SupplementTissue engineering: the design and fabrication of living replacement devices for surgical reconstruction and transplantation
Section snippets
Current approaches in tissue engineering
The primary goal of all approaches in tissue engineering is the restoration of function through the delivery of living elements which become integrated into the patient. Although some techniques of guided tissue regeneration rely on matrices alone, and other approaches rely on cells alone, most investigators in tissue engineering use cells combined with matrices to achieve new tissue formation (figure). Below, we summarise progress with matrices, cells, in-vitro bioreactor systems, and the
Matrices
Most of the materials used as substrates or encapsulating materials for mammalian cells are either synthetic materials such as lactic-glycolic acid or polyacrylonitrile-polyvinyl chloride, or natural materials such as collagen, hydroxyapatite, or alginate. The former allow control of such material properties as strength, processability, degradation, microstructure, and permeability. Natural materials may be the actual in-vivo extracellular matrix components for cells, and as such would possess
Cells used in tissue engineering
Virtually every tissue type in the human body has been investigated in terms of tissue engineering and most studies have looked at specific cell types (figure). For clinical applications, the cells are generally derived from the patients themselves, from close relatives, or other individuals. For example, autologous chondrocyte transplantation for knee repair is in clinical use.19 In the case of tissue-engineered skin, neonatal dermal fibroblasts have been used. However, to provide cells for
In-vitro culture systems
Most of the early work in tissue engineering relied on the use of standard static cell-culture conditions for the in-vitro fabrication of tissue before implantation. However, stirred conditions have been shown to improve the quality of certain tissues, for example, cartilage.24
The use of bioreactors enables the in-vitro culture of greater volumes of cells than can be obtained with conventional tissue-culture techniques. Flow and mixing within bioreactors can be controlled to enhance mass
The generation of complex vascularised tissues and organs
Although the approaches discussed above will meet the needs of many tissue types, the fabrication of large tissue and whole organs de novo remains a major challenge.
The use of localised slow release of growth factors is one approach that is being tested. For example, locally released epidermal growth factor over several weeks led to a several-fold increase in the vascularisation and engraftment of liver cells in animal models.25 Another approach involves the creation of devices that have a
Concluding remarks
Tissue engineering is a new technology, but encouraging results are already being reported. The need is enormous and the potential benefits profound. However, much work needs yet to be done, and the research requires close interdisciplinary cooperation among clinical scientists, biologists, materials engineers, and chemists.
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