In order to restore or assume the function of a damaged or lacking tissue or organ the transplantation of natural tissues or organs from another donor or, if possible, the concerned individual himself is an established practice that has long been known. Due to the constant lack of suitable donor tissues and donor organs and other disadvantages of natural tissue, e.g., rejection reactions and the risk of the transfer of diseases from the donor to the recipient, many efforts are being directed to the production of artificial tissues and organs as alternatives.
A customary procedure for this is the provision of a carrier or matrix structure from material compatible with the body that is colonized with differentiated cells of the target tissue, and the cultivation of the cells in vitro until a tissue-like cell structure has been produced. The differentiated cells are obtained either from cultures of explanted tissue samples or from stem cells that had been stimulated to differentiate. The use of stem cells permits a more rapid production of larger amounts of the desired cells in many instances. Traditionally, pure cell populations of a certain type are produced. Most of the in vitro organs or in vitro tissues known in the state of the art are disadvantageous in as far as that they do not have or do not develop the tissue structure that corresponds to the morphological constitution of the native tissue or organ even after implantation and a fairly long residence time in the body. This applies as a rule even when the carrier matrix had been colonized with several different populations of tissue-typical cells.
Another approach for treating degenerative diseases or damage to tissues and organs using stem cells consists in implanting the stem cells and/or differentiated cells derived from them directly into the damaged tissue/organ in order to proliferate there and result in a regeneration of the damaged tissue/organ. In this instance too the implantation or regeneration of a certain cell type traditionally is in the foreground. The problem is, however, that in very many degeneration phenomena or damages to various organs a plurality of cells is always involved so that, e.g., in the skin keratinocytes, epithelial cells and blood vessels are also affected in addition to fibroblasts. In the case of nerve damage even glia cells often have to be replaced too and muscle damage often means destruction of the accompanying nerves.