Biomedical Engineering Reference
In-Depth Information
[277]. The reinforcing mechanisms in calcium orthophosphate/
polymer biocomposites have yet to be convincingly disclosed.
Generally, if a poor filler choice is made, the polymeric matrix might
be affected by the filler through reduction of molecular weight
during composite processing, formation of an immobilized shell of
polymer around the particles (transcrystallization, surface-induced
crystallization or epitaxial growth), and changes in conformation of
the polymer due to particle surfaces and inter-particle spacing [102].
On the other hand, the reinforcing effect of calcium orthophosphate
particles might depend on the molding technique employed: a higher
orientation of the polymeric matrix was found to result in a higher
mechanical performance of the composite [282, 283].
Many other blends of calcium orthophosphates with various
polymers are possible, including rather unusual formulations
with dendrimers [284]. Even light-curable polymer/calcium
orthophosphate formulations are known [285]. The list of the
appropriate calcium orthophosphates is shown in Table 1.1 (except
of MCPM and MCPA—both are too acidic and, therefore, are not
biocompatible [27]; however, to overcome this drawback, they
might be mixed with basic compounds, such as HA, TTCP, CaCO
,
CaO, etc.) many biomedically suitable polymers have been listed
above. The combination of calcium orthophosphates and polymers
into biocomposites has a twofold purpose. The desirable mechanical
properties of polymers compensate for a poor mechanical behavior
of calcium orthophosphate bioceramics, while in turn the desirable
bioactive properties of calcium orthophosphates improve those
of polymers, expanding the possible uses of each material within
the body [158-160, 286-290]. Namely, polymers have been added
to calcium orthophosphates in order to improve their mechanical
strength [158, 286] and calcium orthophosphate fillers have been
blended with polymers to improve their compressive strength and
modulus, in addition to increasing their osteoconductive properties
[52, 160, 168, 291-295]. Furthermore, biocompatibility of such
biocomposites is enhanced because calcium orthophosphate fillers
induce an increased initial flash spread of serum proteins compared
to the more hydrophobic polymer surfaces [296]. What's more,
experimental results of these biocomposites indicate favorable
cell-material interactions with increased cell activities as compared
3
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