̽��ֱ�� of Cambridge - biomechanics

Why Spider-Man can’t exist: Geckos are ‘size limit’ for sticking to walls

jeh98 — Mon, 18 Jan 2016 20:05:00 +0000

A new study, published today in PNAS, shows that in climbing animals ranging in size from mites to geckos, the percentage of body surface covered by adhesive footpads increases as body size increases, setting a limit to the size of animal using this strategy because larger animals would require impossibly big feet.

Dr David Labonte and his colleagues in the ̽��ֱ�� of Cambridge’s Department of Zoology found that tiny mites use approximately 200 times less of their body surface area for adhesive pads than geckos, nature's largest adhesion-based climbers. And humans? We’d need as much as 40% of our total body surface, or roughly 80% of our front, to be covered in sticky footpads if we wanted to do a convincing Spider-Man impression.

Once an animal is so big that a substantial fraction of its body surface would need to be sticky footpads, the necessary morphological changes would make the evolution of this trait impractical, suggests Labonte.

“If a human, for example, wanted to climb up a wall the way a gecko does, we’d need impractically large sticky feet – and shoes in European size 145 or US size 114,”says Walter Federle, senior author also from Cambridge’s Department of Zoology.

“As animals increase in size, the amount of body surface area per volume decreases – an ant has a lot of surface area and very little volume, and an elephant is mostly volume with not much surface area” explains Labonte.

“This poses a problem for larger climbing animals because, when they are bigger and heavier, they need more sticking power, but they have comparatively less body surface available for sticky footpads. This implies that there is a maximum size for animals climbing with sticky footpads – and that turns out to be about the size of a gecko.”

̽��ֱ��researchers compared the weight and footpad size of 225 climbing animal species including insects, frogs, spiders, lizards and even a mammal.

“We covered a range of more than seven orders of magnitude in body weight, which is roughly the same weight difference as between a cockroach and Big Ben” says Labonte.

“Although we were looking at vastly different animals – a spider and a gecko are about as different as a human is to an ant – their sticky feet are remarkably similar,” says Labonte.

“Adhesive pads of climbing animals are a prime example of convergent evolution – where multiple species have independently, through very different evolutionary histories, arrived at the same solution to a problem. When this happens, it’s a clear sign that it must be a very good solution.”

There is one other possible solution to the problem of how to stick when you’re a large animal, and that’s to make your sticky footpads even stickier.

“We noticed that within some groups of closely related species pad size was not increasing fast enough to match body size yet these animals could still stick to walls,” says Christofer Clemente, a co-author from the ̽��ֱ�� of the Sunshine Coast.

“We found that tree frogs have switched to this second option of making pads stickier rather than bigger. It’s remarkable that we see two different evolutionary solutions to the problem of getting big and sticking to walls,” says Clemente.

“Across all species the problem is solved by evolving relatively bigger pads, but this does not seem possible within closely related species, probably since the required morphological changes would be too large. Instead within these closely related groups, the pads get stickier in larger animals, but the underlying mechanisms are still unclear. This is a great example of evolutionary constraint and innovation.”

̽��ֱ��researchers say that these insights into the size limits of sticky footpads could have profound implications for developing large-scale bio-inspired adhesives, which are currently only effective on very small areas.

“Our study emphasises the importance of scaling for animal adhesion, and scaling is also essential for improving the performance of adhesives over much larger areas. There is a lot of interesting work still to be done looking into the strategies that animals use to make their footpads stickier - these would likely have very useful applications in the development of large-scale, powerful yet controllable adhesives,” says Labonte.

This study was supported by research grants from the UK Biotechnology and Biological Sciences Research Council (BB/I008667/1), the Human Frontier Science Programme (RGP0034/2012), the Denman Baynes Senior Research Fellowship, and a Discovery Early Career Research Fellowship (DE120101503).

Reference:

Labonte, D et al "Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing." PNAS 18 January 2016. DOI: 10.1073/pnas.1519459113

Inset images: Vallgatan 21D, Gothenburg, Sweden (photo by Gudbjörn Valgeirsson, footprints added by Cedric Bousquet, ̽��ֱ�� of Cambridge); How sticky footpad area changes with size (David Labonte); Diversity of sticky footpads (David Labonte).

Latest research reveals why geckos are the largest animals able to scale smooth vertical walls – even larger climbers would require unmanageably large sticky footpads. Scientists estimate that a human would need adhesive pads covering 40% of their body surface in order to walk up a wall like Spider-Man, and believe their insights have implications for the feasibility of large-scale, gecko-like adhesives.

If a human wanted to climb up a wall the way a gecko does, we’d need impractically large sticky feet – and shoes in European size 145

Walter Federle

A Hackmann & D Labonte

Gecko and ant

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Attribution

Power up: cockroaches employ a “force boost” to chew through tough materials

jeh98 — Wed, 11 Nov 2015 19:01:00 +0000

̽��ֱ��study, published today in PLOS ONE, shows that cockroaches activate slow twitch muscle fibres only when chewing on tough material such as wood that requires repetitive, hard biting to generate a bite force 50 times stronger than their own body weight.

“As insects play a dominant role in many ecosystems, understanding the amount of force that these insects can exert through their mandibles is a pivotal step in better understanding behavioural and ecological processes and enabling bioinspired engineering,” explains Tom Weihmann from the ̽��ֱ�� of Cambridge’s Department of Zoology, lead author of the study. “Insects provide a major part of the faunal biomass in many terrestrial ecosystems. Therefore they are an important food source but also crucial as decomposers of plants and animals. In this way they are crucial for material cycles and the ecological balance.”

“Ours is the first study to measure the bite forces of ordinary insects, and we found that the American cockroach, Periplaneta americana, can generate a bite force around 50 times stronger than their own body weight. In relative terms that’s about five times stronger than the force a human can generate with their jaws,” he adds.

Previous studies have focused on the biting action of larger animals, particularly vertebrates, which have jaws full of teeth that they use to grind food, catch prey, or fend off other animals. But insects, like cockroaches, have different biting mouthparts; they have a pair of strong, horizontally aligned bladelike jaws, or mandibles. ̽��ֱ��mandibles have an important role in the life of insects: being used not only for shredding food, but also for digging, transport, defence, and feeding offspring.

An insect’s mandibles are attached to the head capsule, which consists of thin multi-layered cuticle and forms a complexly structured part of their exoskeleton. ̽��ֱ��head capsule encloses the driving muscles for all mouth parts and a number of other vital organs of the central nervous and digestive systems. This means that space is limited for the muscles required to operate their scissor-like mandibles; so many insects have muscles with oblique fibres that reduce the amount of thickening that occurs when the muscles contract.

When it comes to investigating biting, cockroaches are the perfect model system – as Weihmann says, they are “extraordinarily ordinary insects with regard to their mouthparts and biting abilities.”

̽��ֱ��researchers measured the force of 300 bites made by specimen cockroaches across the whole range of mandible opening angles. They found that the cockroaches could exert various levels of force with their bites, from short, weak bites, to particularly strong bites that lasted much longer.

“ ̽��ֱ��weaker, shorter bites were generated by relatively fast muscle fibres, while the longer, stronger bites were driven by additional muscle fibres that take time to reach their maximum force,” explains Weihmann, “these slower muscle fibres give the mandibles a force boost to allow them to exert up to 0.5 Newtons during sustained grasping or chewing.”

“ ̽��ֱ��employment of slow muscle fibres allows very efficiently generated muscle forces with only a minimum of cross section area, and therefore head volume, required,” he adds.

Weihmann explains that gaining a better understanding of how the delicate structure of the head capsule withstands such powerful forces over an insect’s lifetime could also have interesting applications for bioinspired engineering.

“It is interesting whenever forces have to be transferred within small hollow capsules, particularly if actuators such as tiny motors, advanced piezo-electric actuators or other sophisticated drives need to be attached to the inner sides of the structure, just like mandible muscles do. With increasing miniaturisation, such designs will become increasingly important. Recent technical implementations in this direction are for instance micro probes inserted into blood vessels or micro surgical instruments.”

̽��ֱ��work was funded by the German Research Foundation (DFG) and the Daimler and Benz Foundation.

Reference:

Tom Weihmann, et al. Fast and powerful: Biomechanics and bite forces of the mandibles in the American cockroach Periplaneta Americana PLOS ONE 11^th November 2015. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0141226

Inset images: A side view onto the experimental setup with the force sensor at the left and the specimen at the right (Tom Weihmann); A micro-computed tomography image of a cockroach head showing the driving muscles of the left mandible (Tom Weihmann).

New research indicates that cockroaches use a combination of fast and slow twitch muscle fibres to give their mandibles a “force boost” that allows them to chew through tough materials.

̽��ֱ��American cockroach can generate a bite force around 50 times stronger than their own body weight – in relative terms about five times stronger than the force a human can generate with their jaws

Tom Weihmann

Left - micro-computed tomography image of a cockroach head showing the driving muscles of the left mandible; right - side view onto the experimental setup

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Close-up film shows for the first time how ants use ‘combs’ and ‘brushes’ to keep their antennae clean

jeh98 — Mon, 27 Jul 2015 15:53:30 +0000

For an insect, grooming is a serious business. If the incredibly sensitive hairs on their antennae get too dirty, they are unable to smell food, follow pheromone trails or communicate. So insects spend a significant proportion of their time just keeping themselves clean. Until now, however, no-one has really investigated the mechanics of how they actually go about this.

In a study published in Open Science, Alexander Hackmann and colleagues from the Department of Zoology have undertaken the first biomechanical investigation of how ants use different types of hairs in their cleaning apparatus to clear away dirt from their antennae.

“Insects have developed ingenious ways of cleaning very small, sensitive structures, so finding out exactly how they work could have fascinating applications for nanotechnology – where contamination of small things, especially electronic devices, is a big problem. Different insects have all kinds of different cleaning devices, but no-one has really looked at their mechanical function in detail before,” explains Hackmann.

Camponotus rufifemur ants possess a specialised cleaning structure on their front legs that is actively used to groom their antennae. A notch and spur covered in different types of hairs form a cleaning device similar in shape to a tiny lobster claw. During a cleaning movement, the antenna is pulled through the device which clears away dirt particles using ‘bristles’, a ‘comb’ and a ‘brush’.

To investigate how the different hairs work, Hackmann painstakingly constructed an experimental mechanism to mimic the ant’s movements and pull antennae through the cleaning structure under a powerful microscope. This allowed him to film the process in extreme close up and to measure the cleaning efficiency of the hairs using fluorescent particles.

What he discovered was that the three clusters of hairs perform a different function in the cleaning process. ̽��ֱ��dirty antenna surface first comes into contact with the ‘bristles’ (shown in the image in red) which scratch away the largest particles. It is then drawn past the ‘comb’ (shown in the image in blue) which removes smaller particles that get trapped between the comb hairs. Finally, it is drawn through the ‘brush’ (shown in the image in green) which removes the smallest particles.

“While the ‘bristles’ and the ‘comb’ scrape off larger particles mechanically, the ‘brush’ seems to attract smaller dirt particles from the antenna by adhesion,” says Hackmann, who works in the laboratory of Dr Walter Federle.

Where the ‘bristles’ and ‘comb’ are rounded and fairly rigid, the ‘brush’ hairs are flat, bendy and covered in ridges – this increases the surface area for contact with the dirt particles, which stick to the hairs. Researchers do not yet know what makes the ‘brush’ hairs sticky – whether it is due to electrostatic forces, sticky secretions, or a combination of factors.

“ ̽��ֱ��arrangement of ‘bristles’, ‘combs’ and ‘brush’ lets the cleaning structure work as a particle filter that can clean different sized dirt particles with a single cleaning stroke,” says Hackmann. “Modern nanofabrication techniques face similar problems with surface contamination, and as a result the fabrication of micron-scale devices requires very expensive cleanroom technology. We hope that understanding the biological system will lead to building bioinspired devices for cleaning on micro and nano scales.”

Dr Federle’s laboratory and, in part, this project receive financial support from the Biotechnology and Biological Sciences Research Council (BBSRC).

Inset images: Scanning electron micrograph of the antenna clamped by the cleaner (Alexander Hackmann); Scanning electron micrograph of the tarsal notch (Alexander Hackmann).

Reference:

Alexander Hackmann, Henry Delacave, Adam Robinson, David Labonte, Walter Federle. Functional morphology and efficiency of the antenna cleaner in Camponotus rufifemur ants. Open Science; 22 July 2015.

Using unique mechanical experiments and close-up video, Cambridge researchers have shown how ants use microscopic ‘combs’ and ‘brushes’ to keep their antennae clean, which could have applications for developing cleaners for nanotechnology.

Insects have developed ingenious ways of cleaning very small, sensitive structures, which could have fascinating applications for nanotechnology – where contamination of small things is a big problem

Alexander Hackmann

How ants use ‘combs’ and ‘brushes’ to keep their antennae clean

Alexander Hackmann

Scanning electron micrograph of the tarsal notch

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Baby mantises harness mid-air ‘spin’ during jumps for precision landings

fpjl2 — Thu, 05 Mar 2015 16:48:31 +0000

̽��ֱ��smaller you are, the harder it is not to spin out of control when you jump. Miniscule errors in propulsive force relative to the centre of mass results in most jumping insects – such as fleas, leafhoppers and grasshoppers – spinning uncontrollably when they jump.

Until now, scientists worked under the hypothesis that such insects can’t control this, and spin unpredictably with frequent crash landings.

But new high-speed video analysis of the jumps of wingless, baby praying mantises has revealed a technique which actually harnesses the spinning motion, enabling them to jump with accuracy at the same time as repositioning their body mid-air to match the intended target – all in under a tenth of a second.

Researchers used a thin black rod distant from the platform on which the mantises sat as a target for them to jump at.

During the jumps, the insects rotated their legs and abdomen simultaneously yet in varying directions – shifting clockwise and anti-clockwise rotations between these body parts in mid-air – to control the angular momentum, or ‘spin’. This allowed them to shift their body in the air to align themselves precisely with the target on which they chose to land.

And the mantises did all of this at phenomenal speed. An entire jump, from take-off to landing, lasted around 80 milliseconds – literally faster than the blink of a human eye.

At first, scientists believed the mantis had simply evolved a way to mitigate the natural spin that occurs when such small insects jump at speed.

On closer inspection, however, they realised the mantis is in fact deliberately injecting controlled spin into the jump at the point of take-off, then manipulating this angular momentum while airborne through intricate rotations of its extremities in order to reposition the body in mid-air, so that it grasps the target with extreme precision.

For the study, published today in the journal Current Biology, the researchers analysed a total of 381 slowed-down videos of 58 young mantises jumping to the target, allowing them to work out the intricate mechanics used to land the right way up and on target virtually every time.

“We had assumed spin was bad, but we were wrong – juvenile mantises deliberately create spin and harness it in mid-air to rotate their bodies to land on a target,” said study author Professor Malcolm Burrows from Cambridge ̽��ֱ��’s Department of Zoology, who conducted the research with Dr Gregory Sutton from Bristol ̽��ֱ��.

“As far as we can tell, these insects are controlling every step of the jump. There is no uncontrolled step followed by compensation, which is what we initially thought,” he said.

In fact, when the researchers moved the target closer, the mantises spun themselves twice as fast to ensure they got their bodies parallel with the target when they grasped it.

For Sutton, the study is similar to accountancy, only with distribution of momentum instead of money. “ ̽��ֱ��mantis gives itself an amount of angular momentum at take-off and then distributes this momentum while in mid-air: a certain amount in the front leg at one point; a certain amount in the abdomen at another – which both stabilise the body and shift its orientation, allowing it to reach the target at the right angle to grab on,” he said.

̽��ֱ��researchers tested what would happen if they restricted the ability of the mantis to harness and spread the ‘spin’ to its extremities during a jump. To do this, they glued the segments of the abdomen together, expecting the mantis to spin out of control.

Intriguingly, the accuracy of the jump wasn’t impeded. ̽��ֱ��mantises still reached the target, but couldn’t rotate their bodies into the correct position – so crashed headlong into it and bounced off again.

̽��ֱ��next big question for the researchers is to understand how the mantis achieves its mid-air acrobatics at such extraordinary speeds. “We can see the mantis performs a scanning movement with its head before a jump. Is it predicting everything in advance or does it make corrections at lightning speed as it goes through the jump? We don’t know the answer between these extreme possibilities,” said Burrows.

Sutton added: “We now have a good understanding of the physics and biomechanics of these precise aerial acrobatics. But because the movements are so quick, we need to understand the role the brain is playing in their control once the movements are underway.”

Sutton believes that the field of robotics could learn lessons from the juvenile mantis. “For small robots, flying is energetically expensive, and walking is slow. Jumping makes sense – but controlling the spin in jumping robots is an almost intractable problem. ̽��ֱ��juvenile mantis is a natural example of a mechanical set-up that could solve this,” he said.

Professor Malcolm Burrows and Dr Gregory Sutton

High-speed videos reveal that, unlike other jumping insects, the juvenile praying mantis does not spin out of control when airborne. In fact, it both creates and controls angular momentum at extraordinary speeds to orient its body for precise landings.

As far as we can tell, these insects are controlling every step of the jump

Malcolm Burrows

Malcolm Burrows and Greg Sutton

A juvenile praying mantis

̽��ֱ��text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

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Functioning ‘mechanical gears’ seen in nature for the first time

fpjl2 — Thu, 12 Sep 2013 18:05:28 +0000

̽��ֱ��juvenile Issus - a plant-hopping insect found in gardens across Europe - has hind-leg joints with curved cog-like strips of opposing ‘teeth’ that intermesh, rotating like mechanical gears to synchronise the animal’s legs when it launches into a jump.

̽��ֱ��finding demonstrates that gear mechanisms previously thought to be solely man-made have an evolutionary precedent. Scientists say this is the “first observation of mechanical gearing in a biological structure”.

Through a combination of anatomical analysis and high-speed video capture of normal Issus movements, scientists from the ̽��ֱ�� of Cambridge have been able to reveal these functioning natural gears for the first time. ̽��ֱ��findings are reported in the latest issue of the journal Science.

̽��ֱ��gears in the Issus hind-leg bear remarkable engineering resemblance to those found on every bicycle and inside every car gear-box. Each gear tooth has a rounded corner at the point it connects to the gear strip; a feature identical to man-made gears such as bike gears – essentially a shock-absorbing mechanism to stop teeth from shearing off.

̽��ֱ��gear teeth on the opposing hind-legs lock together like those in a car gear-box, ensuring almost complete synchronicity in leg movement - the legs always move within 30 ‘microseconds’ of each other, with one microsecond equal to a millionth of a second.

This is critical for the powerful jumps that are this insect’s primary mode of transport, as even miniscule discrepancies in synchronisation between the velocities of its legs at the point of propulsion would result in “yaw rotation” - causing the Issus to spin hopelessly out of control.

“This precise synchronisation would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required,” said lead author Professor Malcolm Burrows, from Cambridge’s Department of Zoology.

“By developing mechanical gears, the Issus can just send nerve signals to its muscles to produce roughly the same amount of force - then if one leg starts to propel the jump the gears will interlock, creating absolute synchrony.

“In Issus, the skeleton is used to solve a complex problem that the brain and nervous system can’t,” said Burrows. “This emphasises the importance of considering the properties of the skeleton in how movement is produced.”

"We usually think of gears as something that we see in human designed machinery, but we've found that that is only because we didn't look hard enough,” added co-author Gregory Sutton, now at the ̽��ֱ�� of Bristol.

“These gears are not designed; they are evolved - representing high speed and precision machinery evolved for synchronisation in the animal world.”

Interestingly, the mechanistic gears are only found in the insect’s juvenile – or ‘nymph’ – stages, and are lost in the final transition to adulthood. These transitions, called ‘molts’, are when animals cast off rigid skin at key points in their development in order to grow.

It’s not yet known why the Issus loses its hind-leg gears on reaching adulthood. ̽��ֱ��scientists point out that a problem with any gear system is that if one tooth on the gear breaks, the effectiveness of the whole mechanism is damaged. While gear-teeth breakage in nymphs could be repaired in the next molt, any damage in adulthood remains permanent.

It may also be down to the larger size of adults and consequently their ‘trochantera’ – the insect equivalent of the femur or thigh bones. ̽��ֱ��bigger adult trochantera might allow them to create enough friction to power the enormous leaps from leaf to leaf without the need for intermeshing gear teeth to drive it, say the scientists.

Each gear strip in the juvenile Issus was around 400 micrometres long and had between 10 to 12 teeth, with both sides of the gear in each leg containing the same number – giving a gearing ratio of 1:1.

Unlike man-made gears, each gear tooth is asymmetrical and curved towards the point where the cogs interlock – as man-made gears need a symmetric shape to work in both rotational directions, whereas the Issus gears are only powering one way to launch the animal forward.

While there are examples of apparently ornamental cogs in the animal kingdom - such as on the shell of the cog wheel turtle or the back of the wheel bug - gears with a functional role either remain elusive or have been rendered defunct by evolution.

̽��ֱ��Issus is the first example of a natural cog mechanism with an observable function, say the scientists.

Inset image: an Issus nymph

For more information, please contact fred.lewsey@admin.cam.ac.uk

Previously believed to be only man-made, a natural example of a functioning gear mechanism has been discovered in a common insect - showing that evolution developed interlocking cogs long before we did.

In Issus, the skeleton is used to solve a complex problem that the brain and nervous system can’t

Malcolm Burrows

Mechanical gears in jumping insects

Burrows/Sutton

Cog wheels connecting the hind legs of the plant hopper, Issus

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Yes

Collagen mechanics: learning from nature

bjb42 — Mon, 01 Sep 2008 15:37:11 +0000

Mention the word ‘biology’ and most people think immediately about cells. However, large portions of the human body are non-cellular and are made instead from an extracellular matrix (ECM) that provides much of the structural support around cells. This supportive function of the ECM is especially evident in the connective tissues of the body. Many load-bearing structures such as bones, teeth and ligaments are connective tissues and these have been the focus of recent bioengineering research in Cambridge.

Dr Michelle Oyen, Lecturer in the new Engineering for Life Sciences programme in the Department of Engineering, is studying the mechanical functions of connective tissues. Her research ranges from fundamental science and engineering projects through to collaborative projects with clinicians for developing mechanics-based tools for use in medical practice. ̽��ֱ��unifying theme of this research lies with the primary component of many connective tissues: the structural protein collagen.

Building blocks of natural materials

Collagen is ubiquitous; this triple-helical protein makes up a quarter of all proteins in the body. It self-assembles from the molecular scale up to large fibre-like structures, creating a hierarchical material with remarkable physical properties. Collagen combines with other ECM components – mainly water, non-collagenous proteins and sugars – and, in mineralised tissues, with bioceramics analogous to earth minerals. These non-living, but cell-derived, materials combine with cells to form living yet mechanically robust tissues.

Collagen takes on different roles in different parts of the body. In structural tissues, like bones and ligaments, it’s found in rope-like fibres that provide resistance to stretching and tearing forces. In cartilage, which is mostly loaded in compression, collagen has more of a ‘holding’ function, with the fibres arranged rather like a basket, retaining other hydrated proteins and sugars. In the lens of the eye, collagen is crystalline, organised precisely for optical transparency. In fact, there are over 20 different types of collagen in the body, and it is not even known precisely what functions they all fulfil.

Mechanics in medicine

̽��ֱ��study of the biomechanical properties of collagen and ECM is a particularly exciting and fast-growing field in reproductive medicine. One aspect of Dr Oyen’s research has been to examine the physical properties of the ECM in the amniotic sac, the membrane that ruptures (the ‘breaking of waters’), signalling imminent birth.

Rupture occurring before full-term gestation results in approximately a third of all premature births. Following the first-ever set of rigorous bioengineering studies on placental membranes, Dr Oyen and clinical colleagues at the ̽��ֱ�� of Minnesota concluded that the phenomenon is due to localised damage, not widespread overall membrane deterioration, and that diagnostic techniques may be developed to detect localised thinning and ECM damage for intervention into premature birth.

This project is taking a new direction since Dr Oyen’s arrival in Cambridge. By teaming up with researchers at the newly opened Centre for Trophoblast Research (www.trophoblast.cam.ac.uk), she will be able to examine placental development from an engineering and mechanics perspective.

Mimicking nature

Nature clearly creates dynamic, mechanically functional tissues that are different from anything engineers have made. As an example, cartilage, which forms the gliding surface that permits joint movement, is approximately 75% water and only 25% collagen, sugar and other proteins, and yet its stiffness and shock-absorbing capability make it comparable to solid rubber. Moreover, the cartilage-on-cartilage sliding interface has lower friction than ice sliding on ice.

In fact, when engineers design materials, uniformity and simplicity are often prized. Engineering materials do not always feature the multi-level hierarchical organisations found in protein-based materials, nor do they exemplify the dramatic spatial non-uniformity that has been found to strengthen natural materials. So, by learning from nature, novel engineering systems might be developed that utilise the principles found in natural materials – a field of technology that has been termed biomimetics.

In some instances, biomimetics takes the form of direct imitation, as in the case of a nanocomposite of mineral and proteins similar to natural bone. For cases of major bone defects, such as occurs through trauma or cancer, a bone-like material that is biocompatible can be seeded with cells to form a ‘tissue-engineered’ construct and implanted within the body. However, if you consider just how lightweight, yet stiff, strong and tough, a bone-like material is, why not use it for other structural applications such as architecture? This is a challenge that Dr Oyen is investigating.

To do this, you need to go back to first principles – how the material forms. With funding from the Royal Society, Dr Oyen is examining biomineralisation and the formation of mechanically robust bone-like materials. ̽��ֱ��work differs from tissue-engineering approaches in that there is no cellular component and the end applications are viewed as being remote from medicine. Although a large number of groups have considered the synthesis of biomimetic materials, far fewer have taken a primary angle associated with the measurement of mechanical properties. Dr Oyen views the materials as successful when they replicate both bone composition and mechanical behaviour.

Inspirational materials

It is also possible to abstract ideas from nature without directly imitating the materials themselves. As examples, key concepts that could guide the formation of ‘bone-inspired’ materials include: composite materials with a very large stiffness mismatch between the phases; materials that form from room-temperature deposition of a ceramic onto a self-assembled polymer; materials with up to seven different levels of hierarchical organisation; and materials that are self-healing. Each of these concepts could be applied to a system that is not protein based, and ongoing research both at Cambridge and across the world is incorporating these types of principles for materials development.

Compared with many branches of engineering, biomimetic engineering is comparatively new. In this rapidly expanding field, the lessons learnt from the physical and mechanical properties of natural materials such as collagen and bone offer great promise within an engineering framework. Not only is this sure to make a difference to 21st-century healthcare, but there are also ways in which engineering will itself benefit from the abstraction of ideas from nature.

For more information, please contact the author Dr Michelle Oyen (mlo29@cam.ac.uk)

at the Department of Engineering.

Because of their unique structure, biological tissues exhibit physical and mechanical properties that are unlike anything in the world of engineering.

So, by learning from nature, novel engineering systems might be developed that utilise the principles found in natural materials – a field of technology that has been termed biomimetics.

Dr Jon Heras, Equinox Graphics

collagen

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Yes