Object Manipulation by a Formation-controlled Euglena Group

 This study investigates how to use protist group as huge group of liv-ing micromachines. Motion control of protist is made by using the orientation phototaxis of Euglena. Blue laser scanning system is made to form the group of Euglena. Euglena gather around the blue laser irradiated area. The construction of the experimental system is that blue laser passed through two galvano-scanners to make the two dimensional positioning of laser possible, concentrated by a convex lens and then irradiated into the experimental pool. After that, blue light is attenu-ated by high cut filter, and recorded by CCD camera with macro lens. Since there is little response of phototaxis of Euglena, red LED light is used for background illumination. Experimental results show that this system can make any shape of Euglena group by gathering along the scanned laser beam by their positive orientation phototaxis. If the moving speed of the laser beam is under 4jam/s, Eu-glena group can follow to the laser. The formed Euglena group can transport objects by moving its group. The maximum transportation weight force transported by the Euglena group was about 70nN. Key words. Micromachine, Micro Cyborg, MicMicro Manipulation System, Laser Scanning System and Automatic Motion Control. 1 Introduction Recently, many studies have been done to investigate the moving mechanisms of microorganisms to make use of making future micromachines. Typical examples are studies of bacterial flagellar motor. When we see the recent great results of biotechnology, however, we can find that almost all of these results are applied the real biological systems of living things, such as gene manipulation, tissue engi-neering, etc. Therefore, it is very important to investigate the applicability of bio-applied mechanical system or mechano-bio fusion system in the micro-mechanical research field. As far as the author have known, the idea of using micro organisms as living mi-cromachines are firstly seen in the paper of R. Fearing et al. (Fearing 1991). They controlled Paramecium's motion along the square shaped guide route

The author had the same idea independently with Fearing et al, and made auto-matic motion control system using negative galvano-taxis of Paramecium. They succeeded to control Paramecium automatically along the star shaped guide route. They could also rotate (|)0.5mm micro impeller by using motion controlled Para-mecium. This result showed that we can use micro organisms as micromachines (Itoh 2000). The author et al. also developed the positioning control system of the downward flow of bioconvection using Tetrahymena. They can move 20mm span seesaw re-ciprocatedly by the position controlled downward flow of bioconvection. This is an example of the shapeless actuation system using huge groups of microorganism (Itoh etal. 2001). Negative galvano-taxis was applied in all of these experiments. The taxis of mi-croorganism, however there are a lot of variety of taxis like phototaxis, magneto-taxis, thermotaxis, gravitaxis, etc. If we can apply the other taxis to control micro organisms, we can choose so many varieties of micro organisms to use. From this point of view, the author et al. also developed the motion control system for mas-tigophoran using their phototaxis (Itoh 2004). The control method is that a shadow is made in the strong intensity bright field and a Euglena can be captured into the shadow by its negative photophobic response. And the position of the Euglena can be controlled by moving the shadow. The experimental results showed that the po-sition of the Euglena can be controlled by this system. The flexibility of this sys-tem, however, is not so high. Therefore, it is necessary to modify the control sys-tem. Based on these details, a phototaxis based motion control system for Euglena was constructed by using a blue laser and galvano scanners. Motion of a huge group of Euglena was controlled and objects are manipulated by using this Euglena group. Main results are reported as follows.  

Experimental System and Specimen

The main features of laser beam are, high density distribution of energy, high di-rectivity, mono wave length light and coherency. High density energy distribution and high directivity have advantages for trying various control methods. Laser light is mono wave length, therefore, if we choose the frequency which is very ef-fective to Euglena, we can get high response rate of Euglena. Basic biological study showed that the wave length range between 460 and 500 nm is the most ef-fective for Euglena (Egans et al. 1975). It was also confirmed by the basic reac-tion experiment using LED mono wave length light. Based on these facts, the blue laser of which wave length A-=473nm (5mW output, CrystaLaser Inc. BIOL-005) was used to generate phototaxis. Red LED light (l=644nm) was used for background illumination since the light over 600nm is not affected to Euglena. Basic construction of the laser motion control system is depicted in Fig.l. Laser beam is refracted twice by the mirrors which were positioned by galvano scanners.

43 They make laser beam positioned in any place in the x-y plane of the experimental pool. Then, beam was concentrated by the convex lens and irradiated into the ex-perimental pool. After that, the beam was attenuated by a polarizing filter and a high cut filter. After attenuation, we can see the experiment by normal CCD cam-era with x200 macro lens. We cannot see the laser light during experiments. Therefore, an automatic calibration program was made to make the open-loop po-sitioning of laser beam possible. The experimental protists are typical photo-responsive mastigophora, "Euglena gracilis". The body length of euglena is about 40-50|Lim. A long flagellum is grown from the front side for a motor organ. The optical sensor of euglena is con-sidered as an eyespot and a subflagellum body, which are both located at the base of the flagellum

  Experimental System for Motion Control Experiments

Basic Reaction Properties to The Blue Laser

Reaction Beliaviors to The Fixed Laser beam

First, the reaction properties of Euglena to the fixed blue laser spot were exam-ined. Experimental pool is a shallow pool (0.13mm depth). The top of this pool is sealed by a cover glass. The experimental results showed that every Euglena reacted to the fixed laser beam. There were two types of reaction. (1) Avoiding reaction: When the laser beam was irradiated to the Euglena, the Euglena turned its swimming direction.

44 This is the typical Euglena's negative photophobic response. Fig.2 (a) depicts this motion. (2)Rotating reaction: When the laser beam was irradiated to the Euglena, the Euglena started rotating and kept rotating. Fig.2 (b) depicts this motion. This mechanism is unknown; however, the possibility of continuous avoiding reaction is very high. The positive orientation phototaxis has not seen when these re-sponses were observed. This fact seems that the observation magnification is too high and the energy density distribution is too keen to observe positive reaction. The results of avoiding reaction and rotating reaction have counter side effects. Avoiding reaction means "escape". However, rotating reaction means "capture". Therefore, it is very important to predict which reaction will be appeared. It is also important to predict the turning angle when Euglena shows avoiding reaction. Therefore, the observation results are summarized and the effect of reacting dis-tance, reacting direction and laser power were investigated.