Biomedical Engineering Reference
In-Depth Information
words, identification of growth factors that stimulate the
proliferation of MSCs and support their multilineage
differentiation potential is a critical step towards the
clinical application of MSCs.
adipose-derived adult stem (ADAS) cells. Under lineage-
specific biochemical and environmental conditions,
ADAS cells will differentiate into osteogenic, chondro-
genic, myogenic, adipogenic, and even neuronal path-
ways. Although it remains to be determined whether
ADAS cells meet the definition of stem cells, they are
multi-potential, are available in large numbers, are easily
accessible, and attach and proliferate rapidly in culture,
making them an attractive cell source for tissue engi-
neering. Moreover, ADAS cells demonstrate a substantial
in vitro
bone formation capacity, equal to that of bone
marrow, but are much easier to culture. It has been
empirically shown that several growth factors and hor-
mones, in combination with cellular condensation and
rounded cell morphology, may promote the chondro-
genic differentiation of ADAS cells.
Cell differentiation
The forces driving stem cell differentiation, or main-
taining stem cells in a state of suspended undiffer-
entiation, include secreted and bound messengers or
homing signals. Specific chemicals and hormones that
cause the transformation of MSCs to osteoblasts, chon-
drocytes, and adipocytes have been elucidated.
Table
7.2-10
represents the commonly used
in vitro
environ-
ments for differentiations. For instance, osteogenic dif-
ferentiation occurs when MSCs are treated with
dexamethasone, b-glycerophosphate, and ascorbic acid
(AA), and this differentiation to osteoblasts is charac-
terized by gene expression of osteopontin (OP) and al-
kaline phosphatase (ALP). Just as important are the
cellular environmental sensors sensitive to oxygen, tem-
perature, chemical gradients, mechanical forces, and
others cues in the microenvironment. The notion of
microenvironments affecting stem cell division and func-
tion is not new. Schofield dubbed these ''niches'' with
respect to hematopoietic stem cells, and subsequent re-
ports have described their presence in numerous tissues
including neural, germline, skin, intestinal, and others
[31]
.
7.2.8.2.3 Umbilical cord blood-derived cells
Human umbilical cord blood-derived cells may be alter-
native autologous or allogeneic cell source. Umbilical
cord blood cells contain multipotent stem cells and these
cells have been used to generate tissue-engineered pul-
monary artery conduits in a pulsatile bioreactor
[32]
.
Cells from umbilical cord artery, umbilical cord vein,
whole umbilical cord, and saphenous vein segments were
compared for their potential as cell sources for tissue-
engineered vascular grafts
[33]
. All four cell sources
generated viable myofibroblast-like cells with ECM for-
mation including types I and III collagen and elastin.
There were also CD34
umbilical cord cells which have
the capacity to generate endothelial cells.
7.2.8.2.2 Adipose-derived stem cells
A
second large stromal compartment found in human
subcutaneous adipose tissue has received attention be-
cause of
the presence of multipotent cells named
Table 7.2-10 Lineage specific differentiation induced by media supplementation
Medium
Media
Serum
Supplementation
Osteogenic
Dulbecco's minimal essential medium
(DMEM)
10% Fetal calf serum (FCS)
50
m
M ascorbic acid 2-phosphate,
10 mM
b
-glycerophosphate,
100 nM dexamethasone
Chondrogenic
High-glucose DMEM
10 ng/ml transforming growth factor
(TGF)-
b
3,100 nM dexamethasone, 6
m
g/ml
insulin, 100
m
M ascorbic acid 2-phosphate,
1 mM sodium pyruvate, 6
m
g/ml transferrin,
0.35 mM proline, 1.25 mg/ml bovine serum
albumin
Adipogenic
DMEM
10% FCS
1
m
M dexamethasone, 0.2 mM
indomethacin, 10
m
g/ml insulin, 0.5 mM
3-isobutyl-l-methylxanthine
Myogenic
DMEM
10% FCS, 5% horse serum
10
m
M 5-azacytidine, 50
m
M
hydrocortisone
Cardiac
Isocove's modified DMEM
20% FCS
3
m
M 5-azacytidine
