Engineering researchers at The University of Texas at Austin have developed ultra-flexible, nano-electronic thread (NET) brain probes and have published their work in a recent research article in the journal Science Advances. The probes don’t cause scar formation when implanted and provide more reliable long-term neural recording than existing probes.
The research team was led by Chong Xie, an assistant professor in the Department of Biomedical Engineering in the Cockrell School of Engineering, and Lan Luan, a research scientist in the Cockrell School and the College of Natural Sciences.
The new probes have mechanical compliances that approach that of the brain tissue and improve the flexibility of other neural probes by a factor of more than 1,000. This ultra-flexibility results in an improved ability to track and record the electrical activity of individual neurons for long periods reliably. Developing long-term tracking of individual neurons for neural interface applications is a growing field. One application would be extracting neural control signals for amputees to control high performance prostheses. It also opens up new potential to follow the progression of neurodegenerative and neurovascular diseases such as Alzheimer’s and Parkinson’s diseases, and strokes.
One of the disadvantages of conventional probes is that their stiffer structures and larger dimensions often cause damage around the tissue they envelop. While it is possible to record brain activity for months using the conventional electrodes, they do however often provide degrading and unreliable recordings. It is also challenging to track individual neurons electro-physiologically for more than a few days with conventional electrodes.
The UT Austin team’s new electrodes are in contrast flexible enough to comply with the microscale movements of tissue and still stay in place. The brain interface is also more stable and the readings are more reliable for longer periods, as the probe’s smaller size reduces the tissue displacement considerably. As far as the researchers know, the UT Austin probe is the smallest among all neural probes. It has a cross section that is only a fraction of that of a neuron or blood capillary, and is only 10 microns big with a thickness of less than 1 micron.
Xie explained that the results prove that tissue reaction can be suppressed while maintaining a stable recording. This is because the electrodes are extremely flexible, resulting in no sign of brain damage. Even when in contact with the NET probes, the vasculature didn’t become leaky, neurons stayed alive and glial cells remained inactive.
In experiments done on mice, the researchers found that glial cells were not agitated due to the probe’s flexibility and size. Glial cell activation is the normal biological reaction to a foreign body and this leads to neuronal loss and scarring. Luan noted that for them the most surprising part of their research is that the living brain tissue doesn’t mind having an artificial device around for months at a time.
Advanced imaging techniques were also used in collaboration with Jenni Siegel from the Institute for Neuroscience at UT Austin, biomedical engineering professor Andrew Dunn and neuroscientists Raymond Chitwood. The imaging confirmed that in over four months of experiments, the NET enabled neural interface did not degrade in the mouse model.
The researchers will continue testing their probes in animal models and hope to progress to clinical testing eventually.