Abstract
The articulation performance of silicon nitride against conventional and highly cross-linked polyethylene, as well as for self-mated silicon nitride bearings, was examined in a series of standard hip simulation studies. Wear rates for polyethylene liners against silicon nitride femoral heads were consistent with reported literature, although higher than cobalt chromium controls. Excessive protein precipitation was a confounding factor in interpretation of the wear data. Post wear-test Raman spectroscopy of the cross-linked polyethylene liners showed no oxidative degradation. Wear of self-mated silicon nitride was found to be essentially zero and indistinguishable from alumina controls using continuously orbital hip simulation for up to three million cycles. However, introduction of an alternative loading profile from three to five million cycles, including a stop-dwell-start sequence, significantly increased wear for two of six silicon nitride couples. This behavior is associated with formation and disruption of a gelatinous silicic acid tribochemical film, and is consistent with a recurrent transition from fluid-film to boundary lubrication. Overall, these results suggest that silicon nitride articulation against dissimilar counterface surfaces (e.g., highly cross-linked polyethylene) is preferred.
Highlights
Since 2008 silicon nitride (Si3 N4 ) has been used as arthrodesis devices in the cervical and thoracolumbar spine [1], and has been proposed as a new bearing material for total joint arthroplasty [2,3,4,5].Si3 N4 has a favorable combination of properties, such as high strength and fracture toughness [4], inherent phase stability [4], biocompatibility [6], hydrophilicity [7], and bacterial resistance [7,8], all of which make it ideal for these applications
In articulation against polyethylene (PE), low friction is typically observed for all ceramics, including various Si3 N4 compositions (i.e.,
Considering the observed confounding effects of preferential protein adsorption and polyethylene debris adhesion to the cobalt chromium (CoCr) femoral heads, it was concluded that the ultra-high molecular weight polyethylene (UHMWPE) wear using Si3 N4 was likely at least equivalent to CoCr. These results indicate that Si3 N4 femoral heads can be effectively used in CoP total joint arthroplasty devices, and suggest that oxidative protection of the polyethylene may be an added benefit
Summary
Since 2008 silicon nitride (Si3 N4 ) has been used as arthrodesis devices in the cervical and thoracolumbar spine [1], and has been proposed as a new bearing material for total joint arthroplasty [2,3,4,5]. Lubricants 2016, 4, 35 and continuous motion devices; whereas high friction (>0.7) and accelerated wear are apparent for slow-speed, high-loads, and interrupted (stop-start) conditions [10]. A ceramic-on-ceramic (CoC) hip simulator study compared Si3 N4 head and liner pairs to similar components made from Al2 O3. These studies provide both qualitative and quantitative understanding of the potential in vivo capability of this biomaterial
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