Polyethylene wear of dual mobility cups: a comparative analysis based on patient-specific finite element modeling

Purpose Concerns remain about potential increased wear with dual mobility cups related to the multiple articulations involved in this specific design of implant. This finite element analysis study aimed to compare polyethylene (PE) wear between dual mobility cup and conventional acetabular component, and between the use of conventional ultra-high molecular weight PE (UHMWPE) and highly cross-linked PE (XPLE). Methods Patient-specific finite element modeling was developed for 15 patients undergoing primary total hip arthroplasty (THA). Five acetabular components were 3D modeled and compared in THA constructs replicating existing implants: a dual mobility cup with a 22.2-mm-diameter femoral head against UHMWPE or XLPE (DM22PE or DM22XL), a conventional cup with a 22.2-mm-diameter femoral head against UHMWPE (SD22PE) and a conventional cup with a 32-mm-diameter femoral head against UHMWPE or XLPE (SD32PE or SD32XL). Results DM22PE produced 4.6 times and 5.1 times more volumetric wear than SD32XL and DM22XL (p < 0.0001, Cohen’s d = 6.97 and 7.11; respectively). However, even if significant, the differences in volumetric wear between DM22XL and SD32XL as well as between DM22PE and SD22PE or SD32PE were small according to their effect size (p < 0.0001, Cohen’s |d|= 0.48 to 0.65) and could be therefore considered as clinically negligible. Conclusion When using XLPE instead of UHMWPE, dual mobility cup with a 22.2-mm-diameter femoral head produced a similar amount of volumetric wear than conventional acetabular component with a 32-mm-diameter femoral head against XLPE. Therefore, XLPE is advocated in dual mobility cup to improve its wear performance.

ASSESSMENT OF ABRASIVE WEAR RATE FOR PTFE-BASED COMPOSITES IN COMBINATION WITH STEEL

This paper presents a study of the tribological wear rate for PTFE-based composites in combination with C45 steel. PTFE composites with the addition of glass fibre, bronze, carbon fibre, and graphite were selected for the study. Tribological tests were conducted in a roller-block combination over an expanded contact area with no lubrication, using an SMC-2 machine. The study assessed the mass and volumetric wear for the test materials and the wear rate index. The highest wear values were noted for the PTFE composite with the addition of bronze, while the lowest was for the PTFE composite with the addition of glass fibre. For all the test materials, the formation of a polymer film on the steel counter specimen was noted.

SOME COMMENTS ON THE INTERPRETATION OF THE TRIBOLOGICAL WEAR COEFFICIENT

An original model of tribological wear is presented, an alternative to the commonly used J.F. Archard’s model. The impossibility is established of a full conversion of mechanical work into the heat of dissipation and thereby of avoiding wear in the sliding friction of solids. The assumption is consequently questioned that only some contacts of surface asperities are subject to temporary wear. Material wastage is assumed to occur at each contact of asperities. The volume of worn material is dependent on the volumetric wear coefficient of the “energy dissipation zone” in friction. The dimensions of the zone are determined in both the elements in friction. Linear wear intensities and volumetric wear are described in analytical terms. The thermodynamic analysis of the tribological process indicates some limitations to these intensities. Energetic efficiencies of solid wear and heating as a result of friction are defined. Some new interpretations of the wear coefficient are proposed.

Investigation of Micromechanical Properties and Tribological Behavior of WE43 Magnesium Alloy after Deep Cryogenic Treatment Combined with Precipitation Hardening

This study investigated the micromechanical and tribological properties of WE43 alloy (Mg-Y-Nd-Zr) alloy subjected to cryogenic treatment and precipitation hardening. Microindentation tests were carried out in the range of load from 100 to 1000 mN. The introduction of deep cryogenic treatment (DCT) was shown to increase hardness and Young’s modulus, and reduce the total indentation work. As the load set during the tests increased, a gradual decrease in the measured values was observed, indicating a significant relationship between the indent size and the value of the measured parameters. Cryogenic treatment used in conjunction with precipitation hardening (after solutioning and after aging) reduces the tribological wear of the alloy. Tests have shown an almost twofold reduction in the area of the wear trace and in the volumetric wear of the alloy, as well as a more than twofold reduction in linear wear, with relatively small fluctuations in the coefficient of friction. Abrasion was the main mechanism of wear. Areas where microcutting, adhesion and plastic deformation occurred were also observed. The results indicate the significant effectiveness of the applied heat treatment in improving the service life of the WE43 alloy containing rare earth metals.

The Effect of Ball Burnishing on Dry Fretting

Experiments were conducted under a dry gross fretting regime. Steel discs were put in contact with ceramic balls. Before tribological tests, discs were subjected to ball burnishing with different pressures. Due to ball burnishing, a decrease in surface amplitude and an increase in microhardness occurred. Ball burnishing caused decreases in the friction force and volumetric wear of up to 45% in comparison to sliding pairs containing milled discs. The friction force and volumetric wear were higher for a higher roughness of disc.

Abrasive resistance of polyetherurethane ureas

The relationship between the structure of the polymer chains and the abrasion resistance of segmented polyurethane ureas based on polyoxytetramethylene oligoether was studied. Experimental data were obtained for systems with the hard segments content above 39%. It was found that the function of the volumetric wear of polyurethane-urea samples on the content of hard segments had an extremum; at high contents of these segments (more than 35%), a further increase in this content lead to a deterioration in the abrasion resistance. The reasons for this effect can be associated with a sharp deterioration in the strength and strain properties of the studied elastomers when additional amounts of diisocyanate are introduced into the system, which can lead to the formation of excessive interchain bonds.

OPTIMIZATION OF USE CONDITIONS FOR CATHODIC ARC NICKEL COATING DOPED WITH PHOSPHORUS

The results of tribological tests for a cathodic arc nickel coating doped with phosphorus are presented. The coating (thickness of 2 μm) is applied by a vacuum arc method from a nickel target with 6% phosphorus. The friction coefficient (Cfr) was determined on the tribometer, the depth of wear h of the coating after tribological tests was determined by the contact profilometry method, and the specific volumetric wear (ω) was calculated. The obtained values of Cfr, ω, and h were used to optimize the parameters of tribological tests (load and slip frequency).

Nanomechanical and Nanotribological Properties of Nanostructured Coatings of Tantalum and Its Compounds on Steel Substrates

The present paper addresses the problem of identification of microstructural, nanomechanical, and tribological properties of thin films of tantalum (Ta) and its compounds deposited on stainless steel substrates by direct current magnetron sputtering. The compositions of the obtained nanostructured films were determined by energy dispersive spectroscopy. Surface morphology was investigated using atomic force microscopy (AFM). The coatings were found to be homogeneous and have low roughness values (<10 nm). The values of microhardness and elastic modulus were obtained by means of nanoindentation. Elastic modulus values for all the coatings remained unchanged with different atomic percentage of tantalum in the films. The values of microhardness of the tantalum films were increased after incorporation of the oxygen and nitrogen atoms into the crystal lattice of the coatings. The coefficient of friction, CoF, was determined by the AFM method in the “sliding” and “plowing” modes. Deposition of the coatings on the substrates led to a decrease of CoF for the coating-substrate system compared to the substrates; thus, the final product utilizing such a coating will presumably have a longer service life. The tantalum nitride films were characterized by the smallest values of CoF and specific volumetric wear.