The hygroscopic deformation of pine cones, featured by opening and closing their scales depending on the environmental humidity, is a well-known stimuli-responsive model system for artificial actuators. However, it has not been noted that the deformation of pine cones is an ultra-slow process. Here, we reveal that vascular bundles with unique parallelly arranged spring/square microtubular heterostructures dominate the hygroscopic movement, characterized as ultra-slow motion with the outer sclereids. The spring microtubes give a much larger hygroscopic deformation than that of the square microtubes along the longitudinal axis direction, which bends the vascular bundles and consequently drives the scales to move. The outer sclereids with good water retention enable the vascular-bundle-triggered deformation to proceed ultra-slowly. Drawing inspiration, we developed soft actuators enabling controllable yet unperceivable motion. The motion velocity is almost two orders of magnitude lower than that of the same-class actuators reported, which made the as-developed soft actuators applicable in camouflage and reconnaissance.

松果的吸湿变形，其特点是根据环境湿度打开和关闭鳞片，是一种众所周知的人工执行器刺激响应模型系统。然而，没有人注意到松果的变形是一个超慢的过程。在这里，我们揭示了具有独特平行排列的弹簧/方形微管异质结构的维管束主导吸湿运动，其特征是外巩膜的超慢运动。弹簧微管沿纵轴方向产生比方形微管大得多的吸湿变形，使维管束弯曲，从而驱动鳞片移动。具有良好保水性的外巩膜使维管束触发的变形能够超缓慢地进行。汲取灵感，我们开发了软致动器，可实现可控但不可感知的运动。运动速度比已报道的同类执行器低近两个数量级，这使得所开发的软执行器适用于伪装和侦察。