Self-Regulating Plant Robots: Bioinspired Heliotropism and Nyctinasty.

Self-regulation (or so-called homeostasis) is a property of all living organisms to maintain an internal stable state through specialized biofeedback mechanisms under varying external and internal conditions. Although these feedback mechanisms in living organisms are complex networks and hard to implement one-to-one in artificial systems, the new approaches in soft robotics may benefit from the concept of self-regulation-especially in the new endeavors of making untethered, autonomous soft robots. In this study, we show a simple system, in which plant robots display heliotropism (sun tracking) and nyctinasty (leaf opening) through artificial self-regulation attained through a bioinspired transpiration mechanism. The feedback involves dehydration/hydration and transpiration events that keep the stem continuously in a metastable position, which maximizes light on plant leaves and the efficiency of light harvesting when solar panels are attached on leaves. We also demonstrate that this artificial feedback can be regulated by doping with light-absorbing chemicals or by changing the geometry of the system, and it can further be expanded to other lightweight systems. Implementing self-regulation into (soft) robots through bioinspired material feedback is beneficial not only for energy efficiency and harvesting but also for achieving embodied intelligence in autonomous soft robots.

Slit Tubes for Semisoft Pneumatic Actuators.

This article describes a new principle for designing soft or 'semisoft' pneumatic actuators: SLiT (for SLit-in-Tube) actuators. Inflating an elastomeric balloon, when enclosed by an external shell (a material with higher Young's modulus) containing slits of different directions and lengths, produces a variety of motions, including bending, twisting, contraction, and elongation. The requisite pressure for actuation depends on the length of the slits, and this dependence allows sequential actuation by controlling the applied pressure. Different actuators can also be controlled using external "sliders" that act as reprogrammable "on-off" switches. A pneumatic arm and a walker constructed from SLiT actuators demonstrate their ease of fabrication and the range of motions they can achieve.