Total hip replacement with artificial ball-and-socket prostheses
is now a common, almost routine surgical procedure, with literally
millions of operations having been carried out in recent decades.
While early devices were typically all metallic alloys, more recent
devices use more corrosion- and wear-resistant ceramic materials.
The ultimate success of such operations is closely linked to the
strength and longevity of ceramic ball heads in the implanted devices.
While quality of life for the patient remains of the utmost importance,
improved implant quality can also help to limit the number of costly
re-replacements that have to be carried out because of osteolysis.
Challenging Japanese domination
This project was launched in 1993, at a time when the market in
advanced ceramic powders for the production of medical implants
and other important items was dominated by the Japanese. Its goal
was the development of a European high-purity yttria-stabilised
zirconia powder for the production of ceramic materials for biomedical
applications, including artificial hip joints. Research focused
on obtaining durable materials with extremely low levels of chemical
and radiochemical impurities, a key to their suitability for biomedical
Several tests were carried out, comparing ceramic materials produced
from Japanese powder, with those using European yttria-coated zirconia
powder. The European powder exhibited excellent sintering behaviour,
even at very low temperatures, and the resulting ceramic materials
showed high mechanical strength, fracture toughness and hydrothermal
stability (type B). Strength loss after 120 hours of hydrothermal
treatment at 140° C was only about 10%, while the Japanese materials
showed a strength loss of 25%. Furthermore, cross sections revealed
no corrosion effects or strength loss in European ceramics following
exposure to an established method for testing the effects of ageing
on biomedical implants, whereas a significant corrosion of Japanese
materials was observed.
Qualified biomedical implants
Finally, the qualification of 'type B' materials for biomedical
applications, based on in-vitro and in-vivo experiments, was achieved.
The highly chemically and radiochemically pure zirconia was shown
not to elicit carcinogenic effects on experimental cell lines. Furthermore,
oncogenic effects were never observed at the site of the implant
or in separate 'distant' organs following the implantation of both
ceramic cylinders and porous parts. No tumours were observed under
Partners claim that good planning was a key factor in their success.
Clear objectives were set for each stage of the project, including
the exploitation strategy. The highly motivated and co-operative
partnership included industrial, research and development and academic
Business is booming
Biomedical materials producer and project partner Ceramtec has
now had over 2.5 million of its conventional alumina ceramic ball
heads implanted in hip replacement operations. The company is currently
exploiting project results in the form of improved ball heads. While
the medical sector is notoriously conservative in its forecasting
of expected gains, additional turnover from hip replacements alone
have been estimated at around 12.6 million euro for the first five
years following the end of the project.
While the new material was designed specifically for biomedical
applications, other potential uses include machine parts requiring
high strength and toughness, as well as in other areas of structural
engineering and electronics components.