Reconfigurable Soft Actuators with Multiple-Stimuli Responses

Empowering artificial muscles with intelligence: recent advancements in materials, designs, and manufacturing

Drawing on foundational knowledge of the structure and function of biological muscles, artificial muscles have made remarkable strides over the past decade, achieving performance levels comparable to those of their natural counterparts. However, they still fall short in their lack of inherent intelligence to autonomously adapt to complex and dynamic environments. Consequently, the next frontier for artificial muscles lies in endowing them with advanced intelligence. Herein, recent works aimed at augmenting intelligence in artificial muscles are summarized, focusing on advancements in functional materials, structural designs, and manufacturing techniques. This review emphasizes memory-based intelligence, enabling artificial muscles to execute a range of pre-programmed movements and refresh stored actuation states in response to changing conditions, as well as sensory-based intelligence, which allows them to perceive and respond to environmental changes through sensory feedback. Furthermore, recent applications benefiting from intelligent artificial muscles, including adaptable robotics, biomedical devices, and wearables, are discussed. Finally, we address the remaining challenges in scalability, dynamic reprogramming, and the integration of multi-functional capabilities and discuss future perspectives of augmented intelligent artificial muscles to support further advancements in the field.

Synthesis of Self-healing and Light-, Thermal-, and Humidity-induced Deformative Polyurethane Actuator

Intelligent actuating materials have drawn enormous attention because of their potential applications in soft robots, smart sensors, bionics, etc. Aiming to integrate light, thermal, and humidity stimuli deformations and self-healing function into a single polymer, a smart actuating polyurethane material CPPU-50 is designed and successfully synthesized through co-polymerization of azobenzene-containing Azo-C12 , polyethylene glycol 200 (PEG200), and 4,4'-diphenylmethane diisocyanate (MDI) at a ratio of 1:1:2. The obtained polyurethane CPPU-50 exhibits good photoinduced bending, thermal responsive shape memory effect, humidity triggered deflections and self-healing properties. Furthermore, an actuator combining light and thermal stimuli is created and the self-healing CPPU-50 film can withstand the object of 1800 times without tearing. This work can pave a way for further development of long-lived multi-stimuli-responsive actuating devices and intelligent materials.

Development and challenges of smart actuators based on water-responsive materials

Water-responsive (WR) materials, due to their controllable mechanical response to humidity without energy actuation, have attracted lots of attention to the development of smart actuators. WR material-based smart actuators can transform natural humidity to a required mechanical motion and have been widely used in various fields, such as soft robots, micro-generators, smart building materials, and textiles. In this paper, the development of smart actuators based on different WR materials has been reviewed systematically. First, the properties of different biological WR materials and the corresponding actuators are summarized, including plant materials, animal materials, and microorganism materials. Additionally, various synthetic WR materials and their related applications in smart actuators have also been introduced in detail, including hydrophilic polymers, graphene oxide, carbon nanotubes, and other synthetic materials. Finally, the challenges of the WR actuator are analyzed from the three perspectives of actuator design, control methods, and compatibility, and the potential solutions are also discussed. This paper may be useful for the development of not only soft actuators that are based on WR materials, but also smart materials applied to renewable energy.

Programmable Stimuli-Responsive Actuators for Complex Motions in Soft Robotics: Concept, Design and Challenges

During the last years, great progress was made in material science in terms of concept, design and fabrication of new composite materials with conferred properties and desired functionalities. The scientific community paid particular interest to active soft materials, such as soft actuators, for their potential as transducers responding to various stimuli aiming to produce mechanical work. Inspired by this, materials engineers today are developing multidisciplinary approaches to produce new active matters, focusing on the kinematics allowed by the material itself more than on the possibilities offered by its design. Traditionally, more complex motions beyond pure elongation and bending are addressed by the robotics community. The present review targets encompassing and rationalizing a framework which will help a wider scientific audience to understand, sort and design future soft actuators and methods enabling complex motions. Special attention is devoted to recent progress in developing innovative stimulus-responsive materials and approaches for complex motion programming for soft robotics. In this context, a challenging overview of the new materials as well as their classification and comparison (performances and characteristics) are proposed. In addition, the great potential of soft transducers are outlined in terms of kinematic capabilities, illustrated by the related application. Guidelines are provided to design actuators and to integrate asymmetry enabling motions along any of the six basic degrees of freedom (translations and rotations), and strategies towards the programming of more complex motions are discussed. As a final note, a series of manufacturing methods are described and compared, from molding to 3D and 4D printing. The review ends with a Perspectives section, from material science and microrobotic points of view, on the soft materials’ future and close future challenges to be overcome.