Joule Heating Activation of 4D Printed Conductive PLA Actuators

Four-dimensional (4D) printed structures have great potential to be deployed in various sectors, such as industrial and biomedical applications. The high complexity allowed by additive manufacturing, coupled with the shape change allowed by shape memory materials (SMMs) opened a wide range of applications for this field. However, most methods used to activate SMMs rely on the use of hot air or hot water. Such methods limit the application ranges of 4D printed structures. Thus, in this paper, polylactic acid combined with carbon black is used as the filament material for the printing process, which relies on the fused deposition modeling approach. The carbon black makes the filament conductive, allowing it to be heated by an electrical current. Joule heating is used to activate four actuators printed at different printing speeds, causing larger bending as the printing speed increases. The activation of the actuators is made by allowing electrical current to pass through the actuators and gradually heating them from 30 °C to 80 °C. The heating process requires 69 to 85 seconds to reach full deformation while the voltage and current are stable. The actuators achieved bending angles of 13°, 19°, 26°, and 32° when the printing speed of the active layers was 20, 40, 60, and 80 mm/s, the respectively. The developed actuators show promising performance, making them suitable for various applications in robotics.