快猫短视频

HOW would you feel about a robot smaller than a grain of rice patrolling your
body, hunting down disease? Well, they could be on the way, and they might even
be able to cure your ills as well. A team of micromachine experts report this
week that they have developed tiny spinning screws that could swim along veins,
ferrying drugs to infected tissues, or even burrow into tumours to kill them off
with a hot lance.

Kazushi Ishiyama at Tohoku University in Japan has designed swimming
micromachines based on cylindrical magnets. Measuring 8 millimetres long and
less than a millimetre in diameter, each magnet is made of a
neodymium-iron-boron alloy.

Ishiyama made two prototypes to test his idea. The first was designed to move
in liquids and had a short section of ceramic pipe attached to each end of the
magnet (see Graphic).
A wire wound around the pipe鈥檚 surface gave it a screw-like thread.

To test the device, Ishiyama immersed it in a container of silicone oil,
which was fixed between two vertical coils of wire. By pumping alternating
current through the coils, Ishiyama produced a rotating magnetic field around
the container, which set the screw spinning. Because of its threaded surface,
the screw slowly began to cut through the oil. Its speed increased as the
frequency of the rotating magnetic field was ramped up.

Ishiyama鈥檚 second prototype, designed to swim and burrow into tissue, used a
similar magnet but instead had a pointed, threaded brass tip at one end. This
time, Ishiyama tested the device in liquids thicker than oil. He found that it
could move at nearly 2 centimetres per second in a thick agar gel. Again, the
device moved faster the quicker the magnetic field was rotated, up to a maximum
of 20 hertz (see Graph).
Above this frequency, the magnet stopped spinning and
ground to a halt. After the gel tests, Ishiyama decided to see how well the
device could burrow through real tissue. He found it could screw itself through
a 2-centimetre thick chunk of beef steak in 20 seconds.

Because the devices are so small, Ishiyama says they could be injected into
the body using standard hypodermic needles. Once inside a vein, they could be
steered around the body magnetically. 鈥淯sing a 3D magnetic field supply system
and controller, we can steer the machine in any direction,鈥� he says.

Inside the body, Ishiyama says the devices could carry drugs to the sites of
infection. His latest prototype is even armed with a tiny metal spike that heats
up when you apply a second magnetic field vibrating at 100 kHz. The hot spike
could be useful for destroying cancerous tissue, Ishiyama believes. The high
frequency field used to heat the metal tip doesn鈥檛 interfere with steering the
device, he adds. He plans to show off the latest model in August, at the Joint
European Magnetic Symposia in Grenoble.

鈥淭he simplicity appeals to me,鈥� says Edwin Jager at Linkoping University in
Sweden, who is designing tiny robots to manipulate single cells in the body. But
Jager adds that surgeons are understandably cautious about the idea of microbots
floating free in the body. If one blocked a blood vessel, for example, it could
be disastrous. He also says that Ishiyama鈥檚 prototypes might be too long to
safely navigate some of the tighter turns in blood vessels.

While Ishiyama concedes that his swimming machines won鈥檛 replace standard
tools such as catheters for medical operations any time soon, he thinks that
nanobots even smaller than this could have a distinct advantage. 鈥淚f our
machines become smaller than catheters, they could be used for treatment in very
thin blood vessels, like in the brain,鈥� he says.