Soft actuators have become a particular focus in the field of robotics. To investigate and consider the current state of the field of soft actuators, a review has been published in Nature Reviews Materials.
Study: Soft actuators for real-world applications. Image Credit: Gorodenkoff/Shutterstock.com
What are Soft Actuators?
In recent years, soft actuators have been explored for numerous applications in the field of soft robotics. These devices are inspired by muscles in humans and animals, which are agile, reconfigurable, physically adaptive, and multifunctional. However, accurately imitating biological structures presents several challenges for researchers and engineers and so far, no truly analogous soft artificial soft actuator has been developed.
Applications for soft actuators include artificial muscles, wearable technologies, medical devices, haptic devices, and soft grippers. Manufacturing soft actuators that accurately mimic biological systems will provide robots with superior human and animal-like physical behaviors. This will improve the entire field of robotics, providing innovative solutions to current key challenges facing the industry.
Muscles: The Biological Counterparts to Soft Actuators
Muscles are complex biological structures that have evolved over hundreds of millions of years. Muscles perform well under various mechanical stresses and conditions with complex actions and actuations. They can undergo reversible contraction, extension, and rotation without suffering excessive damage to their structure. Muscles are able to operate robustly with high performance, speed, efficiency, and power. They also possess tunable repair mechanisms and stiffness.
Furthermore, muscles can bend and twist and have specific power, energy, strain, and force performance metrics. All these properties of biological muscles are challenging to replicate in artificial systems. Combining physical intelligence such as self-repair and self-adaptive behaviors and performance metrics in soft actuators will greatly benefit their applications in fields such as mobility, healthcare, and industry.
Considering Soft Actuators
To overcome current issues in research and development and lead the way toward truly human and animal-like robots, the field of soft robotics needs components with enhanced life-like properties that behave like their biological counterparts.
The review study in Nature Letters Materials has set out to consider the real-world applications of soft actuators, In the review, structural designs and materials that provide synthetic soft actuators with advanced properties and physical intelligence are discussed. Properties that are advantageous to soft actuators include self-healing, multi-responsiveness, adaptability, and multimodal locomotion.
Soft Materials for Soft Actuators
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Promising soft actuation methods were discussed in the review study. These include tethered, untethered, and biohybrid actuation methods. Programmable soft materials that improve soft actuators’ multifunctionality and performance were discussed, as well as actuation strategies based on them. State-of-the-art real-world applications such as sensor-integrated soft robots and artificial muscles were explored in the review.
Furthermore, the review also discussed challenges and identified opportunities for future research in the field of soft actuators and soft robotics. These include scalability, integrated physical intelligence, encoded adaptability, and improvements in soft robot durability.
Key factors in designing these devices are fabrication methods, material choices, and structural design. Many approaches have been explored in previous research studies.
Actuation in tethered approaches is caused by fluidic pressure, electrically driven shape change, or passive deformation achieved via motion. Several different tethered actuation approaches have been developed including fluidic soft actuators, electrohydrodynamic actuators, and tension induced by external motors.
Untethered actuation methods use induced stimuli such as magnetic fields, light, chemical, temperature, and acoustic stimuli. These actuators are completely soft or have minimal rigid structures, and they can be wirelessly controlled and scaled-down in size. This gives them several advantages that tethered systems do not possess, and they can be used internally as medical devices. Additionally, they can respond to environmental changes.
However, they possess some drawbacks. Their force output and work density are less than tethered methods, and they can display unpredictable deformation, making it hard to design an inverse design strategy. Additionally, their motion and deformation are dynamically coupled to the stimuli. For example, light-actuated untethered systems can suffer from self-shadowing after deformation.
Biohybrid systems use organic elements that have actuating and sensing functions integrated with synthetic structures. The main advantage of these actuators is that they possess actuating and sensing functions without the need for complex integration and miniaturization processes. These biohybrid actuators are well-suited to biomedical applications.
In this review study, several promising methods for building truly bio-mimicking soft actuators for a multitude of real-world applications such as soft grippers, artificial muscles, smart wearable sensors, and biomedical devices have been discussed, and key challenges and future opportunities identified. This benefits the soft robotics industry, providing a solid knowledge base that will help it realize its future potential as a key technology in the 4th industrial revolution.
Li, M et al. (2021) Soft actuators for real-world applications [online] Nature Reviews Materials | nature.com. Available at: https://www.nature.com/articles/s41578-021-00389-7
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