In a study recently published in Nature Materials, Prof. Wang Shutao from the Technical Institute of Physics and Chemistry (TICP) of the Chinese Academy of Sciences (CAS) and Prof. Liu Huan from Beihang University revealed the secret of ultra-slow motion of pine cones and developed mimicking actuators enabling unperceivable motion.
Responsive actuators have attracted extensive attention by virtue of their great potential applications in flexible robotics, sensors, energy conversion and other fields. Pine cones are a well-known bionic model for constructing artificial actuators.
However, little attention has been paid to the fact that the hygroscopic motion of pine cones is an ultra-slow process. Hygroscopic deformation has long been attributed to the uneven hygroscopic expansion of vascular bundles (VBs) and sclereids, controlled by their different microfibril orientations. The mechanism cannot explain the observation that VBs themselves are capable of reversible hygroscopic motion. Therefore, the mechanism of ultra-slow motion in pine cones has long been unclear.
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