Figure 1: Conceptual image of proposed system

ULTRA-HIGH-SPEED ROBOT HAND AND EYE FOR INVESTIGATION OF MICROORGANISMS IN A CHIP

T. Kawahara1*, M. Sugita1, M. Hagiwara1, Y. Yamanishi1,2, and F. Arai1,3

1Nagoya University, JAPAN,2PRESTO, JST, JAPAN, and

3Seoul National University, KOREA

ABSTRACTIn this paper, we propose a novel high-speed microrobotic system toward swimming-microorganism capturing and sens-

ing in a microfluidic chip. This system consists of high-speed on-chip microrobots as robotic hands with a maximum speed of 10 Hz to handle a microorganism and a high-speed on-line vision sensor as a robotic eye with maximum speed of 2000 frames/s to track the trajectory of microorganisms/microrobots. The performance of microrobot a and vision sensor is con-firmed through basic experiments. Finally, we succeeded in on-chip separating, capturing, stimulation and evaluation of mi-croorganisms by using the developed high-speed robotic system.

KEYWORDS: On-chip robotics, Magnetically driven microtool (MMT), On-line high-speed vision sensor, Microorganisms

INTRODUCTIONIn the biomedical field, mechanical stimulation to a single cell is highly required to figure out function and mechanical

property of cells. Especially, in terms of neurology and bio-fuel technology, this approach is very useful for understanding the mechanism of aquatic microorganisms. However, conventional cell manipulation was carried out manually or by using micromanipulators. Therefore, throughput and repeatability of investigation were very low.

To deal with this issue, there have been many works that have developed micro-nano-robots based on MEMS/NEMS technology to measure specific characteristics of single cell [1][2]. These robots, however, did not have enough force to push 100 um size microorganisms, even though the speed of robots is larger than 10 mm/s. Furthermore, after microorgan-ism stimulation, precise observation of cell or microorganism with chemical reactions under the no-disturbance environment is highly required. Therefore, in order to evaluate the relationship between stimulation and response of microorganism, on-chip measurement is required to maintain a stable experimental condition.

Recently, investigation of motile microorganisms is also highly required, because it has large proportion of aquatic mi-croorganisms. Conventionally, high-speed vision sensor (high-speed camera) which capable of 10,000 Hz order image re-cording have been used to observe the high-speed behavior of microorganisms [3]. However, since the volume of image da-ta is too large, it is difficult to perform the image processing in real-time. This means that we cannot use this sensor for robotic feedback system. On the other hand, high-speed on-line vision sensor have been used for real-time observation of microorganisms. Especially, Ogawa et al. developed the high-speed tracking system which is composed of the on-line high-speed vision sensor and the XY motorized stage [4]. By utilizing the electrotaxis of paramecium, they succeeded in the high-speed position control of paramecium. However, there are no works for capturing/sensing of swimming microorganisms by mechanical probe, because it is required both high-speed microactuator and high-speed vision sensor.

By considering these backgrounds, we newly propose an on-chip high-speed robotic capturing and sensing system, as shown in Figure 1. This system consists of high-speed on-chip microrobots as robotic hands to handle a micro-organism and a high-speed on-line vision sensor as a robotic eye to track the trajectory of microorganisms and/or microrobots.

THEORYMicrorobot (HAND): In the previous works of our group, magnetically

driven microrobot has been proposed for automation of cell manipulation [5]. The microrobot placed in the microfluidic chip is composed of magnetic mate-rial and it is actuated by the permanent magnets from the outside of the micro-fluidic chip, as shown in Figure 1. Therefore, we can manipulate the cells in the perfectly closed biochip. There are mainly three advantages of our micro-robot described as follows;

(1) Powerful: the microrobot controlled by permanent magnets can apply mN order stimulation to single microorganism, while optical tweezers and AFM are difficult to apply enough force to microorganisms which has a stiff structure.

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October 2-6, 2011, Seattle, Washington, USA

(2) High dexterity: since the microrobot has 3-DOF (degree of freedom), the microorganisms can be manipulated by mi-crorobots where they are expected to be moved.

(3) On-chip: environment of microchip gives stable conditions and less contamination during measurements. It contrib-utes to the continuous observation of response with chemical reaction of microorganisms after stimulation.

Figure 2 shows the fabricated magnetically driven microrobot which is composed of Si structure with Ni parts. Si is use-ful for both making of force sensing structure and biocompatibility. In order to add the force sensing function to the micro-robot, we design the frame shaped force sensing structure on the tip of microrobot [6], as shown in Figure 2. From the beam deformation captured by vision sensor, we can estimate the applied force. Furthermore, by introducing the layer fabrication technique, we can avoid the friction between the force sensing structure of microrobot and the substrate of the microchip (normally glass) during measurements. This sensing structure can sense the applied force with the accuracy of 10 uN order in a microfluidic chip. In addition, by using a layered structure, the thin structure of the microrobot is protected, and it iseasy to assemble the microparts to the microchip.

Figure 3 shows the 5-step fabrication process for microrobot. [STEP1] To make the spacer layer, SU-8 (PerMX3050, DuPont) was patterned on the glass substrate with the thickness of 100 um. [STEP 2] The structure of microrobot made by Si with the thickness of 200 um was fabricated by deep reactive-ion etching. [STEP 3] The Ni part to obtain magnetic force is fabricated by 2-step electroplating. [STEP 4] To make a top cover of microchip, the PDMS was molded by patterned sub-strate. [STEP 5] By bonding the Si structure and the Ni part, the microrobot was assembled. Finally, the PDMS and the glass substrate were bonded by air plasma.

Vision sensor (EYE): Normally, it is difficult to process captured images in real-time by using a high-speed camera, due to limitation of data transfer rate. In our system, the images from the camera head are transferred through 8 serial lines to the processing board which is included dual FPGA Field-Programmable Gate Array circuits. By using this specialized high-speed vision sensor, we can handle the captured images with a maximum speed of 2000 Hz at 512 x 512 pixels. Figure 4(a) shows the overview of the camera head with the dimension of 35 x 35 x 35 mm.

Figure 2: Fabricated microrobot

Figure 3: Fabrication process of the microrobot

(a) Camera head (b) 3DOF-stage (XY�)Figure 4: High-speed vision and High-speed stage

Figure 5: System architecture EXPERIMENTAL

The fabricated microrobots are placed in a microchip and it is driven by computer controlled 3-DOF stages with four ne-odymium magnets with the each diameter of 1 mm, as shown in Figure 4(b). The performance of stage is 200 nm position-ing accuracy and 400 mm/s operable velocity. Figure 5 shows the system architecture which is included the vision sensor and the 3-DOF stages to actuate the microrobots. All components of this system are controlled by a single computer.

By using the developed system, we confirm that the performance of the fabricated microrobot and the vision sensor. Fi-nally, we apply the on-chip robotic system for stimulating and evaluation of the microorganisms.

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RESULTS AND DISCUSSION Figure 6 shows the high-speed image processing of microrobot by the vision sensor. It was confirmed that the center of

gravity of microrobot was detected by vision sensor with the measurement speed of 1000 Hz order. Figure 7 shows the demonstration of combination of the developed microrobot and the high-speed vision sensor. In this experiment, the micro-robot was controlled by visual feedback control. From this result, we can see that the position of microrobot was tracked to the target position by controlling the XY-stage up to 10 Hz. Figure 8 shows the overview of application experiments by us-ing Pleurosira laevis which is one of centric diatom. We succeeded in on-chip separating, capturing, stimulation and evalua-tion of microorganisms by developed high-speed system.

Figure 6: Real-time detection of microrobot by vision sensor Figure 7: Results of the feedback control of microrobot

Figure 8: On-chip manipulation, capturing, and sensing of microorganisms (Pleurosira laevis) by developed system

CONCLUSIONWe developed the on-chip microrobotic system which is composed of the high-speed microrobot (10 Hz) and the high-

speed on-line vision (2000 Hz). Our ultra-high-speed robotic system makes a major contribution to the understanding of un-known biological mechanism of microorganisms.

ACKNOWLEDGEMENTSThis research is supported by the JSPS Grant-in-Aid for Scientific Research (23226007, 22860030), the JST-SENTAN,

and the Nagoya University Global COE program for Education and Research of Micro-Nano Mechatronics. Finally, we would like to acknowledge Prof. Ishii, Hiroshima University for his great support on vision system.

REFERENCES[1] D.R. Frutiger et al., Small, fast, and under control: wireless resonant magneticmicro-agentschip, International Journal of Robot-

ics Research, 29(5), pp. 613–636, (2010).[2] M. Ikeuchi et al., Multifunctional optically driven microrobot for realtime 3D bio-manipulation and imaging, 24th MEMS, 97,

013701, pp. 29–32, (2011). [3] Y. Hanada et al., Nano-aquarium with microfluidic structures for dynamic analysis of Cryptomonas and Phormidium fabricated

by femtosecond laser direct writing of photostructurable glass, Applied Surface Science, 255(24), pp. 9893–9897 (2009). [4] N. Ogawa et al., Microrobotic visual control of motile cells using high-speed tracking system, IEEE Transactions on Robotics,

21(4), pp. 704–712, (2005). [5] M. Hagiwara et al., On-chip magnetically actuated robot with ultrasonic vibration for single cell manipulations, Lab on a Chip,

11, pp. 2049–2054, (2011). [6] T. Kawahara et al., Micro-Aquatic-Farm: On-chip stimulation and evaluation system for microorganisms by magnetically driv-

en microtools, 16th TRANSDUCERS, 21(4), pp. 1946–1949, (2011).

CONTACT*T. Kawahara, tel: +81-52-789-5026; tkawahara@mech.nagoya-u.ac.jp

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