Tissue Engineering
Regenerative medicine is a broad definition for innovative medical therapies that will enable the body to repair, replace, restore and regenerate damaged or diseased cells, tissues and organs. Regenerative medicine promises to extend healthy life spans and improve the quality of life by supporting and activating the body s natural healing. This broad field encompasses a variety of research areas including cell therapy, tissue engineering, biomaterials engineering, growth factors (induction of regeneration by biologically active molecules) and transplantation science.
The term regenerative medicine is often used synonymously with tissue engineering. Tissue engineering was once categorised as a subfield of biomaterials, but having grown in scope and importance, it can be considered as a field in its own right. It is the use of a combination of cells, engineering and materials methods, and suitable biochemical and physio-chemical factors to improve or replace biological functions. While most definitions of tissue engineering cover a broad range of applications, in practice the term is closely associated with applications that repair or replace portions of or whole tissues. The term has also been applied to efforts to perform specific biochemical functions using cells within an artificially-created support system.
Tissue engineering / regenerative medicine is an emerging multidisciplinary field involving biology, medicine, and engineering that is likely to revolutionize the ways we improve the health and quality of life by restoring, maintaining, or enhancing tissue and organ function. In addition to having a therapeutic application, where the tissue is either grown in a patient or outside the patient and transplanted, tissue engineering can have diagnostic applications where the tissue is made in vitro and used for testing drug metabolism and uptake, toxicity, and pathogenicity.
The foundation of tissue engineering or regenerative medicine for either therapeutic or diagnostic applications is the ability to exploit living cells in a variety of ways. Tissue engineering utilizes living cells as engineering materials. Examples include using living fibroblasts in skin replacement or repair, cartilage repaired with living chondrocytes, or other types of cells used in other ways. Cells are often categorized by their source: Autologous cells, Allogeneic cells, Xenogenic cells, Syngenic or isogenic cells (cells isolated from genetically identical organisms, such as twins), Stem cells, Primary cells, Secondary cells.
Cells are often implanted or ‘seeded’ into an artificial structure capable of supporting three-dimensional tissue formation. These structures, typically called scaffolds, are often critical, both ex vivo as well as in vivo, to recapitulating the in vivo milieu and allowing cells to influence their own microenvironments. Tissue engineers use artificial and natural materials that provide structure and biochemical instructions to cells as they grow into specific kinds of tissue. These materials known as scaffolds provide support and materials for tissue regrowth. Many different materials (natural and synthetic, biodegradable and permanent) have been investigated. Biodegradability is often an essential factor since scaffolds should preferably be absorbed by the surrounding tissues without the necessity of a surgical removal. New biomaterials have been engineered to have ideal properties and functional customization: injectability, synthetic manufacture, biocompatibility, non-immunogenicity, transparency, nano-scale fibers, low concentration, resorption rates, etc. Scaffolds may also be constructed from natural materials: in particular different derivatives of the extracellular matrix have been studied to evaluate their ability to support cell growth. A number of different methods has been described in literature for preparing porous structures to be employed as synthetic tissue engineering scaffolds.
Biomolecules can be used in tissue engineering procedure including angiogenic factors, growth factors, differentiation factors and bone morphogenic proteins.
Tissue engineering has been an active field of research for several decades now. However, the amount of clinical applications in the field of tissue engineering is still limited. One of the current limitations of tissue engineering is its inability to provide sufficient blood supply in the initial phase after implantation. Insufficient vascularization can lead to improper cell integration or cell death in tissue-engineered constructs. Recent advances in understanding the process of blood vessel growth has offered significant tools for therapeutic neovascularization. Several angiogenic growth factors including vascular endothelial cell growth factor (VEGF) and basic fibroblast growth factor (bFGF) were used for vascularization of ischemic tissues. Three approaches have been used for vascularization of bioengineered tissue: incorporation of angiogenic factors in the bioengineered tissue, seeding endothelial cells with other cell types and prevascularization of matrices prior to cell seeding. Advantages and limitations of recent strategies aimed at enhancing the vascularization of tissue-engineered constructs has been an area of tissue engineering research. Combining the efforts of different research lines might be necessary to obtain optimal results in the field.
