This publication by Isha Datar and Mirko Betti was summarized by Francis Runge, with edits by John Nahay. The original paper can be accessed here.
There are many different proposals on how to go about growing cultured meat and developing an in vitro meat production system (IMPS) that works. This area of biotechnology has been of interest of late due to the great demand for meat by consumers, but also because of the ethical issues associated with factory farming, greenhouse gas pollution, and tissue engineering for the medical field. There are many benefits to IMPS as well as many limitations and the work to be done is significant and complex. Reactions which occur in living animal tissue are myriad and dynamic involving many different aspects including but not limited to internal organs, chemical cycles, and oxidation processes. All of these help to deliver the right nutrients necessary for muscle to grow and mature. Replicating these chemical bio-systems from basic culture mix or a bioreactor and finishing with a product similar to that of native animal tissue requires an understanding of how exactly these processes work. Despite all of this, progress is coming along and researchers offer many different proposals, methods, and theories, which are discussed below.
Current methods of meat production require vast resources, from land, to grain, to water, to fossil fuels; not to mention the disastrous effects on the environment, from deforestation, greenhouse gas emissions, and extensive and unnecessary demand from countries overseas. Alternatively, the pros of IMPS are that meat can be grown on location, less resources are needed to grow it, chances of disease can be decreased or eliminated, there are faster tissue growth rates, cruel husbandry and factory farming techniques are put to an end. There is even the possibility of creating new meat products by manipulating certain conditions giving meat new texture, nutritional value, and taste profile.
The current thinking for growing cultured meat includes the growth of myoblasts or myosatellite cells on a scaffold in a suspension culture medium within a bioreactor. The starting culture could be embryonic stem (ES) cells or myosatellite cells. ES cells divide easily, but they must be specifically stimulated to differentiate into muscle cells. Myosatellite cells can easily become muscle cells, but have limited capacity to divide.
Another potential cell type is adipose tissue-derived adult stem cells (ADSCs), derived from fat tissue. And yet one other option comes from adipocytes (fat cells). Cells have an upper limit on the number of times they can divide: the Hayflick limit. This limit can be avoided immortalizing cells by stabilizing telomeres, the ends of chromosomes.
Muscle cells like to be attached onto a surface. The scaffold is what the cells would grow on. Scaffolding differs in shape, composition and characteristics to optimize muscle cell and tissue morphology. An ideal scaffold would have:
• Large surface area for growth and attachment
• Be flexible to allow for contraction
• Maximum medium diffusion
• Be easily dissociated from the meat culture
• Closely mimics in vivo situation
• Natural and edible
Possible shapes include beads, a sponge, large elastic sheets, or an array of long, thin filaments. Various textures and scaffold materials could assist in cell growth.
The culture medium formulation is difficult to figure out. Myoblast culturing has traditionally been done in animal sera, though there are many problems associated with this method. Serum-free options offer a better alternative and help keep costs down.
Many factors are necessary to create a culture medium that serves its purpose. For instance, different stages of myosatellite growth may require a different mixture promoting the different periods of tissue maturation.
Next to consider is the bioreactor, the machinery necessary to bring nutrients to the growing tissue. High oxygen concentrations in the solution, similar to that of blood, are ideal. There are two distinct types of oxygen carriers: modified versions of hemoglobin and artificially produced perfluorochemicals (PFCs) are of interest.
The future of cultured meat holds promise but many questions. Will the product reproduce native animal meat, nutritionally, morphologically? Cost-effectiveness and consumer acceptance have to be considered as well as production on a large industrial scale.
With government subsidies and cooperation with the biomedical, pharmaceutical, and agriculture industries, research can continue. The pace of progress depends upon these industries working together to fund the research, which should hopefully not be difficult considering the extraordinary benefits such scientific discovery affords.