Researchers at the USC Information Sciences Institute
have demonstrated a way to manufacture miniscule closed containers that
might be used to deliver precise micro- or even nano-quantities of
drugs.
 | | After starting the folds using magnetic forces, the structure is sealed using capillary action. Credit: USC Information Sciences Institute |
According to ISI project leader Peter Will, who is also a
research professor in the Viterbi School of Engineering, the new
technique, described in a paper in the Journal of Micromechanics and
Microengineering, is a two-step process.
Part one is the creation of flat patterns, origami, of exactly
the fold up shapes familiar to kindergarten children making paper
pyramids, cubes or other solids, except that these are as small 40
micrometers (µm) on a side. (1 inch = 25,400 µm)
Instead of paper, the USC researchers created the patterns in
polysilicon sitting on top of a thin film of gold, using a
well-established commercial silicon wafer process called PolyMUMPs. The
next step was clearing the polysilicon off the hinge areas by etching.
When the blanks were later electrocoated with permalloy to
make them magnetic, the photomask used left hinge areas uncoated, to
make sure they were the places that folded.
Then the folding had to be accomplished. First the researchers
bent the hinges by application of magnetic force to the permalloy.
Water pressure and capillary forces generated by submerging the tiny
blanks in water, and drying them off did the final folding into shape.
The experiments spend considerable time comparing various
methods of controlling the closure effects of water drying with simple
flaps designed to close over each other to form "envelops," the
directing water from different directions sequence the closing. Varying
the time of trying could produce tighter seams.
"Our experiments show" says the paper, that "the combination
of partial folding of structures by magnetic actuation and liquid
closure to bring the structures to their final closed state is an
extremely promising technique for mass production of large arrays of
micrometer size …voxels. Furthermore, we believe that future
optimization of the voxel hinge geometry and composition should allow
for extensions of our work to" much smaller voxels.
The Voxel team - consisting of Will, professor of chemistry
Bruce Koel (who has since gone to Lehigh University), former
post-doctoral researcher Alejandro Bugacov and former grad student (now
graduate) Rob Gagler folded a number of different shapes, including
four- and five-sided pyramids, pentagonal 'lotus' shapes, and also
simple square plates that folded over each other to make flat
mini-envelopes.
Will has been pursuing the idea of creating voxels for many
years, "way back to my days in HP labs, when I was working in Medical
and Chemical applications." The USC team designed the chips using
MEMSPRO CAD software; the actual chip fabrication was done in France.
"The experimental work was done on campus," said Will, "since
ISI doesn't have a wet lab."
Posted 30th April 2008
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