Toughening implants with zirconia

Ceramic implants are an attractive new development in orthopedic surgery. They are being extensively used in total hip replacement, knee replacement and other joint replacement surgeries. However, wear in these implants is a serious limitation on their use, especially for young and active people.

The introduction of ceramics like alumina and zirconia drastically reduces the wear rate. Yet neither of these materials is optimal for the task due to their brittleness and susceptibility to crack propagation at the sites of small surface defects. Moreover, zirconia based implants have problems related to steam sterilization and hydrothermal degradation.

In the BIOKER project, funded under the European Commission's GROWTH programme, methods and materials were investigated with the aim to increase the life span of ceramic-ceramic knee and hip orthopaedic implants. In this direction, zirconia-toughened alumina nanocomposites were used to form ceramic-ceramic implants with potential life spans of more than 30 years.

This material is produced by means of a specially developed processing technology in which powder alcoxide mixtures and a pressure casting forming technique are employed. More specifically, a new technology was developed to use powder alcoxide suspensions in two different forming technologies: dry pressing after powder drying, and casting of slurries with and without pressure. With the use of the innovative pressure casting technique, knee components of high 'green' (unsintered) densities could be achieved, demonstrating an improved mechanical behaviour.

The BIOKER project led to a material, which contains numbers of zirconia nanoparticles distributed uniformly among the alumina grains. Most importantly, the methods developed and the know-how obtained will facilitate these life-enhancing interventions to become an even larger part of medical service.