b2815 Tissue Engineering and Nanotheranostics “9.61x6.69”8 Tissue Engineering and Nanotheranostics3.1. Embryonic Stem Cells
The embryonic body is the home for many stem cells that have
been shown to be pluripotent (capable of differentiation into
almost any tissue type found in the body). Their role in the devel-
opment of new organisms requires that they have a theoretically
unlimited potential for self-replication and proliferation.^36 Both of
these traits make ESCs an attractive source for tissue engineering
purposes. Theoretically, implantation of ESCs into a wound site
would provide everything necessary for complete replacement of all
damaged tissues. However, a number of significant disadvantages
are associated with this cell type. First are the ethical concerns with
the harvesting of such cells, which necessarily deprives the embry-
onic body of the ability to develop into an adult.^27 Furthermore,
due to the cells’ proliferative and pluripotent nature, the risk of
teratoma formation is high.^36 Finally, use of ESCs to form tissue
engineered constructs for allografts can result in a detrimental
immune response.^28
3.2. Induced Pluripotent Stem Cells
Recently, it was discovered that it is possible to genetically repro-
gram somatic cells to behave as pluripotent stem cells.^29 This is
conducted with genes that have been identified as essential in the
maintenance of the embryonic environment, and has been best
demonstrated on fibroblasts.^29 The benefit of this cell type, besides
the pluripotency, is the ability to use cells harvested from the
patient. The cells could be obtained from a small skin biopsy, and
would theoretically be completely compatible with the patient’s
immune system if used as an autograft. iPSCs are not without their
drawbacks, however, which include the risk of teratoma formation
and low yield of the induction process.30,31 Furthermore, the full
ramifications of genetic manipulation are not yet known.^31 Myogenic
differentiation has been accomplished through overexpression of
critical genes including Pax7 or MyoD.37,
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