Researchers at the Univ. of Southern California Information Sciences Institute have demonstrated a way to manufacture miniscule containers that might be used to deliver precise micro- or even nano-quantities of drugs.
According to ISI project leader Peter Will, who is 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 as 30 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. Then 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”, then directing water from different directions to sequence the closing. Varying the time of drying 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 Univ.), 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," says Will, "since ISI doesn't have a wet lab."
The National Science Foundation supported the research, under an exploratory research grant. The paper is "Voxels: volume-enclosing microstructures," J. Micromech. Microeng. 18 (2008) 055025. The abstract is available here: http://www.iop.org/EJ/abstract/0960-1317/18/5/055025
