When politicians, as was recently the case with Minister of Health Daniel Bahr, think out loud about restricting the use of artificial hip or knee joints in future for cost/benefit reasons for certain categories of the population, the denial mostly follows hot on the heels. Nevertheless, it is of major importance to society to reduce the costs for permanent implants, such as for example joint prostheses/endoprostheses if health care in Germany is to be assured and endoprostheses are also to become affordable in developing and emerging countries. Scientists from the Institute for Manufacturing Technology of Ceramic Components (IFKB) from the University of Stuttgart are working on a new technology on the basis of ceramic injection moulding which could considerable reduce the manufacturing costs of such implants.
Routinely, implants made of special steel and an artificial antibody comprising low pressure
polyethylene (NDPE) are traditionally used for hip and knee operations. These are indeed reasonably
priced in comparison; however, their use depending on the load is limited to ten to 15 years.
Ceramic implants are considerably more durable, and their superior material features guarantee a
reduction in the wear and tear and a better bio-compatibility (tolerance), which reduces
inflammations in the tissue and slows down the implant loosening. In addition, they grow in more
quickly and the patients are soon on their feet again after an operation. Their disadvantage: the
manufacturing and end processing of the hard and tough ceramic, polished as smooth as glass,
require a multitude of work steps and are therefore expensive.
Mohammed Abou El-Ezz from the Institute of Manufacturing Technology of Ceramic Components
(IFKB) addressed these problems as part of his doctoral thesis at the Graduate School of Excellence
for advanced Manufacturing Engineering Stuttgart (GSaME). The 26-year old graduate from the German
University of Cairo (GUC) has attempted to make ceramic implants available to a wider and less
wealthy group of patients using a significantly cheaper manufacturing method. The work is financed
by the Hans-Böckler Foundation and supported by the head of the institute, Prof. Rainer Gadow as
well as the head of the high performance ceramics division Dr. Frank Kern.
Fundamentally new approach
In order to reconcile the required high qualities of implant ceramic products with the cost
targets for a broader market, the scientists are choosing a fundamentally new approach along the
entire process chain from raw materials conditioning to moulding processes up to the final
processing. Their aim is to manufacture implants in geometry using ceramic injection moulding
(CIM), which comes really very close to the final shape. This concept described in specialist terms
as “net-shape-forming” in connection with the CIM process makes it possible to considerably reduce
the cycle time as well as the costly reworking. However, the process requires a higher amount of
bonding agents and auxiliary materials, making the heat treatment and the chemical technology more
complicated.
In the framework of the project high-strength and tenacious mixed oxide ceramics were
initially developed, which are suitable for injection moulding technology: aluminium
oxide-zirconium oxide-nanocomposites (ZTA: zirconia toughened alumina). The abbreviation stands for
high-performance ceramic materials for biomedical applications that display a high degree of
strength, biocompatibility and hardness. This makes them superior to metallic materials in
orthopaedic applications. The common disadvantages of ceramics, in particular the susceptibility to
brittle fracture, can be avoided through strengthening mechanisms on the microscopic level of the
structure of the material, which lead to an increase in the fracture toughness, hardness and
durability. On the basis of detailed analyses of the component microstructure and the failure
criterion, the processes and materials are ultimately to be optimised in such a way that reasonably
priced implants of extreme reliability can be manufactured in large numbers.
Initial attempts are promising
The first injection moulded cast hip joint implants made of ZTA composite ceramics were
already manufactured in spring at the IFKB, whereby an injection moulded form was used, which the
German-Egyptian company HBW Gubesch Egypt designed and manufactured in Cairo in the framework of a
technology transfer pro-ject. ”The results are promising and are a hopeful sign that this new
process route for ceramic implants can contribute towards reducing the direct manufacturing costs
of these products by up to 30 percent“, Mohammed Abou El-Ezz and his supervisor Prof. Gadow are
pleased to say. ”We assume that through this the circle of patient groups benefitting from this
modern material technology in medicine technology will be expanded greatly in future.“ By
increasing the life cycle of the prostheses, it is not only the quality of life of those concerned
individuals that will increase. Health costs will also be reduced in real terms since fewer
replacement operations and after care measures will be necessary. This is of considerable social
interest considering the demographic development with an increasing number of old people, which
underlines the significance of research and development of the material up to the industrial
manufacturing technology for the location of Baden-Württemberg.
Further information from Prof. Rainer Gadow, Institute for Manufacturing
Technology of Ceramic Components (Institut für Fertigungstechnologie keramischer Bauteile - IFKB),
tel. 0711/685-68301, email: rainer.gadow (at) ifkb.uni-stuttgart.de, www.ifkb.uni-stuttgart.de
