AI News, BOOK REVIEW: Medical Microbots Take a Fantastic Voyage Into Reality

Medical Microbots Take a Fantastic Voyage Into Reality

In the 1966 film Fantastic Voyage, scientists at a U.S. laboratory shrink a submarine called Proteus and its human crew to microscopic size and then inject the vessel into an ailing scientist.

In the past 10 years or so, a menagerie of whimsical-sounding designs has emerged: microrobots driven by bull sperm and bacteria, starfishlike microgrippers that can close their arms around tissue as they get warm, spinning magnetic helices that can deliver DNA to cells, steerable magnetic spheres packed with drugs, micromotors powered by gastric acid, and microscallops that can flap their way through the vitreous humor of the eye.

With the right design, researchers say, a microrobot—or a swarm of them—could deliver a highly targeted dose of drugs or radioactive seeds, clear a blood clot, perform a tissue biopsy, or even build a scaffold on which new cells could grow.

These sorts of activities could help extend two current trends in medicine: diagnosing diseases earlier and targeting therapies more precisely, says Bradley Nelson, a professor of robotics and intelligent systems at ETH Zurich.

And working in the human body applies extra constraints: You need to be able to keep track of where an object is, make sure it isn’t toxic and won’t injure tissue, and design it to degrade safely or leave the body once its mission is complete.

And in 2012, the U.S. Food and Drug Administration gave Proteus Digital Health, headquartered in Redwood City, Calif., the green light to market a much smaller swallowable technology: a single-square-millimeter silicon circuit that can be embedded inside a pharmaceutical pill.

For 5 or 10 minutes, the chip has enough power—between 1 and 10 milliwatts—to modulate a current, transmitting a unique identifier code that can be picked up by an external skin patch.

The chip is more than sufficient, Christen says, to help patients keep track of drug consumption and help pharmaceutical companies monitor how closely subjects in clinical trials follow a regimen when they’re testing a new drug.

Shrink an object down below 1 millimeter, he says, and “the battery’s capacity will go down drastically.” One alternative is wireless power transfer—piping in radio waves, for example, from outside the body to generate electricity.

His strategy borrows a page from the imperfect world of biology: “If you have a large number of not-perfect devices, you may be able to achieve the same functionality as one perfect one.” The gastrointestinal tract is a fairly forgiving place to work inside the human body.

An autonomous swimmer might be able to muster only 20µm or so of fast, directed motion, he says, so it’s likely that external guidance will be needed to get the device most of the way to its destination.

To move an object with a robotic arm in any arbitrary way, he explains, you need six actuators for a full six degrees of freedom: movement in the x, y, and z directions, and rotation around each of those axes.

When he and his colleagues worked out a way to finely control a simple magnetic microrobot with five degrees of freedom, they found that eight separate external magnetic coils were needed.

In the near term, Nelson is looking to see how his magnetic control technology could be used by doctors in a tethered fashion, as a way of finely guiding the tips of catheters through the cardiovascular system.

Inner Workings: Medical microrobots have potential in surgery, therapy, imaging, and diagnostics

In 2013, a group at the Institute for Integrative Nanosciences in Dresden, Germany, debuted a device that traps bull sperm in magnetic nanotubes and uses the cells for propulsion (5);

In 2014, researchers from the University of Illinois at Urbana–Champaign built a device that propels itself through viscous fluids, such as blood, using constantly contracting heart cells (8).

In those laboratory experiments, Douglas and his team attached proteins to folded DNA in random configurations and showed how the molecular robot could deliver drugs to target cells.

While internal imaging approaches can achieve a resolution of about 100 microns, the leaky blood vessels that would offer inroads for drug delivery robots are only a few microns in diameter.

In August 2016, he and his team reported that when they injected drug-bearing bacteria near the cancer site in mice, more than half of the microbes migrated into the heart of the tumors (11), autonomously seeking hypoxic areas after being steered the right region with magnetic fields.

He hypothesizes that hybrids like these, which combine the functionality of genetically modified microorganisms with state-of-the-art technology, have the best chance of becoming part of medical treatments in the future.

Propellers for Microrobots

Researchers have developed a novel form of propulsion for microrobots that mimics the way bacteria zip about using corkscrew-like appendages called flagella.

Tests show that the tiny rotating nanocoils–just 27 nanometers thick and 40 micrometers long–are capable of spinning at 60 revolutions per minute and that it is possible to propel an object at nearly 5 micrometers per second.

Such propulsion could be used as part of smart drug delivery systems, which are steered through the bloodstream directly to their target, says Bradley Nelson, a professor of robotics and intelligent systems at the Swiss Federal Institute of Technology, in Zurich, who led the research.

Moving through fluids at the nanoscale can be a real challenge because of the viscosity of the liquid, says Sylvain Martel, an associate professor at the department of computer engineering at Montreal Polytechnique in Canada.

To make this helical nanocoil rotate, Nelson and his colleagues then created a set of four magnetic coils positioned so that they would produce an electromagnetic field that would rotate around a single axis.

Even so, says Martel, before such devices are made sophisticated enough to be autonomous, they will still need to be monitored, tracked, and steered through the 80,000 kilometers of blood vessels in the human body.

New remote-controlled microrobots for medical operations

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