Key Engineering Materials Vols. 309-311

Abstract: A new zirconia-toughened alumina ceramic (JMM-ZTA) for a ceramic-on-ceramic hip replacement has been developed. The JMM-ZTA has a fracture toughness superior to zirconia, and the JMM-ZTA/JMM-ZTA combination has superior wear-resistant performance to alumina/alumina. Moreover, the JMM-ZTA shows an excellent crystalline phase stability. Therefore, the JMM-ZTA is believed to be useful for artificial hip prostheses.

Abstract: Several clinical reports pointed out that the monoclinic transformation of crystalline structure of zirconia femoral head with clinical service time can cause the changes of surface roughness and mechanical properties. To elucidate the relationship between these surface roughness change induced by phase transformation and UHMWPE socket wear, hip simulator wear tests were performed on total hip prostheses (THP) up to 6 million cycles running. Four groups of different surface monoclinic phase fraction of Kyocera zirconia heads were prepared by aging treatment prior to the wear tests. The surface roughness/ wear rate of zirconia heads with 0, 10, 50 and 80mol% monoclinic phase fraction were 0.009/ 3.8, 0.014/ 3.9, 0.012/ 3.7 and 0.010µmRa/ 3.1mg/million cycles, respectively. These results exhibit that the surface roughness change induced by phase transformation does not significantly influence extent of the generation of UHMWPE debris in Kyocera zirconia /UHMWPE THP system. In contrast, the surface roughness exhibited complex relation with the monoclinic phase fraction and therefore the morphological analysis was performed on the zirconia articulating surfaces

Abstract: The phase stability under aqueous condition and changes in the wear region after the Pin-on-Flat wear testing were evaluated using Raman and fluorescence spectroscopy techniques and X-ray diffractometry for a newly developed zirconia toughened alumina (JMM-ZTA). This study suggests that JMM-ZTA is a highly stable material under aqueous environment in the human body and has a high wear resistance in Pin-on-Flat wear tests. This results from a transformation toughening mechanism operative in JMM-ZTA. Therefore, JMM-ZTA appears to have a possibility to improve the performance of monolithic alumina as a material for hip and knee joint prostheses.

Abstract: Abstract. A new ceramic material for orthopaedic applications was investigated. Therefore a gradient ceramic was prepared with a zirconia gradient within an alumina matrix by an infiltration process. This material was characterized regarding its microstructure, stress distribution inside the ceramic, zirconia phase analysis and strength. It could be shown that the flexural strength of the new ceramic is twice as high as of pure alumina ceramic. By this and the low monoclinic zirconia content this material offers a potential for its use in high load bearing implants like hip heads for joint endoprostheses.

Abstract: The surface of retrieved alumina (Al2O3) femoral heads was investigated by piezo-spectroscopic techniques based on confocal photo-stimulated fluorescence. The micrometric spatial resolution of the laser beam impinging on the investigated joint surface (typically about 1 $m in lateral resolution) enabled us estimating patterns and magnitude of residual stress in extremely narrow zones, at least comparable with the grain size of the material. According to a statistical collection of data on a microscopic level, it was possible to assess the retrieved femoral heads in-toto, thus extending the microscopic analysis to the entire surface of the joint. A stress field was found, which mainly arose from loading history, and displacements acting on the femoral head during its lifetime. Residual stress data enabled us to draw interesting conclusions about the role of the material microstructure and the peculiar kinetic mechanisms involved with the use of the joint. Spectroscopic techniques, which are complementary to in vitro testing procedures and theoretical stress analyses based on finite-element methods, can be very useful in improving the design of the femoral head and in optimizing the microstructural characteristics of the ceramic materials employed.

Abstract: For orthopaedic applications an Alumina Toughened Zirconia Ceramic was tested regarding its mechanical behaviour. We observed a marked higher strength compared to the requirements according to FDA guidelines and a significantly higher strength compared to alumina ceramic despite of 15 % decreased fatigue burst strength. The wear resistance after ring-on-disc method is significantly improved comparing to standard Al2O3/Al2O3 pairings. It means the application of endoprosthetic components made of ATZ-ceramic offers more safety and reliability.

Abstract: The sliding wear behaviors of three different compositions of novel low temperature degradation-free zirconia/alumina (LTD-free Z/A) composites were examined in a ceramicceramic contact pair. The wear tests were performed by using a pin-on-disk type wear tester in a linear reciprocal sliding motion with a line contact in both dry and bovine serum lubricated conditions at room temperature. From the results of dry sliding wear tests, Z/A#1 ((5.3Y,4.6Nb)-TZP/80 vol% Al2O3) showed the best wear resistance among three kinds of LTD-free Z/A composites. For the bovine serum lubricated sliding wear tests, wear was too little to be measured for all kinds of Z/A composites. These novel LTD-free Z/A composites having excellent wear resistance demonstrated a potential as the alternative materials for the ceramicceramic contact pairs of femoral head and acetabular liner in total hip replacement.

Abstract: The contact conditions and the resulting contact stresses for ceramic on ceramic pairings with diameter 28, 32 and 36mm were determined. A hip simulator according ISO 14242 was used to measure the wear behaviour of these hard – hard couplings in comparison with the common hard – soft pairing ceramic on polyethylene. It was found that there isn’t a significant dependence of the wear behaviour from articulation diameter for ceramic on ceramic but a strong increase of polyethylene wear with larger hip joint heads.

Abstract: The calf serum solution was defined as the international standard lubricant for wear characterization of artificial hip joints. It is, however, known that its composition varies according to age, manufacturing processes or production areas of bovine cattle, and that the difference in composition has large effect on the wear characterization. It was difficult to compare the results obtained by different laboratories. Therefore, it is desirable to develop an artificial lubricant whose composition can be always set to a specified value as an alternative to bovine serum. In the present study, the effect of each major constituent in bovine serum on wear property was studied by hip simulator. As a result, transparent and stable lubricant solutions were prepared. It showed quite similar wear property to bovine serum by controlling the composition. These results serve as a guide to propose the new lubricant suitable for the wear characterization of hip joint.