Alumina Bearings Research Articles

Flaking of PEEK under one-point rolling contact fatigue using Al2O3 ball

The growth of flaking as tribological fatigue failure in PEEK was investigated through the one-point type rolling contact fatigue test between a machined PEEK polymer shaft and an alumina bearing's ball. Due to Hertzian contact of cyclic compressive stress, the subsurface fatigue cracks in the PEEK shaft propagated in rolling and axial directions. When the rolling fatigue life of the PEEK shaft reached 106 fatigue cycles, many narrow angled cracks occurred in the near-surface of the rolling track without flaking. On the other hand, when the flaking ocuurred on the PEEK shaft before 106 fatigue cycles, semicircular surface and subsurface crack propagations were observed. From these observations, it was found that micro-flaking occurred due to the linkages between subsurface and surface cracks. Flakingdeveloped due to the accumulation of these micro-flakings.

Sodium fluoride assisted acid leaching of coal fly ash for the extraction of alumina

Coal fly ash, generated in thermal power plants was processed through sulphuric acid leaching for the extraction of alumina. Both fly ash and alkali treated fly ash residue, obtained after partial removal of silica, were leached in sulphuric acid medium. Solubilisation of alumina in the acidic medium was found to be more efficient while processing the alkali treated fly ash residue as compared to the fly ash. The effect of addition of sodium fluoride (NaF) on leaching of alumina was examined at varied acid concentrations, temperatures, and time of leaching. A marked improvement in leaching recovery for alumina was observed due to the addition of NaF in the acidic leaching medium. XRD pattern of the leach residue confirmed that the alumina bearing phase i.e. mullite got dissociated in the presence of fluoride ions releasing alumina to the leaching medium for which a significant improvement in leaching efficiency was observed. A process flowsheet has been developed for the extraction of alumina from fly ash and production of a by-product, calcium silicate, for the regeneration of NaOH to make the process industrially viable.

Observation of Fatigue Fracture on PEEK Shaft against Alumina Bearing’s Ball under One-Point Rolling Contact

Tribological fatigue failure of the machined PEEK shaft was investigated through the one-point type rolling contact fatigue test between a PEEK shaft and an alumina ball, in order to explore fatigue fracture mechanism of frictional parts working at high frequency in various mechanical elements. Due to Hertzian contact of cyclic compressive stress, the subsurface crack occurred within approximately 300 μm depth from thesurface and propagated along the rolling direction. After that, the subsurface crack propagation direction changed toward the surface. The flaking occurred on the raceway of the PEEK shaft when the subsurface crack reached to the PEEK shaft surface.

Effects of in vitro shocks and hydrothermal degradation on wear of ceramic hip joints: Towards better experimental simulation of in vivo ageing

In an ageing world population, increasing the lifetime of orthopedic devices is of vital importance for reducing surgical risks for patients and reducing medical costs. Ceramic materials are gaining interest because of their hardness and chemical inertia with respect to metal prosthesis. Wear of the prosthetic couple (femoral head and cup) is one of the main rationales for using ceramic hip implants, because they induce much lower wear debris. The present study investigates the combined effects of shocks due to microseparation and hydrothermal ageing on the wear of Zirconia Toughened Alumina (ZTA) bearings, which have been under strong development these past ten years. Wear stripe patterns are formed on femoral heads tested on a shock device. 3D profilometry is used to evaluate the volume of worn material released from the head that averages at 0.46mm3/year during simulation mimicking about 15 years of ageing. This volume is larger than formerly estimated with hip walking simulators with microseparation, an effect that we tentatively attribute to a larger force (9000N) applied here than on hip simulators where the force was not specified. The present experiment should allow refining the effect of force on the wear of ceramic femoral head, hence to simulate different patient conditions (weight, activity, accidents,…). Micro Raman spectroscopy reveals significant zirconia phase transformation within wear stripes. ZTA components show minor phase transformation during hydrothermal degradation in an autoclave when compared to changes induced by shocks. Finally, five clinically retrieved bearings are characterized for in vivo comparison, and also reveal phase transformation within wear track areas. The association of phase transformation enhancement with wear areas on in vivo samples indicates that wear is induced by shocks, rather than by hydrothermal ageing. Shock simulations are therefore essential for in vitro experimentation aiming at reproducing wear of ceramic implants and in vivo environment. On a material׳s point of view, it is shown that the ZTA ceramics can exhibit a beneficial phase transformation under stress, which may limit wear stripes, without suffering from significant ageing.

Aluminium recovery from NALCO fly ash by acid digestion in the presence of fluoride ion

The safe disposal and utilisation of coal fly ash (CFA) for value addition are still major problems worldwide. Al2O3 is a major valued material associated with it. Till date no methods are available to treat CFA for recovering its valued materials. Leaching of alumina from CFA in an economical way is very difficult, which either requires higher chemical consumption or application of stringent reaction conditions such as high temperature and pressure. In this paper a simple alternative method has been attempted to dissolve alumina from CFA. Addition of fluoride ion as HF improved the acid leaching performance of fly ash to a large extent. XRD data showed mullite, the alumina bearing phase, as the major phase which gets dissolved during leaching operation. A standard procedure for the precipitation of alumina can be employed after the leached solution is obtained.

Pristine and coated LiNi1/3Mn1/3Co1/3O2 as positive electrode materials for li-ion batteries

Layered LiNi1/3Mn1/3Co1/3O2 (NMC) positive materials were synthesized by efficient, low cost and easy manageable methods such as oxalate co-precipitation and sol-gel processes. Preliminary electrochemical results show that sol-gel sample provide better results than co-precipitated samples. With the aim to improve the properties of the co-precipitated samples these were coated with carbon and alumina bearing in mind the co-precipitated method is suitable for large scale production. The subsequently performed local structure investigations revealed well crystallized layered cathode materials with α-NaFeO2-type structure (R-3m space group). Sample tests using both the scanning electron microscope (SEM) and the transmission electron microscope (TEM) showed submicron particles with a slight tendency to agglomerate and furthermore the existence of a thin film that encapsulates the oxide particles. 7Li magic angle spinning nuclear magnetic resonance (7LiMAS NMR) measurements were carried out for pristine and coated samples to compare the cation arrangement in the transition metal layers. Finally, electrochemical tests revealed a remarkable improvement in capacity retention of the coated oxides compared to the parent compounds.

The reliability of modern alumina bearings in total hip arthroplasty—Update to a 2006 report

Ceramic components׳ clinical fractures in total hip arthroplasty (THA) are a rare but, nonetheless, serious complication. As a result of continued improvements in ceramic material quality, manufacturing methods, and implant design made over the last 30 years, the incidence of such failures has been drastically reduced. In this report, the frequency of these ceramic components׳ clinical failures in THA will be examined. In addition, some information regarding the contribution that can be made by the surgeon to enhance the reliability of ceramic components will also be presented. In order to get a broad view, the largest supplier of these components, CeramTec Medical Products (Plochingen, Germany), was contacted, and they agreed to share their most recent data. In the year 2000, the largest supplier of alumina–ceramic bearings for orthopedic applications (CeramTec GmbH, Plochingen, Germany) began a rigorous program of collecting clinical fracture data for all of its ceramic components. The clinical fracture data for the period of January 2000–June 2013 are reported here, with a review of the material properties, historical component fracture trends, and relative risk of fracture associated with alumina THA bearings. The data reported is divided into two separate groups. The first one is the incidence of clinical fracture of the Biolox®forte material. This is their original material developed in the 1970s and is still available today and optimized over the years. The overall clinical fracture rate of these alumina components was 0.021%, or 21 in 100,000, during the January 2000–June 2013 time period. The second group is composed of components manufactured from their Alumina Matrix Composite, Biolox®delta. The overall clinical fracture rate for these components is 0.0001% or 1 in 100,000. Almost 80% of these alumina bearing failures occurred within 36 months following surgery. Using the latest material and increasing femoral head diameter were associated with a substantially reduced risk of fracture. Alumina bearings used in modern THA implants are safe and reliable, with a very low risk of failure. Improvements in the materials, developments in the manufacturing, the introduction of the Alumina Matrix Composite, and the trend to utilize larger-diameter ball heads are likely to continue to reduce the concerns that have been in the mind of surgeons using ceramics in THA.

The use of ceramic-on-ceramic bearings in isolated revision of the acetabular component

The practice of removing a well-fixed cementless femoral component is associated with high morbidity. Ceramic bearing couples are low wearing and their use minimises the risk of subsequent further revision due to the production of wear debris. A total of 165 revision hip replacements were performed, in which a polyethylene-lined acetabular component was revised to a new acetabular component with a ceramic liner, while retaining the well-fixed femoral component. A titanium sleeve was placed over the used femoral trunnion, to which a ceramic head was added. There were 100 alumina and 65 Delta bearing couples inserted. The mean Harris hip score improved significantly from 71.3 (9.0 to 100.0) pre-operatively to 91.0 (41.0 to 100.0) at a mean follow up of 4.8 years (2.1 to 12.5) (p < 0.001). No patients reported squeaking of the hip. There were two fractures of the ceramic head, both in alumina bearings. No liners were seen to fracture. No fractures were observed in components made of Delta ceramic. At 8.3 years post-operatively the survival with any cause of failure as the endpoint was 96.6% (95% confidence interval (CI) 85.7 to 99.3) for the acetabular component and 94.0% (95% CI 82.1 to 98.4) for the femoral component. The technique of revising the acetabular component in the presence of a well-fixed femoral component with a ceramic head placed on a titanium sleeve over the used trunnion is a useful adjunct in revision hip practice. The use of Delta ceramic is recommended.

Do Obesity and/or Stripe Wear Increase Ceramic Liner Fracture Risk? An XFEM Analysis

Hypothesized risk factors for fracture of ceramic liners include impingement, edge-loading, and cup malpositioning. These risk factors are similar to those for generation of stripe wear. However, it is unclear whether the biomechanical conditions contributing to stripe wear generation also increase the risk for ceramic liner fracture We asked whether (1) head stripe wear propensity; and (2) cup orientation would correlate with alumina liner fracture risk for instances of normal and elevated body weight. An eXtended Finite Element Method (XFEM) model was developed to investigate these mechanisms. Liner fracture risk for 36-mm alumina bearings was studied by simulating two fracture-prone motions: stooping and squatting. Twenty-five distinct cup orientations were considered with variants of both acetabular inclination and anteversion. Four separate body mass indices were considered: normal (25kg/m(2)) and three levels of obesity (33, 42, and 50kg/m(2)). Material properties were modified to simulate alumina with and without the presence of dispersed microflaws. The model was validated by corroboration with two previously published ceramic liner fracture studies. Of 200 XFEM simulations with flaw-free alumina, fracture occurred in eight instances, all of them involving obesity. Each of these occurred with cups in≤37° inclination and in 0° anteversion. For 200 corresponding simulations with microflawed alumina, fracture propensity was greatest for cups with higher (edge loading-associated) scraping wear. Fracture risk was greatest for cups with lower inclination (average 42° for fractured cases versus 48° for nonfractured cases) and lower anteversion (9° versus 20°). Fracture propensity for 36-mm liners was elevated for cups with decreased anteversion and/or inclination and under conditions of patient obesity. Factors causing stripe wear, including obesity and cup malpositioning, also involve increased risk of ceramic liner fracture and merit heightened concern.

Minimum 5-Year Results of Titanium Tapered Stem with Alumina Bearing in Cementless Total Hip Arthroplasty Using a Modified Direct Lateral Approach

Minimum 5-Year Results of Titanium Tapered Stem with Alumina Bearing in Cementless Total Hip Arthroplasty Using a Modified Direct Lateral Approach

Alumina-on-alumina hip implants

Alumina-alumina bearings are among the most resistant to wear in total hip replacement. Examination of their surfaces is one way of comparing damage caused by wear of hip joints simulated in vitro to that seen in explanted bearings. The aim of this study was to determine whether second-generation ceramic bearings exhibited a better pattern of wear than those reported in the literature for first-generation bearings. We considered both macro- and microscopic findings. We found that long-term alumina wear in association with a loose acetabular component could be categorised into three groups. Of 20 specimens, four had 'low wear', eight 'crescent wear' and eight 'severe wear', which was characterised by a change in the physical shape of the bearing and a loss of volume. This suggests that the wear in alumina-alumina bearings in association with a loose acetabular component may be variable in pattern, and may explain, in part, why the wear of a ceramic head in vivo may be greater than that seen after in vitro testing.

Alumina Ceramic Bearings in Total Hip Arthroplasty: The Rationale for Patient Selection

The use of alumina ceramic bearings in total hip replacement is not new; extensive clinical outcomes have been reported since at least the past 3 decades. During that time, material advances have changed the basic composition and properties of alumina, such that femoral heads and acetabular inserts made of this material today are vastly superior in reliability, consistency, and durability than counterparts made previously. The question addressed by this article pertains to patient selection for alumina bearings during total hip surgery. To answer this question, the paper is organized to (1) present an overview of the material improvements in modern alumina bearings, (2) review the most recent clinical data related to ceramic bearing performance in total hip replacement, and (3) present practical guidelines based on literature evidence for patient selection for alumina bearings. It is hoped that this information will be of value to the hip arthroplasty surgeon.

Ceramic Bearings for Total Hip Arthroplasty Have High Survivorship at 10 Years

Ceramic bearings were introduced to reduce wear and increase long-term survivorship of total hip arthroplasty. In a previous study comparing ceramic with metal-on-polyethylene at 5 to 8 years, we found higher survivorship and no osteolysis for the ceramic bearings. We asked whether ceramic bearings have equal or superior survivorship compared with that for metal-on-polyethylene at longer followup; we also determined survivorship of the implant systems, the presence or absence of radiographic osteolysis, and incidence of device squeaking. Five surgeons at five sites have followed 189 patients (216 hips) for a minimum of 10 years and average of 10.3 years (range, 10-12.4 years) comparing alumina ceramic bearings (144 hips) with cobalt chrome-on-polyethylene bearings (72 hips). We determined Kaplan-Meier survivorship of the bearing surface and implant systems and collected radiographic and clinical data. We observed no difference between the control metal-on-polyethylene and the alumina-bearing couple cohorts with regard to bearing-related failures (98.9% versus 99.1%). Revisions for any reason occurred in 10.5% of the control patients and 3.1% of the patients with alumina bearings. All femoral implants remain well fixed (100%), whereas one acetabular component (1%) is unstable in the control group. Osteolysis occurred in 26% of the control patients and in none of the patients with alumina bearings. Squeaking occurred in two of 144 hips (1.4%) of the patients with ceramic bearings. Patients receiving the ceramic-on-ceramic bearings had fewer revisions for any reason and less osteolysis than the control metal-on-polyethylene at 10 years. Our data suggest ceramic bearings continue to provide an option for the young and more active patient and provide for a measure to compare other new alternative bearings that are currently available. Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Straight Tapered Titanium Stem With Alumina Bearing in Cementless Primary Total Hip Arthroplasty: A Minimum 5-Year Follow-Up

The aim of this study was to assess the midterm results of primary cementless total hip arthroplasty using a tapered stem and alumina bearing couple in active patients. After a minimum of 5 years of follow-up, 78 arthroplasties in 72 patients were reviewed retrospectively. The mean Harris hip score was 94 points, and 2 hips had thigh pain. All components radiographically demonstrated stable fixation by bone ingrowth and mild stress shielding of the proximal femur were noted in 14% of hips. There was no significant osteolysis or aseptic loosening. There was a ceramic head fracture in 1 hip and audible sounds in 2 hips. The results of total hip arthroplasty with a straight, tapered, proximally porous-coated stem and alumina-on-alumina bearing were encouraging for active patients.

Metal neck and liner impingement in ceramic bearing total hip arthroplasty

Although impingement between the neck of the metallic stem and the ceramic liner has been suspected to be the cause of ceramic liner failure in ceramic-on-ceramic total hip arthroplasty (THA), no report has directly demonstrated microscopic damage on ceramic liner. We performed 18 reoperations on 18 patients who had undergone third generation ceramic-on-ceramic THA. Considering impingement, 16 patients, who were reoperated more than 1 year after previous ceramic bearing THA, were evaluated. Retrieved alumina liners, showing evidence of impingement, were examined by means of visual inspection and scanning electron microscopy (SEM). Four of the 16 hips showed neck notching and black stained liners, evidence of metallic neck to ceramic impingement. Impinged alumina bearings had been implanted for an average of 62.5 months (range: 35-99 months) before reoperation. SEM of the black stained area demonstrated disruptive wear and loss of surface integrity. Furthermore, one liner had multiple microcracks, and its cross-sectional SEM analysis revealed one microcrack propagating into the deep portion of the ceramic liner. Our observations suggest that metal neck-to-ceramic impingement in ceramic-on-ceramic THA can cause microcrack formation in ceramic liner.

S-37 In-Vivo like Testing of Ceramic Ball Heads

Alumina (Al2O3) bearings in total hip arthroplasty lead to low wear rates, but catastrophic failure of Al2O3 femoral heads, while rare, remains a concern. In the present work, a composite of Al2O3 and niobium (Nb) was tested in vitro for potential use as an alternative femoral head material in vivo. Dense composite laminates of Al2O3 and Nb were fabricated by hot pressing, and their microstructure and mechanical properties were evaluated. The flexural strength of Al2O3–Nb laminates in four-point loading was 720 ± 40 MPa, compared with a value of 460 ± 110 MPa for Al2O3. Scanning electron microscopy and X-ray diffraction showed a well-bonded interface between the Al2O3 and Nb without measurable formation of an interfacial reaction phase. The interfacial shear strength between Al2O3 and Nb, measured by a double-notched specimen test, was 290 ± 15 MPa. The feasibility of fabricating prototype femoral heads (32 mm in diameter), consisting of an Al2O3 surface layer (2–3 mm thick) and a Nb core, by hot pressing was shown. The composite femoral head combined the low wear of an Al2O3 articulating surface with the safety of a ductile metal femoral head.

Incidence and Factors Associated with Squeaking in Alumina-on-Alumina THA

The alumina-on-alumina bearing surface, which has a high wear resistance and a good biocompatibility, is widely used in THA but recently has been associated with squeaking. While various authors have reported factors associated with squeaking, they remain poorly understood. To contribute to the debate on squeaking we therefore asked the following questions: (1) What is the incidence of squeaking in alumina-on-alumina THA? (2) What factors are associated with squeaking in alumina bearings in our practice? We retrospectively reviewed 168 patients (173 hips) who had primary alumina-on-alumina THAs. The mean age of the patients was 53 years (range, 18 to 81 years). Minimum followup was 5.6 years (average, 7.3 years; range, 5.6-9.4 years). All patients were evaluated clinically and radiographically with attention to periprosthetic osteolysis, squeaking, and ceramic fracture. When the patient reported squeaking, we determined the onset, reproducibility, and activities associated with the squeaking. We recorded patient (gender, age, height, weight, and body mass index) and surgical factors (abduction angle of cup, size and length of ceramic head component, and diameter of cup in the implant). Eight of the 168 patients (5%) had squeaking hips. Squeaking was more common in males and in those with large ceramic heads. There were no complications or revisions in the squeaking group. One ceramic liner fracture was associated with trochanteric nonunion. When recommending alumina-on-alumina bearing surfaces to patients they should be clearly informed of the possibility of squeaking. Patients with risk factors for squeaking should be followed at regular intervals.

In vitro testing of Al 2O 3–Nb composite for femoral head applications in total hip arthroplasty

Alumina (Al 2O 3) bearings in total hip arthroplasty lead to low wear rates, but catastrophic failure of Al 2O 3 femoral heads, while rare, remains a concern. In the present work, a composite of Al 2O 3 and niobium (Nb) was tested in vitro for potential use as an alternative femoral head material in vivo. Dense composite laminates of Al 2O 3 and Nb were fabricated by hot pressing, and their microstructure and mechanical properties were evaluated. The flexural strength of Al 2O 3–Nb laminates in four-point loading was 720 ± 40 MPa, compared with a value of 460 ± 110 MPa for Al 2O 3. Scanning electron microscopy and X-ray diffraction showed a well-bonded interface between the Al 2O 3 and Nb without measurable formation of an interfacial reaction phase. The interfacial shear strength between Al 2O 3 and Nb, measured by a double-notched specimen test, was 290 ± 15 MPa. The feasibility of fabricating prototype femoral heads (32 mm in diameter), consisting of an Al 2O 3 surface layer (2–3 mm thick) and a Nb core, by hot pressing was shown. The composite femoral head combined the low wear of an Al 2O 3 articulating surface with the safety of a ductile metal femoral head.

Hip-simulator wear studies of an alumina-matrix composite (AMC) ceramic compared to retrieval studies of AMC balls with 1–7 years follow-up

Wear in large diameter ceramic-on-ceramic bearings were compared in both simulator and patient-retrieval studies. Four combinations of 36 mm diameter alumina matrix composite bearings (AMC: alumina–zirconia) were run in a hip simulator using alumina (ALX) bearings as the historical control. The hip simulator was run in microseparation test mode to 5-million cycles (5Mc) duration. Run-in and steady-state wear, mapping of wear-stripes, monoclinic transformations, surface roughness and wear debris morphology were analyzed sequentially. The balls and cups were inspected at every event and surface changes recorded. For AMC bearings, the zirconia transformation was studied by confocal Raman microprobe spectroscopy (RMS). Bearing surfaces were analyzed by SEM imaging and surface roughness was measured by white-light interferometry. The same techniques were used on the retrieved AMC balls with the exception that zirconia phase transformation was measured by X-ray diffraction (XRD). All balls and cups revealed stripe wear within 0.1Mc duration. Stripes expanded over 5Mc duration to span a 45–90° arc on the balls and covered an area of 150–350 mm 2. The narrow wear scar on cup rims expanded circumferentially and radially with duration. The AMC/AMC performance represented a 5–12-fold wear reduction compared to controls; hybrid ALX/AMC combinations showed a 3-fold reduction. Tetragonal to monoclinic transformation was detected in all AMC bearings and peaked at less than 30% by end of study. In non-wear zones, monoclinic content averaged less than 20%. SEM and roughness mapping at 5Mc showed that AMC surfaces had superior resistance to stripe wear. The stripe wear and monoclinic transformations in the two retrieved AMC balls with alumina liners (3–7 years use) appeared similar to the laboratory study. Thus the monoclinic transformation was anticipated by the laboratory performance. It is therefore hypothesized that once the concentration of monoclinic reaches a certain level, further zirconia transformation is suppressed until the compressive alumina constraint can be overcome by additional wear. This appears to be a very different process compared to that seen with the yittria-stabilized zirconia balls used from year 1985.

3D surface reconstruction and FIB microscopy of worn alumina hip prostheses

Interest in alumina-on-alumina total hip replacements (THR) continues to grow for the young and active patient due to their superior wear performance and biocompatibility compared to the alternative traditional polymer/metal prostheses. While alumina on alumina bearings offer an excellent solution, a region of high wear, known as stripe wear, is commonly observed on retrieved alumina hip components that poses concern. These in-vivo stripe wear mechanisms can be replicated in vitro by the introduction of micro-separation during the simulated walking cycle in hip joint simulation. However, the understanding of the mechanisms behind the stripe wear processes is relatively poor. 3D topographic reconstructions of titled SEM stereo pairs from different zones have been obtained to determine the local worn surface topography. Focused ion beam (FIB) microscopy was applied to examine the subsurface damage across the stripe wear. The paper presents novel images of sub-surface microcracks in alumina along with 3D reconstructions of the worn ceramic surfaces and a classification of four distinct wear zones following microseparation in hip prostheses.