Pointing out how fingerprints help us feel fine details

In a piece of true science detective work, researchers at the Laboratoire de Physique Statistique in Paris have found another reason why we have fingerprints.

It’s been known for a while that the distinctive ridges on the pads of our fingers help us to grip things, but now Julien Schiebert and colleagues have shown that fingerprints also help us to feel fine textures and tiny objects, less that 200 micrometers, through vibrations.

Writing in the journal Science, they developed a special mechanical sensor which is fitted with a rubbery cap to act like a fingertip.  Using either smooth caps, or ones ridged to simulate fingerprints, they rubbed their artificial finger across finely textured surfaces.

They found that the cap with a ‘fingerprint’ was made to vibrate by the contact, at a frequency of around 250Hz, that’s 250 vibrations per second.  This coincides with the sensitive range of a type of nerve endings found in the skin, called “Pacinian corpuscles”.

Two types of nerve ending are known to be involved in detecting texture, slow reacting nerves are responsible for identifying relatively coarse textures by detecting different pressures at different places on the skin, while fine details are reported by the Pacinian nerve endings.

They have only tested this with a series of straight, parallel ridges, so not exactly the same as the swirly lines of our fingerprints, but their findings suggest that our fingerprints actually fine tune the vibrations, selectively amplifying certain frequencies to ensure our nerves can pick up the fine details.

1st Feb 2009

Implanted Electronics and Artificial Skin

Kat - We’re joined by Stephanie Lacour from the Cambridge Nanoscience Centre where she’s working on making flexible electronics that could be worn over your skin or maybe even under your skin. Hello, Stephanie. Thanks for coming on the show. Tell us about your aim. What’s the issue that you’re trying to address?

Stephanie - What we’re trying to do is to interface electronic components with the human body. One of the challenges is that conventional electronics is typically made on very hard and flat surfaces. If you look at our own body we are a 3D object that is moving all around. The challenge is not only electrical but also mechanical because we need to find ways to make electronic things that can conform the body and therefore use materials that are no longer hard and brittle but materials that can be elastic, similar to our own skin, for example.

Kat - A kind of bionic man-type thing?

Stephanie - Yeah, I was thinking about the six million dollar man, basically.

Kat - What are the sort of challenges? What do you need to make electronics do to make them like skin?

Stephanie - There are two challenges. The first one is to find ways to put electronic components onto a substrate that is very soft. The electronic processes that are available today are usually using fairly high temperature deposits using material. The substrate we’re using to make skin-like devices are polymers. In particular we’re working with materials called elastomers.

Kat - So they’re very bendy?

Stephanie - It’s like a rubber band material. These materials don’t withstand very high temperature. We need to find processes to deposit the device material at very low temperatures, specifically below 150 degrees C. That’s one challenge. Once we’ve found a way to deposit this material directly on the soft material we have to find a good design or overall architecture for the system so that the electronics can withstand the mechanical deformation. It’s one thing to actually deposit the materials onto the substrate but we also want to make sure the transistor is still working when there’s cooling onto the transistor.

Kat - Because obviously transistors are made of things like silicon and you don’t think of that as very flexible. How are you trying to get round this problem?

Stephanie - The approach we’re following is to distribute onto the very soft substrate tiny platforms that would be rigid. This tiny platform would host a very fragile material like the silicon for the transistors. Once you have this pig cell structure all across the elastomer we would need to use very elastic interconnects to connect one platform to the other so they can talk together. What we found a few years ago – I found a way to make stretchable metal. By depositing very thin layers of gold directly into an elastomer on a rubber band I found that I can stretch it up to twice its length and it will not fade electrically. From there we’ve decided to push forward the technology and use these stretchable metals as interconnects for the electronics.

Kat - Basically, you’ve got an elastic band covered in gold with all these little transistors studded into it. They’ll communicate with each other?

Stephanie - Yes, exactly.

Kat - What sort of applications do you see for this kind of technology?

Stephanie - I’m particularly interested in interfacing with the human body. There is a lot of application in biomedical research. One particular project we’re looking at is how to make prosthetic skin. The skin of a patient who’s lost a limb, for example, they could wear this like a glove. They could wear this on top of the prosthetic limb and the skin would allow them to get some sensory feedback which is not possible today.

Kat - So they’d be able to feel how hard they were touching something or how hot and cold they were?

Stephanie - Exactly. We’re trying to implement various sensors directly onto this rubbery substrate like temperature or touch sensors so that we can mimic sensory function that is embedded in our own skin.

Kat - how are things going at the moment? What sort of stage are we at?

Stephanie - We’re at the very first stage. At the moment we’re really evaluating the technology to make these. We know how to make stretchable metal so we’re investigating how we can implement this to make touch sensors. This is where we’re pretty much in the sensing at the moment. We’re also evaluating how to make the transistors directly onto this rubbery substrate with a platform. We’re just starting so this is where we’re at.

Kat - Presumably a big issue is trying to make all this electronics talk to the human brain. It is nerves and electrical impulses.

 Stephanie - Right. This is the second aspect of the project. In my group we’re looking at ways to make these prosthetic skins but there’s also this application where we’re looking at a way to use these very soft electronic devices to interface everything with the nervous system. Because the human body and particularly the nervous system is made of extremely compliant material we cannot use a silicon chip to interface directly with your nerve for a long time. What we’re doing is to use this polymer and elastomer substrate with embedded electrodes in it to connect directly with a peripheral nerve – so a nerve which is in the limb, not in the spinal cord or the brain - really in the limb, from the electrical signal from the neurons. Once we can do that then the idea would be to connect these peripheral implant directly to the prosthetic skin so that we could take the signals  that are coming out of the prosthetic skin and convert them into a neuron format and feed that directly into the implant which would then communicate to the nerve and back to the brain.

Kat - It sounds like exciting stuff. Presumably you have a multidisciplinary team so you have to bring a lot of different people together. What sort of range of scientists are working on this kind of technology?

Stephanie - I’m an electrical engineer by training but in the team we have people who are material scientists, biophysicists and neurosurgeons. Particularly for the project onto the peripheral implant I’m working with lots of people in Cambridge and a couple of other universities in the UK – it’s extremely important to collaborate between engineers  and the medical field. Without good collaboration we could not do that.

Kat - And when do you think we might see the bionic man?

Stephanie - Not tomorrow! It will take quite a long time. Surely along the way we’ll have some devices where you’ll have for clinical application but for the final project it could be 25 years or so.

February 2009

Writing the world’s smallest letters

Keeping with our theme of nanotechnology this week, researchers at Stanford University in the States have managed to write the smallest letters ever – assembled from subatomic particles just 0.3 nanometres in size.  The researchers are particularly pleased with their achievement, because it was Stanford scientists that first created the world’s smallest writing in 1985, but lost the record in 1990 to IBM, when they famously arranged xenon atoms to spell out the company’s name. Now they have it back.

But how did they do it? The researchers encoded the letters "S" and "U" (standing for Stanford University) by using the interference pattern of electron waves on the surface of a film of copper. The technique actually projects a tiny hologram of the letters, which can only be seen using a very powerful microscope.

Writing about their work in the journal Nature Nanotechnology, the Stanford team’s letters are more than four times smaller than the IBM initials, and were created using a scanning tunnelling microscope, which can be used to push atoms around. The scientists used it to put individual molecules of carbon monoxide in a special pattern on a film of copper the size of a fingernail.

Electrons are constantly whizzing around on the copper, because it is a metal. And because electrons can act as waves, as well as the more traditional view that they are   particles, the electron waves get shaped by the carbon monoxide, and interfere with each other like ripples in a pond. These interference patterns depend on the position of the carbon monoxide molecules on the copper surface. So eventually they create a consistent pattern that can be read, like a molecular hologram.

It all sounds quite nerdy, but the technique could be very important for the future of computing, as it would enable information to be stored at a very high density in small chips. For example, the researchers could create different holograms on the same chip by using different electron wavelengths, increasing the amount of information that can be stored, and pushing it beyond current boundaries.

1st Feb 2009

Mob rule to scare away cuckoos

Researchers studying Reed warblers have found out that mob rule can avoid being cuckolded by cuckoos.

Cuckoos live a parasitic lifestyle – laying eggs in the nest of other birds and letting them spend their time and resources bringing up their young.  From an evolutionary perspective, it’s a good trick if you can get away with it, but if you’re the victim you’re wasting your own resources on someone else’s DNA.

Writing in Current Biology, Cambridge University researcher Nick Davies reports on how Reed Warblers use mobbing techniques to keep the parasitic cuckoos away from their nests.

Mobbing is a risky strategy – it’s energy intensive and it exposes you to predators, and may not prevent the cuckoo from getting through.  Worse still, sometimes they mistakenly mob a sparrowhawk, which looks a bit like a cuckoo and actually prays on reed warblers.

Some birds would save their energy, and just reject any eggs that don’t look like their own, but the cuckoos have evolved to be able to lay ‘mimic’ eggs which look similar, establishing an evolutionary arms race between parasite and host.

By placing model cuckoos near the reed warbler’s egg-bearing nests, Davies and colleagues could observe how the warblers attempted to defend their nests.  About half the time, the warblers became aggressive and attempted to mob the cuckoos.  In the high risk areas, this made them far less likely to be subject to a cuckoo visit than their more peaceful neighbours.

Significantly, in areas where the Warblers were at much lower risk of being parasitized, they were far less likely to show this mobbing behavior – in fact, in those areas mobbing was likely to attract cuckoos, rather than scare them away

Reed warblers also reserved mobbing behavior only for cuckoos, showing that they adapt their nest defense strategy according to their conditions, not unlike our own military!

1st Feb 2009

Turning up the heat on cereal genome

It’s clear that the global climate is changing, and this is having a big impact on food supplies.  For example, if the climate changes in a major crop-growing region, it may not be possible to grow that crop successfully any more. So scientists are investigating whether people living in dry regions – that are only getting drier – can grow alternatives to wheat and other food crops.

One such alternative is a plant called sorghum. This is a type of grass that originally came from Africa, and it grows well under hot and dry conditions.  Now farmers in warm parts of America, Asia and Europe are growing sorghum for food and animal fodder, as well as for using in biofuels.  Not only that, but it can be burnt to provide energy.

It sounds like an all-round wonder-plant, and in order to uncover the secrets to its versatility and hardiness, researchers in Munich have analysed the whole sorghum genome. This is the first time the genome of a plant of African origin has been sequenced.

Publishing their results in the latest issue of the journal Nature, the scientists say that their results will help us understand more about how plants like sorghum resist drought and high temperatures, and could help with the development of hardier versions of other crops in the future.

And the new data will also enable researchers to compare the genome of sorghum with rice and maize, two important crop plants that have had their genomes sequenced. This will tell us a lot about how crop plants evolve, and the genes that give them their specific properties.

1st Feb 2009

New LEDs to Slash household bills

Ben - There's a new way to make LEDs and this could slash household lighting bills and help to make clean drinking water accessible to everybody.  Professor Colin Humphreys from the University of Cambridge joins us now on the line. Hi, Colin.

Colin - Hi.

Ben - Tell us a bit about this. We’ve had LEDs for a long time. They are already turning up in torches, in home lighting. What’s the new method that you’ve got?

Colin - They’ve been around for some time. They’re not really in home and office lighting and the reason is they’re too expensive. All the LEDs you can buy in the shops now are grown on a sapphire substrate and sapphire is quite expensive. What we’ve done is to develop a method for growing these LEDs on a silicon substrate. In fact we’re growing them on a six inch substrate wafer instead of on a two inch sapphire wafer. That’s going to be bringing costs down by a factor of ten or so, a really big reduction.

Ben - Wow. These LEDs are very energy efficient, I understand. How will it compare to a normal incandescent light bulb?

Colin - They’re very energy efficient and they’re really going to help global warming. In fact, they’ll help it much more than wind power will. In terms of an incandescent light bulb we’re aiming to be twelve times as efficient as a tungsten light bulb and we’re aiming to be 3 times as efficient as a low energy light bulb. Already they’re more efficient than a low energy light bulb.

Ben - Is that for the same brightness as well?

Colin - That’s for the same brightness, absolutely. We want to make them better quality and better bright light than the low energy bright light ones, which as you know are not very popular. They’re a popular cause for divorce in the country now, I’m told, low energy light bulbs!

Ben - Hopefully your gallium nitride LED light won’t be a cause for divorce but I’ve also heard these could be used to make clean drinking water. I understand what you can do with these is make ultraviolet light.

Colin - That’s right so the light emission from the gallium nitride – we actually add some indium to it to get visible light emission. If you add aluminium you can get deep ultraviolet. Deep ultraviolet has certain wavelengths, it’s about 270nm. It destroys the nucleic acid in both DNA and RNA and it stops viruses and bacteria from reproducing so it effectively kills them. If we can make LEDs that emit this deep UV we can kill all known viruses, all known bacteria and you could put a ring of these LEDs on the inside of a water pipe coming into a home in the third world. Water riddled with bacteria and viruses, you can make it harmless. Also it could be useful for our country as well, particularly for third world people.

Ben - And we could use them in hospitals as well to ensure things are sterile without having to go through the chemical cleansing that we do now. As they are so efficient does this mean we can set this up with a solar panel and make this water purification very portable?

Colin - Absolutely. That’s absolutely right. These are very efficient. They’ll run of 4 volts, which is ideal for a solar panel, you have a solar panel and a battery connected as well if you like and then have these connected to that. You have these for lighting in the developing world but also for water purification in the developing world.

Ben - These sound fantastic but what’s different about gallium nitride that allows us to make this seemingly wider range of frequencies? If we can make UV that we couldn’t before. Why is gallium nitride so special?

Colin - Gallium nitride’s called a wideband gap semiconductor. Before it came along the only light emission which you get from semiconductors was in the infrared and in the red and rather weakly in the green and the yellow. Silicon doesn’t emit light anyway. Gallium arsenide emits light and indium phosphate but they’re narrow band gap materials. If it’s a much wider band gap material, gallium nitride itself emits near ultraviolet and then there’s another material called indium nitride which emits in the infrared. If you mix those two together you can get any energy you want from the near-infrared going right through the visible spectrum to near-ultraviolet. If you add some aluminium to it you can go really into deep ultraviolet. This is a new material system. It’s man-made. It can cover this range of the electro-magnetic spectrum that we’ve never had before form a solid state semiconductor.

Ben - This sounds quite incredible. When should we expect to see these on the market?

Colin - For the home and office lighting –scientists always predict thing will happen before they’re going to happen! I think within the next five years, certainly. Maybe two or three years. The UV problem is more difficult to solve. We’ve already got the right wavelength being emitted but the intensity at the moment is too low. We’ve got to push up that intensity. I think realistically that may be 5-10 years. I really believe it’s going to happen.

Ben - Clearly getting clean and drinkable water to everyone in the world is going to be a challenge and I suspect unfortunately it will still be a challenge in those 5-10 years. Good luck, I hope we get them to market as soon as possible!

February 2009

Silver from soot

Convert normal soot into a beautiful silvery substance using just a candle, some water and a mug...

What you need

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