麻豆传媒

DINNER party recipes don鈥檛 come much weirder than this. Working in a tissue culture lab installed in a French art gallery, conceptual artists Oron Catts, Ionat Zurr and Guy Ben Ary will lovingly coax frog muscle precursor cells to grow into a miniature frog steak. Each day, the artists will 鈥渇eed the food鈥�; giving nutrients to the growing steak as well as feeding some live frogs displayed alongside. The pi猫ce de r茅sistance will be a 鈥渇east鈥�, where the artists, clad in grey chef鈥檚 uniforms, fry the steak and serve it on a table decked with silver cutlery and crystal goblets. There, watched curiously by an entourage of ribbiting frogs, they will solemnly eat it.

鈥淒isembodied Cuisine鈥� opens at France鈥檚 National Culture Centre in Nantes in March next year as an exploration of 鈥渧ictimless鈥� meat consumption. It鈥檚 a commentary on how consuming food is related to exploitation, the artists explain, depicting a time 鈥渨hen GM and other manufactured food is shoved down the throats of unsuspecting consumers鈥�. But don鈥檛 scoff 鈥� real life could soon be imitating art. Although you鈥檙e unlikely to be serving up engineered frog鈥檚 legs any time soon, tissue engineers in the US are already experimenting with ways of growing meat in the lab dish. The aim of the work is to develop food for astronauts on long space journeys, such as a mission to Mars. But like so much other space research, what happens up there could one day become commonplace down here too 鈥� just look what happened to Velcro. And in an era where our taste buds have been blunted by processed nuggets and hamburgers, we may not even notice the difference.

Last spring, a NASA-funded team led by Morris Benjaminson, professor of applied biosciences at Touro College in Long Island, New York, took the first steps towards growing meat in the lab. The team removed 10-cm chunks of live muscle tissue from freshly killed goldfish. They then plopped them into a standard cell-culture fluid containing fetal bovine serum 鈥� made from the blood of cow fetuses 鈥� and left them for a week.

Benjaminson found that the tissue grew by as much as 14 per cent. Partially differentiated 鈥渕yoblast鈥� cells in the adult muscle had divided to make more muscle cells, he says, enabling the tissue to keep growing. Thus, the team became the first in the annals of science to grow fish fillets in the lab 鈥� albeit highly unappetising ones (麻豆传媒, 23 March, page 23).

In a scene that eerily echoes the frog feast planned by the artists, Benjaminson鈥檚 team held a press conference where they fried up the fish bits with some olive oil and herbs. None of the researchers actually sampled their culinary creation, however, claiming that lab-grown goldfish flesh was not approved for human consumption by the FDA. Benjaminson said that he didn鈥檛 want to risk ingesting any prions from the serum because they can cause the human form of mad cow disease.

Nonetheless, he was pleased with the dish. 鈥淭he fish smelled and looked like something straight out of the supermarket,鈥� he insists. 鈥淭he muscle we grew in vitro looked fresh. It looked pretty darn good. That is my humble opinion. The fish wasn鈥檛 revolting 鈥� the serum was revolting.鈥� Benjaminson now plans to experiment with mushroom extract as a more palatable growth medium.

There is clearly quite some way to go, but Benjaminson hopes that such techniques will one day mean that astronauts on long voyages don鈥檛 have to put up with poor diet and nutrition. 鈥淭he havoc and discord of early pioneering sea voyages, punctuated by bad water, weevily hard tack, rancid salt pork and rampant scurvy, is not necessary or desirable in the space age,鈥� he says.

Growing larger pieces of muscle tissue in the lab is going to be a tricky business, however. The main problem is ensuring a constant supply of nutrients for the growing cell mass. In tissue fed by a blood supply, the capillaries must be no more than 200 micrometres apart or else the cells in between become necrotic and the tissue dies. Although the Touro team developed techniques for growing white and dark chicken muscle in the lab, without a blood supply the chicken meat grew for just two months before it was dead in the dish.

Robert Langer at the Massachusetts Institute of Technology and the brothers Joseph and Charles Vacanti at Massachusetts General Hospital famously overcame this problem when they grew a cartilage ear by grafting it on the back of a mouse. Blood vessels from the mouse鈥檚 skin gradually grew into the graft to supply it with nutrients. Unfortunately, muscle cells demand more oxygen and food than 鈥渟edentary鈥� tissues such as cartilage, and the mouse blood vessels would grow too slowly to support the tissue. So while this approach is good for bone, cartilage and vascular tissue, it probably won鈥檛 work for rack of lamb. Benjaminson is now submitting another NASA proposal to investigate mechanical or electrical methods of stimulating blood vessel growth.

The good news is that you only need to establish a good blood supply if you want to grow thick slabs of muscle. Vladimir Mironov, director of the Shared Tissue Engineering Laboratory at the Medical University of South Carolina in Charleston, has other ideas. His team thinks the meat of the future will be more of a processed food, closer to a sausage or hamburger. Rather than culturing a sample of muscle tissue, he plans to grow cells on protein spheres suspended in growth medium. These could then be harvested and made into nuggets or patties (see 鈥淗ow to grow your own nuggets鈥�).

In a detailed project proposal to NASA, Mironov describes how he plans to make 鈥渁nimal-free animal meat鈥�. His starting cells will be myoblasts 鈥� the same partially differentiated cells that allowed the fish fillets to grow. Myoblasts normally live at the edges of muscle fibres and help repair the muscles if they are damaged. They are more suitable than embryonic stem cells, Mironov says, because they are already part of the way down the road to forming the desired cell type, rather than being totally undifferentiated. Unfortunately, myoblasts do have a big drawback: they cannot survive unless they attach themselves to something, and this makes them harder to grow in a stock.

Sausages in space

To get round the problem, Mironov plans to mix the myoblasts with tiny spheres of the protein collagen and then keep them in suspension with the help of a machine called a microgravity bioreactor. It spins rapidly, creating a centrifugal force that keeps everything in conditions of permanent free fall. This environment helps the cells cling to the collagen scaffolds and each other, as well as simulating the weightless conditions aboard a spaceship. Once the myoblasts have grown and differentiated into muscle cells, the spheres can be harvested and turned into food.

That just leaves the question of which synthetic meat will hit the menu first. According to Mironov, the simplest to grow is seafood because the myoblasts can be coaxed to divide better, but 鈥渃hicken is nice鈥�, he says. His dream is that we will eventually be able to grow and cook fresh sausage overnight at home in special machine, just like you bake bread in a home bread maker.

Although processed meat is likely to become a reality before more traditional cuts, researchers haven鈥檛 yet given up the dream of growing the perfect filet mignon in the lab. Mironov, for one, has thought of other ways of getting round the blood supply problem. He suggests using a bioreactor with a branching network of hundreds of tiny edible tubes that act like artificial capillaries to convey nutrients to the growing meat. Chitin, the protein that forms the tough shells of insects, would be ideal for this 鈥� if someone could figure out how to make edible chitin tubes. Luckily there are promising alternatives, including polymers, 鈥減olyglycolic gel鈥�, and possibly edible collagen.

But to satisfy those who crave the texture and mouthfeel of a good steak, you need to develop something that mimics the texture of real meat. That means generating a complex structure of muscle and connective tissue, and to do that the muscle myoblasts need to stretch and contract regularly. In other words, not only must you feed your steak well, you have to give it plenty of exercise.

Herman Vandenburgh of Brown University in Providence, Rhode Island, has proposed a regime for the physical conditioning of sedentary steaks. Rather than just stimulating them with electricity or chemicals, Vandenburgh鈥檚 team has developed chitin beads that change size when the temperature changes. Myoblasts cling to the beads, which force the cells to stretch and contract. Adding fat can improve flavour and texture, and there are at least 20 firms based in New Jersey that specialise in making artificial flavour enhancers and food additives for the processed and fast-food industry. Barbecue, anyone?

Mironov believes that in the long term, tissue-engineered food will end up in the supermarket. But at the moment it鈥檚 probably still cheaper to fly in your personal chef to grill you the real thing. The prototype synthetic hamburger is aimed at travellers to Mars or other planetary settlements, and will cost $10,000 a throw, and that鈥檚 just the spaceship fare. Mironov isn鈥檛 too worried, pointing out that the first TVs and cars were very expensive, before mass production dramatically slashed the price.

However, in a cruel setback for astronaut omnivores, NASA has rejected Mironov鈥檚 proposal, apparently preferring astronauts to be vegetarians for the time being. Besides, NASA hopes to transfer genes for meat proteins into plants to make the diet more comprehensive. 鈥淧eople are vegetarians and vegans on Earth and they do quite well,鈥� comments Thomas Dreschel, director of NASA鈥檚 Fundamental Space Biology Outreach Program. 鈥淚t is more efficient to grow plants and feed on them,鈥� he says. 鈥淭he vegetarian diet is about 10 times more efficient than a diet of meat. If astronauts really need essential amino acids, they can eat a pill.鈥�

Douglas McFarland, professor of animal sciences at South Dakota State University in Brookings, disagrees. 鈥淎nimal protein is a more balanced and complex protein than a plant protein,鈥� he argues. 鈥淭he body would absorb and metabolise protein from a pill too rapidly. If you eat protein, then it takes more time to digest.鈥� McFarland, who collaborates with Mironov, has studied myoblast cell lines of chicken, pork, beef, lamb and turkey. 鈥淚 believe that cell-culture techniques may be able to provide for the dietary protein requirements of space travellers and for others in special circumstances,鈥� he says. But growing a steak in a Petri dish is a 鈥渕ajor stretch of the imagination鈥�, he admits.

NASA has sunk millions of dollars into its 鈥淎dvanced Life Support鈥� research, investigating algae and plants such as rice and dwarf wheat that can be grown in the cramped conditions on board spaceships. Everything taken into space must serve multiple purposes, and that means plants must supply food and oxygen and remove carbon dioxide from the atmosphere. Animals too must pull their weight. NASA had to abandon its attempts to grow tilapia, a fish also known as an 鈥渁quatic goat鈥� because it will eat anything and tolerates poor water quality. Although the fish survived on a strict diet of leaves, they didn鈥檛 grow.

Another problem NASA has identified is that the microgravity and the much higher level of radiation in space seem to change not only the structure of plants, but also their nutritional content. So corn grown in space might have a different fat-to-starch ratio, say, making it a nutritional unknown for astronauts.

But it鈥檚 no good worrying about nutrition if the food isn鈥檛 tasty and interesting enough for the astronauts to eat it in the first place. 鈥淚 personally ate a couple of algae pills a year ago and I was underwhelmed,鈥� says Bob Phillips, a researcher at NASA Advanced Life Support. 鈥淲ith only a few minor exceptions, astronauts come back from space losing weight. We tried to send more food, but the astronauts wouldn鈥檛 eat it. What we need is really palatable food for space flight that has great variety to it. It has got to be varied and be an interesting diet.鈥�

At the moment, the average meat takeout to space consists of freeze-dried, pre-cooked hamburger patties vacuum-sealed in polythene. To resuscitate the hamburger, you simply add five millilitres of hot water to the packet. The verdict, perhaps unsurprisingly, is that they are tasteless. More popular among astronauts is freeze-dried shrimp cocktail. While it tastes good, 鈥渋t looks horrible鈥�, Phillips says. 鈥淚f you rehydrate it and eat it too quickly, the shrimp are crunchy.鈥�

Even if NASA is focusing on veggies, maybe Mironov can find funding elsewhere. 鈥淥perations like McDonald鈥檚 are interested in particular cuts of meat and efficiency,鈥� says Vern Anderson, adjunct professor of ruminant nutrition at the University of North Dakota. Designer meat could be engineered to be healthier and more nutritious, he says. 鈥淵ou could select for leanness, or low cholesterol. Or select species, flavour, and texture as desired.鈥�

Of course, by far the biggest obstacle to engineered steaks is convincing people to eat them. 鈥淓ating is still a decadent experience to most people,鈥� says Anderson. 鈥淔ew of us eat solely what is good for us, so the concept of creating a homogenous mass of a specific food from a lab without some semblance of currently accepted taste, flavour, and cooking flexibility may be a challenge.鈥�

How vegetarians and animal rights campaigners would react to the idea is another matter. If no animal is farmed or slaughtered, and if culturing cells were more energy efficient than growing meat on the hoof, would that make it ethically acceptable? If not, there might still be another way. Catts recalls one of his students, a vegan, who asked if she could just biopsy herself, grow up a steak and eat it. It sounds revolting, but think again. If you want to eat truly victimless meat, perhaps it鈥檚 time to put yourself on the menu