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Alternative Bearing Materials for Intervertebral Disc Arthroplasty

In this study, researchers from Aesculap tested alternative PEEK polymer-on-polymer articulations for cervical total disc arthroplasty with favourable biotribological properties and the benefit of radiolucency in comparison to the clinically well established metal-on-polyethylene coupling. In vitro wear simulation was performed according to ISO 18192-1:2008 (E) with the clinically introduced activ C cervical artificial disc (Aesculap AG Tuttlingen, Germany) made of UHMWPE/CoCr29Mo6 in a direct comparison to experimental disc articulations made of PEEK, CFR-PEEK and PEK. Whereas the polymer-on-polymer articulation of PEK showed no substantial benefit in comparison to polyethylene-on-cobalt-chromium and whereas natural PEEK tends towards pitting and delamination, the carbon fibre reinforced PEEK demonstrated an excellent wear behaviour with a reduction in order of a magnitude.

Mechanical Properties of Hydroxyapatite Whisker Reinforced Polyetherketoneketone Composite Scaffolds

The apparent mechanical properties of hydroxyapatite (HA) whisker reinforced polyetherketoneketone (PEKK) scaffolds were evaluated in unconfined, uniaxial compression to investigate the effects of the porosity, HA content, and mold temperature. HA whisker reinforcement generally resulted in an increased elastic modulus from 0 to 20 vol% HA and a subsequent decrease from 20 to 40 vol% HA, while the yield strength and strain was decreased in scaffolds with 40 vol% HA compared to those with 0 or 20 vol% HA. Increased mold temperature resulted in an increased elastic modulus, yield strength and yield strain. These effects enabled the mechanical properties to be tailored to mimic human trabecular bone. HA whisker reinforced PEKK scaffolds may be advantageous for permanent implant fixation, including interbody spinal fusion.

Hydroxyapatite Whisker Reinforced Polyetherketoneketone Bone Ingrowth Scaffolds

Hydroxyapatite (HA) whisker reinforced polyetherketoneketone (PEKK) bone ingrowth scaffolds were prepared and characterized. High levels of porosity (75-90%) and HA whisker reinforcement (0-40 vol%) were attained using a powder processing approach to mix the HA whiskers, PEKK powder and a NaCl porogen, followed by compression molding at 350-375°C and particle leaching to remove the porogen. The scaffold architecture and microstructure exhibited characteristics known to be favorable for osteointegration. Scaffold porosity was interconnected with a mean pore size in the range 200-300 μm as measured by micro-computed tomography (micro-CT). HA whiskers were embedded within and exposed on the surface of scaffold struts, producing a micro-scale surface topography, shown by von Kossa staining and scanning electron microscopy (SEM).

Strontium-Containing Hydroxyapatite/Polyetheretherketone Composites

Strontium-containing hydroxyapatite/polyetheretherketone (Sr-HA/PEEK) composites were developed as alternative materials for load-bearing orthopaedic applications. The amount of strontium-containing hydroxyapatite (Sr-HA) incorporated into polyetheretherketone (PEEK) polymer matrix ranged from 15 to 30 vol% and the composites were successfully fabricated by compression molding technique. Strontium, in the form of strontium-containing hydroxyapatite (Sr-HA), was confirmed to enhance bioactivity in the PEEK composites.

Biomechanical Evaluation and Comparison of a PEEK Rod System to Traditional Ti Rod Fixation

PEEK lumbar fusion rods have recently become available for use in posterior lumbar fusion procedures. In this study, researchers from Jefferson and DePuy Spine performed biomechanical testing to evaluate PEEK rods in compressive bending and torsion. The rods were fabricated from an image-contrast grade of PEEK (6% BaSo4). Because of the flexibility of the PEEK rods, an angular displacement control variant of F1717 fatigue testing was performed in parallel with biomechanical studies in a cadaver model. PEEK rods provided comparable stability to titanium rods of equivalent diameter in cadaveric testing. Mechanical testing suggested that PEEK rods can withstand far beyond the angular displacements suggested by cadaveric testing and that of normal physiologic range of motion.

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