Key Engineering Materials Vols. 284-286

Abstract: The present study has been aimed to combine the advantages of the two single-phase materials, Al2O3 and ZrO2 while avoiding their disadvantages, by producing a mixed ceramic. Within a study of an ATZ ceramic we tested the influence of aging by a hydrothermal treatment on the strength, phase composition and surface properties. We found that the hydrothermal treatment of the ATZ ceramic did not significantly influence these parameters, unlike those of a single-phase ZrO2 ceramic.

Abstract: The nano-composite of a ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP) and alumina (Al2O3) polycrystals (Ce-TZP/Al2O3) is attractive as a load-bearing bone substitute because of its mechanical properties and phase stability. We have developed a new method of hydrofluoric acid and heat treatment (HFT) to give a microporous structure to the surface of this Ce-TZP/Al2O3 nanocomposite ceramic. Bone-bonding ability of a microporous surface and calcium phosphate coating on Ce-TZP/Al2O3 composite has been investigated through in vivo detaching model. Thin calcium phosphate coating layer was added by alternate soaking process, and thick CaP layer was produced by soaking in simulated body fluid for 5 days. HFT treated Ce-TZP/Al2O3 composite showed high bone-bonding ability compared with the control group. Thick and thin CaP coating accelerated bone-bonding ability in early post-implantation period. The submicron microporous surface was beneficial for achieving mechanical interlocking between the ceramic and surrounding bone. These results suggest the possibility of using a Ce-TZP/Al2O3 nanocomposite ceramic with microporous surface and calcium phosphate coating as the bearing material for uncemented total joint replacements.

Abstract: This study evaluated the wear performance of cobalt-chromium, zirconia and alumina/zirconia composite heads against moderately crosslinked ultra-high-molecular-weight polyethylene liners under different temperature conditions. A temperature control unit was utilized to allow direct cooling/heating the head components at 4, 20, 37 and 45 °C in addition to the conventional no temperature control method. Results showed that the polyethylene wear was affected by the coolant temperature. The CoCrMo and the alumina/zirconia groups had similar wear rate without temperature control, however, the CoCrMo group generated 50% more wear than the alumina/zirconia group did when the coolant temperatures were above 20 °C. The zirconia group had the lowest wear rate of the three groups in all temperature conditions. The monoclinic phase content of the zirconia heads were about 0.2 M% before the test and 6.0 M% after the test, while the X-ray diffraction remained similar before and after the test in alumina/zirconia composite heads. The current study was able to reproduce the phase transformation of zirconia ceramics as reported in some clinical retrieval reports. A temperature control feature is recommended in a wear study in order to better simulate implant wear performance under the physiological condition in human body.

Abstract: It is well known, that wear of the articulation partners of hip joint prostheses affect the long-term durability of the implants in vivo. The wear is dramatically increased if particles in the artificial joint gap act as third body. Those particles can also occur after a fracture of a ceramic component. Until now there are some different guidelines which coupling (metal-polyethylene, ceramic-polyethylene, ceramic-ceramic) should be used for revision. We tested and compared the wear behaviour of a ceramic-PE-pairing and a ceramic-ceramic-pairing under third body wear conditions with alumina-particles in a hip joint simulator.

Abstract: The monoclinic zirconia content in clinically failed ceramic heads was investigated in order to identify the cause of the failure. High percentages of the monoclinic zirconia were associated with the fractured surface. In vitro, accelerated aging of some components shows that the monoclinic transformation is site related: the closer to the bore, the more the monoclinic transformation. This phenomenon may be associated with the composition and the manufacturing process.

Abstract: Alumina ceramic is an excellent material for biologic implantation. Decreased particulate wear debris should increase implant longevity. The purpose of this study is to examine clinical and radiological results of ceramic-on-ceramic hip implants compared to cobalt chrome on polyethylene. Four cementless systems were compared, three alumina-on-alumina bearing systems: System I, porous coated cup; System II, hydroxyapatite-coated cup; Trident system, hydroxyapatite-coated cup with metal sleeve backing on ceramic cup liner; and System III (control), porous-coated cup with polyethylene and cobalt chromium bearing system. Patients were randomized to receive System I, II, or III. Trident patients were not randomized. Examinations are performed at 6 months, 1 year and yearly thereafter including x-rays, clinical exam and Harris Hip Score (HHS). Minimum 24-month followup was performed in 562 ceramic hips and 154 control hips. Age, height, weight, gender and diagnosis were similar in all groups. HHS was rated good/excellent by 95 percent of ceramic hips and 97 percent of control hips. Radiographic results demonstrated radiolucency in Femoral Gruen Zone 1 in 3.8 percent (18/474) of ceramic hips and in 8 percent (10/128) of control hips. Unstable acetabular components were reported in none of ceramic hips and in 3.2 percent (5/154) of control hips. Revision was performed in 7 (1.2 percent) ceramic hips, none due to failure of ceramic materials, and in 9 (5.8 percent) control hips. Alumina ceramic materials show promise, but continued evaluation of long-term clinical results is needed.

Abstract: The sliding wear behavior of ultra high molecular weight polyethylene (UHMWPE) was examined on four different compositions of novel low temperature degradation-free zirconia/alumina (Z/A) composite material used for a femoral head in total hip joint replacement. The wear of UHMWPE pins against these Z/A composite disks were evaluated by performing the linear reciprocal sliding and repeat pass rotational sliding tests for one million cycles in a bovine serum. The novel low temperature degradation (LTD)-free tetragonal zirconia polycrystal (TZP)/alumina composite (90(5.3Y, 4.6Nb)-TZP/10Al2O3) induced the less wear amount of UHMWPE than the other Z/A composites. Linear reciprocal motion wore more the UHMWPE pin than did repeat pass rotational motion for all disk materials. It was observed that few transfer film on the sliding track of Z/A composite disks and the matching contact surfaces of pins had relatively less scratch. Getting rid of transfer film, there is no change of surface roughness on the sliding track of Z/A composite disks. This novel Z/A composite (90(5.3Y, 4.6Nb)-TZP/10 Al2O3) demonstrates the potential as an alternative material for the femoral head in total hip replacement.

Abstract: A wide variety of materials are currently under consideration for use in biomedical implants. Within the scope of certain implants is the need to withstand extensive wear created by repeated use and pressure on high stress joints. Substantial research is directed toward metal-onmetal technology and cobalt chrome molybdenum (CoCrMo) is a prime candidate given its longevity [1]. Wear-resistant surface coatings for the standard CoCrMo biomedical alloy may be a simple and effective way to extend implant lifetime. In this study, we show that an initial plasma nitriding step for CoCrMo alloy is beneficial for attaining adhesion of a nanostructured diamond coating subsequently grown by microwave plasma chemical vapor deposition (CVD). The initial plasma nitriding step is quickly and easily performed in the CVD reactor and results in the formation of chromium nitride phases (CrN, Cr2N) as well as a phase transformation of cobalt from hexagonal to face centered cubic. We suggest that the success in terms of achieving adhesion of the diamond coating to the CoCrMo alloy involves chromium nitride phases acting as a diffusion barrier to carbon, thus preventing direct reaction of carbon with cobalt and the extensive graphitization that would follow.

Abstract: The objectives of this study were to investigate the mechanical properties of a ZrO2- Al2O3 composite ceramic. The mechanical strenght, wear behaviour and phase composition of the ceramic composite were analysed. The tested material showed a significantly higher bending strength compared to Al2O3- and ZrO2-Ceramic. According to the results of ring-on-disc, the wear rates were comparable to the Al2O3-Ceramic.