A Polyurethane Soft Actuator with Two Basic Contractions

Polymeric materials with compliant inner structures have brought great development to soft actuators, which have characters of low cost, high adaptability and operability, and being competent for complex motions simultaneously. From the viewpoint of muscle physiology, contraction is not limited to the shortening of muscle length but also means that a force can be produced in isometric condition without shortening. Generation of both force and stroke under a given stimulus are two fundamental functions. Accordingly, isometric and isotonic contraction are two main categories. In this work, a semi-crystal-based polyurethane soft actuator (PSA) was fabricated with abilities to perform two basic contractions. Effect of structures and thermodynamic properties on muscle contraction capability were investigated. The degree of contraction can be easily manipulated and memorized by changing crystallinity, chain orientation through preloaded and stimulated conditions. Due to the high sensitivity of crystal phase to temperature, sensing ability are reported here and energy source from enthalpy change are unprecedentedly explored. This work expands mechanism of thermal-stimulated muscle to a new direction and realizes the multi-functions of muscle in one single polymer without any complicated structure design and control system.