Biomedical Engineering Reference
In-Depth Information
of the implant [1089, 1090]. Interestingly, but Fe
O
/HA composites
3
4
possess photocatalytic properties [1003, 1004].
Various biocomposites of calcium orthophosphates with metals
and alloys have been fabricated as well [540, 928, 967, 997, 1028-
1045]. For example, an HA-based biocomposite reinforced with 20
vol.% of Ti particles was fabricated by hot pressing [1030]. Besides,
calcium orthophosphate/Ti biocomposites might be prepared by
powder metallurgy processing [1032-1034]. At high temperatures,
the presence of Ti metal phase was found to promote dehydration
and decomposition of HA into β-TCP and TTCP [1030, 1032] or partial
formation of β-TCP and calcium titanate instead of HA [661, 1033,
1034]. Comparing with pure HA bioceramics manufactured under
the same conditions, the HA/Ti biocomposites possessed a higher
fracture toughness, bending strength, work of fracture, porosity
and lower elastic modulus, which is more suitable for biomedical
applications. However, the mechanical properties appeared to
be not high enough to use HA/Ti biocomposites in load-bearing
applications. Luckily, the histological evaluations revealed that HA/
Ti biocomposites could be partially integrated with newborn bone
tissues after 3 weeks and fully osteointegrated at 12 weeks
in vivo
[1030]. Similar findings had been earlier made for HA bioceramics
reinforced by addition of silver particulates (5-30 vol.%) and
subsequent sintering of the HA/Ag powder compacts [1028, 1029].
Besides, addition of silver imparts an antimicrobial activity [1042].
Other studies on calcium orthophosphate/Ti biocomposites are
available elsewhere [1035-1038].
To conclude this part, biocomposites consisting of calcium
orthophosphates only should be briefly described. First of all, all
multiphasic and polyphasic calcium orthophosphates (section
1.3.14
) should be mentioned. For example, in 1980s, BCP was called
as “TCP ceramics complexed with HA” [1091]. Even nowadays BCP is
occasionally called as a “nanocomposite” [1092]. Furthermore, FHA
or HFA (see section
for details) might mentioned
as composites [1093]; however, an applicability of the “composite”
term for such systems is doubtful. One should better consider
70% HA-powder + 30% HA-whisker biocomposites, which were
fabricated by pressureless sintering, hot pressing and hot isostatic
pressing. These biocomposites were found to exhibit an improved
1.3.11. FA (or FAp)
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