Biomedical Engineering Reference
In-Depth Information
bone formation was also observed in the fi rst three implants in which the MBCP
granules were fi lled with both compact bone at the border, and trabecular bone
within the granules. Neither acellular, avascular areas nor fi brous encapsulation
was observed in either sample. No statistical difference was observed between
the centre and the quarters of the length defect according to the ceramic and
newly-formed bone calculated with SEM image analysis.
As autologous bone grafts or biomaterial alone have failed to reconstruct
large defects, BM cells have been proposed in this indication. BM is composed of
haematopoietic cells and mesenchymal stem cells (MSC). The latter are multi-
potent and can differentiate, among others, into an osteoblastic lineage. BM has
been reported to contain almost one-to-two percent of cells with the potential for
osteoblastic differentiation [76] and MSC osteoinduction properties have been
well demonstrated [77,78]. Some studies have reported several differences in the
quantity and quality of bone marrow MSC depending on the location of the bone,
especially between orofacial and long bone. There are also limitations for collect-
ing suffi cient BM samples because of the limited size or inaccessibility of certain
bones. Therefore, determining an appropriate technique and most favorable site
for BM collecting could be critical for completing experimental models. This
study revealed that BM samples are signifi cantly less rich in the tibia than in the
humerus and ilium in dogs while no signifi cant difference was observed in rabbits.
BM samples are signifi cantly less rich in dogs than in rabbits (p
0.05). The
humerus collecting technique appeared to be more reproducible than that of the
ilium, essentially because it was relatively easier to approach. These signifi cant
differences in relation to bone location and species are consistent with the need
to better defi ne experimental models in BM-based tissue engineering. Moreover,
comparisons of studies conducted in different animal models should be made
with caution.
Few studies have focused on large segmental defects in high weight bearing
bones. The viability of a critical size segmental defect in a rabbit femur is a chal-
lenge in itself as osteosynthesis must support physiological loading and the defect
should not heal spontaneously until the end of the implantation delay. Two cm
defects in rabbit femurs have been described as critical size defects at 16 weeks
[79,80]. The presented defect was considered to be critical and for ethical reasons
no control group was constituted. Potential use of faster resorbable ceramics in
bone tissue engineering have been suggested [81] and the authors chose a bio-
ceramic with a 20/80 HA/TCP ratio for this study. As periosteum was removed, a
porcine collagen membrane was used to maintain the granules in the defect.
External radiotherapy after major bone removal and reconstruction is a
common situation either in orthopedic and orofacial oncology. The effects of
radiation on normal bone are well known: BM is deprived, and there is less
vascularisation, bone ingrowth and bone remodeling [82-86]. The adjunction of
an osteogenic component to the ceramic thus appears to be necessary when bone
formation limitation factors (large and segmental defect, maximal biomechanical
stimulation, radiation) are cumulated. Although MSC adjunction has proved its
effi cacy in improving bone ingrowth in these critical conditions, there are still
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