Researchers have designed a communication system through which dispersed implantable therapeutics such as insulin pumps and pacemakers can communicate with wearables through signals transmitted by the body’s own tissues.
The in-body Smart Wireless Autonomous Networking System (SWANS) framework enables communication between therapies connecting distant, related physiological dynamics using circuits so small they can be injected through a syringe.
The multiplexed cross-body network, outlined in Science, harnesses the conductive nature of body tissue to transmit communication signals ionically through epidermal, subcutaneous, intraperitoneal, and gastrointestinal spaces.
The system has more than ten times the communication coverage of radiofrequency methods such as Bluetooth, transmitting through 30 cm of tissue or more.
“SWANS establishes a framework in which dispersed wearable and implantable therapeutic devices communicate throughout the body via ionic tissue conduction,” reported Ramy Ghanim, PhD, from Georgia Institute of Technology, and co-workers.
They added: “SWANS uses off-the-shelf components and can be implemented into any bioelectronic device.”
Smart bioelectronic therapeutics such as insulin pumps, pacemakers, neurostimulators, electronic pills, drug delivery implants, and prosthetics improve patient outcomes by linking sensors and actuators through closed-loop feedback control.
These systems can function better by distributing additional coordinated, miniaturized nodes throughout the body to synchronously monitor and treat multiple interconnected physiological sites.
However, current forms of wireless communication require bulky components that limit their use and acceptability for patients, and perform poorly within tissues, with only a limited number of coordinated independent nodes.
SWANS circuits are made entirely of passive electrical components only micrometers in size. This allows devices to consume microwatt levels of power when in a listening state, enabling them to last for a year or more. It also means the devices can be minute, enabling entire systems to be injected using a syringe.
The SWANS architecture consists of three components: wearable hubs that coordinate wearable sensor readouts and therapeutic actuation via in-body ionic communication; microneedle patches that interface between the wearables and the body; and syringe-implantable circuits that receive and transmit signals and perform therapeutic actions.
Each SWANS implant possesses two tissue-interfacing receiving pads connected to the gate pins of a transistor that detect emitted voltage gradient signals in the tissue and facilitate switching.
To communicate, SWANS devices emit low-frequency characteristic voltage pulses into tissue that generate temporary electric fields across the body that selectively activate other devices.
The gradients are received by other devices in contact with the tissue, which causes passive transistor switches to briefly turn on when their gate threshold voltage is met.
Each device possesses a specific transistor circuit that only responds to its corresponding voltage and pulse length, enabling multiplexing.
Through ionic signaling, SWANS enables cross-body bidirectional communication between wearables and implants as well as communication between implants.
SWANS reduces the size of implanted communication components and improves battery life of implantable devices by using low-power transistor switches to regulate the device’s DC output.
It maintains near-zero standby current until the transistor enters its active region and, by minimizing standby consumption, extends device lifetime by more than 15 times relative to Bluetooth and near-field communication.
By using different transistor types and passive circuit components, each SWANS implant responds only to characteristic pulse magnitudes, widths, and frequencies emitted by the wearable hub, enabling individual implant control.
The researchers found the system performed well in several ex vivo tissue types from pigs, chickens and rodents. In vivo, they also engineered a SWANS-enabled network of wearable front-paw sensors that was able to detect front limb motion and independently control hind leg motor control.
The team summarized: “Compared with other wireless approaches, SWANS requires less power, operates over a larger working area, works without external antennae, reduces device alignment constraints, and is small enough to enable minimally invasive syringe-implantable bioelectronics.”
