Biomedical Engineering Reference
In-Depth Information
marine sponge skeletons, echinoderm skeletal elements, and coral skeletons. The utility of
selected species of these marine animals has been applied to the regeneration of human
bone and cartilage. However, their full utility in these tissues and other tissues has yet to
be harnessed and exploited.
Coral and Coralline Apatite
Natural coral exoskeletons have been used widely as a bone replacement in orthopedic,
craniofacial, dental, and neurosurgery owing to their combination of good mechanical
properties, open porosity, and ability to form chemical bonds with bone and soft tissues
in vivo (Ben-Nissan 2004). In fact corals have the best mechanical properties of the porous
calcium-based ceramics and resorb at a rate equivalent to host bone formation.
The abundance, conformation, and composition of the organic matrices are responsible
for successful biological integration of coral with human host (Dauphin 2003). Use of coral
skeletons for general routine orthopedic surgery and tissue engineering has so far been
limited to external fixation devices as they are inappropriate for strictly load-bearing appli-
cations. Sol-gel coating technologies can be used to enhance the strength of corals and
this enables them to be used at more skeletal locations. Corals offer great opportunities
to tissue engineering of bone either in their natural form or as hybridized synthetic forms
(Petite et al. 2000). Coral skeleton combined with in vitro expanded human bone marrow
stromal cells (HBMSC) increased osteogenesis more than that obtained with scaffold alone
or scaffold with fresh marrow. In vivo large animal segmental defect studies led to com-
plete recorticalization and formation of a medullary canal with mature lamellar cortical
bone giving rise to clinical union in a high number of cases (Petite et al. 2000). Structural
and biomineralization studies of coral can be used as a guide for the development of new
advanced functional materials because of the unique nanoscale organization of organic
tissue and mineral as highlighted by Ehrlich et al. (2006). At a macrostructural level, the
deep-sea bamboo coral exhibited bonelike biochemical and mechanical properties. A spe-
cialized collagen matrix (acidic fibrillar) serves as a model for future potential tissue engi-
neering applications. The matrix supported both osteoblast and osteoclast growth and
the exceptional bioelastomeric properties of the collagen matrix (gorgonin) of this coral
make it potentially suitable for blood vessel implants. Quinones cross-link and harden the
collagenous gorgonin proteins and closely resemble human keratin. The mechanism by
which gorgonin is synthesized and interacts with the process of mineralization may pro-
vide lessons for the generation of a synthetic collagen-like material (Ehrlich et al. 2006).
Nanocoated Coralline Apatite
Current commercially available bone graft materials using hydrothermal conversion only
achieve partial conversion of coralline calcium carbonate to HAp. Unfortunately, being
limited to the outer surface, the inner core remains as unconverted calcium carbonate of
the original coral (Shors 1999). This material has the advantage of retaining a favorable pore
size and bioactivity, with improved properties, compared to native coral. Unfortunately,
this also generates an unknown factor of biodegradation due to the differing solubility
rates of hydroxyapatite and unconverted calcium carbonate. As a result, this material is
subject to fast dissolution in the physiologic environment, compromising strength, dura-
bility, tissue integration, and ultimately the longevity.
It was discovered (Hu et al. 2001; Ben-Nissan et al. 2004) that the application of a hydroxy-
apatite sol-gel coating onto the monophasic HAp derived from the hydrothermally
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