining the micromechanics of other cellular organelles.

Mechanical impulses can control metaphase progression in a mammalian cell.

Chromosome segregation machinery is controlled by mechanochemical regulation. Tension in a mitotic spindle, which is balanced by molecular motors and polymerization-depolymerization dynamics of microtubules, is thought to be essential for determining the timing of chromosome segregation after the establishment of the kinetochore-microtubule attachments. It is not known, however, whether and how applied mechanical forces modulate the tension balance and chemically affect the molecular processes involved in chromosome segregation. Here we found that a mechanical impulse externally applied to mitotic HeLa cells alters the balance of forces within the mitotic spindle. We identified two distinct mitotic responses to the applied mechanical force that either facilitate or delay anaphase onset, depending on the direction of force and the extent of cell compression. An external mechanical impulse that physically increases tension within the mitotic spindle accelerates anaphase onset, and this is attributed to the facilitation of physical cleavage of sister chromatid cohesion. On the other hand, a decrease in tension activates the spindle assembly checkpoint, which impedes the degradation of mitotic proteins and delays the timing of chromosome segregation. Thus, the external mechanical force acts as a crucial regulator for metaphase progression, modulating the internal force balance and thereby triggering specific mechanochemical cellular reactions.

A Standing Micro Coil for a High Resolution MRI

This paper reports on a standing micro coil as a receiver for a high resolution MRI (Magnetic Resonance Imaging). A standing micro coil was fabricated by post release folding process. Our coil standing in free space had uniform sensitive area and high sensitivity. We demonstrated that a 12×12×1000 ¿m3 resolution image of pine needles was taken by using the standing micro coil.

Augmented reality system for oral surgery using 3d auto stereoscopic visualization

We present an augmented reality system for oral and maxillofacial surgery in this paper. Instead of being displayed on a separated screen, three-dimensional (3D) virtual presentations of osseous structures and soft tissues are projected onto the patients body, providing surgeons with exact knowledge of depth information of high risk tissues inside the bone. We employ a 3D integral imaging technique which produce motion parallax in both horizontal and vertical direction over a wide viewing area in this study. In addition, surgeons are able to check the progress of the operation in real-time through an intuitive 3D based interface which is content-rich, hardware accelerated. These features prevent surgeons from penetrating into high risk areas and thus help improve the quality of the operation. Operational tasks such as hole drilling, screw fixation were performed using our system and showed an overall positional error of less than 1 mm. Feasibility of our system was also verified with a human volunteer experiment.

A grasping forceps with a triaxial MEMS tactile sensor for quantification of stresses on organs

This paper reports on a grasping forceps with a triaxial Micro Electro Mechanical Systems (MEMS) tactile sensor on a tip. The laparoscopic surgery is minimally invasive because the incisions are smaller than the open surgery. This results in fast recovery. However, it is a problem in the laparoscopic surgery to damage an organ by localized stress generated by grasping with a thin forceps. To avoid excessive stress applying to the organ, real time evaluation of the stress is important. However, there is no acceptable tool to measure the stress. We propose a grasping forceps with a triaxial MEMS tactile sensor on a tip for a measurement tool. We attached a triaxial MEMS tactile sensor which we have developed on a tip of a grasping forceps. The MEMS sensor can measure not only the pressure but also two directional shear stresses applied to the sensor surface. The sensor size is 7 mm × 7 mm × 2 mm. It is enough small to attach the sensor to the tip of a forceps 12 mm in diameter. In this paper, the characteristics of the forceps with the MEMS sensor during grasping, pushing and pulling actions were evaluated. In these experiments, output of each sensor for pressure and shear stress was proportional to the applied stresses, respectively. Moreover, as an in vivo experiment, we measured the shear stress applied to a pig liver block when it is lifted after being grasped with the forceps. We obtained that the shear stress applied to the liver block increased with the increase of the weight of the liver block.

3D airflow velocity vector sensor

In this paper, we propose a sensor for measuring the three-dimensional (3D) velocity vector of airflows. The sensor, which was a 10 mm spherical figure, had a laminated structure with three channels fabricated inside. The components of the airflow velocity vector were measured respectively by three piezo-resistive cantilevers fabricated in each of the three channels. Experiments with a wind tunnel demonstrated that our sensor can measure not only the velocity amplitude but the 3D velocity direction as well.

Developing essential rigid-flexible outer sheath to enable novel multi-piercing surgery

We have developed a new generation device called rigid-flexible outer sheath with multi-piercing surgery (MPS) to solve the issues of tissue closure, triangulation, and platform stability in natural orifice transluminal endoscopic surgery (NOTES), and the problems of restricted visual field, organ damage, and removing a resected organ from body in needlescopic surgery (NS). The shape of the flexible outer sheath can be selectively locked by a novel pneumatic shapelocking mechanism. Major features include four directional flexion at the distal end, four working channels, and suction and water jet functions. The insertion part of the prototype is 330 mm long with a 25 mm maximum outer diameter. The outer sheath system has successfully preformed in vivo experiment using a swine on partial gastrectomy. The advanced outer sheath system has shown great promise for solving NOTES and NS issues.

Nonmetallic rigid-flexible outer sheath with pneumatic shapelocking mechanism and double curvature structure

Single port access (SPA) surgery is a laparoscopic procedure using only one transumbilical-placed port. Natural orifice transluminal endoscopic surgery (NOTES) offers the possibility of surgery without visible scars. To address the access and stability problems in SPA and NOTES, we developed a device called rigid-flexible outer sheath. This sheath can be switched between flexible and rigid modes by a novel pneumatic shapelocking mechanism, and it has a double curvature structure that enables it to flex in four directions at the distal end and three directions on the rigid-flexible shaft. The insertion part of the prototype is 300 mm long with a 20 mm outer diameter, and the part is equipped with four working channels. In vivo experiments using a swine show that the outer sheath has high potential for solving access and stability problems. We expect that the outer sheath will be useful for SPA and NOTES.

Photodiode with micro texture for improving sensitivity at large angle of incidence for particle sensors

This paper reports on a photodiode (PD) with micro texture for miniaturizing particle sensors. We proposed an optical system for a small particle-sensor without focus lenses. The system requires a PD which is high sensitive at large angle of incidence. The micro texture was fabricated on a surface of the PD to achieve the required property. The micro texture was an array of columnar-like structures that had a part of inverse-tapered shape. The all surface of the structures was n-type doped layer. Experimental results show that the sensitivity of the PD with micro texture increased with an increase in the incident angle. Furthermore, we demonstrated that the proposed optical system using the PD detected light scattered from smoke of an incense stick. Hence, the PD is suitable for realizing small particle-sensors.

Implantable telemetry capsule for monitoring arterial oxygen saturation and heartbeat

In this study, we have developed an implantable telemetry capsule for monitoring heartbeat. The capsule has three main functions, monitoring vital signs, transmitting the vital signs, and receiving energy for driving the capsule without wires. We used two wavelengths of LEDs and a photodiode sensitive to the two wavelengths for heartbeat sensor. The arterial oxygen saturation is calculated from the amplitude of the heartbeat signal. We fabricated an FM transmitter whose carrier frequency was 80 MHz. Though the GHz range frequency is generally used in transmission, the attenuation in the human body is large. The size of a common linear antenna is about a quarter of its operating wavelength. We employed a coil-based antenna which can reduce size below the quarter of the wavelength. We fabricated a miniaturized transmitter with the coil-based antenna at lower frequency. Our capsule was driven intermittently. We used a rechargeable battery. When the battery ran down, the battery was charged by wireless using the induced electromotive force. This means that the capsule is capable of monitoring vital signs over the long term. We measured the heartbeat from the middle finger of hand in a water tank as a model of a human body.