Surgical Implant Could Pave Way for Real-Time Sensing of Biochemical, pH and Blood-Oxygen

A wireless millimetric magnetoelectric implant for the endovascular stimulation of peripheral nerves could lead to a wide range of low-risk, highly precise therapies as well as enable real-time sensing of biochemical, pH and blood-oxygen levels to provide diagnostics or support other medical devices.

Engineers at Rice University (Houston, TX, USA) have published the first proof-of-concept results from a years-long program to develop tiny, wireless devices that can treat neurological diseases or block pain. The nerve stimulators require no batteries and instead draw both their power and programming from a low-powered magnetic transmitter outside the body. The MagnetoElectric Bio ImplanT - aka ME-BIT - is placed surgically and an electrode is fed into a blood vessel toward the nerve targeted for stimulation. Once there, the device can be powered and securely controlled with a near-field transmitter worn close to the body. The researchers successfully tested the technology on animal models and found it could charge and communicate with implants several centimeters below the skin. The implant could replace more invasive units that now treat Parkinson’s disease, epilepsy, chronic pain, hearing loss and paralysis.

The ability to power the implants with magnetoelectric materials eliminates the need for electrical leads through the skin and other tissues. Leads like those often used for pacemakers can cause inflammation, and sometimes need to be replaced. Battery-powered implants can also require additional surgery to replace batteries. ME-BIT’s wearable charger requires no surgery. The researchers showed it could even be misaligned by several inches and still sufficiently power and communicate with the implant. The programmable, 0.8-square-millimeter implant incorporates a strip of magnetoelectric film that converts magnetic energy to electrical power. An on-board capacitor can store some of that power, and a “system-on-a-chip” microprocessor translates modulations in the magnetic field into data. The components are held together by a 3D-printed capsule and further encased in epoxy.

According to the researchers, the magnetic field generated by the transmitter - about 1 milliTesla - is easily tolerated by tissues. They estimated the current implant can generate a maximum of four milliwatts of power, sufficient for many neural stimulation applications. The research suggests endovascular bioelectronics like ME-BIT could lead to a wide range of low-risk, highly precise therapies. Having electrodes in the bloodstream could also enable real-time sensing of biochemical, pH and blood-oxygen levels to provide diagnostics or support other medical devices. The team ultimately hopes to employ multiple implants and communicate with them simultaneously.

“Because the devices are so small, we can use blood vessels as a highway system to reach targets that are difficult to get to with traditional surgery,” said Jacob Robinson of the Rice Neuroengineering Initiative. “We’re delivering them using the same catheters you would use for an endovascular procedure, but we would leave the device outside the vessel and place a guidewire into the bloodstream as the stimulating electrode, which could be held in place with a stent.”

“One of the nice things is that all the nerves in our bodies require oxygen and nutrients, so that means there’s a blood vessel within a few hundred microns of all the nerves,” Robinson said. “It’s just a matter of tracing the right blood vessels to reach the targets. With a combination of imaging and anatomy, we can be pretty confident about where we place the electrodes.”

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