Chemical Reactions for Gas-Driven Pneumatic Soft Actuators—From Catalysts to Neutralisation Reactions for Oscillating Pneumatic Systems

Soft robotics offers solutions to problems where human or animal-like architectures and materials are needed. Tasks requiring strength yet finesse, currently only achieved through human operators, may in the future be automated by developments in soft robotics. Beyond mimicking biological systems performance, soft robotics aims to develop robots that are both safe and compliant for human interaction and are able to overcome the energy and power limitations. Pneumatic actuators are widely studied in soft robotics as the compliant actuation of these systems is comparable to that found in Nature. However, conventional pneumatic actuators are powered by externally tethered hard air compressors or accumulators, big systems that are difficult to be implemented in areas with limited space or with limited access to electricity sources. Gas evolution reactions (GER) are found in chemical and biochemical processes [1]. Hydrogen peroxide is a sub-product of cellular metabolism. Given its reactivity, it must be quickly transformed into less harmful or reactive compounds (oxygen and water) catalysed enzymatically by catalase [2]. Soft, porous catalytic nanocomposites can perform a similar function to enzymes while also mimicking the desirable compliance of biological systems [3]. Other gases like hydrogen, carbon dioxide and nitrogen dioxide are subproducts of other known reduction, decomposition and acid-base reactions [4,5]. The release of these gases to the atmosphere and the limitations on its re-usability has reduced the interest in implementing chemical reactions in soft pneumatic systems. This work reports the development and characterisation of a reusable nanocatalyst laden 3D printing filament, created by loading a commercially available filament with catalytic nanoparticles. The nanocomposite filament is used to create a multi-material 3D-printed soft pneumatic artificial muscle. The resulting actuator with embedded nanocatalysts converts energy-dense liquid chemical fuel (hydrogen peroxide) into actuating gases (oxygen). The developed material allows reusability and actuation control achieved by the addition rate and the catalyst load. The possibility of coupling GER with reactions that use the evolved gas as precursors and tailor-made smart materials for oscillating and controlled actuation is discussed. Actuator geometries for optimising the amount of gas harnessed from the chemical reactions are explored through finite element analysis. The potential for the configuration to create a fully soft oscillating device capable of gentle movements for locomotion or handling of delicate objects is discussed. Developing such advanced methods for manufacturing and powering soft robots is critical to realise their potential to generate societal and environmental impact in many areas including agriculture, physical rehabilitation and industry.<br/><br/>[1] Zhang L, Happe T and Melis A 2002 Biochemical and morphological characterization of sulfur-deprived and H 2 -producing Chlamydomonas reinhardtii (green alga) <i>Planta</i> <b>214</b> 552–61<br/>[2] Jones D P, Eklöw L, Thor H and Orrenius S 1981 Metabolism of hydrogen peroxide in isolated hepatocytes: Relative contributions of catalase and glutathione peroxidase in decomposition of endogenously generated H2O2 <i>Arch. Biochem. Biophys.</i> <b>210</b> 505–16<br/>[3] Serra-Maia R, Bellier M, Chastka S, Tranhuu K, Subowo A, Rimstidt J D, Usov P M, Morris A J and Michel F M 2018 Mechanism and Kinetics of Hydrogen Peroxide Decomposition on Platinum Nanocatalysts <i>ACS Appl. Mater. Interfaces</i> <b>10</b> 21224–34<br/>[4] M. Okui, Y. Nagura, S. Iikawa, Y. Yamada and T. Nakamura, 2017 A pneumatic power source using a sodium bicarbonate and citric acid reaction with pressure booster for use in mobile devices, <i>2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) </i>1040-1045<br/>[5] Vladimir M. Petruševski, M. Taseska, M. Monković, 2005 Reaction of Copper with Fuming Nitric Acid: A Novel Lecture Experiment in Passivation, TCE <b>3 </b>208-210