ABSTRACT
Carbon-fibre-reinforced polyether ether ketone (CFR-PEEK) exhibits excellent biomechanical properties as it has an elastic modulus similar to bone. However, CFR-PEEK displays inferior biocompatibility compared with titanium alloy and coating techniques are therefore of interest in order to improve integration. In this paper, the early biological response to CFR-PEEK implants, with and without hydroxyapatite coating, was investigated. Furthermore, a hydroxyapatite-coated titanium alloy reference served as a clinically relevant control. The study was conducted in a rabbit model, both in femur trabecular bone as well as in tibia cortical bone. The results demonstrated that an hydroxyapatite coating significantly enhances the bone response to PEEK implants in vivo. Moreover, in cortical bone, hydroxyapatite-coated PEEK implants induced superior bone response compared with hydroxyapatite-coated Ti ones. These results suggest that hydroxyapatite-coated CFR-PEEK is a suitable material for in vivo implantation.
ABSTRACT
The role of surface tension in the lubrication of metal-on-metal (CoCrMo alloy) hip resurfacings has been investigated to try to explain why all metal joints fail to be lubricated with simple water-based lubricants (sodium carboxymethyl cellulose), which have similar rheology to synovial fluid, but are lubricated with the same fluid with the addition of a proportion of bovine serum. As part of this study, surfactants, in the form of detergents, when added to carboxymethyl cellulose, have been shown to produce a predominantly fluid-film lubrication mechanism with friction even lower than the biological lubricant containing serum. Friction factors were reduced by 80% when a detergent was added to the lubricant. It is considered that the failure of the water-based fluids to generate fluid-film lubrication is due to the fact that 'boundary slip' takes place where the fluid does not fully attach to the bounding solid surfaces as assumed in Reynolds' equation, thereby drawing in less lubricant than predicted from hydrodynamic theory. The addition of surfactants either in the form of natural materials such as serum or in the form of detergent reduces surface tension and helps the water-based lubricant to attach more fully to the bounding surfaces resulting in more fluid entrainment and thicker fluid-film formation. This was confirmed by up to 70% lower wear being found when these joints were lubricated in a detergent solution rather than 25% bovine serum.
Subject(s)
Hip Prosthesis , Lubricants/chemistry , Vitallium/chemistry , Animals , Carboxymethylcellulose Sodium/chemistry , Cattle , Detergents/chemistry , Equipment Failure Analysis/instrumentation , Equipment Failure Analysis/methods , Friction , Prosthesis Design , Serum/chemistry , Surface Tension , Viscosity , WettabilityABSTRACT
Tripolar total hip arthroplasty (THA) prosthesis had been suggested as a method to reduce the occurrence of hip dislocation and microseparation. Precisely measuring the motion of the intermediate component in vitro would provide fundamental knowledge for understanding its mechanism. The present study validates the accuracy and repeatability of a three-dimensional motion analysis system to quantitatively measure the relative motion of the intermediate component of tripolar total hip arthroplasty prostheses. Static and dynamic validations of the system were made by comparing the measurement to that of a potentiometer. Differences between the mean system-calculated angle and the angle measured by the potentiometer were within +/-1 degrees . The mean within-trial variability was less than 1 degrees . The mean slope was 0.9-1.02 for different angular velocities. The dynamic noise was within 1 degrees . The system was then applied to measure the relative motion of an eccentric THA prosthesis. The study shows that this motion analysis system provides an accurate and practical method for measuring the relative motion of the tripolar THA prosthesis in vitro, a necessary first step towards the understanding of its in vivo kinematics.
