Takuya Tsukagoshi

Traction force of smooth muscle cell during growth on a rigid substrate

This paper reports on the sensor for traction force measurement of a smooth muscle cell during cell growth on a rigid substrate, specially designed for horizontal and vertical directional forces. For quantitative measurement, the cells are cultured only on the sensor pads using a cover chip. The length of the sensor is 1130μm. The size of the sensor pad is 125μm×15μm×5μm (length×width× thickness). The gaps between the sensor pads are 3μm. We confirmed that the cells spread on the two sensor pads at least. We measured the traction forces of bovine aortic smooth muscle cells (BAOSMCs, CAB35405) using the proposed sensor. When the three cells spread on the pads, the measured traction forces in x and z direction increased 30nN and 20nN for 8 min, respectively.

Measuring the vibration of cells subjected to ultrasound using a MEMS-based force sensor array

This paper reports on a method to measure vibration occurring on the membrane of a mammalian cell which is subjected to ultrasound. The measurement is based on an array of piezoresistive MEMS force sensors. Experimental results with the fabricated sensors showed a change in frequency response to the ultrasound-induced vibration of NIH3T3 cells adhered to the fabricated sensor.

Depinning-Induced Capillary Wave during the Sliding of a Droplet on a Textured Surface

Surfaces covered with hydrophobic micro-/nanoscale textures can allow water droplets to slide easily because of low contact angle hysteresis. In contrast to the case of a droplet sliding on a smooth surface, when a droplet slides on a textured surface, it must recede from the textures at its rear edge and the resultant depinning events induce a capillary wave on the surface of the droplet. Although this depinning-induced capillary wave can be observed to some extent through high-speed imaging, important parameters of the wave, such as the wavelength and frequency, and the factors that determine these parameters are not fully understood. We report direct measurements of this depinning-induced capillary wave using microelectromechanical systems (MEMS)-based force sensors fabricated on a textured surface. Such sensor measurements reveal the frequency of the vibration occurring on the surface of the droplet, from which it is possible to calculate the wavelength of the capillary wave. We show that the frequency and wavelength of the depinning-induced capillary wave during the sliding of a water droplet on a micropillar array depend upon neither the size of the droplet nor its sliding velocity. However, the frequency (wavelength) decreases (increases) as the pitch of the micropillar array increases. We argue that the wavelength of the depinning-induced capillary wave is equal to the maximum length of the liquid bridges that develop at the micropillars before depinning. This hypothesis is confirmed by comparing the wavelengths obtained from the sensor measurements to the maximum liquid-bridge lengths calculated from observations using a high-speed camera.

Rigid two-axis MEMS force plate for measuring cellular traction force

Cellular traction force is one of the important factors for understanding cell behaviors, such as spreading, migration and differentiation. Cells are known to change their behavior according to the mechanical stiffness of the environment. However, the measurement of cell traction forces on a rigid environment has remained difficult. This paper reports a micro-electromechanical systems (MEMS) force plate that provides a cellular traction force measurement on a rigid substrate. Both the high force sensitivity and high stiffness of the substrate were obtained using piezoresistive sensing elements. The proposed force plate consists of a 70 µm × 15 µm × 5 µm base as the substrate for cultivating a bovine aortic smooth muscle cell, and the supporting beams with piezoresistors on the sidewall and the surface were used to measure the forces in both the horizontal and vertical directions. The spring constant and force resolution of the fabricated force plate in the horizontal direction were 0.2 N m−1 and less than 0.05 µN, respectively. The cell traction force was measured, and the traction force increased by approximately 1 µN over 30 min. These results demonstrate that the proposed force plate is applicable as an effective traction force measurement.

MEMS force and displacement sensor for measuring spring constant of hydrogel microparticles

This paper reports on a method to measure spring constant of hydrogel microparticles by a MEMS sensor. For calculating spring constant, not only force but also displacement is necessary. The MEMS sensor consists of two sidewall doped piezoresistive cantilevers in the ranges of μΝ and μm so that both parameters can be measured simultaneously. When one cantilever pushes a target to a wall, the cantilever can measure the restoring force of the target. At the same time, the other cantilever measures the displacement by pushing the wall directly. By measuring both force and displacement on the same sensor chip, the spring constant of targets can be obtained only from the sensor outputs, which makes the sensor system simple and compact. With this advantage, our method can be useful in actual experiments with microscopes and other systems.

Micropillar type three-axis force sensor for measurement of cellular force

This paper reports a three-axis force sensor that can measure cellular forces in real time with high sensitivity. The sensor features a photoresist micropillar fabricated on a flexible cross-shaped Si structure. The three dimensional forces acting on the micropillar can be detected from the resistance changes of three piezoresistors designed on the Si structure. Due to the flexibility of the Si beams, a sensing resolution on the order of several nN was obtained for both shear forces and normal force. Moreover, in our sensor design, the sensing beams are covered by a photoresist cap that prevents cells from attaching to the piezoresistors while it maintains the space for the beams and the micropillar to deform. We confirmed that our sensor can detect the normal and shear forces acting on the micropillar caused by an osteosarcoma cell during its detachment from the surrounding walls.

Compact Surface Plasmon Resonance System with Au/Si Schottky Barrier

Ethanol concentration was quantified by the use of a compact surface plasmon resonance (SPR) system, which electrically detects hot electrons via a Schottky barrier. Although it is well known that SPR can be used as bio/chemical sensors, implementation is not necessarily practical, due to the size and cost impediments associated with a system with variable wavelength or angle of incidence. However, scanning capability is not a prerequisite if the objective is to use SPR in a sensor. It is possible to build a small, inexpensive SPR sensor if the optics have no moving parts and a Schottky barrier is used for electrical current detection in place of a photodetector. This article reports on the design and performance of such a novel SPR sensor, and its application for quantifying ethanol concentration. As the concentration of ethanol is increased, the change in the angle dependence of the SPR current is observed. This change can be understood as a superposition of contributions of SPR coupled with the +3rd- and −3rd-order diffraction. Moreover, real-time monitoring of ethanol concentration was demonstrated using the proposed SPR system.

Mems force sensor array for evaluating the contractility of IPS cell-derived cardiomyocytes

We report a force sensor array that can measure iPS cell-derived cardiomyocytes (iPS-CMs) contractility with high sensitivity and high temporal resolution. The fabricated device has six piezoresistive cantilevers whose sensitivities were higher than 9.1 × 10−5 nN−1. Using the device, we measured the contraction force of an iPS-CMs layer. As a result, contractile forces ranging from 1 to 12 nN were measured.

Cantilever array for measuring traction forces of cells in a confined space

This paper reports a sensor to directly measure the traction forces generated by migrating cells in a confined space. The sensor consists of an array of miniaturized piezoresistive cantilevers which are surrounded by a pluronic-F127 pattern. The pattern allows the self-alignment and directional migration of the cells to the cantilever array as the adhesion of cells to pluronic-F127 is poor. Our method enables the quantitative evaluation of the traction forces of cells with controlled migrating direction.

Piezoresistive cantilever integrated microfluidic channel for measuring cellular properties

We propose a microfluidic device that has piezoresistive cantilever on the bottom wall of its microchannel to measure cellular mechanical property. This sensor allows us to measure force applied to the wall of microfluidic channel directly with high sensitivity and high temporal resolution. Moreover, feedback from the sensor can be used to control liquid flow above the cantilever. We demonstrate that our device is able to detect the force acting on the channel bottom wall during the passing-through of mammalian cells by the piezoresistive cantilever.