Researchers at North Carolina State University have developed dynamic structures known as “metashells” that can leap into the air on a predetermined schedule without relying on computers or external stimuli. The timing and height of these jumps are engineered into the materials’ physical structure.
Jie Yin, an associate professor of mechanical engineering at NC State and corresponding author of the paper on this work, explained, “There are structures that ‘jump’ immediately when loading is removed – such as when a coiled spring is released. We wanted to create a structure that does not rely on external stimuli and allows us to dictate the timing of the jump in advance.”
The metashells are made from polyethylene terephthalate (PET) strands connected in a complex lattice pattern. This design maximizes energy storage within the material. When a load is applied, the structure deforms but returns to its original shape once the load is removed. Due to PET’s viscoelastic properties, it slowly creeps back to its original form before snapping back entirely at a critical point.
Haitao Qing, first author of the paper and a Ph.D. student at NC State, described how controlling the duration of applied load dictates when and how high the metashell jumps: “When the flower bud snaps back into the spherical shape, the release of energy hurls the structure into the air.”
Yin emphasized that both material properties and structural design are crucial for this technology’s performance: “Material properties play a critical role, and the design of the structure we created amplifies those properties.”
Tests showed that jumps could be scheduled from three seconds to 58 hours in advance. The metashells were capable of jumping up to nine times their height or as little as 0.5 times their height based on scheduling. They functioned effectively on various surfaces and temperatures down to minus 15 degrees Celsius.
The researchers also demonstrated potential applications by loading metashells with cargo like seeds for dispersal upon jumping. Qing noted inspiration from nature: “We were inspired by explosive seed dispersal… such as Impatiens balsamina.”
Looking ahead, Yin expressed interest in exploring biodegradable materials and collaborating with other researchers or private sector entities: “We are interested in exploring biodegradable materials that would work with this design.”
The study titled “Programmable seconds-to-days long delayed snapping in jumping metashell” will be published in Proceedings of the National Academy of Sciences during June’s first week. Co-authors include Caizhi Zhou and Fangjie Qi from NC State.
Funding was provided by National Science Foundation grants 2126072 and 2329674. Qing and Yin are co-inventors on a pending patent filed by North Carolina State University related to this work.
