Characteristics Of Debris Research Articles

The performance of gamma- and EtO-sterilised UHMWPE acetabular cups tested under severe simulator conditions. Part 2: wear particle characteristics with isolation protocols

Ultra-high molecular-weight polyethylene (UHMWPE) has been used in total joint replacement for the last three decades. Despite the recent advancements in prosthesis design, the wear of UHMWPE remains a serious clinical problem; the release of wear debris may induce osteolysis and implant loosening. Controlling the quality of the polyethylene is essential to improve its wear resistance and any potential adverse effect caused by processing, manufacturing or sterilisation should be avoided. To evaluate the influence of the sterilisation method (gamma-irradiation and ethylene oxide (EtO)-treatment) and third-body particles, gamma- and EtO-sterilised UHMWPE acetabular cups were tested against CoCrMo femoral heads in a hip joint simulator run for 2.5 million cycles in bovine calf serum in the presence of third-body polymethylmethacrylate (PMMA) particles. A method not requiring ultra-centrifugation has been proposed for the isolation of polyethylene wear debris from the serum lubricant. SEM analysis allowed debris shape and morphology to be determined, and the wear mechanism operating in this study to be hypothesised. The morphological features of the wear debris were in agreement with clinical findings, enabling the hip simulator function to be validated. Micro-Raman spectroscopy coupled to PLS analysis showed that the mechanical friction during in vitro tests induced significant crystallinity changes in all the cups. The most significant changes were observed for the EtO-sterilised cups, which showed the highest weight loss.

Investigation of tribological properties of Al 2O 3-polyimide nanocomposites

Polyimide (PI) nanocomposites with different proportions of nanoparticle Al 2O 3 were made by compression molding at elevated temperature. The mechanical and tribological properties of the resulting PI-based nanocomposites were investigated. The bending strength and microhardness of the nanocomposite specimens were determined, and the tribological behavior of the nanocomposite blocks in dry sliding against a plain carbon steel ring was evaluated on an M-2000 friction and wear tester. The morphologies of the worn nanocomposite surfaces and transfer films on the counterpart steel ring were observed on a scanning electron microscope. Results indicated that the PI-based nanocomposites with appropriate proportions of nanometer Al 2O 3 exhibited lower friction coefficient and wear volume loss than PI under the same testing conditions. The nanocomposite containing 3.0wt.%–4.0wt.% nanometer Al 2O 3 registered the lowest wear volume loss under a relatively high load. The differences in the friction and wear behaviors of PI and PI–Al 2O 3 nanocomposites were attributed to the differences in their worn surface morphologies, transfer film characteristics, and wear debris features. The agglomerated abrasives on the worn composite and transfer film surfaces contributed to increase the wear volume loss of the nanocomposites of higher mass fractions of nanometer Al 2O 3.

Channel and woody debris characteristics in adjacent burned and unburned watersheds a decade after wildfire, Park County, Wyoming

Large variability in responses of stream sediment and large woody debris (LWD) to severe fire has limited the accurate prediction of the magnitude and duration of fire effects on streams. Conditions in one Absaroka Range stream that was severely burned in 1988 were compared to those in an adjacent, undisturbed stream to improve understanding of fire effects on channel and LWD characteristics beyond the first few years. Ten reaches of each stream were sampled during summer 1999. Average bankfull channel width was greater in burned Jones Creek than in unburned Crow Creek. LWD frequency and overall frequency of LWD accumulations were greater in Crow Creek than Jones Creek. Debris-jam frequency was greater in Jones Creek after accounting for differences in the frequency of pieces with length greater than channel width. Larger piece size and better anchoring contributed to more frequent, small accumulations of LWD in Crow Creek. Differences between streams in LWD frequency are consistent with greater mobility of debris in burned Jones Creek. LWD-associated fine-sediment deposits were thicker but less frequent along Jones Creek than Crow Creek.

Influence of forest structure on habitat use by American marten in an industrial forest

American marten ( Martes americana) are associated with late-successional, coniferous forests throughout much of their range. In the northeastern US, however, marten also occur in forests dominated by mid-successional, mixed coniferous–deciduous and deciduous stands. Structural attributes other than forest-stand age and dominant overstory type may be important determinants of habitat quality for marten. To identify structural conditions associated with patterns of habitat use by marten, we compared characteristics of coarse woody debris (CWD), understory vegetation, and overstory vegetation between 16 ha areas receiving different intensities of use by 24 (13 male, 11 female) resident, nonjuvenile (≥1 year) marten in an extensively clearcut industrial forest in Maine. Overstory features related to stand maturity were most useful for discriminating between areas receiving high use, low use, and no use by marten. Used areas had taller trees, higher live-tree basal areas, and greater snag volumes than unused areas, which were regenerated by clearcutting 13–21 years prior to our study. Unused areas apparently lacked vertical structure required by marten. Among areas receiving use, higher use intensity was associated with greater basal area of deciduous trees. Understory vegetation and woody debris was abundant in all use-intensity categories, although areas used most intensively had larger downed logs. We conclude that where horizontal structure is not limiting, forest stands regenerated by clearcutting may provide suitable habitat for resident, nonjuvenile marten when the following thresholds are reached: live-tree basal area ≥18 m 2/ha, mean tree height ≥9 m for trees with dbh ≥7.6 cm, and snag volume ≥10 m 3/ha. Suitability of harvested stands may be enhanced if large woody debris is retained, and mean maximum diameter of downed logs exceeds 22 cm. Methods of harvesting that provide for retention and recruitment of woody debris and vertical structure characteristic of mature forests may be consistent with maintenance of marten populations in managed forests. Our proposed thresholds can be used for developing stand-scale harvesting strategies in forests that support marten, although landscape-scale habitat requirements of marten should also receive management consideration.

Trash or habitat? Fish assemblages on offshore oilfield seafloor debris in the Santa Barbara Channel, California

We assessed the significance of offshore oilfield debris as fish habitat in central and southern California using video taken from a remotely operated vehicle to enumerate the fish assemblages and to measure debris characteristics. Among 33 species (belonging to 9 families) identified in four regions (from Pt. Conception to Los Angeles), rockfish (genus Sebastes) made up approximately 78%. Total fish abundance varied by region, with greater numbers present in the west than in the east. In comparing abundance of fish per debris item among regions, two rockfish species showed no spatial differences, one species was significantly more abundant in the western region and one had the highest abundance in the central region. Water depth, vertical profile, shelter availability, and item volume may be used to predict presence/absence or abundance of different species of rockfish, but none of these characteristics was consistently applicable to all species. 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd.

Alumina–alumina artificial hip joints. Part I: a histological analysis and characterisation of wear debris by laser capture microdissection of tissues retrieved at revision

The aims of this study were to investigate the tissues from uncemented Mittelmeier alumina ceramic-on-ceramic total hip replacements using histological methods and to isolate and characterise the ceramic wear debris using laser capture microdissection and electron microscopy. Tissues from around 10 non-cemented Mittelmeier alumina ceramic on ceramic THRs were obtained from patients undergoing revision surgery. Tissues were also obtained from six patients who were undergoing revisions for aseptic loosening of Charnley, metal-on-polyethylene prostheses. Tissue sections were analysed using light microscopy to determine histological reactions and also the location and content of alumina ceramic wear debris. Tissue samples were extracted from sections using laser capture microdissection and the characteristics of the particles subsequently analysed by TEM and SEM.The tissues from around the ceramic-on-ceramic prostheses all demonstrated the presence of particles, which could be seen as agglomerates inside cells or in distinct channels in the tissues. The tissues from the ceramic-on-ceramic retrievals had a mixed pathology with areas that had no obvious pathology, areas that were relatively rich in macrophages and over half of the tissues had in the region of 60% necrosis/necrobiosis. In comparison, the Charnley tissues showed a granulomatous cellular reaction involving a dense macrophage infiltrate and the presence of giant cells and <30% necrosis/necrobiosis. The tissues from the ceramic prostheses also showed the presence of neutrophils and lymphocytes, which were not evident in the tissues from the Charnley retrievals. There were significantly more macrophages (p<0.05), and giant cells (p<0.01) in the Charnley tissues and significantly more neutrophils (p<0.01) in the ceramic-on-ceramic tissues.TEM of the laser captured tissue revealed the presence of very small alumina wear debris in the size range 5–90nm, mean size±SD of 24±19nm whereas SEM (lower resolution) revealed particles in the 0.05–3.2μm size range. This is the first description of nanometre sized ceramic wear particles in retrieval tissues. The bi-modal size range of alumina ceramic wear debris overlapped with the size ranges commonly observed with metal particles (10–30nm) and particles of ultra-high molecular weight polyethylene (0.1–1000μm). It is possible that the two size ranges of contributed to the mixed tissue pathology observed. It is speculated that the two types of ceramic wear debris are generated by two different wear mechanisms in vivo; under normal articulating conditions, relief polishing wear and very small wear debris is produced, while under conditions of microseparation of the head and cup and rim contact, intergranular and intragranular fracture and larger wear particles are generated.

Alumina–alumina artificial hip joints. Part II: Characterisation of the wear debris from in vitro hip joint simulations

Until recently it was not possible to reproduce clinically relevant wear rates and wear patterns in in vitro hip joint simulators for alumina ceramic-on-ceramic hip prostheses. The introduction of microseparation of the prosthesis components into in vitro wear simulations produced clinically relevant wear rates and wear patterns for the first time. The aim of this study was to characterise the wear particles generated from standard simulator testing and microseparation simulator testing of hot isostatically pressed (HIPed) and non-HIPed alumina ceramic-on-ceramic hip prostheses, and compare these particles to those generated in vivo.Standard simulation conditions produced wear rates of ≈0.1mm3 per million cycles for both material types. No change in surface roughness was detected and very few wear features were observed. In contrast, when microseparation was introduced into the wear simulation, wear rates of between 1.24 (HIPed) and 1.74mm3 per million cycles (non-HIPed) were produced. Surface roughness increased and a wear stripe often observed clinically on retrieved femoral heads was also reproduced. Under standard simulation conditions only nanometre-sized wear particles (2–27.5nm) were observed by TEM, and it was thought likely that these particles resulted from relief polishing of the alumina ceramic. However, when microseparation of the prosthesis components was introduced into the simulation, a bi-modal distribution of particle sizes was observed. The nanometre-sized particles produced by relief polishing were present (1–35nm), however, larger micrometre-sized particles were also observed by both transmission electron microscopy (TEM) (0.02–1μm) and scanning electron microscopy (SEM) (0.05–>10μm). These larger particles were thought to originate from the wear stripe and were produced by trans-granular fracture of the alumina ceramic.In Part I of this study, alumina ceramic wear particles were isolated from the periprosthetic tissues from around Mittelmeier ceramic-on-ceramic hip prostheses. Characterisation of the particles by TEM and SEM revealed a bi-modal size distribution. SEM analysis revealed particles in the 0.05–3.2μm size range, and TEM revealed particles in the 5–90nm size range, indicating that microseparation of the prosthesis components may be a common event in vivo. This study (Part II) has revealed that the introduction of microseparation of the prosthesis components during the swing phase of the wear simulation reproduced clinically relevant wear rates, wear patterns and wear particles in in vitro hip joint simulators.

A Multi-Band Photometric Study of Tidal Debris in a Compact Group of Galaxies: Seyfert’s Sextet

Abstract In order to investigate the properties of the prominent tidal debris feature extending to the northeast of a compact group of galaxies, Seyfert’s Sextet, we analyzed multi-band ($U$, $B$, $V$, $VR$, $R$, $I$, $J$, $H$, and $K^{\prime }$) photometric imaging data and obtained the following results: 1) The radial surface brightness distribution of this tidal debris in Seyfert’s Sextet (TDSS) in each band appears to be well approximated by an exponential profile. 2) The observed $B-V$ color of TDSS is similar to those of dwarf elliptical galaxies in nearby clusters. 3) Comparing the spectral energy distribution (SED) of TDSS with theoretical photometric evolution models and with the SED of the stars in the outer part of HCG 79b, we find that its SED is comparable to that of a $\sim 10 \,\mathrm{Gyr}$-old stellar population with solar metallicity, similar to the stellar population in the outer part of HCG 79b. This suggests that TDSS consists of stars that may have been liberated from HCG 79b by strong galaxy interactions, not a pre-existing dwarf galaxy as previously thought.

Sampling coarse woody debris for multiple attributes in extensive resource inventories

Information on the amount, distribution, and characteristics of coarse woody debris (CWD) in forest ecosystems is in high demand by wildlife biologists, fire specialists, and ecologists. In its important role in wildlife habitat, fuel loading, forest productivity, and carbon sequestration, CWD is an indicator of forest health. Because of this, the USDA Forest Service Pacific Northwest Research Station’s Forest Inventory and Analysis (FIA) program recognized the need to collect data on CWD in their extensive resource inventories. This paper describes a sampling method, measurement protocols, and estimation procedures to collect and compile data on CWD attributes within FIA’s forest inventory. The line-intersect method was used to sample CWD inside the boundaries of the standard inventory field plot. Previously published equations were customized to allow for easy calculation of per-unit-area values, such as biomass and carbon per hectare, log density per hectare, or volume per hectare, for each plot. These estimates are associated with all other information recorded or calculated for an inventory plot. This allows for indepth analysis of CWD data in relation to stand level characteristics. The data on CWD can be used to address current, relevant issues such as criteria no. 5 outlined in the 1994 Montreal process and the 1995 Santiago declaration. This criteria assesses the contribution of forests to the global carbon cycle by measuring such indicators as CWD, live plant biomass, and soil carbon.

Characterizing secondary debris impact ejecta

All spacecraft in low earth orbit are subject to high-speed impacts by meteoroids and orbital debris particles. These impacts can damage flight-critical systems, which can in turn lead to catastrophic failure of the spacecraft. In addition to threatening the operation of the spacecraft itself, on-orbit impacts also generate a significant amount of damaging ricochet ejecta particles. These high-speed particles can destroy critical external spacecraft subsystems, which also poses a threat to the spacecraft and its inhabitants. Since the majority of on-orbit debris impacts are expected to occur at oblique angles, the characterization of ricochet debris created in an orbital debris particle impact is an issue that must be addressed. This paper presents the results of a study performed to develop an empirical model that characterizes the secondary ejecta created by a high speed impact on a typical aerospace structural surface. Specifically, the model predicts the spread and trajectory of ricochet debris particles created in a hypervelocity impact as well as the size an velocity of the most damage particle in the ricochet debris cloud. Results obtained using the model are compared with experimental results and predictions obtained in a previous study.

Impact fragmentation of high-velocity compact projectiles on thin plates: a physical and statistical characterization of fragment debris

The high-velocity impact of a projectile onto a structure results in the creation and energetic expulsion of fragments of the interacting materials. The nature of this fragment debris is of concern in certain applications. Although more broadly applicable, the present study is motivated by a need to characterize the size and velocity distribution of fragments generated by orbital debris impacting external components of spacecraft structure, such as shielding and radiators. In this effort, statistical relations are developed to predict size, momentum and trajectory distributions of the debris. The underlying physics applied are those used in the fields of impact mechanics, thermodynamics of shocks, and statistical fragmentation. Equations from impact mechanics lead to predictions for mass, global momentum, and excess energy of the fragment debris. Relations from shock thermodynamics are developed to partition the initial kinetic energy into thermal and mechanical energies, and therefore to predict mass fractions of solid, liquid and vapor components and the subsequent dispersing motion of this fragment debris. Statistical methods of the energy-based Maxwell-Boltzmann type are pursued to characterize the inherently stochastic fragmentation event, emphasizing the extremes of fragment size and velocity. Computational simulations of impact events and data from impact fragmentation experiments are exploited in validating the underlying theoretical assumptions and the resulting impact fragmentation model.

Characterisation of wear debris from UHMWPE on zirconia ceramic, metal-on-metal and alumina ceramic-on-ceramic hip prostheses generated in a physiological anatomical hip joint simulator

There is currently much interest in the characterisation of wear debris from different types of artificial hip joints. There have been numerous studies on the wear of UHMWPE in hip joint simulators, but relatively few studies on the wear of alternative materials such as metal-on-metal (MOM) and ceramic-on-ceramic (COC). The aim of this study was to compare the wear volumes and wear debris generated from zirconia ceramic-on-UHMWPE, MOM and COC hip joints under identical conditions in the same hip joint simulator.All prostheses showed an initial higher ‘bedding in’ wear rate, which was followed by a lower steady state wear rate. The zirconia ceramic-on UHMWPE prostheses showed the highest wear rates (31±4.0mm3/million cycles), followed by the MOM (1.23±0.5mm/million cycles), with the COC prostheses showing significantly (P<0.01) lower wear rates at 0.05±0.02mm3/million cycles. The mode (±95% confidence limits) of the size distribution of the UHMWPE wear debris was 300±200, 30±2.25nm for the metal particles, and 9±0.5nm for the ceramic wear particles. The UHMWPE particles were significantly larger (P<0.05) than the metal and ceramic wear particles, and the metal particles were significantly larger (P<0.05) than the ceramic wear particles. A variety of morphologies and sizes were observed for the UHMWPE wear particles, including submicrometer granules and large flakes in excess of 50μm. However, the wear particles generated in both the MOM and COC articulations were very uniform in size and oval or round in shape.This investigation has demonstrated substantial differences in volumetric wear. The in vitro wear rates for the zirconia-on-UHMWPE and MOM are comparable with clinical studies and the UHMWPE and metal wear particles were similar to the wear debris isolated from retrieved tissues. However, the alumina/alumina wear rate was lower than some clinical retrieval studies, and the severe wear patterns and micrometer-sized particles described in vivo were not reproduced here.This study revealed significant differences in the wear volumes and particle sizes from the three different prostheses. In addition, this study has shown that the alternative bearing materials such as MOM and COC may offer a considerable advantage over the more traditional articulations which utilise UHMWPE as a bearing material, both in terms of wear volume and osteolytic potential.

Sliding speed-temperature wear transition maps for Si3N4/iron alloy couples

The superior high temperature resistance of silicon nitride (Si3N4) based ceramics makes them suitable for tribological applications above room temperature or in high speed unlubricated sliding. There are some published works on the wear behaviour of Si3N4/metal alloys. However, experimental data are shown in a form that is not of direct use for engineers involved in materials selection. In the present work, Si3N4 pins were tested against tool steel and grey cast iron on a pin-on-disc tribometer. Ceramics were produced by hot-pressing and tested without lubrication at variable temperature and sliding speed. SEM/EDS and XRD analysis were used for chemical and microstructural characterisation of worn surfaces and wear debris. At low speeds (0.05–0.5ms−1) and room temperature, Si3N4 surfaces are polished-like due to a combination of humidity-assisted tribo-oxidation and abrasive action of very fine wear debris. At high sliding speeds (2–3.5ms−1), as well as for temperatures in the range 400–600°C, an extensive coherent tribolayer mainly composed by iron oxides spreads over the ceramic surfaces. Polishing and protection by adherent tribolayers are the mechanisms responsible for observed severe and mild wear regimes, respectively. Wear maps are constructed showing the transition of wear regimes in Si3N4/iron alloys contacts determined by constant flash temperature curves. Equations for calculation of bulk and flash contact temperatures in tribocontacts between dissimilar materials are deduced.

The characteristics of woody debris and sediment distribution in headwater streams, southeastern Alaska

Large woody debris (LWD), fine woody debris (FWD), fine organic debris (FOD), and sediment deposition were measured in 15 steep headwater streams with five management and disturbance regimes. Clear-cut channels logged in 1995 contained large accumulations of logging residue that initially provided sites for sediment storage. Half of the LWD in clear-cut channels was recruited during and immediately after logging. Woody debris from logging activities remains in young growth conifer channels 37 years after logging. Numbers of LWD in clear-cut and young conifer channels were significantly higher than in old-growth channels, although numbers of FWD pieces were not significantly different because of higher recruitment from old-growth stands. Channels that experienced recent (1979 and (or) 1993) and earlier (1961 and (or) 1979) scour and runout of landslides and debris flows contained less LWD and FWD, although large volumes of LWD and FWD were found in deposition zones. The volumes of sediment stored in young alder and recent landslide channels were higher than in the other channels. Because of the recruitment of LWD and FWD from young alder stands, the ratio of sediment stored behind woody debris to total sediment volume was higher in young alder channels compared with recent landslide channels. Numbers of LWD and FWD pieces in all streams were significantly correlated with the volumes of sediment stored behind woody debris. Timber harvesting and soil mass movement influence the recruitment, distribution, and accumulation of woody debris in headwater streams; this modifies sediment storage and transport in headwater channels.

Isolation and morphological characterisation of UHMWPE wear debris generated in vitro

Wear tests are generally carried out on materials used in prosthetic hip implants, in order to obtain a better understanding of the tribological processes involved and improve the quality control of joint prostheses, directed towards reducing the risk of implant failure of innovative prostheses. Ceramic femoral heads of mixed alumina–zirconia oxides as well as zirconia and alumina single oxide heads were tested against UHMWPE acetabular cups in a hip joint simulator. Polyethylene cups and ceramic femoral heads were mounted in a simulator apparatus moving according to a sinusoidal function, under load and in the presence of bovine calf serum as lubricant. Wear particles were isolated from the bovine calf serum collected during the wear tests. An easy to follow method was used to separate the wear particles from the lubricant. Chemical digestive methods were used to separate the wear particles from the lubricant and the isolated particles were studied using scanning electron microscopy. The morphologies of the polyethylene debris showed considerable differences, both in size and shape of the particles, as a function of the coupled head material.

Characterization of coarse woody debris across a 100 year chronosequence of upland oak–hickory forests

In most forest ecosystems, the total amount of coarse woody debris and its distribution into decay classes change over time from harvest to old growth stages. The relationship of decomposition classes to substrate quality is important to determine the contribution of woody debris to ecosystem nutrient cycling and forest development. The two objectives of this study were: (1) to determine if down dead wood (DDW) nutrient content varied with decomposition class or forest stand age; (2) to determine if DDW decomposition classes were related to indicators of substrate quality. Volume, mass, and indicators of substrate quality, such as N content and lignin:N ratio, were determined for woody debris from several decomposition classes in upland hardwood forest stands of different ages in southern Indiana, USA. Results showed a large decrease in volume and mass of DDW from recently harvested to mature stands. The dominant decomposition class shifted from Class II to Classes III and IV with increasing stand age. No Class I woody debris was found within any of the study plots. Nutrient concentration (N, S, and P) and carbohydrate fractions (soluble, hemicellulose, cellulose, and lignin) all varied significantly among certain decomposition classes, but N and P concentration and the C:N ratio were the best indicators of decomposition class. Patterns of P retention in decomposition classes suggested a strong potential for immobilization of this nutrient in woody debris. Based on substrate quality groupings, there were three distinguishable decomposition classes: Classes II and III, Class IV, and Class V.

Characterization of Dust and Debris Collected from the Nova Facility

Dust and debris were collected from the Nova laser facility in April 1999 to provide evidence of particulate generation and transport mechanisms relevant to fusion power safety analyses. Samples were obtained at specified locations within the Nova chamber with a vacuum filter system, cascade impactors, and metallurgical replicating tape (acetate tape). Average surface mass density of material collected from locations with measured surface area ranges from 3.13 μg/cm2 on the mid-plane vertical surface to 3250 μg/cm2 on the vessel bottom. Estimated total dust inventory is 44 grams. Specific surface area of dust collected from several locations is nearly uniform with an average value of 0.435 m2/g. Particle size distributions of the collected material show a range of count median diameters (CMD) between 0.67 and 1.19 μm with geometric standard deviations (GSD) between 1.63 and 2.76. Mass median diameters for dust collected with the two cascade impactors are 5.26 μm and 8.85 μm. The shape of the volumetric size distribution indicates dust particles of various shapes. Composition analysis performed by energy dispersive X-ray analysis indicated the presence of O, Al, Cu, along with trace quantities of Fe, Au, and Be. Atomic emission ICP analysis also indicated the presence of Si, O, and Cu in dust samples.

The characteristics of woody debris and sediment distribution in headwater streams, southeastern Alaska

The characteristics of woody debris and sediment distribution in headwater streams, southeastern Alaska

Quantitative characterization of polyethylene debris isolated from periprosthetic tissue in early failure knee implants and early and late failure Charnley hip implants.

This study isolated and characterized UHMWPE particles from 3 explant groups: early Charnley hip failures (ECE; < 10 years), late Charnley hip failures (LCE; > 10 years) and early knee failures (EKE; < 10 years). Debris isolated from the 3 groups had percentage particle number and percentage volumetric concentration distributions that were not significantly different. The greatest number of particles were found in the 0.1-0.5 microm size range and 19-20.6% of the volumetric concentration was below 1 microm in size in all groups. However, there were significant differences in the total volumetric concentration of debris isolated per g of tissue. LCE had significantly higher volumes of debris than ECE and EKE, there was no significant difference in the volume of debris from the EKE and ECE. The mean aspect ratio and mean irregularity ratio of the LCE group were also significantly higher than the ECE and EKE, suggesting that different wear mechanisms were occurring in the late Charnley group compared to the early Charnley and knee groups. These results also suggest that early knees, with normal surface wear, may have similar wear mechanisms to early Charnley hips and indicate that similar volumes of biologically active micrometer and sub-micrometer UHMWPE particles were produced. This may have important implications in the longer-term outcome of total knee arthroplasties, because it indicates a similar potential for osteolysis induced by wear debris.

Structural Characterization of Wear Debris Produced During Friction Between Two Austenitic Stainless Steel Antagonists

Ball-on-flat friction experiments between two austenitic stainless steel antagonists in sliding contact are carried out under very low loads and in two liquid environments, namely demineralized water and methanol. The wear debris produced during long-duration tests are characterized by different techniques such as X-ray diffraction, transmission electron microscopy and Mossbauer spectroscopy. Martensite is observed as a dominant phase in the wear debris but other phases have been also identified. In the debris produced under demineralized water, there is significant contribution of a second phase, which is poorly crystallized and which was identified as the hydrous iron oxide called ferrihydrite. In the debris produced under methanol, there is a remaining amount of austenite that is not transformed into martensite, and the presence of ferrihydrite has been also detected in very small quantities. The formation of the martensitic debris which occurs from the beginning of the wear tests supports the fact that under our experimental conditions the main damaging mode is abrasive wear by hard particles.