Biodegradable electronics
are not a usual feature of our high tech society in which our devices are
obsolete in two to three years. Also biodegradable electronics implies
disposable units and this limits the materials that can be used.
Currently the ‘clever bit’
of our electronics is silicon based and silicon is biofriendly. It oxidizes and
dissolves in water, so this is a starting point from which a large team led by
Rodgers and Omenetto took up the challenge for developing biodegradable
electronics, which they call transient electronics (1,2).
At normal body and most
environmental situations, the solubility of silicon is very low and their
solution is to use it in very thin nanomembranes, thus there is very little of
it to go into solution. So nanomembranes of silicon, with some metal oxides to
make semiconductors, form the basis of electronic devices that could be
implanted into a person, an animal or perhaps a sensitive environmental
situation which would make it difficult to retrieve.
The proof of principle
gadget was a circuit embedded in a wound which could be heated to act as a
bacteriocide. It worked like a charm, the wound healed and the device was
absorbed into a now happy rat. No antibiotics were required.
The next problem is that we
might want some circuits to last longer than others and making them thicker
isn’t a very good option for a uniform production process. The answer the team
used was to sign up some silk worms into the work force. The fibroin in silk
forms sheets which then stick together via weak hydrogen bonds. The
nanomembranes can be coated with dissolved silk, which is then allowed to
re-crystalize. This controls the subsequent dissolution of the coating and then
the device.
A number of devices are
under lab test and one can imagine that in addition to the bacteriocide concept
mentioned above, the biodegradable electronics could be used for sensors
(chemicals released by sepsis or temperature changes for example after surgery) or for a controlled
release of a drug. With modern wireless technology, perhaps the release and
data acquisition could be controlled and read by our smartphones.
