Biomedical Engineering Reference
In-Depth Information
To establish that stem cells are as multi-
potent, researchers have isolated single adher-
ent cell clones that were then expanded in
culture [
cells express genes from osteoblasts and syn-
thesize proteins including type I collagen, bone
sialoprotein, osteocalcin, osteopontin, and
osteonectin. In vivo, BM-MSCs that are loaded
either onto allogenic demineralized or miner-
alized bone matrix or onto to synthetic
hydroxyapatite matrices generate osteoid tissue
[
]. Initial in vitro studies
demonstrated that the BM-MSCs divide more
than
41
,
90
,
93
,
99
times and differentiate into smooth
muscle, osteoblastic, adipocytic, and chond-
rogenic phenotypes [
50
] and, later, into
tendon, ligament, and even cardiomyocytes
(Fig.
90
,
93
]. It was therefore obvious
that stem cells derived from human bone
marrow would be a source of osteoblasts for
bone tissue engineering.
In order for BM-MSCs to be used for generat-
ing tissue-engineered bone, two important
problems had to be solved. First, BM-MSCs are
quite rare; by some estimates there are as few
as one to two cells per million isolated mono-
nuclear cells [
19
,
18
,
60
,
61
,
63
,
85
]. These cells can also be
induced to display characteristics of endoderm
and ectoderm tissues such as hepatic, neuro/
glial, endothelial, and epithelial markers [
1
.
1
) [
94
,
124
91
,
97
]. Transplantation of labeled stem cells
produced chimeric mice and demonstrated
differentiation of the stem cells into cells of
endodermal, ectodermal, and mesodermal
origin [
,
121
]. It was therefore neces-
sary to develop methods to increase the number
of stem cells, while maintaining their osteo-
potential. This was accomplished by Bruder
and colleagues in
19
,
93
,
99
].
The osteogenic potential of BM-MSCs has
been extensively characterized in vitro [
52
16
,
17
,
90
,
93
,
99
]. Under appropriate conditions these
1996
[
16
,
17
].
Figure 1.1.
Adult adipose-derived stem cells (ADSCs) have the potential to differentiate into many different mature cell pheno-
types. From top to bottom: Row 1: undifferentiated adult ADSCs in expansion culture, 10
×
phase objective. Row 2: ADSCs possess
the ability to differentiate into adipocytes (left), osteoblasts (middle), and chondrocytes (right). Row 3: ADSCs also possess the
ability to differentiate into neurons (left) and myocytes (right).
