Mantis Shrimp Stronger than Airplanes

Helicoidal structure of the mantis shrimp club.

“Biology has an incredible diversity of species, which can provide us new design cues and synthetic routes to the next generation of advanced materials for light-weight automobiles, aircraft and other structural applications”

Inspired by mantis shrimp, researchers design composite material stronger than standard used in airplane frames

Inspired by the fist-like club of a mantis shrimp, a team of researchers led by University of California, Riverside, in collaboration with University of Southern California and Purdue University, have developed a design structure for composite materials that is more impact resistant and tougher than the standard used in airplanes.

“The more we study the club of this tiny crustacean, the more we realize its structure could improve so many things we use every day,” said David Kisailus, a Kavli Fellow of the National Academy of Science and the Winston Chung Endowed Chair of Energy Innovation at the UC Riverside’s Bourns College of Engineering.

The peacock mantis shrimp, or stomatopod, is a 4- to 6-inch-long rainbow-colored crustacean with a fist-like club that accelerates underwater faster than a 22-calibur bullet. Researchers, led by Kisailus, an associate professor of chemical engineering, are interested in the club because it can strike prey thousands of times without breaking.

The force created by the impact of the mantis shrimp’s club is more than 1,000 times its own weight. It’s so powerful that Kisailus needs to keep the animal in a special aquarium in his lab so it doesn’t break the glass. Also, the acceleration of the club creates cavitation, meaning it shears the water, literally boiling it, forming cavitation bubbles that implode, yielding a secondary impact on the mantis shrimp’s prey.

Previous work by the researchers, published in the journal Science in 2012, found the club is comprised of several regions, including an endocuticle region. This region is characterized by a spiraling arrangement of mineralized fiber layers that act as shock absorber. Each layer is rotated by a small angle from the layer below to eventually complete a 180-degree rotation.

In a paper “Bio-Inspired Impact Resistant Composites,” just published online in the journal Acta Biomaterialia, the researchers applied that spiraled, or helicoidal, layered design when creating carbon fiber-epoxy composites. Composites with this design structure could be used for a variety of applications, including aerospace and automotive frames, body armor and football helmets.

In experiments outlined in the paper, which were led by Lessa Grunenfelder, who formerly worked in Kisailus’ lab and is now a post-doctoral student at USC, carbon fiber-epoxy composites were created with layers at three different helicoidal angles ranging from about 10 degrees to 25 degrees.

They also built two control structures: a unidirectional, meaning the layers were placed directly on top and parallel to each other, and a quasi-isotropic, the standard used in the aerospace industry, which has alternating layers stacked upon each other in an orientation of 0 degrees (first layer), -45 degrees (second layer), +45 degrees (third layer), 90 degrees (fourth layer) and so on.

The goal was to examine the impact resistance and energy absorption of the helicoidal structures when they were struck and to quantify the strength after the impact.

The researchers used a drop weight impact testing system with a spherical tip that on impact creates 100 joules of energy at USC with their collaborator, Professor Steven R. Nutt. This replicates testing done by the aircraft industry. Following the tests, they measured external visual damage, depth of the dent and internal damage by using ultrasound scans.

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Repeated Self-Healing Now Possible in Composite Materials

3D microvascular networks for self-healing composites: Researchers were able to achieve more effective self-healing with the herringbone vascular network (top) over a parallel design (bottom), evidenced by the increased mixing (orange-yellow) of individual healing agents (red and green) across a fracture surface. Credit: Jason Patrick

A small, internal crack can quickly develop into irreversible damage from delamination – this remains one of the most significant factors limiting more widespread use of composite materials.

Internal damage in fiber-reinforced composites, materials used in structures of modern airplanes and automobiles, is difficult to detect and nearly impossible to repair by conventional methods. A small, internal crack can quickly develop into irreversible damage from delamination, a process in which the layers separate. This remains one of the most significant factors limiting more widespread use of composite materials.

However, fiber-composite materials can now heal autonomously through a new self-healing system, developed by researchers in the Beckman Institute’s Autonomous Materials Systems (AMS) Group at the University of Illinois at Urbana-Champaign, led by professors Nancy Sottos, Scott White, and Jeff Moore.

Sottos, White, Moore, and their team created 3D vascular networks—patterns of microchannels filled with healing chemistries—that thread through a fiber-reinforced composite. When damage occurs, the networks within the material break apart and allow the healing chemistries to mix and polymerize, autonomously healing the material, over multiple cycles. These results were detailed in a paper titled “Continuous self-healing life cycle in vascularized structural composites,” published in Advanced Materials.

“This is the first demonstration of repeated healing in a fiber-reinforced composite system,” said Scott White, aerospace engineering professor and co-corresponding author. “Self-healing has been done before in polymers with different techniques and networks, but they couldn’t be translated to fiber-reinforced composites. The missing link was the development of the vascularization technique.”

“The beauty of this self-healing approach is, we don’t have to probe the structure and say, this is where the damage occurred and then repair it ourselves,” said Jason Patrick, a Ph.D. candidate in civil engineering and lead author.

The vasculature within the system integrates dual networks that are isolated from one other. Two liquid healing agents (an epoxy resin and hardener) are sequestered in two different microchannel networks.

“When a fracture occurs, this ruptures the separate networks of healing agents, automatically releasing them into the crack plane—akin to a bleeding cut,” Patrick said. “As they come into contact with one another in situ, or within the material, they polymerize to essentially form a structural glue in the damage zone. We tested this over multiple cycles and all cracks healed successfully at nearly 100 percent efficiency.”

Notably, the vascular networks within the structure are not straight lines. In order for the healing agents to combine effectively after being released within the crack, the vessels were overlapped to further promote mixing of the liquids, which both have a consistency similar to maple syrup.

Fiberglass and other composite materials are widely used in aerospace, automotive, naval, civil, and even sporting goods because of their high strength-to-weight ratio—they pack a lot of structural strength into a very lean package. However, because the woven laminates are stacked in layers, it is easier for the structure to separate between the layers, making this self-healing system a promising solution to a long-standing problem and greatly extending their lifetime and reliability.

“Additionally, creating the vasculature integrates seamlessly with typical manufacturing processes of polymer composites, making it a strong candidate for commercial use,” said Nancy Sottos, materials science and engineering professor and co-corresponding author.

Fiber-composite laminates are constructed by weaving and stacking multiple layers of reinforcing fabric, which are then co-infused with a binding polymer resin. Using that same process, the researchers stitched in a sort of fishing line, made from a bio-friendly polymer and coined “sacrificial fiber,” within the composite. Once the composite was fabricated, the entire system was heated to melt and evaporate the sacrificial fibers, leaving behind hollow microchannels, which became the vasculature for the self-healing system.

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Researchers develop 4D printing technology for composite materials

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The 4D printing concept allows materials to “self-assemble” into 3D structures

Researchers at the University of Colorado Boulder have successfully added a fourth dimension to their printing technology, opening up exciting possibilities for the creation and use of adaptive, composite materials in manufacturing, packaging and biomedical applications.

A team led by H. Jerry Qi, associate professor of mechanical engineering at CU-Boulder, and his collaborator Martin L. Dunn of the Singapore University of Technology and Design has developed and tested a method for 4D printing.  The researchers incorporated “shape memory” polymer fibers into the composite materials used in traditional 3D printing, which results in the production of an object fixed in one shape that can later be changed to take on a new shape.

“In this work, the initial configuration is created by 3D printing, and then the programmed action of the shape memory fibers creates time dependence of the configuration – the 4D aspect,” said Dunn, a former CU-Boulder mechanical engineering faculty member who has studied the mechanics and physics of composite materials for more two decades.

The 4D printing concept, which allows materials to “self-assemble” into 3D structures, was initially proposed by Massachusetts Institute of Technology faculty member Skylar Tibbits in April of this year. Tibbits and his team combined a strand of plastic with a layer made out of “smart” material that could self-assemble in water.

“We advanced this concept by creating composite materials that can morph into several different, complicated shapes based on a different physical mechanism,” said Dunn. “The secret of using shape memory polymer fibers to generate desired shape changes of the composite material is how the architecture of the fibers is designed, including their location, orientation and other factors.”

The CU-Boulder team’s findings were published last month in the journal Applied Physics Letters. The paper was co-authored by Qi “Kevin” Ge, who joined MIT as a postdoctoral research associate in September.

“The fascinating thing is that these shapes are defined during the design stage, which was not achievable a few years ago,” said Qi.

The CU-Boulder team demonstrated that the orientation and location of the fibers within the composite determines the degree of shape memory effects like folding, curling, stretching or twisting. The researchers also showed the ability to control those effects by heating or cooling the composite material.

Qi says 3D printing technology, which has existed for about three decades, has only recently advanced to the point that active fibers can be incorporated into the composites so their behavior can be predictably controlled when the object is subjected to thermal and mechanical forces.

The technology promises exciting new possibilities for a variety of applications. Qi said that a solar panel or similar product could be produced in a flat configuration onto which functional devices can be easily installed. It could then be changed to a compact shape for packing and shipping. After arriving at its destination, the product could be activated to form a different shape that optimizes its function.

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Mixing Nanoparticles to Make Multifunctional Materials

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Brookhaven National Laboratory DNA linkers allow different kinds of nanoparticles to self-assemble and form relatively large-scale nanocomposite arrays. This approach allows for mixing and matching components for the design of multifunctional materials.

Standardized technique opens remarkable opportunities for ‘mix and match’ materials fabrication

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have developed a general approach for combining different types of nanoparticles to produce large-scale composite materials. The technique, described in a paper published online by Nature Nanotechnology on October 20, 2013, opens many opportunities for mixing and matching particles with different magnetic, optical, or chemical properties to form new, multifunctional materials or materials with enhanced performance for a wide range of potential applications.

The approach takes advantage of the attractive pairing of complementary strands of synthetic DNA-based on the molecule that carries the genetic code in its sequence of matched bases known by the letters A, T, G, and C. After coating the nanoparticles with a chemically standardized “construction platform” and adding extender molecules to which DNA can easily bind, the scientists attach complementary lab-designed DNA strands to the two different kinds of nanoparticles they want to link up. The natural pairing of the matching strands then “self-assembles” the particles into a three-dimensional array consisting of billions of particles. Varying the length of the DNA linkers, their surface density on particles, and other factors gives scientists the ability to control and optimize different types of newly formed materials and their properties.

“Our study demonstrates that DNA-driven assembly methods enable the by-design creation of large-scale ‘superlattice’ nanocomposites from a broad range of nanocomponents now available-including magnetic, catalytic, and fluorescent nanoparticles,” said Brookhaven physicist Oleg Gang, who led the research at the Lab’s Center for Functional Nanomaterials (CFN). “This advance builds on our previous work with simpler systems, where we demonstrated that pairing nanoparticles with different functions can affect the individual particles’ performance, and it offers routes for the fabrication of new materials with combined, enhanced, or even brand new functions.”

Future applications could include quantum dots whose glowing fluorescence can be controlled by an external magnetic field for new kinds of switches or sensors; gold nanoparticles that synergistically enhance the brightness of quantum dots’ fluorescent glow; or catalytic nanomaterials that absorb the “poisons” that normally degrade their performance, Gang said.

“Modern nano-synthesis methods provide scientists with diverse types of nanoparticles from a wide range of atomic elements,” said Yugang Zhang, first author of the paper. “With our approach, scientists can explore pairings of these particles in a rational way.”

Pairing up dissimilar particles presents many challenges the scientists investigated in the work leading to this paper. To understand the fundamental aspects of various newly formed materials they used a wide range of techniques, including x-ray scattering studies at Brookhaven’s National Synchrotron Light Source (NSLS) and spectroscopy and electron microcopy at the CFN.

For example, the scientists explored the effect of particle shape. “In principle, differently shaped particles don’t want to coexist in one lattice,” said Gang. “They either tend to separate into different phases like oil and water refusing to mix or form disordered structures.” The scientists discovered that DNA not only helps the particles mix, but it can also improve order for such systems when a thicker DNA shell around the particles is used.

They also investigated how the DNA-pairing mechanism and other intrinsic physical forces, such as magnetic attraction among particles, might compete during the assembly process. For example, magnetic particles tend to clump to form aggregates that can hinder the binding of DNA from another type of particle. “We show that shorter DNA strands are more effective at competing against magnetic attraction,” Gang said.

For the particular composite of gold and magnetic nanoparticles they created, the scientists discovered that applying an external magnetic field could “switch” the material’s phase and affect the ordering of the particles. “This was just a demonstration that it can be done, but it could have an application-perhaps magnetic switches, or materials that might be able to change shape on demand,” said Zhang.

The third fundamental factor the scientists explored was how the particles were ordered in the superlattice arrays: Does one type of particle always occupy the same position relative to the other type-like boys and girls sitting in alternating seats in a movie theater-or are they interspersed more randomly? “This is what we call a compositional order, which is important for example for quantum dots because their optical properties-e.g., their ability to glow-depend on how many gold nanoparticles are in the surrounding environment,” said Gang. “If you have compositional disorder, the optical properties would be different.” In the experiments, increasing the thickness of the soft DNA shells around the particles increased compositional disorder.

These fundamental principles give scientists a framework for designing new materials. The specific conditions required for a particular application will be dependent on the particles being used, Zhang emphasized, but the general assembly approach would be the same.

Said Gang, “We can vary the lengths of the DNA strands to change the distance between particles from about 10 nanometers to under 100 nanometers-which is important for applications because many optical, magnetic, and other properties of nanoparticles depend on the positioning at this scale. We are excited by the avenues this research opens up in terms of future directions for engineering novel classes of materials that exploit collective effects and multifunctionality.”

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Tanks, graphene! Rice advances compressed gas storage

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Rice University mix of graphene nanoribbons, polymer has potential for cars, soda, beer

A discovery at Rice University aims to make vehicles that run on compressed natural gas more practical. It might also prolong the shelf life of bottled beer and soda.

The Rice lab of chemist James Tour has enhanced a polymer material to make it far more impermeable to pressurized gas and far lighter than the metal in tanks now used to contain the gas.

The combination could be a boon for an auto industry under pressure to market consumer cars that use cheaper natural gas. It could also find a market in food and beverage packaging.

Tour and his colleagues at Rice and in Hungary, Slovenia and India reported their results this week in the online edition of the American Chemistry Society journal ACS Nano.

By adding modified, single-atom-thick graphene nanoribbons (GNRs) to thermoplastic polyurethane (TPU), the Rice lab made it 1,000 times harder for gas molecules to escape, Tour said. That’s due to the ribbons’ even dispersion through the material. Because gas molecules cannot penetrate GNRs, they are faced with a “tortuous path” to freedom, he said.

The researchers acknowledged that a solid, two-dimensional sheet of graphene might be the perfect barrier to gas, but the production of graphene in such bulk quantities is not yet practical, Tour said.

But graphene nanoribbons are already there. Tour’s breakthrough “unzipping” technique for turning multiwalled carbon nanotubes into GNRs, first revealed in Nature in 2009, has been licensed for industrial production. “These are being produced in bulk, which should also make containers cheaper,” he said.

The researchers led by Rice graduate student Changsheng Xiang produced thin films of the composite material by solution casting GNRs treated with hexadecane and TPU, a block copolymer of polyurethane that combines hard and soft materials. The tiny amount of treated GNRs accounted for no more than 0.5 percent of the composite’s weight. But the overlapping 200- to 300-nanometer-wide ribbons dispersed so well that they were nearly as effective as large-sheet graphene in containing gas molecules. The GNRs’ geometry makes them far better than graphene sheets for processing into composites, Tour said.

They tested GNR/TPU films by putting pressurized nitrogen on one side and a vacuum on the other side. For films with no GNRs, the pressure dropped to zero in about 100 seconds as nitrogen escaped into the vacuum chamber. With GNRs at 0.5 percent, the pressure didn’t budge over 1,000 seconds, and it dropped only slightly over more than 18 hours.

Stress and strain tests also found that the 0.5 percent ratio was optimal for enhancing the polymer’s strength.

“The idea is to increase the toughness of the tank and make it impermeable to gas,” Tour said. “This becomes increasingly important as automakers think about powering cars with natural gas. Metal tanks that can handle natural gas under pressure are often much heavier than the automakers would like.”

He said the material could help to solve long-standing problems in food packaging, too.

“Remember when you were a kid, you’d get a balloon and it would be wilted the next day? That’s because gas molecules go through rubber or plastic,” Tour said. “It took years for scientists to figure out how to make a plastic bottle for soda. Once, you couldn’t get a carbonated drink in anything but a glass bottle, until they figured out how to modify plastic to contain the carbon dioxide bubbles. And even now, bottled soda goes flat after a period of months.

“Beer has a bigger problem and, in some ways, it’s the reverse problem,” he said. “Oxygen molecules get in through plastic and make the beer go bad.” Bottles that are effectively impermeable could lead to brew that stays fresh on the shelf for far longer, Tour said.

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