Self-Propelled Swimming Microrobot Using Electroosmotic Propulsion and Biofuel Cell

Self-propelled swimming microrobots have significant potential for medical applications. The outstanding technical challenges are the realization of a propulsion mechanism suitable for micro/nanoscale fluids and of an energy supply mechanism that can function inside the human body. Our proposed concept uses electroosmotic propulsion (EOP) and biofuel cell (BFC). The BFC mechanism has a bioanode and a biocathode that generate an open-circuit potential (OCP) by redox reactions of biofuels. The EOP mechanism has an insulating tube arranged between the electrodes. Electroosmotic flow is generated inside the tube by the electric force from the OCP. A reaction force then propels the robot. We derived a theoretical model of the EOP mechanism, which suggested that a smaller robot would have a greater velocity. A microscale prototype was designed and fabricated using an insulating SU-8 layer and two conductive SU-8 layers incorporating enzymes, with glucose and oxygen as the biofuels. “Proof-of-Concept” experiments were conducted using the 100 $\mu$m prototypes. The observed self-propulsion in the glucose solution was compared with the theoretically estimated values. The results confirmed the validity of the concept. This configuration can be used as a standalone biomedical microrobot, or as an actuator element in a robot system.