Wear Debris Particles Research Articles

Tissue digestion for wear debris particle isolation

Tissue digestion for wear debris particle isolation

Tribo-oxidation of a TiN coating sliding against corundum

This paper is aimed at understanding the tribo-oxidation of a physical vapor-deposited TiN coating when sliding against a corundum ball. This is achieved through a compositional and structural analysis of the wear debris. Wear debris particles generated at three different sliding speeds were analyzed with micro-Raman spectroscopy, transmission electron microscopy, and electron probe microanalysis. The analysis showed that the wear debris when formed at the low and medium sliding speed consist of TiO2 with a nanocrystalline structure containing both anatase and rutile structural elements. Only rutile structural elements could be observed in the debris formed at the high sliding speed. These results on the characterization of the wear debris are interpreted with calculations of the flash temperature in the tribo-contact and with recent ball-on-disk results on the wear rate of TiN as a function of the sliding speed to propose a mechanistic view of the tribo-oxidation and wear process. The relation with previous and recent experimental results on the static oxidation of TiN is also given.

Macrophage/particle interactions: effect of size, composition and surface area.

Particulate wear-debris are detected in histiocytes/macrophages of granulomatous tissues adjacent to loose joint prostheses. Such cell-particle interactions have been simulated in vitro by challenging macrophages with particles dosed according to weight percent, volume percent, and number of particles. Each of these dosage methods has inherent shortcomings due to varying size and density of challenging particles of different compositions. In this study we challenged P388D1 macrophages with titania and polystyrene particles (< 2 microns), with dosage based on the ratio of the surface area of the particles to the surface area of the cells. The effect of size and composition on (1) the bone resorbing activity, (2) fibroblast proliferation, and (3) secretion of IL-1 and PGE2 was determined. Macrophage response to particulate debris appears to be dependent on particle size, composition, and dose as given by surface area ratio. P388D1 macrophages challenged with titania particles released IL-1, but did not stimulate fibroblasts. Inhibition of macrophage DNA synthesis at higher surface area ratios suggests cell damage or death. Particle-stimulated cells increased bone resorption up to 125% of controls but released only basal levels of PGE2. Macrophages stimulated by wear particles are expected to synthesize numerous factors affecting events in the bone-implant interface. Using the concept of surface area ratio allows us to study and compare such cellular responses to wear particles in a standardized manner.

Using the atomic-force microscope to measure roughness characteristics of acetabular prosthetic shells used as hip-socket replacements

Total replacement of a diseased or traumatized hip joint is fast becoming one of the most common surgical procedures. The acetabular prosthetic shell is gaining widespread acceptance as a socket replacement for this procedure. Bio-materials research is providing a wealth of information regarding the life span, wear characteristics, and performance of these replacements, with a major clinical finding being the destruction of bone (osteolysis) at interfaces with the implants. Osteolysis is widely thought to be associated with the particulate wear debris released from articulation of the ball and socket. Formation and release of these particulates will depend not only on the relative motion occurring but also the surface roughness of the metal.In this study we used the Atomic Force Microscope (AFM) to compare the internal surface topography of two acetabular shells, one polished to a mirror finish and the other unpolished. The ultimate goal of the study was to determine whether a polished shell reduces the amount of wear and tear on the ultra-high molecular weight polyethylene (UHMWPE) insert that is fitted between the shell and the Femoral ball (Figure 1).

Bone resorption activity of particulate-stimulated macrophages.

Particulate wear debris from bone cement or prosthetic components can stimulate macrophages to cause bone resorption in a dose-dependent manner. This bone resorption activity of particulate-stimulated macrophages is associated with increased levels of both prostaglandin E2 (PGE2) and interleukin-1 (IL-1). In this study we compared the effect of particulate size, concentration, and composition on the secretion of IL-1 and PGE2 by peritoneal macrophages and on the bone-resorbing activity of conditioned medium (CM) harvested from particulate-challenged macrophages. Particulates (titanium, Ti; polymethylmethacrylate, PMMA; and polystyrene, PS) only with phagocytosable size stimulated peritoneal macrophages to secrete IL-1 and PGE2 in a dose- and time-dependent manner. Ti particles (1-3 microns) exhibited significantly enhanced bone-resorbing activity measured as 45Ca release. The maximum bone-resorbing response was observed at a concentration of 0.1% Ti (approximately 10-15 Ti particulates per cell), which also corresponded with the highest IL-1 levels measured in particulate-challenged CM. This was measured using either conditioned media from Ti-stimulated macrophages or in cocultures of calvarial bone and macrophages in the presence of Ti. Exogenous PGE2 and recombinant human IL-1 could significantly increase the 45Ca release; indomethacin (IM) significantly reduced both the spontaneous calcium efflux and active 45Ca release from in vivo labeled calvarial bones. However, IM and/or anti-IL-1 antibodies could suppress only partly the macrophage-mediated bone resorption, indicating that, in a macrophage-bone coculture system, factors other than PGE2 and IL-1 also may regulate particulate-induced bone resorption, probably involving multiple cell types.

Extramedullary porous coating to prevent diaphyseal osteolysis and radiolucent lines around proximal tibial replacements. A preliminary report.

Nineteen patients who had a primary malignant bone tumor of the proximal end of the tibia were managed with wide resection and implantation of a tibial endoprosthesis with cement, combined with a rotating-hinge knee replacement. In the first ten patients, a ring of porous coating was applied to the part of the tibial replacement that was just proximal to the intramedullary portion of the stem, to encourage ingrowth of bridging bone. No growth of bone into these porous rings occurred, and the rings were not applied to the next nine endoprostheses. During the subsequent follow-up period, progressive osteolysis (resorption of more than two millimeters of the proximal end of the remaining tibial cortex) developed in only one patient (who had a deep infection) in the group of ten patients who had a porous ring, compared with five of the nine patients who did not have a porous ring but in whom osteolysis developed. This difference was significant (p < 0.001). In addition, the tibial osteolysis was associated with the subsequent development of progressive periprosthetic radiolucent lines at the bone-cement interfaces (p = 0.001). We postulated that, in the patients who had an extramedullary porous ring, the periprosthetic fibrous capsule that formed around the extramedullary portion of all the implants became firmly adherent to the ring, thereby sealing off the part of the capsule that was distal to the ring. The particulate wear debris that was contained within the articular portion of the capsule could not reach the distal tibial bone surrounding the prosthetic stem, and debris-incited osteolysis, which leads to loosening, did not develop. If this mechanism is confirmed, it could have important implications for the design of implants that are used in joint replacement.

A quantitative study of bone and soft tissues in cementless porous-coated acetabular components retrieved at autopsy

The authors examined 11 cementless acetabular components of one design retrieved at autopsy and made observations concerning tissue ingrowth and local tissue reaction, radiographic-histologic correlation, and the distribution of particulate wear debris. The cups were hemispherical in design with a commercially pure titanium fibermetal porous coating. All of the prostheses were implanted with screws. The implants were in place for an average of 41 months (range, 5 weeks to 75 months). Ten of the cups had bone ingrowth, with the average volume fraction being 12.1±8.2%. There were no differences in the amount of bone ingrowth when the component was partitioned into nine anatomic regions. However, there was more bone adjacent to screw holes through which screws were inserted compared with empty screw holes. As the number of radiolucent zones increased on the clinical radiographs less bone ingrowth was observed histologically. The amount of metal debris in holes with screws and holes without screws was similar. In the longest term cases, polyethylene debris was noted within empty screw holes, but no granulomatous reactions or osteolytic processes were observed.

Fretting Behavior of Titanium Alloys

Fretting wear tests were performed on three titanium alloys, α + β-Ti-6Al-4V, α-Ti-15V-3Al-3Cr-3Sn, and β-Ti-15V-3Al-3Cr-3Sn, in air. Friction conditions were chosen in order to get gross slip at the interface. The tangential load was recorded during each cycle of the test. Optical and scanning electron microscopy, grazing incidence X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscopy (TEM) were used to characterize the superficial surface layers of the specimens after the fretting test. Particle detachment was observed in every case and the friction coefficient was always very high. A hard tribologically transformed structure (TTS) was detected in some areas of the superficial layers. TEM revealed that TTS was formed of ultra fine non-oriented grains of alpha-titanium. No beta phase was detected. The wear debris particles were produced from the transformed areas of the contact zone and were then quickly oxidized in the interface. The formation of the TTS is interpreted...

Mechanism and Clinical Significance of Wear Debris-Induced Osteolysis

Loosening of joint replacement components is often multifactorial. The quality of initial fixation is very important to the outcome of the arthroplasty and is often a factor in short-term and long-term failure. This paper discusses another important factor of implant loosening, namely wear debris induced osteolysis. Macrophages activated by the phagocytosis of particulate wear debris are the key cells in this process, which can potentially occur in any implant system regardless of implant design or fixation mode. This is because each implant system creates wear debris from the articulating surfaces and the interfaces. The clinical consequences of wear debris cover a broad spectrum from radiolucencies to massive osteolysis and implant failure. For this reason, the reduction of wear debris should be a primary goal of orthopedic research in the future.

Metallic Debris in Femoral Endosteolysis in Failed Cemented Total Hip Arthroplasties

A prospective study was undertaken to quantitate metallic and cement debris in 12 consecutive patients with femoral endosteolysis (FE) and aseptic loosening of a cemented total hip arthroplasty. The mean interval between primary and revision surgery was 9.6 years. The average time to onset of FE was 8.9 years. There were four stems each of cobalt-chromium (Co-Cr), stainless steel (SS), and titanium alloy. At revision, tissue was retrieved from FE, the femoral bone-cement pseudomembrane, and the joint pseudocapsule. Histology of these tissues was studied using light and polarized microscopy. Metal and barium levels were measured by atomic absorption spectrophotometry. A histiocytic reaction and particulate cement debris were seen in every case. Polyethylene wear debris was noted in 11 of 12 cases (92%), and metallic debris in four cases (33%). Detectable metal levels were found in the FE in all cases. Metal levels were on average 2.5 times higher in FE than in femoral pseudomembrane, and 4.2 times higher than in joint pseudocapsule. This difference was statistically significant for the Co-Cr and SS groups. Barium levels in areas of FE were on average 1.7 times and 42.4 times higher than in femoral pseudomembrane and joint pseudocapsule, respectively. The difference seen between the FE and the joint pseudocapsule tissue was significant for all three alloy groups. The authors' data demonstrated higher metal and barium levels in FE than in the other tissue sites. Polyethylene and cement debris were noted in nearly every case. Cement, polyethylene, and metallic particulate wear debris may contribute to the pathogenesis and progression of FE.

Effects of hardness on the wear mode diagram in lubricated sliding friction of carbon steels

The predominant wear mechanisms were studied using discs with five different hardnesses as a function of contact pressure and sliding velocity in thin-film-lubricated sliding under conditions of concentrated contact with a hard chromium steel ball. Mild flow wear, severe flow wear, adhesive wear and oxidative wear were found. These wear mechanisms were plotted in a wear mode diagram for each hardness, representing the predominant wear mechanism as a function of the applied contact pressure and sliding velocity. It was found that the location of each possible region in the diagram changed, depending strongly on the hardness. It was also found that the shapes and sizes of wear debris particles depended strongly on the predominant wear mechanism as well as on the specific wear rate. This diagram was related to the abrasive wear mode diagram and discussed.

Mechanism of transfer film formation during repeat pass sliding of ceramic materials

The formation of transfer film and the consequent effects on the friction and wear behavior of ceramic materials during repeat sliding contact were studied. This was done using four structural ceramics, namely silicon nitride, silicon carbide, alumina and zirconia, with a cylinder-on-flat test configuration. The transfer film consists of reattached fine wear debris particles, the film, whenever formed, is strongly attached, enough to resist being wiped off by the slider. Calculations suggest that the fine particles are attached primarily by van der Waals forces and to a lesser extent by electrostatic attractive forces. As a consequence, the formation of transfer film leads to a decrease in the wear rate because of the ‘protecting’ role of the film. The presence of the film at the contact interface also results in high friction. The presence of a liquid environment and/or surface active species reduces the particle adhesive forces and hence can inhibit the formation of a transfer film.

Adhesion theories of transfer and wear during sliding of metals

A regular solution model based on nearest-neighbor pair bonding is applied in this paper to predict the effect of adhesion on transfer and wear during the dry sliding of metals. A transfer event is treated as depending on interface separation and junction adhesion. The energies of a free surface and of a large-angle grain boundary are incorporated. The results indicate that transfer is favored over direct generation of wear debris particles. To predict relative transfer trends during early stages of sliding it is sufficient to concentrate on interface separation. After continued sliding, transfer material normally consists of contributions from both sliding components, and transfer trends will also be affected by junction adhesion. Based on an ideal solution model, transfer from the component with smaller surface energy is preferred. In addition, the transfer tendency of a single-phase binary alloy, and hence its wear rate, is suppressed if the alloying element has a larger surface energy. Although the adhesion models presented in this paper are rather simplified, reviews of published experimental data show that the above surface energy criteria can serve as a crude guide for predicting transfer tendencies for simple metal-metal and metal-binary alloy combinations.

A comparative evaluation of RPD and ferrographic diagnostic methods for turbine engine lubricant samples

A rotary particle depositor (RPD) was evaluated and compared with analytical (AF) and direct reading (DR) ferrographs to ascertain if the RPD is better suited for analysis of wear debris in turbine engine lubricant samples than the AF and DR. Sieved iron particles were added to synthetic turbine engine lubricants at various concentrations and were analysed by RPD and ferrographic methods and compared. Lubricant samples containing a fine test dust were also analysed by RPD and AF to determine the effectiveness of the RPD's centripetal acceleration and the AF's gravity flow in eliminating non-ferrous contamination from the sample. Finally, comparisons were made between actual lubricant samples from a turbine engine simulator analysed by RPD and ferrographic methods. For lubricant samples with relatively small amounts of non-ferrous contamination or samples where non-ferrous particles are important in machine health condition assessment, the AF and DR ferrographs are equal or superior to RPD for lubricant analyses. For samples with high levels of non-ferrous contamination, the RPD is superior in eliminating unwanted non-magnetic particles and permitting a less obstructed view of the important ferrous wear debris particles.

Metallographic evidence for the nucleation of subsurface microcracks during unlubricated sliding of metals

The location, surface or subsurface, for nucleation and propagation of microcracks during sliding wear has been a continuing source of discussion and controversy in the tribology community. Rather than to suggest that there is only one correct answer to this question, the authors propose that, depending on the contact conditions and materials involved, several preferred sites for microcrack nucleation can exist. The present paper discusses a model which involves nucleation ahead of the slider, material flow under the slider, crack closure and reopening after the slider passes. Once microcracks nucleate, subsequent slider passes can cause crack propagation, coalescence and the eventual formation of wear debris particles. Recent metallographic evidence for crack nucleation ahead of a pyramidal slider which has a large negative rake angle is presented and suggests that this process is occurring to some extent; however, unequivocal substantiation of the model's principal hypothesis still awaits research with a slider whose geometry promotes material flow underneath it rather than forming chips or flowing around the sides.

On the wear and failure of high speed roller bearings

A laboratory bearing test rig was constructed to study wear and failure mechanisms in high speed roller bearings under different conditions of loading and lubrication. The design of the rig permitted three bearings to be tested simultaneously. A test run of 720 h duration was performed during which wear of the bearings was monitored using ferrography and atomic absorption oil analysis. Wear debris particles collected from the bearings by ferrography were studied with scanning electron microscopy using energy-dispersive X-ray analysis. The results of ferrography were correlated with the metallographic observations made on the worn bearings. It was found that for lightly loaded high speed roller bearings rolling contact fatigue including surface pitting is not a significant wear or failure mechanism. However, misalignment due to shaft deflection above a critical point cannot be tolerated. Wear of high speed engine bearings can successfully be monitored by ferrography but, as the wear condition accelerates, frequent oil sample collections are beneficial.

Transfer during unlubricated sliding wear of selected metal systems

Results of pin-on-disk sliding tests in vacuum, with copper, CuNi, nickel and molybdenum sliding against iron, indicate that initial transfer events involve discrete fragments. We propose that the process involved in the initial transfer events is a consequence of local shear instabilities which develop at large plastic strains. In copper samples the initial transfer elements are lamellar, with layer thickness equal to the cell thickness in the highly deformed base material adjacent to the sliding interface. Prolonged sliding gives rise to the formation of transfer layers or patches on the specimen surface. These layers or patches are composed of finely mixed material derived from the two sliding counterparts as well as scattered pieces of more recently transferred fragments. Typical wear debris particles are generated from the transfer layers or patches. Transfer tendencies for different materials combinations can be predicted from an adhesion point of view if geometrical effects are properly considered. Combining theoretical predictions of transfer tendencies and experimental observations of transfer and geometrical effects, one finds that for a pin-and-disk system the disk should be made of the material having the higher cohesive strength.

Human enamel-dental amalgam pin on disc wear.

Abstract Cyclic wear tests with human enamel pins on rotating amalgam discs at 9.8 MPa contacting stress were conducted with Sybraloy, Cupralloy, Aristalloy C. R., and Minimax amalgams. Surface profile tracings were made across the wear tracks, as well as SEM-EDS of the microstructure. Results indicate that Minimax exhibited the greatest wear depth for all amalgams but Sybraloy showed the greatest wear for the higher copper-containing amalgams. For all amalgams wear grooves appeared and were attributed to wear by shear. These grooves appeared more distinctly for Sybraloy, and this is thought to be due to a more efficient removal of wear debris from the contacting surfaces, leading to a lesser degree of surface smearing. Wear debris particles and smearing of this debris was attributed to wear by welding. For the higher copper-containing amalgams the gamma-1 phase is thought to be related to this adhensive welding because of its deterioration from the wear surfaces. For the conventional Minimax amalgam, the gamma-2 phase precedes the gamma-1 phase in being worn from the surface. Gross amalgam transfer in the form of silver and mercury to the enamel pin occurred. A hardened stainless steel pin, which did not wear, generated amalgam wear tracks of a similar appearance to that generated from enamel. This supports the wear by shear and by welding instead of a 3-body abrasive wear model based upon the wear particles from the enamel pin. No Ca or P was ever detected on the amalgam surfaces.

Carbon Fiber Reinforced Triazin Resin for Endoprostheses

ABSTRACTMetal alloys, ceramics, and thermoplastics are commonly used as materials for endoprostheses, especially artificial hip joints. Prostheses made of these materials still retain disadvantages which have been responsible for failures in the past. A new material, without the abovementioned disadvantages, has been developed. It is a carbon fiber reinforced thermo set based on the triazin resin. Its principle mechanical properties can be matched with those of bone. The new material (referred to as TCF) has a higher bending and fatigue strength than cast metallic alloys if endless fibers are applied. Its creep rate at 37°C under high load (3000 N), as well as its wear rate against metallic or ceramic wear partners, is negligible. Experiments with animals based on ten years of experience show good osteocompatibility of the TCF. Toxic reactions of the tissue caused by the TCF implants themselves, or by fine wear debris found in membranes of connective tissue (or lymph nodes), were not observed at all. Tissue reacts on large particles of TCF wear debris in the same manner as it does on particulates of the same size of polyethylene. It can be expected that the favorable biomechanical and biological properties of the TCF material will make it a good alternative to other materials already in use for construction of endoprostheses, especially hip joints.

The Influence of Experimental Variables on the Development and Maintenance of Wear-Protective Oxides during Sliding of High-Temperature Iron-Base Alloys

An investigation has been carried out into the development and maintenance of wear-protective oxide on iron-12 per cent chromium-base alloys during sliding in air at 20–600°C, with particular reference to the effects of temperature, of intermittent changes in temperature, and of sliding speed. It has been established that the wear-protective surface develops on and from compacted oxide and oxide-coated metal debris and involves deformation of the oxide. The wear process in the early stages of sliding generates metallic wear debris particles. These are fractured and re-fractured until they have a high surface to volume ratio. These surfaces are oxidized at the ambient temperature, to produce considerable amounts of oxide debris. Additional amounts are generated by transient oxidation of the specimen surfaces and removal of this oxide during each transversal of the sliding action. The rate of production of such oxide debris is determined by the ease of fracture of the metal debris and the rate of oxidation. Under these sliding conditions, this results in a minimum in the time required to generate a wear-protective oxide surface at 400°C. Development of such a surface takes a longer period at higher and lower temperatures, and indeed it does not develop at all at room temperature. Once established, the wear-protective oxide remains adherent and stable during isothermal sliding at 300°C and higher temperatures. Thermal stresses imparted by cooling to room temperature and reheating to 300° C do not cause loss of effectiveness of the oxide on subsequent further sliding at 300°C. However, subsequent sliding at room temperature results in rapid breakdown of the oxide and metal-metal contact, presumably due to a decrease in plasticity of the fine oxide debris with decreasing temperature or to a decrease in the adhesion between the oxide and the metal substrate or in oxide cohesion.