Researchers at Harvard University have developed a shape-shifting material that can take and hold any shape. The advance paves the way for new multifunctional material, with applications ranging from biotechnology to architecture.
“Today’s shape-shifting materials and structures can only transition between a few stable configurations, but we’ve shown how to create structural materials with an arbitrary range of shape-shifting capabilities,” said Professor Lakshminarayanan Mahadeva, a renowned expert in the organization of matter. . “These structures provide independent control of geometry and mechanics, and lay the groundwork for designing functional shapes using a new type of morphable unit cell.”
A major challenge in designing shape-shifting materials is balancing the seemingly conflicting needs of formability and rigidity. Formability allows transformation into new shapes, but going too far in this direction compromises the ability of the material to hold its shape. Stiffness helps hold the material in place, but very stiff material cannot reshape.
The researchers, from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), started with a “neutrally stable” unit cell with two rigid elements — a strut and lever — and two stretchable springs.
In general, neutral stable systems balance the energy of unit cells with a combination of rigid and elastic elements. The famous bounce lamp seen at the beginning of Pixar movies is a good example of a neutral stable material; the lamp head is stable in any position, as its weight is always counteracted by springs that stretch and compress in a coordinated manner to balance it in any configuration. This quality allows for a transition between an infinite number of positions and orientations, maintaining stability throughout.
“Having a neutrally stable unit cell allows us to separate the geometry of the material from its mechanical response at both the individual and collective level,” says Dr. Gaurav Chaudhary, co-first author of the study. “The geometry of the unit cell can be varied by changing both the overall size and length of the single movable strut, while the elastic response can be changed by changing either the stiffness of the springs in the structure or the length of the struts and links.” .”
The researchers describe the unique assemblage as “trimorphic materials” or “totimorphs,” thanks to its ability to transition into any stable form.
hey, connected individual trimorphic cells with naturally stable joints to build 2D and 3D structures. Using mathematical modeling and practical experiments, they demonstrated the material’s shape-changing ability. A single sheet of connected trimorphic cells can be twisted into all kinds of shapes – including the shapes of faces – and even bear weight.
“We show that we can assemble these elements into structures that can take any shape with heterogeneous mechanical reactions,” said Dr. S. Ganga Prasath, another co-first author. “Since these materials are geometry-based, they can be scaled down to be used as sensors in robotics or biotechnology, or they can be scaled up to be used on an architectural scale.”