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Researchers from Harvard’s School of Engineering and Applied Sciences developed a shape-shifting material that can morph into and hold any 3D shape, opening the door to a potentially infinite number of applications.
Featured in the Proceedings of the National Academy of Sciences in October, the researchers developed small morphable units, which they called unit cells, that can be attached to each other to create “totimorphic” structures, which have the ability to stably take on any shape.
According to Harvard postdoctoral researcher and co-first author of the paper S. Ganga Prasath, the traditional approach to constructing shape-transforming structures is to have a material that can shift into a predetermined target shape once an external force or stimulus is applied.
“This approach was successful, but it could only create materials that could go between two shapes,” Prasath said. “What we came up with was to extend this notion of shape-transforming materials, but to arbitrary shapes.”
Prasath said that the new idea was inspired by the concept of “neutral stability,” which describes the state of a structure that is equally stable in all of its possible 3D conformations.
Postdoctoral fellow and co-first author Gaurav Chaudhary said the group only found one example in previous literature of a structure displaying neutral stability, known as the Anglepoise lamp.
Chaudhary said the Anglepoise lamp — used as the mascot of Pixar Animation Studios — can take on any spatial position and remain there stably. The researchers aimed to replicate this in a more general structure.
“What we have done is taken that simple idea and try to see if we can generalize this, to basically now make any material which is not just a lamp,” Chaudhary said.
The “neutrally stable unit cell” created by the researchers deforms from its current shape by transferring energy between two elastic springs but still displays a “rigid-plastic” stability at every position. These unit cells can be attached to each other like building blocks, per the group’s paper.
The result is the ability to construct “infinitely morphable structures” while allowing for “independent control of their geometry and mechanical properties,” according to Harvard professor and senior author Lakshminarayanan Mahadevan.
Mahadevan wrote in an email that the discovery offers new practical possibilities in material design.
“I think it will provide a new alphabet for engineers, designers and architects since totimorphic assemblies allow for much more exquisite control of shape at multiple scales,” Mahadevan wrote.
Prasath said the totimorphic material has potential biomedical applications, such as the construction of stents — mesh tubes that hold open passageways such as arteries and veins that have narrowed.
“That is one place that you could use this, but we haven’t started working at that scale at all,” he said.
Chaudhary noted the development holds implications for “soft robotics,” in which engineers seek to replace hard robot parts with soft, elastic materials that can deform in “very certain, very specific ways.”
Per Mahadevan, the next research steps are to explore the possibility of “different types or classes” of these unit cells and to devise simpler ways to manufacture the materials.
—Staff writer Justin Lee can be reached at email@example.com.
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