In context
In early 2024, soft robotics was rapidly evolving beyond traditional rigid robots, with a growing focus on smart materials that respond to external stimuli. This review article from the journal Robot, authored by researchers at Zhejiang University, captured the state of the art in ionic and electroactive polymer actuators, which are key to enabling lifelike movements in soft robots for applications ranging from underwater exploration to wearable devices.
What was reported
The article systematically reviews two major classes of soft actuating materials: dielectric elastomers (DEs) and hydrogels. For DEs, it compares silicone rubber, polyurethane, and acrylic-based materials, noting their respective advantages and limitations. Silicone rubbers have low dielectric constants (~2.7) requiring high voltages, while acrylics offer large strains but need pre-straining and suffer from viscoelasticity. Polyurethanes have higher dielectric constants but are prone to electromechanical instability.
To overcome these issues, the authors highlight structural modifications such as bottle-brush elastomers (BBE) and interpenetrating polymer networks (IPN). For instance, a BBE with incorporated carbon nanotubes achieved a Young's modulus below 11 kPa, and an IPN-based film reached area strains up to 233%. A novel bimodal network elastomer (PHDE) achieved 189% area strain without pre-stretching, with a breakdown field of 330 V/µm.
For hydrogels, the review covers electromagnetic-responsive, osmotic-pressure-responsive, and photo-responsive actuators, explaining their working principles and applications. These materials respond to ionic migration or external fields to produce volume changes, enabling soft actuation in diverse environments.
Why it mattered
This review underscored the critical role of material science in advancing soft robotics. By identifying pathways to improve DE performance—such as reducing Young's modulus and increasing dielectric constant—it provided a roadmap for developing low-voltage, high-strain actuators. These advances are essential for creating practical artificial muscles and soft robots that can operate in extreme conditions, such as deep-sea exploration, as demonstrated by the robotic fish tested at 10,900 meters in the Mariana Trench.
“Dielectric elastomers and hydrogels possess some special physical and chemical properties, and respond well to external stimuli, which make them important components of new soft actuators, wearable devices, medical healthcare equipment, and human-machine interactive robots.”
Source: 《机器人》期刊 (robot.sia.cn) · Published 2024-03-27 · “软体机器人离子/电响应驱动材料与结构进展”