Tomohiro Kawahara

On-chip magnetically actuated robot with ultrasonic vibration for single cell manipulations

This paper presents an innovative driving method for an on-chip robot actuated by permanent magnets in a microfluidic chip. A piezoelectric ceramic is applied to induce ultrasonic vibration to the microfluidic chip and the high-frequency vibration reduces the effective friction on the MMT significantly. As a result, we achieved 1.1 micrometre positioning accuracy of the microrobot, which is 100 times higher accuracy than without vibration. The response speed is also improved and the microrobot can be actuated with a speed of 5.5 mm s(-1) in 3 degrees of freedom. The novelty of the ultrasonic vibration appears in the output force as well. Contrary to the reduction of friction on the microrobot, the output force increased twice as much by the ultrasonic vibration. Using this high accuracy, high speed, and high power microrobot, swine oocyte manipulations are presented in a microfluidic chip.

Driving method of microtool by horizontally arranged permanent magnets for single cell manipulation

This paper presents an innovative driving method for a magnetically driven microtool to achieve precise positioning control while maintaining a high power output derived from commercialized permanent magnets. An effective driving methodology using permanent magnets, whose axes are parallel to driving direction, is applied to reduce friction force on the microtool. The positioning accuracy improves by five times and the response speed becomes ten times faster against the driving stage than in the conventional method. Furthermore, this method has been extended to two-degree-of-freedom movements, and the performance of the magnetically driven microtools is experimentally validated by oocyte manipulation.

Precise Control of Magnetically Driven Microtools for Enucleation of Oocytes in a Microfluidic Chip

This paper presents two innovative driving methodologies using a magnetically driven microtool (MMT) for precise cell manipulations and automation systems. First, magnetic analysis has been conducted to show the current MMT problem and proved that static friction makes MMT control difficult. New driving methodologies that reduce the friction on the MMT effectively are introduced, and supported by finite element analysis and experimental results. The positioning accuracy improves 3–10 times and the response speeds become 10 times faster against the driving linear stage than in the conventional drive method. Stage feedback control by PI with a disturbance observer has been also investigated in order to obtain precise positioning accuracy and this was successfully improved by 16 times as compared to the conventional drive. Using this methodology, the enucleation of oocytes is demonstrated to show the effectiveness of the method. The required force to cut a swine oocyte is also estimated by the simplified model to prove that the MMT has sufficient force. Two MMT blades made of nickel were set on the microfluidic chip with a new drive methodology and successfully achieved the enucleation process with high throughput.

On-chip single particle loading and dispensing

In this paper, on-chip particle loading and dispensing modules are presented with their results for the automation of a single particle retrieving from a microfluidic channel. Our proposed microfluidic chip has several modules. Each one of them has important functions as (a) loading micro-particles singly to main microfluidic flow by the aid of magnetically driven microtools (MMT); (b) finding particle position in a microfluidic channel by micro-capacitance sensors; (c) adjusting micro-channel height locally by pneumatic pressure valve; (d) dispensing particles out from the microfluidic chip to incubation environment. Novelty of this paper is summarized as follows: (1) Multi-photoresist combination technique for the pneumatic pressure valve; (2) Automatic on-chip particle dispensing with micro-capacitance sensors. We showed feasibility of automatic dispensing of a single polystyrene bead (about 100 µm) from the chip to atmosphere. The performances of each module (hybrid structure, sensor and dispensing parts) were evaluated individually. We succeeded in determination of the movement of micro-particles (about 50–100 µm) with the velocity of over 6 mm/sec. by the micro-capacitance sensors. The advantages of the proposed system are that composed of the reusable drive system such as xy motorized stage, pumps and a disposable microfluidic chip.

Air-flow-based single-cell dispensing system

We discuss a design and fabrication approach to increase the success rate of single-cell dispensing. Two pairs of capacitance sensors are placed in a biochip to detect the flow velocity of cells and air pressure is applied to eject cells by synchronizing the timing. A comprehensive design theory, which takes into account the back-pressure caused by the air pressure, the response time of the system, the sensor properties and the delay of the dispensing from the air pressure, is developed in order to minimize the disturbance of the system and maximize the throughput of the ejection system. Then, the system theoretically has a capability to eject 3 cells/s and the maximum flow velocity is 10 mm/s. The novelty of the system is that the biochip is disposable, which is unlike the conventional mechanical inkjet system; because the biochip is low cost and disposable this prevents contamination and means the drive system is reusable. Finally, we succeeded in automatic dispensing of a single polystyrene bead (100 μm) from a biochip to a culture well atmosphere using the developed cell ejection system with a success rate of 50%. Furthermore, we also succeeded in single swine oocyte dispensing by using the developed system.

Micro-aquatic-farm: On chip stimulation and evaluation system for microorganisms by magnetically driven microtools

In this paper, we propose micro-aquatic-farm, which mimic fluvial environment for an aquatic microorganism. The system provides ideal environment to measure and understand characteristics of the single microorganism. On-chip force sensor is fabricated by assembling layers to neglect the friction issue and it is actuated by permanent magnets, which supply mN order force to stimulate microorganisms. The displacement is magnified by designing beams on the force sensor and the sensor achieved 100 µN resolutions. We succeeded in on-chip stimulation and evaluation of Pleurosira laevis by magnetically driven microtool.

On-chip force sensing by magnetically driven microtool for measurement of stimulant property of P. laevis

In this paper, we newly propose an on-chip force sensing by using a magnetically driven microtool (MMT) equipped with a frame structure for measurement of stimulant property of Pleurosira laevis. The design and fabrication of the force sensing structure with a displacement magnification mechanism based on beam deformation is discussed. Through the basic experiments, the advantages of the proposed layer fabrication technique and the performance of the force sensor are confirmed. The basic characteristics of P. laevis are also confirmed by using the developed MMT.

Control and sensing platform of magnetically driven microtool for on-chip single cell evaluation

In this paper, we discuss a development of control and sensing platform for an on-chip single cell evaluation by magnetically driven microtool (MMT). The design and fabrication of the MMT is shown. Through the basic experiments, the advantage of the proposed platform, the performance of the position control (positioning accuracy: 30 µm), and the force sensing (sensing accuracy: 100 µN) of the MMT are confirmed.

Design and fabrication of air-flow based single particle dispensing system

In this paper, we discuss the design and fabrication approach to increase the success rate of single particle dispensing. Two pairs of capacitance sensors are placed in a biochip to detect the flow velocity of particles, and the air pressure is applied to eject particles by synchronizing the timing. Comprehensive design theory, which is taken into account of the back pressure caused by air pressure, the response time of the system, sensor property, and the delay of the dispensing from the air pressure, is developed in order to minimize the disturbance of the system and maximize the throughput of the ejection system. Then, the system has capability to eject 3 particles/sec and maximum flow velocity is 10 mm/s. The novelty of the system is that the biochip is disposable which is unlike the conventional mechanical inkjet system and it can prevent contamination. Therefore, the fabricated disposable biochip based on photolithography is low cost and the drive system is reusable. Finally, we succeed in automatic dispensing of a single particle (=100 µm) from a biochip to culture well atmosphere using developed cell ejection system with the success rate of 50 %.

Robotic-Investigators for microorganisms in a microfluidic chip

In this paper, we propose 3 degree-of-freedom dual-arm microrobot called Robotic-Investigator (RI) which enables manipulation and force sensing for microorganisms in a microfluidic chip. The untethered RI is actuated by permanent magnets. Therefore, the RI can supply mN order force to stimulate microorganisms with measuring the applied force. To develop the untethered RI with force sensing structure, the layered fabrication technique and on-chip separation mechanism are introduced. Through the basic experiment, we confirmed that the untethered RI with thin structure was developed by proposed fabrication methods without any damage to RI. We also perform the manipulation and force sensing experiment for microorganisms in a microfluidic chip by the developed RI.