This paper reports on a microelectromechanical systems (MEMS)-based sensor for pulse wave measurement. The sensor consists of an air chamber with a thin membrane and a 300-nm thick piezoresistive cantilever placed inside the chamber. When the membrane of the chamber is in contact with the skin above a vessel of a subject, the pulse wave of the subject causes the membrane to deform, leading to a change in the chamber pressure. This pressure change results in bending of the cantilever and change in the resistance of the cantilever, hence the pulse wave of the subject can be measured by monitoring the resistance of the cantilever. In this paper, we report the sensor design and fabrication, and demonstrate the measurement of the pulse wave using the fabricated sensor. Finally, measurement of the pulse wave velocity (PWV) is demonstrated by simultaneously measuring pulse waves at two points using the two fabricated sensor devices. Furthermore, the effect of breath holding on PWV is investigated. We showed that the proposed sensor can be used to continuously measure the PWV for each pulse, which indicates the possibility of using the sensor for continuous blood pressure measurement.

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.

This paper reports on a method to measure a spring constant on site using a micro electro mechanical systems (MEMS) force and displacement sensor. The proposed sensor consists of a force-sensing cantilever and a displacement-sensing cantilever. Each cantilever is composed of two beams with a piezoresistor on the sidewall for measuring the in-plane lateral directional force and displacement. The force resolution and displacement resolution of the fabricated sensor were less than 0.8 µ N and 0.1 µ m, respectively. We measured the spring constants of two types of hydrogel microparticles to demonstrate the effectiveness of the proposed sensor, with values of approximately 4.3 N m ⁻¹ and 15.1 N m ⁻¹ obtained. The results indicated that the proposed sensor is effective for on-site spring constant measurement.

It is expected that human iPS cell-derived cardiomyocytes (hiPSC-CMs) can be used to treat serious heart diseases. However, the properties and functions of human adult cardiomyocytes and hiPSC-CMs, including cell maturation, differ. In this study, we focused on the temperature dependence of hiPSC-CMs by integrating the temperature regulation system into our sensor platform, which can directly and quantitatively measure their mechanical motion. We measured the beating frequency of hiPSC-CMs at different environmental temperatures and found that the beating frequency increased as the temperature increased. Although the rate at which the beating frequency increased with temperature varied, the temperature at which the beating stopped was relatively stable at approximately 20 °C. The stopping of beating at this temperature was stable, even in immature hiPSC-CMs, and was considered to be a primitive property of cardiomyocytes.

We propose a measurement method with a feedback system to evaluate the contraction forces of human iPS cell-derived cardiomyocytes (hiPSC-CMs) in a dynamic mechanical environment. The measurement of the hiPSC-CM contraction forces is important for regenerative medicine; however, conventional methods are not able to evaluate these forces when the cells are subjected to a dynamic load similar to that from the heart. The proposed measurement system is composed of a micromachined piezoresistive cantilever attached to a feedback-controlled piezo stage and a micromachined movable plate where cells are cultured. A high sampling rate (2 kHz) and real-time control of the cell length were realized via the feedback-controlled piezo stage, while the contraction forces were measured by the cantilever. We evaluated the contraction forces of hiPSC-CMs in conditions of isometric and auxotonic contractions. Due to feedback-controlled loading for isometric contraction, the cell shrinkage was controlled to be less than 200 nm. Auxotonic contraction forces of 3.9 μN were measured without feedback control, while the contraction forces of isometric contraction were 6.0 μN with feedback-controlled loading. The results showed that the method leads to a work-loop evaluation of the hiPSC-CM cardiac cycle.

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.