Source: American Association For The Advancement Of Science
Date: Posted 6/30/2000
Desktop Biofactories? New Microrobots Might Manipulate Single Cells, Science
Tiny, submersible robots may suggest a single-cell retrieval system, desktop
biofactories, or even tools for minimally invasive surgery, according to a 30
June report in the international journal, Science.
At 670 micrometers tall and 170 to 240 micrometers wide, the new microrobots
are shorter than this hyphen--and no wider than the following period. Unlike
many previous designs, the Swedish-made microrobots can function in salty
broths, blood, urine, cell-culture medium and other liquids, suggesting a
host of biotechnology uses.
"Being able to manipulate many individual cells at the same time is becoming
increasingly important for genomics, proteomics, and metabolic research,"
says Edwin W.H. Jager, a graduate student at Sweden's Linköpings Universitet
and lead author of the Science paper. "We think that these microrobots would
be helpful for fundamental studies, or for manufacturing other small devices,
especially if we set up arrays of them."
The robot's miniature hand might someday pluck single cells, bacteria,
multi-cellular organisms and other biological entities from a sample, then
transfer them to an analysis station. Coupled with a multisensor area, the
microrobots also may suggest lab-on-a-chip designs, or "factory-on-a-desk"
tools, programmed to assemble various microstructures, say coauthors Olle
Inganäs and Ingemar Lundström, faculty members at Linköpings Universitet.
Positioned at the end of a catheter, the polymer-and-gold microrobots might
increase the range of surgeons, too.
How do the microrobots work? Imagine a human hand, opening and closing.
Similarly, conducting polymers such as polypyrrole can be forced to shrink
and swell on command. The researchers combine layers of gold and polypyrrole,
then use electricity to manipulate contractions of the polymer.
To make the microrobot grab a glass bead, for instance, researchers plump up
the polymer by drawing positively charged ions, called cations, away from an
electrolyte solution and into the material. Shrinking the polymer is as easy
as applying a positive charge to the gold, which oxidizes the polypyrrole and
causes cations to flee.
Previous microrobots have included electronic devices featuring rods and
levers, artificial flying insects made of polysilicon, and a walking silicon
microrobot. But, "none of these operate in water, and would not be suitable
as microactuators for the manipulation of cells," Jager notes. Whenever pure
silicon is exposed, he explains, it oxidizes and stops working. In the new
design, silicon provides a skeletal framework, which is encased and protected
by gold and polypyrrole "micromuscles."
The Swedish team's invention was etched into part of a four-inch silicon
wafer, which allowed them to create separate gold-and-polypyrrole electrodes
for each joint in a robotic arm. From one-fourth of a single wafer, they
created 140 microrobots with an elbow, a wrist, a hand, and two to four
The team used photolithography to pattern the titanium-coated silicon. Next,
using a patterned chromium layer as a kind of glue, they added a thin layer
of gold to the template. More etching defined individual electrodes on the
silicon. This step was followed by a rigid material called BCB
(Benzocyclobutene, or Cyclotene), which provided a framework for the
electrodes. Finally, the polypyrrole was deposited over the gold. After a
final etching step, the robots were released and ready for action.
Submerged in an electrolyte solution, several robots were wired to an
electrical source and videotaped as they as hoisted a glass bead. Much like
puppeteers pulling one string or another, the researchers stimulated the
microrobots' fingers, wrists and elbows by applying a charge to specific
joints. To open and close the microrobots' hand, for example, they
successively applied positive and negative potentials.
The microrobots successfully moved a bead up to 250 micrometers. They also
hoisted beads 270 micrometers, from one miniature conveyor belt or "track" to
another, proving their potential as tiny factory workers. Treated with
adhesion molecules, the robot's fingers might select particular cells or
bacteria from a sample, or they might support surgical procedures. In
addition, the Science authors say, an array of microrobots could
simultaneously handle many cells.
Research described in the Science paper was supported by the Swedish
Foundation for Strategic Research and the Swedish Research Council for
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