SYNTHETIC ENROUTES TO ENGINEER ELECTROSPUN SCAFFOLDS FOR STEM CELLS AND TISSUE REGENERATION - Micro and Nanotechnologies in Engineering Stem Cells and Tissues - page 131

5.3 NOVEL NANOFIBROUS STRATEGIES FOR STEM CELL
REGENERATION AND DIFFERENTIATION
Stem cells are biological cells found in all multicellular organisms and have the
capacity to self-renew; they divide via mitotic cell division and differentiate into
diverse specialized cell types (tissue or organ). In mammals, there are two broad
types of stem cells, embryonic stem cells, which are isolated from the inner cell mass
of blastocysts, and adult stem cells, which are found in various tissues. During
development of an embryo, stem cells differentiate into many different types of
specialized cells, and they also maintain the normal turnover of regenerative organs,
such as blood, skin, or intestinal tissues. Another type is adult stem cells, which are
undifferentiated cells found along with the differentiated cells in an organ or tissue,
which can renew themselves and can differentiate to yield major specialized cell
types of organ or tissue.
In mature organisms, stem cells and progenitor cells act as a repair system in the
body, replenishing matured tissues. These adult stem cells maintain and repair the
tissues in which they constitute. They can be collected from tissues such as adipose
tissue, bone marrow, mammary tissue, central nervous system, olfactory bulb, and
so on. Transdifferentiation ability has also been demonstrated by adult stem cells
(i.e., they can switch their specific developmental lineage to another cell type of a
different lineage). 74 However, the molecular mechanism that drives transdiffer-
entiation is not clearly understood. Stem cells have the unique property of self-
renewal without differentiation if appropriate biological and physical induction
conditions are provided. In the context of tissue engineering, the use of stem cells
has the following advantages compared with engineered tissue constructs: (1) they
have high proliferative capacity, (2) they provide excellent regenerative capability
that will likely lead to desired integrity and functionality of the engineered
construct, (3) they make it possible to contemplate multifunctional tissue con-
structs (e.g., osteochondral tissue), and (4) they reduce or eliminate tissue rejection
or failure.
Although the application of living cell therapy is associated with challenges, stem
cells constitute the functional elements of tissue engineering and regenerative
medicine. 75 The following are the prerequisites for researchers and clinicians to
work out the success in cell-based treatments. For transplantation practices, stem
cells must be reproducibly made to (1) differentiate into the desired cell types;
(2) survive in the recipient after transplantation; (3) integrate into the surrounding
tissue after transplantation; (4) function appropriately for the duration of the
recipient's life; and (5) avoid harming the recipient in any way.
Researchers are working in the direction of minimizing or avoiding the problem
of immune rejection of regenerated tissues with different research strategies. The
most commonly studied stem cells are the bone marrow stem cells, especially the
MSCs and hematopoietic stem cells (HSCs). Under controlled conditions,
the MSCs have the ability to differentiate into cell lineages 76 such as osteoblasts,
chondrocytes, cardiomyocytes, and fibroblasts. The in vitro cell culture of hMSCs,
proliferation and differentiation into tissue specific cell phenotype such as