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New Blood-Resistant Glue Mends Broken Hearts Without Sutures

How do you mend a broken heart? You’re operating on a heart and it’s got a tear in it. How do you seal it?

Sutures? Staples? These are the traditional answers, but they aren’t good ones. Both involve piercing tissue and creating holes, which is bad news for an organ that’s constantly moving, and vigorously pumping blood. Holes lead to clots. They also bleed.

And if you specialise in doing heart surgeries on babies, as Pedro del Nido from Boston Children’s Hospital does, you can add small size and delicate tissues to those other challenges. “The holy grail for heart surgeons, especially for those who work on babies, is to attach things without damaging the normal underlying tissue,” he says.

A glue, then. The trouble is that a heart adhesive must be strong enough to hold despite the heart’s constant beating, but flexible enough to allow those same beats to happen. It has to work in wet conditions—something that most glues aren’t designed to do. It needs to repel water so it doesn’t dissolve. It must thicken slowly or blood will wash it away. It can’t thicken immediately because you want to be able to position and adjust it. It has to be biodegradable.

These design specifications are an engineer’s nightmare, which explains why viable heart glues don’t exist. That is, until now.

Working with del Nido, Jeff Karp at the Brigham and Women’s Hospital and MIT’s Bob Langer have created a glue that ticks all the boxes. It seals heart tissue and blood vessels, it’s strong but flexible, and it’s made only from naturally-occurring substances already found in the body. It can be applied as a viscous gel, and then hardened into a strong adhesive with a burst of ultraviolet light. And, best of all, it works in flowing blood.

“I’m very excited about this project,” says del Nido. “There’s a huge clinical need for it. It’ll allow us to do much more sophisticated reconstructions than what we can do today.”

Karp has a history of making “bioinspired” adhesives, from sticky tape based on a parasitic worm to medical needles based on a porcupine’s quills. This time, he drew inspiration from several animals that can stick to wet surfaces.  Insects, for example, often secrete viscous, water-repellent substances from their feet, which push water out of any gaps in the underlying surfaces. Meanwhile, the sandcastle worm builds underwater tubes by exuding a glue from its head. This substance is also water-repellent and viscous, and hardens over time into a strong adhesive.

A sandcastle worm, sticking out of its tube. Credit: Fred Hayes, University of Utah
A sandcastle worm, sticking out of its tube. Credit: Fred Hayes, University of Utah

The team realised that they had already made something similar—a substance called PGSA. It’s a union of glycerol, a basic building block of fats and oils, and sebacic acid, which is produced when certain fats break down.  The team had originally made PGSA to create scaffolds on which they could grow new tissues or organs. (See here for Langer’s work on growing organs.) “We had hints that it could adhere to tissue but we never tested that,” says Karp.

Working with del Nido, Karp and Langer tweaked the formula of PGSA to create a viscous liquid that could be easily spread but would hold its shape. They also added a substance that creates bridges between the PGSA molecules on exposure to ultraviolet light, quickly curing the glue on demand. “Other adhesives like crazy glue cure immediately in the presence of moisture or water,” says Karp. “Ours doesn’t. We can place it in a very wet environment completely filled with blood and it only becomes adhesive when we cure it with light.”

These traits give the glue time to seep in between the fibres of the underlying tissues, displacing water along the way. That’s why it’s so strong once it hardens—it’s part of the tissue, rather than just a layer on the surface.

The new glue outcompeted cyanoacrylate, or super glue, in several tests: it stuck better, it swelled less, and it triggered less inflammation. “This is a major feat, as super glue is considered to be the strongest tissue adhesive around,” says Christian Kastrup from the University of British Columbia. The only potential damage comes from the ultraviolet light, which is infamous for its ability to damage DNA. Still, a five-second burst is unlikely to do much lasting harm.

Karen Christman at the University of California, San Diego, says the technology is exciting, but that “several preclinical tests need to be performed before translation to patients.” First and foremost, they need to check that it’s safe for use inside actual hearts. “It is also unclear if this could work with Gore-Tex patches, which are one of the most common patch materials used for the heart,” she says. “If this is possible, this could definitely make surgeries easier considering there is often bleeding at the suture lines with these synthetic patches.”

The team is on the case. So far, they have successfully tested the glue in four live pigs, using it to attach patches to their beating hearts, and to seal damaged carotid arteries. The animals survived, fared well, and showed no signs of clots or bleeding after the operations.

A Paris-based company called Gecko Biomedical has now licensed the technology and raised 8 million euros to bring it to market. They’re now scaling up the manufacture of the glue and, once that’s done, they hope to move to clinical trials. If it succeeds, Karp hopes to put it in the hands of clinicians within three years. For his part, del Nido wants to see if the glue can stop blood from leaking from holes around sutures. If that’s safe and effective, he will move on to more complex things.

This isn’t just about hearts, either. Karp suggests that the glue might also work in the gut—another environment characterised by lots of liquid and constant movement. “It really opens the door for more minimally invasive approaches,” he says.

Reference: Lang, Pereira, Lee, Friehs, Vasilyev, Fein, Ablasser, Cearbhaill, Xu, Fabozzo, Padera, Wasserman, Freudenthal, Ferreira, Langer, Karp & del Nido. 2013. A Blood-Resistant Surgical Glue for Minimally Invasive Repair of Vessels and Heart Defects. Science Translational Medicine. Vol 6 Issue 218 218ra6

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This Giant Fish Has Adaptable Piranha-Proof Armour

Piranha jaws. Credit: Silk666
Piranha jaws. Credit: Silk666

A piranha’s jaws contain rows of triangular teeth, which interlock like rows of flesh-shearing scissors. They’re powered by huge muscles that take up most of the space in the fish’s head, giving it the strongest bite (for its body weight) of any back-boned animal.

But the arapaima doesn’t care. This giant South American fish has evolved piranha-proof armour, allowing it to happily share water with schools of these fearsome predators. For the piranhas, it must be like finding that the juiciest steak in the supermarket is coated with an impregnable shield.

The arapaima, with its streamlined body and flattened head, looks like a cross between a torpedo and a doorstop. It can grow to over 2 metres long and the heaviest specimen weighed 200 kilograms, making it one of the largest freshwater fish in the world. And it is surely one of the toughest.

A few years back, materials scientist Marc Meyers arranged a bloodless bout between arapaima and piranha, in his lab at from the University of California, San Diego. He mounted arapaima scales on a rubbery surface, and pressed into them with piranha teeth attached to an industrial hole-puncher. The teeth managed to penetrate the scale, but only slightly. Before they reached the underlying “flesh”, they cracked.

The scales’ toughness comes from their microscopic structure. A hard outer layer resists the penetration of a piranha’s tooth, but is also relatively brittle. Thankfully, a soft but tough inner layer absorbs the incoming force so that the whole scale doesn’t snap. “It’s how body armour should be made,” says Robert Ritchie from the Lawrence Berkeley National Laboratory, who is working with Meyers to study the scales. “If it was just the hard shell, the thing would shatter.”

Structure of arapaima scales. From Chen et al, J. Mater. Res., 2011
Structure of arapaima scales. From Chen et al, J. Mater. Res., 2011

The properties of the outer layer are easily explained. It’s heavily mineralised, which makes it hard. It also has a corrugated shape to give it flexibility—cut through it, and you’d see what looks like a row of dark mountains. That allows the layer to bend without breaking, so the arapaima can flex and move its body while still repelling piranha jaws.

The inner layer is more interesting. It’s made largely of collagen, the same protein found throughout your flesh. Long strands of collagen are bundled to form fibres, each a micrometre (a millionth of a metre) thick. The fibres are arranged in parallel sheets, and each is rotated slightly against the one above it. This is technically known as a “Bouligand-type” structure. “I call it a Liberace-type spiral staircase,” says Ritchie.

That’s the default shape, but it can change. When the team placed the scales in an X-ray beam and applied force to them, they saw that the collagen fibres lose their neat spiral arrangement. Suddenly, they realign to face the direction of the force. This microscopic shape-shifting toughens the scale—imagine trying to break a pencil by pushing or pulling against its tips, rather than on its midpoint.

Arapaima head, by Jeff Kubina.
Arapaima head, by Jeff Kubina.

There are plenty of other examples in nature where microscopic cylinders are aligned to resist incoming forces. Ritchie also studies the abalone, an edible sea snail with a phenomenally hard shell. It has a series of mineral plates, which are all aligned perpendicular to the surface. The arapaima scale behaves in the same way, but the amazing thing is that it does so in real-time. It has adaptable body armour!

Ritchie suspects that the structure of the arapaima’s scales may inspire human engineers who are designing new types of body armour. “Lightweight body armour is something everyone wants,” he says. “The Kevlar armour our troops get is extremely heavy and many people don’t bother wearing them. But nature does it very well.”

Reference: Zimmermann, Gludovatz, Schaible, Dave, Yang, Meyers & Ritchie. 2013. Mechanical adaptability of the Bouligand-type structure in natural dermal armour. Nature Communications. http://dx.doi.org/10.1038/ncomms3634

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This Insect Has Gears In Its Legs

The image above is an extreme close-up of a common British insect called a planthopper. You’re looking at it from below, at the point where its two hind legs connect to its body. In the middle, you can clearly see that the top of each leg has a row of small teeth, which interlock together. As the planthopper jumps, the teeth ensure that its legs rotate together and extend at the same time.

This insect has gears.


It’s a steampunk bug!

The gears are found on many young planthoppers but Gregory Sutton from the University of Cambridge first discovered them on a common British species called Issus coeleoptratus. “We didn’t have to go to some obscure monastery in Outer Slaubvinia to find these things,” he says. “We had to go to a place called The Garden, in The Backyard. Either the most complicated gearing in nature happens to be in our backyard, or there is stuff that’s vastly more intricate and complicated that hasn’t been found yet.”

A baby Issus coleoptratus. Credit: Malcolm Burrows
A baby Issus coleoptratus. Credit: Malcolm Burrows

Sutton has been working with Malcolm Burrows from the University of Cambridge for the last 10 years, to study the movements of jumping insects like fleas, locusts, leafhoppers and pygmy mole crickets. When they filmed young planthoppers taking off, they saw that the hind legs would always move within 30 microseconds (millionths of a second) of each other. Such extreme coordination makes sense—the slightest difference in timing would send the insects spinning off to the side. But how could they achieve such tightly synchronised movements?

The nervous system can’t be involved. In 30 microseconds, a neuron can barely begin to fire, much less trigger something that tweaks the insect’s movements.

The answer lies on the insect’s undersides. Back in the 1950s, other scientists noted that young planthoppers have small bumps on their trochanters—the first segment of the legs, which connect to the hip-like coxa. They were only found on the hind legs, and not the other pairs. No one knew what they were for. No one seemed to care. “It was one of those odd little footnotes in anatomical books,” says Sutton.

Burrows and Sutton discovered the function of the bumps by planthoppers that had been restrained on their backs. The insects would try to jump whenever the duo gently prodded their abdomens. Just before their legs shot out, their trochanters would squeeze together. The bumps engaged and rolled against each other, exactly like man-made gears. “I was gobsmacked,” says Sutton.

A close-up of the planthopper's gears. Credit: Malcolm Burrows
A close-up of the planthopper’s gears. Credit: Malcolm Burrows

Gears allow two machines to rotate together in opposite directions. That’s exactly what the planthopper’s trochanter bumps do. Sutton tested this by pulling on the tendons of its jumping muscles with some forceps (“It’s the Serious Edition of Operation”, he says.). Even if he only pulled one tendon, both legs would extend because the gears transmitted the motion of one trochanter into the other.

“Then, we got really lucky because we saw a few jumps where the gears wouldn’t engage perfectly,” says Sutton. When this happened, one leg was partially extended before the gears finally snagged and the planthopper’s nigh-perfect coordination was ruined.

Wait! It gets better. These gears are training wheels!

The planthopper nymphs lose them when they become adults. But the adults don’t shoot off in uncoordinated spins—if anything, they’re better jumpers than the youngsters. Their hind trochanters make much closer contact with each other, and Sutton thinks that the friction between them helps to keep them in time. “We’re kind of sure about that, but not entirely sure,” he says.

“This is to our knowledge the first time that proper, engaging, counter-rotating gears have been seen in the animal kingdom,” says Sutton. Crocodiles have cog-like teeth in their heart valves, and the wheel bug and cog-wheel turtle have teeth on their shells. But none of these structures actually act like gears. “You never see one cog-wheel turtle sidle up next to another, engage their shells, and spin in opposite directions,” says Sutton. “If you did, I want you to call me. If I see that on your website, and I haven’t been called, I will be an angry man.”

The discovery is astounding in itself, but Sutton—a mechanical engineer—thinks that they could help us to make more effective machines at incredibly small scales. The teeth of most modern gears harken back to the 18th century, when mathematician Leonhard Euler designed a shape that could be easily cut by a machine. It’s called an involute and it looks like a hill with a plateau at the top. It has been a standard part of gears ever since.

But the planthopper’s gear teeth look more like a shark fin. “What we have is a prototype for a tooth shape for a high-speed, one-directional gear that’s not constrained by the machining techniques of the 18th century,” says Sutton.

Modern machines, such as 3-D printers, could easily create gears with these shark-fin teeth. Sutton is really excited by the prospect, and suspects that they may perform better in very small machines. “Modern machinery often doesn’t work at very small scales,” he says. “Friction doesn’t matter so much when you have two big gears next to each other but when you get small, friction starts killing you.”

The planthoppers might help to solve that problem. “We’re still being impressed and shocked by what we find in the back garden,” says Sutton.

Reference: Burrows & Sutton. 2013. Interacting Gears Synchronize Propulsive Leg Movements in a Jumping Insect. Science http://dx.doi.org/10.1126/science.1240284

More on jumping insects:

Pygmy Mole Crickets Leap from Water with Spring-Loaded Oars

Leaproach leaps, is roach

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Insect-Eye Digital Camera Sees What You Just Did

Almost all of our cameras form images by using a single lens to focus light onto a light-sensitive sheet. That’s how our own eyes actually work, but there are many other ways of seeing the world. Arthropods—insects, spiders and their kin—have compound eyes, which consist of hundreds or thousands of individual units or ommatidia. Each one has its own lens and light detectors. They form separate images, which are then united in the brain. And since arthropods greatly outnumber all other animals, the vast majority of eyes are compound ones.

Now, John Rogers from the University of Illinois at Urbana-Champaign has developed a camera that mimics compound eyes. It might not have the same resolution as a state-of-the-art digital camera, but it compensates with many advantages that make it ideal for surveillance. Perhaps in the future, we’ll be watched by man-made flies on the walls.

Rogers chose to mimic apposition eyes—a type of compound eye where each ommatidium sees a narrow part of the insect’s visual field, effectively capturing just one pixel of a full image.

First, his team makes a grid of tiny light-sensitive diodes out of silicon. They’re connected by flexible S-shaped wires that allow the grid to flex without breaking. On top of that, they lay a sheet of silicone (PDMS) that’s moulded into small bubble-shaped lenses, one sitting over each diode. The two layers are fused together and deformed into a dome. Each diode-and-lens combo acts as an ommatidium and the full camera has 180 of them, each pointing in a slightly different direction.

Fly-Eye-cameraThe camera builds on decades of Rogers’ work on flexible electronics—devices that are largely made of brittle, rigid materials like silicon, but can flex and curve like living tissues. He has created “electronic-skin” that can be applied like tattoos and used to measure muscle and nerve activity, sensors that can mould to the shape of the brain or heart, and even electronics that dissolve over time.

Rogers’ inventions include a flexible camera that’s based on our own eyes. Like other cameras, this one has a lens and a sheet of light detectors that acts as a retina. But while modern cameras have flat ‘retinas’, Rogers’ machine has a curved one, just like our actual eyes. This makes it more compact. Much of the weight of modern cameras comes from bulky secondary lenses that correct the incoming light so it can project onto a flat surface without distortions. With a curved retina, you don’t need these lenses, and the camera can shrink.

With one eyeball camera in the works, it might seem strange that the team decided to build a compound one too. After all, compound eyes—especially apposition ones—aren’t that sensitive to light and have fairly low resolution. Dan-E. Nilsson, who studies insect vision at Lund University, says, “The type of compound eye they have mimicked has long been known to be a poor solution to vision. And to have one private lens for every pixel in the image is the most inefficient use possible of the space available for an eye.”

But, wait! Compound eyes have some advantages. Since their ommatidia point in all directions, they give their owners a panoramic 180-degree view of the world that’s clear over the entire field of view. By contrast, our eyes can only see a narrow angle ahead of us, and the images they form are only sharp at the very centre of our visual field.

Compound eyes also have an almost infinite depth of field—that is, objects stay in focus regardless of how far they are from the eye. So, flies can clearly see something far and near objects at the same time, without having to adjust any lenses. And compound eyes are also exquisitely sensitive to movement, since their owners can compare the passage of shapes across different ommatidia.

Wide angles. Sharp focus at all distances. Sensitivity to movement. If you were building a surveillance camera, these are exactly the properties you’d want. Indeed, Rogers thinks that surveillance is an obvious application for his fly-eye design.

In a related editorial, Alexander Borst and Johannes Plett from the Max-Planck-Institute of Neurobiology suggest that the cameras might be useful for controlling tiny drones. At the moment, these use normal cameras with fish-eye lenses to give them a wide field of view. An insect-eye camera could do the same, while possibly making the robot more sensitive to movements.

“It’s great work, and a nice example of biomimetics,” says Nicholas Roberts from the University of Bristol, who studies animal eyes. Although it doesn’t tell us anything that “crosses back to biology”, the camera’s huge depth of field is a “nice benefit over single lens designs”.

And though Rogers admits that while the fly-eye camera will never match the resolution of a normal one, he thinks that’s not a deal-breaker. “If you can combine multiple images over time, you can effectively get a high resolution,” he says. “Surveillance cameras use this trick to spot speeding cars – the resolution from a single frame can’t identify the letters on a licence plate.”

There’s obviously room for improvement but with 180 ommatidia, the digital camera is already more sophisticated than the eyes of some insects—some worker ants, for example, only have 100 in each eye. But it’s a long way off from the best insect eyes, like those of the green darner dragonfly (28,000 ommatidia) or the praying mantis (15,000). For the moment, nature still wins.

Reference: Song, Xie, Malyarchuk, Xiao, Jung, Choi, Liu, Park, Lu, Kim, Crozier, Huang & Rogers. 2013. Digital cameras with designs inspired by the arthropod eye. Nature http://dx.doi.org/10.1038/nature12083

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Parasitic Worm Inspires Better Sticky Medical Tape

Say you’re looking to make the next generation of medical tape. You want something that will hold skin and other organs together while they heal. You want it to be more convenient than sutures and less brutal than staples. It has to stick easily, hold on tightly, and come off painlessly.

There are worse places to search for inspiration than the guts of a fish.

'Corynosoma wegeneri', a spiny-headed worm.  Taken by Dr Neil Campbell, University of Aberdeen.
‘Corynosoma wegeneri’, a spiny-headed worm. Taken by Dr Neil Campbell, University of Aberdeen.

Fish intestines are home to a group of parasites called spiny-headed worms, or acanthocephalans. Their most distinctive feature is a spine-covered snout that the worm stabs into the gut walls of its host. Once inside, it contracts two muscles and the long snout rapidly swells into a bulb, anchoring the worm in place. The fastened parasite can now drink deeply from the river of nutrients washing over it, absorbing them through its skin.

To the fish, the worm’s spiny head is a health hazard. To Jeffrey Karp, it was something to emulate. His team at the Brigham and Women’s Hospital in Boston have spent many years developing medical adhesives, constantly looking to nature for inspiration. In 2008, for example, they developed a sticky tape based on the feet of a gecko. And last year, they created artificial microneedles based on a porcupine’s quills, whose structure allows them to easy to stab into flesh but hard to pull back out.

Geckos are famously sticky, and porcupines are famously stabby, but Karp also realised that parasites must have fantastic ways of fastening themselves to their hosts. That’s how he came across the spiny-headed worms and one species in particular—Pomphoryhnchus laevis.

Karp’s team member Seung Yun Yang mimicked P.laevis’s hooks by creating two-layered microneedles. They have a stiff, cone-shaped core made of polystyrene, covered by a soft outer layer made of polyacrylic acid—an absorbent chemical used in disposable diapers. When the needles pierce flesh, the cores stay the same while the outer layers quickly absorb water and swell, just like P.laevis’s snout. The swollen tips are like arrow-heads, locking the entire needles into place. If a bandage or a piece of tape is coated with these needles, they’d easily hold two pieces of tissue together.

Needles_skinTo Karp, the most obvious application for the worm-based needles is to hold skin grafts in place. These patches of skin are often used to close up gaping wounds from burns, trauma or major surgeries. For now, most surgeons fasten them to patients by stapling or stitching them around their edges. But these methods have problems.

Staples, in particular, go in so deeply that they can damage tissue, blood vessels and nerves. The torn tissue creates a hole that’s slightly wider than the width of the staple, creating an easy entrance for infectious bacteria. And since the staples are only applied around the edges, fluid can pool into the central space and prevent the graft from fusing to the underlying skin.

By contrast, the worm-based patches made continuous contact with any flesh they sit over. They barely damage the underlying tissue and the swollen tips automatically seal any holes they create, preventing bacteria from getting in. They’re also stronger than current adhesives. When Yang built 100-needle patches and tested them on the skins and intestines of dead pigs, they took more than three times as much force to pull out as regularly stapled grafts.

Karp’s needles have other advantages. Unlike sutures, they are easy to apply, and unlike most bandages and plasters, they work equally well on dry and wet surfaces. This means that they could also be used inside the body to hold tendons or ligaments in place, or to seal leaks in intestines of lungs.  “This could be a universal adhesive for soft tissues,” says Karp.

Other groups have tried to create patches of microneedles that do the same job, but these tend to be stiff so they can penetrate the skin. This means that awkward movements can break the needles off inside a patient’s fleshBy contrast, Karp says, “The worm system is stiff going in but, after swelling, one can rotate the patches without any breakage of microneedles.”

And unlike most microneedles, the worm-based ones stick in place because of swollen heads rather than backwards-pointing barbs. When they are peeled away, the tips can squeeze down to fit through the holes that have already been made and since they are barb-free they don’t snag on tissue on the way out. Once the needles are removed, they return to their original shape within just 15 minutes, while the holes they leave close up in an hour.

Microneedles can also be used to inject medicine as well as fasten tissues. Just dip their tips in your drug-of-choice, and they will slowly release it into the surrounding flesh when they swell. And once you remove them, you can use them again.

And what if you don’t want to remove them at all? “We are currently developing a degradable version,” says Karp.

Reference: Yang, Cearbhaill, Sisk, Park, Cho, Villiger, Bouma, Pomahac & Karp. 2013. A bio-inspired swellable microneedle adhesive for mechanical interlocking with tissue. Nature Communications. http://dx.doi.org/10.1038/ncomms2715

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Can We Fake Leaves That Stab Bed Bugs in the Feet?

Bed bugs have been sucking human blood for thousands of years and they’re enjoying a new resurgence. They are among the most difficult pests to control, and infestations have risen in the last few decades. Old defences like insecticides are failing us, leaving scientists racing to find new solutions. But in the Balkan countries of southeastern Europe, there’s a old folk remedy that might be the insects’ undoing.

Before nightfall, people would scatter the leaves of bean plants on the floor by their beds. In the morning, the leaves would be full of immobilised bed bugs, which could then be taken outside and burned.

In 1944, a scientist called H. H. Richardson realised that this works because of tiny hooked hairs called trichomes dotting the surface of the bean leaves. Each is just a tenth as wide as a human hair and Richardson thought that they tangle the claws of walking bed bugs. Velcro, which was conceived at roughly the same time, works along similar principles.

But no one followed up on Richardson’s discovery. There was the small matter of a distracting world war, and there was little impetus to research other forms of control when insecticides like DDT were so good at killing bed bugs. But since their post-war nadir, the bugs are on the rise again and many have evolved resistance to the pesticides. The bean leaves are looking pretty tempting again.

Mike Potter from the University of Kentucky heard about Richardson’s work and decided to create a synthetic version of the leaves. After a few failed attempts, he turned to Catherine Loudon from the University of California, Irvine, who specialises in insect movements.

Loudon and former student Megan Szyndler discovered that Richardson got one crucial detail wrong about the bean leaves. By photographing and filming them under a microscope, they saw that the hairs aren’t merely tangling the bugs’ feet—they are actually impaling them, stabbing through at their weakest spots. (Bed bugs, of course, are no stranger to awkward stabbings.)

When a bed bug walks onto a bean leaf, it strides across a lethal minefield. The hooked hairs are so dense, that it takes just a few seconds (and around 50 footsteps) for the insect to become inescapably trapped. Sometimes, the hairs just wrap around their claws as Richardson envisioned, in which case they always managed to pull free. But often, they became irreversibly stuck, unable to break away.

When Szyndler scanned the trapped feet using a powerful electron microscope, she saw that the hairs had actually pierced the bugs’ feet. They typically penetrated the softest parts, like the underside of the claws, or the thin membranes between their segments. They’re less like Velcro, and more like butchers’ hooks. Even if the bugs could pull themselves free—which involved either breaking the trichome or their own shells—they would immediately get recaptured.

The results will be unsurprising to some, since bean trichomes are known to puncture the feet of other insects, including agricultural pests like leafhoppers and aphids, and (unfortunately) guardian insects like ladybirds. In fact, these are probably the victims that the beans’ stabby hairs have evolved to entrap. The fact that they also capture bed bugs is (for us) a happy offshoot of a different evolutionary conflict.

But few people have studied the hairs in detail—how many are needed, how sharp they need to be, whether insects can pull free, and so on. Those details could point the way to new ways of controlling bed bugs. After all, people have tried to trap the insects with glue or double-sided sticky tape with little success.

The team returned to the original goal of creating materials that mimic the penetrating bean hooks. You could just scatter bean leaves, but these dry out fairly rapidly and they can only be applied to horizontal surfaces—they’d do nothing to trap bed bugs that are already living in a mattress.

Szyndler first made a mould of a bean leaf’s surface and then used this to create replicas. They looked indistinguishable. They had the same density of trichomes, which came in the same size and had the same sharp, hooked tips. But there was one big difference—they were rubbish at capturing bed bugs. Disappointingly, the fake leaves completely failed to pierce the bugs’ feet.

It’s not clear why. In some cases, the tips of the real trichomes broke off during the moulding process and became incorporated into the synthetic hairs. But even these hybrid trichomes didn’t pierce bed bugs like their natural cousins. Clearly, the real and fake hairs differ in some subtle physical property.

The team thinks that stiffness might be the key one. The natural trichomes are solid at their tips but hollow down their length, while the synthetic ones are completely solid. That makes them stiffer. When a bed bug walks on a natural trichome, Szyndler suspects that the hair would bend and twist, allowing the tip to skit the surface of the bug’s foot until it ‘finds’ a weak spot. By contrast, an artificial trichome would just bend out of the way. The next step is to create synthetic trichomes that mimic the full properties of the real ones, and that’s exactly what the team is working on.

Reference: Szyndler, Haynes, Potter, Corn & Loudon. 2013. Entrapment of bed bugs by leaf trichomes inspires microfabrication. Interface http://dx.doi.org/10.1098/rsif.2013.0174




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Why Porcupine Quills Go In Easily but Are Hard to Pull Out

A shorter version of this story appears at Nature News.

In August of this year, Allison Noles rushed her bulldog Bella Mae to the vet. The dog’s face looked like a pincushion, with some 500 spines protruding from her face, paws and body. The internet is littered with such pictures, of Bella Mae and other unfortunate dogs. To find them, just search for “porcupine quills”.

North American porcupines have around 30,000 quills on their backs. While it’s a myth that the quills can be shot out, they can certainly be rammed into the face of a would-be predator. Each one is tipped with microscopic backwards-facing barbs, which supposedly make it harder to pull the quills out once they’re stuck in. That explains why punctured pooches need trips to the vet to denude their faces.

But that’s not all the barbs do. Woo Kyung Cho from Harvard Medical School and Massachusetts Institute of Technology has found that the barbs also make it easier for the quills to impale flesh in the first place. “This is the only system with this dual functionality, where a single feature—the barbs—both reduces penetration force and increases pull-out force,” says Jeffrey Karp, who led the study.


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Robots in disguise: soft-bodied walking machine can camouflage itself

None of our machines can do what a cuttlefish or octopus can do with its skin: change its pattern, colour, and texture to perfectly blend into its surroundings, in matter of milliseconds. Take a look at this classic video of an octopus revealing itself.

But Stephen Morin from Harvard University has been trying to duplicate this natural quick-change ability with a soft-bodied, colour-changing robot. For the moment, it comes nowhere near its natural counterparts – its camouflage is far from perfect, it is permanently tethered to cumbersome wires, and its changing colours have to be controlled by an operator. But it’s certainly a cool (and squishy) step in the right direction.

The camo-bot is an upgraded version of a soft-bodied machine that strode out of George Whitesides’ laboratory at Harvard University last year. That white, translucent machine ambled about on four legs, swapping hard motors and hydraulics for inflatable pockets of air. Now, Morin has fitted the robot’s back with a sheet of silicone containing a network of tiny tubes, each less than half a millimetre wide. By pumping coloured liquids through these “microfluidic” channels, he can change the robot’s colour in about 30 seconds.


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Beetle walks and sticks underwater by creating dryness with every footstep

Sticking to surfaces and walking up walls are so commonplace among insects that they risk becoming boring. But the green dock beetle has a fresh twist on this tired trick: it can stick to surfaces underwater. The secret to its aquatic stride is a set of small bubbles trapped beneath its feet. This insect can plod along underwater by literally walking on air.

The green dock beetle (Gastrophysa viridula) is a gorgeous European resident with a metallic green shell, occasionally streaked with rainbow hues. It can walk on flat surfaces thanks to thousands of hairs on the claws of their feet, which fit into the microscopic nooks and crannies of whatever’s underfoot. Most beetles have the same ability, and some boost the adhesive power of their hairs by secreting a sticky oil onto them.

These adaptations work well enough in dry conditions, but they ought to fail on wet surfaces. Water molecules should interfere with the hairs’ close contact, and disrupt the adhesive power of the oil. “People believed that beetles have no ability to walk under water,” says Naoe Hosoda from the National Institute for Material Science in Tuskuba, Japan.

They were clearly wrong. Together with Stanislav Gorb from the Zoological Institute at the University of Kiel, Germany, she clearly showed that the green dock beetle has no problems walking underwater. The duo captured 29 wild beetles, and allowed them to walk off a stick onto the bottom of a water bath. Once there, they kept on walking. (more…)

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Bacteria cities cannot form on a super-slippery surface, inspired by meat-eating plants

When bacteria start building cities, we’re in trouble. The normally free-floating cells can gather in large numbers and secrete a slimy matrix that they live within. These communities are called biofilms, and they grow wherever there is a surface to support them. Hospital catheters are prime real estate, but they’ll settle on everything from plumbing to oil refineries to ship hulls.

Within a biofilm, bacteria are extraordinarily durable. Antibacterial chemicals have a tough time reaching them within their slimy fortress. Even if they do, there’s always a batch of dormant cells that can persist through a chemical onslaught and restart the community. They’re involved in the majority of persistent hospital infections, and it’s easy to see why. You could bleach a biofilm for an hour and still fail to kill it. They’ve survived in pipes that are flushed with toxic chemicals for a week.

Since killing biofilms is a Sisyphean task, some scientists are trying to prevent them from forming at all. They’ve tried textured surfaces, chemical coats, and antibiotic-releasing layers. But Joanna Aizenberg has developed a new solution that goes well beyond what the competitors can do. Inspired by the flesh-eating pitcher plant, she created a material so slippery that biofilms simply cannot form upon it.


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“We took a rat apart and rebuilt it as a jellyfish.”

Kit Parker has built an artificial jellyfish out of silicone and muscle cells from a rat heart. When it’s immersed in an electric field, it pulses and swims exactly like a real jellyfish. The unusual creature is part of Parker’s efforts to understand the ways in which muscles work, so that he can better engineer heart tissue. And it has a bizarre intended purpose: Parker wants to use it to test heart drugs. I wrote about his work for Nature, so head over there for the main story. Meanwhile, here’s my full interview with Parker about the jellyfish. He’s a fantastic interviewee – you’ve got to imagine him almost shouting this stuff.

Building a jellyfish using rat tissue isn’t exactly a typical everyday idea. Where did it come from?

My group does cardiovascular research and I spend a lot of time thinking about building tools for early-stage drug discovery. We’re known for making actuators and things you can measure contractility with, and using micro-scale tissue engineering to build tissues on chips. Several years ago, I got really frustrated with the field. Drug companies are screaming because their drug pipelines are running dry. We don’t have good ways of treating a lot of these heart diseases in the clinic. It dawned on me that probably the reason why is that we’re failing to understand the fundamental laws of muscular pumps.

I started looking around for inspiration in a simpler system. This was late 2007, and I was visiting the New England aquarium. I saw the jellyfish display and it hit me like a thunderbolt I thought: I know I can build that.

That spring, we had a visitor: John Dabiri from CalTech, a famous fluid mechanician. He does a variety of propulsion studies on various species. He was walking down the hall and I grabbed him and said: John, I think I can build a jellyfish. He didn’t know who I was. He looked at me like I had a horn growing out of my head but I was pretty excited and waving my arms, and I think he was afraid to say no. So, he said yeah. He sent a graduate student Janna Nawroth to my lab for four years. Three of my postdocs who are on that paper are now professors – this is the best of the best that we put on that project.

And what did you actually do?

We took a jellyfish, and did a bunch of studies to understand how it activates its muscles. We studied its propulsion and we made a map of where every single cell was. We used a software programme that we had developed a few years ago, borrowed from law enforcement agencies for doing quantitative analysis of fingerprints, and we used it to analyse the protein networks inside the cells.

We found something very interesting right away: the electrical signals that the jellyfish uses to coordinate its pumping are exactly like that of the heart. In the heart, the action potential [electrical signal that travels along nerves – Ed] propagates as a wave through cardiac muscle. That’s how you get this nice, smooth contraction. The activation has to spread like when you drop a pebble in water. The same thing happens in the jellyfish, and I don’t think that’s by accident. My bet is that to get a muscular pump, the electrical activity has got to spread as a wavefront

After we had the map of where every cell was, we took a rat apart and rebuilt it as a jellyfish.

Why study jellyfish?

The one that we used is a juvenile – it’s like a thin monolayer of cells. It’s a very simple structure to build.

The great thing about this is that most tissue engineering is just arts and crafts. We throw cells together and we say, ‘It looks like a liver; there’s a bunch of cells’. Or we throw heart cells together and hope that we build bits of heart. But if I’m building an aircraft or bridge, we don’t just throw concrete and aluminium and alloys together. We do mechanical testing on the substrates. We have mathematical models and computer simulations to understand the flight of the aircraft. We know how the bridge is going to work. Some engineers build out of copper or concrete or steel. I build things out of cells. If I’m going to be an engineer rather than an artist, I’m going to need to build quality control methods into what I’m doing.

Nobody is going to get into an airplane unless they’ve done computer simulations and assumed that they’ve manufactured this within allowable tolerance. It’s not just guesswork. No one’s going to want a tissue-engineered heart or other organ put into their body unless they’ve got some manufacturers’ specification. The great thing about the jellyfish is that you can do all these highly quantitative propulsion studies. That’s why I had to have John Dabiri’s team with this – they’re the best in the world at biological propulsion. And we were able to match quantitatively match the exact same propulsion characteristics in our medusoid – our engineered jellyfish – as the real one.

The most interesting thing is that the mouth of the jellyfish is inside the bell. In order to feed itself, it creates a vortex on the power stroke that throws particulate matter up towards its mouth. We thought if we’re good, if we’re really good at this, we’re going to recreate that vortex, and we did. We found that it depended on some very precise organisation of the protein networks inside the cells.

The whole idea was to bring engineering design methodology with tissue engineering, with a very rigorous set of parameters to show that our tissue-engineered jellyfish is very much a jellyfish. Morphologically, we’ve built a jellyfish. Functionally, we’ve built a jellyfish. Genetically, this thing is a rat.

So, the jellyfish isn’t the endpoint. The point of building it, and getting it to behave exactly like a normal jellyfish, is to show how much you understand about how the cells work. Is that it?

That’s right, but it depends on the lens through which you do this. For the marine biologist who’s interested in how jellyfish swim, we’ve demonstrated how important the muscular structure is and the protein alignment inside these cells for the jellyfish to survive and feed itself. The jellyfish scientist looks at this different rather than someone who’s trying to mimic biological propulsion. They look at this as how do you build something that can propel itself with this peristaltic pumping. The tissue engineer looks at this as applying the tissue engineering methodology to the highest possible standard to tissue engineering, which hadn’t been done before.

If you’re a cardiovascular physiologist or a company doing discovery, you look at this and say: wow, for years, all we’ve measure in a dish is contractility. But there’s a big difference between that and pumping. Now we’ve shown that we can build a muscular pump in a dish. You’ve got a heart drug? You let me put it on my jellyfish, and I’ll tell you if it can improve the pumping.

The first two or three years of any drug’s lifetime is always spent in a dish. We filed a patent on this to use this and variations on it as a drug discovery assay. The next stage is to see if we can build this out of human cells. And we’ll probably build a variation on the jellyfish for actual drug-testing.

In your paper, you describe the jellyfish as a synthetic organism.

Usually when we talk about synthetic life forms, somebody will take an existing living cell and put new genes into the cell so that it behaves in a different manner. That’s synthetic biology but I think it’s overstating what you did. We built an animal. I think we’re taking synthetic biology to a new level. It’s not just about genes. It’s about morphology and function.

So has this study got you further towards understanding the “fundamental laws of muscular pumps”?

Yeah it has. The heart and your guts both have action potential wavefronts that propagate through the tissue. We’re going to try this in an octopus and squid, but my bet is that to get a muscular pump, you have to organise the electrical activity in the same way. You have this clean wavefront, not a single pulse down a one-dimensional nerve fibre. It’s got to spread as a wavefront.

We also found that the muscle cells in a jellyfish are shaped freakishly differently to a cardiac muscle cell. But if you strip away the outer part of the cells, the protein networks within that cell are universally built in the same way and aligned among cellular aggregates in the same way. We think structure begets function. What I’m really pleased about is that everything that my group has learned about the heart in terms of structure and function equally applies to the jellyfish. I feel like we’re learning some fundamental biology here. Some people do basic biology by deconstructing stuff. Engineers do basic science in a different way. What we’ve done is learned something about the basic science by building it de novo.

What’s next?

Bait. Tissue-engineered bait. I want to go fishing and have a much better form of bait. That’s the only thing that’s going to impress my family. They could care less about this high-order science. They want to know if they can win a bass tournament.

Seriously, there are lots of different things. We’re going to develop this into assays for drug discovery. That’s pretty important to use. We’re working on that. We’re looking to reverse-engineer other marine life-forms too; we’ve got a whole tank of stuff in there, and an octopus on order. We’re trying to build larger and smaller versions of the jellyfish so we can look at drug effects.


How mantis shrimps deliver armour-shattering punches without breaking their fists

For engineers looking to create the next generation of armour, the ocean is the place to look. Animals from snails to crabs protect themselves with hard shells whose microscopic structures imbue them with exceptional durability, surpassing even those of most man-made materials. They are extreme defences.

The mantis shrimp smashes them apart with its fists.

That’s the animal that David Kisailus from the University of California, Riverside is studying. “People have been studying molluscs for decades because they’re thought to be very impact-resistant,” he says. “The mantis shrimp eats these guys for dinner.”


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Cockroaches and geckos disappear by swinging under ledges… and inspire robots

One minute, a cockroach is running headfirst off a ledge. The next minute, it’s gone, apparently having plummeted to its doom. But wait! It’s actually clinging to the underside of the ledge! This cockroach has watched one too many action movies.

The roach executes its death-defying manoeuvre by turning its hind legs into grappling hooks and its body into a pendulum. Just as it is about to fall, it grabs the edge of the ledge with the claws of its hind legs, swings onto the underneath the ledge and hangs upside-down. In the wild, this disappearing act allows it to avoid falls and escape from predators. And in Robert Full’s lab at University of California, Berkeley, the roach’s trick is inspiring the design of agile robots.

Full studies how animals move, but his team discovered the cockroach’s behaviour by accident. “We were testing the animal’s athleticism in crossing gaps using their antennae, and were surprised to find the insect gone,” says Full. “After searching, we discovered it upside-down under the ledge. To our knowledge, this is a new behavior, and certainly the first time it has been quantified.”


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Razor clam creates quicksand to bury itself. So does RoboClam

Anyone who has tried to pull a razor clam from a sandy beach knows that they can dig fast. These edible animals can bury themselves at around one centimetre per second, and they go deep. A clam the length of a hand can create a burrow up to 70 centimetres down.

Like all molluscs, the clam has a muscular foot, but it’s not that muscular. Based on measurements of the foot’s strength, Amos Winter from Massachussetts Institute of Technology calculated that it should only be able to dig a couple of centimetres into the mud. It shouldn’t be able to submerge its body, much less create a burrow five times longer.

But Winter knows the razor clam’s secret: it doesn’t just rely on raw power. The clam adds water to the soil just below it, making it softer and easier to penetrate. It digs by turning part of a beach into quicksand.

The clam’s digging equipment couldn’t be simpler: a pair of long valves that run the length of its body and open or close its shell; and a foot that sits beneath the them. It extends the foot downwards and pushes against it to lift the shell up slightly. Then, it contracts the valves, sending blood into the foot and inflating it. This foot becomes an anchor. By pulling against it, the clam can drag its shell downwards.

To understand how these motions create a burrow despite the foot’s weedy nature, Winter had to capture several clams. And to do that, he had to become a licensed clam digger. Back in the lab, studying the clams wasn’t easy. As Winter writes in a wonderfully deadpan academic way: “The adage ‘clear as mud’ is used to describe the difficulty of visually investigating burrowing animals.” He finally saw what the clams were doing when he created a homemade “visualiser”— a repurposed ant farm. The animal was trapped between two transparent plates, filmed with high-speed cameras, and surrounded by a ‘beach’ of glass beads.

Winter’s videos revealed that when the clam contracts its valves, it does more than just pump the foot with blood. The contraction closes its shell, which relieves the pressure on the surrounding soil. The soil starts to crumble, and mixes with water pulled into the gap from above. The water “fluidises” the soil, making it soft and loose like quicksand. It offers far less resistance, and the clam can move through it with around ten times less energy. It does so quickly, before the soil has a chance to solidify again.

Winter isn’t just studying clams for the sake of it. The list of sponsors for his study is telling: Battelle Memorial Institute, a science and technology development company; Bluefin Robotics; and the Chevron Corporation, an energy company that explores for oil and gas.

Winter used his newfound knowledge to create RoboClam: a robot that duplicates the clam’s burrowing technique. It’s about the size of a lighter, but it comes with a much larger supportive frame of pistons and regulating elements. After further development, RoboClam could act as a lightweight anchor that could be easily set and unset. It could tether small robotic submarines for studying the ocean floor; help to install undersea cables or deep-water oil rigs; or even detonate buried underwater mines.

Reference: Winter, Deits & Hosoi. 2012. Localized fluidization burrowing mechanics of Ensis directus. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.058172

Photo by Arne Huckelheim

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How leaping lizards, dinosaurs and robots use their tails

What do a leaping lizard, a Velociraptor and a tiny robot at Bob Full’s laboratory have in common? They all use their tails to correct the angle of their bodies when they jump.

Thomas Libby filmed rainbow agamas – a beautiful species with the no-frills scientific name of Agama agama – as they leapt from a horizontal platform onto a vertical wall. Before they jumped, they first had to vault onto a small platform. If the platform was covered in sandpaper, which provided a good grip, the agama could angle its body perfectly. In slow motion, it looks like an arrow, launching from platform to wall in a smooth arc (below, left)

If the platform was covered in a slippery piece of card, the agama lost its footing and it leapt at the wrong angle. It ought to have face-planted into the wall, but Libby found that it used its long, slender tail to correct itself (below, right). If its nose was pointing down, the agama could tilt it back up by swinging its tail upwards.