An experimental brain implant containing tens of thousands of living neurons can form cell connections with the brains of mice. Such a device could eventually enable sophisticated control over millions of neurons on the level of individual cells 鈥� but without relying on surgically implanted electrodes that penetrate and destroy brain tissue.
The biohybrid implant, developed by California-based start-up Science Corporation, differs from many other brain-computer interface devices, which usually contain arrays of electrodes that penetrate the brain and sometimes damage cells. In comparison, Science Corporation鈥檚 implant is less invasive: it sits on top of the brain, where the neurons it contains can form natural connections with the brain鈥檚 cells.
鈥淭he principal advantages of a biohybrid implant are that it can dramatically change the scaling laws of how many neurons you can interface with versus how much damage you do to the brain,鈥� says at Science Corporation.
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The idea of introducing foreign neurons to brains is not new. Some research labs have experimented with living animals鈥� brains by inserting silicon probes coated with stem cells that eventually form neurons or even transplanting clumps of neurons.
But Science Corporation鈥檚 implant keeps the foreign neurons separate: it houses individual neurons in their own compartments, arranged in a honeycomb-like array, while a thin layer of biocompatible hydrogel separates these cells from the brain. The implant鈥檚 neurons can still send cell extensions through the hydrogel barrier, which enables them to transmit signals to the brain, creating neuronal connections.
For the technology鈥檚 proof-of-concept demonstration, Mardinly and his colleagues equipped the implant with cortical brain cells extracted from mice embryos, then used a technique called聽optogenetics聽to genetically alter the neurons so they could be controlled with light. Next, the researchers surgically installed the biohybrid implant so that it pressed firmly against the brains of living mice.
Several weeks later, they ran experiments that rewarded the mice for responding to light signals transmitted directly to the implant. Because the mice couldn鈥檛 see the light, their response to it indicated that the light-sensitive neurons in the implant had formed connections with the mice鈥檚 brains.
It will still be important to confirm the connections between the implant and host brain with further tests, such as using a fluorescent chemical marker that can pass from the implant鈥檚 transplanted neurons to the host brain, says at the University of Pennsylvania.
The initial experiments showed that up to 21 days after surgery, 50 per cent of the implant鈥檚 neurons survived, so future experiments showing longer-term survival would be helpful, says Cullen. The initial demonstrations were done several years ago but were just recently , says Mardinly. The company is working toward enabling the technology to 鈥渞ead and write from thousands of neurons鈥� and potentially do more useful brain-computer interface tasks, he says.
Cullen says the biohybrid design also provides a 鈥渞eally important stepping stone鈥� toward an implant that could read or stimulate neurons on an individual level. He expects Science Corporation to do future demonstrations showing the implant is capable of such fine control.
Mardinly notes that there are also many 鈥渟ignificant but ultimately manageable safety concerns鈥� to consider, such as immune system compatibility and preventing the implant鈥檚 engineered cells from forming tumour-like clumps.
But in the long term, he says, biohybrid implants that enable control on a single-neuron level could help circumvent the brain damage from strokes and other conditions, perhaps even restoring lost abilities, such as speech.
biorXiv
