Mechanisms induced by transition metal contaminants and their effect on the hydrothermal stability of zirconia-containing bioceramics: an XPS study.

Zirconia containing bioceramics suffer from low temperature degradation in biological and hydrothermal environments, and the presence of transition metal contamination has been shown to greatly affect the zirconia stability in different materials. In this paper, X-ray photoelectron spectroscopy was used to investigate the compositional and structural variations of different zirconia containing hip-joint bioceramics with and without transition metal stains in hydrothermal environments. Non-stained and stainless-steel-stained femoral head samples of 3 mol% Y2O3 doped tetragonal zirconia polycrystals (3Y-TZP) and zirconia-toughened alumina (ZTA) subjected to isothermal treatments in water vapor were investigated with quantifying their respective compositional XP lines. The outputs of these spectroscopic experiments revealed a significant difference in the off-stoichiometric reactions taking place at the surface of zirconia-containing ceramics in the presence and absence of transition metal contamination. The complex off-stoichiometric chemistry that occurred in the presence of metal contaminants could be interpreted in terms of defect-related chemical reactions among metal, water vapor, and oxide lattice, with a crucial contribution of the alumina phase in the transformation kinetics of ZTA.

Oxide ceramic femoral heads contribute to the oxidation of polyethylene liners in artificial hip joints.

Experimental evidence demonstrates that a loss of stoichiometry at the surface of oxide bioceramic femoral heads enhances the oxidation rate of polyethylene acetabular liners in artificial hip joints. Contradicting the common notion that ceramics are bioinert, three independent experiments confirmed substantial chemical interactions between the ceramic femoral heads and their polyethylene counterparts. The experiments reported herein included hydrothermal tests, frictional tests, and hip-simulator experiments. It was discovered that oxide and non-oxide femoral heads differently affected the oxidation processes at the surface of the polyethylene liners, all other testing parameters being equal. Analytical data from X-ray photoelectron (XPS), cathodoluminescence (CL), Fourier-transform infrared (FTIR), and Raman spectroscopies unequivocally and consistently showed that the oxidation rate of polyethylene liners was greater when coupled with oxide as opposed to non-oxide ceramic heads. XPS analyses of O-Al-O bond fractions at the surface of a zirconia-toughened alumina (ZTA) short-term (20 months in vivo) femoral heads retrieval showed a ~50% reduction in favor of oxygen vacancy O-Al-VO and hydroxylated Al-O-H bonds. Off-stoichiometry drifts were confirmed in vitro under both static and dynamic conditions. They triggered oxidation and tangibly affected an advanced highly cross-linked sequentially irradiated and annealed ultra-high molecular weight polyethylene (UHMWPE) liner (increase in oxidation index up to ΔOI~1.2 after 5 × 105 cycles under dynamic swing conditions). Second-generation UHMWPE liners infused with vitamin E were also affected by the free flow of oxygen from the oxide femoral heads, although to a lesser extent. The fundamental findings of this study, which were also confirmed on retrievals, call for revised standards in material design and testing. Adopting these new criteria will provide an improved understanding of the importance of off-stoichiometry at the head/liner interface and may lead to significant extensions in artificial joint lifetimes.