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image: Ion Communication: (top left) A schematic cross-sectional illustration of an ion communication device consisting of a pair of transmitting electrodes implanted inside biological tissue and a pair of receiving electrodes at the fabric surface. (Top right) The highlight of ion communication frequency responses is the ability to operate at megahertz frequencies. A 10-bond ion communication transmitter (TX) and receiver (RX) array conforming to the surface of an orchid petal.
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Credit: Dion Khodagholy/Columbia Engineering

Wireless, high-speed, low-power communications for implantable devices

A new technique uses the body’s natural ions to facilitate data transmission

New York, NY – April 6, 2022 – Implantable bioelectronics are now often essential for assisting or monitoring the heart, brain, and other vital organs, but they often lack a safe and reliable way to transmit their data to physicians. Now, researchers from Columbia Engineering invented a way to augment implantable bioelectronics with simple, high-speed, low-power wireless data links using ions, positively or negatively charged atoms that are naturally available in the body.

Implantable bioelectronics are increasingly playing a key role in healthcare. For example, pacemakers can help ensure that a patient’s heart maintains a healthy rhythm, and neural interface devices can help patients with epilepsy and other disorders by stimulating specific brain regions to reduce their neurological symptoms, or even by connecting the brain of a paralyzed patient to robotic limbs. However, a major challenge that implanted bioelectronics faces is how to communicate its data through the body to external devices for further analysis and diagnostics by doctors and scientists.

“From brain or muscle activity to hormone concentrations, these data need to be passed on so that they can undergo advanced processing and expert review before medical decision-making,” said the co-lead author of the study. Dion Khodagholyassociate professor of electrical engineering at Columbia University.

“This is particularly important for conditions where there may be large fluctuations over time, such as epilepsy or movement disorders,” added the study’s co-lead author. Jennifer Gelinas, assistant professor of neurology at Columbia University Irving Medical Center. “An example of this is the NeuroPace device for epilepsy – the data it contains needs to be downloaded for the clinician to adjust their stimulation protocols to best treat seizures.”

Although cables provide a simple way to quickly transmit implant data to outside machinery, the way they penetrate tissue limits their long-term use. At the same time, conventional wireless approaches using radio waves or visible light are often poorly successful in penetrating biological tissues.

“Safe, efficient and long-term wireless communications with implanted devices are still lacking,” Khodagholy said.

Use body ions

An intriguing strategy that bioelectronics could use for communications is one the body often uses: ions. Inside the body, cells regularly mix ions to communicate with each other.

Now Khodagholy and his colleagues have developed a way to use body ions to transmit data at rates of megahertz, or millions of bits per second. Their study, “Ionic communication for implantable bioelectronics”, appears on April 6 in the journal Scientists progress.

The way living tissue is rich in ions means that it stores electrical potential energy, much like electrical batteries do. The new technique, called ion communication, exploits this fact to help implanted bioelectronics exchange data with external devices.

Ion communication involves a pair of electrodes implanted inside a tissue and another pair of electrodes resting on the surface of that tissue. The implanted device encodes data into alternating electrical pulses that store energy in the tissue. In turn, the surface receiver can detect this energy and decode it.

In the new study, the researchers detailed which geometric properties govern the depths to which ion communication could reach inside the body, as well as strategies for establishing multiple parallel lines of communication between electrodes. They found that ion communication was able to transmit data over distances that could help it target a variety of tissue types, from human skin to visceral organs.

“Ion communication is a biological form of data communication that establishes long-term, high-fidelity interactions across intact tissues,” Khodagholy said.

From theory to prototype

In experiments, scientists created a fully implantable neural interface using ion communication for rats. They showed that it could noninvasively acquire and transmit brain data from freely moving rodents over a period of weeks with enough stability to isolate signals from individual neurons.

Using 10 lines of communication with currently available commercial electronics, scientists have achieved communication rates of 60 megahertz. They estimated that a single ion communication line could potentially achieve communication speeds of up to 14 megahertz.

The scientists note that ion communication required low voltages and much less energy than radio or ultrasonic communications. Their experiments also revealed that their ion communication device was found to be thousands to millions of times more energy efficient at communicating data than other approaches used with implantable bioelectronics.

Ion communication devices can be made from materials that are soft, flexible, commercially available, biocompatible – i.e. not harmful to living tissue – and even biodegradable, suggesting that they could easily be used in convenient implantable devices that can dissolve once they are no longer needed. Khodagholy and his colleagues now aim to combine ion communication with organic transistors in an implantable biosensor.

A common theme

This latest work continues Khodagholy’s global research aimed at connecting bioelectronic devices to the human brain. For example, he and his colleagues recently developed a material that helps ion signals conduct only in specific chosen directions. This can help scientists develop circuits that use ions instead of electrons to better interface with the body. Such circuits would normally not work if the ions could move in all directions and cause unwanted interference between different parts of each circuit. The new “anisotropic ion conductor” is a soft, biocompatible composite material, suggesting that it could prove useful in implantable bioelectronics, and the processes to synthesize it are simple and scalable. Their study“Anisotropic Ion Conducting Particulate Composites for Bioelectronics”, published on January 27 in the journal Advanced sciences.

“The new material we have developed has unique properties that enable the implementation of large-scale organic bioelectronic devices, which may improve their translation into human health applications,” Khodagholy said. “Then, we aim to design compact and complex integrated circuits based on anisotropic ionic conductors composed of many organic transistors for bioelectronic applications.”

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