Liquid crystalline elastomers as artificial muscles and flexible actuators for robotics/hybrid engineered machinery

Abstract Reducing the weight and profile of machinery and robotics is currently a prime challenge for materials scientists and engineers alike. Solving this challenge could lead to an improvement in space travel feasibility, manufacturing capability, and the birth of new medical interventions and technologies altogether. LCEs are currently considered to hold good potential as artificial muscles due to their unique molecular structure. With the recent boom in materials science and the emergence of advanced fabrication techniques, LCE-based artificial muscles/flexible actuators are at the cusp of commercialization. LCEs can now be fabricated into several different forms (films, fibers, and 3D printed arbitrary shapes). Furthermore, LCE artificial muscles fabricated using these advanced techniques can also be functionalized so that they can controllably be triggered into actuating via stimuli such as light or electrical currents. This has led to reports of several LCE-based artificial muscles which boast impressive performance as artificial muscles. For example, recently certain Joule heating LCE fibers can directly be stimulated into actuation via the application of electrical currents and can actuate on sub-second time frames and outperform human skeletal muscles in terms of actuation stress. Given this, whilst currently there are no commercial applications of LCEs as artificial muscles in robotics, we believe that LCEs are poised to soon be directly applicable as artificial muscles in the broader field of robotics, which inspired us to author this review. This review presents an overview of the mechanisms, synthetic methods, and alignment methods for LCEs. In addition, we provide the latest achievements in fabrication techniques and means of inducing/controlling the actuation of LCEs. We do so in the aspiration that this review can bridge the gap that exists between academia and industry on the topic of LCEs. Graphical abstract Illustration of LCEs acting as artificial muscles in robotics.