Logo: University of Southern California

Mini-Origami: ISI Folds Up Tiny Packages for Drug Delivery

Egypt has the great pyramids; Viterbi now has the micropyramids
Eric Mankin
April 28, 2008 — Researchers at the Viterbi School's Information Sciences Institute have demonstrated a way to manufacture submicroscopic containers that could be used to deliver precise micro- or even nano-quantities of drugs.
The new technique described in Journal of Micromechanics and Microengineering is a two-step process, according to ISI project leader Peter Will, who is also a Viterbi School research professor in the Epstein Department of Industrial and Systems Engineering, 
Not exactly Pharaonic: 80-micrometer pyramid folded up.

Part one is the creation of flat pattern -- origami -- just like the fold up shapes familiar to kindergarten children making paper pyramids, cubes or other solids. However, these pyramids are as small 40 micrometers on a side. (1 inch = 25,400 micrometers -- see illustration)

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 left hinge areas uncoated, to make sure thyat they would fold.

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 accomplished the final folding into shape.

The experimentor spent 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."  They directed water from different directions to sequence the closing. They found that 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, Prof. Bruce Koel, a chemist 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 (right) 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."

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.

Below: additional images and schematics: