23 July 2023: Researchers from Queen Mary University of London have achieved a momentous feat in the realm of bionics by engineering a novel self-sensing, variable-stiffness artificial muscle that closely mimics the characteristics of natural muscle. This groundbreaking technology has far-reaching implications in the field of soft robotics and medical applications, representing a significant step towards seamless human-machine integration.

Drawing inspiration from nature's muscle contraction hardening, the team of scientists at QMUL's School of Engineering and Materials Science successfully created an artificial muscle capable of transitioning effortlessly between soft and hard states, while also possessing the remarkable ability to sense external forces and deformations.

Dr. Ketao Zhang, the lead researcher and a Lecturer at Queen Mary, emphasises the crucial role of variable stiffness technology in creating truly bionic intelligence for robots, especially those composed of flexible materials.

The newly developed artificial muscle exhibits impressive flexibility and stretchability, akin to natural muscle, making it ideal for integration into intricate soft robotic systems and adapting to various complex shapes. Its outstanding durability is demonstrated by withstanding over 200% stretch along its length. The muscle's stiffness can be rapidly adjusted by applying different voltages, achieving continuous modulation with a remarkable stiffness change of over 30 times. This voltage-driven characteristic provides a significant advantage in terms of response speed over other artificial muscle types. Furthermore, the technology allows for deformation monitoring through resistance changes, eliminating the need for additional sensors, streamlining control mechanisms and reducing costs.

The fabrication process for this self-sensing artificial muscle is both simple and reliable. Carbon nanotubes are blended with liquid silicone using ultrasonic dispersion technology and uniformly coated to create the thin layered cathode, which also functions as the sensing part of the artificial muscle. The anode is made directly with a soft metal mesh cut and the actuation layer is positioned in between the cathode and anode. Upon curing of the liquid materials, a fully functional, self-sensing variable-stiffness artificial muscle is formed.

The potential applications of this flexible variable stiffness technology are extensive, ranging from enhancing soft robotics to transformative medical uses. The integration of this artificial muscle with the human body holds promise for assisting individuals with disabilities or patients in their daily activities. Wearable robotic devices can monitor patients' movements and provide resistance by adjusting stiffness levels, facilitating muscle function restoration during rehabilitation training.

Dr. Zhang acknowledges that there are challenges to be addressed before these medical robots can be deployed in clinical settings, but this research represents a crucial step towards achieving human-machine integration and sets a blueprint for the future development of soft and wearable robots.

This groundbreaking development of self-sensing electric artificial muscles marks a significant milestone in the field of bionics and opens the door to remarkable advancements in soft robotics and medical applications.