Dissertations / Theses on the topic 'Metal Wear Debris Detection'

Total disc replacements, are valuable interventions for the spinal surgeon for the treatment of back pain associated with degeneration of the intervertebral disc. The longevity of these devices is compromised by wear and there are growing concerns within the neurosurgical community regarding the exposure of periprosthetic tissues to metal particles and/or ions. Considering the potential for metallic wear debris and ions to trigger inflammation, genotoxicity, cytotoxicity, hypersensitivity and pseudotumour formation, coupled with evidence that nanoscale metal particles can compromise the barrier function of the outer meningeal layer, it is imperative to determine the effects of metallic wear particles on cells of the spinal cord. It was hypothesised that, utilising a 3D type-I collagen gel, enabling glial cells to behave in a more physiologically relevant manner than when cultured in monolayer, the effects of increasing concentrations of metallic wear particles on glial cell viability, cellular reactivity, and cytokine release could be more accurately determined. Clinically relevant cobalt chrome and stainless steel wear particles were generated using a six-station pin-on-plate wear simulator. Initially in 2D culture C6 glial, PC12 neuronal cells and primary astrocytes with microglia were cultured with increasing concentrations of metallic particles (0.05μm3-50μm3 debris per cell) and their effect on cell viability and DNA integrity assessed. Using a more physiologically relevant 3D culture environment the effects of increasing metallic particles (0.5μm3-50μm3 debris per cell) on cell viability, cellular activity and cytokine expression were investigated using live/dead staining, immunocytochemistry and an enzyme linked immunosorbent assay, respectively. This study highlighted the necessity for appropriate cell culture environments in biomaterial biocompatibility testing. In 2D culture all cobalt chrome particle doses triggered significant reductions in primary astrocyte and microglia viability, however, in 3D culture, cobalt chrome particles (30-39nm in length) only adversely affected the viability of primary astrocytes and microglia in co-culture when cultured with the highest cobalt chrome particle dose (50μm3 debris per cell) after two and five days in culture (41.8% and 54.2% viable cells, respectively) and with 5μm3 debris per cell after five days in culture (70.5% viable cells). In 2D culture, after 24 hours in culture 0.5μm3, 5μm3 and 50μm3 stainless steel particles per cell caused significant reductions in cell viability (38.8%, 38.9% and 24.9% reductions respectively) however, no adverse effect on viability was observed in 3D culture. Ions released from cobalt chrome caused significant reductions in astrocyte viability (in isolation) at all doses after two days in culture, this effect was not as pronounced after five days. Ions from cobalt chrome particles only caused adverse effects on the viability of astrocytes and microglia after five days at the 5μm3 per cell ion concentration in 3D culture. Ions released from stainless steel caused significant reductions in astrocyte viability (in isolation) at all doses after five days in culture. Stainless steel ions caused adverse effects on the viability of astrocytes and microglia after five days with the 50μm3 per cell ion concentration. DNA damage was observed with both astrocytes and microglia and astrocytes in isolation with both biomaterials tested. Intriguingly, when glial cells were cultured with stainless steel wear particles, the DNA damage observed did not correlate with cell death. Increasing particle volumes of cobalt chrome did not trigger the release of TNF-a, however 50μm3 stainless steel debris per cell caused the release of significantly elevated levels of TNF-a after 48 hours in culture (29.9 pg.ml-1). Stainless steel wear particles did not stimulate astrocyte reactivity unlike cobalt chrome wear products, which had a dose dependent affect on astrocyte activation. The effect was more pronounced in the presence of microglia. Thus the use of 3D culture, whereby glial cells behaved in a more physiologically relevant manner, with a low baseline of reactivity and more representative of the in vivo cellular spatial arrangement was a more appropriate cell culture environment for determining the biological response of cells of the central nervous system to metal wear particles. The results from this study would suggest that stainless steel is more biocompatible than cobalt chrome.

Total hip replacement is an effective treatment for arthritis of the hip. Its use has expanded to include younger patients with higher functional demands resulting in poor implant survival when conventional arthroplasty designs are employed. This has resulted in the development of alternative bearing materials and designs including resurfacing arthroplasties. The effects of particulate and ionic debris generated by these bearings have recently come to light. Metal alloys including cobalt chromium are often employed as bearings in young patients and are associated with genotoxic and teratogenic effects. The potential for this debris to cause damage to the foetus of a mother with a metal implant is a cause for concern. This risk is difficult to assess using epidemiological methods. The aim of this study was to investigate factors associated with an increase in metal levels in the blood and urine of patients undergoing resurfacing arthroplasty. We aimed to investigate the potential for debris generated by metal hip replacements to cause chromosomal aberrations in the foetus. To do this, we employed an in vitro cellular barrier to investigate the transport of material across the human placenta, and human fibroblasts and embryonic stem cells to record the effect. Nanoparticles of cobalt chrome but not ceramic or ionic cobalt and chromium, induced chromosomal aberrations, the majority of which were tetraploidy. When indirectly exposed to human embryonic stem cells, nanoparticles of cobalt chrome resulted in DNA damage only when exposed to differentiated cells. Metallic debris indirectly induces chromosomal aberrations in human cells, depending on the nature of the material and its surface characteristics. The foetus is most susceptible to damage at the time of differentiation. These results raise further concerns about the use of metallic bearings in women of child bearing age.

This PhD thesis studies the performance of metal-on-metal bearings, which are used in hip arthroplasty. Three aspects in particular were studied, namely the clinical results, the release of cobalt and chromium wear debris from the bearings, and the effects of this debris on a cell's DNA. The clinical results showed that large diameter metal-on-metal bearing hip resurfacing (BHR) restored hip function to an excellent level and had an extremely low failure rate up to eight years after the operation. This makes a metal-on-metal bearing an attractive option for hip replacementin high-demand patients.

Thesis (M.S.)--University of Akron, Dept. of Mechanical Engineering, 2008.
"December, 2008." Title from electronic thesis title page (viewed 12/9/2009) Advisor, Jiang John Zhe; Faculty Readers, Joan Carletta, Dane Quinn; Department Chair, Celal Batur; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Joint replacements have been used for over 30 years with considerable success as treatment for bone diseases. As a surgical alternative to metal on metal (MoM) total hip replacement, hip resurfacing was developed using Cobalt-Chromium (CoCr) alloys. However, debris particles are generated by wear at the articulating CoCr surfaces. The nanoparticles and ions produced disseminate throughout the body and interact with different cell types. In order to evaluate the effects of CoCr particles and ions released from MoM implants, U937 cells and primary human lymphocytes were exposed in vitro to artificially produced wear debris derived from an ASRTM MoM hip resurfacing. MoM implants release both Cr and Co ions into patients' circulation, with the latter ion being more mobile, and disseminating more widely in the body. U937 cells were treated with Co ions before being exposed to wear debris to investigate the scenario of patients undergoing revision surgery or receiving a second implant. In addition to this, metal ion levels were measured in clinical whole blood samples of patients with MoM hip implants and the relationship between those levels and the expression of key genes involved in the process of bone remodelling was explored. The findings from this study demonstrated that exposure to high concentrations of CoCr wear debris led to decrease in U937 cell viability after 120h but increased cell proliferation of primary human lymphocytes. Moreover, assessment of apoptosis revealed that metal debris, but not low concentrations of Co ions (0.1μM), induced apoptosis in both U937 cells and primary human lymphocytes. Additionally, results showed that whereas cytokine production by U937 cells is affected by both metal debris and metal ions, it is mainly affected by metal debris in primary human lymphocytes. Changes in human general toxicology-related gene expression in response CoCr wear and Co ions exposure was also evaluated in U937 cells. Real time PCR analysis indicated that CoCr particles were more effective as an inducer of changes in gene expression when cells were pre-treated with Co ions. Together, results seemed to suggest that the toxicity of Co ions in macrophages could be related to nitric oxide metabolic processes and apoptosis and to IL-2 production modulation in lymphocytes. ICP-MS analysis of culture medium from cells exposed to increasing concentration of CoCr wear debris demostrated increasing Co and Cr ion levels representing the corrosion process of the metal debris. Since metal wear debris corrodes under physiological conditions, the ions released may play an important role in the cellular response at the peri-implant tissues. Finally, whole blood Co and Cr ion levels from patients with MoM implants were also analysed by ICP-MS. The ion levels measured were elevated compared to patients without implants, and one patient had levels that were just above the 7μg/l(7ppb)threshold recommended by the Medicines and Health care products Regulatory Agency (MHRA) for Co+Cr in the circulation. A correlation between the ion levels measured and gene expression changes could not be established, due to the low number of patients available for this study. Results from this investigation showed that metal debris tends to be more toxic and has a greater influence on gene expression in the presence of Co ion pre-treatment. This could have great health implications as it potentially means that patients undergoing revision surgery or receiving a second implant may be at higher risk of adverse tissue response and implant failure.

Bosch Rexroth in Mellansel is manufacturing hydraulic motors and constantly trying to improve their products to reduce downtime for their customers. An important thing to get a reliable system is to know the condition. In a hydraulic motor, it is crucial to determine the particle contamination of the oil to determine the condition. To do so many particle sensors have been tested by Bosch Rexroth but also other related companies during the past years. To this point, no sensor has been performing good enough to replace the ordinary magnetic plug for the laboratory tests at Bosch Rexroth.  The ordinary magnetic plug is based on an openable lid that has a magnet attached to it. The lid is opened to review the particle contamination of the system. To open the lid the motor has to be stopped and a competent person needs to be present to review the particles.To ease the work for the laboratory personal and also getting one step closer to a reliable condition monitoring solution a new idea was coined by employees at Bosch Rexroth. The idea was to use a magnet outside a glass disc and by that be able to detect the particles from outside the motor. Initial testing of the idea had been performed with promising results but more development was needed. The idea has therefore been investigated and developed further in this project. This has been done in parallel with an investigation of state-of-the-art techniques available on the market. The testing showed that the new type of magnet/glass solution was performing well and was able to detect particles of different sizes. Some other interesting options were also found during the investigation of other techniques but the new magnet/glass idea was the most prominent.