. 24/7 Space News .
A new model for how twisted bundles take shape
by Staff Writers
Amherst MA (SPX) Mar 28, 2016

Cyindrical (left) and tape-like (right) twisted filament bundles: model morphologies (simulated assemblies) and experimental observations (amyloid fibers). Greg Grason and colleagues have for the first time identified key factors that govern the final morphology of self-assembling chiral filament bundles. Image courtesy UMass Amherst/Greg Grason. For a larger version of this image please go here.

In the current issue of Nature Materials, polymer scientists Greg Grason, Douglas Hall and Isaac Bruss at the University of Massachusetts Amherst, with Justin Barone at Virginia Tech, identify for the first time the factors that govern the final morphology of self-assembling chiral filament bundles. They also report experimental results supporting their new model.

At the molecular level, Grason explains, chiral filament bundles are many-stranded, self-twisting, yarn-like structures. One example are amyloid fibers, assemblies of misfolded proteins linked to diseases like Alzheimer's and Parkinson's. Many other proteins take this shape, including collagen, the most abundant protein in the body, and sickle-hemoglobin proteins found in sickle-cell anemia. But how they attain their final size and shape has not been well understood.

Previous work by Bruss and Grason described the formation of cable-like filament bundles. When Grason presented this at Virginia Tech, Justin Barone, a biological systems engineer, approached him with a question about the geometric structure of amyloid fibers he had been studying. Barone asked why the shapes he was observing were in some cases flat and tape-like, while under other conditions they were cylindrical.

Grason recalls, "Justin's questions about the shape of amyloid fibers set us on the track to figure out how fibers form from many copies of identical filaments and know what shapes to be. Since filaments attract one another, understanding what makes fibers grow fatter is not so hard. The challenge is to understand what makes the process stop at certain sizes, and why a fiber sometimes grows larger in one direction than the other, leading to different cross-sectional shapes."

He adds, "Based on our new model, we have new design rules for controlling the size and shape of 'self-spinning' nano-fiber materials used in applications such as soft-gel scaffolds that can be deployed in filters, sensor patches or any place where you need material architectures with tunable mechanics and size scales."

In the human body, many structures are made of collagen bundles or other protein filaments, Grason explains. "The bundles in your eye are small and more uniform because the cornea has to be transparent, compared to fibers that make up your tendons, which have to be thicker and stronger. These different tissues are formed from basically the same building blocks, yet they assemble into different architectures."

He adds, "We wanted to develop a physical model of what governs the structure of protein fibers and other fiber-forming systems. How do they self-organize and what determines their size and shape? The basic ingredients are molecular-scale, nano-filaments that stick to one another, forming a structure that looks like rope or cable, made of strands that twist together."

Grason says it was already known that the "screw-like" structure of chiral filaments caused them to twist around one another in bundle assembles. What was not known, and is the focus of the current study, is how this structure along the length controls the lateral distribution of strands in the fiber.

Using geometric and mathematical models combined with computational simulations, the researchers discovered that the number of strands involved is a significant predictor of how strong the final structure is and whether its protein filaments will take a cylindrical shape or the ribbon-like shape in cross section.

Grason explains that the key insight made earlier by his group was to show that filament twisting in the bundles 'frustrates' the packing between neighbor filaments, making it impossible to evenly space filaments in cross section. The upshot of this frustration is that it leads to a feedback mechanism between the twist pattern and the lateral shape of the bundle. "We now have a model that explains how the number of strands underlies morphology selection."

He adds, "A smaller number of strands allows them to keep the right distance from their neighbors, so even though there is a twist, if the twist is not too big and the strand number not too big, the structure doesn't get too crowded and keeps a cylindrical cross section. But once the number of strands gets larger, outer strands get too close for comfort and a tape-like, or twisted ribbon structure will emerge."

"For the first time, we are able to predict that the frustration will lead to new shape transitions. For relatively narrow and weakly twisted bundles, the cost of fewer contacts at the sides of the bundle favors a cylindrical shape. But above a critical size, the cost of the frustration causes the morphology to change dramatically, leading to bundle shapes that are very anisotropic, much wider in one dimension and thinner in the other."

To test their new predictions, Hall worked with Bruss, now at the University of Michigan, to develop and implement a simulation model to show how the filament twist pattern determines how large these assemblies will grow, how fat they can be and what shape their cross sections will have. In the end, they found that both simulated and experimental amyloid fibers could be classified as either cylinder-forming and tape-forming according to a relatively simple combination of molecular and geometric parameters of the assembly.

Grason says, "To start out with complex and unexplained observations, then to design the model that let others run the simulations to show it was true, then to bring it all the way back to confirm in the experimental data was particularly satisfying. It doesn't always happen this way." This work was supported by a National Science Foundation CAREER award and by the Alfred P. Sloan Foundation.

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only


Related Links
University of Massachusetts at Amherst
Space Technology News - Applications and Research

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
Local fingerprint of hydrogen bonding captured in experiments
Berlin, Germany (SPX) Mar 28, 2016
Molecules are composed of atoms that maintain specific intervals and angles between one another. However, the shape of a molecule can change, for example, through proximity to other molecules, external forces and excitations, and also when a molecule makes a chemical connection with another molecule, for instance in a chemical reaction. A very useful concept in describing the changes that ... read more

Ancient Polar Ice Reveals Tilting of Earth's Moon

Moon Mission: A Blueprint for the Red Planet

The Lunar Race That Isn't

Earth's moon wandered off axis billions of years ago

Mars Express keeps watch on frosty Martian valleys

HiRISE: 45,000 Mars Orbits and Counting

Opportunity moves to new locations to the southwest

NASA: Manned mission to Mars still 'long way' off

ASU to develop the next generation science education courseware for NASA

The latest technology helping take mankind to new planets

Space-Related Budget Requests for FY17

New DNA/RNA Tool to Diagnose, Treat Diseases

Has Tiangong 1 gone rogue

China's 1st space lab Tiangong-1 ends data service

China's aim to explore Mars

China to establish first commercial rocket launch company

Cargo ship reaches space station on resupply run

Unmanned Cygnus cargo ship launches to ISS on resupply run: NASA

Cygnus Set to Deliver Its Largest Load of Station Science, Cargo

Three new members join crew of International Space Station

India to launch 22 satellites by single rocket in May

MHI signs H-IIA launch deal for UAE Mars mission

Launch of Dragon Spacecraft to ISS Postponed Until April

ILS and INMARSAT Agree To Future Proton Launch

Instrument Team Selected to Build Next-Gen Planet Hunter

Oddball planet raises questions about origins of 'hot Jupiters'

Investigating the Mystery of Migrating 'Hot Jupiters'

Most eccentric planet ever known flashes astronomers with reflected light

Local fingerprint of hydrogen bonding captured in experiments

Printing nanomaterials with plasma

Lockheed Martin Opens Space Fence Test Facility

Uncovering bacterial role in platinum formation

The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.