Testing of silicon nitride ceramic bearings for total hip arthroplasty
Department of Orthopaedic Surgery, University of Missouri-Columbia, Columbia, Missouri 65211, USA.Journal of Biomedical Materials Research Part B Applied Biomaterials (Impact Factor: 2.76). 11/2008; 87(2):447-54. DOI: 10.1002/jbm.b.31123
Modern ceramic bearings used in total hip arthroplasty (THA) consist of a femoral head (ball) articulating inside a hemispherical acetabular cup (socket); the ball and socket are made of alumina (Al(2)O(3)) and Al(2)O(3)-based composite materials. In the present study, total hip bearings were made from a different ceramic material, silicon nitride (Si(3)N(4)), by sintering and hot isostatic pressing of powders. The resulting material had improved mechanical properties over modern Al(2)O(3) THA bearings, with a flexural strength of 920 +/- 70 MPa, a Weibull modulus of 19, and a fracture toughness of 10 +/- 1 MPa m(1/2). Unlike zirconia-based ceramics that have also been used in THA, accelerated aging of Si(3)N(4) did not adversely affect the flexural strength. In simulated wear tests, Si(3)N(4) acetabular cups produced low-volumetric wear whether articulating against Si(3)N(4) or cobalt-chromium (CoCr) femoral heads. The results of this investigation suggest that Si(3)N(4) may allow improved THA bearings that combine the reliability of metal femoral heads with the low wear advantages of ceramic materials.
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- "To deal with this problem, zirconia-toughened alumina (ZTA) composites are the most recent solution available in the market (Biolox-Delta from Ceramtec), bearing with improved fracture toughness decreasing the ceramic fracture rate and wear . Another well-known ceramic material for structural applications is silicon nitride (Si 3 N 4 ), which presents a marked fracture toughness value of 10 MPa m 1/2  higher than 6.5 MPa m 1/2 from ZTA . Indeed, Si 3 N 4 ceramics were far-seeing proposed by Zhou et al.  as a structural material for articular implants, and in the last decade by others [7,10–17]. "
ABSTRACT: A hip joint wear simulator is used for the first time to evaluate the performance of acetabular liners and femoral heads made of silicon nitride ceramic coated with nanocrystalline diamond (NCD), grown by a hot filament chemical vapor deposition (HFCVD) method. Wear is assessed by gravimetry, by which volume and linear wear are estimated. Even with only one million cycles of test, a very stimulating finding is the extremely low wear rate of the head after the diamond polishing running-in step, of about 0.005 mm(3)/million cycles (Mc). This corresponds to a linear wear of 0.08 mu m/Mc, one order of magnitude better than the best value currently known for ceramic-on-ceramic hip joints. Small scale abrasion is found as the dominant wear mechanism.
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- "While long-term exposure to autoclaving did not degrade Si 3 N 4 bearings in terms of phase changes and flexural strength (B. Sonny Bal et al., 2008). A high fracture toughness of 10 ± 1 MPa m 1/2 with Weibull modulus of 19 demonstrates its superior mechanical reliability. "
ABSTRACT: This chapter examines the importance of surface characteristics such as microstructure, composition, crystallographic texture, and surface free energy in achieving desired biocompatibility and tribological properties thereby improving in vivo life of artificial articulating implants. Current implants often fail prematurely due to inadequate mechanical, tribological, biocompatibility, and osseointegration properties, apart from issues related to design and surgical procedures. For long-term in vivo stability, artificial implants intended for articulating joint replacement must exhibit long-term stable articulation surface without stimulating undesirable in vivo effects. Since the implant's surface plays a vital and decisive role in their response to biological environment, and vice versa, surface modification of implants assumes a significant importance. Therefore, overview on important surface modification techniques, their capabilities, properties of modified surfaces/implants are presented in the chapter. The clinical performance of surface modified implants and new surfaces for potential next-generation articulating implant applications are discussed at the end.
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- "Today, silicon nitride is used for spinal implants and in early 2011 the first silicon nitride femoral head was implanted in USA. The choice of silicon nitride as an implant material is motivated by its excellent biocompatibility, low wear rates as well as relatively high fracture toughness and strength (Mazzocchi and Bellosi, 2008; Mazzocchi et al., 2008; Sonny Bal et al., 2008, 2009). "
ABSTRACT: Total joint replacements currently have relatively high success rates at 10-15 years; however, increasing ageing and an active population places higher demands on the longevity of the implants. A wear resistant configuration with wear particles that resorb in vivo can potentially increase the lifetime of an implant. In this study, silicon nitride (SixNy) and silicon carbon nitride (SixCyNz) coatings were produced for this purpose using reactive high power impulse magnetron sputtering (HiPIMS). The coatings are intended for hard bearing surfaces on implants. Hardness and elastic modulus of the coatings were evaluated by nanoindentation, cohesive, and adhesive properties were assessed by micro-scratching and the tribological performance was investigated in a ball-on-disc setup run in a serum solution. The majority of the SixNy coatings showed a hardness close to that of sintered silicon nitride (∼18GPa), and an elastic modulus close to that of cobalt chromium (∼200GPa). Furthermore, all except one of the SixNy coatings offered a wear resistance similar to that of bulk silicon nitride and significantly higher than that of cobalt chromium. In contrast, the SixCyNz coatings did not show as high level of wear resistance.
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