In Vitro-Cultured Meat Production

P.D. Edelman, D.C. McFarland, V.A Mironov, J.G. Matheny. Commentary: In vitro-cultured meat production. Tissue Eng. 2005 May-Jun;11(5-6):659-62

http://www.hedweb.com/animimag/invitro-culturedmeat.pdf

Most of what we consider edible meat is formed of skeletal muscle tissue. The idea of creating cultured meat basically involves growing large numbers of myoblasts on a scaffold that are differentiated into myofibers which can be harvested, processed and cooked into a meat product (boneless, ground). More ambitious ideas would be producing highly structured meat, like steak, which has been shown to be more difficult to tissue engineer in vitro due to the lack of blood circulation.

Skeletal muscle is formed of various cell types. Fibers are formed from myoblasts and satellite cells that join to form large multinucleated syncytia. The most practical cell source for cultured meat is either embryonic myoblasts or skeletal muscle satellite cells. Satellite cells have been cultured from chickens, turkeys, pigs, lambs, and cattle. They have differentiated to form immature muscle fibers called myotubes. Replicating unprocessed meat would be difficult requiring fibroblasts for the connective tissue and possibly fat cells within the same culture organized into a 3D structure. Replicating a processed meat source would be much simpler and could use a single line of myogenic cells.

The quantity of cells that could be reproduced is not known and may be limited by a fixed number of doublings called the Hayflick limit. Satellite cells from turkey were shown to express telemorase giving them a higher Hayflick limit. A single satellite cell with a Hayflick limit of 75 could theoretically satisfy the world demand for meat. Species not expressing telemorase may require transfection with the telemorase gene or proliferation of stem cells in culture before differentiation into myoblasts. Differentiation of myoblasts into myotubes has been shown with the aid of mechanical or electromagnetic stress on the growing cells.

Myoblasts require a scaffold for attachment allowing proliferation and differentiation. The scaffold must be edible for production of meat and flexible to allow stressing of myoblasts to induce differentiation. One possible scaffold would be to use edible, porous microspheres that stretch in responses to changes in pH or temperature. These spheres could be made of collagen, cellulose, alginate or chitosan. Thin sheets of muscle fiber could be cultured and mechanically stretched to induce development of aligned myotubes. The thin scaffold membranes could be extracted from the meat or left on if made of edible material. Several sheets of tissue could be combined to get the required thickness or processed to make a meat product. A scaffold for non-processed meat would be much more difficult to produce because of vascularization requirements that would require a network of edible, elastic, and porous material to exchange nutrients with the cells.

The media used to grow these cells would likely have to be cheap yet contain high levels of nutrients. Some promising alternatives include serum free media made from shitake mushroom extract. Proper levels of growth factors are also necessary for the media. Large volume bioreactors that maintain low shear and uniform perfusion such as rotating bioreactors would enhance the growth process.

Cultured meat could provide many benefits including control of ratio of saturated and unsaturated fat, reduction of food borne disease, improvement of meat nutrient content, and reduction of resources and pollution associated with farm animals. Whether or not cultured meat will be cost efficient is debatable but the technological obstacles are fewer than those for tissue engineering in clinical applications