Nanotubes that easily self-assemble into large and uniform stacks are here

These have advantages in drug delivery as shown in another study.

Scientists have created self-assembling nanostructures that stack together to form long and uniform nanotubes in a precision manufacturing that can be used from targeted drug delivery to desalinating seawater. Made from polymers, these hollow tubes with diameters of few billionths of a meter, assemble without much help. Such nanostructures can be as complex as natural proteins and function like them while avoiding breakdown.

Researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) discovered a family of nature-inspired polymers of the peptoid family that, when placed in water, spontaneously assemble into hollow crystalline nanotubes. All had the same diameter of five to ten nanometers. Large quantities of the uniform structure can be created.

"This points to a new way we can use synthetic polymers to create complex nanostructures in a very precise way," said Ron Zuckermann, who directs the Biological Nanostructures Facility in Berkeley Lab's Molecular Foundry, where much of this research was conducted. "For example, if you can control the diameter of nanotubes, and the chemical groups exposed in their interior, then you can control what goes through—which could lead to new filtration and desalination technologies, to name a few examples."

The research in published in the journal Proceedings of the National Academy of Sciences.

The scientists have in the past studied a peptoid, called a diblock copolypeptoid, for its use as a battery electrolyte given it binds with lithium ions. Accidentally they found the compounds form nanotubes in water. Peptoids are synthetic polymers that mimic peptides, which nature uses to form proteins.

The two peptoid blocks are such that one is hydrophobic one that's hydrophilic. Both blocks crystallize when they meet in water, and form rings consisting of two to three individual peptoids. The rings then form hollow nanotubes.

Cryo-electron microscopy imaging revealed the highly uniform structure and also a striped pattern across the width of the nanotubes, which rules out other packing arrangements. The brick-like pattern is due to hydrophobic blocks lining up with other hydrophobic blocks, and the same with hydrophilic blocks.

Popular scifi novel Prey by Michael Crichton used a narrative around such self-assembling, self-reproducing clouds of intelligent nanorobots that ran amok, creating panic and disaster. The science was based on nanotechnology and artificial intelligence.

Drug delivery
In another study, involving nanotechnology in drug delivery, scientists have devised a triple-stage "cluster bomb" system using nanoparticles that break up on arriving at a tumour and deliver the chemotherapy drug cisplatin. The method was shown to be more effective than the usual administering of the drug.

The particles100 nanometers wide travel through leaky blood vessels and on encountering acidic conditions found close to tumors, they discharge the tiny "bomblets" just 5 nanometers in size. Once inside the tumour, a second step activates the platinum-based cisplatin which kills the DNA.

Side-effects of cisplatin include damage to kidneys, nerves and inner ear. The targeted delivery of the drug could reduce this. The nanoparticles were effective also in some drug resistant cancer and invasive breast cancers in mice models and prolonged survival. Though not tested in humans, similar ways of packaging cisplatin have been in clinical trials.

The work was a collaboration between a team led by professor Jun Wang, PhD at the University of Science and Technology of China, and researchers led by professor Shuming Nie, PhD in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory.

The study was published March 28 in PNAS.