Engineers use the human body to transmit wireless device signals

Using the human body to transmit signals, Georgia Tech engineers have created a wireless networking system that allows tiny implantable sensors and actuators to communicate with each other as well as wearable devices.

Their system means devices can work together like never before, sensing in one part of the body and triggering a therapeutic response elsewhere - perhaps releasing medicine or stimulating a nerve.

Described Sept. 24 in the journal Science, their communication method is expandable to include multiple interconnected devices across the body, even deep inside the stomach.

With our system, you can now place sensors in the best possible place to detect a biological signal and place actuators in the best possible place to perform a therapeutic action. They don't need to be connected, aligned, or even near each other; they can just send signals to each other through the surrounding tissue."

Alex Abramson, study's senior author and assistant professor, School of Chemical and Biomolecular Engineering

The researchers aimed to imitate the same level of connectedness the body achieves through the nervous system. They call their invention SWANS for Smart Wireless Autonomous Networking System.

Abramson said our bodies are terrible at allowing traditional wireless signals such as Bluetooth or NFC to pass through, and that has traditionally limited how much wearable devices and implants can work together. Those signals also require large antennas and lots of power, so implants must be large to accommodate those components.

SWANS removes those limitations by using body tissue's natural ionic conductivity as the connection between devices.

Each implant is programmed to respond to electrical pulses of specific voltage and length passed through the tissue from one device to another, allowing them to be selectively activated. They also can be programmed to coordinate so data from multiple sensors on and inside the body can coordinate and trigger a potential therapeutic action.

"I've always been passionate about creating devices that improve patient quality of life," said Ramy Ghanim, a Ph.D. student and first author of the Science study. "Automation improves outcomes and simplifies treatment regimens for patients."

In their study, the researchers demonstrated dual-limb motor control in a rat by coordinating a full-body network of sensors and neural interfaces. Their sensors detected when the rat's front paw moved and autonomously triggered another device to stimulate and contract the muscle in the hind leg, simulating the animal's natural walking pattern.

With their low-power network, the engineers can create implants smaller than 3 millimeters - tiny enough to be implanted through a syringe. They're made of passive electronic components that use essentially no power while they wait to be triggered but wake up to perform an action instantly.

The low power requirements mean devices last a long time: In their experiments, the team found a tiny actuator triggered once a day should last about a year before needing replacement. They also reported the tiny electrical pulses caused no damage to tissue samples.

SWANS is designed to transmit only small amounts of data between and among devices - the presence or absence of something or a yes/no trigger for some action. Larger data exchanges or heavy computation happens on an external wearable hub that can coordinate sensor readings from implants and direct therapeutic actions by others.

Ghanim and Abramson collaborated with Georgia Tech mechanical, biomedical, and electrical engineering researchers on the study, including W. Hong Yeo and former Ph.D. student Yoon Jae Lee. They also worked with Massachusetts Institute of Technology materials science and engineering researchers Aristide Gumyusenge and Camille Cunin.

"Our ultimate hope is to be able to fully automate human health - to be able to deliver a therapy exactly when it's needed, where it's needed, and to do so in a coordinated fashion across the body," Abramson said. "With our new system, you can now coordinate multiple sensors and actuators in completely disparate locations of the body, which is a huge step forward in the quest for personalized bioelectronic medicine."