Materials as Machines

• Published in: Advanced materials (Weinheim) Vol. 32; no. 20; pp. e1906564 - n/a
• Main Authors: McCracken, Joselle M., Donovan, Brian R., White, Timothy J.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.05.2020
• Subjects: Actuators; Bimorphs; Coils; Cones; Elastomers; Electroactive polymers; Extreme environments; Fluid dynamics; Fluid flow; Hydraulics; Hydrogels; liquid crystalline elastomers; Liquid crystals; Martensitic transformations; Materials science; Pneumatics; Response time; robotics; Ruggedness; Shape memory alloys; stimuli‐responsive materials; Swimming; Tubes; shape memory alloys; robotics; actuators; stimuli-responsive materials; liquid crystalline elastomers
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201906564

Machines are systems that harness input power to extend or advance function. Fundamentally, machines are based on the integration of materials with mechanisms to accomplish tasks—such as generating motion or lifting an object. An emerging research paradigm is the design, synthesis, and integration of responsive materials within or as machines. Herein, a particular focus is the integration of responsive materials to enable robotic (machine) functions such as gripping, lifting, or motility (walking, crawling, swimming, and flying). Key functional considerations of responsive materials in machine implementations are response time, cyclability (frequency and ruggedness), sizing, payload capacity, amenability to mechanical programming, performance in extreme environments, and autonomy. This review summarizes the material transformation mechanisms, mechanical design, and robotic integration of responsive materials including shape memory alloys (SMAs), piezoelectrics, dielectric elastomer actuators (DEAs), ionic electroactive polymers (IEAPs), pneumatics and hydraulics systems, shape memory polymers (SMPs), hydrogels, and liquid crystalline elastomers (LCEs) and networks (LCNs). Structural and geometrical fabrication of these materials as wires, coils, films, tubes, cones, unimorphs, bimorphs, and printed elements enables differentiated mechanical responses and consistently enables and extends functional use. Advances in the development and integration of responsive materials are comprehensively surveyed with a particular emphasis on robotics, spanning shape‐memory alloys, piezoelectrics, electroactive polymers, shape‐memory polymers, hydrogels, and liquid crystalline polymer networks and elastomers.