Tissue Engineering

Tissue engineering (TE ) ( engl. tissue structure or tissue engineering ) is the umbrella term for the artificial production of biological tissue by the directed cultivation of cells in order to replace diseased tissue in a patient or regenerate.

Properties

In tissue engineering, cells are usually taken from the donor organism and grown in the laboratory in vitro. Depending on the cell type, these can be cultured as a monolayer or two-dimensionally by means of specific cell - dimensional scaffolds. They can then be transplanted to the recipient ( re-). These can then be implanted in mostly the same organism and thus maintain or restore tissue function. Tissue Engineering Products (TEP ) belong to the group of advanced therapy medicinal products and are one of the application examples of the regenerative and personalized medicine.

" Tissue engineering is the application of principles and methods of engineering, materials science and life sciences to obtain a fundamental understanding of structure -function relationships in normal and pathological mammalian tissues; and the development of biological substitutes to regeneration, preservation or improvement of the function of tissue. " In a narrower sense, it refers to the removal of cells to the patient for the cultivation of the desired organ.

Tissue engineering involves four elements, namely

The biological or synthetic scaffold is combined to a 3D cell culture prior to culture with the extracted vital material. The cultivation can be carried out either in the body ( in vivo tissue engineering) and in the laboratory ( in vitro tissue engineering ). In both cases, ideally, there is a control of signaling molecules which reach the cell, so that the formation of new tissue is supported. The cells can be partially printed with a Bioprinter to a surface.

The Regenerate or constructs are by adoptive cell transfer implanted into the target region of the organism. The advantage of such an implant with autologous ( patient's own ) cell content is that it is accepted by the immune system of the patient, since only the cultured cells have such proteins on the cell surface that the immune system recognizes as "own". This tissue-engineered implants should not normally be rejected. A good example is the production of completely autologous heart valves and vascular grafts, which then are used, for example, when a clogged artery can not be replaced by a body's vein. In such a case is typically a plastic prosthesis is used, which represents an unsatisfactory alternative.

The problem of tissue engineering is that specified cells lose their functionality ( dedifferentiation ). An animal experimental study in adult sheep, were implanted into the autologous vascular grafts, showed up to the end of the experiment continuous vessels, which built a solid tissue. So far it has managed to grow skin and cartilage tissue and blood vessels for commercial application.

This differentiated cells from the organism in vitro are propagated mostly already. A new approach is the use of adult or induced pluripotent stem cells ( iPS). The adult cells may be harvested from the bone marrow or internal organs of adults and iPS are generated by reprogramming of cells (eg, fibroblasts from the skin). The stem cells can be propagated in culture vessel and then differentiated by chemicals to specific cell types required.

Engine for the development of tissue engineering is the growing demand for safe replacement tissues and organs as well as the basic research.

Four types of implants are generally distinguished here:

• Derived from other organisms ( xenogeneic) - eg heart valves
• By an individual of the same species (allogeneic ) - eg kidney
• From the patient (autologous ) - eg skin
• Of genetically identical individuals ( syngeneic ) - such as identical twins

Applications

In the previously successful TE approaches are exclusively tissue from a single cell type. Especially suitable for tissue culture is cartilage, as cartilage is already in the living body from a single cell type, is nourished only by the synovial fluid and its scaffolding of collagen fibers and proteoglycans establishes itself. Other important, indeed vital tissues such as Liver or renal parenchyma, are so complex in their structure that in - vitro culture is not so far been successful. In order to use the effectiveness of specific organ cells with life-threatening diseases, the parenchymal cells are previously exposed in dialysis systems the bloodstream. For tissue engineering of functional organs would in addition to the parenchymal cells (such as hepatocytes) and supporting tissue, blood vessels and biliary vessels, lymphatic vessels may also be grown. Such co-cultures of different cell types are a challenge for the future. Cocultures have so far been carried out for chondrocytes and osteoblasts and endothelial cells and vascular smooth muscle cells. Before these problems of co-culture are not solved, TE will not achieve the broad goals of breeding organ vital organs. Only then transplantation of donor organs through targeted breeding of organs with the help of the body's cells are replaced.

Another important application of tissue engineering is the application in basic research. The natural tissue modeled constructs are used there to investigate cellular mechanisms. In addition, the methods allow the preparation of the TE -dimensional tissue-like constructs cell where the effect of pollutants (e.g. pesticides ), but also the effect of pharmaceuticals can be tested. He might have had another future application in the biotechnological production of in vitro meat to bypass factory farming and the associated problems.