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Tissue engineering: a biotechnologic challenge and chance for the future of operative medicine

Tissue engineering (TE) has been defined as “the application of the principles and methods of engineering and the life sciences toward the fundamental understanding of structure-function relationships in normal and pathological mammalian tissues and the development of biological substitutes that restore, maintain, or improve tissue function” (Skalak & Fox 1988). There are prognoses that the economic volume of TE will soon exceed that of gene therapy, and that it may be one of the developments in biotechnology with the most impact. TE offers bright prospects especially for surgeons, and clinically practicing surgeons may play a major role to ensure the success of TE. Notably tissue engineering may offer more functional solutions for chronic diseases and degenerative ailments than conventional treatments. These chronic deficiencies constitute an increasing social and economic burden, especially in western societies with aging populations. Two relatively simple tissue types – epithelium (epidermis and oral mucosa) and cartilage – have already been introduced into routine clinical practice (BioSeedS/BioSeedC). They share the peculiarity that they do not need an intrinsic vascular system for parenchymal cell survival and function. Other clinically relevant tissue defects currently under investigation for this kind of tissue substitution include nervous tissue, cornea, liver, endocrine pancreas, kidney tubules, urothelium and bladder, adipose, cardiovascular and musculoskeletal tissues (bone, cartilage, muscle, tendons, ligaments), abdominal wall and many more. For practical application, tissue engineering approaches can be categorized into more substitutive approaches, where the aim is the ex vivo construction of a living tissue or organ similar to a transplant, versus histeoconductive or histeo inductive concepts. With regard to this aspect a frequently used synonym is regenerative medicine. The latter approach attempts to optimize the structure and composition of biogenic or (semi)synthetic matrix materials, boost or select living cells for optimal proliferation in vivo, and to use highly specific growth factors or gene therapy transfecting for such cytokines. For the successful development of products applicable in TE a close co-operation between material sciences, biology (cell biology, molecular biology, genetics), medicine (clinical sciences, embryology, anatomy, physiology) and industry is a prerequisite. Only a comprehensive understanding of the components involved (biomaterials, cells, cytokines, genes) can lead to successful manipulation of reparative processes. With increasing experimental success in the development of TE products, the importance of a complex medical technology (including minimally invasive surgery) to transfer them into clinical application becomes increasingly important. Materials used for TE applications must be biocompatible, non-toxic (including their breakdown products), non-carcinogenic, sterilizable and surgically handable. They should have an intrinsic mechanical stability as requested for the tissue type to be substituted for. In most cases they should be resorbable in the order in which they are replaced in vivo by the newly produced matrix. They should also be tissue conductive (guide migrating and proliferating cells) and possibly tissue inductive (induce specifically the proliferation of cells). To permit the survival of living cells they must be permeable for nutrients, cytokines and waste products. Ideally they may contain binding sites for cells (e.g. fibronectins). Currently used Min Invas Ther & Allied Technol 2002: 11(3) 85–86