Micro hydraulic actuators have been fabricated to improve the operability of minimally invasive medical instruments, such as guidewires, catheters, and endoscopes. The actuators consist of a metal spring coil, evaporated parylene membrane, and a metal wire. Since parylene is used as the membrane, the actuator can be made with a diameter smaller than 1 mm and several actuators can be batch fabricated. As shown in Fig.1, the actuator elongates except for the side that is restricted by a metal wire when water is injected, allowing the actuator to bend. Since the actuators use water to achieve the bending motion and consist of biocompatible materials, they are safe in the human body.
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