Micro-wireless devices slated for surgery

Tiny objects may have medical application in the future

In the not-too-distant future, your surgeon may be someone who — instead of wielding a scalpel — injects you with a flock of dust-sized wireless devices that grab and remove infected or damaged tissue in response to chemical signals.

These microgrippers, less than 1/254th of an inch (1/10th of a millimeter) in diameter, have been developed by researchers at John Hopkins University in Baltimore, USA, and tested in biopsy-like procedures with animal tissue. One writer described them as working like a hand: a "palm" surrounded by six "fingers" that can open and close around an object.

The crab-like devices are moved and guided by external magnets, and grab or release in response to non-toxic biochemicals or temperature changes. By contrast, today's generation of microgrippers are physically controlled via thin wires or tubes, which make it difficult to maneuver the devices through convoluted twists and turns.

The microgrippers created at Hopkins have gold-plated nickel, so magnets outside the body can be used to move and guide the devices remotely, over relatively long distances.

The bioengineering project was directed by David Gracias, assistant professor of chemical and biomolecular engineering at the university's Whiting School of Engineering. His lab's focus is on applying the science of miniaturisation to the interface between engineered and biological systems.

Results of experiments using the new crop of wireless microgrippers were reported in the online edition of "Proceedings of the National Academy of Sciences" last month. The lead author of the paper is Timothy Leong, along with Gracias and  co-authors Christina Randall, Brian Benson, Noy Bassik and George Stern, all students supervised by Gracias.

The John Hopkins Technology Transfer staff has obtained a provisional US patent covering the team's inventions, and is seeking patent protection.

Gracias sees the devices as the first generation of technologies that could eventually result in autonomous micro- and nano-scale surgical tools, inexpensively reproducible on a mass scale, that could help doctors in diagnosing and treating a range of illnesses much less invasively than is possible today.

To build the devices, the team used photolithography, the same process used for computer chips. A layer of gold-plated nickel in the palm and fingers of the device make it visible to the watchers, who can then guide it, using medical imaging systems like an MRI.

The joints of the microgrippers fingers have thin layers of chromium and copper. These layers are "stressed" in such a way that they would naturally curl themselves close, like fingers wrapping around a baseball, according to the Hopkins press release. The research team added a layer of polymer resin, which keeps the fingers rigid and open.

The team used two methods to allow the fingers to close. One relies on raising the temperature of surrounding tissue to 104 degrees Fahrenheit (40 degrees celsius), "equivalent to a moderate fever in humans". The heat softens the polymer, and the fingers curl up. The second uses biological solutions which have a similar affect on the polymer.

In one experiment, the team used the devices to grab dozens of animal cells from a live cell mass held at the end of a tube. "The cells were still alive 72 hours later, indicating the capture process did not injure them," according to the Hopkins release.

One current drawback that the researchers are working on: once closed, these grippers can't be re-opened to release what they've grabbed. The team has created a separate device that can re-open, but it's targeted at industrial "pick and place" applications (for example, miniaturised assembly) because it relies on chemical triggers, such as hydrogen peroxide, that are unsafe for humans.

Last year, Gracias won a US$1.5 million (NZ$2.8 million) New Innovators Award, from the US National Institutes of Health. He plans to use the five-year grant to "develop an entire mobile, biochemically responsive micro- and nanoscale surgical tool kit", according to the release.

Funding for the original micrograbber research was from the US National Science Foundation, the National Institutes for Health, and the Dreyfus and Beckman Foundations.

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Tags Johns Hopkins Universitytechnologydavid graciasmicro-wireless devices

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