Researchers have developed groundbreaking hybrid fibrous artificial muscles with the ability to actuate reversibly under external compression, significantly enhancing their application potential in robotics and materials science. These muscles can expand upon cooling and contract upon heating, presenting new functionalities for devices requiring adaptive movement.
The innovative design incorporates pre-tensioned polymeric fibers with reversible actuation capabilities inserted within pre-compressed helical metallic springs. This hybrid approach allows for actuation without reliance on external loads. Previous iterations of artificial muscles faced limitations, as they typically required external tensile loads for actuation. The new models, leveraging two types of two-way shape memory polymers, one variant of fishing line artificial muscle, and seven configurations of helical springs, demonstrate how these materials can achieve remarkable performance, including the capacity to actuate reversibly under exceptionally high compressive stresses of up to 24 MPa.
The research, published by Feng et al. and funded by multiple institutions, reflects ten years of advancements since the inception of synthetic polymeric muscles capable of reversible actuation—an area pioneered by Haines et al. The development of advanced polymers and innovative composites has opened doors to applications ranging from soft robotics to vibration dampening materials.
To explore the various configurations of the hybrid artificial muscles, seven different prototypes were fabricated. Each prototype's construction involved integrating helical springs with either cis Polybutadiene (PBD) or Polycaprolactone (PCL) to assess how each performed under compression and tension.
The modeling and simulation efforts conducted to evaluate these hybrid actuators employed structural mechanics principles. The results indicated all the muscles could actuate independently and resist buckling under high loads—thus behaving both as free-standing and beyond free-standing actuators. Notably, the muscle based on cPBD showed about 8.4% expansion during compressive loading, exceeding the capacity of previously established polymeric configurations.
These findings indicate strong potential for enhancing robotic systems with hybrid muscular structures, enabling responsive actuation under various environmental conditions. According to the designing team, combining materials with distinct thermomechanical profiles allows them to improve efficiency and sensitivity, making it possible to produce actuators under much broader compressive scenarios. The actuation strains of the prototypes varied under different loading conditions: under tension, their responses were optimal, followed by those under zero load, with the least amount of movement occurring when subjected to compression.
Similar work includes the development of new all-organic field-type electroactive polymer composites by Zhang et al., capable of functioning with significantly reduced activation voltages—suggesting there are vast possibilities for continued innovation within this field. The ability of these hybrid muscle systems to demonstrate reverse thermal actuation brings to light the possibility of creating adaptive machinery capable of dynamic responses based on temperature fluctuations.
The research outlines key parameters influencing the actuation behavior of these hybrid muscles, including material stiffness, equivalent stiffness of the polymeric wires, and pre-strain applied during the assembly, which dramatically influence operational efficiency. The development of such hybrid artificial muscles provides numerous opportunities to create versatile applications, preparing them for integration and use across environmental and structural settings.
What distinguishes this approach from traditional designs is the focus on combining the positive aspects of polymers with metallic frameworks to avert the buckling effects often faced by slender structures under duress. The creation process incorporates unique properties of two-way shape memory materials, ensuring adaptability and reversibility—crucial features desired for today’s advanced engineering applications.
Overall, the project showcases not only the advancements made within artificial muscle research over the past decade but also redefines the boundaries of functional actuators. With varied designs potentially offering efficiency gains across soft robotics and more, the team believes future efforts will yield even stronger hybrid systems with optimized performance characteristics. This initiative sets the stage for new inquiries and developments, addressing both unresolved challenges and mechanistic behaviors of composite materials required for enhancing and propelling the future of soft robotics.