Your Body as Platform

Your Body as Platform

I'm at NetExplo at UNESCO in Paris today. They're presenting awards to the year's most innovative technologies today and tomorrow (including our project, LazyTruth). I'll liveblog as long as wifi and battery (personal and laptop) allow!

Nanshu Lu, Assistant Professor at the University of Texas Austin, won Grand Prix for epidermal electronics, or bio-integrated peel-on electronic devices. The technology works within the metaphor of a temporary tattoo. Nanshu specializes in the material science involved (which, one can imagine, is considerable). She's worked with a team led by Professor John Rogers, a pioneer in the space.

The field of bio-integrated electronics allows new interfaces to measure human bio feedback data, like body temperature, activity, stress.

Nanshu says the team's research is motivated in large part by the imagination of science fiction writers, and specifically threatens to bring us T-2000 from Terminator.

Silicon still outperforms organic electronics for medical purposes: it's super fast, reliable, and established in the industry. There's a lot of work being done to improve the conductivity of organic materials, because it's well behind silicon.

Silicon is flexible, and it's shape is tunable. There's a range of thickness in materials between bulk wafers and nano-membranes. Silicon's a little bendable, but when you reduce the thickness down to the submicron-level, it becomes as flexible as the bows girls tie their hair with.

Printing the silicon onto a pre-stretched silicon substrate allows the ribbons to buckle, and provide stretchability properties that doesn't break the silicon. They're building networks of Si islands on the pre-stretched substrate that allow the circuit to stay intact despite stretching with flexibility approaching that of human skin.

One day, Rogers showed Nanshu a temporary tattoo given to him by his son, and asked her if it would be possible to build medical devices that worked with this degree of flexibility. Nanshu looked into the properties of human skin. It's a multilayer system and the outer layer, the stratum comeum, is a very tough barrier for electrical signals.

By measuring the micron roughness and wavelengths of human skin, pore size, and hair diameter, Nanshu derived the parameters within which their silicon needed to work within. The device needs to stretch with skin, and recover its shape when the stretching is completed and the skin returns to its original position.

How do they accomplish this? Micro-transfer printing, a technology developed with Rogers's group, involves stamping a nano-membrane onto a silicon wafer.

They see the electronic tattoo as a multi-functional platform. It has temperature sensors, string gauges to measure motion of the skin, LEDs, and wireless data transmission via RF coil. Functional apps include:

  • amplifier to transmit EEG signals
  • LEDs
  • Solar cells which capture and covert solar energy into electrical energy
  • Inductive coils
  • String gauges of conductive polymers
  • Temperature sensor used to measure local body temperature using platinum

There are many more apps to come for this platform.

Stretchability and reliability remain constraints for this system. The system is four times stiffer than human skin with the islands-of-silicon approach. The team took a new approach to build a system that's actually slightly softer than human skin. Playing with the shape of coils allows the material to take on more flexible properties.

A water-solubule film, borrowing from the peelable backing of temporary tattoos, allows further thinning down of the eletronics. The square tattoo is flat and easy to place and position on the body. A little bit of water dissolves the backing, leaving the electronic piece intact on the body.

The material is so soft, it remains on through static eletric force, rather than bio-adhesives. It's very easy to remove and peel off without damage to hairs or skin.

One example of functionality is to measure the electrical rhythms emanating from the forehead when we do different activities like close one eye. EMG sensing can be improved by profiling the signals from our muscles. Doctors will be able to recognize patterns within patients who can't speak as long as they can move their muscles.

The device can also record very high signal to noise ratio from muscle movement recordings.

What about wearability? After one week, the device remains intact despite bathing. The device also made it through airport security checks.

The team took the metaphor full circle and disguised the device underneath an actual temporary tattoo (of the University of Illinois's pirate mascot). Once the idea is popularized, it becomes a platform for any number of potential applications.

The product is being commercialized via a startup in Cambridge, MA, called MC10. Early commercialized applications include measurement of gate, acceleration, muscle measurement, heartrate, and EEG of the head. Reebok is involved with at least some of this.

They've also convinced NASCAR racer Paulie Narraka to wear the device on his neck while driving. It can record his body's temperature in the easily-overheated racecar.

Nanshu sees the future of these electronics as dependent on continued improvements in interface, power, and data. Advancements in all three are required to move us forward. Nanshu looks forward to using the devices to not only measure, but deliver treatment. Wireless transmission technologies could drastically improve the device's power usage. Energy is a big concern, but the solar cell on-site could help. Piezo-electric membranes with zinc oxide films could also help capture mechanical motion for energy. Research into a thin film lithium ion battery could follow the same thin format.

In case our minds aren't already blown, Nanshu concludes with several other exciting examples. Electrotactile fingertip stimulators could allow blind people to read electronically-programmable Braille rather than mechanically-produced bumps on paper.

The tattoo could go inside the human body, onto our organs. It's been tested on a rabbit's heart, where it measures the heart rhythm, and can detect aberrations.

The team is funded by the US National Science Foundation, the US Air Force, and the universities involved. Nanshu sees a future where a tattoo on our foreheads can tell us how our lovers really feel about us.