A medical device may include a micro-machined substrate, at least one thermo-electric assembly associated with the substrate, and a cooling system configured to configured to remove heat from the a region of the substrate proximal the substrate. According to various aspects, a method of clearing plaque from a blood vessel may include implanting a micro-device in the blood vessel, wherein the micro-device may include at least one ultrasonic transducer, and operably controlling the micro-device to emit high frequency ultrasonic waves for breaking up said plaque.