Cultured livers
THE liver, a dark red gland situated in the upper right side of the abdomen, performs a wide range of important functions like secretion of bile (important for the digestion of fat) and the conversion of sugars into glycogen. Due to the complex nature of the functions performed by it, its structure is also extremely complicated with different types of cells arranged in a three dimensional pattern (Science, Vol 270, No 5234).
Tissue engineering is a field which involves the developing and growing of tissues like skin and cartilage in the lab. These are used as possible replacements for damaged tissues. The field is about a decade old and has most recently tried creating liver tissue.
Growing skin and cartilage is comparatively simple as these consist of just one or two types of cells arranged on a synthetic polymer scaffold or mesh. The mesh in turn is made up of a protein, collagen. However, a laboratory-grown liver would involve an extremely sophisticated process because a number of cells have to be arranged and grown in a particular way.
Chemical engineer Linda Griffith Chime from the Massachusetts Institute of Technology (MTT), LISA, has designed a scaffold called 'heptameters' that attract liver cells and rejects other types of cells. Others ire attempting to grow nerve cells on similar lines in the hope that the repair of damaged nerves or the creation of synthetic blood vessels would be possible. Researchers are also exploring the possibilities of growing other tissues like bone, tendon, intestine and heart valves in the laboratory.
Teflon fabric mesh is being used in the process because it is considered to be fairly safe for biological implants. A pattern made on it guides neuritis (the cell arms which carry nerve impulses over gaps caused in the central and peripheral nervous systems by illness or accident). The pattern is made with the protein lamina (which acts as a guide and blinds nerve cells). The Polymer mesh is covered with a nickel mask and is exposed to hot ionised gas which penetrates the nickel and converts fluorine atoms to active hydra groups. These active groups then act as links to which reposed sequences called YIGSR sequences are attached. The researchers are now trying to roll this modified fabric into tubes that can be wrapped around damaged nerves in the body.