New protein-inspired nanotube could be used to build water-filtering membranes

Jan. 18 (UPI) -- Inspired by protein structures called microtubules, material scientists at the Department of Energy's Pacific Northwest National Laboratory have developed a self-rolling nanotube with a variety of potential applications, including water filtration.

Microtubules are found in eukaryotic cells and are essential to a variety of biological processes.

"They are the pathways for ion and molecule transport," lead researcher Chun-Long Chen told UPI.

Chen and his colleagues were interested in the biomechanical potential of microtubules, but to tap into the structure's unique dynamism, they couldn't simply isolate the protein and pluck it from a cell. They needed to replicate it.

Inside the cell, chains of the dynamic proteins form tiny, hollow tubes through which various molecules can be transported.

To replicate the protein structure, scientists first synthesized protein-like molecules called peptoids. The molecules are designed to mimic lipids. The peptoids feature two components, a hydrophilic part and a hydrophobic part -- or one part that likes water and another that doesn't.

"We chose chemical features that we hoped would encourage the individual molecules to pack together," Chen said. "After putting the lipid-like peptoids into a liquid solution, the molecules spontaneously crystallized and formed what the scientists call nanosheets first -- straight-edged sheets as thin as cell membranes -- floating in the beaker."

"Later, these nanosheets will fold and roll into single-walled nanotubes," he added. "These nanotubes maintain their structure."

A water filtration sheet can be formed by inserting the self-rolled, tightly-zipped nanotubes into a 2D sheet of peptoids. The nanotubes can also be programmed to form a 3D matrix structure, which can assist with applications that require cell adhesion, such as drug delivery.

"We can fine-tune the tubes' dynamic structure by modifying their chemistry," Chen said. "We are still trying to find all the potential mechanisms."

Researchers were able to further manipulate the nanotubes' structural properties by altering the acidity of the solution used to trigger their formation. The size, diameter, thickness and stiffness of the nanotubes can be altered according to desired effect.

When the scientists tested the strength of the nanotubes, they found their rigidity falls somewhere between biological tissue and harder materials like glass.

The team published their work this week in the journal Nature Communications.

Chen said he and his colleagues are "still very much working on the fundamental side of things," but hopes to partner with experts in other fields to work on the technology's applications, whether it's drug delivery, water filtration or stem cell differentiation.

"Our dream is to make a complete cell membrane using pure synthetic molecules," he said.