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Glass steaks

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Nature reports:

Mark Post has never been tempted to taste the ‘fake’ pork that he grows in his lab. As far as he knows, the only person who has swallowed a strip of the pale, limp muscle tissue is a Russian TV journalist who visited the lab this year to film its work. “He just took it with tweezers out of the culture dish and stuffed it in his mouth before I could say anything,” says Post. “He said it was chewy and tasteless.”

Post, who works at the Eindhoven University of Technology in the Netherlands, is at the leading edge of efforts to make in vitro meat by growing animal muscle cells in a dish.

The prospect of an alternative to slaughtering animals led People for the Ethical Treatment of Animals based in Norfolk, Virginia, to announce two years ago a US$1-million prize for the first company to bring synthetic chicken meat to stores in at least six US states by 2016. In the Netherlands, where the vast majority of work has been done so far, a consortium of researchers convinced the government to grant them £2 million (US$2.6 million) between 2005 and 2009 for developing in vitro meat.

Such incentives have helped to solve some of the basic challenges, applying human tissue-engineering techniques to isolate adult stem cells from muscle, amplify them in culture and fuse them into centimetre-long strips. But far more money and momentum will be needed to make in vitro meat efficient to produce, cheap and supermarket-friendly

Embryonic stem cells would provide an immortal (and therefore cheap) stock from which to grow endless supplies of meat. But attempts to produce embryonic stem cells from farm animals have not been successful. Most work so far has been on myosatellite cells, the adult stem cells that are responsible for muscle growth and repair.

The fundamental problem is that myosatellite cells will only divide dozens of times, probably because their telomeres — the protective ends of the chromosomes — wear down with age. There are ways of boosting their proliferation. One is to add a gene for the repair enzyme telomerase. Another, being investigated by the start-up company Mokshagundam Biotechnologies in Palo Alto, California, involves inserting a tumour-growth-promoting gene. But genetically modified lab-grown meat might be too much for consumers to swallow.

Myosatellite cells grown on a scaffold will fuse into myofibres, which then bundle together to make up muscle. But lab-assembled muscles are weak and textureless. “It’s like when you take off a cast after six weeks,” says Post. To get the muscle to bulk up with protein requires exercise. Assembling the myofibres between anchor points helps, as this creates a natural tension for the muscle to flex against. Post uses this type of arrangement to boost the protein content of a muscle strip from 100 milligrams to about 800 milligrams over a few weeks. He also administers 10-volt shocks every second, which can bump protein content up to about a gram. This much electricity would be expensive in a scaled-up industrial process, so his group is hoping to learn how to mimic chemical signals that tell muscles to contract.

Vladimir Mironov of the Medical University of South Carolina in Charleston is instead using a scaffold made of chitosan microbeads — chitosan can be sourced from crabs or fungi — that expand and contract with temperature swings, thus making a natural fitness centre for his muscle strips.

If lab-grown muscle gets more than about 200 micrometres thick, cells in the interior start to die as they become starved of nutrients and oxygen. Post simply grows many small strips that could be ground up into a sausage. Others, including Mironov, are using blender-sized bioreactors of the type developed by NASA to study muscle growth in low gravity. These conditions help prevent cell clumping and improve transport of oxygen and nutrients.

Growing meat on an industrial scale would require large, customized bioreactors like those used by biopharmaceutical companies. Mironov estimates that a commercial in vitro meat facility would need a five-storey building of bioreactors; with a similarly huge investment. And all that is just for manufacturing ground meat. The prospect of growing steaks is a much bigger challenge, requiring a system of fake ‘blood vessels’ built into the meat. That is decades away.

So why is this article creating such a buzz in the science pages of newspapers? After all there is no dearth of real science stories. Could it be the dearth of real science reporters?

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