Biomedical Engineering Reference
In-Depth Information
has therefore been used clinically for iliac and vertebrae prostheses
and as intervertebral spacers [16, 206-208].
6.3.3.3
Ceramics
Metal
oxide
ceramics,
such
as
alumina
(Al
O
,
high
purity,
2
3
polycrystalline, fine grained), zirconia (ZrO
), and some other oxides
2
) have been widely studied due to their bioinertness,
excellent tribological properties, high wear resistance, fracture
toughness and strength, as well as a relatively low friction [16,
209]. Unfortunately, due to transformation from the tetragonal to
the monoclinic phase, a volume change occurs when pure zirconia
is cooled down, which causes cracking of the zirconia ceramics.
Therefore, additives such as calcia (CaO), magnesia (MgO), and
yttria (Y
(e.g., TiO
, SiO
2
2
) must be mixed with zirconia to stabilize the material in
either the tetragonal or the cubic phase. Such material is called PSZ
[210-212]. However, the brittle nature of any ceramics has limited
their scope of clinical applications and hence more research needs to
be conducted to improve their properties.
O
2
3
6.3.3.4
Carbon
Due to its bioinertness, excellent tribological properties, fracture
toughness and strength, as well as a low friction, elemental
carbon has been used as a biomaterial, at least, since 1972 [213].
Applications include orthopedic prostheses, vitreous carbon roots
for replacement teeth, structural skeletal extensions, bone bridges
and hip prostheses. Biomedical properties of amorphous carbon
were studied as well [214]. However, current trends represent
investigations on biomedical applications of carbon nanotubes [215,
216].
Carbon nanotubes with their small dimensions, a high aspect
(length to diameter) ratio as well as the exceptional mechanical
properties, including extreme flexibility and strength, significant
resistance to bending, high resilience and the ability to reverse any
buckling of the tube, have the excellent potential to accomplish
necessary mechanical properties [217]. Recent studies have even
suggested that they may possess some bioactivity [218-221].
However, non-functionalized carbon nanotubes tend to agglomerate
and form bundles. Besides, they are soluble in neither water nor
organic solvents. Luckily, chemical functionalization [82, 222] allows
carbon nanotubes to be dispersed more easily, which can improve
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