Researchers from MIT Media Lab and Microsoft have created a gold-leaf infused tattoo that turns the skin into a touchpad capable of controlling wireless devices.
DuoSkin tattoos function as extensions of circuits on the skin. When touched and manipulated, the different circuits are completed, sending signals to a mobile device like a smartphone.
The core material used in DuoSkin is gold leaf, which was chosen for its skin-friendly and robust properties, allowing use in everyday wear, and being user-friendly to fabricate. Because not much gold is actually used in the construction of the circuits, the tattoos are still fairly cheap to manufacture.
DuoSkin devices are capable of three types of interactions: sensing touch input, displaying output, and communicating wirelessly with other devices via induction (NFC).
The engineers embarked on the DuoSkin project after realising that epidermal electronics is expensive, requiring materials and fabrication processes that are limited to the medical domain and material sciences. While on-skin devices are already used to monitor vital signals, glucose levels and skin conditions, this limitation has limited applications of on-skin devices beyond the medical realms.
Attaching gold leaf directly to the skin allows the team behind the DuoSkin to bring on-skin user interfaces to the wider community.
The creation of DuoSkin happens in three steps. In the first step, the researchers placed paper stencils on the body to decide the location and size of user interfaces. They then design the actual on-skin circuitry in 2D design tools.
Once the design has been digitised, the DuoSkin is fabricated in three sub-steps. Firstly the stencil for the circuitry is created by applying a layer of vinyl film on thin tattoo paper. The researchers then cut the film layer with a low-cost electronic cutter, exposing a positive of the pattern on the tattoo paper.
The researchers then spray adhesive onto the tattoo paper and stack multiple layers of gold leaf on it. They then remove the remaining film layer, leaving conductive gold leaf traces.
Finally, the researchers attached surface-mount electronics to the gold leaf traces with conductive fabric tape, before adding a layer of thin tattoo paper adhesive. In the final step, the researchers applied the fabricated components to the skin via water transfer, similar to applying temporary tattoos. A layer of tattoo paper insulates the electrode from the skin, preventing electric charges on the surface of the skin from interfering with the capacitive touch signals.
With different patterns, the DuoSkin can be shaped to resemble various user interfaces, such as buttons, discrete sliders, continuous sliders, and 2D trackpads.
Additionally, the addition of thermochromics allows DuoSkin to be used as soft displays. Thermochromics change colours when they are heated to beyond body temperatures. Gold leaf with resistive heating elements positioned under the thermochromic layers trigger the temperature changes that cause the colour to change.
The researchers were also able to create NFC tags, by fabricating coils on the skin using gold-leaf, then attaching an NFC integrated circuit to the coil.
According to the researchers, the DuoSkin solution is much more comfortable, skin safe, and aesthetic compared to alternatives like copper tape and thread. Additionally, they play a part as temporary body art, so reducing the boundary to their use.