Electronics
though, is not the most stable material, so the team spent a long time fabricating metal nanostructures that could mechanically lock it in place. Eventually, Dayeh was struck by the fact that the nanostructures his graduate students were developing were themselves capable of volumetric sensing. All the work that had been done to make them suitable for securing PEDOT had made the PEDOT unnecessary. As platinum – the standard material for clinical electrodes – is the most biocompatible metal conductor, it was the obvious one to use for these PEDOT-free sensors. Using a dealloying technique modified from an old Nature paper, the team created high-surface area nanorods with a pure, stable and crystalline platinum ideal for interacting with tissue. Importantly, unlike most approaches to fabricating nanostructures, that dealloying technique can happen at relatively low temperatures, which means it is compatible with parylene C, a material best known in the medical device industry as a coating for implants (including the Utah Array’s needles).
On top of the biocompatibility that suits it to that job, parylene C is soft and pliable enough to conform and move with the surface of the brain without obscuring it. “You can deposit it at thicknesses that are less than 10µ, and at those thicknesses, it becomes conformal to the brain curvature and compliant to the brain movements,” says Dayeh. “Because it’s a thin sheet that the brain feels is so light, it won’t have a biofouling reaction against it, and therefore, you can record with very high fidelity and isolate the activity in local brain regions because the electrical contact is always in intimate contact with the surface of the brain.” That is helped further by the perfusion holes etched in the parylene C, which prevent spinal fluid building up beneath the grid. “That facilitates the grid to stick to the surface of the brain,” explains Raslan. “And not only that – you’re also able to send electrical current through the holes, so we could use a clinical stimulator device. The presence of the grid on the surface of the brain does not impede any of the normal clinical activity.” Perhaps most impressively, it’s even possible to incorporate flaps into the parylene C, meaning surgeons can monitor brain activity and function, peel back the flap and perform the resection before folding the flap back over to continue recording and make an informed decision over what to do next. It is nothing like the current practice, which usually involves a neurophysiologist copying ECoG readings of different brain regions from a computer screen onto a printed map. “The surgeon will then try to project based on the context or put a
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sterile paper on the surface of the brain to mark these regions and match them to the grid,” Dayeh explains. “There’s a lot of back and forth and shouting – and that’s a big theme already in the OR.” But there are other difficulties; not least the challenge of displaying and interpreting data from a grid of 1,000 channels, as opposed to a few tens. Dayeh’s team is working to smooth the transition with real-time displays of ECoG readings that can zoom in or highlight certain channels to present surgical teams with only the information they need at any given moment in a procedure. “It would really simplify the procedure a lot if we’re able to have a real-time display either directly from the surface of the brain using light emitting diodes, or on a computer screen next to the surgeon, where he could visibly see the regions and correlate them with the anatomy on the brain surface,” Dayeh notes. That’s not the only intersection between Dayeh and Raslan’s next-generation ECoGs and high- resolution screens. For Dayeh in particular, making use of modern display technology is key to achieving the holy grail and bringing effective treatments like resections to more people – not just by making procedures easier for surgical teams, but also as a way of manufacturing ECoGs as quickly and affordably as possible. Today’s ubiquitous screens are made using a low- temperature process that just so happens to be ideal for working with parylene C. “The problem of the temperature has been solved by the display industry, so why don’t we learn from them and apply it to the brain?” asks Dayeh. “They’re doing displays for flexible phones on glass substrates at low temperatures, and, because there are very big screens, production on glass exceeds 2m in height and width, so you can make hundreds of grids on one plate. It’s really scalable, and it can be done at low cost.” It is a convincing case. Dayeh and Raslan’s new ECoGs promise to improve upon the capabilities of the Utah Array while being much better suited to use in the clinic, thanks largely to manufacturing techniques that are already well established for producing the screens that our brains so love to be distracted by. Clinical trials are ahead, and the team still needs to work out how best to transfer and communicate data from so many channels, but the potential is staggering. “It’s a platform technology,” says Raslan. “People will develop uses that we haven’t found. You could use it for brain stimulation, for brain-computer interfaces, for rehabilitation, or for epilepsy detection. It’s really a device that connects you with the brain in an unprecedented way.” ●
Medical Device Developments /
www.nsmedicaldevices.com
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