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In the biomedical field, investigation of the mechanical characteristics of organs, tissues, cells, and molecules is quite important for understanding the unknown mechanisms of living organisms to contribute to state-of-the-art biomedical technologies (e.g., minimally invasive surgery, regeneration medicine, and drug discovery). For example, surgeons take a cue from the stiffness distribution of internal organs to judge the presence or absence of a tumor. Further, biologists have a strong desire to study a single cell to determine specific functions and mechanisms of living organisms. Based on this background, his research is focused on mechanical manipulation and sensing of living organisms of different sizes using robotics and automation technologies. In order to achieve this goal, he has developed new sensors and actuators by using newly developed techniques that have made a technical breakthrough in medical robotics and micro robotics.

Design and development of non-contact stiffness sensor for medical applications

The stiffness of environments may have to be measured for various reasons, such as a medical examination of cancer tissue, judgment of the best time for eating fruits or meat, and evaluation of the degree of completeness of compliant material in industrial products. With the aim of measuring the stiffness of objects with large deformation, he proposed a non-contact approach that would prevent damage and sanitary issues. This sensing approach, which employs fluid flow has two key advantages over a direct contact approach:

1. Since the friction between the probe and the environment is quite small when a fluid flow is used, the environment does not sustain damage easily.
2. Since the air probe is colorless and transparent, the condition of the pushed area can be observed.

After the design and sensing theory for the sensor were established for estimating the impedance parameters (stiffness, viscosity, and mass) of an object, the developed sensor was commercialized with a company in the automation field. Furthermore, the sensing theory was expanded as a “Non-contact Stiffness Imager” to measure the stiffness distribution of objects such as internal organs [IJRR 2006]. This methodology—a novel on in medical robotics—was applied to an endoscopic examination to detect a stiff area. As a result, he succeeded in detecting the difference in stiffness patterns between normal and diseased tissues by applying a water jet from the endoscope, owing to which a doctor would be able to identify the stiff area through the pseudo-stiffness pattern.

For detecting a tumor during minimally invasive surgery, he established a vibration-based non-contact sensing method by using the principle of earthquake seismology [T-MECH 2010]. The sensor can detect the stiff area on the basis of the phase shift between the input air pulse and the measured vibration, even if the measured amplitude of vibration is strongly influenced by the refraction condition of the environment. He developed the sensor head (10 mm diameter), which is small enough to be inserted into the body via small incision without any electric wiring. After he passed the performance/safety test through animal experiments and the ethical examination conducted by the committee in the Hiroshima University Hospital, he finally applied the sensor system to an actual clinical trial in vivo and succeeded in the detection of lung cancer by scanning the developed non-contact sensor.

Design and fabrication of on-chip microrobot for bio application

To subject 100-um-order living cells to manipulation and sensing with high dexterity, we need to use a special actuator. In addition, because conventional manipulation is conducted in an environment open to air owing to the large size of the manipulator, cell contamination issues arise. In contrast, cell manipulations in the confined space of a microfluidic chip have significant advantages in the field of biotechnology: low contamination, high repeatability, and high throughput ability. In particular, robots on a chip have considerable advantages over human handling of the treatment of biological cells, owing to their independence from operator skill. Based on this background, he has developed an “on-chip microrobot” made of magnetic material, which can output a force on the order of millinewtons by using permanent magnets. A magnetic field can be used to power an on-chip robot that is made of magnetic material, because the magnetic field offers the advantages of non-contact drive, low invasiveness with respect to a cell, and low production cost of the magnetic body through the Micro Electro Mechanical Systems (MEMS) fabrication techniques. The three approaches have been developed by their group to improve the poor positioning performance of the magnetic drive method [APL 2010, Lab Chip 2011, and T-RO 2011].

He designed and fabricated a force-sensing structure (5 um-wide frame structure) using MEMS techniques to measure the applied force to cells [Lab Chip 2012]. He applied the fabricated microrobots to the quantitative evaluation of the stimulation of Pleurosira laevis which is one of the centric diatoms and has an unexplained unique behavior. By using the fabricated microrobots, he succeeded in evaluating the relationship between the applied stimulation and the response of a single cell of Pleurosira laevis by a mechanical approach to the best of our knowledge, this is the first time such a result has been achieved. In the fields of biofuels and cognitive science, the microrobot has an important contribution in that it enables a quantitative evaluation of aquatic algae by mechanical stimulation, for investigating the unknown functions of a single cell.

The developed microrobot, which has high positioning accuracy, high speed, a force sensing function, as well as high power performance, is quite useful for manipulating and sensing floating single cells in a closed microfluidic chip. This technology created a great impact in the fields of robotics and automation [ICRA 2011 Best Video Award, ICRA 2012 Best Conference Paper Award], because through this technology, robotic systems can be introduced into the field of lab-on-a-chip as a new micro-factory automation technology.

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