January 21, 2009: A range of complex surgical operations necessary to treat stroke victims, confront hardened arteries or address blockages in the bloodstream are about to be made safer as researchers from the Micro/Nanophysics Research Laboratory at Australia’s Monash University put the final touches to the design of micro-motors small enough to be injected into the human bloodstream.
A research paper, published January 20 in IOP Publishing’s Journal of Micromechanics and Microengineering details how researchers are harnessing piezoelectricity, the energy force most commonly used to trigger-start a gas stove, to produce microbot motors just 250μm wide.
Methods of minimally invasive surgery, such as keyhole surgery and a range of operations that utilize catheters, tubes inserted into body cavities to allow surgical maneuverability, are preferred by surgeons and patients because of the damage avoided when contrasted against cut and sew operations. Serious damage during minimally invasive surgery is however not always avoidable and surgeons are often limited by, for example, the width of a catheter tube which, in serious cases, can fatally puncture narrow arteries.
Remote controlled miniature robots small enough to swim up arteries could save lives by reaching parts of the body, like a stroke-damaged cranial artery, that catheters have previously been unable to reach because of the labyrinthine structure of the brain and catheters’ lack of mobility. With the right sensor equipment attached to the microbot motor, the surgeon’s view of, for example, a patient’s troubled artery can be enhanced and the ability to work remotely also increases the surgeon’s dexterity.
Photo of the micro-motor prototype showing the Φ241 μm helically cut stator, 1mm stainless-steel ball as a rotor and the PZT element. (b) Magnets were used to increase the friction coupling preload. (Source: Journal of Micromechanics and Microengineering)
As Professor James Friend, leader of the research team at Monash University, explained, motors have lagged behind in the age of technological miniaturization and provide the key to making robots small enough for injection into the bloodstream. “If you pick up an electronics catalog, you’ll find all sorts of sensors, LEDs, memory chips, etc that represent the latest in technology and miniaturization. Take a look however at the motors and there are few changes from the motors available in the 1950s.”
Friend and his team began their research over two years ago in the belief that piezoelectricity was the most suitable energy force for micro-motors because the engines can be scaled down while remaining forceful enough, even at the sizes necessary to enter the bloodstream, for motors to swim against the blood’s current and reach spots difficult to operate upon.
Piezoelectricity is most commonly found in quartz watches and gas stoves. It is based on the ability of some materials to generate electric potential in response to mechanical stress. In the case of a gas stove, the ignition switch on a stove triggers a spring to release a ball that smashes against a piece of piezoelectric material, often kinds of crystal, which translates the force of the ball into more than 10,000 volts of electricity which then travels down wires, reaches the gas, and starts the stove fire.
As Professor Friend explains, “Opportunities for micro-motors abound in fields as diverse as biomedicine, electronics, aeronautics and the automotive industry. Responses to this need have been just as diverse, with designs developed using electromagnetic, electrostatic, thermal and osmotic driving forces. Piezoelectric designs however have favorable scaling characteristics and, in general, are simple designs, which have provided an excellent platform for the development of micro-motors.”
The team has produced prototypes of the motors and is now working on ways to improve the assembly method and the mechanical device which moves and controls the micro-motors.