Tag Archives: Xiaobing Zuo

Self-assembled molecular nanofibers that are stronger than steel

A January 26, 2021 news item on Nanowerk announces a promising discovery in ‘self-assembly research’ (Note: A link has been removed,

Self-assembly is ubiquitous in the natural world, serving as a route to form organized structures in every living organism. This phenomenon can be seen, for instance, when two strands of DNA — without any external prodding or guidance — join to form a double helix, or when large numbers of molecules combine to create membranes or other vital cellular structures. Everything goes to its rightful place without an unseen builder having to put all the pieces together, one at a time.

For the past couple of decades, scientists and engineers have been following nature’s lead, designing molecules that assemble themselves in water, with the goal of making nanostructures, primarily for biomedical applications such as drug delivery or tissue engineering.

“These small-molecule-based materials tend to degrade rather quickly,” explains Julia Ortony, assistant professor in [Massachusetts Institute of Technology] MIT’s Department of Materials Science and Engineering (DMSE), “and they’re chemically unstable, too. The whole structure falls apart when you remove the water, particularly when any kind of external force is applied.”

She and her team, however, have designed a new class of small molecules that spontaneously assemble into nanoribbons with unprecedented strength, retaining their structure outside of water. The results of this multi-year effort, which could inspire a broad range of applications, were described in Nature Nanotechnology (“Self-assembly of aramid amphiphiles into ultra-stable nanoribbons and aligned nanoribbon threads”) by Ortony and coauthors.

“This seminal work — which yielded anomalous mechanical properties through highly controlled self-assembly — should have a big impact on the field,” asserts Professor Tazuko Aida, deputy director for the RIKEN Center for Emergent Matter Science and professor of chemistry and biotechnology at the University of Tokyo, who was not involved in the research.

A January 26, 2021 MIT news release, which originated the news item, describe the work in more detail,

The material the MIT group constructed — or rather, allowed to construct itself — is modeled after a cell membrane. Its outer part is “hydrophilic,” which means it likes to be in water, whereas its inner part is “hydrophobic,” meaning it tries to avoid water. This configuration, Ortony comments, “provides a driving force for self-assembly,” as the molecules orient themselves to minimize interactions between the hydrophobic regions and water, consequently taking on a nanoscale shape.

The shape, in this case, is conferred by water, and ordinarily the whole structure would collapse when dried. But Ortony and her colleagues came up with a plan to keep that from happening. When molecules are loosely bound together, they move around quickly, analogous to a fluid; as the strength of intermolecular forces increases, motion slows and molecules assume a solid-like state. The idea, Ortony explains, “is to slow molecular motion through small modifications to the individual molecules, which can lead to a collective, and hopefully dramatic, change in the nanostructure’s properties.”

One way of slowing down molecules, notes Ty Christoff-Tempesta, a PhD student and first author of the paper, “is to have them cling to each other more strongly than in biological systems.” That can be accomplished when a dense network of strong hydrogen bonds join the molecules together. “That’s what gives a material like Kevlar — constructed of so-called ‘aramids’ — its chemical stability and strength,” states Christoff-Tempesta.

Ortony’s team incorporated that capability into their design of a molecule that has three main components: an outer portion that likes to interact with water, aramids in the middle for binding, and an inner part that has a strong aversion to water. The researchers tested dozens of molecules meeting these criteria before finding the design that led to long ribbons with nanometer-scale thickness. The authors then measured the nanoribbons’ strength and stiffness to understand the impact of including Kevlar-like interactions between molecules. They discovered that the nanoribbons were unexpectedly sturdy — stronger than steel, in fact. 

This finding led the authors to wonder if the nanoribbons could be bundled to produce stable macroscopic materials. Ortony’s group devised a strategy whereby aligned nanoribbons were pulled into long threads that could be dried and handled. Notably, Ortony’s team showed that the threads could hold 200 times their own weight and have extraordinarily high surface areas — 200 square meters per gram of material. “This high surface-to-mass ratio offers promise for miniaturizing technologies by performing more chemistry with less material,” explains Christoff-Tempesta. To this end, they have already developed nanoribbons whose surfaces are coated with molecules that can pull heavy metals, like lead or arsenic, out of contaminated water. Other efforts in the research group are aimed at using bundled nanoribbons in electronic devices and batteries.

Ortony, for her part, is still amazed that they’ve been able to achieve their original research goal of “tuning the internal state of matter to create exceptionally strong molecular nanostructures.” Things could easily have gone the other way; these materials might have proved to be disorganized, or their structures fragile, like their predecessors, only holding up in water. But, she says, “we were excited to see that our modifications to the molecular structure were indeed amplified by the collective behavior of molecules, creating nanostructures with extremely robust mechanical properties. The next step, figuring out the most important applications, will be exciting.”

Here’s a link to and a citation for the paper,

Self-assembly of aramid amphiphiles into ultra-stable nanoribbons and aligned nanoribbon threads by Ty Christoff-Tempesta, Yukio Cho, Dae-Yoon Kim, Michela Geri, Guillaume Lamour, Andrew J. Lew, Xiaobing Zuo, William R. Lindemann & Julia H. Ortony. Nature Nanotechnology (2021) DOI: https://doi.org/10.1038/s41565-020-00840-w Published: 18 January 2021

This paper is behind a paywall.

Small, soft, and electrically functional: an injectable biomaterial

This development could be looked at as a form of synthetic biology without the genetic engineering. From a July 1, 2016 news item on ScienceDaily,

Ideally, injectable or implantable medical devices should not only be small and electrically functional, they should be soft, like the body tissues with which they interact. Scientists from two UChicago labs set out to see if they could design a material with all three of those properties.

The material they came up with, published online June 27, 2016, in Nature Materials, forms the basis of an ingenious light-activated injectable device that could eventually be used to stimulate nerve cells and manipulate the behavior of muscles and organs.

“Most traditional materials for implants are very rigid and bulky, especially if you want to do electrical stimulation,” said Bozhi Tian, an assistant professor in chemistry whose lab collaborated with that of neuroscientist Francisco Bezanilla on the research.

The new material, in contrast, is soft and tiny — particles just a few micrometers in diameter (far less than the width of a human hair) that disperse easily in a saline solution so they can be injected. The particles also degrade naturally inside the body after a few months, so no surgery would be needed to remove them.

A July 1, 2016 University of Chicago news release (also on EurekAlert) by , which originated the news item, provides more detail,

Each particle is built of two types of silicon that together form a structure full of nano-scale pores, like a tiny sponge. And like a sponge, it is squishy — a hundred to a thousand times less rigid than the familiar crystalline silicon used in transistors and solar cells. “It is comparable to the rigidity of the collagen fibers in our bodies,” said Yuanwen Jiang, Tian’s graduate student. “So we’re creating a material that matches the rigidity of real tissue.”

The material constitutes half of an electrical device that creates itself spontaneously when one of the silicon particles is injected into a cell culture, or, eventually, a human body. The particle attaches to a cell, making an interface with the cell’s plasma membrane. Those two elements together — cell membrane plus particle — form a unit that generates current when light is shined on the silicon particle.

“You don’t need to inject the entire device; you just need to inject one component,” João L. Carvalho-de-Souza , Bezanilla’s postdoc said. “This single particle connection with the cell membrane allows sufficient generation of current that could be used to stimulate the cell and change its activity. After you achieve your therapeutic goal, the material degrades naturally. And if you want to do therapy again, you do another injection.”

The scientists built the particles using a process they call nano-casting. They fabricate a silicon dioxide mold composed of tiny channels — “nano-wires” — about seven nanometers in diameter (less than 10,000 times smaller than the width of a human hair) connected by much smaller “micro-bridges.” Into the mold they inject silane gas, which fills the pores and channels and decomposes into silicon.

And this is where things get particularly cunning. The scientists exploit the fact the smaller an object is, the more the atoms on its surface dominate its reactions to what is around it. The micro-bridges are minute, so most of their atoms are on the surface. These interact with oxygen that is present in the silicon dioxide mold, creating micro-bridges made of oxidized silicon gleaned from materials at hand. The much larger nano-wires have proportionately fewer surface atoms, are much less interactive, and remain mostly pure silicon. [I have a note regarding ‘micro’ and ‘nano’ later in this posting.]

“This is the beauty of nanoscience,” Jiang said. “It allows you to engineer chemical compositions just by manipulating the size of things.”

Web-like nanostructure

Finally, the mold is dissolved. What remains is a web-like structure of silicon nano-wires connected by micro-bridges of oxidized silicon that can absorb water and help increase the structure’s softness. The pure silicon retains its ability to absorb light.

Transmission electron microscopy image shows an ordered nanowire array. The 100-nanometer scale bar is 1,000 times narrower than a hair. Courtesy of Tian Lab

Transmission electron microscopy image shows an ordered nanowire array. The 100-nanometer scale bar is 1,000 times narrower than a hair. Courtesy of
Tian Lab

The scientists have added the particles onto neurons in culture in the lab, shone light on the particles, and seen current flow into the neurons which activates the cells. The next step is to see what happens in living animals. They are particularly interested in stimulating nerves in the peripheral nervous system that connect to organs. These nerves are relatively close to the surface of the body, so near-infra-red wavelength light can reach them through the skin.

Tian imagines using the light-activated devices to engineer human tissue and create artificial organs to replace damaged ones. Currently, scientists can make engineered organs with the correct form but not the ideal function.

To get a lab-built organ to function properly, they will need to be able to manipulate individual cells in the engineered tissue. The injectable device would allow a scientist to do that, tweaking an individual cell using a tightly focused beam of light like a mechanic reaching into an engine and turning a single bolt. The possibility of doing this kind of synthetic biology without genetic engineering [emphasis mine] is enticing.

“No one wants their genetics to be altered,” Tian said. “It can be risky. There’s a need for a non-genetic system that can still manipulate cell behavior. This could be that kind of system.”

Tian’s graduate student Yuanwen Jiang did the material development and characterization on the project. The biological part of the collaboration was done in the lab of Francisco Bezanilla, the Lillian Eichelberger Cannon Professor of Biochemistry and Molecular Biology, by postdoc João L. Carvalho-de-Souza. They were, said Tian, the “heroes” of the work.

I was a little puzzled about the use of the word ‘micro’ in a context suggesting it was smaller than something measured at the nanoscale. Dr. Tian very kindly cleared up my confusion with this response in a July 4, 2016 email,

In fact, the definition of ‘micro’ and ’nano’ have been quite ambiguous in literature. For example, microporous materials (e.g., zeolite) usually refer to materials with pore sizes of less than 2 nm — this is defined based on IUPAC [International Union of Pure and Applied Chemistry] definition (http://goldbook.iupac.org/M03853.html). We used ‘micro-bridges’ because they come from the ‘micropores’ in the original template.

Thank you Dr. Tian for that very clear reply and Steve Koppes for forwarding my request to Dr. Tian!

Here’s a link to and a citation for the paper,

Heterogeneous silicon mesostructures for lipid-supported bioelectric interfaces by Yuanwen Jiang, João L. Carvalho-de-Souza, Raymond C. S. Wong, Zhiqiang Luo, Dieter Isheim, Xiaobing Zuo, Alan W. Nicholls, Il Woong Jung, Jiping Yue, Di-Jia Liu, Yucai Wang, Vincent De Andrade, Xianghui Xiao, Luizetta Navrazhnykh, Dara E. Weiss, Xiaoyang Wu, David N. Seidman, Francisco Bezanilla, & Bozhi Tian. Nature Materials (2016)  doi:10.1038/nmat4673 Published online 27 June 2016

This paper is behind a paywall.

I gather animal testing will be the next step as they continue to develop this exciting technology. Good luck!