By Darren Quick
Via Technology review22:52 November 11, 2009 PST
Tattooing dates back to at least Neolithic times and has experienced a resurgence in popularity in many parts of the world in recent years. Advancements in tattoo pigments and the refinement of tattooing equipment has seen an improvement in the quality of tattoos being produced. Today it’s possible to get ink that glows under UV light, but a new technology could see tattoos that emit their own light. Researchers have been able to build thin, flexible silicon electronics on silk substrates that almost completely dissolve inside the body, paving the way for embedded LED tattoos that offer much more than just aesthetic appeal.
The devices are made of a thin film of silk on which silicon transistors about one millimeter long and 250 nanometers thick are placed. The silk holds the electronics in place and conforms to the biological tissue when implanted inside the body and wetted with saline. Unlike current electronic devices that need to be isolated from the body and are on rigid silicon, the silk substrates are completely broken down by the body into harmless by-products. And because they are just nanometers thick, the thin silicon circuits left behind don’t cause irritation.
Although the prospect of LED tattoos brings to mind science-fiction scenarios of gangs sporting futuristic illuminated designs that can be animated to move across a person’s body, the technology is being developed for medical applications such as photonic tattoos to show blood-sugar readings.
The technology also offers the prospect of arrays of conformable electrodes that could interface with the nervous system to allow improved control of prostheses. Also, arrays of silk electrodes conforming to the brain’s crevices thereby reaching regions inaccessible with current technology could be used to control Parkinson’s symptoms.
Silk is already approved for medical implants by the U.S. Food and Drug Administration and the researchers are able to control the rate at which it degrades, which can range from immediately after implantation up to years. Silicon has not conclusively been proven to be biocompatible, but all studies so far have shown it to be safe. The devices also contain gold and titanium, which are required for the electrical connections. Because they are biocompatible but not biodegradable the researchers are working on biodegradable contacts so that all that would remain inside the body is silicon.
The silk-silicon technology is being developed by researchers at the Beckman Institute at the University of Illinois at Champaign-Urbana, Tufts University in Medford, MA, and the University of Pennsylvania. They managed to implant silk-silicon devices in animals with no adverse effects and no impact on the performance of the transistors on the silk. Their findings appear in a Paper published in the journal Applied Physics Letters.