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 applications.
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 radiological examination.
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 organisations.

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.