Blood vessels guide stimulating implants

An implant little bigger than a grain of rice, placed gently alongside a blood vessel, could replace bulkier devices that stimulate nerves.

Rice University engineers in collaboration with a host of Texas Medical Center institutions have published the first proof-of-concept results from a years-long program to develop tiny, wireless devices that treat neurological diseases or block pain. The nerve stimulators require no batteries, instead drawing power and programming from a low-powered magnetic transmitter outside the body.

The MagnetoElectric Bio ImplanT (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 team, led by Jacob Robinson and Kaiyuan Yang of the Rice Neuroengineering Initiative and the George R. Brown School of Engineering and Sunil Sheth of the University of Texas Health Science Center’s McGovern Medical School, successfully tested its 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 now treating Parkinson’s disease, epilepsy, chronic pain, hearing loss, and paralysis.

“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,” Robinson says. “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.”

The ability to power the implants with magnetoelectric materials eliminates the need for electrical leads through the skin and other tissues. Leads often used for pacemakers can cause inflammation and sometimes need to be replaced. Battery-powered implants can also require 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 power and communicate with the implant.

The programmable, 0.8mm² implant incorporates a strip of magnetoelectric film converting magnetic energy to electrical power. An on-board capacitor can store some 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.

The researchers said 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 4mW of power, sufficient for many neural stimulation applications.

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“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 says. “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.”

The research suggests endovascular bioelectronics like ME-BIT could lead to a 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.