Biomedical Engineering Reference
In-Depth Information
such as the gut and bone marrow, stem cells divide to repair and replace dam-
aged tissues perpetually as long as the person or animal is still alive. Each new
cell from a stem cell has the potential either to remain a stem cell or become
another type of cell with a more specialized function, such as a muscle cell, a
red blood cell, or a brain cell. In some other organs like the pancreas and the
heart, stem cells only divide under special conditions.
Mammalian and humans have two known kinds of stem cells: embryonic
stem cells and somatic or adult stem cells. These cells are important for living
organisms for many reasons. In the 3- to 5-day-old embryo called blastocyst,
the inner cells give rise to the organism and many of the specialized cell types
and organs such as the heart, lung, skin, sperm, eggs, and other tissues. In some
adult tissues including the bone marrow, brain, and muscle discrete populations
of adult stem cells generate replacements for cells that are lost through normal
wear and tear, disease, or injury.
Having unsurpassed regenerative abilities, stem cells are promising alterna-
tives for treating diseases such as diabetes and heart disease. Studies of stem
cells enable scientists to learn about the cells' essential properties making them
different from specialized cell types. Stem cells are now in use in the laboratory
for new drug screening and to develop model systems for the study of normal
growth and to identify possible causes of birth defects. At the same time, stem
cell research continues to advance knowledge about how an organism devel-
ops from a single cell and how healthy cells replace damaged cells in adult
organisms.
Stem cells and progenitor cells act as a repair system for the body and
replenish adult tissues. On the other hand, developing embryo consists of stem
cells that can differentiate into all the specialized cells called pluripotent cells
and at the same time maintain the normal turnover of regenerative organs such
as blood, intestinal tissues, and skin. Stem cells are young cells that can differ-
entiate into multiple cell types making them advantageous for cellular therapy 46
and are advantageous in that they can potentially be used for cellular therapies
due to the fact that they can differentiate into multiple cell types 353 including
cardiovascular cells. 354,355 Studies involving nanoparticles and stem cells have
recently been published. 42,44,46 Previous work demonstrated that PEGylated
fibrin gels 356 promote mesenchymal stem cell (MSC) tubulogenesis and dif-
ferentiation toward a vascular cell type 355,46 which suggests that MSCs could be
delivered to an injury site after an ischemic event that will assist in neovascular-
ization and tissue repair. 357,358
MSC migration were tracked in vivo using PEGylated fibrin gels to assess
the role of MSCs in the process of neovascularization and tissue repair that
can potentially lead to the development of better therapies and therapeutics
involving MSCs, for tissue repair. 46 The gold nanoparticle-loaded MSCs dem-
onstrated that nanoparticle loading decreased exponentially over time 46 which
previous investigators have cited as dilution of nanoparticle concentration per
cell as a result of cell proliferation and division. 359 In other studies, exocytosis
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