Brain-Computer Interface technology has converged the fields of engineering and medicine to give birth to various technologically advanced and therapeutic devices. Neurological disorders, such as ALS, can lead to impaired motor control, preventing the person from performing basic activities that require moving the limbs and speaking. BCI devices give these people hope for a better future by acting as an interface between their brain impulses and the desired action. Although we have come a long way in developing these amazing devices, there are still a few bumps on the road. But the tremendous progress made by scientists worldwide gives us hope that the future we’ve been waiting for is just around the corner.
One such advancement was made by the amazing team of scientists at Synchron, a neurotechnology company, who developed a revolutionary, minimally-invasive brain implant called ‘Stentrode’. Traditional brain implants, like microelectrodes and electrode arrays, require open-brain surgeries, leading to tissue inflammation. Therefore, there is a demand for less invasive electrodes that are made of biocompatible materials, provide high-resolution signal transduction, and are more stable.
Learn more about the evolution of brain implants here.
What Are Stentrodes?
Stentrode is an endovascular electrode array placed in a vein alongside the brain designed to record or stimulate the nerves from within the blood vessels. They are administered directly into a blood artery by catheterization technique, thus circumventing brain surgery.
Stentrode was implanted in two ALS patients in the first human experiment. By the end of the study, they had mastered using a Windows 10 computer for tasks as varied as buying online, sending and receiving text messages, and handling their finances.
The stentrode array was a key part of the device components, and it was linked to the ITU (Internal Telemetry Unit) through a lengthy, malleable lead. The ITU is inserted into the chest for transmitting the electrocorticographic signal to the external telemetry unit (ETU) through infrared transmission. This signal was then used for decoding the movements and helping the user operate the computer.
History of Endovascular Treatment
Synchron’s Stentrode is based on Endovascular Surgery, a minimally-invasive procedure to treat problems affecting the blood vessels. Catheters, long, thin, flexible tubes, are used to guide an endovascular graft, a fabric tube device encased with stainless steel self-expanding stents, through the arteries, and into the aorta. A number of cardiac conditions, including aneurysms, have been successfully treated using this method since the turn of the century. Just like cardiothoracic surgery progressed from open heart surgery with the development of minimally invasive endovascular techniques, neurosurgery may follow the same course.
In the 1960s, brain activity was recorded using endovascular catheterization wherein small, magnetically-guided catheters were introduced into the artery close to the brain and since then have been used in cerebral angiography. These endovascular recording devices went through various iterations over the years experimenting with different types of wires, materials, the number of electrodes, and sizes to finally reach the stentrode recording device. Intracranial stenting of cerebral blood vessels is an established technique in endovascular neurosurgery for the treatment of both arterial and venous neurological conditions.
Synchron’s CEO, a vascular and interventional neurologist at New York’s Mount Sinai Hospital, Thomas J. Oxley, and his team expanded on the aforementioned method to develop Stentrode, an endovascular device capable of recording intracranial neural activity. The stent, which is already in clinical use for intracranial stent technology, had platinum disc electrodes attached to it. These self-expanding stent electrode arrays (stentrode) were placed in veins near the sensorimotor cortex, the region of the brain that regulates essential bodily activities.
Fabrication of Stentrode
Stentrode is fabricated by mounting electrodes or sensors on Nitinol stents, commercially used in endovascular surgery. Nitinol (NiTi) is an alloy of nickel and titanium with a unique mechanical characteristic. It is considered to be a shape memory alloy, i.e. it restores its original shape after deformation, widely used in medical devices especially as stents because of its biocompatibility, superelasticity and fatigue, and kink resistance. It was discovered by William Buehler in the 1960s at US Ordnance Laboratory. The alloy, due to its atomic properties, can be deformed and then brought back to its original shape by slightly heating the metal.
Catheterization technology is used to insert the Stentrode into the blood vessel. Catheters are thin tubes made from biocompatible materials which can be inserted into the body to treat diseases or perform surgery. The stentrodes are manufactured to a diameter larger than the vessel diameter and are compressed to fit into the catheter. When they are released from the catheter tube into the vessel, they ‘remember’ their original shape and expand outwards to the vessel walls, thus supporting it.
Fun Fact: Nitinol was discovered by chance when Buehler and his team were developing fatigue-resistant materials for missile cones. The alloy was actually first used in fighter aircraft before breaking into the medical industry.
Advantages of Stentrodes over traditional Electrode Arrays
The primary advantage of Stentrode over conventional electrode array implants is that it does not require a craniotomy for implantation, thereby increasing the clinical utility of this implant. It facilitates access to superficial and deep brain targets by injecting the stentrode to the veins lying adjacent to the structure of the brain to be monitored. This stent electrode can be deployed in blood vessels as small as 1.7 mm. Avoiding direct contact with cortical neurons can mitigate brain trauma and chronic local inflammation.
Stentrode arrays can be used in brain-machine interfaces and for seizure prediction in epilepsy. Deep brain stimulation required in Parkinson’s disease and OCD can be done without having to go for craniotomy.
- Oxley, T., Opie, N., John, S. et al. Minimally invasive endovascular stent-electrode array for high-fidelity, chronic recordings of cortical neural activity. Nat Biotechnol 34, 320–327 (2016). https://doi.org/10.1038/nbt.3428
- Oxley TJ, Yoo PE, Rind GS, et al Motor neuroprosthesis implanted with neurointerventional surgery improves capacity for activities of daily living tasks in severe paralysis: first in-human experience Journal of NeuroInterventional Surgery 2021;13:102-108.
- Sefcik, R.K., Opie, N.L., John, S.E., Kellner, C.P., Mocco, J.D., & Oxley, T.J. (2016). The evolution of endovascular electroencephalography: historical perspective and future applications. Neurosurgical focus, 40 5, E7 .
Do you think Stentrode can change the course of BCI technology? Let us know in the comments section.
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