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Components included in engineered tissues. Any combination (one or more) of the following components may be included in engineered tissue constructs. Tissue-inducing factors (i.e. growth factors) mediate endogenous or exogenous cell growth and differentiation, often aiding in vascularization of complex tissues. Physical supports or scaffolds are often present to provide a 3D microenvironment that allows for cell integration or differentiation. Synthetic materials (i.e. polymeric hydrogels) or biologically derived substances (i.e. extracellular matrix [ECM] proteins) are also effective. Incorporation of exogenous progenitors endows engineered tissue with a regenerative capacity, improving the in vivo lifespan of the construct.