Biomedical Engineering Reference
In-Depth Information
preserved as HAp (containing some CO 3 2- ) is formed. The coral-converted
HAp constructs exhibited in the framework was around 130 µm in diameter,
and their interconnections were 220 µm. The average porosity was 600 µm,
and their interconnections were around 260 µm in diameter, which is favor-
able for the continued health of bony ingrowth (Shors 1999). The use of CaPs,
since they are the most important inorganic constituents of hard tissues in
vertebrates, is valid due to their chemical similarity to the mineral compo-
nent of mammalian bone. It would, thus, have the advantage that it would be
structurally, chemically, and mineralogically “identical” to normal human
hard tissue, and stable in contact with tissue fluid. After that, some research-
ers took advantage of such hydrothermal reaction to prepare various car-
bon-containing HAp porous bioceramics. However, the partially converted
coral-derived HAp/CC substrate with a “coating” of several micron depth
of HAp on the porous resorbable framework of coral failed to induce the
intrinsic induction of bone morphogenesis. Such partially converted HAp/
CC biphasic biomimetic matrices did not induce bone formation even when
reconstituted with naturally derived bone osteogenic proteins within a short
time stage postoperatively. More recently, Ripamonti et al. (2009) implanted
the HAp/CC constructs containing 5% and 13% HAp in heterotopic rectus
abdominis sites. They found that induction of bone occurred in the con-
cavities of the matrices at all-time points from 60 to 365 days. In particular,
resorption of partially converted HAp/CC was apparent as well as remod-
eling of the newly formed bone. Northern blot analyses of samples from
heterotopic specimens showed high levels of mRNA expression on BMP-7
and collagen type IV in all specimen types of 60 days, correlating with the
induction of the osteoblastic phenotype in invading fibrovascular cells. This
study demonstrates that partially converted HAp/CC constructs also induce
spontaneous differentiation of bone, albeit only seen one year postimplanta-
tion (Ripamonti et al. 2009).
The echinoderm known as Mellita eduardobarrosoi , whose skeleton contains
calcite as an inorganic constituent, can be used as the porous template for
HAp bioceramics preparation as well. Araiza et al. (1999) investigated the
influence of the initial pHs in the KH 2 PO 4 -KOH boiling solution on the for-
mation of HAp during a nonhydrothermal treatment. Chemical and x-ray
diffraction analysis of the resulting material showed that the conversion of
calcite by this technique is mostly higher than 70%, yielding the highest con-
version from pH 10 to 11. The obtained material is a mixture of the original
calcite and HAp with varying stoichiometry and composition. Nevertheless,
the interconnected porosity is preserved.
There are some other replication methods available to make porous CaP
ceramics. The cancellous bone can be converted to HAp ceramic with high
porosity after suffering high thermal treatment. The chemical composition,
mechanical integrity, and macro- and microstructure of such HAp bio-
ceramics (e.g., Endobon ® ) are similar to the natural bone mineral. In gen-
eral, this kind of biomimetic HAp bioceramics possess a range of apparent
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