Cells

Cells for Tissue Engineering

 * The starting point for any attempt to engineer a tissue or organ substitute is a consideration of the cells that are to be employed
 * Considerations when selecting cells
 * A supply of sufficient quantity, or rather, the off-the-shelf availability of the cells
 * For emergency surgeries
 * It is only with off-the-shelf availability that the tissue engineered products will be used for the wide variety of patients
 * Free of pathogens and contamination
 * Source (autologous, allogenic, or xenogenic)
 * Type (stem cells or differentiated cells)

Cell Source

 * Autologous
 * Patient's own cells
 * Immune acceptable
 * Not viable for off-the-shelf applications
 * Allogenic
 * Cells from another human source
 * Viable for off-the-shelf applications
 * May require engineering immune acceptance
 * Xenogenic
 * From different species
 * Not only requires immune acceptance, but must be concerned with animal virus transmission

Differentiated Cells

 * Cells that are specialized for a particular function and do not maintain the ability to generation to generate other kinds of cells, or revert back to a less specialized cell
 * Present in adult tissues
 * There are more than 210 types of differentiated mammalian cells
 * Blood Vessels: Smooth Muscle Cells, Endothelial Cells, Fibroblasts
 * Heart: Cardiomyocytes
 * Cartilage: Chondrocytes
 * Bone: Osteoblasts
 * Skin: Fibroblasts, Epithelial Cells
 * Many researchers are focused on using differentiated cells in engineered tissues
 * Smooth muscle cells are used for engineering smooth muscle, blood vessels (with endothelial cells)
 * Cardiomyocytes are used for engineering cardiac tissue like cardiac muscle
 * Chondrocytes are used for engineering cartilage
 * Advantages of using differentiated cells
 * in vitro proliferation in a controllable way
 * Same cell type as in the target tissue can be used
 * Cardiomyocytes to engineer cardiac tissue
 * No ethical implications
 * Problems in using differentiated cells
 * May have immune response if using allogenic cells
 * Limited availability of autologous cells
 * Limited proliferation capacity
 * Each cell type has a different life span
 * Can not culture cells from the elderly for very long

Stem Cells

 * Stem cells are cells that have the ability to divide for indefinite periods in culture and give rise to specialized cells
 * Stem cells may solve many of the problems of using differentiated cells
 * Have the capacity to differentiate into different cell types
 * BMSCs can differentiate into blood cells
 * Important in engineered tissues for tissues that don't have the ability to regenerate like cardiac tissue
 * Stem cells posses two properties
 * Self-renewal, the ability to go through numerous cycles of cell division while maintaining the undifferentiated state
 * Potency, the capacity to differentiate into specialized cell types
 * Multipotent: can only differentiate into closely related family of cells.
 * Ex. Hematopepoietic stem cells differentiate into blood cells
 * Pluripotent: can differentiate into most tissues of an organism
 * Ex. Embryonic stem cells

Stem Cell Types

 * Embryonic Stem Cells
 * Pluripotent stem cells that can differentiate into all of the specialized embryonic tissues


 * Adult Stem Cells
 * Multipotent stem cells found in adult tissues