Transient electronics which ‘melt in the body’

Science and Technology
This is a transient electronic device for monitoring and treating bacterial infection in surgical incision is implanted into a rat. Credit: Beckman Institute, University of Illinois and Tufts University

When it comes to development in electronics, we expect to see a trend towards smaller, faster and longer lasting devices.  However, a team of researchers at the University of Illinois and Northwestern University are working on ‘transient electronics’ which physically disappear over time in a controlled way.  Aside from reducing the amount of consumer electronics in landfills, this military backed venture into ‘melting’ electronics also has huge medical implications.

In order to produce electronics which don’t last for decades, the researchers needed to find materials which are transient but also work well together to yield high-performance electronic properties.  The paper published last week in Science explains how the tiny, but high performing, gadgets are made using ultrathin sheets of silicon called nanomembranes.  The sheets are so thin that they dissolve in biofluids, like those found within the body, in a matter of days.  The rate at which the nanomembranes melt is controlled using silk which is used as a package to encapsulate the circuits.  This can be done by purifying silkworm cocoons and then recrystallising the material at different degrees of crystallinity.  Magnesium is used as the conductor, replacing copper found in standard electronics.  Its conductivity is not as good as copper, but most importantly, it is water soluble.

When the small electronic devices melt, the different components degrade into products which are thought to be harmless to bodily function.  The silicon dissolves into silicic acid which, like magnesium, is a well-known nutritional supplement whilst silk is a natural biopolymer which is easily broken down within the body.  This means that the prospects for long-term biocompatibility are very good which is crucial if these electronics are to be used within the human body.

This new concept could provide numerous medical opportunities but the team led by John Rogers at the materials science and engineering department at the University of Illinois have been looking specifically at preventing wound reinfection.  This is a growing problem as more and more bacteria become resistant to antibiotics but bactericidal transient electronics provide an alternative.  They can be inserted into the body at the site of surgery before the patient is sewn up and then disappear as the patient moves beyond the period of greatest risk.  The device is powered wirelessly by exposing it to radio-frequency radiation through the skin and heats up the wound to kill off unwanted bacteria.  This technique has been tested in mice to see whether or not the device had the lifetime which was programmed and that it is biocompatible.  The studies showed that no inflammation associated with the device or its reabsorption was found but the bactericidal effects are yet to be tested.

Other ideas for this technology include using it to dispense drugs slowly at specific sites in vivo or to provide electrical stimulation and sensors for the brain and heart.  The devices have many advantages over currently used implantable electronics which are painful or costly to remove.  Another suggestion is that similar devices could be used as environmental sensors which can be dispersed over an oil spill in order to collect and transmit data before dissolving into the sea.

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