Bright-field image showing the mesh electronics being injected through sub-100 micrometer inner diameter glass needle into aqueous solution. Image Credit: Lieber Research Group, Harvard University
The ability to manipulate objects on a very small scale through nanotechnology has opened the door to new ways of monitoring what’s going on with our bodies. The brain is no exception, and now researchers have created microscopic, flexible electronics that can be implanted into parts of the brain using nothing but a small needle. These electronic probes could vastly change how we monitor brain activity and treat ailments.
The new electronics, reported this week in Nature Nanotechnology, come from Charles Lieber and his colleagues. Lieber, a professor of chemistry at Harvard’s School of Engineering and Applied Sciences, says many existing microscopic electronic devices come in the form of chips built to work on a flat surface. “That’s not really enough when you’re looking at most biological systems because they’re 3D,” he says. “Even if the surface can be bent, it’s still more or less a two-dimensional structure.”
While doctors can already surgically implant electronics into the brain, such as in cases of Parkinson’s Disease where deep brain stimulation is used to treat tremors, many of these devices are quite large. Implanting them is an invasive surgical procedure, and they cause an immune response from the body, which sees the devices as foreign.
Leiber wanted to create an electronic device small enough and flexible enough to be implanted inside the body swiftly and silently, without eliciting a negative response. For inspiration, he looked to bioscaffolds, lab-grown 3D materials often implanted in damaged tissue to serve as a sort of support structure for the development of new, healthy tissue. Scaffolds are used in procedures like bone and cartilage regeneration. Lieber set out to create a microscopic bioscaffold made from electronics.
The result is a tiny mesh of electrodes that be can be implanted in living tissue by a tiny needle just 0.1 mm in diameter. The mesh is incredibly thin and up to a million times more pliable than existing flexible electronic probes. “The flexibility is really approaching that of the tissue,” Lieber says, “so it starts to look structurally like a neural network and have mechanical property of dense neural tissue.”
The team rolled up the electronics within a needle and then injected them into the hippocampuses of lab mice, where they unfolded to their original shape within an hour without sustaining any damage. They then were able to monitor, live, the neural activity of the mice. Five weeks later, the mice's immune systems showed no response to the foreign objects.
Lieber also implanted the flexible electronics into mice brain ventricles—the fluid-filled spaces—and was surprised to see the neurons attach themselves to the mesh and multiply. “These neurons were migrating onto our mesh electronic scaffold,” he says. “They were very happy and starting to proliferate.”
How might these tiny electric probes be used in the future? They could help improve procedures in stroke patients where stem cells are implanted in the brain to repair damaged tissue. “The cells do need some support to develop well,” Lieber says. His electronics could provide that initial support and then monitor the progress. Or, imagine if you could skip invasive heart surgery and instead just implant electronics with the prick of a needle.
Lieber says a lot more research is needed to understand all the potential applications. “I think a good sign of a research area is there are a lot more questions that you can get excited about than you have the time or resources to answer,” he says. “Can we wire things up the way biology does? If we can do that then we are going to be able to measure things that we couldn’t before and improve therapeutic care in a dramatic fashion.”