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Hydroxyapatite Scaffolds:
The effects of microporosity on the strength, degradation,
and damage mechanisms of hydroxyapatite/tissue composites
publication: Woodard et al 2007
Hydroxyapatite (HA) is an osteoconductive, biocompatible ceramic that
has been used in both solid and porous forms. The interconnectedness of
porous HA is conducive to tissue ingrowth. Unfortunately, the porosity
diminishes mechanical strength. Fully dense HA exhibits higher strength
but does not allow for ingrowth and therefore retards healing. The ideal
bone substitute would allow for complete tissue ingrowth prior to
significant biodegradation, could be shaped to
location-specific defects, and would have the mechanical integrity
to withstand loads, such as those required for the head, spine, and
extremities. Such a bone substitute does not currently exist
Recent advances in the
fabrication process of ceramic structures with tailored shape,
architecture, and porosity have made it possible to create HA
scaffolds suitable for load-bearing applications rapidly and at
low cost. These scaffolds are unique in that they contain porosity
on the meso- micro- and nano-length scales. Our recent results
strongly suggest that the micro- and nanoscale porosity directly
affect cell attachment and proliferation in vitro, and
are therefore expected to increase tissue ingrowth rates and healing
time in vivo.
Top View HA sample |
Schematic cross section
meso-porosity
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SEM image
micro- & nano-porosity |
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Images courtesy of the
Jamison Group |
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This porosity may also increase scaffold degradation rates to
the degree that the mechanical strength decreases to an
undesirable level. In order for
such scaffolds to be viable candidates for clinical use, the relationship
between the competing mechanisms of ingrowth and degradation and
their effects on the mechanical behavior of these scaffolds must
be determined. The objective of the proposed research is to quantify
the effects of in vivo degradation and tissue ingrowth on the
mechanical behavior and damage mechanisms of HA scaffolds.
The knowledge gained will be of critical importance in designing
scaffolds for clinical use. Results will not only strongly influence
the design and fabrication of next generation scaffolds, but will
also provide guidelines for clinical rehabilitation for recovering
patients.
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