Papers by Author: Thomas Oberbach

Abstract: Surface biofunctionalization is a common strategy to improve the material-tissue interface of inert implant surfaces. In this context we coated alumina-toughened zirconia (ATZ) ceramics after titanium plasma spraying with two different porous calcium phosphate layers and subsequently functionalized the obtained surfaces either with an RGD containing cell adhesion peptide sequence or a bone morphogenetic protein (BMP)-glycosaminoglycan complex. We studied initial cell adhesion densities, integrin expression, and alkaline phosphatase activity as an osteogenic marker of the coatings in vitro in comparison to the non-functionalized ATZ ceramics to evaluate the bone ingrowth potential of these biofunctionalized implant coatings.

Abstract: Wear of the articulation partners in artificial joints for hip or knee is known to influence the in vivo survival rate of the implants. Wear amount can be strongly increased if third body wear occurs in the joint gap. Alumina ceramic is noted for a good wear resistance even under these worst case conditions. We tested the wear behaviour of the new dispersion ceramics ZTA (Zirconia Toughened Alumina) and ATZ (Alumina Toughened Zirconia) in comparison to alumina for the couplings ceramic on PE and ceramic on ceramic in a hip joint simulator in presence of third body particles.

Abstract: The primary purpose of this work was the examination of the surface and the strength of ATZ ceramic after hydrothermal treatment. Hydrothermal treatment of ATZ ceramic leads to changes of roughness and phase composition on the surface. The phase composition and the microstructure on the surface and within the peripheral zone were determined after applying a stepwise broad ion beam polishing technique and quantitative phase analysis. With this technique a penetration depth of the phase transformation of less than 14 µm was observed. Investigations of the cross sectional area by means of FESEM have shown a transformation zone of about 9 µm. Both methods lead to comparable results with a very small, morphologically changed peripheral layer. The study of the strength after ageing with different thickness of the samples showed that for a thickness of 2.0 mm there is no negative influence on mechanical behaviour. In consideration of this fact no significant change of tribological properties is expected.

Abstract: In the present investigation, three ceramic-ceramic-couplings (alumina - alumina) were examined for possible reasons of the squeaking noise which occurred after surgery. Under certain conditions like, for example, a suboptimal position of the implant and corresponding soft tissue relations, a subluxation or microseparation of the ceramic head from the ceramic liner may occur; this, in turn, may lead to a squeaking noise of the joint. Apart from the psychological stress for the patient due to the awkward noise and the resulting feeling of instability, the squeaking noise is a sign for damages on the implant in most cases.

Abstract: Ceramic hip joint heads are used in the field of endoprosthetics for more than 30 years. There are a lot of in vitro tests to determine the behaviour of these implants under body like conditions that means hip simulator testing etc. But it is accepted, that these tests can only reflect ideal conditions in vivo. Therefore it is necessary to examine also retrievals after different periods in vivo. Six explanted ceramic heads after times in vivo between 0.5 and 19 years were investigated concerning their geometrical dimensions and surface conditions.

Abstract: Wear of hip implants is a significant problem for the life expectancy of artificial joints. By using alumina ceramic on ceramic couplings the wear can be decreased. But for further improvement of the safety of THR the aim is the development of new ceramic materials. For orthopaedic applications an Alumina Toughened Zirconia Ceramic ATZ (80% ZrO2-20%Al2O3) and a Zirconia Toughened Alumina ZTA (25% ZrO2-75%Al2O3) were tested regarding their tribological behaviour by means of hip simulator testing after hydrothermal treatment. The absolute wear amount for the aged samples after 5 million cycles is slightly increased on a very low level, but even less wear than for common alumina pairings. In consideration of these excellent results both dispersion ceramics are highly suitable for long term applications.

Abstract: Alumina and zirconia ceramics have been successfully used as materials for joint endoprostheses. The present study has been aimed at combining the advantages of the two singlephase materials, Al2O3 and ZrO2 while avoiding their disadvantages, by producing a composite ceramic. Within the scope of a study of an ATZ ceramic we tested the influence of aging by a hydrothermal treatment on 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 aim of the examinations was to produce various dispersion ceramics in the range of 0 -100% Al2O3, and to determine the strengths and selected characteristics such as density, fracture toughness KIC, thermal conductivity, elastic modulus and hardness. Furthermore, the phase composition of all samples was examined by means of X-ray diffraction following Rietveld refinement. The examinations showed that the material parameters can be specifically influenced by the corresponding adjustment of the ZrO2 portion. The utilisation of the effects of the dispersion and transformation reinforcement can be exploited particularly with the mixture 20 % Al2O3-80 ZrO2(Y-TZP). Significant differences between the two forming procedures – slip casting and pressing – could not be established.

Abstract: Alumina and zirconia have been used for hip joint prostheses for decades. With mixtures of both materials (ZTA and ATZ) mechanical strength can be increased. The resistance against damaging of the surface of the ceramic articulation partners head and liner was investigated using a special luxation apparatus (PI-3:1997-07, Endolab GmbH, Thansau, Germany). Both new ceramic materials ZTA and ATZ showed a better resistance against roughening and damaging of the stressed surface areas during the luxation test compared to alumina.

Abstract: Alumina and zirconia have been used in joint prostheses for decades. With mixtures of both materials (ZTA and ATZ) mechanical strength can be increased. The wear behaviour was investigated using standard and microseparation conditions. Both materials ZTA and ATZ showed similar or better wear resistance compared to alumina.