Biomedical Engineering Reference
In-Depth Information
materials developed by combining with biodegradable polymers,
introducing macroporocity, etc., are some of the strategies to
improve degradation, bone ingrowth, and osteoconductivity.
38
The
pore size of the scaffold is an important parameter for good cellular
distribution.Ithasbeensuggestedthathighporosity isbeneficialin
cellgrowthanddistribution.
39
Ithasbeensuggestedthataporesize
of 200-400 microns as optimum for cell ingrowth, however, is cell
specific.
40
-
43
Bone tissue mainly consists of matrix-producing osteoblasts,
tissue-resorbing osteoclasts, and osteocytes. All these cells are
required for developing an engineered bone tissue. However,
osteoblasts and osteocytes may be derived from stem cells that
synthesize and regulate the mineralization. Human bone marrow-
derived MSCs can be differentiated into the osteogenic lineage
by culturing the cells in the presence of the osteogenic dif-
ferentiation supplements dexamethasone, ascorbic acid, and
β
-
glycerophosphate.
44
,
45
Osteogenic differentiation of mouse and
human embryonic stem cells has been established
in vitro
by cul-
turing the cells in a medium supplemented with ascorbic acid,
β
-glycerophosphate, dexamethasone,
46
-
48
bone morphogenetic
protein 2 (BMP2), compactin,
49
orvitamin D
3
.
50
For favoring tissue ingrowth, growth factors are also usually
incorporated into the scaffold materials. These include BMPs, basic
fibroblast growth factor (bFGF), transforming growth factor-beta
(TGF-
β
), vascular endothelial growth factor (VEGF), etc., that are
used commonly because of their osteoinductive properties and
vascularisation.
38
BMPs are the regulatory molecules that are
involvedinskeletaltissueformationduringembryogenesis,growth,
adulthood, and healing
51
and are known to be very important reg-
ulators of proliferation and osteogenic differentiation of MSCs.
52
BMP-2 and BMP-7 have been demonstrated to enhance bone regen-
eration in variousexperiments.
53
-
56
4.6 Conclusion
Compared with natural human bone, the presently studied poly-
mer scaffolds and ceramic scaffolds have insu
cient elastic stiff-
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