Physics: Wrinkling passion fruits may inspire robot design

A previously unknown type of wrinkling pattern that occurs on the surface of dehydrated passion fruits is described in a paper published in Nature Computational Science. The finding and resulting theoretical predictions may improve our understanding of the complex physics behind non-linear, natural changes in the size and shape of objects, and inspire new designs for adaptive robotics.

Wrinkling is one of the most important natural patterns of change in the surface of objects, occurring throughout life and to different extents. In theory, the spontaneous breakdown of symmetry during growth (for example in embryos, tumours, and brains) and dehydration (such as in fruits and skin) are two factors that can cause complex wrinkling. Accurate prediction and precise control of such structural changes are of crucial technological relevance, such as during the fabrication of nanodevices.

Fan Xu, Xi-Qiao Feng and colleagues report an unknown type of chiral wrinkling pattern—chiral symmetry is when objects are not reflectively symmetrical, but may have rotational symmetry axes—on the surface of dehydrated passion fruits. Inspired by this arrangement, the authors develop a mechanical model that they use to derive a universal scaling law to reveal the underlying structural-elastic mechanisms behind the formation of buckyball patterns (for example, hexagons and pentagons) and chiral modes (such as left or right rotations). The authors further demonstrate that this chiral wrinkling process can be mimicked on the surface of silicon core–shells that have been made in the laboratory, and further use the high local sensitivity of the chiral pattern to design a self-adaptive robot that can grasp small objects, such as a diamond, screw or mung bean.

The study not only explains and predicts the structural changes on the surface of dehydrating passion fruits, but also facilitates the development of an adaptive robot for target-adaptive grasping inspired by the chiral wrinkling arrangement observed in nature.