In a number of recent posts I’ve looked at the ways that nanotechnology coatings like those produced by P2i can be used to make everything from mobile phones to trainers water repellent – and at the natural examples of this same phenomenon – but I haven’t really considered the science behind this technology – which is all about the electromagnetic interaction of molecules.

We’re probably most familiar with this kind of interaction in an attractive way. As I write this, there is a heavy frost outside. Water is turning from liquid to solid. Yet were it not for a particular molecular interaction, this would be an impossibility because water would boil below -70 °C. There would be no liquid or solid water on the Earth and, in all probability, no life.

The interaction that makes life possible is hydrogen bonding. This is an electromagnetic attraction between a hydrogen atom in one molecule, and an atom like oxygen, nitrogen or fluorine in a second molecule. When hydrogen is bonded to one of these atoms there is a relative positive charge on the hydrogen and a relative negative charge on the oxygen (say). This happens because the hydrogen atom’s only electron is in its bond, leaving a positively charged ‘end’ to the molecule, while the oxygen atom has four outer electrons not in its bonds, which are repelled away from the electrons in the bonds, giving it a negative charge.

Put two molecules alongside each other and the positively charged hydrogen is attracted to the negatively charged oxygen in its neighbour. The two molecules are drawn towards each other. There’s a force pulling the molecules together, and that means if you want to break them apart – say to boil liquid water – then it takes more energy that it otherwise would, as you have to overcome that force. Result: a much higher boiling point.

This inter-molecular attraction also accounts for another oddity that means aquatic creatures can survive in icy cold weather. Solid water – ice – is less dense than the liquid form, so it floats, leaving the water beneath still liquid. It’s sometimes said this is a unique property of water. It’s not – acetic acid and silicon, for instance, are both denser as a liquid than a solid – but it is unusual. It happens because the six-sided shape of a water crystal won’t fit with the way the hydrogen bonds pull the hydrogen of one water molecule towards the oxygen of another. To slot into the structure, these bonds have to stretch and twist, pulling water molecules further apart than they are in water’s most dense liquid form.

Hydrogen bonding would not be a good mechanism to consider if you wanted to keep liquids off an object. It would tend, rather, to keep them in place. So to produce a water resistant coating, you are looking instead for molecules that won’t attract. I have a personal interest in this. My father was an industrial chemist and was part of the team that developed one of the world’s first fabric conditioners. He used to bring home experimental jars of turquoise gloop from work to try out at home. And the principle behind a fabric conditioner or fabric softener is the opposite of cosy hydrogen bonds.

Such conditioners work by making clothes dirty with a special kind of dirt. Conditioners leave a thin residue on the fabric fibres. These molecules have several roles, but the significant one here is that they tend to repel each other, making the detailed structure of the fibres fluff up and giving the fabric a softer, more luxurious feel, lubricating the fibres when they move against each other.

This is very much fabric conditioner on fabric conditioner interaction. But to achieve a water-repellent coating we need to combine aspects of the two effects to get an interaction between the molecules in the coating and the water molecules that we are trying to get away from a product as quickly as possible.

P2i’s nanocoating is a polymer with molecules that are long-chains which can be either hydrocarbons or poly fluorinated . These start out as individual monomers – the molecules that will eventually be bound together in a polymer – which are exposed to a low power radio signal at 13.56 MHz to produce a plasma, a gas-like collection of ionised monomers, which then polymerize directly on the object being coated. It’s not a case of applying a polymer like sticking on an outer coating, but rather of creating it in place on all surfaces of the object to be protected.

Water forming into droplets on a tissue with a P2i coating

The molecular action here is rather more subtle than in a fabric conditioner. The coated surface has a low surface energy – significantly lower than that of water. Surface energy is a way of describing how much ability the surface of a substance has to produce interactions. P2i’s coating is unusually reluctant to interact, giving it a very low surface energy, around 1/3 that of the non-stick substance PTFE (Teflon). This means that the water is much more attracted to itself, through hydrogen bonding, than it is to the surface of the material. The result is that rather than wetting the surface – spreading out as a thin layer – the water forms spherical drops, because most of the attraction the water molecules feel is towards other water molecules and with all this inward attraction the natural result in the formation of a sphere.

As the water is in self-contained droplets on the surface, it will roll off in these beads without interacting with the material. This is why you can have the kind of remarkable result shown in the Richard Hammond TV show where he pulled a ringing phone out of a toilet and it still worked. The water was not given a chance to wet the surface and short out or corrode the electronics.

We tend to think of a substance in terms of its macro properties – those that we can see and feel. But we can only properly understand what’s going on by taking a close up look. When it comes to how stuff works, it’s a molecule versus molecule world.

Images courtesy of P2i

Nanotechnology, like genetically modified food or nuclear power, often produces a knee-jerk reaction. It’s somehow ‘not natural’ and so is considered scary and dangerous. This is primarily a reaction to words, the same way that it easy for advertisers to push emotional buttons with ‘natural’ as good and ‘artificial’ as bad.

This is a silly distinction. There is a lot in nature that is very dangerous indeed – and much that is artificial protects us from that. If you doubt this, try removing everything artificial when you are flying in a plane over shark infested waters. For that matter, many of the most virulent poisons like ricin and botulinus toxin are natural. Water crammed with bacteria and faecal matter is natural. Clean, safe drinking water from a tap is artificial. Yet we can’t help reacting like puppets when the advertisers use those magic words.

What we’re not talking about – nano machines

Some concerns about nanotechnology are down to what is at best futurology and at worst science fiction. Prince Charles infamously caused headlines back in 2003, when newspapers reported ‘The prince has raised the spectre of the “grey goo” catastrophe in which sub-microscopic machines designed to share intelligence and replicate themselves take over and devour the planet.’

Charles later denied ever meaning this, commenting that he never used the expression ‘grey goo’ and saying ‘I do not believe that self-replicating robots, smaller than viruses, will one day multiply uncontrollably and devour our planet. Such beliefs should be left where they belong, in the realms of science fiction.’ But he certainly did express concerns that not enough was being done to assess and manage any risk associated with the use of nanotechnology.

Unlike the grey goo headlines, this is a perfectly reasonable attitude. The very nature of nanotechnology implies using substances in physical formats that our bodies might not have encountered, and hence we can’t make assumptions without appropriate testing and risk assessment.

If we are to be sensible about this, we need to first avoid a blanket response to nanotechnology. You would be hard pressed to find a reason for being worried about the impact of nanometer thin coatings, such as that used by P2i (sponsors of the Nature’s Nanotech series) There is a big difference between manipulating coatings at the nanoscale and manufacturing products with nanoparticles and small nanotubes.

A carbon nanotube

We know that breathing in nanoparticles, like those found in soot in the air, can increase risk of lung disease, and there is no reason to think that manufactured nanoparticles would be any less dangerous than the natural versions. When some while ago the Soil Association banned artificial nanoparticles from products they endorsed, I asked them why only artificial particles. Their spokesperson said that natural ones are fine because ‘life evolved with these.’

This, unfortunately, is rubbish. You might as well argue it is okay to put natural salmonella into food because ‘life evolved with it.’ Life also evolved with cliffs, but it doesn’t make falling off them any less dangerous. There is no magic distinction between a natural and an artificial substance when it comes to chemical makeup, and in practice if there is risk from nanoparticles it is likely to be from the physics of their very small size, rather than anything about their chemistry.

There are three primary concerns about nanoparticles – what will happen if we breathe them, eat them and put them on our skin. The breathing aspect is probably the best understand and is already strongly legislated on in the UK – we know that particulates in the air can cause a range of diseases and have to be avoided. There is really no difference here between the need to control nanoparticles and any other particles and fibres we might breathe. Whenever a process throws particulates into the air it ought to be controlled. (And this applies to the ‘natural’ smoke from wood fires, say, which is high in dangerous particulates, as well as any industrial process.)

When it comes to food, we have good coverage from The House of Lords Science and Technology committee in a 2010 report. They point out that nanotechnologies have a range of possible applications in food that could benefit both consumers and industry. ‘These include creating foods with unaltered taste but lower fat, salt or sugar levels, or improved packaging that keeps food fresher for longer or tells consumers if the food inside is spoiled.’

The committee’s report sensibly argued ‘Our current understanding of how [nanoparticles] behave in the human body is not yet advanced enough to predict with any certainty what kind of impact specific nanomaterials may have on human health. Persistent nanomaterials are of particular concern, since they do not break down in the stomach and may have the potential to leave the gut, travel throughout the body, and accumulate in cells with long-term effects that cannot yet be determined.’

Their recommendation was not to abandon these technologies, but rather that it was essential to perform appropriate research, preferably across the EU, to check the impact of such nanomaterials when consumed, and to ensure that all such materials that interact differently with the body from ordinary foodstuffs are assessed for risk before they are allowed onto the market. This seems eminently sensible.

The final area, applying nanoparticles to the skin, is perhaps most urgent, because most of apply them on a regular basis. Most sun defence products, and a number of cosmetics contain them. It is hard to find a good reason to allow for any risk in a pure cosmetic, and arguably they should be prevented from containing nanoparticles. But the story is more nuanced with sun creams.

Most sunscreens contain particles of titanium dioxide or zinc oxide. These invisible particles, ranging from nanoscale to significantly larger, provide most of the sunscreen’s protection against dangerous ultraviolet. What has to be weighed up is the benefits of using products to prevent a cancer that kills over 65,000 people a year worldwide – and would kill many more if sunscreens weren’t used – against a risk that has not been associated with any known deaths.

The potential for these nanoparticles to cause harm depends on them penetrating through the outer layers of the skin to reach cells where they could cause damage. In theory a nanoparticle is capable of doing this. But the current evidence is that the particles remain on the surface of the skin and do not reach viable skin cells. Skin cancer is a particular risk in Australia, so this is a topic that has been studied in depth there. As Cancer Council Australia concludes: ‘there is no credible evidence that sunscreens containing nanoparticles pose a health risk. There is plenty of evidence however, proving that sunscreen can help reduce the risk of skin cancer, in particular non-melanoma skin cancer.’

Overall, then, we should not be lax about nanoparticles and their effect on our bodies. We need careful testing and where necessary regulation. But equally we should not be swayed into knee-jerk reactions by emotional words carrying little meaning.

Images from iStockPhoto

The final entry in our Nature’s Nanotech series

There is something stunning about the colours of a peacock feather. It’s not just a simple matter of the sort of coloured pigments an artist mixes up on a palette. The colours in the feathers almost glow in their iridescence, changing subtly with angle to catch the eye. To produce this effect, the feather contains a natural nanotechnology that has the potential to transform optics when this remarkable approach is adapted for use in human technology.

Both the iridescence of that peacock’s tail and the swirly, glittering appearance of the semi-precious stone opal are caused by forms of photonic lattices. These are physical structures at the nano level that act on light in a way that is reminiscent of electronics, like the semiconductors that act to switch and control electrons, giving unparalleled manipulation of photons.

The colours of the peacock feather bear no resemblance to those of a pigment. In blue paint, for example, the pigment is a material that tends to absorb most of the spectrum of white light but re-emits primarily blue, so we see anything painted with the pigment as being blue. In the peacock feathers it’s the internal structure of the feather (or to be precise the tiny ‘barbules’ on the feather) that produce the hue.

The colouration is primarily due to internal reflections off the repeated structure of the barbule, similar to the way the lattice arrangement of a crystal can produce enhanced reflection. What happens is that photons reflected from a deeper layer are in phase with those from an outer layer, reinforcing the particular colours of light (or energies of photons) that fit best with the lattice spacing. This is a photonic lattice. These effects depend on the angle at which the light reflects, giving the typical ‘shimmer’ of iridescence.

The practical applications of artificially created photonic crystals can do much more than produce a pretty effect and striking colours. Because a photonic lattice acts on light as semiconductors do on electrons, they are essential components if we are ever to build optical computers.

These theoretical machines would use photons to represent bits, rather than the electrical impulses we currently employ in a conventional computer. This could vastly increase the computing power. Because photons don’t interact with each other, many more can be crammed into a tiny space. What’s more, one of the biggest restrictions in current computer architecture is the complex spaghetti of links joining together different parts of the structure. With photons, those links can flow through each other in a basket of light – unlike wires and circuits, photons can pass through each other without interacting, allowing more complex and faster architectures. Equally, optical switching – and in the end, a computer is just a huge array of switches – could be much faster than the electronic equivalent.

There are significant technical problems to be overcome, but the potential is great. Photonic crystals are already used in special paint and ink systems which change colour depending on the angle at which the paint is viewed, reflection reducing coatings on lenses and high transmission photonic fibre optics.

Another example of nanotechnology having a quantum effect on light is plasmonics. Something remarkable happens, for example, if light is shone on a gold foil peppered with millions of nanoholes. It seems reasonable that only a tiny fraction of the light hitting the foil would pass through these negligible punctures, but in fact in a process known as ‘extraordinary optical transmission’ they act like funnels, channelling all the light that hits the foil through the sub-microscopic apertures. This bizarre phenomenon results from the interaction between the light and plasmons, waves in the two dimensional ocean of electrons in the metal.

The potential applications of plasmonics are remarkable. Not only the more obvious optical ones – near perfect lenses and supplementing the photonic lattices in superfast computers that use light rather than electrons to function – but also in the medical sphere to support diagnostics, by detecting particular molecules, and for drug delivery. Naomi Halas of Rice University in Texas envisions implanting tiny cylinders containing billions of plasmonic spheres, each carrying a minuscule dose of insulin. Infra red light, shone from outside the body, could trigger an exact release of the required dose. ‘Basically, people could wear a pancreas on their arm,’ said Halas.

Over the last seven weeks since the first post, we have explored a wide range of the ways that nanotechnology, given a push in the right direction by nature, is starting to be important in our lives. At the moment we are most likely to come across relatively simple applications like the nanoparticles in sun block or technology making fabrics and electronics water repellent.

As our abilities to construct nanostructures improve we will see increased use of the likes of carbon nanotubes and the nano-optics described in this piece. And eventually? It is entirely possible that we will see Richard Feynman’s 1950s speculation about nanomachines come to fruition, though they are likely to be more like the ‘wet’ machines of nature than a traditional mechanical device.

When nanotechnology appears in the news it is often in a negative light. We might hear that Prince Charles is worrying about the threat of grey goo, or the Soil Association won’t allow artificial nanoparticles in organic products. But the reality is very different. Nanotechnology is both fascinating and immensely valuable in its applications. I, for one, can’t wait to see what comes next.

This series has been sponsored by P2i, a British company that specializes in producing nanoscale water repellent coatings. P2i was founded in 2004 to bring technologies developed at the UK Government’s Defence Science & Technology Laboratory to the commercial market. Applications range from the Aridion coating, applied to mobile technology inside and out after manufacture using a plasma, to protection for filtration media preventing clogging and coatings for trainers that reduce water absorption.

Image from Wikipedia

Sixth in our Nature’s Nanotech series

Anyone who talks to young children about science knows that there are two things that really grab their attention – dinosaurs and space. While I’m not aware of any antediluvian nanotechnology, there is certainly an absolutely stunning potential space application that has some natural inspirations. (I’m aware, by the way, that the word ‘antedeluvian’ is both anachronistic and unscientific… but it’s a lovely word that we really shouldn’t lose from the language.)

Nature has some amazing, extremely fine fibres. Take, for example, that everyday wonder, a spider’s web. The spider silk that makes up the web is a spun fibre constructed from proteins. Though light, these filaments are extremely resistant to fracture – tougher than steel. Spider silk is typically 3,000 nanometers across, but its toughness is down to its structure at the nano level.

A team at MIT discovered that the unusual strength is down to a substructure of ‘beta sheet crystals’, which hold the silk together. The linking is done by hydrogen bonds, the same kind of bonding that stops water from boiling at room temperature. Such bonds are easy to break, but the MIT scientists discovered that if they are confined to spaces just a few nanometers in span – as they are in the beta sheet crystals – they become exceedingly strong. So spider silk depends on a kind of nano-glue for its strength.

In the nanotechnology world, the equivalent of spider silk is the carbon nanotube. We are all familiar with the way carbon comes in different physical structures or ‘allotropes’ that have remarkably different properties. Chemically there is no difference between diamond and the graphite in a pencil ‘lead’ but physically one is extremely hard and the other has multiple planes that slide easily over each other making it effectively soft (although those planes themselves are surprisingly tough).

Another way to fit together a structure of carbon atoms is to form a tube. Imagine taking a plane of graphite a single atom thick (technically graphene) and folding it around to make a tubular shape. Carbon nanotubes are amongst the most amazing artefacts ever made. Though simple in structure, they are remarkable both in their strength and their other physical properties.

Electrically they can behave as if they were a metal or a semiconductor, simply as a result of the shape of the tube. Although carbon nanotube electronics is in its infancy, there is considerable speculation about the capabilities of nanotube products. They could be used to make everything from transistors that are switched by a single electron to batteries built into a sheet of paper. But their pièce de résistance is their strength. Carbon nanotubes make spider silk look like tissue. When you compare a nanotube’s strength per unit weight with steel it comes out around 300 times greater.

All kinds of applications are possible for such a remarkable material. Nanotubes are present in the much thicker carbon fibres used to reinforce everything from tennis rackets to bike frames, but only incidentally and in small quantities. At the moment they tend to be used in random bulk combinations of many small fragments – not as strong as a set of individual aligned nanotubes, but still enough to add strength and to change electrical properties. But one potential application could totally transform the space industry.

Getting things into space is expensive. Hugely expensive. To reach a geosynchronous orbit (of which more later) typically costs around $20,000 per kilogram. But there is a hypothetical nanotube technology that once developed could deliver satellites and even people into space for around 1/100th of this cost. What’s more, rocket technology is inherently risky. You will inevitably lose some of your space missions. Yet the nanotube technology could, once established, run day after day without problem.

Imagine you were sitting on top of a house and wanted to get something up there. You could have someone attach your payload to a rocket and shoot it in your direction. But like the space launch it’s a dangerous and expensive solution. Instead you are more likely to throw a piece of string off the roof, have a basket tied to it and then haul the object up.

Now extend this picture to the Empire State Building. Your piece of string would have to be very strong, which would make it quite heavy to haul up and down, increasing the cost of the process. What might be better is to keep the string (or more likely a piece of metal) in place and have the basket haul itself up and down along the supporting structure.

Time to take another jump into that geosynchronous orbit. An object in orbit is in a very strange state. It is in free fall, dropping towards the Earth – but at the same time it is moving sideways at just the right speed so it always misses. This, incidentally, is why people float around in the International Space Station. It’s not because there’s no gravity – the Earth’s gravitational pull at its height (350 kilometres above the Earth’s surface) is around 90% Earth normal. The astronauts float because they and the station are falling. But they stay in orbit because their sideways motion means they keep missing the planet.

Because of this balance, at any particular height there is one speed that keeps you in orbit. And if you go high enough – around 35,786 kilometres up – that speed is the same as the rotational speed of the Earth, making you geosynchronous. Point the orbit in the right direction and you will stay over the same point on the Earth’s surface (this is a geostationary orbit).

So, imagine you could drop a piece of string from a geostationary satellite down to the ground. You could then just send a lift (elevator) up the string and replace all that dangerous, expensive rocketry. What you’ve got is a space elevator – and to make it work, that string needs to be made from carbon nanotubes.

Of course this is a long way in the future, though a range of companies (including, bizarrely Google) are working on the technology required. There’s no doubt that Bradley Edwards of NASA’s Institute of Advanced Concepts was being over-optimistic when in 2002 he commented ‘[With nanotubes] I’m convinced that the space elevator is practical and doable. In 12 years, we could be launching tons of payload…’ However in a more reasonable timescale – perhaps another 30 or 40 years – it is entirely feasible. And you can’t fault the scope of imagination that allows the inspiration of spider silk to transport us into space.

Next week, in the final piece in the series, we will be learning the lesson of the peacock’s tail and the amazing optics it inspires.

Images from Wikipedia and iStockPhoto.com

Fifth in our Nature’s Nanotech series

Isaac Asimov was a great science fiction writer, but even the best has his off days, and Asimov’s low point was probably his involvement with the dire science fiction movie Fantastic Voyage. Asimov wasn’t responsible for the story, but provided the novelization – and he probably regretted it. The premise of the film was that miniaturization technology has made it possible shrink a submarine and its crew down to around 1,000 nanometres, sending it into a man’s bloodstream to find and destroy a blood clot on his brain.

Along the way the crew have various silly encounters with the body’s systems – but strip away the Hollywood shlock and underneath is an idea that has been developed in a lot more detail by IT pioneer and life extension enthusiast Ray Kurzweil. Based on the idea of miniature robotic devices – nanobots – Kurzweil believes that in the future we will not have a single manned Proteus submarine as featured in Fantastic Voyage in our bloodstreams but rather a whole host of nanobots that will undertake medical functions and keep humans of the future alive indefinitely.

As we have seen in The Importance of Being Wet, the chances are that any such devices would not be a simple miniaturization of existing mechanical robots with their flat metal surfaces and gears, but rather would be based on the wet technology of the natural nanoscale world.

Among the possibilities Kurzweil suggests are on the cards are self-propelling robotic replacements for blood cells (this eliminates the importance of the heart as a pump, and hence the risk of heart disease), built in monitors for any sign of the body drifting away from ideal operation, nanobots that can deliver drugs to control cancer or remove cancer cells, and even miniature robots that make direct repairs to genes.

Kurzweil also expects we might separate the pleasure of eating from getting the nutrients we need, leaving the latter to nanobots in the bloodstream that release the essentials when we need them, while other nano devices remove toxins from the blood and destroy unwanted food without it ever influencing our metabolism. You could pig out on anything you wanted, all day and every day, and never suffer the consequences. (Given Kurzweil is notorious for living on an unpleasant diet to attempt to extend his life until nanotechnology is available, perhaps this is wishful thinking.)

If we are to develop this kind of nanotechnology, there are two aspects of nature that we will need to use as guides. One is to listen to the bees. Bearing in mind just how small a medical nanobot would have to be, even with the best developments in electronics the chances are it would have to be relatively unintelligent – yet it would need to achieve quite complex tasks. Bees are an excellent natural model for a way to achieve this.

A colony of bees achieves remarkable things in the construction and maintenance of its hive – yet taken as individuals, bees have very little capacity for mental activity. The realization that transformed our understanding of bees is that they form a super-organism. In effect, a whole colony is a single organism, not a collection of individual bees. A bee is more like a cell in a typical animal than it is a whole creature. By having appropriate mechanisms for communicating between the component parts – in the case of bees, using everything from chemical scent markers to waggle dances – relatively incapable individuals can come together to make a greater whole.

It would be sensible to expect something similar from medical nanobots at work in a human body. Individually they could not be intelligent enough to carry out their functions properly – but collectively, if they can interact to form a super-organism, they could operate autonomously without an external control mechanism continuously providing them with orders.

A second model for these miniature medics is a piece of natural nanotechnology that we usually regard as a bad guy – the virus. Viruses are very small – typically between 20 and 400 nanometres in size – and they lack many of the essential components of a living entity. However they are able to reproduce and thrive by using a remarkably clever cheat. Lacking the physical space to carry all the components of a living cell, they take over an existing cell in their host and subvert its mechanism to do their reproduction for them.

The particular class of virus that may be particularly useful as a model for medical nanobots is the phage. These are amongst the weirdest looking natural structure – some have an uncanny resemblance of the Apollo Lunar module: they actually look as if they are the sort of nanotechnology we might construct.

The word ‘phage’ is short for bacteriophage – ‘bacteria eater’. These are viruses than instead of preying on human cells – or those of any other large scale animals – attack and destroy bacteria. Because there are so many bacteria out there (even the human body has ten times more bacteria than human cells on board), their predators are also immensely populous and diverse. Phages may not be common fare on David Attenborough’s nature programmes, but they play a major role in the overall biological life of the Earth.

Because phages attack bacteria, they can be beneficial to human life. Throughout human existence we have been plagued with bacterial infections. (Literally – bacteria, for example, cause bubonic plague.) It is only relatively recently that antibiotics have provided us with a miracle cure for bacterial attacks – but that miracle is weakening. Bacteria breed and evolve quickly. There are strains of bacteria that can resist most of the existing antibiotics. But phages have the potential to attack bacteria resistant to all antibiotics. For a long time phage therapy was restricted to the former Soviet Union, but interest is spreading in making use of phages in medical procedures.

The biggest problem with phages is getting them to the right place. But medical nanobots based on a phage’s ability to attack or modify particular cells, combined with a super-organism’s ability to act in a collective manner would have huge potential. Modified viruses are already used to insert genetic payloads into cells – but the nanotechnology of the future, inspired by the phage and the bee, could see something much closer to Kurzweil’s vision.

Moving away from the medical, and from individual nanoscale elements, in the next installment of Nature’s Nanotech we will see how natural nanotechnology plays a role in silk and how fibres based on a nanotechnology structure could make rockets obsolete for putting satellites into space.

Images from iStockPhoto.com

The third in our Nature’s Nanotech series.

If you’ve ever seen gecko walking up a wall, it’s an uncanny experience. Okay, it’s not a 40 kilo golden retriever, but we are still talking about an animal weighing around 70 grams that can suspend itself from a smooth wall as if it were a fly. For a gecko, even a surface like glass presents no problems. This is nature’s Spiderman.

It might be reasonable to assume that the gecko’s gravity defying feats were down to sucker cups on its feet, a bit like a lizard version of a squid, but the reality is much more interesting. Take a look at a gecko’s toes and you’ll see a series of horizontal pads called setae. Seen close up they look like collections of hairs, but in fact they are the confusingly named ‘processes’ – very thin extensions of the tissue of toe which branch out into vast numbers of nanometer scale bristles.

These tiny projections add up to a huge surface area that is in contact with the wall or other surface the gecko decides to encounter. And that’s the secret of their glue-free adhesion. Because the gecko’s setae are ideally structured to make the most of the van der Waals force. This is a quantum effect resulting from interaction between molecules in the gecko’s foot and the surface.

We are used to atoms being attracted to each other by the electromagnetic force between different charged particles. So, for example, water molecules are attracted to each other by the hydrogen bonding we saw producing spherical water droplets in the previous feature. The relative positive charge on one of the hydrogen atoms is attracted to the relative negative charge on an oxygen. But the van der Waals force is a result of additional attraction after the usual forces that bond atoms together in molecules and hydrogen bonding have been accounted for.

Because of the strange quantum motion of electrons around the outside of an atom, the charge at any point undergoes small fluctuations – van der Waals forces arise when these fluctuations pair up with opposite fluctuations in a nearby atom. The result is a tiny attraction between each of the nanoscale protrusions on the foot and the nearby surface, which add up over the whole of the foot to provide enough force to keep the gecko in place.

Remarkably, if every single protrusion on a typical gecko’s foot was simultaneously in contact with a surface it could keep a heavy human in place – up to around 133 kg. In fact the biggest problem a gecko has is not staying on a surface, but getting its foot off. To make this possible its toes are jointed unusually and it seems to secrete a lubricating fluid that makes it easier to detach its otherwise dry but sticky pads.

Not surprisingly, there is a lot of interest in making use of gecko-style technology. After all, master this approach and you have a form of adhesion that is extremely powerful, yet doesn’t deteriorate with repeated attaching and detaching like a conventional adhesive. A number of universities have been researching the subject.

The first publication seems to have been from the University of Akron in Ohio, where a paper in 2007 described a gecko technology sticky tape with four times the sticking power of a gecko’s foot, meaning fully deployed gecko-sized pads could hold up around half a tonne. With these on its feet, a 40 kilogram golden retriever would have no problem walking up walls – the only difficulty would be managing to apply enough force to detach its paws as it walked. In the tape, the gecko’s setae are replaced by nanotubes of carbon fibre which are attached to a sheet of flexible polymer, acting as the tape.

The great thing about carbon nanotubes, which are effectively long, thin, flexible carbon crystals, is that they can be significantly narrower than the smallest protrusions from a gecko’s foot. A typical nanotube has a diameter of a single nanometer – pure nanotechnology – maximising the opportunity for van der Waals attraction. Within a year, other researchers at the University of Dayton (Ohio again!) were announcing a glue with ten times the sticking power of the gecko’s foot.

Such adhesives are available commercially on a small scale, offering the ability to stick under extreme temperature conditions and to surfaces that are wet or flexible that would defeat practically any conventional adhesive. We can expect to see a lot more gecko tapes (like the Geckskin product) and gecko glues in the future.

There have been other theories to explain the mechanism of the gecko’s foot, including a form of capillary attraction, but the best evidence at the moment is in favour of van der Waals forces. This seems to be borne out by the problem geckos have sticking to Teflon – PTFE has very low van der Waals attractiveness. To find out more about the gecko’s foot (and other technological inspirations from nature) I would recommend the aptly titled The Gecko’s Foot by Peter Forbes.

The action that keeps a gecko in place is a dry application of natural nanotechnology, but the more you look at the nanotech biological world, the more you realize it’s mostly a wet world. In the next feature in this series we’ll look at why conventional ‘dry’ engineering often won’t work on nanoscales and how we need to take a different look at the way we build our technology, bringing liquids into the mix.

Image from Wikipedia

The second in our Nature’s Nanotech series.

Living things are built on hidden nanotechnology components, but sometimes that technology achieves remarkable things in a very visible way. A great example is the ‘lotus leaf effect.’ This is named after the sacred lotus, the Nelumbo nucifera, an Asian plant that looks a little like a water lily. The plant’s leaves often emerge into the air covered in sticky mud, but when water runs over them they are self cleaning – the mud runs off, leaving a bare leaf exposed to the sunlight.

Water on a Lotus leaf – image from Wikipedia

Other plants have since been discovered to have a similar lotus leaf effect, including the nasturtium, the taro and the prickly pear cactus. Seen close up, the leaves of the sacred lotus are covered in a series of tiny protrusions, like a bad case of goose bumps. A combination of the shape of these projections and a covering of wax makes the surface hydrophobic. This literally means that it fears water, but more accurately, the leaf refuses to get too intimate with the liquid. This shouldn’t be confused with hydrophobia, a term for rabies!

Water is naturally pulled into droplets by the hydrogen bonding that links its molecules and ensures that this essential liquid for life exists on the Earth (without hydrogen bonding, water would boil at around -70 Celsius). This attraction is why raindrops are spherical. They aren’t teardrop shaped as they are often portrayed. Left to their own devices, water drops are spherical because the force of the hydrogen bonding pulls all the molecules in towards each other, but there is no equivalent outward force, so the water naturally forms a sphere.

The surface of the lotus leaf helps water stay in that spherical form, rather than spreading out and wetting the leaf. The result is that the water rolls off, carrying dirt with it, rather like an avalanche picking up rocks as it passes by. Because of the shape of the surface pimples on the leaf, known as papillae, particles of dirt do not stick to the surface well, but instead are more likely to stick to the rolling droplets and be carried away. As well as letting the light through to enable photosynthesis, this effect is beneficial to the leaves as it protects them against incursion by fungi and other predatory growths.

Although the papillae themselves can be as large as 20,000 nanometres tall, the effectiveness of these bumps is in their nanoscale structure, with multiple tiny nobbly bits that reduce the amount of contact area the water has with the surface to a tiny percentage. After the effect was discovered in the 1960s, it seemed inevitable that industry would make use of it and there have been several remarkable applications.

One example that is often used is self-cleaning glass – which seems very reasonable as the requirement is identical to the needs of the lotus leaf – yet strangely, what is used here is entirely different. Pilkington, the British company that invented the float glass process, has such a glass product known as Activ. This has a photo-catalytic material on its surface that helps daylight to break down dirt into small particles, but it also has a surface coating that works in the opposite way to the lotus leaf. It’s an anti-lotus leaf effect.

The coating on this glass, a nanoscale thin film, is hydrophilic rather than hydrophobic. Instead of encouraging water to form into droplets that roll over the glass picking up the dirt as they go, this technology encourages water to slide over the surface in a sheet, sluicing the dirt away. In practice this works best with heavy rainfall, where the lotus effect is better at cleaning surfaces with less of a downpour – but both involve nanoscale modification of the surface to change the way that water molecules interact.

Increasingly now, though, we are seeing true lotus leaf effect inspired products, that make objects hydrophobic. A process like P2i’s Aridion technology applies a nano-scale coating of a fluoro-polymer that keeps water in droplets. The most impressive aspect of this technology is just how flexible it is. Originally used to protect soldiers clothing against chemical attack , the coatings are now being applied to electronic equipment like smartphones, where internal and external components are coated to make them hydrophobic, as well as lifestyle products such as footwear, gloves and hats. Working like self-cleaning glass would be disastrous here. The whole point is to keep the water off the substance, not to get it wetter.

We are really only just starting to see the applications of the lotus leaf effect come to full fruition. For now it is something of a rarity. Arguably it will become as common for a product to have a protective coating as it for it to be coloured with a dye or paint. Particularly for those of us who live in wet climates like the UK, it is hard to see why you wouldn’t want anything you use outdoors to shrug water off easily. I know there have been plenty of times when I have been worriedly rubbing my phone dry on my shirt that I would have loved the lotus leaf effect to have come to my rescue.

Seeing nanotechnology at work in the natural world doesn’t have to help us come up with new products. It could just be a way of understanding better how a remarkable natural phenomenon takes place. In the next article in this series I will be looking at a mystery that was unlocked with a better understanding of nature’s nanotech – but one that also has significant commercial implications. How does a gecko cling on to apparently smooth walls?

When we think of nanotechnology, it’s easy to jump to the conclusion that we are dealing with the ultimate in artificial manufacturing, the diametric opposite of something that’s natural. Yet in practice, nature is built on nanotechnology. From the day-to-day workings of the components of every single biological cell to the subtle optics of a peacock feather, what we see is nanotechnology at work.

Not only are the very building blocks of nature nanoscale, but natural nanotechnology is a magnificent inspiration for ways to make use of the microscopic to change our lives and environment for the better. By studying how very small things work in the natural world we can invent remarkable new products – and this feature is the first in a series that will explore just how much we can learn and gain from nature’s nanotech.

As I described in The Nanotechnology Myth the term ‘nanotechnology’ originates from the prefix nano- which is simply a billionth. Nanotechnology makes use of objects on the scale of a few nanometres, where a nanometre is a millionth of a millimetre. For comparison, a human hair is around 50,000 nanometres across. Nanotechnology encompasses objects that vary in size from a large molecule to a virus. A bacterium, typically around 1,000 nanometres in size, is around the upper limit of nanoscale items.

A first essential is to understand that although nanotechnology, like chemistry, is involved in the interaction of very small components of matter, it is entirely different from a chemical reaction. Chemistry is about the way those components join together and break apart. Nanotechnology is primarily about their physics – how the components interact. If we think of the analogy of making a bicycle, the ‘chemistry’ of the bicycle is how the individual components bolt together, the ‘nanotechnology’ is how, for example, the gear interacts with the chain or pushing the pedals makes the bike go.

This distinction is necessary to get over the concern some people raise about nature and nanotechnology. A while ago, when I wrote my book on environmental truth and lies, Ecologic, I had a strange argument with a representative of the Soil Association, the UK’s primary organic body. In 2008 the Soil Association banned nanoparticles from their products. But it only banned man-made nanoparticles, claiming that natural ones, like soot, are fine ‘because life has evolved with these.

This is a total misunderstanding of the science. If there are any issues with nanotechnology they are about the physics, not the chemistry of the substance – and there is no sensible physical distinction between a natural nanoparticle and an artificial one. In the case of the Soil Association, the reasoning was revealed when they admitted that they take ‘a principles-based regulatory approach, rather than a case-by-case approach based on scientific information.’ In other words their opposition was a knee-jerk one to words like ‘natural’ and ‘artificial’ rather than based on substance.

Of themselves, like anything else, nanoparticles and nanotechnology in general can be used for bad or for good. Whether natural or artificial they have benefits and disadvantages. A virus, for example, is a purely natural nanotechnology that can be devastatingly destructive to living things. And as we will see, there are plenty of artificial nanotechnologies that bring huge benefits.

In nature, nanotechnology is constructed from large molecules. A molecule is nothing more than a collection of atoms, bonded together to form a structure, which can be as simple as a sodium chloride molecule – one atom each of the elements sodium and chlorine – or as complex as the dual helix of DNA. We don’t always appreciate how significant individual molecules are.

I had a good example of this a few days ago when I helped judge a competition run by the University of the West of England for school teams producing science videos. The topic they were given was the human genome – and the result was a set of very varied videos, some showing a surprising amount of talent. At the awards event I was giving a quick talk to the participants, looking at the essentials of a good science video. I pointed out that they had used a lot of jargon without explaining it – a common enough fault even in mainstream TV science.

Just to highlight this, I picked out a term most of them had used, but none had explained – chromosomes. What, I asked them was a chromosome? They told me what it did, but didn’t know what it was, except that it was a chunk of DNA and each human had 46 of them in most of their cells. This is true, but misses the big point. A chromosome is simply a single molecule of DNA. Nothing more, nothing less. One molecule.

Admittedly a chromosome is a very large molecule. Human chromosome 1 is the biggest molecule we know of, with around 10 billion atoms. Makes salt look a bit feeble. But it is still a molecule. The basic components of the biological mechanisms of everything living, up to an including human beings are molecules. Chromosomes provide one example, effectively information storage molecules with genes as chunks of information strung along a strip of DNA. Then there are proteins, the workhorses of the body. There are neurotransmitters and enzymes, and a whole host of molecules that are the equivalent of gears to the body’s magnificent clockwork. These are the building blocks of natural nanotechnology.

So with a picture of what we’re dealing with we can set out to see nature’s nanotech in action and the first example, in the next feature in this series, will show how nanotechnology on the surface of a leaf has inspired both self-cleaning glass and water resistant trainers.