Medical soft robotics constitutes a rapidly developing field in the treatment of cardiovascular diseases, with a promising future for millions of patients suffering from heart failure worldwide. Herein, the present state and future direction of artificial muscle‐based soft robotic biomedical devices in supporting the inotropic function of the heart are reviewed, focusing on the emerging electrothermally artificial heart muscles (AHMs). Artificial muscle powered soft robotic devices can mimic the action of complex biological systems such as heart compression and twisting. These artificial muscles possess the ability to undergo complex deformations, aiding cardiac function while maintaining a limited weight and use of space. Two very promising candidates for artificial muscles are electrothermally actuated AHMs and biohybrid actuators using living cells or tissue embedded with artificial structures. Electrothermally actuated AHMs have demonstrated superior force generation while creating the prospect for fully soft robotic actuated ventricular assist devices. This review will critically analyze the limitations of currently available devices and discuss opportunities and directions for future research. Last, the properties of the cardiac muscle are reviewed and compared with those of different materials suitable for mechanical cardiac compression.
Polymeric gel‐based artificial muscles exhibiting tissue‐matched Young's modulus (10 Pa–1 MPa) promise to be core components in future soft machines with inherently safe human–machine interactions. However, the ability to simultaneously generate fast, large, high‐power, and long‐lasting actuation in the open‐air environment, has yet been demonstrated in this class of ultra‐soft materials. Herein, to overcome this hurdle, the design and synthesis of a twisted and coiled liquid crystalline glycerol‐organogel (TCLCG) is reported. Such material with a low Young's modulus of 133 kPa can surpass the actuation performance of skeletal muscles in a variety of aspects, including actuation strain (66%), actuation rate (275% s−1), power density (438 kW m−3), and work capacity (105 kJ m−3). Notably, its power density is 14 times higher than the record of state‐of‐the‐art polymeric gels. No actuation performance degradation is detected in the TCLCG even after air exposure for 7 days, owing to the excellent water retention ability enabled by glycerol as co‐solvent with water. Using TCLCG, mobile soft robots with extraordinary maneuverability in unstructured environments are successfully demonstrated, including a crawler showing fast bidirectional locomotion (0.50 mm s−1) in a small‐confined space, and a roller that can escape after deep burying in sand.
Coiled Artificial Muscles
In article number 2210419, Zhen Jiang, Geoffrey M. Spinks, and co‐workers introduce a liquid crystalline organogel combined into a twisted and coiled fiber geometry to generate a powerful soft artificial muscle with fast response to small temperature changes.
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