For a variety of medical reasons, it’s useful to implant devices inside the body. These devices may be needed to help regulate the cardiovascular system, or they can release drugs inside the body. Unfortunately, they’re also problematic. Once such a device has served its function, it must be removed, which necessitates another surgery. Plus, its presence can lead to complications such as infection, inflammation, and pain.

To address some of these problems, scientists have developed new kinds of circuitry that can safely dissolve in the body. While these water-soluble devices don’t need to be removed, they come with a new problem—they dissolve too quickly for many purposes. So a group of researchers have now reported that they’ve developed a new way to control how long the devices last. The researchers propose that dissolving devices could be encased in a material made from silk protein and magnesium. The advantage of this approach comes from a property of the silk: its crystallinity.

Different preparations of silk dissolve in water at different rates depending on their crystallinities. Altering this property allows researchers to choose among a range of dissolution times from only a few minutes up to a few weeks. This gives more control over the duration of the device, which is important, since different medical situations require devices that can last vastly different times.

The researchers tested actual devices encased in silk in two ways, first in vitro (in test tubes filled with saline solution to mimic body fluids) and next in vivo (in live mice) to determine if they would actually work as intended. The results are promising: both tests show that the devices could be controlled wirelessly while inside the body over the time periods needed, and they can survive the process of surgical implantation.

The devices were also tested for their effectiveness at actually treating an infection in the mice. They were implanted surgically right below the infection and were wirelessly activated for two separate ten-minute periods of heating to kill the infection. The treatments were effective—after 24 hours, a visual examination revealed that the wounds were healing. Examinations of the mice revealed that the devices completely dissolved within 15 days, as intended.

"This is an important step forward for the development of on-demand medical devices that can be turned on remotely to perform a therapeutic function in a patient and then safely disappear after their use, requiring no retrieval," said Fiorenzo Omenetto, professor of biomedical engineering at Tufts University and one of the paper’s authors. "These wireless strategies could help manage post-surgical infection, for example, or pave the way for eventual 'Wi-Fi' drug delivery."

This approach will open the window to a wide range of therapies that are more effective than their non-invasive counterparts and come with none of the drawbacks of traditional implanted devices. The devices can be controlled wirelessly to release drugs, create a local high temperature, and more.

PNAS, 2014. DOI: 10.1073/pnas.1407743111 (About DOIs)

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