In the 1966 film Fantastic Voyage, scientists shrink a vessel down to the size of a microbe and inject it into the body of a colleague to repair damage to his brain. The shrinking concept remains strictly science fiction, of course, but the idea of using a tiny mechanical device to repair damage to the body is getting closer to science fact.
Eric Diller, a U of T professor in the department of mechanical and industrial engineering, and his team build robots a few microns (a thousandth of a millimetre) in size, no larger than a bacteria cell. Their aim is to put these tiny gadgets inside the human body to deliver drugs to their precise target. Getting drugs exactly to where they’re needed in the body allows patients to take lower doses – and experience fewer side-effects. This is particularly important for chemotherapy treatment, which aims to destroy cancer cells while leaving healthy ones alone.
The team’s microscopic machines don’t look like traditional robots, but they are able to carry out basic tasks, such as grasping and releasing nearby objects. Because the devices are so small, there’s no room for batteries to power them. Instead, they respond to the action of external magnetic fields to move them through the body. “I think of the robot as the whole system: the device, the external electromagnetic coils, the computer that controls them and the microscopes that track where they are,” says Diller.
The external magnetic fields can also make the robot change shape – for example, opening and closing its claw – by causing magnets in the device to switch between attracting and repelling modes.
Some of Diller’s most recent work has focused on building machines that can efficiently swim through human blood. This is challenging because everyday physical forces have very different effects at the micro-scale: to a miniscule robot, the attractive forces between individual water molecules make it feel like a much thicker liquid. “It’s like they’re swimming through molasses,” says Diller. “A tail that flaps from side to side like a fish is not a good strategy at this scale.”
Diller and his team have designed a “micro-swimmer,” which is only one-tenth of a millimetre thick and about one millimetre long. It looks flat, but contorts itself into undulating waves when subjected to a rotating magnetic field. Its movement is similar to a flounder or other flatfish. “It turns out to be a great way to move objects around at this size,” he says. “We can go forward or backward very easily.”
It will be some time before the team’s devices can undertake more complex operations, but their potential is vast. “The first medical applications of this research are going to be in augmenting the capabilities of minimally invasive surgery,” says Diller. “This is particularly appealing for operations that require a lot of dexterity and precision, such as in the brain or the eye. Then we’ll build on that to develop tools that can travel through the body under their own power.”