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Figure 10.67 Scanning electron micrographs of the surfaces and cross sections of titanium
plates [130] .
additions to HAw/HA composites. They found that all sodium phosphates improved
sinterability without forming tricalcium phosphate or CaO. Beta-NaCaPO 4 proved the
only sodium phosphate to provide the weak fiber
matrix interface needed for com-
posite toughness [273,274,320] .
There are several kinds of HAp/bioactive glass composites. The first one is also
called bioactive glass ceramics. In these composites, HAp and/or wollastonite or other
crystalline phases crystallize from the glassy matrix during an appropriate heat treat-
ment [322
326] . The bioactive glass ceramics exhibit strength of 100
200 MPa, K Ic
2.6 MPa, m 1/2 ,fractureenergyof6
26 J/m 2 , and Weibull modulus of nine.
of 1.0
η
Coefficient of subcritical crack growth (
33.
Bioactive glass ceramics maintain high strength for a longer time than HAp, both
under in vitro and in vivo conditions [265] . HAp/bioactive glass composites can also
be prepared by simple sintering of appropriate HAp/bioactive glass powder mixtures.
In another approach, small quantities of bioactive glass are added to HAp ceramics in
order to improve densification and/or mechanical properties.
In spite of high bioactivity, high biocompatibility, and superior (but still insuffi-
cient) mechanical properties of HAp ceramics, the HAp/bioactive glass composites
did not find wide applications as bone substitutes.
) is reported to be in the range of 18
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