Scientists Inject Tiny, Rolled-Up Electronics Into The Brain

by Monica Joshi

How would you like to have your brain injected with teeny-tiny electronics? I bet that's a question you didn't think you'd be asked today. A simple injection, it seems, can now fire up a brain and help to analyze biological activity.

Researchers from Harvard and Beijing have developed stretchy, bendy electronics that are so thin that they can be rolled up and jammed into a small needle with a 0.1-millimeter diameter. These electronics are then injected into living tissue using syringes. The research involved injecting the electronics into the brains of live mice. Within an hour of being injected, the electronics unfurled and began monitoring biological activity.

Previous research revealed that electronics like these can be surgically implanted, but so far, it hasn’t been possible to precisely control their delivery to non-invasively target areas within the body. The team led by Charles Lieber, from Harvard, and Ying Fang, from the National Center for Nanoscience and Technology in Beijing, has designed mesh-shaped electronics consisting of a polymer–metal combination. Once rolled up and loaded into a syringe, the electrical components can be injected into cavities or specific regions of living tissues. Once the needle is withdrawn, the electronics unfold to about 80% of their original configuration without loss of function. Mesh electronics with widths more than 30 times that of the metal or glass needle have been known to be successfully injected.

The work described in Nature Nanotechnology this week discusses the ways in which the flexible, implantable electronics would make it possible for continuous bio-monitoring. Bio-monitoring could help to check electrophysiological signals related to epilepsy and arrhythmia, among other biomedical applications.

There were several issues that neuroscientists had to overcome. One was that they still do not understand how the activities of individual brain cells translate to higher cognitive powers such as perception and emotion. The problem has spurred a hunt for technologies that will allow scientists to study thousands, or ideally millions, of neurons at once. The use of brain implants, however, is currently limited by several disadvantages. Even the best technologies, thus far, have been composed of relatively rigid electronics that act like sandpaper on delicate neurons; eventually destroying them instead of being able to mesh around them. They also struggle to track the same neuron over a long period, because individual cells move with heart beats or breathing. 

To specifically examine the behaviour of the mesh electronics, the team overcame these obstacles by using a glass needle to inject them into anaesthetized mice in two distinct brain regions: the lateral ventricle and the hippocampus. Over a five-week period, the mice showed no immune response, and the foldable electrical units even began to network with the healthy neurons. To the right is a 3D microscopy image of mesh electronics that have been injected into the lateral ventricle. As 95% of the mesh is free space, it allows for cells to arrange themselves around it. You can see the innervation of the neural tissue, as well as the migration of neural progenitor cells onto the mesh within the cavity.

The team was effectively able to monitor brain activity in the hippocampus using the electronics, not wireless but rather connected to input and output wires, and with limited damage to the surrounding tissue.

The next step for the team is to implant larger meshes containing hundreds of devices, with different kinds of sensors, and to record activity in mice that are awake, either by fixing their heads in place, or by developing wireless technologies that would record from neurons as the animals moved freely. It would also be interesting to have the device injected into the brains of newborn mice, where it would unfold further as the brain grew. This could allow for probes in the mesh to record electrical activity inside and outside cells for a longer duration of time and see the development of the device from birth to perhaps even death – unless, of course, the material that the device is made from causes ill-effects in the long term.

Nicholas Negroponte, co-founder of the MIT Media Lab, says that biotechnology will be like digital was 20 years ago. In this clip, he imagines a future in which information and knowledge can be delivered to the brain via tiny robots in your bloodstream.