Biomedical Engineering Reference
In-Depth Information
Density of the LP was 3.096 gram per cm 3
±
0.003 and was 3.093 gram per cm
3
0.002 for the HP (no signifi cant difference, p = 0.18). SEM image analysis
showed that the LP granules had a mean diameter granulometry of 780
±
μ
m
±
148
and the HP samples of 814
207 (no signifi cant difference, p = 0.13).
After three and six weeks of implantation, newly-formed bone was observed
in both samples. Bone ingrowth was less apparent at three weeks than at six weeks
and seemed to develop faster after implantation of high porosity granules. In the
early stages, it consisted of woven bone containing many osteocytes. Newly-
formed bone was observed mainly in the deep zones of the implanted defects
from the surface to the core, initially in close contact with the BCP particles (with-
out fi brous interposition) but always close to the bordering bone. Osteoid ap-
peared around the ceramic particles and was observed at the early time of three
weeks. Using SEM, bone ingrowth at three weeks in the LP group was 5%
μ
m
±
±
0.3
of the implanted defect, and was greater than in the HP group (1.6%
±
0.4,
p
0.0001). At six weeks, in the LP group, the amount of newly-formed bone was
4.3%
<
1.6,
p = 0.044). Between three and six weeks, the amount of newly-formed bone in-
creased in the HP group (p
±
0.5 of the implanted defect, and was lower than in the HP group (8.6%
±
0.0001).
During the same interval, the amount of newly-formed bone did not signifi -
cantly increase in the LP group (p = 0.25). The BCP surface area in the implanted
bone defects at three weeks was not statistically different between the two groups
(p = 0.1), and no more signifi cant at six weeks (p = 0.8). The decrease in the BCP
surface area was not signifi cant between three to six weeks in the LP group
(p = 0.4) or in the HP group (p = 0.3). With the LP granules, new bone formation
was signifi cantly greater at three weeks than with HP. This could be related to
higher macrophagous activity with regard to the release of large particles (as con-
fi rmed by histological examination), in addition to the release of Ca and P ions.
Between three and six weeks, newly-formed bone did not signifi cantly increase in
the LP granules, whereas it did with the HP (5-fold increase), confi rming previous
studies about high initial infl ammation, and macrophagous activity acting as a
booster for osteogenic cell differentiation [52].
At the later time of six weeks, there was an inversion in the amount of newly-
formed bone, with more newly-formed bone in the HP implants confi rming the
osteo-inductive property of the micropores as described in other animal models.
The reason why granules that are less porous can induce faster bone ingrowth is
not clear and needs further experiments. It has not been clearly elucidated why
higher porosity is related to a huge increase in new bone formation after three
weeks.
<
4.4.2 BCP-Based Macroporous Cements
The need for a material for Minimally Invasive Surgery (MIS) prompted the
development of a concept for injectable, mouldable calcium phosphate cement
(CPC) as bone substitutes. Currently, several calcium phosphate bone cements
are commercially available and more are being investigated. The concept was fi rst
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