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Implant Releases Painkillers for Several Days, Then Biodegrades

Magnesium resonators open capsules surgically placed near pain site.

Patients fitted with an orthopedic prosthetic commonly experience intense pain after surgery. To control the pain, surgeons inject painkillers into the tissue during the operation. When that wears off a day or two later, patients are given anesthetics through a catheter placed near the spine. Yet catheters are not particularly comfortable, and the anesthetic spreads throughout the body, affecting all organs and potentially causing problems.

Researchers at École Polytechnique Fédérale de Lausanne in Switzerland are developing a biodegradable implant that releases a local anesthetic on-demand over several days. The implant reduce patients’ post-op discomfort, and there would be no need for further surgery to remove it. The painkilling drug would also be limited to the area closed to the implant.

The implant contains a small biodegradable electronic heating circuit made from magnesium that could be activated wirelessly from outside the body. The circuit controls the release of small doses of anesthetic over several days. After that, the implant degrades safely inside the body.

The electronic circuit, a spiral-shaped resonant circuit, is just a few microns thick. When exposed to an alternating electromagnetic field, the resonator generates an electric current that creates heat.

The researchers’ end-goal is to pair the resonators with painkiller-filled capsules and then insert them into the tissue during surgery. The contents of the capsules could be released when an electromagnetic field sent from outside the body melts the capsule membrane. The heat-and-release process should take less than a second.

“We can now fabricate resonators that work at different wavelengths,” says Matthieu Rüegg, Ph.D. student and leader on the project. “That means we can release the contents of the capsules individually by selecting different membrane materials and frequencies.”

Researchers had to get creative when it came time to making the resonators. “We immediately ruled out fabrication process that involved contact with water because it will dissolve magnesium in just a few seconds,” says Rüegg.

They ended up shaping the magnesium by depositing it on a substrate and then showering it with ions. They were eventually able to create some of the smallest magnesium resonators in the world: two microns thick, with a diameter of three millimeters.

The team’s invention is not quite ready for the operating rooms. “We still need to work on putting the resonators into the final device and show that it’s possible to reliably release drugs in patients,” says Ruegg.

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