Proceedings of the 2006 IEEE International Conference on Robotics and Automation
Orlando, Florida - May 2006
Organized Motion Control of a lot of
Microorganisms Using Visual Feedback
Kiyonori Takahashi*
Naoko Ogawa and Hiromasa Oku
*Graduate School of Information Science
Tohoku University
Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan
Email: [email protected]
Graduate School of Information Science and Technology
the University of Tokyo
7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Email: Naoko [email protected]
Hiromasa [email protected]
Koichi Hashimoto*
Email: [email protected]
Abstract— We propose a novel method to control a lot of microorganisms by using visual feedback for micro-robotic application. Our goal is to control a cluster of microorganisms as microscale smart robots for various applications, since microorganisms
have efficient actuators and accurate sensors. Compared with
single-cell level actuation methods proposed before, this method
has the following advantages: (1) A cluster of microorganisms can
cancel stochastic perturbations of behavior by taking the average;
(2) A cluster of microorganisms can be more powerful than a
single microorganism, and thus it can perform a variety of tasks.
A visual feedback system is constructed to control cells using
galvanotaxis (response to the electric field). Experimental results
show the feasibility of visual feedback control of a paramecium
cell cluster. In addition, Micro-manipulation of small objects by
the cell cluster is also demonstrated.
I. I NTRODUCTION
Recently, much effort has been devoted to development of
technologies for micro-robots or MEMS [1]. One of the major
problems to make them is how to miniaturize devices such as
sensors, actuators or battery packs. In addition, many microrobotic applications in the field of biotechnology require the
system to work in liquids, which makes the miniaturization
problem harder.
To overcome these difficulties, a concept of utilizing a
microorganism cell as a living micro-robot has been proposed [2], [5], [6]. Microorganisms have accurate sensors and
efficient actuators required for realizing smart micro-robots. In
addition, most of microorganisms have an orienting response
to the external stimulus, which is called “taxis.” For example,
paramecium cells, a kind of protozoa, go toward the cathode
in a given electric field, which is called galvanotaxis. By
utilizing such phenomena, we can control cell motions. Hence,
a microorganism is expected to be utilized as a micro-robot
and perform a variety of micro-robotic tasks such as delivery
of liquid, manipulation of small mechanical parts and sensing
of environment (Fig. 1).
In previous works, several micro-robotic tasks such as
rotation of a micro impeller by using a paramecium were
demonstrated [3], [4], [5]. Trapping of a cell within a small
region by high-speed visual tracking was also achieved [6].
0-7803-9505-0/06/$20.00 ©2006 IEEE
Micro-Delivery
Microsensors
Cont
nttrol
Me
easurement
surem
sure
!
!
Fig. 1.
Concept of utilizing microorganisms as smart micro-robots.
In order to improve control accuracy, a dynamics model of
paramecium galvanotaxis has been proposed [7]. In these
works, authors utilized a paramecium as a stand-alone microrobot. The method using a paramecium has the following
problems. First, the performance achieved by a single microorganism is not high, which leads to the limitation in
micro-robotic application. Moreover, stochastic perturbations
of the cell behavior cause considerable variation in cell motion
patterns, which make control of a paramecium hard.
To solve these problems, we propose a visual feedback
control method of a cluster of paramecia. A cluster of
paramecia can be more powerful than a paramecium. Hence,
they can manipulate a large object which a paramecium can
not move. In addition, a cluster of paramecia can cancel
stochastic perturbations of behavior by taking the average. A
Feedback control of paramecia is required to achieve a variety
of tasks with high performance. Vision sensors are suitable
among various sensors for measuring of positions of a cluster
for feedback. Actuation of a cluster of paramecia is a key
technology for realization of our goal. In particular, noncontact
and noninvasive methods are desirable. One possible technique
is to utilize galvanotaxis of paramecia.
This paper is organized as follows. In section II we first
show that motion control of a cluster of paramecia by galvanotaxis is possible. The experiment indicate that a cluster
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TABLE I
C OMPONENTS OF THE SYSTEM .
component
CCD camera
macro-lens
D/A converter
image processing module
LED light
computer
anode
cathode
a
specification
PULNiX, TM-7EX
Edmund Optics, 1× InfiniStix Video Lens
Interface, PCI-3329
HICOS, IP7500EB
KEYENCE, CA-DLR
SAMUSNG
b
image Processing Module
CCD camera
Fig. 2. (a)Paramecia swimming freely without electric field. (b)Paramecia
swimming toward cathode along the electric field.
D/A Converter
of paramecia can be regarded as a a team of micro-robots.
We then explain the configuration of experimental system. In
addition we propose a visual feedback control algorithm. The
method includes a real-time measuring technique of positions
of paramecia and a actuation method of a cluster of paramecia
control of an electric field. we proposes a visual feedback
control system and a algorithm for control of a paramecium
cluster. In section III we demonstrate an experiments using
proposed visual feedback control method. In section IV we
discusses the experimental results.
II. C ONTROL METHOD OF M ICROORGANISM C LUSTER
computer
container
LED Light
Fig. 3.
System configuration.
B. Configuration of the Experimental System
In this section, we propose a novel control system and
method of control a cluster of microorganisms using visual
feedback.
A. Galvanotactic Control of Paramecia
In this study, we use galvanotaxis to control the motion of
a cluster of paramecia. Paramecium is a kind of unicellular
protozoa with an ellipsoidal shape, inhabiting freshwater. As
reported in previous works [9], [10], a paramecium in an
electric field swims toward a cathode along the electric field.
This property is called galvanotaxis. By setting the gradient of
the electric field properly, we can control the moving direction
of a cluster of paramecia.
Our aim is control of a cluster of paramecia as the same way
of a single paramecium. Fig. 2 shows a cluster of paramecia in
two different conditions. Paramecia swam in random direction
when no electric field was applied to the experimental container (Fig. 2-a). On the other hand, paramecia swam toward
cathode along the electric field when the electric field (4 V/cm)
was applied (Fig. 2-b). The results show that the condensed
paramecia sharply respond to the electric field. Thus, a motion
of a cluster of paramecia was also controlled by a electric
field. Note that too high electric field intensity would cause
an adverse effect on vitality of paramecium cells. Hence, the
maximum of applied electric field intensity is about 4 V/cm.
A configuration of the experimental system for control
of a cluster of microorganisms is shown in Fig. 3. The
system consists of a container for cells, a CCD camera, an
image processing module, a D/A converter, a LED light, and
a Computer. Specifications of the component are shown in
table I. The experimental container is illustrated in Fig. 5. It
has four electrodes which produce a two-dimensional electric
field. The electrodes are fixed on a glass slide with epoxy
adhesive. Carbon electrodes are used instead of metal ones,
because metal ion eluted by the electrolysis reaction would
cause an adverse effect on vitality of paramecium cells. The
size of the container is 4.0mm× 6.0mm, and 0.5mm in depth
which is fitted to the field of view of the CCD camera. The
CCD camera is equipped a macro-lens. Recall that proper
magnification of a lens should be chosen: high magnification
makes it harder to obtain the whole image of paramecia, while
low magnification makes it harder to distinguish the paramecia
from image noise. The image of the paramecia cluster taken
by the CCD camera is transferred to an image processing
module. The image processing result is transferred to the PC.
The PC outputs the voltage to the electrodes fixed on the
experimental container via a D/A converter according to the
image processing result. When plus and minus voltage were
applied to a pair of the electrodes, unidirectional electric field
(from anode to cathode) was produced in the container.
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Image processing module
Camera
paramecium
Image Processing
Measurement
(a)
PC
Fig. 4.
image processing window
Control
Schematic concept of visual feedback control of the cell cluster.
(b)
(c)
glass slide
carbon electrode
epoxy adhesive
electric leads
(e)
Fig. 5.
(d)
Fig. 6. Sequence of the circulation algorithm. (a) initialization (no voltage),
(b) pattern 1, (c) pattern 2, (d) pattern 3, (e) pattern 4.
Experimental container of cells.
C. Visual Feedback Control Algorithm
In the micro-robotic control of a cell cluster, visual feedback
is essential for autonomous actuations with high performance.
Fig. 4 illustrates visual feedback control framework. Here we
propose a visual feedback algorithm for controlling a cluster of
paramecia. Using this algorithm, we show that even a simple
electric field pattern, such as unidirectional one, can control a
motion of a cluster of paramecia properly.
For simplicity of implementation, only four electric field
patterns are used: 1. Up, 2. Right, 3. Down, 4. Left. These
electric field patterns are switched properly according to the
position of the cluster of paramecia to control the cluster twodimensionally. As a basic step of motion control, we tried
to circulate a cluster of paramecia in a square container. The
cluster of paramecia is circulated with the following steps.
1) Apply or switch the electrical field pattern.
2) Set a image-processing window (dashed line boxes in
Fig. 6) near the cathode.
3) Binarize the image and calculate the summation of pixel
intensities, denoted as S.
4) When S ≥ Sth , we assume that a cluster of paramecia
has moved to cathode, where Sth is a threshold value.
5) Go to step 1.
If all paramecia moved to the image processing region, S
is supposed to equal to N s, where s is pixel intensities of a
single cell and N is the number of cells, under the ideal and
simple condition. In reality, however, a few paramecia do not
respond to electric stimulus because of individual variability in
each cell. In addition, overlap of the paramecia images reduces
the whole pixel intensities. For these reasons, S becomes
smaller than N s in the actual experiment. Hence, the threshold
value Sth was set as between 0.4N s and 0.6N s in this paper.
N s was estimated in advance from the image in the initial
condition without the electric field.
The algorithm realizes simple control of the cluster. By
combination of its elements as the bases, it can be applied
to more complicated patterns of control.
III. E XPERIMENT
We demonstrated the feasibility of the proposed visual
feedback control method of a cluster of microorganisms by
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the following three experiments. First, the “manual” motion
control of a cluster of paramecia is carried out. Secondly,
visual feedback control of the cluster’s motion is demonstrated.
At the last, micro-manipulation of an object by the cluster is
shown as an application of our method.
A. Manual Control of a Cluster of Paramecia
In this section, in order to show the feasibility of motion
control of a cluster of microorganisms, we first demonstrate
the “manual” motion control of a cluster of paramecia. The
purpose of this experiment is two-dimensional motion control
of a cluster number of paramecia.
The system described in Fig. 3 was used for the experiment
in this section. Image processing and visual feedback control
mentioned above was not used here. The electric stimulus was
controlled manually.
Concentrated paramecia were contained in the experimental
container illustrated in Fig. 5. When plus and minus voltages
were applied to a pair of the electrodes, unidirectional electric
field (from the anode to the cathode) was produced in the
container. The direction of the electric field was switched
by 90degree clockwise in every 10 sec. The gradient of the
applied electric field was set to 4V/cm. By changing the
gradient of the electric field, we tried to make a cluster of
paramecia circulate along the inner side of the experimental
container.
The result of the experiment is shown in Fig. 7. Arrows in
the figure indicate the direction of a cathode. Fig. 7 shows
that most of the paramecia moved to the cathode along the
electric field. A few paramecia did not gather near the cathode;
it is considered that they did not respond to the electric
field because of the individuality existing universally in living
organisms. However the number of such cells was small and
they can be ignored.
This experiment showed that motion of a cluster of microorganisms can be controlled by the electric field.
electric field
b
d
c
Fig. 7. Motion control of a cluster of paramecia. The arrows in the figures
indicate the gradient of the electrical field.
micro sphere
21s
t=0s
d
a
B. Visual Feedback Control of a Cluster of Paramecia
In order to verify effectiveness of the proposed visual
feedback method, we demonstrate the motion control of a
cluster of paramecia using proposed method.
We performed a circulation experiment described in Section
III-B. The procedure of the experiment was similar to the
previous section III-B. Applied electric field was 4V/cm.
The result is shown in Fig 8. Fig. 8 shows that we could
circulate a cluster of paramecia along the wall of the container
as expected. The cycle of circulation was about 18.5 sec on
an average, where one cycle is defined as the sequence from
Fig. 6-b to Fig. 6-e.
This experiment verified that the proposed algorithm is
effective for the motion control of a cluster of paramecia via
visual feedback.
C. Micro-manipulation by Visual Feedback Control
As a micro-robotic application of visual feedback control of
a cell cluster, a micro-manipulation experiment using the visual feedback system is carried out. The aim of this experiment
a
electric field
15s
3s
b
e
24s
9s
c
f
Fig. 8. Sequential movie frames illustrating visual feedback control of a
cluster of paramecia for the motion control. Arrows indicate the gradient of
electric field. (A micro-sphere in frames is used for micro-manipulation in
the next section.)
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0.40
micro-sphere
17s
X position [mm]
electric field
before
after
134s
a
b
0.35
0.30
0.25
Fig. 9. Feedback control of a cluster of paramecia for micro-manipulation
of a micro-sphere. (a) A photograph of a cluster of paramecia transporting a
micro-sphere, while arrows indicate the gradient of electric field. (b) Positions
of the micro-sphere before and after the manipulations.
0
20
40
60
80
100
120
140
160
0
20
40
60
80
100
120
140
160
1.5
We proposed a novel method to control a cluster of
microorganisms by using visual feedback for micro-robotic
application. A visual feedback system was constructed to
control cells using galvanotaxis. Experimental results showed
the feasibility of visual feedback control of a Paramecium cell
cluster. Micro-manipulation of small objects by the cell cluster
was also demonstrated. It is expected that the proposed method
will be applicable for various micro-robotic tasks in the future.
IV. D ISCUSSION
R EFERENCES
These experimental results showed that we could control
the motion of a cluster of paramecia using visual feedback,
which supports the validity of the proposed method. The task
demonstrated in this paper is basic and essential element for
micro-robots. It is expected that the proposed method will be
applicable for various micro-robotic tasks in the future.
On the other hand, there are some problems.First, the
accuracy of the micro-manipulation was not so high in this
experiment. Our aim in this experiment was transport the
[1] R. S. Muller, “MEMS: Quo Vadis in Century XXI?,” Microelectronic
Engineering, vol. 53, pp. 47-54, 2000.
[2] R. S. Fearing, “Control of a Micro-Organism as a Prototype MicroRobot,” in 2nd Int. Symp. on Micromachines and Human Sciences.,
vol. 12, no. 9, pp. 1149-1155, 1991.
[3] A. F, “Motion control of protozoa for micro manipulator,” in Proc. Int.
Conf. New Frontiers in Biomechanical Engineering, pp. 22-228, 1997.
[4] A. Itoh, “Application of protozoa’s Alano-taxis for bio micro electro
mechanical system,” in Proc. 3rd World Congr. Biomechanics, p. 313,
1998.
[5] A. Itoh, “Motion Control of Protozoa for Bio MEMS,” IEEE/ASME Trans.
Mechatronics, vol. 5, no. 2, pp. 181-188, 2000.
Y position [mm]
is (1) the visual feedback control of a cluster of paramecia
and (2) transportation of a micro object in x direction using a
cluster of paramecia.
There is one problem in micromanipulation; when paramecia collide with a obstacle, they tend to escape from it. Because
of this escape behavior, continuous and smooth transport of
the object is difficult. Hence, manipulations in a little-by-little
manner by hitting a cluster on the object repeatedly several
times are needed. In order to repeat collisions, circulation of a
cluster of paramecia in the container is effective. We applied
the circulation method to this manipulation task.
One manipulation cycle consists of two phases: (1) Manipulation phase and (2) Return phase. In phase (1), a cluster of
paramecia collide to an object and tries to manipulate it. In
phase (2), a cloister of paramecia returns to the initial position
of actuation phase by circulation. A cluster of paramecia
iterate these two phases by circulating in the container.
The object manipulated in this experiment was a polystyrene
micro sphere (the specific gravity was 1.05g/cm3, the diameter was 200μm). Applied electric field was set to 4 V/cm.
Fig. 9 shows a cluster of paramecia transporting a microsphere. The Arrow in the figure indicates the gradient electric
field. Paramecia collided with the object several times and
succeeded to transport the object. One cycle of circulation
was about 18.5sec on an average.
The X and Y positions of the object are shown in Fig. 10,
perspectively. Dashed lines indicate the start of the manipulation phase. In the every manipulation phase, the object moved
little-by-little. The object was transported along the distance
about 500μm through 7 cycles.
1.0
0.5
0
time [sec]
Fig. 10. X, Y position of the object during manipulation. Dashed vertical
lines indicate the start times of each manipulation phase.
object in only x direction. Hence, applied electric field was
unidirectional in x direction. However, in Fig. 10, the object
position varied slightly also in y direction. More accurate
position control method is to be investigated. Secondly, the
circulation algorithm takes a long time, 18.5sec for a circulation. Hence, we need to improve time efficiency.
V. C ONCLUSION
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[6] N. Ogawa, H. Oku, K. Hashimoto and M. Ishikawa, “Microrobiotic Visual
Control of Motile Cells using High-Speed Tracking System,” IEEE Trans.
Robotics, Vol. 21, No. 4, pp. 704-712, Aug. 2005.
[7] N. Ogawa, H. Oku, K. Hashimoto and M. Ishikawa, “Dynamics Model of
Paramecium Galvanotaxis for Microbiotic Application,” Proc. IEEE Int.
Conf. Robotics and Automation (ICRA 2005), pp. 1258-1263, 2005.
[8] A. Itoh, W. Tamura, T. Mishima, “Motion Control of Euglena Group by
Weak Laser Scanning System and Object Manipulation Using Euglena
Group,” IEEE/ASME Int. Conf. Advanced Intelligent Mechanics, 2005.
[9] A. M. Roberts, “Motion of Paramecium in Static Electric and Magnetic
Fields,” J. Theor. Biol., pp. 107-155, 1970.
[10] Y. Naitoh, Behavior of Protozoa-Its Control Mechanism. Univ. Tokyo
Press, 1990.
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