Materials and
Medicine
As people live
longer and longer replacement part surgery becomes more and more
important, with hip replacement operations now running at 40,000 a year.
Replacement parts (implants or prostheses) are designed, tested and
manufactured by Materials Engineers using a variety of materials which
attempt to mimic the mechanical behaviour of the original natural part;
such as the natural femur (bone) (see fig) which is a ceramic (hydroxyapatite)/polymer
(Collagen - a long chain protein) composite. The parts also have to be
nontoxic and biocompatible to avoid the natural body rejection processes.
Hip and Knee Joint Replacement
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Hip and knee total joint
replacements are shown as illustrations on this skeleton.
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Total knee replacement with 316 stainless steel (Fe-18% Cr-3% Mo-12%
Ni-0.08%C) and ultra high molecular weight polyethylene parts.
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X-ray of two replacement
hips with vitallium (Ti-6% Al-4%V) metallic stems and polyethylene
cups.
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Hip replacements consist
of a ball and socket joint. The ball (metallic or ceramic) is mounted
on a stem which is held in place in the femur using a poly-methylmethacrylate
cement. The ball rotates in the acetabular cup manufactured from a
ceramic (Alumina A12O3 or Zirconia ZrO2),
a metallic alloy or ultra high molecular weight polyethylene)
Hip replacement with a
cobalt chrome (Co-28% Cr-6% Mo-2.5% Ni) metallic stem and alunmina
cups and balls.
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Heart Valve Replacement
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Position for a
replacement
heart valve in the aorta.
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Tilting disc heart valve
with titanium metal parts coated in pyrolitic carbon to improve
biocompatibility and to reduce rates of thromboembolism (blood clots).
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Ball and cage heart
valve. Consists of a silicone polymer ball and a titanium cage.
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Bovine pericardium (pig) valve. This is
treated in glutaraldehyde and held in place with a stent manufactured
from an acetal homo polymer.
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Working in Industry:
Companies in this sector which
employ materials scientists and engineers include:
 Johnson
and Johnson
DuPuy
Zimmer
Biomet
Biocompatibles
International
Devicelink
Smith
and Nephew
Joint
Replacement Instrumentation Group Limited
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a biomedical materials engineer
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