Study on a Cuff Microelectrode using MEMS Technology
Shoji Takeuchi, Associate Professor, Institute of Industrial Science, The University of Tokyo
1. Introduction
This study aims at developing a cuff microelectrode capable of easily
being fixed to nerve cords having micro-sized diameters. While nerve
regeneration type and insertion type microelectrodes have been proposed,minimally invasive electrodes that do not cut or pierce the nerve are needed
for measuring electric potentials during activity. Therefore, in this study, weincorporated a shape memory alloy (SMA) thin film microactuator in anelectrode and attempted to attach the electrode to a nerve by electricallycontrolling the fixing operations. We proposed a 3D shape memory
technique required at this time to develop a microcuff structure.
2. Fabricating Microelectrodes
A TiNi-based shape memory alloy was formed in a thin film to serve as
the electrode structure. We fabricated a clipping mechanism (Fig. 1) that
actively grips the nerve when driven by an electric current. Conventional
TiNi thin films have lower responsiveness than other actuators due to thedifficulty in raising their Martensite transformation temperatures because
they are severely deformed at room temperature. By modifying thecomposition of the thin film and conditions of thermal treatment, we wereable to raise the transformation temperatures to obtain a thin film that wasMartensite at room temperature. Therefore, rather than allowing theclipping mechanism to be used repeatedly, we gave the mechanism
unidirectionality, so that once clipped it could not be removed. This enabled
us to manufacture a SMA thin film clipping mechanism that avoids theproblem of responsiveness, normally a shortcoming in SMA actuators, hasgreat elasticity at room temperature, and takes full advantage of its strength
in high output.
3. Evaluating Electrode Properties
We recorded neural activity using the fabricated electrode. The 3D
clipping mechanism was fixed to the ventral nerve cord of an insect withoutcausing injury. It was also determined that heating had no effect on thenerve. Based on the measurements, no problems-and particularly no noisewere observed in the waveform of activity compared to those of normal
electrodes (Fig. 2). Since the structure is highly elastic, the body tissue ofthe insect incurred no damage even when the mechanism collided with thetissue. It was also seen that neural activity could be measured while theinsect was active, without the electrode coming loose.
4. Conclusion
The smaller the nerve to be treated, the more difficult it is to position theelectrode near to or in contact with the nerve. It is impossible to record clear
signals when an electrode has poor contact with the nerve. Electrodes using
SMA thin films can easily perform this operation and remain fixed to the nerve
even when the insect is active.

Fig. 1 (a) The fabricated SMA thin film microelectrode(b) the electrode clipped to a 100-µm wire

Fig. 2 Neural activity measured from the ventral nerve cord of an insect using thefabricated electrode

Study on Heart-Emulating Microactuators Using Self-Oscillating Gel
Ryo Yoshida, Associate Professor, Graduate School of Engineering, The University of Tokyo
1. Introduction
We developed a novel self-oscillating gel that, under fixed conditions, iscapable of oscillating autonomously in a spontaneous rhythm like a heartbeat,as opposed to the conventional stimuli-responsive gels. Through a molecular
design that converts chemical energy into mechanical energy by inducing theBelousov-Zhabotinsky reaction (BZ reaction) with a cyclic reaction circuit in
the gel, also found in a chemical model of a metabolic response (TCA cycle),
we demonstrated that the gel is made to periodically swell and deswell. This
self-oscillating gel can conceivably enable the design of new materials capableof imitating biological functions, such as microactuators capable ofautonomous periodic motion, self-beating (peristaltic) micropumps,
molecular pacemakers, and information transfer elements. With the aim ofdeveloping new micromachines equipped with these functions, weestablished a technology for developing micro-size self-oscillating gel,analyzed the behavior of the oscillations, and conducted a basic study on
constructing a material system.
2. Manufacturing microactuators (artificial cilia) through gel
micromachining
We attempted two methods of micromachining self-oscillating gel. In thefirst method, shown in Fig. 1, we introduced a photocrosslinked section(phenyl azide group) into a polymer chain and micromachined the gel to adesired shape through photolithography using a photomask. The othermethod was performed according to a cutting-edge 3D micromachining
technique (LIGA, moving mask X-ray lithography) using synchrotron
radiation. In the latter method, we produced artificial cilia in the gel surface.
The cilia comprised hundreds of protrusions of several ten to several hundred
microns in size that were arranged in an array (Fig. 2). When effecting achemical reaction wave in the gel, we observed periodic changes in thesurface protrusions accompanying the wave propagation. This technique canconceivably be applied to a micro-transport system, for example, fortransporting minute particles, cells, and the like added to the surface.
3. Conclusion
We designed and constructed a gel with a novel functionality for
oscillating in a spontaneous rhythm like a heart muscle. This gel is of greatinterest for use as a microdevice element because of its ability to produce arhythmical periodic motion and to transmit this rhythm as data. This maylead to the development of a novel material system having such functions asrhythmical motion, mass transport, and data conversion and transfer.

Fig. 1 Gel micromachining through photolithography

Fig. 2 Ciliary motion actuator formed of gel through LIGA

3