Let’s take a moment to consider the phrase “injectable brain implant.” Because it exists.

Nature describes (and even has photos of) an electronic mesh that can be rolled up and squirted out of a syringe into a mouse brain where it can monitor (and stimulate) individual neurons:

If eventually shown to be safe, the soft mesh might even be used in humans to treat conditions such as Parkinson’s disease, says Charles Lieber, a chemist at Harvard University on Cambridge, Massachusetts, who led the team. The work was published in Nature Nanotechnology on 8 June.

So far, even the best technologies have been composed of relatively rigid electronics that act like sandpaper on delicate neurons. They also struggle to track the same neuron over a long period, because individual cells move when an animal breathes or its heart beats.

The Harvard team solved these problems by using a mesh of conductive polymer threads with either nanoscale electrodes or transistors attached at their intersections. Each strand is as soft as silk and as flexible as brain tissue itself. Free space makes up 95% of the mesh, allowing cells to arrange themselves around it.

In 2012, the team showed that living cells grown in a dish can be coaxed to grow around these flexible scaffolds and meld with them, but this ‘cyborg’ tissue was created outside a living body. “The problem is, how do you get that into an existing brain?” says Lieber.

The team’s answer was to tightly roll up a 2D mesh a few centimetres wide and then use a needle just 100 micrometres in diameter to inject it directly into a target region through a hole in the top of the skull. The mesh unrolls to fill any small cavities and mingles with the tissue…. Nanowires that poke out can be connected to a computer to take recordings and stimulate cells.

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