Shape-shifting materials with infinite possibilities

October 21, 2021
L.Mahadevan shape shifting material_PNAS

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) led by L Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics, have developed a shape-shifting material that can take and hold any possible shape. The study published in the Proceedings of the National Academy of Sciences paves the way for a new type of multifunctional material that can be used in a range of applications, from robotics and biotechnology to architecture. 

“Today’s shape-shifting materials and structures can only transition between a few stable configurations but we have shown how to create structural materials that have an arbitrary range of shape-morphing capabilities,” said Mahadevan.  “These structures allow for independent control of the geometry and mechanics, laying the foundation for engineering functional shapes using a new type of morphable unit cell.”

SEAS researchers dubbed this material “totimorphic” because of its ability to morph into any stable shape. The researchers connected individual unit cells with naturally stable joints, building 2D and 3D structures from individual totimorphic cells.

 

The team started with a neutrally stable unit cell with two rigid elements, a strut and a lever, and two stretchable elastic springs -- similar to the Pixar movie lamp head,  which is a neutrally stable material that is stable in any position because the force of gravity is always counteracted by springs that stretch and compress in a coordinated way, regardless of the lamp configuration. In general, neutrally stable systems, a combination of rigid and elastic elements balances the energy of the cells, making each neutrally stable, meaning that they can transition between an infinite number of positions or orientations and be stable in any of them. 

The researchers dubbed the assembly as “totimorphic materials” because of their ability to morph into any stable shape. The researchers connected individual unit cells with naturally stable joints, building 2D and 3D structures from individual totimorphic cells.

“All together, these totimorphs pave the way for a new class of materials whose deformation response can be controlled at multiple scales,” said Mahadevan.

See also: Faculty News, 2021