CELL - BASED NANOCOMPOSITES AND BIOMOLECULES FOR BONE TISSUE ENGINEERING - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 563

16.4 SOURCES OF STEM CELLS USED FOR BONE TISSUE
ENGINEERING TO INCREASE OSTEOGENIC DIFFERENTIATION

In recent years, the rave on MSCs has been taking the scientifi c community by
storm owing to its very nature of the cells. MSCs are non-hematopoetic stem cells
which have the ability to become many tissues such as bone, adipose, cartilage,
skin, muscle, tendon, and so on. MSCs can be derived from several sources and
comprehensive studies have been done in hope of determining the ideal source of
MSCs for bone applications as discussed in the subsequent sections of this
chapter.

16.4.1 Adipose-Derived Stem Cells
Although for bone applications, bone marrow aspirates seem to be a “more” suit-
able choice for the extraction of stromal cells, the harvesting procedure for bone
marrow is invasive and the number of stem cells from bone marrow varies from
patient to patient, depending on medical condition and age. Bone marrow stromal
cells can be as little as one in 10 7 to 10 8 cells 15 . The number of osteogenic progeni-
tor cells found in bone marrow decreases from 66.2 9.6 for every 10 6 cells in

patients who are under 40 years of age. The number of these cells further decreases
to 14.7

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2.6 per 10 6 cells in older patients 135 . In addition, the amount of bone
marrow drawn from the patient is limited. To counter these issues, adipose tissue
has been used as a source for stem cells as an enormous quantity of fatty tissue
can be harvested. There are about 300 colonies per 100-mm dish for bone marrow
samples and out of which one MSC per 33,000 nucleated cells are present 136 . In
other studies, typically there are one MSC in every 50,000 or one MSC in every
100,000 nucleated cells, which constitute to about a few hundred MSCs for every
milliliter of bone marrow 135,137 . The number of adherent bone marrow MSCs is
about one in 10 5 nucleated cells 138 . For the confl uency of bone marrow-derived
stem cells plated between 20,000 to 400,000 cells/cm 2 , it took about fi ve to seven
days 139,140 . Confl uence was achieved within the same time period using the initial
plating of 3,500 adipose derived stromal cells/cm 2, 141 .
Immortal adipose stromal cell lines (ATSCs) was developed by tranducing
non-human primate-derived ATSCs with a retrovirus expressing TERT (catalytic
protein subunit of the telomerase complex). The expression of TERT can be uti-
lized for creating cell lines that can expand indefi nitely while maintaining the
multi-linage potential. The ATSC-TERT cells exhibited an increase level of
telomerase activity and mean telomere length. These ATSC-TERT cells showed
multi-lineage potential, on a lesser extent in untransduced cells in vitro . The dura-
tion of which calcium was produced by ATSC-TERT cells was greatly shortened
(one week of culture), in comparison, calcium production occurred when native
ATSCs was subjected to three to four weeks of culture in an osteogenic media.
Enhanced expression of ostoblastic markers such as, osteoblast-specifi c factor 2,
chondroitin sulfate proteoglycan etc. was associated with ATSC-TERT cells.
These observations suggested that telomerase expression could open new

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