Biomedical Engineering Reference
In-Depth Information
synthetic HA is not an ideal ceramic for bone tissue engineering
since HA does not degrade properly in the human body.
32
In con-
trast, TCP is a degradable calcium phosphate ceramic; thus, TCP is
considered to be a better ceramic scaffold for bone tissue engineer-
ing. However, the osteoconductive properties of TCP are known to
be less than those of HA.
37
In order to improve the osteoconduc-
tive properties of TCP, several biphasic calcium phosphate ceramics
(HA/TCP) have been developed.
37
,
38
Althoughtheoptimalcomposi-
tion of HA/TCP remains controversial, this approach seems promis-
ing to develop a more reliable ceramic scaffold for bone tissue
engineering.
Porosity of the ceramic scaffold has a great influence on the e
-
cacyofbonetissueengineeringsinceitdirectlyaffectscelladhesion,
migration, and proliferation of the osteogenic cells.
31
,
39
,
40
Anatom-
ically, cortical bone has 3%-12% porosity, while trabecular bone
has porosity in the range of 50%-90%.
41
Since the primary tar-
get of bone tissue engineering is the regeneration of trabecular
bone and ceramic scaffolds should have enough strength to pro-
vide physical support for the cells, 65%-75% porosity might be
ideal for ceramic scaffolds. Pore diameter is also known to influ-
ence cell migration, proliferation, and eventually the ability to sup-
port bone regeneration. The minimum pore size to regenerate
bone is generally considered to be 50-100
μ
m.
38
,
40
Accordingly,
β
-TCP granules, which have 75% porosity and a pore size rang-
ing from 100 to 400
μ
m, were utilized in our clinical trials. Inter-
connectivity of the pore and geometry of the scaffold are also
known to influence the e
cacy of bone tissue engineering, and
these factors might cause a difference in osteoconductive proper-
ties between block- and granule-type ceramic scaffolds.
34
However,
the influence of these factors on osteogenic cells has not been well
investigated.
Although the development of novel biomaterials is a rapidly
expanding area of science, basic understanding of cell-to-material
interactions should be carefully considered to develop an ideal
ceramic scaffold for bone tissue engineering. From a clinical point
of view, degradability, composition, porosity, pore size, intercon-
nection of the pore, and geometry are factors that need to be
considered.
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