Micromotors small enough to swim in human arteries
25 January 2009
Researchers at Monash University in Australia have developed a micro
motor small enough to be injected into human arteries. It could be used
for the safer treatment of stroke victims, hardened arteries or
blockages in the bloodstream.
The researchers from the Micro/Nanophysics Research Laboratory at
Australia’s Monash University have published details of their device in
the Journal of Micromechanics and Microengineering .
The 'microbot', which is just a quarter of a millimetre, wide
is powered by piezoelectricity, the energy most commonly used to
trigger-start a gas stove.
The piezoelectric element vibrates at ultrasonic frequency. This is
turned into rotational movement through clever coupling to a helical
stator, which has so far achieved speeds up to 1295 rpm. The researchers
are now considering adding an E. coli-like flagellum as a means
of propulsion through the bloodstream.
Methods of minimally invasive surgery, such as keyhole surgery and a
range of operations that utilise catheters, tubes inserted into body
cavities to allow surgical manoeuvrability, 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
Remote-controlled miniature robots small enough to swim up arteries
could save lives by reaching parts of the body, lsuch as a
stroke-damaged cranial artery, that catheters have previously been
unable to reach (because of the labyrinthine structure of the brain that
catheters are too immobile to safely reach).
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
As Professor James Friend, leader of the research team at Monash
University, explained, motors have lagged behind in the age of
technological miniaturisation and provide the key to making robots small
enough for injection into the bloodstream. “If you pick up an
electronics catalogue, you’ll find all sorts of sensors, LEDs, memory
chips, etc that represent the latest in technology and miniaturisation.
Take a look however at the motors and there are few changes from the
motors available in the 1950s,” he said.
Professor 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.
The structure of the microbot
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 favourable
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.
1. B Watson, J Friend and L Yeo. Piezoelectric ultrasonic resonant
motor with stator diameter less than 250 μm: the Proteus motor. J.
Micromech. Microeng. 19 (2009) 022001 (5pp).
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