Biomedical Engineering Reference
In-Depth Information
3
.
3
.
1
Bioinert Ceramics
The term bioinert refer to any material that has minimal interaction
with its surrounding tissues once placed within human body. This
type of bioceramic shows minimal interfacial bonds with the living
tissues [53]. Single oxide ceramic, alumina (Al
2
O
3
), zirconia (ZrO
2
),
and carbon are typical examples of bioinert ceramic. In a human
body, they are expected to be nontoxic, non-allergenic, and non-
carcinogenic for a lifetime, which leads to a corresponding range of
engineering design philosophies for medical application [82].
3
.
3
.
1
.
1 Alumina
Aluminum oxide, also known as alumina, is a well-proven,
biocompatible ceramic that has been used as a dental restorative
material for many years. An alumina ceramic has characteristics
of high hardness and high abrasion resistance. The reasons for the
excellent wear and friction behavior of Al
2
O
3
are associated with the
surface energy and surface smoothness of this ceramic. There is only
one thermodynamically stable phase, i.e., Al
2
O
3
that has a hexagonal
structure with aluminum ions at the octahedral interstitial sites
[50, 62]. Abrasion resistance, strength, and chemical inertness of
alumina have made it to be recognized as a ceramic for dental and
bone implants. Aluminum oxide has been used as a dental porcelain
pigment for some 60 years and as a ceramic restoration substructure
for 25 years. Dental patients should rest assured that dental ceramics
composed of aluminum oxide are not a source of soluble metallic
aluminum in the body.
The new generation alumina ceramics are manufactured by hot
isostatic pressing. They have high density (3.98 g/cm
3
), high purity,
and ine grains (1.8 μm). Fine grain structure of alumina allows
achieving very low surface roughness after polishing (less than
0.05 μm R
a
), which determines extremely low wear rate and low
coeficient of friction.
The beneits of alumina-on-alumina hip prostheses are: low wear
rate, high hardness (HV = 2200), high scratch resistance (low three
body abrasive wear), low coeficient of friction, excellent surface
inish, no ion dissolution, high strength, high fatigue strength, good
wetting by the synovial luid, and biocompatibility.
The main disadvantage of alumina as a material for hip prostheses
is its low fracture toughness and strength. The fracture toughness
and four-point lexural strength of alumina were considerably
