1,720,990 research outputs found
The fracture toughness of cancellous bone
No full textThe mechanical capacity and integrity of cancellous bone is crucial in osteoporosis, a condition which is set to become more prevalent with increasing lifespan and population sizes. The fracture toughness (FT) of cancellous bone has never been examined before and the conditions associated with the growth of a major crack through the lattice of cancellous bone, a cellular solid, may improve our understanding for structural integrity of this material. The aim of this study is to provide (i) basic data on cancellous bone FT and (ii) the experimental support for the hypothesis of Gibson, L.J., Ashby, M.F. [1997a. Chapter 10: Wood. In: Cellular Solids: Structure and Properties, second ed. Cambridge University Press, pp. 387–428; Gibson, L.J., Ashby, M.F., 1997b. Chapter 11: Cancellous Bone. In: Cellular Solids: Structure and Properties, second ed. Cambridge University Press, pp. 429–52] that the FT of cancellous bone tissue is governed by the density of the tissue to a power function of between one and two. 294 SENB and 121 DC(T) specimen were manufactured from 45 human femoral heads, 37 osteoporotic and 8 osteoarthritic, as well as 19 equine thoracic vertebrae. The samples were manufactured in two groups: the first aligned with the trabecular structure (A?), the second orientated at 90° to the main trabecular orientation (A?). The samples were tested in either tensile or bending mode to provide values of the stress intensity factor (K). The results which were obtained show a strong and significant link between the density of the cancellous bone tissue and that the critical stress intensity values are governed by the density of the tissue to a power function of between 1 and 2 (KQ vs. apparent density: A?=1.58, A?=1.6). Our results provide some fundamental values for the critical stress intensity factor for cancellous bone and also support the previous hypothesis as set by Gibson, L.J., Ashby, M.F., 1997a. Chapter 10: Wood. In: Cellular Solids: Structure and Properties, second ed. Cambridge University Press, pp. 387–428; Gibson, L.J., Ashby, M.F., (1997b). Chapter 11: Cancellous Bone. In: Cellular Solids: Structure and Properties, second ed. Cambridge University Press, pp. 429–52
Characterisation of the oxide film on the taper interface from retrieved large diameter metal on polymer modular total hip replacements
No full textMany metal joint failures have been associated with adverse local tissue reactions due to the response of the body to wear debris and corrosion products, released from the bearing surfaces or the taper interfaces. It is believed that the oxide film on the CoCrMo alloy is playing an important role on the corrosion resistance, however, there is a lack of quantitative data on this aspect. In the present study, detailed analysis of the surface layer on the taper interfaces is provided using advanced electron microscopies. Two retrieved taper interfaces were analysed. The taper interface varies along the length of the tapers. Site-specific FIB/TEM cross-sections from different regions all show evidence of the oxide film and the carbonaceous layer, separately or mixed. HRTEM results showed the oxide film had porous texture and EELS confirmed the film was chromium oxide
Corrosion resistance enhancement of Ti-6Al-4V Alloy by pulsed electron irradiation for biomedical applications
No full textMetallic materials are commonly used in biomedical applications, especially with the increased use of artificial hip and knee joints in recent years. Ti-6Al-4V alloy is a widely used biomaterial for orthopaedic and dentistry applications, due to its excellent mechanical properties and corrosion resistance. However, the in-vivo environment in which it operates is aggressive in terms of mechanical loading cycles and corrosive activity of bodily fluids. Therefore, metal ions may be released from these alloys due to corrosion and wear, which may cause adverse long-term health effects. Preserving the integrity of component surfaces made from these alloys is critical to ensuring they perform correctly over the required life-cycle and do not generate excessive levels of ion release or wear particles. In this work a large-area pulsed electron beam irradiation technique was investigated to improve corrosion performance of an orthopaedic Ti-6Al-4V alloy. The alloy samples had a lapped surface finish prior to electron beam irradiation using a Sodick PF-32A EBM machine. The process uses an argon plasma as a source of electrons which are accelerated towards and bombard the sample surface, causing surface melting and extremely rapid solidification rates of up to 109 K s-1. For this study, samples were irradiated using a range of acceleration voltages (15-35kV) and numbers of pulses (1-25). The corrosion behaviour of the alloy treated with different acceleration voltages and pulses was investigated by electrochemical techniques including open-circuit potential measurements, polarization tests and electrochemical impedance spectroscopy in a 3.5 wt.% NaCl solution. The corrosion resistance of the titanium alloy treated by e-beam surface melting was enhanced by two orders of magnitude compared to the untreated sample. The enhancement was evaluated by assessing surface topography and microstructure from the treatment as observed by XRD, SEM and TEM characterization
Comparison of questionnaire and quantitative ultrasound techniques as screening tools for DXA
No full textThe aim of the study is to assess the sensitivity and specificity of different techniques and their ability to act as screening tools in relation to dual energy X-ray absorptiometry (DXA) in a group of 208 postmenopausal women. In this study we examined eight screening systems for the diagnosis of osteoporosis, the osteoporosis self-assessment tool (OST), the osteoporosis risk assessment instrument (ORAI), the osteoporosis index of risk (OSIRIS), a risk index derived using data from the study of osteoporotic fractures (SOFSURF), the simple calculated osteoporosis risk estimation (SCORE), patient body weight (pBW), along with two ultrasound based systems, the Sunlight Omnisense (Sunlight Medical, Rehovot, Israel) and the CUBA Clinical (McCue plc, Winchester, UK). The sensitivity and specificity of the different techniques in relation to DXA were plotted as receiver-operating characteristic (ROC) curves at three different levels (DXA T-score -2.5 osteoporosis, -2 and -1 osteopenia). The areas under the curves (AUC) were calculated and showed broadband ultrasound attenuation (BUA) at the calcaneus to provide consistently the highest AUC (0.77-0.81). The velocity of sound (VOS) of the calcaneus (AUC=0.72-0.76) was equally good, but was out-performed by some of the questionnaire systems (AUC=0.66-0.79). Both the questionnaire systems and the CUBA Clinical out-perform the Sunlight Omnisense (AUC=0.58-0.7), which showed comparable performance with body weight (AUC=0.66-0.69). The results show that QUS is capable of selecting patients with low bone density as measured by DXA. A patient displaying a low QUS value should be followed up with a DXA scan to confirm the diagnosi
The ability of peripheral quantitative ultrasound to identify patients with low bone mineral density in the hip or spine
No full textThis study aims to assess the sensitivity and specificity of two commercially available quantitative ultrasound (QUS) scanners (CUBA Clinical™, Sunlight Omnisense™), to differentiate patients with osteoporosis (OP) or osteopenia at the spine and hip confirmed by dual-energy x-ray absorptiometry (DXA) and to investigate the optimum cut-off values to maximize the effectiveness of the screening technique. Participants (n = 268) received DXA scans on their lumbar spine (L1-L4) and hip, with paired QUS scans on their distal radius, proximal phalanx, midshaft tibia and calcaneus. Scanners were evaluated by using receiver-operating characteristics curves and their area under the curve (AUC) values. Measurement of the calcaneus by the CUBA Clinical™ showed a superior ability to predict DXA, with AUC values between 0.75 to 0.83 in comparison with AUC values of 0.60 to 0.70 for the Sunlight Omnisense™. Cut-off values varied according to the technique used and the accuracy of the screening required. Assessment of the calcaneus was the best QUS technique for the prediction of low bone density at the axial skeleton as diagnosed by DX
Evolution of wear on enamel caused by tooth brushing with abrasive toothpaste slurries
No full textMaintaining good oral hygiene is vital to a healthy body and aesthetically attractive smile. Regular tooth brushing prevents cavities, tooth decay and gum disease which if left, can lead to serious health problems. However, cleaning your teeth comes with a drawback. Toothpastes contain abrasive particles, which in combination with the toothbrush, have the potential to wear tooth enamel. To optimise the cleaning efficiency of teeth and minimise the enamel wear it is essential to understand the science behind the tooth/toothpaste/toothbrush interface. An integrated approach is employed in this study to investigate the tribology of brushing, examining the friction and wear evolution. A reciprocating tribometer was modified to enable a toothbrush head to reciprocate against a bovine enamel disk to simulate the tooth brushing action, with a constant feed of either an abrasive free or a silica or alumina containing toothpaste slurry to the contact. The evolution of the friction with time during the brushing simulation as well as the changes in the enamel surface roughness were determined. The alumina slurry resulted in higher friction, increased wear depth and an increased roughening of the enamel surface compared to the silica slurries, with all abrasives causing 2 body grooving to the enamel surface. The spherical silica provided both the lowest friction and material loss of the slurries tested. The abrasive free slurry caused no wear or surface roughening but exhibited the highest friction during brushing
Volumetric assessment of material loss from retrieved cemented metal hip replacement stems
No full textThe aim of this study was to investigate the scale of metallic wear debris generation at the cement-stem interface of polished cobalt-chrome implants. Thirty-one Zimmer CPT cemented femoral stems were retrieved; mean time in vivo was 77.8 months (range 38-97 months), with 70% (n=21) of the stems considered to be well-fixed at the time of revision surgery. Volumetric loss was measured using optical microscopy, with focus variation technology capable of 3D reproduction of the surfaces. The scale of loss was found to be pronounced (mean: 3.1mm3, 0.02-11.4mm3), with a mean rate of 0.5mm3/year (0.003-1.9mm3/year). These results demonstrate that material loss from the cement-stem interface of is comparable to that of a taper interface, even in apparently well-fixed stems
Pulsed electron beam surface melting of CoCrMo alloy for biomedical applications
No full textThe use of CoCrMo alloys in biomedical applications has come under scrutiny recently due to unacceptable revision rates of certain hip resurfacing and total hip arthroplasty designs. Failure analysis has demonstrated that solid and soluble wear debris and corrosion products, released from the joints have resulted in adverse local tissue reactions (ALTR), pseudo-tumour formation and ultimately implant retrieval and replacement. In order to improve the surface properties of a wrought CoCrMo alloy, a low energy high current pulsed electron beam surface treatment process was investigated. Samples were irradiated at two cathode voltages of 15 and 35 kV at pulse numbers of 1, 15 and 25. At low beam energies a polishing effect was observed as a result of surface melting. At higher beam energies a higher Ra value was the result of the formation of surface craters. Nano-indentation and scratch testing of the treated surface were carried out using a nano-indenter. Depth profiling nano-indentation was performed using a Berkovich tip in load control. Loading was performed in 8 mN increments up to 160 mN at a rate of 3.5 mN/s, with a 60 s dwell period and 40% unloading. The results demonstrated that the surface treatment process reduced both the modulus and the hardness of the surface in comparison to the control. Scratching was performed with a 20 ?m radius spherical diamond and loading rate of 2 mN/s up to a maximum of 100 mN, over a 1 mm scratch length. Similar scratch depths for both control and treated surfaces were observed. However, an improvement in the dynamic friction coefficient was observed at certain beam energies. These results are discussed in the light of XRD evidence that suggested rapid cooling of the surface induced preferential formation of an ?-martensite HCP phase which may be beneficial for biomedical applications.<br/
Microstructure characterisation of hypereutectoid aluminium bronze composite coating
No full textHypereutectoid aluminium bronze coating was deposited onto an E.N. 10503 steel using plasma transferred arc welding (PTA). Microstructure characterisation of the coating and a section near the steel substrate joint was carried out using SEM, EBSD, EDS in conjunction with XRD and depth-sensing nano-indentation. The constituent phases in the coating were identified as: martensitic Cu3Al ?1' phase, solid solution of Al in Cu ? phase and the intermetallic Fe3Al ?1 phase. The region near the steel substrate was characterised by high hardness, large grains and presence of Cu precipitates. No cracks were observed in this region. The coating has high hardness of 4.9GPa and Young’s modulus of 121.7GPa. This is attributed to homogeneous distribution of sub microns size Fe3Al intermetallic phase. The implications of the coating to the engineering application of sheet metal forming are discusse
The effect of large-area pulsed electron beam melting on the corrosion and microstructure of a Ti6Al4V alloy
No full textThe use of titanium alloys in biomedical applications continues to increase due to the excellent stiffness to weight ratio and high corrosion resistance. In order to improve the surface wettability and corrosion properties of a Ti-6Al-4V alloy, the surface treatment method, large area electron beam melting technique was investigated. Polished samples were subject to pulsed treatments of 1, 15 and 25 at 1.38 J/cm2 beam energy. Surface roughness and contact wetting angles were reduced as a result of the treatment. Microstructural analysis of the surface by XRD and FIB-TEM revealed a martensitic alpha prime phase formed as a result of the high cooling rates induced by the treatment. The presence of this homogenous martensite layer was shown to facilitate a compact passive oxide layer formation during corrosion, thus improving corrosion rates by several orders of magnitude compared to an untreated sample. Large area electron beam melting of Ti-6Al-4V induced a number of changes to the near surface microstructure of the samples, all of which could be used to tailor mechanical and corrosion properties to that of a desired application, without compromising the bulk material properties. These are explored in detail in this work
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