Biomedical Engineering Reference
In-Depth Information
out the porous structure of the BCP scaffold. Scaffolds made from 100% HA,
higher HA/
-TCP ratios and 100% TCP stimulated lesser amounts of bone
formation at six weeks post-implantation. In this
in
vitro
study of hMSC differen-
tiation on 60/40 HA/
β
-TCP, hMSCs had expressed osteo-
calcin, a specifi c bone marker, when grown on the 20/80 HA/TCP, without the
presence of the osteoinductive media, by four weeks. The enhanced amount of
bone formation for hMSC-loaded 20/80 HA/TCP
in
vivo
and apparent differen-
tiation into the bone cell phenotype, as characterised by the expression of osteo-
calcin
in
vitro
under normal culture conditions, may be due in part to the rate of
degradation, the degradation products, and surface chemistry of 20/80 HA/
β
- TCP versus 20/80 HA/
β
- TCP
in relation to the other BCP compositions. The concentration of degradation
products and hMSC interaction with the surface and its varying chemistries
may be responsible for the optimal bone formation exhibited by the 20/80
formulation.
The rate of degradation or resorption of HA/
β
- TCP ceramics
in
vivo
can be
accelerated by increasing the amount of the more soluble phase, TCP. In order to
design a scaffold that supports bone formation while gradually being replaced by
bone, an optimum balance between the more stable HA phase and the more
soluble
β
β
-TCP phase must be achieved.
4.4.7 BCP Scaffolds for Growth Plate Chondrocyte Maturation
Recently, Teixera et al. [46] reported the effi ciency of an MBCP scaffold for carti-
lage regeneration. The purpose of the study was to create an
in
vitro
cartilage
template as the transient model for
in
vivo
endochondral bone formation. This
study reported successful growth and maturation of chondrocytes (isolated from
chick embryonic tibia on macroporous BCP (MBCP
®
). The thickness of the chon-
drocyte and extracellular matrix layer increased in the presence of retinoic acid.
Alkaline phosphatase activity and expression, proteoglycan synthesis, cbfa1 and
type one collagen mRNA levels also increased in the presence of retinoic acid.
This study demonstrated for the fi rst time the proliferation and maturation of
chondrocytes, and matrix depositing on MBCP, suggesting the potential for such
scaffolds in tissue engineering via the endochondral bone formation mechanism.
4.4.8 BCP Granules and Polymers for Injectable Bioceramics
The need of a material for minimally invasive surgery (MIS) has led to the devel-
opment of BCP granules combined with polymers, producing injectable/mould-
able bone substitutes. Three types of injectable/mouldable bone substitutes have
been developed.
4.4.8.1 Suspension.
MBCP Gel ™ is a non self-hardening injectable bio-
material. It is composed of BCP granules associated with a hydrosoluble poly-
mer. These materials have been shown to be perfectly biocompatible and poten-
tially resorbable and, thanks to their initial plasticity, they assume the shape of
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