Researchers in Australia have developed a unique brain-computer interface device that can be implanted into a patient’s brain via blood vessels, eliminating the need for invasive surgery. The device measures neural signals of the motor cortex — a region of the brain involved in control of movements — and holds great potential to be a key technology in future systems allowing paralysed persons to control exoskeletons or other bionic devices using their brain.

“Essentially what we’re trying to build is a bionic spinal cord“

The device is a stent-based, mesh structure embedded with electrodes. Termed a ‘stentrode’, it’s the size of paperclip, but strong and highly flexible. The device’s attributes mean it can be inserted directly into a blood vessel in the neck and then navigated using real-time imaging — a technique known as angiography — to the motor cortex. Once there, the stentrode can be secured into place by expanding itself against the inner walls of a vein.

While the new device is built off of well-established, existing medical technologies and procedures, their application and approach here is radically removed from conventional techniques for implanting neural interfaces.

Typically, neural implants (including interfaces, but also devices for diagnoses and research) require an open craniotomy procedure, involving dissecting through the blood-brain barrier, before positioning a recording device. These complex activities carry great risk to the patient both during and after the operation, leaving them vulnerable to surgery-related complications.

In addition, the conventional electrodes aren’t ideal as interface devices. Either as patch-like electrode arrays fitted over a portion of the brain, or a vertical array of electrodes implanted through a region of interest; both can be troublesome to surgeons and researchers, liable to infection and complications, before ultimately having to be removed (again via surgery).

With the new stentrode, things are somewhat simpler. Once in place at the motor cortex, the stentrode will record motor-signals generated by the surrounding tissue. These signals, which would ordinarily have contributed to controlled movement prior to paralysis, may then be used as a digital input to other devices, for instance a prosthetic limb or exoskeleton. Indeed, the potential applications of how the information may be used are far-reaching.

For now, the most recent outcomes of the research have been presented in a paper — published in Nature Biotechnology — describing testing of the stentrode after implanting it into a sheep. The paper describes demonstration of the device working as intended: that it’s capable of recording high-fidelity motor cortex signals, comparable to conventional neural interface devices, from within a vein; and that the implant method itself is viable. In the study, the stentrode was left in place, recording data for up to 190 days.

Looking towards the future of the research and moving on to testing with human patients, Nicholas Opie, the project’s co-principal investigator and biomedical engineer at the University of Melbourne said:

“In our first-in-human trial, that we anticipate will begin within two years, we are hoping to achieve direct brain control of an exoskeleton for three people with paralysis”

“Currently, exoskeletons are controlled by manual manipulation of a joystick to switch between the various elements of walking — stand, start, stop, turn. The stentrode will be the first device that enables direct thought control of these devices.”

DARPA’s Quest for Brain-Computer Interfaces

Amongst others, the stentrode research was supported through a program of the US Defense Advanced Research Projects Agency (DARPA) called the Reliable Neural-Interface Technology (RE-NET) program, which was established in 2010 with the following objective:

“…to directly address the need for high performance neural interfaces to control dexterous functions made possible with advanced prosthetic limbs. Specifically, RE-NET seeks to develop the technologies needed to reliably extract information from the nervous system, and to do so at a scale and rate necessary to control many degree-of-freedom (DOF) machines, such as high-performance prosthetic limbs.”

The new study expands on previously successful work in the same field conducted by DARPA, as Dr. Doug Weber, the program manager for RE-NET, explains:

“DARPA has previously demonstrated direct brain control of a prosthetic limb by paralyzed patients fitted with penetrating electrode arrays implanted in the motor cortex during traditional open-brain surgery. By reducing the need for invasive surgery, the stentrode may pave the way for more practical implementations of those kinds of life-changing applications of brain-machine interfaces.”

By way of an indication of DARPA’s commitment to this field of technology, the agency recently announced investment of $60 million over the next four years toward a research focused on accelerating brain computer interfacing technologies (DARPA, January 2016).

The opportunities and applications that await once we learn to safely and effectively interface between the brain and machine are hugely consequential. Of course at the forefront of immediate application, perhaps with the most value, is the possibility to restore mobility and function to paralysed persons and amputees.

In developing a technique and product that circumvents the constraints found in existing interface technologies, the team behind stentrode are opening up new possibilities for development of clinically viable interface technologies. What is safer for patients, and less challenging for surgeons, certainly holds promise in this endeavour.