Tetsuo KAN (菅 哲朗)

Abstract

Confined spaces are omnipresent in the micro-environments, including soil aggregates and intestinal crypts, yet little is known about how bacteria behave under such conditions where movement is challenging due to spatial confinement that limited effective diffusion. Stinkbug symbiont Caballeronia insecticola navigates a narrow gut passage about one micrometer in diameter to reach the stinkbug’s symbiotic organ. Here, we developed a microfluidic device mimicking the host’s sorting organ, wherein bacterial cells are confined in a quasi-one-dimensional fashion, and revealed that this bacterium wraps flagellar filaments around its cell body like a screw thread to control fluid flow and generate propulsion for smooth and directional movement in narrow passages. Physical simulations and genetic experiments revealed that hook flexibility is essential for this wrapping; increasing hook rigidity impaired both wrapping motility and infectivity. Thus, flagellar wrapping likely represents an evolutionary innovation, enabling bacteria to break through confined environments using their motility machinery.

Abstract

Piezoresistive MEMS multi-axis force sensors are widely utilized owing to their high sensitivity and compact form factor. In multi-axis sensing applications, it is essential to measure forces along each axis simultaneously while minimizing crosstalk. To achieve this, forming piezoresistive layers not only on the device surface for out-of-plane force detection but also on the sidewalls for in-plane force detection is highly effective. However, patterning piezoresistive layers on sidewalls remains technically challenging using conventional lithography-based MEMS fabrication processes, thereby increasing fabrication complexity and limiting design flexibility. In contrast, laser doping enables localized and selective formation of piezoresistive layers, offering a promising approach to overcome these limitations. In this study, we propose a piezoresistive cantilever for in-plane force measurement fabricated using liquid-immersion laser sidewall doping. The proposed process consists of two main steps: device structure formation through laser processing and sidewall piezoresistive layer formation via liquid-immersion laser doping. This approach enables direct and selective patterning of piezoresistive layers on device sidewalls. To verify the effectiveness of the proposed method, the electrical and mechanical characteristics of the fabricated sensor were evaluated. The piezoresistive layer exhibited a gauge factor exceeding 13, demonstrating sufficient performance for practical sensing applications.

Abstract

Microelectromechanical system (MEMS) sensors based on piezoresistive elements are widely used in various applications due to their high sensitivity and compact size. Traditionally, silicon‐based MEMS devices have been fabricated using lithography‐based processes, with piezoresistive layers formed through thermal diffusion or ion implantation. However, these processes involve complex fabrication workflows. In response, laser fabrication techniques, such as laser micromachining and laser annealing‐based impurity diffusion, have attracted attention. In this study, a laser‐based approach for fabricating a silicon piezoresistive cantilever using nanosecond‐pulse laser annealing is proposed. The proposed process integrates two steps: localized laser annealing for impurity doping and the formation of a partially 3D cantilever structure through laser cutting and etching. All the fabrication steps are performed using a single‐laser processing system, enabling direct‐write patterning and automatic alignment of the piezoresistive layer with the sensor structure without lithography. In this paper, the effectiveness of the proposed method is evaluated through electrical and mechanical characterizations of the fabricated sensor. The fabricated piezoresistive layer exhibits a gauge factor exceeding 15, indicating that the sensor is sufficiently effective for practical use.