When the first hunk of lab-grown meat finally hits our dinner plates, it’s unlikely to look anything like the flesh of the animal it didn’t come from. We’re more likely to bite into chicken nuggets sculpted out of an amorphous gloop of plant and animal cells, rather than sink our forks into a perfectly-formed chicken breast.
Even the industry’s most optimistic advocates – the lab-grown meat startups themselves – admit that the immediate future of animal-free meat is likely to be on the messier end of the spectrum. That’s why they’re starting with nuggets, foie gras and sausages rather than steaks and pork chops.
While a handful of startups have managed to grow animal cells and package them together in burger or nugget form, growing a cut of meat outside of an animal’s body is a much trickier challenge. As with many things in the so-called clean meat industry – things are never quite as simple as they seem. Even the phrase “clean meat” – the term preferred by most startups – is hotly disputed by the cattle industry, which argues that the term implies that non-lab-grown beef is somehow dirty and researchers who point out that we’re still not sure what the environmental impact of lab-grown flesh will be.
But while the lexical squabble continues, biophysicists are looking to unusual sources of inspiration – plants and cancer cells – to solve an even bigger problem. Growing meat that falls apart in the mouth, not in the frying pan.
Consider a cut of Wagyu beef. To the uninitiated, it looks relatively uncomplicated – not much more than a reddish, homogenous mass waiting to be transformed into an expensive meal. But to Amy Rowat – a biophysicist at the University of California, Los Angeles – there’s a lot going on in that hunk of flesh.
First off, you have muscle cells, crammed with protein and arranged in long fibres that give beef its meaty flavour and structure. Weaving between the muscle fibres there are clumps of fat cells, lending the cut its distinctive marbled appearance and giving it an almost butter-like texture in the mouth. Hidden among all of this you have microscopic blood vessels and protein structures that give the flesh structure and helped channel nutrients towards it while it was still alive.
Every cut of meat is, on one level, a microcosm of the animal that made it – a life support system in miniature. “From a biophysics perspective it’s fascinating to think about how we could recreate that,” says Rowat. And the taste and feel of food is intimately connected to its biology, which is why Rowat devised a class on the science of cooking as a way of teaching students about biophysics.
The challenge for clean meat industry is to recreate this complexity in the lab and find some kind of material that allows different cell types to grow alongside each other in a highly structured way – fitting together the fat, muscle and collagen in a way that looks and feels like a cut of meat. In industry parlance, it’s called the search for a “scaffold”.
One unlikely frontrunner in the nascent search for a meaty scaffold could be the apple. In his laboratory at the University of Ottawa in Canada, Andrew Pelling has managed to grow human skin cells on slices of apple and thinks that plant scaffolds could be one path forward for structured clean meat. “We’re interested in biology, and in pushing cells into really weird artificial scenarios and situations, just to see how they react. It’s surprising how much you can learn from those extreme environments,” he says.
Until now, most research into scaffolding has focused on mimicking mammalian tissue using a process that’s a little like fossilisation, but in reverse. Bioengineers would create synthetic protein structures, and fill them with blood vessels and other cells in the hope that they would eventually dissolve and replace the synthetic scaffold with a biological replica.
In 2011, after an evening spent watching Little Shop of Horrors – a comedy horror film which prominently features a Venus fly trap with a mammalian tongue and teeth – Pelling wondered if an alternative to animal scaffolds could work. Would it be possible to build a scaffold using plant cells alone?
Although cellulose – the main component of plant cell walls – is one of the most abundant substances on Earth, humans are hopeless at digesting it. That’s the main reason why salads have so few calories – we just can’t access all of the material lurking within plant cells. To Pelling, this suggested an advantage of plant-based scaffolds. A cellulose scaffold would never disappear, but it might provide a sturdy framework that animal cells could worm their way around.
Intrigued, Pelling went to his local grocery store and bought a pack of apples. He cut thin slices of apple flesh and bathed them in a soapy solution to remove any trace of proteins or DNA from the plant – a process called decellularisation. He was left with a brittle, translucent scrap of apple flesh that – when it was implanted under the skin of a mouse – provided the perfect home for mammalian flesh to grow into.
“All of a sudden this apple scaffold is now a living piece of tissue – the heart is keeping it alive, there are new nutrients flowing through it,” Pelling says. If you take a look at a piece of apple under an electron microscope, you can start to see why plants make surprisingly useful scaffolds. Up close, apple flesh is riddled with tiny holes and channels that blood vessels can latch onto and weave through. “Because it’s inert all it’s doing is providing a physical support for damaged tissue,” says Pelling.
Now Pelling is exploring whether other plant sources – pears, carrots, rose petals, asparagus and mushroom – could be used as scaffolds for cultured meat. It might be possible to modify scaffolds so specific cell types only cling to certain patches of the scaffold, allowing researchers to recreate the fatty marbling that’s a signature of Wagyu beef, but as with many things in this field, how to do that is a wide-open question.
On the other side of the continent, Rowat is hoping that her studies into the peculiar properties of cancer cells could help us build better scaffolds. In the body, cells are constantly squishing and changing shape and, in the case of cancer cells, sometimes breaking off altogether. Rowat thinks that better understanding the biophysics behind cell structures could lead us towards scaffolds that can host a range of different cells.
Growing one cell type – say muscle cells – in a bioreactor is hard enough, but adding other cell types in close proximity presents a whole set of new challenges. “When you are trying to grow different types of cells together they often have different requirements or mechanical preferences for their microenvironment,” says Rowat. Cells are fickle – each type require greater or lesser amounts of a wide range of nutrients. What is paradise to one cell type could be hell for another. This is problematic when the nutrient soup in a cut of meat changes on an inch-by-inch basis. It’s entirely possible that the cells on the outside of a not-yet-extant lab-grown steak could be having the time of their lives while the ones on the inside are dead, Pelling says.
Undeterred, Pelling and Rowat are just two of a growing number of researchers who are trying to crack the scaffolding problem. In 2017, Marie Gibbons, a researcher at Harvard, grew turkey flesh on pieces of decellularised jackfruit while Glenn Gaudette’s lab at Worcester Polytechnic Institute in Massachusetts is experimenting with filling spinach leaves and stalks with animal cells.
But scaffolding is just one hurdle facing the clean meat industry. So far no startup has managed to scale-up production without using expensive serum derived from animal blood – a huge problem for an industry with the end goal of taking the animals out of meat altogether.
And until firms can scale-up production, the cost of clean meat is likely to remain high. That’s part of the reason why solving the scaffolding problem is so attractive – people might be willing to pay more for lab-grown meat if it feels like premium cut. But that prospect is still a long way off. For now at least, the future of clean meat is more gloop and less steak.
This article was originally published by WIRED UK
