Patients in hospitals, elderly folks and people with heart problems might soon be wearing temporary tattoos instead of heart rate monitors or pulse oximeters. Professor Nanshu Lu and a team at the University of Texas at Austin's Cockrell School of Engineering have come up with a way to quickly print cheap, wearable biosensors.
When the researchers were looking at building tattoo-like wearables, they knew there were plenty of smart, tiny, sensors on the market. The problem wasn’t with the technology, Lu says, it was with the manufacturing process, which was long, tedious and expensive. That made it nearly impossible to develop disposable sensors to temporarily monitor health outcomes.
“Ultimate, if you think about tattoo-like electronics, no one wants to reuse them—not even on yourself—so the disposable nature is key,” Lu says.
Previously, similar sensors had been made by engineering the mechanical component, a metal circuit, and then integrating it with a stretchy adhesive. The process was expensive and time consuming.
The researchers looked at alternative ways to make brittle electronics flexible and sticky. Using the principles of 3D printing, they figured out a way to use a mechanical cutter to carve out patterns on a sheet of metal instead of forming the electronics in a mold.
“We started to look for metal sheets deposited on polymer sheets, basically like aluminum foil laminated onto double-sided tape,” Lu says. They found the cheap, flexible metal surprisingly easily—in the home improvement aisle of a hardware store. Things like gold-coated polymers are used as heat reflection in construction.
“We invented a process that can form cutting patterns onto those sheets, then remove the unnecessary parts,” she says. “The leftover part is transfer printed onto medical tape or tattoo adhesive.”
The printing takes about 20 minutes, and unlike previous methods for building flexible electronics, this one creates minimal waste and doesn't require a special lab. Lu says she wants to get costs down to about $1 per patch.
The team's goal is to integrate multiple sensors and antenna onto a credit-card-size patch, which could monitor vital signs for about a week and wirelessly communicate them to doctors' and patients' computers, tablets and smartphones. Depending on where the patch is placed on the body, it could function like an electrocardiogram (ECG), which measures heart activity, or an electroencephalogram (EEG), which looks at brain function. The patches could measure skin hydration, respiration rate and eye activity, and eventually track blood pressure and oxygen saturation, for a range of patients, from pregnant women to athletes.
One of the biggest challenges to mass manufacturing the wearable is making it wireless, through Bluetooth or a near field communication (NFC) chip. Chip manufacturers haven’t committed to making chips tiny enough yet, so Lu and her team are working on developing one that measures two square millimeters. That said, if people are comfortable with a coin-sized wireless device being a part of the patch, the device could be ready soon.
“The coolest part is that this is really a platform technology," Lu says. "You can keep pushing the frontiers of the skins or the sensors or antenna. You can add to this platform."