"Transient electronics," water soluble circuits (via Tuft University)
As engineers, we want to design things to last. Above that however, we want things to function as best as they can. Paradoxically in some instances, the application calls for transient components that are only needed for a specific, short period of time. With medical applications and others, we can observe the negative effects of making things last too long as they fill up landfills after they are used. For this reason, scientists from the University of Illinois, Northwestern University and Tufts University have created what they call “transient electronics,” or electronics made to dissolve into their surroundings after a predetermined period of time.
The transient electronics are made of nanomembranes of silicon and magnesium oxide that are printed with circuitry much like a PCB, offering robust performance very similar to conventional electronics. Silicone is water-soluble but to prevent immediate disintegration, components are covered in silk. These electronics can be made to dissolve in minutes, days or even years depending on the protective layer of silk. This silk is harvested from silkworm cocoons, dissolved and then allowed to crystallize. The way it recrystallizes, along with thickness, determines how fast it will dissolve and, in turn, how fast the electronic device will melt. Ultimately, the entire devices, including sensors and power supply melt away.
Many applications have been proposed, medical being the primary thought. The team has already tested a device they implanted in rats, made entirely of non-toxic materials, that provides enough heat to surgical cuts and prevents the growth of bacterial infections. This application alone could prove to be perfect for conservation of resources as the most common cause for readmission after surgery is infection. This heating device could be implanted before sutures and could last for only a couple of weeks till the wound heals. Other tested applications include a 64-megapixel camera, solar cells and temperature sensors.
Still theoretical applications include medicine delivery devices, sensors for the brain and heart, sensors that can be deployed in mass quantities into the environment during things like oil spills and manufacturing electronic components that will dissolve like those found in cell phones or computers. DARPA, who funded the project, wants to use them, in mass quantities, to snoop in military operatives.
In a paper published in the Science magazine, the team describes sets of materials, manufacturing schemes, device components and theoretical design tools that could be used to create transient complementary metal-oxide semiconductors (CMOS). Tests are being conducted to see how these transient electronics dissolve at different temperatures, pH levels and other environmental conditions such as light or pressure. The team plans to start human trials in the next couple years while at the same time exploring how these transient electronics can be used along with sensors, actuators, power supplies and wireless controls.