The team published the results in the journal ACS Nano.
The biggest challenge facing researchers trying to culture neurons for study is that it’s very difficult to recreate the soft, 3D environment of the brain. Other techniques have used glass plates or channels carved into hard slabs of material, but the nerve cells look and behave differently than they would in the body. The microtubes provide pliant, 3D scaffolding, the way that the cellular matrix does in the body.
The team uses an array of microtubes, made with a technique developed in Li’s lab for electronics applications such as 3D inductors. Thin membranes of silicon nitride roll themselves up into tubes of precise dimensions. The tubes are about as wide as the cells, as long as a human hair is wide, and spaced apart about as far as they are long. The neurons grow along and through the microtubes, sending out exploratory arms across the gaps to find the next tube.
Froeter devised a way to mount the microtubes on glass slides, the standard for biological cultures. The thin silicon-nitride tubes are transparent, so researchers can watch the live neuron cells as they grow using a conventional microscope.
“Having the ability to see through both the tube and the underlying substrate has been really enlightening,” said Williams, a professor of biomedical engineering at UW-Madison. “Without this we may have noticed an overall increase in growth rates, but we never would have observed the dramatic changes that occur as the cells transition from the flat regions to the tube inlets.”
For Li’s group, the next step is to put electrodes in the microtubes so researchers can measure the electrical signals that the nerves conduct.
“If we place electrodes inside the tube, since they are directly in contact with the axon, we will be able to study signal conduction much better than conventional methods,” Li said.
They also are working to stack the microtubes in multiple layers so that bundles of nerves can grow in a 3D network.