What is an artificial muscle? A comparison of soft actuators to biological muscles

Abstract

Interest in emulating the properties of biological muscles that allow for fast adaptability and control in unstructured environments has motivated researchers to develop new soft actuators, often referred to as ‘artificial muscles’. The field of soft robotics is evolving rapidly as new soft actuator designs are published every year. In parallel, recent studies have also provided new insights for understanding biological muscles as ‘active’ materials whose tunable properties allow them to adapt rapidly to external perturbations. This work presents a comparative study of biological muscles and soft actuators, focusing on those properties that make biological muscles highly adaptable systems. In doing so, we briefly review the latest soft actuation technologies, their actuation mechanisms, and advantages and disadvantages from an operational perspective. Next, we review the latest advances in understanding biological muscles. This presents insight into muscle architecture, the actuation mechanism, and modeling, but more importantly, it provides an understanding of the properties that contribute to adaptability and control. Finally, we conduct a comparative study of biological muscles and soft actuators. Here, we present the accomplishments of each soft actuation technology, the remaining challenges, and future directions. Additionally, this comparative study contributes to providing further insight on soft robotic terms, such as biomimetic actuators, artificial muscles, and conceptualizing a higher level of performance actuator named artificial supermuscle. In conclusion, while soft actuators often have performance metrics such as specific power, efficiency, response time, and others similar to those in muscles, significant challenges remain when finding suitable substitutes for biological muscles, in terms of other factors such as control strategies, onboard energy integration, and thermoregulation.

A Biorealistic Computational Model Unfolds Human-Like Compliant Properties for Control of Hand Prosthesis

“…Their compliance is derived from pneumatic actuation, soft materials and/or flexible structures. But the range of compliance in soft robotic hands may still be limited compared to that of human hand driven by muscles [16] , [17] .…”

Advances in artificial muscles: A brief literature and patent review

“…Nowadays, artificial muscles are the core components of intelligent and interactive soft robotics systems. Researchers even proposed the concept of “artificial super muscles” to give artificial muscles better properties for more complex human-computer interaction and integration drives ( Higueras-Ruiz et al, 2022 ). In the last 2 years, the performance metrics of artificial muscles have been upgraded and have continued to gain new applications in the field of soft robotics.…”

Future bio-inspired robots require delicate structures

“…At a higher level, the brain plans the movement sequence and sends out commands ( Shao et al, 2016 ; Shao et al, 2019 ). At a lower level, the muscles can respond by synthesizing the command from the brain, the local sensory feedback from receptors, and the on-site external stimuli ( Higueras-Ruiz et al, 2021 ). We refer to such a low-level organization subordinating to the central nervous system as the “delicate control architecture”.…”

“…It can stably produce rhythmic motor patterns without rhythmic input, and can be modulated with low-dimensional external signals. The muscle synergy also manifests the existence of delicate structures in the biological nervous control system ( Higueras-Ruiz et al, 2021 ). In mammals, a group of muscles can be activated synergistically to produce a particular movement pattern, reducing the dimensionality of the muscle control.…”