Chapter 069. Tissue Engineering (Part 1)

Harrisons Internal Medicine Chapter 69. Tissue EngineeringTissue Engineering: Introduction The origins of tissue engineering date to the sixteenth century when complex skin flaps were used to replace the nose. Modern tissue engineering combines the disciplines of materials sciences and life sciences to replace a diseased or damaged organ with a living, functional substitute.The most common tissue engineering approach combines cells and matrices to produce a living structure (Fig. 69-1). These strategies also include the use of scaffolding, cells, and growth factors to shape new tissues. The term regenerative medicine has emerged as a concept inclusive of tissue engineering...
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Chapter 069. Tissue Engineering (Part 1) Chapter 069. Tissue Engineering (Part 1) Harrisons Internal Medicine > Chapter 69. Tissue Engineering Tissue Engineering: Introduction The origins of tissue engineering date to the sixteenth century whencomplex skin flaps were used to replace the nose. Modern tissue engineeringcombines the disciplines of materials sciences and life sciences to replace adiseased or damaged organ with a living, functional substitute. The most common tissue engineering approach combines cells and matricesto produce a living structure (Fig. 69-1). These strategies also include the use ofscaffolding, cells, and growth factors to shape new tissues. The term regenerativemedicine has emerged as a concept inclusive of tissue engineering and stem celltherapy (Chap. 67).Figure 69-1 Schematic of basic principles of tissue engineering. [From Langer R, Vacanti J: Tissue engineering. Science 260:1993 (Fig. 1),with permission.] Cellular Components of Tissue Engineering The foundation of tissue engineering is the combination of a three-dimensional scaffold with live and functional cells. Cells used in tissueengineering should be easily accessible and capable of proliferation whilemaintaining their differentiated function. There are three possible sources for cells:autologous, allogenic, and xenogenic. Autologous cells are isolated directly from the patient. They have theadvantage of avoiding immune-mediated rejection. However, a potential limitationis that they may not be available or able to proliferate to the required tissue mass. Allogenic cells are harvested from a donor other than the patient. They havethe advantage of being more readily available, but the immune system must bemodulated to avoid rejection. Xenogenic cells, or those from a different species, may also be used butalso risk immune rejection or transmission of animal pathogens. Although cells such as fibroblasts and smooth-muscle cells proliferaterapidly, other cells proliferate slowly or lose their tissue-specific function whencultured, thereby limiting their use. In addition, cellular characteristics maydepend on their location within the body. For example, the cell-to-cell interactions and function of endothelial cellsin the pulmonary microvasculature are different from those in the blood-brainbarrier. The microenvironment of the cell, including the presence of other celltypes, soluble factors, and the presence of physical or mechanical forces may alsoalter the function of a transplanted cell. Stem cells provide a promising cell source because they are capable ofrapid proliferation and they can be induced to differentiate into multiple celllineages (Chaps. 66 and 67). Human embryonic stem cells are capable of differentiating into endoderm,mesoderm, or ectoderm tissue types. Multipotent adult stem cells have been foundin multiple mature tissues including the bone marrow, brain, heart, and liver. Inaddition to being able to differentiate into numerous lineages, adult stem cellsgenerate a relatively muted immune response.