Worldwide R&D

Biomaterials System Engineering Laboratory, Department of Materials Engineering,Graduate School of Engineering, The University of Tokyo
Ryo Yoshida, Associate Professor
http://www.bmw.t.u-tokyo.ac.jp/yoshida/
The Biomaterials System Engineering Laboratory isentering its fifth year since its launch in April 2001. The
laboratory is currently staffed by three doctoral students (oneworking adult), four master’s students, three undergraduate
students, and one technical assistant.
Living organisms are perhaps the ultimate material systemcapable of transmitting data, transporting materials, andcreating motion and force through cooperation at themolecular level. Using such organisms as a model, we areattempting to artificially design and construct materials andsystems with polymer gels that can replace or imitate thefunctions of these living organisms.
Polymer gels can be broadly defined as a cross-linked
polymer network inflated with a solvent such as water. In
addition to foodstuffs, there are numerous gels that we use in
our daily lives, such as the superabsorbent material indisposable diapers, and soft contact lenses. Polymer gels areused in a variety of fields. Many gel-like tissues can also befound in living organisms, including the cornea of our eye andvitreous bodies.
This type of gel can exhibit a very unusual phenomenon
called volume phase transition in which the gel reversibly anddiscontinuously swells or shrinks in response to environmental
changes, such as changes in the solvent composition,
temperature, and pH, the application of an electric field,
exposure to light, and the addition of specific molecules. Much
research is now being conducted on this quality to findapplications for these gels as functional materials. So far
several “intelligent” gels having organism-like functions havebeen developed, including gels that function as artificial
muscles and gels that release medicine only when heated.
While various stimuli-responsive gels are being created inthis way, our laboratory is developing a “life-like” functional gelthat produces spontaneous pulses under uniform conditions
similar to myocardial cells. By developing a molecular design inthe gel for inducing the BZ reaction, an oscillating reaction
known as a chemical model of biological metabolic reactions(citric acid cycles), and converting the chemical changes todynamic changes, we have succeeded in producing a periodic
swelling and shrinking oscillation in the gel (Fig. 1). This led tothe creation of a new biomimetic gel capable of inducing its
own oscillations in a regular rhythm under fixed conditions,much like the pulsations of a cardiac muscle. Unlike
conventional stimuli-responsive gels, this is the first gel in theworld that produces swelling-shrinking oscillations without anexternal stimulus being turned on and off and is expected tohave applications in molecular pacemakers, pulsating
micropumps, and microactuators having peristalsis. New gelsthat imitate a cardiac muscle have also been developed
recently. These gels are capable of self-induced pulsations in
the presence of ATP.
Currently we are attempting to apply lithography andother micromachining technologies that have made remarkableadvances in recent years to develop micromachines andnanomachines from these functional gels. For example, we are
creating microactuators (artificial cilia) by arranging hundredsof microprotrusions on the surface of self-oscillating gel andgenerating wave propagation through a chemical reaction,
spontaneously producing periodic fluctuations in theprotrusions (Fig. 2). It is thought that such a microactuator
may have applications in a microtransfer system fortransporting minute particles and cells added to a surface.
We are also working on applications for medical chips. By
providing a medicine storage section in a chip and forming agel at the exit passage to this section through local
photopolymerization, we can produce a drug release systemthat opens and closes a gate in response to abnormal signals(Fig. 3). We are designing a drug release chip for releasing
insulin in response to changes in temperature and pH andglucose concentrations. Further, a pulsating gel embedded in achip is anticipated to serve as the power source for a pulsating
micropump designed to releasing drugs periodically. Thischemical engine requires no electrical power and can be used
as a completely independent drug release chip having no wires
connected to an external power source. By fusing this gel withmicromachining technology, we believe that newdevelopments and applications for the gel as a functional
material will continue to expand.
For more information on our research activities, please
visit our Web site. Although our laboratory is relatively new,the students and I are conducting research round the clock.

Pulsation

100Fig. 1 Self-oscillating gel that pulses
spontaneously pulsation

Fig. 2 Gel array createdthrough micromachining(artificial cilia)

Fig. 3 Microvalve formed of gel in a microchannel
for automatically controlling drug release(the valve is closed in the top photo andopen in the bottom photo)

MICROMACHINE No. 51
MICROMACHINE is published quarterly by Micromachine Center (MMC) to promote the international exchange ofinformation related to micromachines, R&D and other technical topics, and is circulated free of change. Please send
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