Study of Novel Micropolymer Actuator Powered by Enzymatic Reactions of Biomolecules
Kazuhiko Ishihara, Professor, Department of Materials Engineering, School of Engineering,
The University of Tokyo
1. Introduction

deswelled in this system. Hence, we achieved a polymer actuator capable ofsupplying chemical energy using the energy source of glucose was achieved.

The central issue in how to achieve autonomous operation ofmicromachines in a living organism is how to supply the energy thatdrives the micromachines. In such an extremely small environment,
there is no space to allocate for a battery or the like, nor is it possible
to supply energy from an external source. In this study, chemical
substances existing in the living organism were employed as polymer
actuators by varying their concentrations. The idea is to produce
mechanical energy from the chemical substance, a process very similar
to the mechanism that living system use to produce energy.

20100Fig. 1 Dependence of the volume of a cross-linked MPC polymer gel on alcoholcomposition Ethanol composition (from left): 0, 20, 40, 60, 80, and 100%

2. Developing a Polymer Gel that Responds to Alcohol
Phospholipid bilayers forming biomembranes have a thickness of 50 nm.
Though they are extremely thin, they have many functions. Polymers with aphospholipid polar group in the side chain, 2-methacrylooyloxyethyl
phosphorylcholine (MPC) polymers, show excellent properties as a new
biomaterial. Further, it was discovered to control the volume of the polymer
reversibly through changes in concentration based on the peculiar solvation
effect of a phospholipid polar group (Fig. 1). The polymer was repeatedlyswelled and deswelled by increasing and decreasing the alcohol concentration(Fig. 2). This indicates that it is possible to manipulate the volume of a bioresponsive polymer gel by causing a reaction with components in an MPC
polymer gel to selectively fix enzymes that generate alcohol.

Percentageof volume 1.0
change0.8

Swelling

0.6
0.4
Deswelling

0.2
0.0

3. Enzymatic Reactions Produced by Alcohol andthe Swelling Function of Gel

51015
No. of repetitions
O=It was attempted to generate movement in an MPC polymer gel bycombining enzymatic reactions using alcohol compounds that exist in thebody. Using an EMP cycle, it was generated ethanol with pyruvic aciddecarboxylase and alcohol deyhdrogenase using pyruvic acid generated fromglucose as the initial substance. It was confirmed that the MPC polymer gel

0CH3+
COOCH2CH2OPOCH2CH- 2N (CH3)3O

20
Phospholipid
polar group variedby solvation

Fig. 2 Reversible volume changes of a cross-linked MPC polymer gel in an
aqueous solution of pure water and 60% ethanol solution

Catheter Tip Position Sensing System Using MI Sensor
Yoichi Haga, Research Associate, Graduate School of Engineering, Tohoku University
1. Introduction

3. Conclusion

Minimally invasive examinations and treatments are performed byinserting a small instrument, such as an endoscope or catheter (a polymer
tube having a diameter of about 0.3-3 mm) into the patient's body. Whilefluoroscopy is currently employed to determine the position of the catheter
tip, this method provides only two-dimensional data, which makes fordifficult determinations, and moreover produces inadequate image
resolution. The capacity to determine the position and attitude (directionin which the tip is pointing) of the catheter tip three-dimensionally and inreal time will benefit catheter navigation.
A practical tip position detecting system that employs micro-coils has
already been developed. However, we are striving to develop a highperformance 3-axis micro-sensor that can be mounted on a catheter using
micro-magnetic vector sensors. These sensors are based on a new principleof the magneto-impedance effect. The system detects exchange magnetic
field emitted by an external coil and geomagnetism using three sensors
mounted on the tip of the catheter, as shown in Fig. 1.

If we liken this sensor system to a car navigation system, the catheter
tip corresponds to the car and the blood vessels to roads. By making thissystem practical, it is expected that minimally invasive therapy will becomesafer and more reliable, enabling us to perform examinations and treatment
not possible before. Applying the system to an endoscope is also anticipated.
3-axis MI sensor

Catheter

Patient
Computerx
3D
angiogramzy

Data of 3D
angiogramCatheter

Excitation coil
Signal processor

2. Developing a 3-axis MI Sensor System
In this sensor, a coil generating a bias magnetic field was wound aroundan amorphous wire having a diameter of 30µm. The sensor generates a
voltage between the ends of the wire that varies according to the strength ofthe magnetic field. Three of the sensors were arranged orthogonally to one
another in a 2-mm square column and achieved a positional resolution lessthan 1 mm and an angular resolution of about 1 degree at the point ofposition and attitude measurement. In order to combine the positions
detected by the three sensors precisely, the sensors were mounted on apolymer which has an electrode patterns, as shown in Fig. 2.
To present 3-dimensional position and attitude data to the doctor, one
could obtain and store three-dimensional blood vessel images in a computer
prior to operation using contrast medium CT or the like and superimpose thethree-dimensional position and attitude of the catheter tip onto the blood vessel
images displayed on the screen. The current display system is configured of athree-dimensional blood vessel model image in a computer, as shown in Fig. 3.
Measurement signals are input into the computer while calculations areperformed to display superimposed position and attitude data in real time.

Fig. 1 A catheter tip position/attitude sensor system
MI Sensor

throughhole

MI Sensor

electrode
1mm

Fig. 2 3-axis micromagnetic sensor

3Fig. 3 Catheter tip position /attitude display system