Biomedical Engineering Reference
In-Depth Information
aspect. In this sense, concrete is not a ceramic but objects of sintered alumina, car-
bides and nitrides are all at least partially crystalline.
2
Glass is consolidated by heat
but is amorphous. A vitreous ceramic contains crystalline particles embedded in
an amorphous matrix and combines the best of two worlds.
3
From the foregoing
discussion, two generic classes emerge. They are kept together under the umbrella
of
ceramics
, both having in common
consolidation by heat
. A third basket was
added collecting mostly the same compounds but used in combination with a (metal)
substrate:
Ceramics: mainly compacted and sintered crystalline compounds but subdivided
in
High performance
and
Low performance
Glasses and glass-ceramics (in-between-glasses and ceramics)
ceramic/glass coatings
High performance
stands here for what is known as
Technical Ceramics
, roughly
subdivided in
Engineering Ceramics
and
Electro-ceramics
(piezo-, etc.).
Low per-
formance
stands for the
Traditional Ceramics
, low strength and/or more recent types
like soluble phosphate ceramics.
9.3
Ceramics
9.3.1
High Performance
High performance refers here to ceramics mainly used in joint replacements, where
they are subjected to high compressive loads and wear. Throughout the earlier chap-
ters, the
pros
and
cons
of metals in hard tissue replacement were discussed and
the high standards, that are actually achieved, were highlighted. Arthroplasty is a
unique clinical success story but what are the criteria for surgeons to select one
device instead of another? A very distinct taste exists among surgeons of different
countries as shown in Table
9.1
for wear couples and femoral ball head materi-
als. In France, the surgeons seem to be more conservative and prefer conventional
polyethylene but without pronounced preference for metal or ceramic heads. The
crosslinked polyethylene is preferred in the USA combined with metal heads, while
Korea seems to make the most advanced selection with an overwhelming preference
for ceramic-on-ceramic couples. The other countries keep the middle between these
two extremes. It is a divergence, which is wider than the documented success rates
of the different devices and materials. Is it due to liability laws, reluctance toward
innovation, lack of understanding or walking only on familiar routes?
2
Notice that solidifying metallic alloys bear exciting similarities to the granular structure/texture
of ceramics [277
].
3
Glassy
and
vitreous
are synonyms.
