Juanchen Li
April 30, 2013
In Vitro Meat: Producing Meat without Animals
Previously nothing more than a fantasy, the prospect of artificially produced
meat, called in vitro meat, is becoming a reality. By forcing muscle cells to
multiply in controlled environments, scientists have been able to grow samples of
in vitro meat, and are continuously refining this process. Ultimately, the primary
goal of in vitro meat research is to offer a viable alternative to conventional meat.
This technology is not ready to be commercialized just yet, and requires far more
research in order to improve efficiency and reduce costs to reasonable levels.
However, it could have a large economic and environmental impact if it becomes
a successful industry.
Introduction
In 1931, Winston Churchill wrote, “We shall escape the absurdity of growing a whole
chicken in order to eat the breast or wing, by growing these parts separately under a
suitable medium,” in his article “Fifty Years Hence” [1]. Although far more than fifty
years have passed since Churchill made this prediction, the idea of artificially grown
meat may still seem more like a gimmick from a science fiction novel than an actual
possibility. However, thanks to recent advances in biotechnology and tissue engineering,
artificially grown meat is already becoming a reality.
In vitro meat, also known as cultured meat, is meat grow independent of a living animal.
Researchers have already successfully grown small amounts of edible meat in labs, and
are actively researching to improve this process. When and to what extent this
technology will become commercially viable, if at all, is to be seen. However, even in its
current state, the ability to artificially grow meat is already an impressive scientific and
engineering feat in itself, with potentially large economic, environmental, ethical and
global health implications should it grow into a large industry.
:
Reuters/Francis Lenior
Figure 1: Small samples of in vitro meat grown at the University of Maastricht.
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Juanchen Li
April 30, 2013
Why In Vitro?
Humans domesticated sheep 10,000 years ago, marking the first instance where
animals were raised for food, a tradition that we have kept ever since. Why would we
want to spend so much money and research effort just to start eating artificial meat
now? Advocates of in vitro meat have a wide array of arguments, but most of them boil
down to one of four major topics: environmental impact, health, economic benefits, and
ethics.
Environmental Impact
Hanna L. Tuomisto and M. Joost Teixeira de Mattos
Figure 2: A comparison of the resource costs of producing various types of meat.
Raising livestock for meat production accounts for 18% of the greenhouse gas
emissions worldwide. The land required for livestock occupies 30% of the global icefree terrestrial land and 8% of the global freshwater. Current estimates of in vitro
meat’s production process place its greenhouse gas emissions, land usage and water
usage at less than 10% of four major conventional meats – beef, sheep, pork, and
poultry – pound for pound. In addition, in vitro meat also consumes less energy than
beef, sheep, and pork, but slightly more than poultry [2]. Should in vitro meat replace
conventional meats in a large scale, it could mean a large reduction in greenhouse gas
emissions, more open land and fresh water, and lower energy consumption worldwide.
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Juanchen Li
April 30, 2013
Health
There are many diseases associated with meat consumption, such as mad cow disease
and salmonella. Because in vitro meat is produced in a maintained environment, the
chance of these diseases infecting meat can be greatly reduced. Furthermore, it may be
possible to engineer meat to contain less harmful components, such as saturated fats,
and more healthy ones, such as proteins [3].
Economic Benefits
Since in vitro meat is still a developing technology, it is difficult to predict what its prices
will be when it becomes commercially available. The price will likely be steep initially,
but drastically decrease as it becomes more readily available and efficiently produced
[4]. While it may be challenging to foresee the direct economic impact of the meat,
many of the speculated benefits come from environmental and healthcare savings. If in
vitro meat were to completely replace conventional meat, an estimated $130 billion
USD would be saved every year from reduced greenhouse gas emissions alone [3].
Ethics
A live animal is only required in the in vitro meat process once, to donate a small
sample of starter cells. After that, it is feasible that those cells can be grown enough to
feed the entire world for many years. Because of this independence from animals,
certain animal advocate groups, such as PETA, have shown support for in vitro meat [4].
Starter Cells
Most of what we consider “meat” consists of the multinuclear muscle cells called muscle
fibers, or myocytes. Thus, in order to successfully create in vitro meat, a process to
artificially grow animal muscle fibers is needed [4]. Since the goal is to produce these
fiber cells, it may seem like an obvious choice to extract muscle cells from an animal
and use these cells as a basis for growing in vitro meat. Unfortunately, the muscles of
most mature animals, livestock included, do not typically undergo cell division. When
muscles grow larger, after exercise for instance, the individual cells grow larger through
a process called hypertrophy, but each cell can only grow a limited amount. Animals
form their muscle cells in the early stages of life, generally ceasing to produce new ones
afterwards [5]. Because of this, it is difficult to create naturally structured muscle from
typical muscle cells.
With the difficulties of growing structured muscle fibers from other fibers, many
researchers have turned their sights to a different method: using stem cells. Stem cells
are cells found in all animals that have the ability to both self-replicate and to
differentiate into many types of specialized cells, including muscle fibers. Together,
these traits mean that a few stem cells have the potential to produce large quantities of
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Juanchen Li
April 30, 2013
muscle meat. However, the due to the vast differentiability of most stem cells, the
process of artificially changing them specifically into muscle fibers is relatively difficult
as well [4].
A compromise between the fast multiplying stem cells and the already differentiated
muscle cells are myosatellite cells, also known simply as satellite cells. When muscles
are damaged, they release dormant satellite cells, a highly specialized type of stem cell.
After being activated, these cells divide, differentiate into muscle cells, and then fuse
into fibers to repair any lost muscle. As a stem cell, satellite cells have the ability to
proliferate, but unlike the other types of stem cells, they are already specialized for
fusing into muscle fibers. This means that it takes much less effort to differentiate these
cells into the muscle fibers needed to produce meat [6]. With the ability to both
proliferate and fuse into muscle fibers, satellite cells are well suited for in vitro meat.
Growing the Cells
Having a viable cell type is only the first step towards producing in vitro meat. The next
step is to be able to multiply the cells. The process of artificially growing cells outside of
their natural environments is called cell culture. Successful cell culture techniques were
established decades before in vitro meat became anything more than an idea [7].
However, when using cell cultures to grow in vitro meat, special considerations must be
made. The first of these is the growth medium, the substance designed to support the
proliferation of the cells in the culture.
A commonly used medium for cell cultures is fetal bovine serum, plasma taken from
fetal calves. Rich in protein, this serum is a byproduct created by slaughterhouses. For
the purposes of in vitro meat, fetal bovine serum is quite effective in promoting muscle
growth [7]. However, while the serum is successful conceptually, it is currently too
expensive to be commercially worthwhile. Furthermore, requiring a continual supply of
animal products undermines the philosophy that the meat can be produced
independently from animals [4].
If animal serum based media are out of the question, then there is no clear runner up
medium. One of the strengths of fetal bovine serum is that it can be used with a wide
variety of cells, including most of those used for in vitro meat. In contrast, most growth
media without serum will likely need to be tailored towards a single cell type, since cells
from different species respond differently to various conditions and growth factors.
Despite these complications, researchers have already produced a variety of serum-free
media for satellite cells, including media for turkey, sheep and pig [8]. In one instance,
a mushroom based media for sheep was reported to be even more effective than fetal
bovine serum [9].
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Juanchen Li
April 30, 2013
Structure and Scaffolding
Queen Mary University of London/Jonathon Hills
Figure 3: Microscopic view of a scaffold used tissue scaffold that can be used for in vitro meat.
In order to proliferate, muscle cells need to be able to attach themselves to a rigid
structure. In nature, muscle cells connect onto the skeleton at the ends. In order to
grow large volumes of cells in an artificial environment, the two dimensional petri
dishes that cell cultures are normally performed on will not suffice. Instead, in vitro
meat is grown on specialized scaffolding that supports three dimensional cell
attachment. A successful scaffold needs to be shaped to promote the diffusion of
nutrients and to maximize surface area. In addition to overall shape, the structure on a
cellular scale is important as well. An ideal microstructure will allow muscle fibers to
easily fuse and align onto the scaffold [8].
Because the ultimate goal of in vitro meat is consumption, the material of the scaffold is
important as well. A large portion of the scaffolds used in tissue engineering is made
out of synthetic materials such as carbon nanotubes. If similar scaffolds are used for in
vitro meat, the scaffolds would need to be removed before processing. Alternatively,
edible scaffolds could be created from polymers, but further research into this
possibility is required before it becomes fully viable [10].
Currently, while there are a variety of proposed scaffold types, there is no clear best
choice among them. One proposed structure is to use a sponge-like matrix scaffold.
This scaffold would have impressive surface area and nutrient diffusion, but would be
heavily interlaced into the muscle, making removal difficult. Another possibility would be
to grow meat around edible bead shaped meshes made from collagen. Other proposals
include using elastic sheets, or arrays of long threads [8].
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Juanchen Li
April 30, 2013
Beefing Up
As livestock move about in their everyday actions, their muscles receive exercise. By
contracting their muscles, animals increases muscle growth and improve protein
content. Without similar contractions, in vitro meat may be prone to atrophy, resulting
in less meat volume and tenderness. In order to overcome this hurdle, producers of in
vitro meat send the cells weak electric impulses. When the cells receive the impulse,
they contract in response, simulating natural contractions. To what extend this process
will be required is not yet known, and will depend on the quality of the each meat
product without it. However, the technique of using electric simulation in lieu of
exercise has already been shown effective for both live animals and in vitro meat [11].
Future Prospects
Despite all of the progress that in vitro meat has made, it still has many hurdles to
overcome. A large one is the price. In its current state, producing a single strip of meat
costs thousands of dollars. A large amount of research and engineering still must be
invested in in vitro meat before it can be competitively priced. Even if the meat drops to
a reasonable price, there is no guarantee that it will taste like conventional meat, and
will likely only initially exist as forms of mixed meat, such as sausages or patties. Of
course, there still remains the problem that meat grown in a lab may seem flat-out
disgusting to some people, and it may take shifts in societal opinions before in vitro
meat becomes popular. So, while we may not all be eating lab grown miracle bacon
when we wake up tomorrow, with enough research and interest, in vitro meat might be
making the world a greener, richer, and healthier place a few years down the line.
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Juanchen Li
April 30, 2013
References
[1] W. Churchill “Fifty Years Hence” Strand, Dec. 1931. [On-line] Available:
http://teachingamericanhistory.org/library/index.asp?document=1914, [Feb 5. 2013]
[2] H. Tuomisto and M. Joost Teixeira de Mattos. “Environmental Impacts of Cultured
Meat Production” Environmental Science and Technology, [On-line] Available:
http://www.new-harvest.org/img/files/tuomisto_teixiera_de_mattos_cultured_
meat_lca_es_t_published.pdf, [Feb. 5, 2013]
[3] N. Fiala. “The Value of Cultured Meat: An Estimate of the Externality Costs of Meat
Consumption” Internet: http://www.new-harvest.org/img/files/fiala_2010.pdf [Feb.
5, 2013]
[4] “Future Food – In Vitro Meat” Internet: http://www.futurefood.org/in-vitromeat/index_en.php, Sept., 2012 [Feb. 5, 2013].
[5] P. Ji. “Muscle Cells – Why They Cannot Divide” Internet: http://voices.yahoo.com/
muscles-cells-why-they-cannot-divide-5687908.html?cat=58, Mar. 23, 2010 [Feb. 5,
2013].
[6] A. Polesskaya, M. Rudnicki and P. Seale. “Adult Stem Cell Specification by Wnt
Signaling in Muscle Regeneration” Cell Cycle, vol 2, pp. 418-419, Sept. 2003.
[7] “Cell Culture Basics” Internet: http://www.invitrogen.com/site/us/en/home/
References/gibco-cell-culture-basics.html, [Feb. 5, 2013].
[8] I. Datar and M. Betti. “Possibilities for an In Vitro Meat Production System”
Innovative Food Science and Emerging Technologies, vol 11, pp. 11-32, 2010.
[9] P. Edelman, et. al. “In vitro cultured meat production” Internet: http://www.newharvest.org/img/files/Invitro.pdf, [Feb. 5, 2013]
[10] P. Edelman, D. McFarland, V. Mironov, and J. Matheny. “In vitro-cultured meat
production” Tissue Engineering, vol 11, pp. 659-662, 2005.
[11] M. Post “Cultured Meat From Stem Cells: Challenges and Prospects” Meat Science,
vol. 92, pp. 297-301, 2012.
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