Most people appreciate electronics that are durable and can last for years before needing to be replaced. If the device in question is a medical implant or a sensor for monitoring environmental conditions, however, designers might prefer the gadget to simply biodegrade without a trace once its purpose is fulfilled.
University of Illinois researchers, working with colleagues at Tufts University and Northwestern University, report in the September 28 issue of Science having developed a way to make "transient" electronics able to do just that by dissolving in small amounts of bodily fluid. Other triggers for dissolution and absorption by the body might someday include heat, radiation and pH levels.
The research described in Science is notable because it describes a wide array of dissolvable, or "bioresorbable," electronics, including transistors, diodes, wireless power coils, sensors and even a 64-pixel digital camera. These bioresorbable electronics are a new twist on degradable medical implants, which are also seeing innovations. Abbott Labs, for instance, recently introduced a vascular scaffold, or stent, that can be used for the treatment of coronary artery disease, restoring blood flow to the heart before dissolving in the body.
The researchers who reported in Science succeeded in creating dissolvable electronics by keeping the components extremely thin and selecting materials such as magnesium, magnesium oxide and silicon that function in electronics but are not toxic to the body. The amount of the mineral magnesium in one device, for example, is actually lower than that in a multivitamin, according to the researchers.
To demonstrate how these devices might work, the researchers fabricated a variety of transient devices, sealed them in water-soluble silk packages, sterilized the packages and implanted them under the skin in mice. In this instance, the implanted devices delivered a drug meant to prevent bacterial infections at surgical wound sites in the animals.
The structure of the silk—collected from silkworm cocoons—determines how quickly it dissolves, whether at a rate of minutes, days, weeks or longer. Tufts engineers, including biomedical engineering professor Fiorenzo Omenetto, who contributed to this project, have for years been developing electronic and photonic materials by patterning metals or thin films onto silk's surface.
This current research furthers the work of John Rogers, the University of Illinois engineering professor who led the multidisciplinary research team, in the area of biological medical sensors. In October 2010 Rogers co-authored a paper in Nature Materials describing flexible light-emitting diodes (LEDs) that might someday be implanted in the body. Although the practical uses of this technology still need to be worked out, Rogers speculated at the time that LEDs might be integrated with tissue in the body and alert physicians to the presence and location of infections after a surgical procedure. (Scientific American is part of Nature Publishing Group.)
Backed by the Defense Advanced Research Projects Agency (DARPA) the researchers are refining their devices for specific applications, conducting more animal tests and working with a semiconductor foundry to determine when such components could be manufactured in large volumes.