Because SWANS implants are made of passive components, they use almost no power while listening, extending battery life by more than fifteen times compared to Bluetooth and NFC. A complete implant with battery measures 3 x 1.1 x 17 millimeters and fits through a 6-gauge needle.
To test the system, Abramson and his colleagues installed it in chicken breasts, bone-in pork bellies, and live rats.
Twitching legs
“Pork belly is a very thick and heterogeneous tissue,” Abramson said. The signal had to penetrate fat, muscle, bone and skin. A single 10-volt pulse created a detectable voltage gradient of more than 30 centimeters across tissue and to a depth of 14 centimeters – more than ten times the range of Bluetooth or NFC.
In living rats, the signals reached implants under the skin, in the abdominal cavity and even in the stomach. The placement didn’t play a big role either. “We placed our wearable on the rat’s stomach and were then able to cause actuation in the rat’s back,” Abramson said.
The most advanced experiment used strain sensors attached to the rats’ front legs. When a sensor detected movement of the left or right front leg, the hub sent a limb-specific impulse through the body, reaching an implant on the corresponding back leg that stimulated the sciatic nerve, causing that leg to twitch. The team also built an implant-to-implant relay in which a device with a temperature sensor relayed a signal to a second implant only when it detected a fever above 40°C (104°F).
Abramson points out that pacemakers and neurostimulators already use similar voltages and pulse lengths, so the team didn’t expect major safety issues. In a two-month study in rats, scar tissue up to a millimeter thick grew around the implants, but by increasing the tension within safe limits, the team was able to maintain communication throughout. The pulses did not stimulate nerves other than the target nerves, did not alter the heart’s electrical activity, and did not cause more cell death or oxidative stress than needles and implants that were not electrified.
