Biomedical Engineering Reference
In-Depth Information
®
(Novabone Products, Alachua, FL) [916, 917] and
with other glasses [918] to form glass-ceramics biocomposites.
Other reinforcement materials for calcium orthophosphates are
differentiated by either shape of the fillers, namely, particles [919,
920], platelets [921, 922], whiskers [579, 923-925], fibers [926-930],
or their chemical composition: zirconia and/or PSZ [313, 911-914,
923, 931-966], alumina [313, 919, 922, 965, 967-996], other oxides
[925, 997-1004], silica and/or glasses [1005-1014], wollastonite
[206, 1015-1025], mullite [1026, 1027], various metals and alloys
[540, 928, 967, 997, 1028-1045], calcium sulfate [1046-1049],
calcium carbonate [1050, 1051], silicon carbide [683, 924], barium
titanate [1052], zeolite [1053], boron nitride [1054] and several
other materials [335, 1055-1057]. More complicated formulations,
such as HA/aluminum oxide/carbon nanotubes [1058], have been
developed as well. All these materials have been added to calcium
orthophosphate bioceramics to improve its reliability. Unfortunately,
significant amounts of the reinforcing phases are needed to
achieve the desired properties and, as these materials are either
bioinert, significantly less bioactive than calcium orthophosphates
or not bioresorbable, the ability of the biocomposites to form a
stable interface with bone is poorer if compared with calcium
orthophosphate bioceramics alone. Due to the presence of bioinert
compounds, such formulations might be called bioinert/bioactive
composites [1005]. The ideal reinforcement material would impart
mechanical integrity to a biocomposite at low loadings, without
diminishing its bioactivity.
There are several types of HA/glass biocomposites. The first one
is also called bioactive glass-ceramics. A dense and homogeneous
biocomposite was obtained after a heat treatment of the parent
glass, which comprised ~38 wt.% oxy-FAP (Ca
with Bioglass
(PO
)
(O,F)
) and
10
4
6
2
~34 wt.% β-wollastonite (CaO·SiO
) crystals, 50-100 nm in size in a
2
glassy matrix [206, 1015-1025]. A-W glass-ceramics
is an assembly of small apatite particles effectively reinforced by
wollastonite. The bending strength, fracture toughness and Young's
modulus of A-W glass-ceramics are the highest among bioactive glass
and glass-ceramics, enabling it to be used in some major compression
load-bearing applications, such as vertebral prostheses and iliac
crest replacement. It combines a high bioactivity with the suitable
MgO-CaO-SiO
2
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