Tissue Engineered or In Vitro Meat

Primary authors: Jessica Heuel, Laurel Neiss, Katherine Thomas, Ilana Webb

          Is it really possible for the world to be supplied meat without having to kill even one animal? Researchers are opening the doors to such possibilities with the recent projects concerning tissue engineered meat. With the current attempts being performed and the continuous progress being made, the possibility of in vitro meat becoming a consumer product is becoming more likely. This product would introduce both health and environmental benefits. There are still many obstacles to overcome, but the production of tissue engineered meat would be so advantageous that  researchers are hard at work trying to overcome them.

Motivation

Although meat is very widely consumed over the world, there are several downsides that come with eating meat that make this kind of research beneficial. One disadvantage is the health risks associated with meat consumption. Each year, foodborne diseases account for approximately 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths due to pathogens including salmonella, listeria, and toxoplasm in the United States⁹. These foodborne illnesses along with other nutrition-related diseases related to over consumption of meat like cardiovascular disease, diabetes, and ischemic heart diseases account for an estimated 30 to 60 billion dollars annually in the United States¹⁰.

            These medical costs could potentially be reduced with cultured meats as it would be possible to select for leanness, cholesterol, and to improve the ratio of poly unsaturated fatty acids, which are beneficial for blood cholesterol, to saturated fatty acids, which are implicated in heart diseases⁶. In addition, the production of cultured meats would lower the risk of bacterial contamination² as well as the exposure of meats to pesticides, arsenic, dioxins, and hormones¹.

            In addition to health benefits, there are several environmental advantages that are related to cultured meat. The process of producing engineered meat is significantly more efficient in its use of nutrients, land, and energy compared to naturally produced meats³. The process does not use a large number of animals, and could theoretically be used to produce the world’s food supply with a single satellite cell¹. As a result, there would be considerably less land used for livestock as well as notably less remnants or waste to dispose of^2,6. Also, the production of tissue engineered meat could also potentially minimize the slaughtering of endangered animals for exotic meats¹. Just in case the health and environmental advantages do not provide a large enough incentive, PETA is offering a $1 million reward for whoever can develop a commercially obtainable tissue engineered meat⁴.

Previous work

            Previously the idea of creating meat would have been just that - an idea, with little possibility of becoming a reality. However in recent years researchers have made a lot of progress in engineering meat and have come up with a good basis to work off of. The technique currently being used begins with placing either embryonic myoblasts or adult skeletal muscle satellite cells (Depicted in Figure 3 below) in a culture medium to allow the cells to proliferate. From previous research certain factors have been found that affect the proliferation and differentiation of myoblasts including “mechanical, electromagnetic, gravitational, and fluid flow fields”¹.  In order to proliferate, the myoblasts need to be placed on a scaffold.  This scaffold needs to be able to stretch and must be edible.  A scaffold that has been used is cytodex-3 microcarrier beads (See Figure 2 below).  However, these beads cannot stretch very far.  Researchers are still looking for a suitable and practical scaffold.  After dividing into millions of cells over a few days, the cells are then placed onto a grooved sheet and placed in a bioreactor.  In the bioreactor, the grooved sheet is flexed to allow the cells to grow properly.  Flexing the sheet also allows the cells to fuse into myotubes, which eventually grow into a thin layer of muscle tissue^1,2.  This can be repeated and the resulting product can be ground up or stacked up in order to create meat. However, with this technique only thin layers and not three-dimensional structures of meat tissue can be created, which restricts the product to processed meats which do not have a specific texture or structure such as steak.

Figure 1. Scaffold-based cultured meat production:                   Figure 2. Turkey Satellite cells grown on Cytodex 3 Beads       Figure 3. Satellite cell-derived turkey myotubes

1.Myoblasts in petri dish; 2. Porous collagen microspheres;

3. Myoblasts form myotubes on collagen microspheres;

4. Bioreactor; 5. Microwave; 6. Hamburger

          However, there are still many problems with today’s techniques.  Researchers are currently trying to find a better, more cost effective medium to proliferate the myoblasts in that would supply the nutrition and growth factors to the cells.  Normally, the muscle cells and other surrounding cells supply these factors in the organism, so it is challenging to find a different way to provide this to the cells.  Also, the medium being used now is extremely expensive and researchers have to find a way to reduce cost in order to mass produce the meat¹. Another issue is trying to make the engineered meat look and taste like real meat⁶.  At this point, it has not been discovered how to create blood vessels in the tissue which are necessary for a three-dimensional structure, so steak-like products are not possible¹.  Currently, the meat does not look as appetizing or much like actual meat (See Figure 4).  In order to help recreate the texture of the meat, researchers are trying to stretch the meat in different ways to change the texture. If the proper appearance, texture and taste were achieved, there is then the dilemma that people may have trouble eating the meat because it was made in a lab and they think it is unnatural^1,5,7.  In order for tissue engineered meat to be mass produced and used as a real consumer product, all of these issues need to be resolved. 

  Figure 4. Appearance of tissue engineered meat currently

Future Strategies

Besides the ascetic aspect, the futures of design and production for tissue engineered meat are vast and there are still many problems to overcome.The design of the meat using explants would be beneficial due to a need for vascularization and it would lead to a low contamination rate, a self healing product, cell proliferation, and increased tissue size.  The current problem with using explants is that maintenance of them requires use of fetal bovine serum that is potentially dangerous due to prions and that the cells become necrotic if separated more than 0.5 millimeters from the nutrient supply¹.  The design needs to contain a scaffold that can mechanically stretch to be able to grow cells on large, flat sheets of membrane and also to be able to grow the cells on three dimensional beads that could stretch with changes in temperatures, have a flexible substratum⁶, and could be used for long term storage¹. 

A factor that effects both design and production is the need for new bioreactors. Their creation is necessary in order to actually make the meat.  Within these bioreactors myoblasts would be mixed into tiny spheres of protein collagen and kept in suspension with microgravity (the bioreactor spins rapidly to keep everything in permanent free fall) and cells then cling to the collagen and the spheres could be harvested as food¹. 

The overall production needs to be improved not only to improve the structure, texture, and quality of the meat but also to reduce the cost. Current costs for producing one kilogram of in vitro meat is about $5 million¹, meaning that costs for consumers could run from $1,000 to $10,000 per pound (however it has been esitmated that using nutrients from plants or fungi could bring costs down to approximately $1 a pound)³. 

Although many improvements and advancements need to be made, the prospect of tissue engineering meat as a reasonably priced and desirable consumer product seems hopeful. Researchers have a good idea of what needs to be done to make it a reality and are slowly developing the means to do so.

Citations

1.    http://www.new-harvest.org/img/files/Invitro.pdf

2.    http://beefmagazine.com/mag/beef_testtube_meat/

3.    http://www.commondreams.org/headlines06/0621-03.htm

4.    http://www.npr.org/templates/story/story.php?storyId=89942776

5.    http://blog.wired.com/wiredscience/2008/01/beef-battle-tis.html

6.    http://www.newsdesk.umd.edu/scitech/release.cfm?ArticleID=1098

7.    http://www.usnews.com/articles/science/plants-animals/2008/07/24/what-will-we-eat-in-a-hungrier-world.html?PageNr=2

8.    http://knol.google.com/k/kurt-schmidinger/cultured-meat-in-vitro-meat/25lkeongjbtve/2#

9.    http://www.cdc.gov/ncidod/eid/Vol5no5/mead.htm

10. http://www.ncbi.nlm.nih.gov/pubmed/8610089

     FIGURES

          Figure 0.  http://knol.google.com/k/kurt-schmidinger/cultured-meat-in-vitro-meat/25lkeongjbtve/2#

          Figure 1.  http://www.new-harvest.org/img/files/Invitro.pdf   

          Figure 2.  http://www.new-harvest.org/img/files/Invitro.pdf 

          Figure 3.  http://www.newsdesk.umd.edu/scitech/release.cfm?ArticleID=1098

          Figure 4.  http://www.tca.uwa.edu.au/disembodied/images.html