A team of researchers from the University of New Hampshire in the US have shown how the seed coats of certain plants could help in the development of new flexible materials that are both strong and resilient. Using 3D printing, a multi-material prototype based on the mosaic-like tiled structures of the seed coat of succulents and some grasses was produced that could provide the foundation of smart materials that are sufficiently robust to be used in body armor, screens and even the panels of airlines.
Plant seed coats act to protect the seed but also need to be sufficiently soft so that the seeds can germinate, which means there is a change in their mechanical property. Their building blocks are epidermal cells in the shape of a star that move using zigzag intercellular joints, making a tight, tiled shell structure that protects the seed from damage and environmental stresses, including drought and freezing, as well as bacterial infection.
“Imagine a window, or the exterior of an airplane, that is really strong but not brittle. That same concept could create smart material that could be adapted to behave differently in different situations.”Yaning Li
The researchers therefore looked to develop an architecture for a smart material that could be programmed to augment the strength and toughness of a seed coat, as well as be flexible enough for a range of applications. As shown in Advanced Materials [Gao et al. Adv. Mater. (2018) DOI: 10.1002/adma.201800579], they examined the seed coat’s microstructure to improve their awareness of the interaction between its structural attributes and functions, demonstating that the waviness of the structures, known as sutural tessellations, is crucial to its mechanical response.
The more wavy it is, the greater an applied load that can move from the soft wavy interface to the hard phase, so the overall strength and toughness can be improved. They also focused on occasions where the amplitude of the undulations is close to the scale of the constituent tiles as it is in many seed coats. As researcher Yaning Li said “Imagine a window, or the exterior of an airplane, that is really strong but not brittle. That same concept could create smart material that could be adapted to behave differently in different situations.”
The design principles involved could offer great potential for significantly improving the mechanical performance of tiled composites of man-made materials. As the mechanical properties of the prototypes can be tuned over a large range by changing the waviness of the structures, the team hope this will provide a route to producing new functionally graded composites for protective purposes, and in energy absorption and dissipation.