Injectable electronics could be the future of neuroscience

An international team of researchers, led by Harvard University Professor Charles Lieber, has developed a method for fabricating nanoscale electronic scaffolds that can be injected via syringe. Once connected to electronic devices, the scaffolds can be used to monitor neural activity, stimulate tissues and even promote regeneration of neurons.

“For the past 30 years, people have made incremental improvements in microfabrication techniques that have allowed us to make rigid probes smaller and smaller, but no one has addressed … the electronics/cellular interface at the level at which biology works,” Professor Lieber said. Writing in the journal Nature Nanotechnology, his team added that “targeted delivery of flexible electronics to internal regions remains difficult”.

Scientists in Professor Lieber’s lab have previously demonstrated that their scaffolds could be used to create ‘cyborg’ tissue, with cardiac or nerve cells grown with embedded scaffolds. The researchers used the devices to record electrical signals generated by the tissues and to measure changes in those signals as they administered cardio- or neuro-stimulating drugs.

“We were able to demonstrate that we could make this scaffold and culture cells within it, but we didn’t really have an idea how to insert that into pre-existing tissue,” Professor Lieber said. “But if you want to study the brain or develop the tools to explore the brain-machine interface, you need to stick something into the body.

“When releasing the electronics scaffold completely from the fabrication substrate, we noticed that it was almost invisible and very flexible like a polymer and could literally be sucked into a glass needle or pipette. From there, we simply asked: would it be possible to deliver the mesh electronics by syringe needle injection?”

Although the insertion of medical devices into the brain is nothing new, Professor Lieber said existing techniques are “crude relative to the way the brain is wired”.

“Whether it’s a silicon probe or flexible polymers … they cause inflammation in the tissue that requires periodically changing the position or the stimulation,” he said. “But with our injectable electronics, it’s as if it’s not there at all.”

The researchers said they have successfully demonstrated “the syringe injection (and subsequent unfolding) of sub-micrometre-thick, centimetre-scale macroporous mesh electronics through needles with a diameter as small as 100 μm”. Professor Lieber said these injectable electronics are “one million times more flexible than any state-of-the-art flexible electronics” and are “what I call ‘neuro-philic’ - they actually like to interact with neurons”.

The fabrication of the injectable scaffolds is said to be surprisingly easy and similar to that used to etch microchips. To create the scaffold, researchers lay out a mesh of nanowires sandwiched in layers of organic polymer. The first layer is dissolved, leaving the flexible mesh, which can be drawn into a syringe needle and administered like any other injection.

After injection, the input/output of the mesh can be connected to standard measurement electronics so the integrated devices can be addressed and used to stimulate or record neural activity. The team said they have already demonstrated the syringe-injectable electronics in several applications, including monitoring internal mechanical strains in polymer cavities; tight integration and low chronic immunoreactivity with several distinct regions of the brain; and in vivo multiplexed neural recording.

The Harvard Office of Technology Development has filed for a provisional patent on the technology and is actively seeking commercialisation opportunities. Professor Lieber said there are “a lot of potential applications” and the technology could “make a huge impact on neuroscience”.

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