Transition metal oxides as novel actuators : fabrication, origami micro-robots and self-integrated sensing systems

Abstract

Compact material constructs that can mimic the complicated motions with some degree of built-in intelligence via exhibiting complex functionalities responsive to multiple stimuli are essential for artificial muscles for insect-scale robots. This thesis reports the development of a versatile approach to actuate origami micro-robots by self-folding creases made of a type of stimuli-responsive transition metal hydroxides/oxides that can undergo large actuation under electrochemical or light stimulations. A few enabling technologies have been developed to achieve the above. First, a micro-scale riveting method is introduced to provide strong adhesion of the stimuli-responsive material on a micro-porous polycarbonate origami body, which allows the successful construction of actuating creases made from different stimuli-responsive transition metal hydroxides/oxides that can self-fold into curvatures exceeding 1 mm-1 under low-intensity visible-light stimulation in ambient conditions, or low-potential electrochemical stimulation in electrolytic environments, with response time as fast as in seconds. Based on the high performance of such active creases, complex miniaturized origami designs powered by hinges activated in response to two stimuli are demonstrated. Secondly, to achieve direct material integration, a special microfluidic electrolyte-delivery methodology has been developed to directly electrodeposit stimuli-responsive nickel hydroxide/oxyhydroxide or manganese oxide into arbitrary 2D patterns on the above micro-porous polymeric-based substrates, thus allowing direct printing of micro-robotic devices of a large variety of designs. These results prove a new, versatile paradigm for micro-robotics, where a transferrable approach is applicable to design and fabricate a wide variety of customizable micro-robots with compact construction and complex motions using different stimuli-responsive ceramic-based materials. Using this method, a finger-mimicking actuator with independently controlled actuating joints in a compact design, as well as centimeter-scale hand giving complex signals, are demonstrated. Moreover, by local controlling the thickness of the printed muscle groups, “on-demand” stiffness-enhancing and actuating functions are directly integrated into a compact thin-film device. Lastly, a high-performing multi-stimuli, multi-responsive material of cobalt-doped manganese dioxide (Co-MnO2) is also discovered, which exhibits large, fast (up to 100 ms for 1 curl) and symmetrically reversible actuation in response to electrochemical, light or humidity stimulations, as well as decreased electrical resistivity under light illumination. The actuation properties of the material are fine-tunable by controlling the amount of Co-doping followed by an electrochemical treatment to activate the light or humidity actuation. Utilizing the dual responsive nature of actuation and resistance change under light stimulation, compact devices capable of performing self-sensing actuation responsive to ultra-low visible light intensities of ~4 mW/cm2, and self-adjusting load-lifting are presented. Furthermore, a fast-responsive micro-robotic finger with built-in capabilities of self-discrimination, tunable movement and stiffness adjustment is also demonstrated. These show that Co-MnO2 is a promising material for intelligent artificial muscle in miniaturized and multi-functional robotic devices.