Characteristic features of the seedcoat of Portulaca oleracea, an annual succulent commonly known as verdolaga or purslane. A) Photograph of the P. oleracea flower. B) Photograph of the tiny black seeds from P. oleracea. C) Scanning electron microscope image of the P. oleracea seedcoat. D) Magnified area of the seedcoat of P. oleracea. Image: UNH.According to researchers at the University of New Hampshire, the puzzle-like wavy structure of the delicate seed coat, found in plants like succulents and some grasses, could hold the secret to creating new smart materials strong enough to be used in body armor, screens and airplane panels.
"The seed coat's major function is to protect the seed, but it also needs to become soft to allow the seed to germinate, so the mechanical property changes," said Yaning Li, associate professor of mechanical engineering at the University of New Hampshire. "By learning from nature, it may be possible to tailor the geometry and create the architecture for a smart material that can be programmed to amplify the strength and toughness but also be flexible and have many different applications."
The building blocks of the seed coat are star-shaped epidermal cells that move via zigzag intercellular joints to form a compact, tiled exterior that protects the seed inside from mechanical damage and other environmental stresses, such as drought, freezing and bacterial infection. To better understand the relationship between the structural attributes and functions of the seed coat's unique microstructure, the researchers designed and fabricated prototypes using multi-material 3D printing. They then performed mechanical experiments and finite element simulations on these prototypes.
"Imagine a window, or the exterior of an airplane, that is really strong but not brittle," said Li. "That same concept could create a smart material that could be adapted to behave differently in different situations, whether it's a more flexible body armor that is still protective or other such materials."
The results, published in a paper in Advanced Materials, show that the waviness of the mosaic-like tiled structures of the seed coat, known as sutural tessellations, plays a key role in determining the mechanical response. Generally, the wavier the seed coat, the more that applied loads can effectively transit from the soft wavy interface to the hard phase, allowing both overall strength and toughness to increase simultaneously.
The researchers say that these design principles offer a promising way to increase the mechanical performance of tiled composites made from man-made materials. The overall mechanical properties of the prototypes could be tuned over a very large range by simply varying the waviness of the mosaic-like structures. This approach could thus provide a roadmap for the development of new functionally graded composites that could be used in protection, as well as energy absorption and dissipation.
This story is adapted from material from the University of New Hampshire, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.