March 4, 2011 10:13 pm

Need human tissue? Just press print

Biological engineers are adapting the latest manufacturing technology, three-dimensional printing, to make living tissues for wound repair and organ transplants.

Bioprinting, as it is known, is already being tested in animals for simple applications, such as skin to treat burns victims and cartilage for knee replacements.

The technology is an extension of ink-jet printing. The computer-guided printing head directs tiny droplets containing living cells, immersed in a biocompatible ink, into a 3D representation of the desired tissue.

The tissue can either be bioprinted directly onto the patient’s body or made outside the body and then transplanted into the patient. The AAAS meeting heard from proponents of both approaches.

Hod Lipson of Cornell University, New York, is making meniscus cartilage outside the body for transplanting into the knee. The process, which is being tested in animals, involves printing cartilage cells in the correct C-shape, and then incubating them in cell culture while they make collagen, the tough fibrous protein that holds the meniscus together. Another team at Cornell, led by Jonathan Butcher, is bioprinting heart valves.

“We started with cartilage tissue because it is relatively simple, amorphous and does not have a lot of vasculature [blood vessels]. That is the entry-level point to start with,” says Lipson. “From there, we will climb the complexity of tissue, going on to bone and perhaps liver.”

But, he adds, “there are severe limitations on what we can do. We are limited to cells that can handle being printed, which involves severe stress, and the ink or gel in which they are printed provides another set of constraints.”

In contrast, James Yoo and colleagues at Wake Forest University, North Carolina, plan to bioprint skin directly onto the wounds of burns victims. “Our system has a scanner to identify the extent and depth of the wound,” he says. “The scan is converted into 3D digital images, which enable us to identify how many layers of skin are needed to restore the tissue.”

Yoo’s team is developing a mobile bioprinter for the US army to treat soldiers in the field, covering a large wound or burn within minutes. “Up to 30 per cent of injuries and casualties that occur in war involve the skin,” he says.

How long bioprinting will take to reach the clinic depends on regulatory as well as scientific and medical factors. Lipson estimates five to 10 years for simple tissues. More complex applications, such as bioprinting brain cells, are decades away – or science fiction.

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Members of an Amazonian tribe

Some Amazonian tribes cannot express numbers greater than three

Three can be a crowd for hunter-gatherers

Learning to count and then manipulate numbers is so much a part of life that it is hard to imagine modern human existence without numerals. Yet many hunter-gatherer languages have no words for numbers beyond two or three.

The US National Science Foundation is funding a large programme to study the world’s 600 or so remaining hunter-gatherer languages before they disappear.

Part of the project focuses on numbers. A survey of 359 tribal languages spoken in north and south America and Australia, which remain essentially the same as before European contact, has found very limited counting systems in Australia, great numerical diversity in south America and more elaborate systems among the native Americans of California and the Great Basin.

At least 29 Australian and nine Amazonian languages have no words for precise numbers greater than two or three. Many more stop at four. For larger quantities, speakers use vague terms, roughly equivalent to few, several or many. No Aboriginal language in Australia has a way to denote numbers above 20.

Most south American languages have an upper limit below 10, though a small minority have documented terms extending into the hundreds or even thousands. All north American native languages have an upper limit above 10 and almost half go above 100.

Patience Epps of the University of Texas, Austin, the project leader, says the etymological sources for numerals provide a fascinating insight into the way a language may take the first steps towards a counting system.

Terms for one are often related from words meaning alone. The favourite source for two is “eyes”. Sources for three include “rubber-tree seed” (which is three-lobed), “rhea bird footprint” (which is three-toed) and “pot-support stones” (which form a tripod shape).

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A bat returns to its roosting cave

A bat returns to its roosting cave

Weather radar: it’s raining bats and dogs

The weather radar networks built across north America and Europe have given birth to a new biological discipline: aeroecology. Although the radar system was designed for raindrops and snowflakes, it can also detect flying insects, birds and bats. For meteorologists their signals are unwanted “bioscatter” to filter out, but biologists have recently realised that they present a new opportunity to study the flight of creatures too small and too numerous to track with satellite radio transmitters.

Thomas Kunz, biology professor at Boston University who coined the term aeroecology two years ago, sees it as a discipline studying creatures that live predominantly in the air, just as marine biology studies life in the oceans.

“Radar is the only tool that makes it possible to track animals in the aerosphere,” he says. But aeroecology makes use of other technologies too, such as thermal imaging of creatures in flight.

The US has about 160 weather radar stations and Europe 200 – all potential sources of aeroecology data. They can be supplemented with observations from smaller portable radar sets.

The technology has so far been used particularly to track bats. Winifred Frick of the University of California, Santa Cruz, has seen bats following weather fronts, in order to feast on the insects caught up in the mixing zone between different air masses. And she has observed that bats emerge from their roosting caves earlier in the day during dry weather than during wet spells.

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Nasa’s cosmic census shows signs of life

A plethora of planets around distant stars is emerging from the first cosmic census conducted by Nasa’s Kepler space observatory. Astronomers are surprised by the quantity and the variety of planets that Kepler has spotted in its first year. William Borucki, the mission’s principal investigator, says the preliminary results suggest that about half the stars in our galaxy have at least one planet; that would give a galactic total of hundreds of billions of planets.

The estimate is an extrapolation of Kepler’s work so far, surveying a tiny fraction of the sky, which has thrown up 1,235 likely planets. Of these, 54 are in their parent star’s “habitable zone” where temperatures might be suitable for life as we know it.

Kepler detects planets indirectly by measuring decreases in the brightness of stars as planets “transit” in front of them. It is too soon for Kepler to have detected any Earth-sized planets in Earth-like orbits because they would transit about once a year – and the astronomers require three transits to locate and verify each detection.

The biggest surprise so far, apart from the sheer number of planets, is how many of them are in multiple planetary systems, orbiting their parent star in a very flat “co-planar” arrangement.

Although our solar system is quite flat, it is not planar enough for more than one planet to show up if a hypothetical observer elsewhere in the galaxy were looking for transits across the face of the sun with a Kepler-like telescope.

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