Using a succession of biological mechanisms, Sandia researchers have created linkages of polymer nanotubes that resemble the structure of a nerve, with many outthrust filaments poised to gather or send electrical impulses.
“This is the first demonstration of biomolecular machines assembling complex polymer structures,” says George Bachand (1132).
Creation of the neural structure, unachievable by normal manufacturing techniques, begins by altering the behavior of kinesin motor proteins — biological machines found in every human cell. These tiny motors, portrayed in videographics as a vertical body with two legs, tote cellular matter as they stride along protein microtubules that form the cell structure. In their purposefulness, the motors resemble the enchanted brooms in Disney’s Fantasia, relentlessly carrying buckets of water up the castle stairs.
Turning nature’s machinery on its head, the researchers used known techniques to glue the “shoulders” of kinesin motors to a glass substrate. This prevents their bodies from traveling, but their “legs” above them continue their vigorous movements. These pass microtubules above them like an audience crowdsurfing entertainers on upraised hands.
In the next laboratory step, these traveling protein microtubules, microns in length, encounter relatively large polymer spheres, tens of microns in diameter, inserted by the researchers.
“At that point, we have structures that want to do work — the kinesin-powered microtubules — and something they want to do work on — the spheres,” says co-primary investigator Wally Paxton (1132).
The microtubules, pre-coated with a sticky substance, pinch off polymer nanotubes from the polymer ball that lengthen as the kinesin motors travel on. The process resembles strands of string cheese lengthening as a piece of pizza is removed from a pan, says Wally.
As the nanotubes lengthen and crosslink, they form structures complex enough to bring to mind the lights of a city seen at night from an airplane at high altitude. The networks range from hundreds of micrometers to tens of millimeters in total size and are composed of tubes 30 to 50 nanometers in diameter.
“One goal of our work is to make artificial, highly branched neural structures,” says George. “The next step is, can we wire them together? The answer is, the motors should do it naturally. And two such networks, joined together, would have self-healing built into them. The motors never stop running until they run out of fuel. A neural branch breaks, and then a motor can act on that area to produce a new branch.”
“This is foundational science,” says Wally. “It’s the first time a chemically created network has been arranged by biological means without going through the macrostage of normal manufacture. Now we have a robust artificial network that could communicate with an artificial limb as a prosthetic interface. Currently, we use hard rigid electrodes to penetrate nerve tissue; they cause inflammation. One possibility we see is to use soft structure like those created here to painlessly interface with the body’s nerve structures.”
The insertion of quantum dots also proved stable, which means that light could be used to carry information through the structure as well as electricity.
A paper on the work was published in April in the journal Nanoscale. Other authors were Nathan Bouxsein, Ian Henderson (both 1132), and Andrew Gomez (1815).
The work is supported by DOE’s Office of Basic Energy Sciences and performed in part at its Center for Integrated Nanotechnologies, an Office of Science user facility.