Biomedical Engineering Reference
In-Depth Information
Hydroxyapatite was used as control sample for this experiment. The canasite
formulation evaluated was not osteoconductive and appeared to degrade in the
biological environment. It was therefore concluded that the canasite formulation
used was unsuitable for use as implant.
3.4.5 Bioinert Ceramics
This section discusses, bioinert materials and their application areas. The use
of carbon and inert glass fi bers have important applications
51
for their typical
anisotropic properties. These engineering fi bers have been mainly used as a
reinforcement for orthopaedic devices, such as femoral hip stems, knee prosthesis
and fracture fi xation plates. Because of the inability of carbon and inert glass to
form any bioactive bonds, they have not been used in bone analogue materials.
Also, the carbon-based composites, used for articulating surfaces, are reported
to have a tendency to cause infl ammatory problems due to the loss of carbon
particles
52
.
One potential bioinert ceramic, that is, Al
2
O
3
, showed good performance
in vivo
, although the low fracture toughness (3-4 MPam
1/2
) typically restricts its
use in demanding applications. On the other hand, tetragonal zirconia ceramic
(8 - 11 MPam
1/2
) has a better edge over alumina. Various attempts have however
been made to toughen Al
2
O
3
by adding monoclinic ZrO
2
, partially stabilized ZrO
2
(PSZ), and so on. This leads to the development of zirconia-toughened alumina
53
.
Dense ZTA has considerably better toughness
54
and wear resistance
55,56
than
monolithic alumina. Although ceramic composite materials have potential use in
load-bearing orthopedic applications, very few materials have been tested clini-
cally so far.
In an important investigation, Hayashi et al.
57
studied the
in vivo
response of
bioinert ceramics such as alumina ceramic (99.5% purity Al
2
O
3
), zirconia ceram-
ic (5 wt% Y
2
O
3
stabilized ZrO
2
), SUS316L stainless steel (Fe: 65%: Cr: 18%; Ni:
13%; Mo: 2%; Mn: 2%). The results were compared with dense sintered hydroxy-
apatite (HAp). The push out test results revealed the bone-implant interface
shear strength for alumina, zirconia, steel and HAp as
0.8, 0.9, 0.5, 12.1 MPa,
respectively. It was concluded that the bioinert ceramics should not be used as
a bone bonding material, but as the material for the articulating surface.
Colon et al.
58
described the function of osteoblast and staphylococcus epider-
midis on nanophase ZnO and TiO
2
inert bioceramics. It was evident from their
result that nanophase ceramics (ZnO, TiO
2
) had decreased staphylococcus epi-
dermidis adhesion and increased osteoblast adhesion in comparison to mac-
ropahse materials.
Among the stabilized zirconia ceramics, Y-TZP (yttria doped tetragonal zir-
conia polycrystal) has been the most attractive material in terms of toughness and
structural properties. However, the leaching of yttria in humid environments and
related degradation in properties have been a major bottleneck for wider applica-
tions of Y-TZP. To this end, PSZ (Mg, Ca-doped) has several advantages and such
systems offer opportunities to control microstructure by tailoring a combination
∼
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