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Unraveling the mysteries of spider-web strength and damage-resistant design

Scientists at MIT have developed a systematic approach to research the structure of spider silk, blending computational modeling and mechanical analysis to 3D-print synthetic spider webs (credit: Zhao Qin et al./Nature Communications)

MIT scientists have developed a systematic approach to research the structure of spider “silk” (which ounce for ounce, is stronger than steel) and how spiders optimize their own webs. The researchers are  blending computational modeling and mechanical analysis to 3D-print synthetic spider webs, with the goal of fabricating and testing synthetic spider-web structures.

“This is the first methodical exploration of its kind,” says Professor Markus Buehler, head of MIT’s Department of Civil and Environmental Engineering (CEE), and the lead author of an open-access paper appearing in Nature Communications. “We are looking to expand our knowledge of the function of natural webs in a systematic and repeatable manner.”

The lessons learned through this approach may help harness spider silk’s strength for other uses, and ultimately inspire engineers to digitally design new structures and composites that are lighter, more reliable, and damage-resistant.

Reverse-engineering the spider’s sophisticated architecture

The study explores the relationship between spider web structure, loading points, and failure mechanisms. By adjusting the material distribution throughout an entire web, a spider is able to optimize the web’s strength for its anticipated prey.

The team, adopting an experimental setup, used metal structures to 3D-print synthetic webs, and directly integrate their data into models. “Ultimately we merged the physical with the computational in our experiments,” Buehler says.

According to Buehler, spider webs employ a limited amount of material to capture prey of different sizes, with materials only a few micrometers (millionths of a meter) in diameter.

The 3D-printed models, Lewis says, open the door to studying the effects of spider-web architecture on strength and damage tolerance — a feat that would have been impossible to achieve using only natural spider webs.

Buehler’s team used orb-weaver spider webs as the inspiration for their 3-D designs. In each of their samples, they controlled the diameter of the thread as a method of comparing homogeneous and heterogeneous thread thickness.

The work revealed that spider webs consisting of uniform thread diameters are better suited to bear force applied at a single point, such as the impact coming from flies hitting webs, while a nonuniform diameter can withstand more widespread pressure, such as from wind, rain, or gravity.

The team now plans to examine the dynamic aspects of webs through controlled impact and vibration experiments, changing the printed material’s properties in real time and opening the door to printing optimized, multifunctional structures.

Abstract of Structural optimization of 3D-printed synthetic spider webs for high strength

Spiders spin intricate webs that serve as sophisticated prey-trapping architectures that simultaneously exhibit high strength, elasticity and graceful failure. To determine how web mechanics are controlled by their topological design and material distribution, here we create spider-web mimics composed of elastomeric filaments. Specifically, computational modelling and microscale 3D printing are combined to investigate the mechanical response of elastomeric webs under multiple loading conditions. We find the existence of an asymptotic prey size that leads to a saturated web strength. We identify pathways to design elastomeric material structures with maximum strength, low density and adaptability. We show that the loading type dictates the optimal material distribution, that is, a homogeneous distribution is better for localized loading, while stronger radial threads with weaker spiral threads is better for distributed loading. Our observations reveal that the material distribution within spider webs is dictated by the loading condition, shedding light on their observed architectural variations.

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NASA challenges ‘makers’ to design 3-D printed habitats for deep-space exploration

One concept for a 3D-printed Moon habitat (credit: NASA)

NASA and the National Additive Manufacturing Innovation Institute (America Makes) are holding a new $2.25 million competition, the 3-D Printed Habitat Challenge, to design and build a 3-D printed habitat for deep space exploration, including the agency’s journey to Mars.

The program is designed to advance the additive construction technology needed to create sustainable housing solutions for Earth and beyond. The idea is to avoid taking along materials and equipment for building a habitat on a distant planet, which would take up valuable cargo space.

The first phase of the competition calls on participants to develop state-of-the-art architectural concepts that take advantage of the unique capabilities 3-D printing offers. A prize purse of $50,000 will be awarded at the 2015 Maker Faire in New York.

“The future possibilities for 3-D printing are inspiring, and the technology is extremely important to deep space exploration,” said Sam Ortega, Centennial Challenges program manager. “This challenge definitely raises the bar from what we are currently capable of, and we are excited to see what the maker community does with it.”

Robot prints a road in front of a hangar for a lunar lander (credit: Behnaz Farahi/NASA)

The second phase of the competition is divided into two levels. The Structural Member Competition (Level 1) focuses on the fabrication technologies needed to manufacture structural components from a combination of indigenous materials (such as Moon regolith) and recyclables, or indigenous materials alone. The On-Site Habitat Competition (Level 2) challenges competitors to actually fabricate full-scale habitats using indigenous materials or indigenous materials combined with recyclables. Both levels are open for registration Sept. 26, and each carries a $1.1 million prize.

Winning concepts and products will help NASA build the technical expertise to send habitat-manufacturing machines to distant destinations, such as Mars, to build shelters for the human explorers who follow. On Earth, these capabilities may be used one day to construct affordable housing in remote locations with limited access to conventional building materials.

 

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3D-printed aerogels enable new energy-storage and nanoelectronic devices

Lawrence Livermore researchers have made graphene aerogel microlattices with an engineered architecture via a 3D printing technique known as direct ink writing (credit: Ryan Chen/LLNL)

Lawrence Livermore National Laboratory researchers have made novel graphene aerogel microlattices with an engineered architecture, using a 3D printing technique known as “direct ink writing.” The research, which could lead to better energy storage, sensors, nanoelectronics, catalysis, and separations, is described in an open-access paper in the April 22 edition of the journal Nature Communications.


Lawrence Livermore National Laboratory | How we 3D-print aerogel

The 3D printed graphene aerogels have high surface area, excellent electrical conductivity, are lightweight, have mechanical stiffness and exhibit supercompressibility (allowing for up to 90 percent compressive strain), and show a ten times improvement over bulk graphene materials and much better mass transport.

Aerogel is a synthetic porous, ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas. It is often referred to as “liquid smoke.”

3D printing with graphene oxide (GO) inks

SEM image of a 3D printed graphene aerogel microlattice. Scale bar: 100nm. (credit: Cheng Zhu et al./Nature Communications)

The graphene oxide (GO) inks are prepared by combining an aqueous GO suspension and silica filler to form a homogenous, highly viscous ink. These GO inks are then loaded into a syringe barrel and extruded through a micronozzle to pattern 3D structures.

“Adapting the 3D printing technique to aerogels makes it possible to fabricate countless complex aerogel architectures for applications such as mechanical properties and compressibility, which has never been achieved before, ” said engineer Cheng Zhu, a co-author of the journal article.

Previous attempts at creating bulk graphene aerogels produced a largely random pore structure, excluding the ability to tailor transport and other mechanical properties of the material for specific applications such as separations, flow batteries, and pressure sensors. “Making graphene aerogels with tailored macro-architectures for specific applications with a controllable and scalable assembly method remains a significant challenge that we were able to tackle,” said engineer Marcus Worsley, a co-author of the paper.

In contrast, “3D printing allows for intelligently designing the pore structure of the aerogel, permitting control over mass transport (aerogels typically require high pressure gradients to drive mass transport through them due to small, tortuous pore structure) and optimization of physical properties, such as stiffness,” he said. “This development should open up the design space for using aerogels in novel and creative applications.”

The work is funded by the Laboratory Directed Research and Development Program.

Abstract of Highly compressible 3D periodic graphene aerogel microlattices

Graphene is a two-dimensional material that offers a unique combination of low density, exceptional mechanical properties, large surface area and excellent electrical conductivity. Recent progress has produced bulk 3D assemblies of graphene, such as graphene aerogels, but they possess purely stochastic porous networks, which limit their performance compared with the potential of an engineered architecture. Here we report the fabrication of periodic graphene aerogel microlattices, possessing an engineered architecture via a 3D printing technique known as direct ink writing. The 3D printed graphene aerogels are lightweight, highly conductive and exhibit supercompressibility (up to 90% compressive strain). Moreover, the Young’s moduli of the 3D printed graphene aerogels show an order of magnitude improvement over bulk graphene materials with comparable geometric density and possess large surface areas. Adapting the 3D printing technique to graphene aerogels realizes the possibility of fabricating a myriad of complex aerogel architectures for a broad range of applications.

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New evidence that electrical stimulation accelerates wound healing

An untreated wound (left) after 10 days is larger than an electrical-stimulation-treated wound (right) (credit: The University of Manchester)

The most detailed study to date of skin wound healing, conducted by University of Manchester scientists with 40 volunteers, has provided new evidence that electrical stimulation accelerates wound healing.

In the new research, half-centimeter harmless wounds were created on each upper arm of the volunteers.  One wound was left to heal normally, while the other was treated with electrical pulses* over a period of two weeks.  The pulses stimulated angiogenesis — the process by which new blood vessels form — increasing blood flow to the damaged area and resulting in wounds healing significantly faster.

Normal-healing tissues (top) vs. electrical-stimulation-treated healing tissues (bottom). Electrical-stimulation sample showed reorganization and accelerated granulation tissue stage development. ED is epidermis, DE is dermis, GT is granulation tissue, FT is fat/adipose tissue. (credit: Sara Ud-Din et al./PLoS ONE)

“The aim of this study was to further evaluate the role of electrical stimulation (ES) in affecting angiogenesis during the acute phase of cutaneous wound healing over multiple time points to identify if the enhanced effect occurred earlier than day 14,” the researchers note in a paper published in open-access PLoS ONE.

“This research has shown the effectiveness of electrical stimulation in wound healing,” said research leader Ardeshir Bayat of the University’s Institute of Inflammation and Repair. “We believe this technology has the potential to be applied to any situation where faster wound healing is particularly desirable, such as human or veterinary surgical wounds, accidents, military trauma, and sports injuries.”

Based on the findings, the researchers plan to work with Oxford BioElectronics Ltd. on a five-year project to develop and evaluate devices and dressings that use these experimental techniques to stimulate the body’s nervous system to generate nerve impulses directed to the site of skin repair.

How electrical stimulation enhances wound healing

The researchers explain in the paper that “ES in its various forms has been shown to enhance wound healing by promoting the migration of keratinocytes and macrophages, enhancing angiogenesis, stimulating fibroblasts, and influencing protein synthesis throughout the inflammatory, proliferative, and remodeling phases of healing.”

The researchers previously “investigated the in vitro effect of different types of ES on the expression of collagen in skin fibroblasts. Importantly, we highlighted the role of a novel waveform termed degenerate wave (DW is a degenerating sine wave, which deteriorates over time) and demonstrated its beneficial effects compared to other known waveforms such as direct and alternating currents.”

Skin wounds that are slow to heal are a clinical challenge to physicians all over the world. Every year, the NHS in the U.K. alone spends £1 billion on treating chronic wounds such as lower limb venous and diabetic ulcers. (Wounds become chronic when they fail to heal and remain open for longer than six weeks.)

* According to the researchers writing in the PLoS ONE paper, the electrical stimulation device used was the Fenzian system (Fenzian Ltd, Hungerford, UK), a transcutaneous low intensity device that  detects changes in skin impedance and adjusts the outgoing microcurrent electrical biofeedback impulses (20–80V, 6-millisecond “degenerate wave” pulses at 0.004 milliamps, with a frequency default of 60Hz).

Abstract of Angiogenesis Is Induced and Wound Size Is Reduced by Electrical Stimulation in an Acute Wound Healing Model in Human Skin

Angiogenesis is critical for wound healing. Insufficient angiogenesis can result in impaired wound healing and chronic wound formation. Electrical stimulation (ES) has been shown to enhance angiogenesis. We previously showed that ES enhanced angiogenesis in acute wounds at one time point (day 14). The aim of this study was to further evaluate the role of ES in affecting angiogenesis during the acute phase of cutaneous wound healing over multiple time points. We compared the angiogenic response to wounding in 40 healthy volunteers (divided into two groups and randomised), treated with ES (post-ES) and compared them to secondary intention wound healing (control). Biopsy time points monitored were days 0, 3, 7, 10, 14. Objective non-invasive measures and H&E analysis were performed in addition to immunohistochemistry (IHC) and Western blotting (WB). Wound volume was significantly reduced on D7, 10 and 14 post-ES (p = 0.003, p = 0.002, p<0.001 respectively), surface area was reduced on days 10 (p = 0.001) and 14 (p<0.001) and wound diameter reduced on days 10 (p = 0.009) and 14 (p = 0.002). Blood flow increased significantly post-ES on D10 (p = 0.002) and 14 (p = 0.001). Angiogenic markers were up-regulated following ES application; protein analysis by IHC showed an increase (p<0.05) in VEGF-A expression by ES treatment on days 7, 10 and 14 (39%, 27% and 35% respectively) and PLGF expression on days 3 and 7 (40% on both days), compared to normal healing. Similarly, WB demonstrated an increase (p<0.05) in PLGF on days 7 and 14 (51% and 35% respectively). WB studies showed a significant increase of 30% (p>0.05) on day 14 in VEGF-A expression post-ES compared to controls. Furthermore, organisation of granulation tissue was improved on day 14 post-ES. This randomised controlled trial has shown that ES enhanced wound healing by reduced wound dimensions and increased VEGF-A and PLGF expression in acute cutaneous wounds, which further substantiates the role of ES in up-regulating angiogenesis as observed over multiple time points. This therapeutic approach may have potential application for clinical management of delayed and chronic wounds.

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First large-scale graphene fabrication

ORNL’s ultrastrong graphene-based material features layers of graphene and polymers  (credit: ORNL)

Fabrication size limits — one of the barriers to using graphene on a commercial scale — could be overcome using a new method developed by researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL).

Graphene, a one-atom-thick material that is about 100 times stronger than steel by weight, has enormous commercial potential but has been impractical to employ on a large scale, mainly because of size limits and expense.

Now, using chemical vapor deposition, a team led by ORNL’s Ivan Vlassiouk has fabricated polymer laminate (layered) composites containing 2-inch-by-2-inch graphene sheets created from large continuous sheets of single-layer graphene. They were also able to produce graphene-based fibers.

Outperforming current composite materials

Graphene-polymer fiber (credit: ORNL)

The new process eliminates flake dispersion and agglomeration (sticking together) problems. The process has potential to outperform current state of the art composite materials in both mechanical properties and electrical conductivity.

The process also uses 50 times less actual graphene in the polymer, compared to current state-of-the-art samples — a key to making the material competitive in the market, Vlassiouk said.

If the ORNL team can reduce cost and demonstrate scalability, graphene could be used in aerospace (structural monitoring, flame-retardants, anti-icing, conductive), the automotive sector (catalysts, wear-resistant coatings), structural applications (self-cleaning coatings, temperature control materials), electronics (displays, flexible printed electronics, thermal management), energy (photovoltaics, filtration, energy storage) and manufacturing (catalysts, barrier coatings, filtration).

The findings are reported in the journal Applied Materials & Interfaces. Scientists at New Mexico State University were also involved in the research, which was supported by ORNL’s Laboratory Directed Research and Development program.

Abstract of Strong and Electrically Conductive Graphene-Based Composite Fibers and Laminates

Graphene is an ideal candidate for lightweight, high-strength composite materials given its superior mechanical properties (specific strength of 130 GPa and stiffness of 1 TPa). To date, easily scalable graphene-like materials in a form of separated flakes (exfoliated graphene, graphene oxide, and reduced graphene oxide) have been investigated as candidates for large-scale applications such as material reinforcement. These graphene-like materials do not fully exhibit all the capabilities of graphene in composite materials. In the current study, we show that macro (2 inch × 2 inch) graphene laminates and fibers can be produced using large continuous sheets of single-layer graphene grown by chemical vapor deposition. The resulting composite structures have potential to outperform the current state-of-the-art composite materials in both mechanical properties and electrical conductivities (>8 S/cm with only 0.13% volumetric graphene loading and 5 × 103 S/cm for pure graphene fibers) with estimated graphene contributions of >10 GPa in strength and 1 TPa in stiffness.

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Limitless, Minority Report sequels coming to TV

Limitless, a TV series sequel to the movie, picks up after the events of the film. Edward Mora (Bradley Cooper), now a powerful senator and presidential hopeful, reveals the power of the mysterious drug NZT to Brian Finch (Jake McDorman) — who is then coerced by the FBI into using his newfound cognitive abilities to solve complex cases. Cooper is also executive producer.

Fall 2015. More at CBS.com

Minority Report (Fox) will be based on the film by Steven Spielberg (and the first of his films to be adapted for television). The show follows the unlikely partnership between a man haunted by the future and a cop haunted by her past, as they race to stop the worst crimes of the year 2065 before they happen.

Set in Washington, D.C., it is 10 years after the demise of Precrime, a law enforcement agency tasked with identifying and eliminating criminals — before their crimes were committed. The agency used three child precogs who were able to see the future. Now, in 2065, crime-solving is different, and justice leans more on sophisticated and trusted technology than on the instincts of the precogs.

Dash (Stark Sands) —  one of the three precogs freed at the end of the film and now driven by his terrifying but fragmented visions — has returned in secret to help police detective Lara Vega (Meagan Good) attempt to stop the murders that he predicts.

Fall 2015. More at Fox.

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Google plans to test its new self driving vehicle prototypes on California roads

Google says its safety drivers will test fully self driving vehicle prototypes like this one on the streets of California this summer — credit | Google

Google announced today (May 15) that it test a few of its new Volkswagen Beetle-like prototype self-driving vehicles on roads in Mountain View, Calif. this summer Unlike Google’s previous prototype test vehicles, these will have safety drivers aboard, and with a steering wheel, accelerator pedal, and brake pedal if needed.

These vehicles are designed for local driving, with speed capped at 25mph.

Google said the new prototypes will “drive with the same software that our existing fleet of self-driving Lexus RX450h SUVs uses. That fleet has logged nearly a million autonomous miles on the roads since we started the project, and recently has been self-driving about 10,000 miles a week.

“When we started designing the world’s first fully self-driving vehicle, our goal was a vehicle that could shoulder the entire burden of driving,” according to the Google statement. “Vehicles that can take anyone from A to B at the push of a button could transform mobility for millions of people, whether by reducing the 94 percent of accidents caused by human error (PDF), reclaiming the billions of hours wasted in traffic, or bringing everyday destinations and new opportunities within reach of those who might otherwise be excluded by their inability to drive a car.”

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