Australian researchers at the Royal Melbourne Hospital and the University of Melbourne have developed an electrode that can record brain activity from the motor cortex, without the need for invasive brain surgery. The electrode, called a stentrode, is implanted into a blood vessel in the brain using minimally invasive surgical techniques. The electrode can record signals from the motor cortex and transmit them wirelessly through the skin to a device outside the body. It is hoped that these signals could be used by paralyzed patients to control assistive devices, such as robotic exoskeletons or wheelchairs. Previous attempts at implanting electrodes to record brain signals have required the removal of a portion of the skull, whereas the stentrode can be implanted much more easily, bringing the concept of wireless, thought-controlled limbs or wheelchairs closer to a clinical reality. The device has been tested successfully in sheep and the team plan a clinical trial in the near future.
Medgadget had the opportunity to interview Dr. Thomas Oxley, a neurologist at the Royal Melbourne Hospital and a Research Fellow at The Florey Institute of Neurosciences and the University of Melbourne, who has led the research.
Conn Hastings, Medgadget: How was this design conceived? Has a catheter-delivered electrode array ever been developed previously?
Thomas Oxley: The design has gone through multiple (perhaps 8) iterations. Previous technology has utilized electrodes on catheters or wires, but the challenge was to create a system that can be permanently deposited within the vessel. Cardiac pacemakers leave behind leads in blood vessels, but we needed our electrodes to have good vessel apposition, and so elected to pursue a stent-based design.
Medgadget: Were there design challenges around miniaturization and ensuring that the device does not cause blood clots? Does the physical architecture and composition of the device differ much from a stent implanted to hold a blood vessel open?
Thomas Oxley: Stents are scaffolds that were initially designed to hold open blood vessels: for instance, in blockages that lead to myocardial ischemia (heart attacks). The biggest risk with our technology is that the device leads to a sudden blockage of the blood vessel. We therefore used the stent technology to ensure that the vessel was scaffolded open. The electrode recording system is on the outside of the stent, such that the electrodes are pushed up against the vessel wall, and immediately adjacent to the brain, to achieve high quality recordings. The patients will require antiplatelet (blood thinning) medication to stop clots forming at the stent. This is standard treatment for all patients receiving stents, whether used to treat conditions relating to the heart or the brain.
Medgadget: Can the stentrode be implanted for a long period? Is there any risk of degradation or malfunction after extended periods, and if so can the device be removed, deactivated or replaced?
Thomas Oxley: The quality of recordings of the stentrode depends on tissue incorporation into the wall of the blood vessel. We demonstrated this in our paper in Nature Biotechnology in 2016. The result of this, is that the device HAS to become permanently implanted. It therefore cannot be removed. We are building upgradeable lead connectors to allow for improvements in the filters and amplifiers, however the electrode array itself will not be upgradeable.
Medgadget: Can you tell us about the planned clinical trial? How many patients will undergo stentrode implantation? Are there any plans to pair the stentrode with an external assistive device during this trial, or will this be the focus of future trials?
Thomas Oxley: We are planning on conducting a clinical trial in the next few years in a low number of patients. Yes: the primary goal is to pair the device with external assistive technologies that are controlled via direct thought, but I can’t reveal which ones just yet!
Medgadget: Will patients fitted with a stentrode be able to instinctively use a device such as an exoskeleton by simply thinking about moving, or will training and practice be necessary? What would such training involve?
Thomas Oxley: No: training will be critical. If a piano is placed in front of you, and you have not learnt how to play it in the past, you can’t begin immediately playing a tune, no matter how strong your immediate will. Teaching an area of your brain to learn control of an external device will require a period of training. We are building a training system that allows development of control over a range of technologies.
Medgadget: Assuming the trial goes well, when do you envisage that this technology will be more widely available?
Thomas Oxley: We remain in an early stage. The FDA process is long, and we are building an entirely new technology that comes with its own individual risks. We are several years from coming to market, however the FDA has implemented a range of pathways that speed up the process for novel technologies. We are currently moving through an FDA process and hopeful that it won’t be as far away as one may expect.
Flashback: Stentrodes for Recording Electrical Activity Within the Brain…