Fig. 1: Bio-inspiration for soft robotic autonomy.
a–d Natural and (e–i) soft robotic examples of harnessing compliance. a Adaptive shape change: octopus can squeeze through tiny openings only limited by the size of their rigid beak. b Fast motion: Venus flytrap (Dionaea muscipula) has bistable leaves that close quickly (in ≈ 0.1 s) as a result of a mechanical instability1. c Versatility: elephant trunks are both flexible and very strong, enabling them to lift a wide range of objects using a limited repertoire of movements2. d Power amplification: bullfrogs and grasshoppers slowly load their tendons and other flexible tissue with elastic energy, which they quickly release to jump3. The optimal series tendon stiffness value depends on loading rate, and this may explain why bullfrogs have more compliant series elements than grasshoppers4. The human Achilles tendon stores and releases energy with every step5. e Adaptive shape change: vine robot can pass through openings much smaller than its nominal body width. From ref. 6. Reprinted with permission from AAAS. f Fast motion: artificial Venus flytrap actuator closes in 50 ms. Reprinted from ref. 7 with permission. Copyright 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. g Versatility: soft grippers can grasp a wide variety of objects using a simple pressure input. Reprinted from ref. 8 with permission. Copyright 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. h, i Power amplification: slow storage and quick release of energy in (h) a jumping popper robot (from ref. 9, reprinted with permission from AAAS) and (i) a bistable spine runner (from ref. 10 reprinted with permission under CC BY-NC 4.0). j The human heart as inspiration towards improved autonomy in soft robots. The human heart pumps blood by periodic contractions of its ventricles, paced by action potentials generated in the sinoatrial node (SAN). The ventricles are highly compliant in the relaxed state, such that the filling volume is variable. Moreover, additional filling intrinsically leads to more energetic contraction. This local loop leads to left-right balance. The frequency of action potential generation is the result of physical processes in the cells of the SAN, and these processes are affected by a multitude of attributes of their direct environment, such as neuronal signals and the concentration of specific chemical compounds. These can be interpreted as external control inputs from the environment to the heart. Energy is control-autonomously harvested from the heart’s environment, i.e., from blood passing through it. At the same time, the heart is a crucial element in the blood circulation.
