Category Archives: biomimcry

The inside scoop on beetle exoskeletons

In the past I’ve covered work on the Namib beetle and its bumps which allow it to access condensation from the air in one of the hottest places on earth and work on jewel beetles and how their structural colo(u)r is derived. Now, there’s research into a beetle’s body armor from the University of Nebraska-Lincoln according to a Feb. 22, 2017 news item on ScienceDaily,

Beetles wear a body armor that should weigh them down — think medieval knights and turtles. In fact, those hard shells protecting delicate wings are surprisingly light, allowing even flight.

Better understanding the structure and properties of beetle exoskeletons could help scientists engineer lighter, stronger materials. Such materials could, for example, reduce gas-guzzling drag in vehicles and airplanes and reduce the weight of armor, lightening the load for the 21st-century knight.

But revealing exoskeleton architecture at the nanoscale has proven difficult. Nebraska’s Ruiguo Yang, assistant professor of mechanical and materials engineering, and his colleagues found a way to analyze the fibrous nanostructure. …

A Feb. 22, 2017 University of Nebraska-Lincoln news release by Gillian Klucas (also on EurekAlert), which originated the news item, describes skeletons and the work in more detail,

The lightweight exoskeleton is composed of chitin fibers just around 20 nanometers in diameter (a human hair measures approximately 75,000 nanometers in diameter) and packed and piled into layers that twist in a spiral, like a spiral staircase. The small diameter and helical twisting, known as Bouligand, make the structure difficult to analyze.

Yang and his team developed a method of slicing down the spiral to reveal a surface of cross-sections of fibers at different orientations. From that viewpoint, the researchers were able to analyze the fibers’ mechanical properties with the aid of an atomic force microscope. This type of microscope applies a tiny force to a test sample, deforms the sample and monitors the sample’s response. Combining the experimental procedure and theoretical analysis, the researchers were able to reveal the nanoscale architecture of the exoskeleton and the material properties of the nanofibers.

Yang holds a piece of the atomic force microscope used to measure the beetle's surface. A small wire can barely be seen in the middle of the piece. Unseen is a two-nano-size probe attached to the wire, which does the actual measuring.

Craig Chandler | University Communication

Yang holds a piece of the atomic force microscope used to measure the beetle’s surface. A small wire can barely be seen in the middle of the piece. Unseen is a two-nano-size probe attached to the wire, which does the actual measuring.

They made their discoveries in the common figeater beetle, Cotinis mutabilis, a metallic green native of the western United States. But the technique can be used on other beetles and hard-shelled creatures and might also extend to artificial materials with fibrous structures, Yang said.

Comparing beetles with differing demands on their exoskeletons, such as defending against predators or environmental damage, could lead to evolutionary insights as well as a better understanding of the relationship between structural features and their properties.

Yang’s co-authors are Alireza Zaheri and Horacio Espinosa of Northwestern University; Wei Gao of the University of Texas at San Antonio; and Cheryl Hayashi of the University of California, Riverside.

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

Exoskeletons: AFM Identification of Beetle Exocuticle: Bouligand Structure and Nanofiber Anisotropic Elastic Properties by Ruiguo Yang, Alireza Zaheri,Wei Gao, Charely Hayashi, Horacio D. Espinosa. Adv. Funct. Mater. vol. 27 (6) 2017 DOI: 10.1002/adfm.201770031 First published: 8 February 2017

This paper is behind a paywall.

Brown recluse spider, one of the world’s most venomous spiders, shows off unique spinning technique

Caption: American Brown Recluse Spider is pictured. Credit: Oxford University

According to scientists from Oxford University this deadly spider could teach us a thing or two about strength. From a Feb. 15, 2017 news item on ScienceDaily,

Brown recluse spiders use a unique micro looping technique to make their threads stronger than that of any other spider, a newly published UK-US collaboration has discovered.

One of the most feared and venomous arachnids in the world, the American brown recluse spider has long been known for its signature necro-toxic venom, as well as its unusual silk. Now, new research offers an explanation for how the spider is able to make its silk uncommonly strong.

Researchers suggest that if applied to synthetic materials, the technique could inspire scientific developments and improve impact absorbing structures used in space travel.

The study, published in the journal Material Horizons, was produced by scientists from Oxford University’s Department of Zoology, together with a team from the Applied Science Department at Virginia’s College of William & Mary. Their surveillance of the brown recluse spider’s spinning behaviour shows how, and to what extent, the spider manages to strengthen the silk it makes.

A Feb. 15, 2017 University of Oxford press release, which originated the news item,  provides more detail about the research,

From observing the arachnid, the team discovered that unlike other spiders, who produce round ribbons of thread, recluse silk is thin and flat. This structural difference is key to the thread’s strength, providing the flexibility needed to prevent premature breakage and withstand the knots created during spinning which give each strand additional strength.

Professor Hannes Schniepp from William & Mary explains: “The theory of knots adding strength is well proven. But adding loops to synthetic filaments always seems to lead to premature fibre failure. Observation of the recluse spider provided the breakthrough solution; unlike all spiders its silk is not round, but a thin, nano-scale flat ribbon. The ribbon shape adds the flexibility needed to prevent premature failure, so that all the microloops can provide additional strength to the strand.”

By using computer simulations to apply this technique to synthetic fibres, the team were able to test and prove that adding even a single loop significantly enhances the strength of the material.

William & Mary PhD student Sean Koebley adds: “We were able to prove that adding even a single loop significantly enhances the toughness of a simple synthetic sticky tape. Our observations open the door to new fibre technology inspired by the brown recluse.”

Speaking on how the recluse’s technique could be applied more broadly in the future, Professor Fritz Vollrath, of the Department of Zoology at Oxford University, expands: “Computer simulations demonstrate that fibres with many loops would be much, much tougher than those without loops. This right away suggests possible applications. For example carbon filaments could be looped to make them less brittle, and thus allow their use in novel impact absorbing structures. One example would be spider-like webs of carbon-filaments floating in outer space, to capture the drifting space debris that endangers astronaut lives’ and satellite integrity.”

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

Toughness-enhancing metastructure in the recluse spider’s looped ribbon silk by
S. R. Koebley, F. Vollrath, and H. C. Schniepp. Mater. Horiz., 2017, Advance Article DOI: 10.1039/C6MH00473C First published online 15 Feb 2017

This paper is open access although you may need to register with the Royal Society of Chemistry’s publishing site to get access.

Effective sunscreens from nature

The dream is to find sunscreens that don’t endanger humans or pollute the environment and it seems that Spanish scientists may have taken a step closer to making that dream a reality (from a Jan. 30, 2017 Wiley Publications press release (also on EurekAlert),

The ideal sunscreen should block UVB and UVA radiation while being safe and stable. In the journal Angewandte Chemie, Spanish scientists have introduced a new family of UVA and UVB filters based on natural sunscreen substances found in algae and cyanobacteria. They are highly stable and enhance the effectivity [sic] of commercial sunscreens.

Good news for sunseekers. Commercial [sic] available sunscreen lotions can very effectively protect from dangerous radiation in the ultraviolet [spectrum], but they need to be applied regularly and in high amounts to develop their full potential. One of the most critical issues is the limited stability of the UV filter molecules. Inspired by nature, Diego Sampedro and his colleagues from La Rioja University in Logrono and collaborators from Malaga University and Alcala University, Madrid, Spain, have screened a natural class of UV-protecting [blocking?] molecules for their possible use in skin protection. They adjusted the nature-given motif [sic] to the requirements of chemical synthesis and found that the molecules could indeed boost the sun protection factor of common formulations.

The natural sunscreen molecules are called microsporine-like amino acids (MAAs) and are widespread in the microbial world, most prominently in marine algae and cyanobacteria. MAAs are small molecules derived from amino acids, thermally stable, and they absorb light in the ultraviolet region, protecting the microbial DNA from radiation damage. Thus they are natural sunscreens, which inspired Sampedro and his colleagues to create [a] new class of organic sunscreen compounds.

Theoretical calculations revealed what is chemically needed for a successful design. “We performed a computer calculation of several basic scaffolds [..] to identify the simplest compound that fulfills the requisites for efficient sunscreens”, the authors write. The result of their search was a set of molecules which were readily synthesized, “avoiding the decorating substituents that come from the biosynthetic route.” Thus the small basic molecules can be tuned to give them more favorable properties.

The authors found that the synthesized compounds are characterized by excellent filter capacities in the relevant UV range. In addition they are photostable, much more than, for example, oxybenzene [sic] which is a widely used sunscreen in commercial formulations. They do not react chemically and dissipate radiation as heat (but not to such an extent that the skin temperature would rise as well). And, most importantly, when tested in real formulations, the sun protection factor (SPF) rose by a factor of more than two. Thus they could be promising targets for more stable, more efficient sunscreen lotions. Good news for your next summer vacation.

There’s some unusual phrasing so, I’m guessing that the writer it not accustomed to writing press releases in English. One other comment, it’s oxybenzone that’s often used as an ingredient in commercial sunscreens.

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

Rational Design and Synthesis of Efficient Sunscreens To Boost the Solar Protection Factor by Raúl Losantos, Ignacio Funes-Ardoiz, Dr. José Aguilera, Prof. Enrique Herrera-Ceballos, Dr. Cristina García-Iriepa, Prof. Pedro J. Campos, and Diego Sampedro. Angewandte Chemie International Edition Volume 56, Issue 10, pages 2632–2635, March 1, 2017 DOI: 10.1002/anie.201611627 Version of Record online: 27 JAN 2017

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

I have previously featured work on another natural sunscreen. In that case it was to be derived from English ivy (July 22, 2010 posting); there was an update on the English ivy work in a May 30, 2016 posting but the researcher has moved in a different direction looking at wound healing and armour as possible applications for the research.

Hairy strength could lead to new body armour

A Jan. 18, 2017 news item on Nanowerk announces research into hair strength from the University of California at San Diego (UCSD or UC San Diego),

In a new study, researchers at the University of California San Diego investigate why hair is incredibly strong and resistant to breaking. The findings could lead to the development of new materials for body armor and help cosmetic manufacturers create better hair care products.

Hair has a strength to weight ratio comparable to steel. It can be stretched up to one and a half times its original length before breaking. “We wanted to understand the mechanism behind this extraordinary property,” said Yang (Daniel) Yu, a nanoengineering Ph.D. student at UC San Diego and the first author of the study.

A Jan. 18 (?), 2017 UCSD news release, which originated the news item, provides more information,

“Nature creates a variety of interesting materials and architectures in very ingenious ways. We’re interested in understanding the correlation between the structure and the properties of biological materials to develop synthetic materials and designs — based on nature — that have better performance than existing ones,” said Marc Meyers, a professor of mechanical engineering at the UC San Diego Jacobs School of Engineering and the lead author of the study.

In a study published online in Dec. in the journal Materials Science and Engineering C, researchers examined at the nanoscale level how a strand of human hair behaves when it is deformed, or stretched. The team found that hair behaves differently depending on how fast or slow it is stretched. The faster hair is stretched, the stronger it is. “Think of a highly viscous substance like honey,” Meyers explained. “If you deform it fast it becomes stiff, but if you deform it slowly it readily pours.”

Hair consists of two main parts — the cortex, which is made up of parallel fibrils, and the matrix, which has an amorphous (random) structure. The matrix is sensitive to the speed at which hair is deformed, while the cortex is not. The combination of these two components, Yu explained, is what gives hair the ability to withstand high stress and strain.

And as hair is stretched, its structure changes in a particular way. At the nanoscale, the cortex fibrils in hair are each made up of thousands of coiled spiral-shaped chains of molecules called alpha helix chains. As hair is deformed, the alpha helix chains uncoil and become pleated sheet structures known as beta sheets. This structural change allows hair to handle a large amount deformation without breaking.

This structural transformation is partially reversible. When hair is stretched under a small amount of strain, it can recover its original shape. Stretch it further, the structural transformation becomes irreversible. “This is the first time evidence for this transformation has been discovered,” Yu said.

“Hair is such a common material with many fascinating properties,” said Bin Wang, a UC San Diego PhD alumna from the Department of Mechanical and Aerospace Engineering and co-author on the paper. Wang is now at the Shenzhen Institutes of Advanced Technology in China continuing research on hair.

The team also conducted stretching tests on hair at different humidity levels and temperatures. At higher humidity levels, hair can withstand up to 70 to 80 percent deformation before breaking (dry hair can undergo up to 50 percent deformation). Water essentially “softens” hair — it enters the matrix and breaks the sulfur bonds connecting the filaments inside a strand of hair. Researchers also found that hair starts to undergo permanent damage at 60 degrees Celsius (140 degrees Fahrenheit). Beyond this temperature, hair breaks faster at lower stress and strain.

“Since I was a child I always wondered why hair is so strong. Now I know why,” said Wen Yang, a former postdoctoral researcher in Meyers’ research group and co-author on the paper.

The team is currently conducting further studies on the effects of water on the properties of human hair. Moving forward, the team is investigating the detailed mechanism of how washing hair causes it to return to its original shape.

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

Structure and mechanical behavior of human hair by Yang Yua, Wen Yang, Bin Wang, Marc André Meyers. Materials Science and Engineering: C Volume 73, 1 April 2017, Pages 152–163    http://dx.doi.org/10.1016/j.msec.2016.12.008

This paper is behind a paywall.

Nanomechanics for deciphering beetle exoskeletons

Beetles carry remarkably light yet strong armor in the form of their exoskeletons and a research team at Northwestern University (US) is looking to those beetle exoskeletons for inspiration according to a Jan. 11, 2017 news item on ScienceDaily,

What can a beetle tell us about good design principles? Quite a lot, actually.

Many insects and crustaceans possess hard, armor-like exoskeletons that, in theory, should weigh the creatures down. But, instead, the exoskeletons are surprisingly light — even allowing the armor-wearing insects, like the beetle, to fly.

Northwestern Engineering’s Horacio D. Espinosa and his group are working to understand the underlying design principles and mechanical properties that result in structures with these unique, ideal properties. This work could ultimately uncover information that could guide the design and manufacturing of new and improved artificial materials by emulating these time-tested natural patterns, a process known as bio-mimicry.

Supported by the Air Force Office of Scientific Research’s Multidisciplinary University Research Initiative (MURI), the research was featured on the cover of Advanced Functional Materials. Postdoctoral fellows Ruiguo Yang and Wei Gao and graduate student Alireza Zaheri, all members of Espinosa’s laboratory, were co-first authors of the paper. Cheryl Hayashi, professor of biology at the University of California, Riverside, was also a co-author.

A Jan. 11, 2017 Northwestern University news release, which originated the news item, expands on the theme,

Though there are more than a million species of beetles, the team is first studying the exoskeleton of the Cotinis mutabilis, a field crop pest beetle native to the western United States. Like all insects and crustaceans, its exoskeleton is composed of twisted plywood structures, known as Bouligand structures, which help protect against predators. Fibers in this Bouligand structure are bundles of chitin polymer chains wrapped with proteins. In this chain structure, each fiber has a higher density along the length than along the transverse.

“It is very challenging to characterize the properties of such fibers given that they are directionally dependent and have a small diameter of just 20 nanometers,” said Espinosa, the James N. and Nancy J. Farley Professor in Manufacturing and Entrepreneurship at Northwestern’s McCormick School of Engineering. “We had to develop a novel characterization method by taking advantage of the spatial distribution of fibers in the Bouligand structure.”

To meet this challenge, Espinosa and his team employed a creative way to identify the geometry and material properties of the fibers that comprise the exoskeleton. They cut the Bouligand structure along a plane, resulting in a surface composed of closely packed cross-sections of fibers with different orientations. They were then able to analyze the mechanics of the fibers.

“With more than a million species, which greatly vary from each other in taxomic relatedness, size, and ecology, the beetle is the largest group of insects,” Hayashi said. “What makes this research exciting is that the methods applied to the Cotinis mutabilis beetle exoskeleton can be extended to other beetle species.”

By correlating the mechanical properties with the exoskeleton geometries from diverse beetle species, Espinosa and his team plan to gain insight into natural selection and better understand structure-function-properties relationships.

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

AFM Identification of Beetle Exocuticle: Bouligand Structure and Nanofiber Anisotropic Elastic Properties by Ruiguo Yang, Alireza Zaheri, Wei Gao, Cheryl Hayashi, and Horacio D. Espinosa. Advanced Functional Materials DOI: 10.1002/adfm.201603993 Version of Record online: 27 DEC 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Antibiotic synthetic spider silk

I have a couple of questions, what is ‘click’ chemistry and how does a chance meeting lead to a five-year, interdisciplinary research project on synthetic spider silk? From a Jan. 4, 2017 news item on ScienceDaily,

A chance meeting between a spider expert and a chemist has led to the development of antibiotic synthetic spider silk.

After five years’ work an interdisciplinary team of scientists at The University of Nottingham has developed a technique to produce chemically functionalised spider silk that can be tailored to applications used in drug delivery, regenerative medicine and wound healing.

The Nottingham research team has shown for the first time how ‘click-chemistry’ can be used to attach molecules, such as antibiotics or fluorescent dyes, to artificially produced spider silk synthesised by E.coli bacteria. The research, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) is published today in the online journal Advanced Materials.

A Jan. 3, 2016 University of Nottingham press release (also on EurekAlert), which originated the news item, provides a few more details about ‘click’ chemistry (not enough for me) and more information about the research,

The chosen molecules can be ‘clicked’ into place in soluble silk protein before it has been turned into fibres, or after the fibres have been formed. This means that the process can be easily controlled and more than one type of molecule can be used to ‘decorate’ individual silk strands.

Nottingham breakthrough

In a laboratory in the Centre of Biomolecular Sciences, Professor Neil Thomas from the School of Chemistry in collaboration with Dr Sara Goodacre from the School of Life Sciences, has led a team of BBSRC DTP-funded PhD students starting with David Harvey who was then joined by Victor Tudorica, Leah Ashley and Tom Coekin. They have developed and diversified this new approach to functionalising ‘recombinant’ — artificial — spider silk with a wide range of small molecules.

They have shown that when these ‘silk’ fibres are ‘decorated’ with the antibiotic levofloxacin it is slowly released from the silk, retaining its anti-bacterial activity for at least five days.

Neil Thomas, a Professor of Medicinal and Biological Chemistry, said: “Our technique allows the rapid generation of biocompatible, mono or multi-functionalised silk structures for use in a wide range of applications. These will be particularly useful in the fields of tissue engineering and biomedicine.”

Remarkable qualities of spider silk

Spider silk is strong, biocompatible and biodegradable. It is a protein-based material that does not appear to cause a strong immune, allergic or inflammatory reaction. With the recent development of recombinant spider silk, the race has been on to find ways of harnessing its remarkable qualities.

The Nottingham research team has shown that their technique can be used to create a biodegradable mesh which can do two jobs at once. It can replace the extra cellular matrix that our own cells generate, to accelerate growth of the new tissue. It can also be used for the slow release of antibiotics.

Professor Thomas said: “There is the possibility of using the silk in advanced dressings for the treatment of slow-healing wounds such as diabetic ulcers. Using our technique infection could be prevented over weeks or months by the controlled release of antibiotics. At the same time tissue regeneration is accelerated by silk fibres functioning as a temporary scaffold before being biodegraded.”

The medicinal properties of spider silk recognised for centuries.

The medicinal properties of spider silk have been recognised for centuries but not clearly understood. The Greeks and Romans treated wounded soldiers with spider webs to stop bleeding. It is said that soldiers would use a combination of honey and vinegar to clean deep wounds and then cover the whole thing with balled-up spider webs.

There is even a mention in Shakespeare’s Midsummer Night’s Dream: “I shall desire you of more acquaintance, good master cobweb,” the character ‘Bottom’ said. “If I cut my finger, I shall make bold of you.”

The press release goes on to describe the genesis of the project and how this multidisciplinary team was formed in more detail,

The idea came together at a discipline bridging university ‘sandpit’ meeting five years ago. Dr Goodacre says her chance meeting at that event with Professor Thomas proved to be one of the most productive afternoons of her career.

Dr Goodacre, who heads up the SpiderLab in the School of Life Sciences, said: “I got up at that meeting and showed the audience a picture of some spider silk. I said ‘I want to understand how this silk works, and then make some.’

“At the end of the session Neil came up to me and said ‘I think my group could make that.’ He also suggested that there might be more interesting ‘tweaks’ one could make so that the silk could be ‘decorated’ with different, useful, compounds either permanently or which could be released over time due to a change in the acidity of the environment.”

The approach required the production of the silk proteins in a bacterium where an amino acid not normally found in proteins was included. This amino acid contained an azide group which is widely used in ‘click’ reactions that only occur at that position in the protein. It was an approach that no-one had used before with spider silk — but the big question was — would it work?

Dr Goodacre said: “It was the start of a fascinating adventure that saw a postdoc undertake a very preliminary study to construct the synthetic silks. He was a former SpiderLab PhD student who had previously worked with our tarantulas. Thanks to his ground work we showed we could produce the silk proteins in bacteria. We were then joined by David Harvey, a new PhD student, who not only made the silk fibres, incorporating the unusual amino acid, but also decorated it and demonstrated its antibiotic activity. He has since extended those first ideas far beyond what we had thought might be possible.”

David Harvey’s work is described in this paper but Professor Thomas and Dr Goodacre say this is just the start. There are other joint SpiderLab/Thomas lab students working on uses for this technology in the hope of developing it further.

David Harvey, the lead author on this their first paper, has just been awarded his PhD and is now a postdoctoral researcher on a BBSRC follow-on grant so is still at the heart of the research. His current work is focused on driving the functionalised spider silk technology towards commercial application in wound healing and tissue regeneration.

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

Antibiotic Spider Silk: Site-Specific Functionalization of Recombinant Spider Silk Using “Click” Chemistry by David Harvey, Philip Bardelang, Sara L. Goodacre, Alan Cockayne, and Neil R. Thomas. Advanced Materials DOI: 10.1002/adma.201604245 Version of Record online: 28 DEC 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

I imagine Mr. Cockayne’s name has led to much teasing over the years. People who have names with that kind of potential tend to either change them or double down and refuse to compromise.

Sea sponges don’t buckle under pressure

You wouldn’t think a sponge (the sea creature) was particularly tough but it is according to a Jan. 4, 2017 news item on Nanowerk,

Judging by their name alone, orange puffball sea sponges might seem unlikely paragons of structural strength. But maintaining their shape at the bottom of the churning ocean is critical to the creatures’ survival, and new research shows that tiny structural rods in their bodies have evolved the optimal shape to avoid buckling under pressure.

The rods, called strongyloxea spicules, measure about 2 millimeters long and are thinner than a human hair. Hundreds of them are bundled together, forming stiff rib-like structures inside the orange puffball’s spongy body. It was the odd and remarkably consistent shape of each spicule that caught the eye of Brown University engineers Haneesh Kesari and Michael Monn. Each one is symmetrically tapered along its length — going gradually from fatter in the middle to thinner at the ends.

Caption: Tiny rods found inside the bodies of orange puffball sea sponges have an interesting tapered shape. That shape, new research shows, turns out to be a match for the Clausen profile, a column shape shown to be optimal for resistance to buckling failure. Credit: Michael Monn, Haneesh Kesari / Brown University

A Jan. 4, 2017 Brown University news release on EurekAlert, which originated the news item, describes the research in more detail,

Using structural mechanics models and a bit of digging in obscure mathematics journals, Monn and Kesari showed the peculiar shape of the spicules to be optimal for resistance to buckling, the primary mode of failure for slender structures. This natural shape could provide a blueprint for increasing the buckling resistance in all kinds of slender human-made structures, from building columns to bicycle spokes to arterial stents, the researchers say.

“This is one of the rare examples that we’re aware of where a natural structure is not just well-suited for a given function, but actually approaches a theoretical optimum,” said Kesari, an assistant professor of engineering at Brown. “There’s no engineering analog for this shape — we don’t see any columns or other slender structures that are tapered in this way. So in this case, nature has shown us something quite new that we think could be useful in engineering.”

The findings are published in the journal Scientific Reports.

Function and form

Orange puffball sponges (Tethya aurantia) are native to the Mediterranean Sea. They live mainly in rocky coastal environments, where they’re subject to the constant stress of underwater waves and tidal forces. Sponges are filter feeders — they pump water through their bodies to extract nutrients and oxygen. To do this, their bodies need to be porous and compliant, but they also need enough stiffness to avoid being deformed too much.

“If you compress them too much, you’re essentially choking them,” Kesari said. “So maintaining their stiffness is critical to their survival.”

And that means the spicules, which make up the rib-like structures that give sponges their stiffness, are critical components. When Monn and Kesari saw the shapes of the spicules under a microscope, the consistency of the tapered shape from spicule to spicule was hard to miss.

“We saw the shape and wondered if there might be an engineering principle at work here,” Kesari said.

To figure that out, the researchers first needed to understand what forces were acting on each individual spicule. So Monn and Kesari developed a structural mechanics model of spicules bundled within a sponge’s ribs. The model showed that the mismatch in stiffness between the bulk of the sponge’s soft body and the more rigid spicules causes each spicule to experience primarily one type of mechanical loading — a compression load on each of its ends.

“You can imagine taking a toothpick and trying to squeeze it longways between your fingers,” Monn said. “That’s how these spicules see the world.”

The primary mode of failure for a structure with this mechanical load is through buckling. At a certain critical load, the structure starts to bend somewhere along its length. Once the bending starts, the force transferred by the load is amplified at the bending point, which causes the structure to break or collapse.

Once Kesari and Monn knew what forces were acting on the spicules and how they would fail, the next step was looking to see if there was anything special about them that helped them resist buckling. Scanning electron microscope images of the inside of a spicule and other tests showed that they were monolithic silica — essentially glass.

“We could see that there was no funny business going on with the material properties,” Monn said. “If there was anything contributing to its mechanical performance, it would have to be the shape.”

Optimal shape

Kesari and Monn combed the literature to see if they could find anything on tapering in slender structures. They came up empty in the modern engineering literature. But they found something interesting published more than 150 years ago by a German scientist named Thomas Clausen.

In 1851, Clausen proposed that columns that are tapered toward their ends should have more buckling resistance than plain cylinders, which had been and still are the primary design for architectural columns. In the 1960s, mathematician Joseph Keller published an ironclad mathematical proof that the Clausen column was indeed optimal for resistance to buckling — having 33 percent better resistance than a cylinder. Even compared to a very similar shape — an ellipse, which is slightly fatter in the middle and pointier at the ends — the Clausen column had 18 percent better buckling resistance.

Knowing what the optimal column shape is, Monn and Kesari started making precise dimensional measurements of dozens of spicules. They showed that their shapes were remarkably consistent and nearly identical to that of the Clausen column.

“The spicules were a match for the best shape of all possible column shapes,” Monn said.

It seems in this case, natural selection figured out something that engineers have not. Despite the fact that it’s been mathematically shown to be the optimal column shape, the Clausen profile isn’t widely known in the engineering community. Kesari and Monn hope this work might bring it out of the shadows.

“We see this as an addition to our library of structural designs,” Monn said. “We’re not just talking about an improvement of a few percent. This shape is 33 percent better than the cylinder, which is quite an improvement.”

In particular, the shape would be particularly useful in a new generation of materials made from nanoscale truss structures. “It would be easy to 3-D print the Clausen profile into these materials, and you’d get a tremendous increase in buckling resistance, which is often how these materials fail.”

Lessons from nature

The field of bio-inspired engineering began at a time when many people viewed adaptive evolution as an unceasing march toward perfection. If that were true, scientists should find untold numbers of optimal structures in nature.

But the modern understanding of evolution is a bit different. It’s now understood that in order for a trait to be conserved by natural selection, it doesn’t need to be optimal. It just needs to be good enough to work. That has put a bit of a damper on the enthusiasm for bio-inspired engineering, Kesari and Monn say.

However, they say, this work shows that nearly optimal structures are out there if researchers look in the right places. In this case, they looked at creatures from a very old phylum — sea sponges are among the very first animals on Earth — with plenty of time to evolve under consistent selection pressures.

Sponges are also fairly simple creatures, so understanding the function of a given trait is relatively straightforward. In this case, the spicule appears to have one and only one job to do — provide stiffness. Compare that to, for example, human bone, which not only provides support but must also accommodate arteries, provide attachment points for muscles and house bone marrow. Those other functions may cause tradeoffs in adaptations for strength or stiffness.

“With the sponges, you have lots of evolutionary pressure, lots of time and opportunity to respond to that pressure, and functional elements that can be easily identified,” Kesari said.

With those as guiding principles, there may well be more ideal structures out there waiting to be found.

“This work shows that nature can hit an optimum,” Kesari said, “and the biological world can still be hiding completely new designs of considerable technological significance in plain sight.”

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

A new structure-property connection in the skeletal elements of the marine sponge Tethya aurantia that guards against buckling instability by Michael A. Monn & Haneesh Kesari. Scientific Reports 7, Article number: 39547 (2017) doi:10.1038/srep39547 Published online: 04 January 2017

This paper is open access.

Kesari and Monn have researched sea sponges previously as can be seen in my April 7, 2015 posting, which highlights their work on strength and Venus’ flower basket sea sponge.

More on the blue tarantula noniridescent photonics

Covered in an Oct. 19, 2016 posting here, some new details have been released about noniridescent photonics and blue tarantulas, this time from the Karlsruhe Institute of Technology (KIT) in a Nov. 17, 2016 (?) press release (also on EurekAlert; h/t Nanowerk Nov. 17, 2016 news item) ,

Colors are produced in a variety of ways. The best known colors are pigments. However, the very bright colors of the blue tarantula or peacock feathers do not result from pigments, but from nanostructures that cause the reflected light waves to overlap. This produces extraordinarily dynamic color effects. Scientists from Karlsruhe Institute of Technology (KIT), in cooperation with international colleagues, have now succeeded in replicating nanostructures that generate the same color irrespective of the viewing angle. DOI: 10.1002/adom.201600599

In contrast to pigments, structural colors are non-toxic, more vibrant and durable. In industrial production, however, they have the drawback of being strongly iridescent, which means that the color perceived depends on the viewing angle. An example is the rear side of a CD. Hence, such colors cannot be used for all applications. Bright colors of animals, by contrast, are often independent of the angle of view. Feathers of the kingfisher always appear blue, no matter from which angle we look. The reason lies in the nanostructures: While regular structures are iridescent, amorphous or irregular structures always produce the same color. Yet, industry can only produce regular nanostructures in an economically efficient way.

Radwanul Hasan Siddique, researcher at KIT in collaboration with scientists from USA and Belgium has now discovered that the blue tarantula does not exhibit iridescence in spite of periodic structures on its hairs. First, their study revealed that the hairs are multi-layered, flower-like structure. Then, the researchers analyzed its reflection behavior with the help of computer simulations. In parallel, they built models of these structures using nano-3D printers and optimized the models with the help of the simulations. In the end, they produced a flower-like structure that generates the same color over a viewing angle of 160 degrees. This is the largest viewing angle of any synthetic structural color reached so far.


Flower-shaped nanostructures generate the color of the blue tarantula. (Graphics: Bill Hsiung, University of Akron)

 


The 3D print of the optimized flower structure is only 15 µm in dimension. A human hair is about three times as thick. (Photo: Bill Hsiung, Universtiy of Akron)

Apart from the multi-layered structure and rotational symmetry, it is the hierarchical structure from micro to nano that ensures homogeneous reflection intensity and prevents color changes.

Via the size of the “flower,” the resulting color can be adjusted, which makes this coloring method interesting for industry. “This could be a key first step towards a future where structural colorants replace the toxic pigments currently used in textile, packaging, and cosmetic industries,” says Radwanul Hasan Siddique of KIT’s Institute of Microstructure Technology, who now works at the California Institute of Technology. He considers short-term application in textile industry feasible.


The synthetically generated flower structure inspired by the blue tarantula reflects light in the same color over a viewing angle of 160 degrees. (Graphics: Derek Miller)  

Dr. Hendrik Hölscher thinks that the scalability of nano-3D printing is the biggest challenge on the way towards industrial use. Only few companies in the world are able to produce such prints. In his opinion, however, rapid development in this field will certainly solve this problem in the near future.

Once again, here’s a link to and a citation for the paper,

Tarantula-Inspired Noniridescent Photonics with Long-Range Order by Bor-Kai Hsiung, Radwanul Hasan Siddique, Lijia Jiang, Ying Liu, Yongfeng Lu, Matthew D. Shawkey, and Todd A. Blackledge. Advanced Materials DOI: 10.1002/adom.201600599 Version of Record online: 11 OCT 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The paper is behind a paywall. You can see the original Oct. 19, 2016 posting for my comments and some excerpts from the paper.

Steering a synthetic nanorobot using light

This news comes from the University of Hong Kong. A Nov. 8, 2016 news item on Nanowerk throws some light on the matter (Note: A link has been removed),

A team of researchers led by Dr Jinyao Tang of the Department of Chemistry, the University of Hong Kong, has developed the world’s first light-seeking synthetic Nano robot. With size comparable to a blood cell, those tiny robots have the potential to be injected into patients’ bodies, helping surgeons to remove tumors and enabling more precise engineering of targeted medications. The findings have been published in October [2016] earlier in leading scientific journal Nature Nanotechnology (“Programmable artificial phototactic microswimmer”).

An Oct. 24, 2016 University of Hong Kong press release (also on EurekAlert), which originated the news item, expands on the theme,

It has been a dream in science fiction for decades that tiny robots can fundamentally change our daily life. The famous science fiction  movie “Fantastic  Voyage” is a very good example, with a group of scientists driving their miniaturized nano-submarine inside human body to repair a damaged brain. In the film “Terminator  2,” billions of nanorobots were assembled into the amazing shapeshifting body: the T-1000. In the real world, it is quite challenging to make and design a sophisticated nanorobot with advanced functions.

The Nobel Prize in Chemistry 2016 was awarded to three scientists for “the design and synthesis of molecular machines.” They developed a set of mechanical components at molecular scale which may be  assembled into  more complicated nanomachines  to  manipulate single  molecule such as DNA or proteins in the future. The development of tiny nanoscale machines for biomedical applications has been a major trend of scientific research in recent years. Any breakthroughs will potentially open the door to new knowledge and treatments of diseases and development of new drugs.

One difficulty in nanorobot design is to make these nanostructures sense and respond to the environment. Given each nanorobot is only a few micrometer in size which is ~50 times smaller than the diameter of a human hair, it  is very difficult  to  squeeze  normal electronic sensors and circuits into  nanorobots with reasonable price. Currently, the only method to remotely control nanorobots is to  incorporate tiny magnetic inside the nanorobot and guide the motion via external magnetic field.

The  nanorobot developed by Dr Tang’s team use light as the propelling  force, and is the first research team globally to explore the light-guided nanorobots and demonstrated its feasibility and effectiveness. In their paper published in Nature  Nanotechnology, Dr Tang’s team  demonstrated  the  unprecedented ability of these light-controlled nanorobots as they are “dancing”  or even spell a word under light control. With a novel  nanotree structure, the nanorobots can respond to the light shining on it like  moths  being drawn to flames. Dr Tang described the motions as if “they can “see” the light and drive itself towards it”.

The team gained inspiration from natural green algae
for the nanorobot design. In nature, some green algae have evolved  with  the  ability  of  sensing  light  around  it.  Even just a single cell, these green  algae can sense the intensity of light and swim  towards the light source for photosynthesis. Dr  Jinyao  Tang’s team successfully developed the nanorobots after over three years’ efforts. With a novel nanotree structure, they are composed of two  common and low-price semiconductor materials: silicon  and titanium oxide. During  the  synthesis, silicon  and titanium oxide are shaped into nanowire and then further arranged into a tiny nanotree heterostructure.

Dr Tang said: “Although the current nanorobot cannot be used for disease treatment yet, we are working on the next generation nanorobotic system which is more efficient and biocompatible.”

“Light is a more effective option to communicate between microscopic world and macroscopic world. We can conceive that more complicated instructions can be sent to nanorobots which provide scientists with a new tool to further develop more functions into nanorobot and get us one step closer to daily life applications,” he added.

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

Programmable artificial phototactic microswimmer by Baohu Dai, Jizhuang Wang, Ze Xiong, Xiaojun Zhan, Wei Dai, Chien-Cheng Li, Shien-Ping Feng, & Jinyao Tang.  Nature Nanotechnology (2016)  doi:10.1038/nnano.2016.187 Published online 17 October 2016

So, this ‘bot’ seems to be a microbot or microrobot with some nanoscale features. In any event, the paper is behind a paywall.

Slip sliding away—making surfaces bacteria can’t grasp onto

Here’s another biomimicry story with a connection to Harvard University. From a Nov. 1, 2016 Beth Israel Deaconess Medical Center (Harvard Medical School Teaching Hospital) news release (also on EurekAlert),

Implanted medical devices like catheters, surgical mesh and dialysis systems are ideal surfaces on which bacteria can colonize and form hard-to-kill sheets called biofilms. Known as biofouling, this contamination of devices is responsible for more than half of the 1.7 million hospital-acquired infections in the United States each year.

In a report published in Biomaterials today, a team of scientists at Beth Israel Deaconess Medical Center (BIDMC), the Wyss Institute for Biologically Inspired Engineering and the John A. Paulson School of Engineering and Applied Sciences (SEAS) at Harvard University has demonstrated that an innovative, ultra-low adhesive coating prevented bacteria from attaching to surfaces treated with it, reducing bacterial adhesion by more than 98 percent in laboratory tests.

“Device related infections remain a significant problem in medicine, burdening society with millions of dollars in health care costs,” said Elliot Chaikof, MD, PhD, chair of the Roberta and Stephen R. Weiner Department of Surgery and Surgeon-in-Chief at BIDMC and an associate faculty member at the Wyss Institute. “Antibiotics alone will not solve this problem. We need to use new approaches to minimize the risk of infection, and this strategy is a very important step in that direction.”

The self-healing slippery surface coatings – known as ‘slippery liquid-infused porous surfaces’ (SLIPS) – were developed by Joanna Aizenberg, PhD, a Wyss Institute core faculty member, Professor of Chemistry and Chemical Biology and the Amy Smith Berylson Professor of Materials Science at SEAS at Harvard University. Inspired by the carnivorous Nepenthes pitcher plant that uses the slippery surface of its leaves to trap insects, Aizenberg engineered surface coatings that work to repel a variety of substances across a broad range of temperature, pressure and other environmental conditions. They are stable when exposed to UV light, and are low-cost and simple to manufacture. The current study is the first to demonstrate that SLIPS not only limit the ability of bacteria to adhere to surfaces, but also impede infection in an animal model.

SLIPS has been mentioned here before, most recently in a March 2, 2016 posting and before that in an Oct. 14, 2014 posting which appears to be precursor work for this latest research.

Getting back to the Nov. 1, 2016 news release, here’s more about plans for SLIPS and about recent trials,

“We are developing SLIPS recipes for a variety of medical applications by working with different medical-grade materials, ensuring the stability of the coating, and carefully pairing the non-fouling properties of the SLIPS materials to specific contaminates, environments and performance requirements,” said Aizenberg. “Here we have extended our repertoire and applied the SLIPS concept very convincingly to medical-grade lubricants, demonstrating its enormous potential in implanted devices prone to bacterial fouling and infection.”

In a series of trials, the researchers tested three SLIPS lubricants for their anti-adhesive qualities. First, they incubated disks of SLIPS-coated medical material ePTFE – a microporous form of Teflon – in a broth of Staphylococcus aureus (S. aureus), a generally harmless bacterium found in the nose and on skin, but one of the most common causes of hospital-acquired infections. After 48 hours, the three variations of SLIPS-treated disks demonstrated 98.3, 99.1 and 99.7 percent reductions in bacterial adhesion.

To test the material’s stability, the scientists performed the same experiment after soaking the SLIPS-coated samples for up to 21 days in a solution meant to simulate conditions inside a living mammal. After exposing these disks to S. aureus for 48 hours, the researchers found similar, nearly 100 percent reductions in bacterial adhesion.

Widely used clinically, medical mesh is particularly susceptible to bacterial infection. In another set of experiments to test the material’s biocompatibility, Chaikof and colleagues implanted small squares of SLIPS-treated mesh into murine models, injecting the site with S. aureus 24 hours later. Three days later, when the researchers removed the implanted mesh, they found little to no infection, compared with an infection rate of more than 90 percent among controls.

“Today, patients who receive implants often require antibiotics to keep the risk of bacterial infection at bay,” the authors wrote. “SLIPS coatings one day could obviate the widespread use of antibiotics and minimize the development of antibiotic resistant micro-organisms.”

“SLIPs have many promising medical applications that are in a very early stage of evaluation,” said Chaikof. “Clearly, there’s more work to be done before its introduction into the clinic, but this is one of a few studies that reinforces the exciting opportunities presented by this strategy to improve device performance and clinical outcomes.”

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

An immobilized liquid interface prevents device associated bacterial infection in vivo by Jiaxuan Chen, Caitlin Howell, Carolyn A. Haller, Madhukar S. Patel, Perla Ayala, Katherine A. Moravec, Erbin Dai, Liying Liu, Irini Sotiri, Michael Aizenberg, Joanna Aizenberg, Elliot L. Chaikof. Biomaterials Volume 113, January 2017, Pages 80–92  http://dx.doi.org/10.1016/j.biomaterials.2016.09.028

This paper is behind a paywall.