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No. 2726:
Rigid Origami

Today, we fold rigid origami The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

We've all played with origami -- made pretty swans, or at least party hats and paper boats. Well, origami takes two forms -- flexible and rigid. We cannot make an iconic paper swan without bending the paper. That's flexible origami. But suppose we were folding rigid steel plates instead. That would be rigid origami.

Flexible origami towel elephantIf we've had the pleasure of staying at a very fancy hotel or riding a cruise ship, we may've found a towel folded into the form of a rabbit or an elephant on our bed. Those are flexible origami. Or fancy folded napkins at a posh restaurant. In another episode I talk about the invention of the paper bag folding machine. The common brown bag is a very practical example of flexible origami.

Rigid origami might first seem to make little sense. Would we really try to make a swan by folding a steel sheet? Actually, we often need collapsible devices that are made from relatively inflexible materials. We already make many things of rigid origami. Certain cardboard boxes that fold flat are conceived without having to bend the cardboard. The Japanese have used rigid origami designs in their storable solar arrays for space. Now we look to make furniture that can be folded flat for storage. 

rigid origami collapsible boxtopWhat especially caught my attention about rigid origami was an article inScience magazine about Oxford engineer Zhong You. Among the many origami forms he's working on are stents. A stent is a fitting used to hold ductwork open within our body. If our artery becomes clogged, the doctor can insert a stent to hold it open. 

But consider the problem: it has to be narrow enough that it can be run up an artery to the point of blockage. There it must first be driven through the blockage, then allowed to expand, creating a clean hole through which blood can flow again. Engineers have created a dizzying array of meshwork that can be squished down into a skinny shaft, then sprung into place.

But, if a stent fails to open just right, it can leave edges that disturb the flow and recreate thrombosis. Even if it fits cleanly, meshwork in the vessel is a threat to the passing blood. Stent designers fight that threat with various coatings. 

Now Zhong You is creating rigid origami stents of tiny plates that fold down into a very small shaft -- then open into nearly smooth cylindrical tubes instead of meshwork. 

Of course the segments of rigid origami need to be hinged in some way. A hinge can be as simple as a crease in the rigid cardboard of a box. Or it might be more complex. No surprise that mathematicians are being drawn into analyzing such foldings.

So this new field leaves us wondering, "Why only now?" Origami has been around for centuries, and only now we're creating whole new technologies from it. It's a delightful reminder: We can turn so many old familiar things to the light in new ways. And, when we do, such unexpected opportunities do arise!

I'm John Lienhard, at the University of Houston, where we are interested in the way inventive minds work.

(Theme music)

Z. Merali, 'Origami Engineer" Flexes to Create Stronger, More Agile Materials. Science, June 17, 2011, Vol. 332, pp. 1376-1377.

Here are two videos of rigid origami:

This is an interesting Japanese paper on deployable rigid origami structures.

I must emphasize that "rigid" origami may be made of partially flexible materials. It is rigid only in the sense that it is contrived in such a way that it would still work it the material is perfectly rigid. Flexible origami will not work without flexing the material in various ways. My thanks to engineers Lewis Wheeler, Ralph Metcalfe and K. Ravi-Chandar for their counsel. Photos by J. Lienhard