Body Battery
by David Pescovitz
Multimedia
Movie:
The diaphragm inside the drug delivery system expands to
pump out precise amounts of the chemical in the reservoir.
(AVI movie)
Movie courtesy Liwei Lin
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While fuel cells
make front page news with the promise of non-polluting automobiles
and energy efficient homes, Berkeley Mechanical Engineering professor
Liwei Lin is thinking smaller. Much smaller. Lin's microbial fuel
cell is just .07 centimeter square in area. Even more amazing though
is that this fuel cell is built to operate inside your body.
The idea is that the microbial fuel cell would power implantable
medical devices such as spinal cord stimulation devices or internal
drug delivery systems. For example, an implantable drug delivery
system integrated with a microbial fuel cell could be employed in
Spinal Drug Infusion Therapy for pain relief applications.
"Of course, people also dream about miniature surgery systems
that travel through your body," Lin says.
Liwei
Lin holds the microbial fuel cell and water-powered drug
delivery
system. (Click for larger image.)
David Pescovitz photo
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Fuel cells vary in design and materials, but the basic chemistry
behind them remains the same. Hydrogen atoms enter at the anode,
a negatively charged electrode, where a catalyst strips them of
their electrons. These electrons provide the current that powers
the device that the fuel cell is connected to. In Lin's device,
the fuel is nothing more than glucose, a sugar abundant in the human
body. It's the catalyst that gives Lin's microbial fuel cell its
name: Saccharomyces cerevisiae, a microorganism commonly known as
Baker's Yeast.
"The fuel cell's only waste product is carbon dioxide and water,"
Lin says. "It's very similar in some ways to how the human
body works."
The prototype
microbial fuel cell contains a tiny chamber where the microbe resides.
Glucose flows into the chamber, causing hydrogen protons and electrons
to be generated during the fermentation process. In a June paper,
Lin and graduate students Mu Chiao, Kien B. Lam, and Yu-Chuan Su
reported that their tiny powerhouse cranked out 300 microvolts for
two hours until the solution dried out in the open air. That kind
of power is plenty for microelectromechanical systems (MEMS), tiny
machines fabricated similarly to the way integrated circuits are
manufactured.
SEM
microphoto of the fluid port and channel of a microfabricated
fuel cell. (Click for larger image.)
Photo courtesy Liwei Lin
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MEMS, microscopic devices with biological applications, are one
of Lin's specialties. In another recent effort with one of Berkeley
MEMS pioneers Al Pisano and graduate student Yu-Chuan Su, Lin fabricated
a drug delivery system not much larger than a single letter on a
penny. The device requires no electrical energy, instead drawing
its pumping power from water flowing into an osmotic chamber filled
with salt. Due to the incompressibility of the water, the diaphragm
expands into a drug reservoir, pushing precise amounts of the drug
through an intricate path of microfluidic channels and valves.
Lin hopes that through collaboration with industry partner Alza
Corporation, acquired last year by Johnson & Johnson, research
into tiny implantable drug delivery systems could improve the quality
of life for individuals who require a steady flow of cancer drugs,
steroids, or hormones.
"The surgeon could implant the delivery system and the patient
wouldn't have to bother with it for a year or until it needed to
be refilled," he says.
Liwei Lin's
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Lab Notes is published online by the Public Affairs Office of the UC Berkeley College of Engineering. The Lab Notes mission is to illuminate groundbreaking
research underway today at the College of Engineering that will dramatically change our lives tomorrow.
Editor, Director of Public Affairs: Teresa Moore
Writer, Researcher: David Pescovitz
Designer: Robyn Altman
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© 2002 UC Regents.
Updated 7/25/02.
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