Bone scaffolds with controllable porosity

The Adaptive Foam Reticulation (AFR) technique, a combination of foam reticulation and freeze casting, has been investigated for producing bone repair bioscaffolds from hydroxyapatite (HA), titanium (Ti) and titanium-aluminium-vanadium (Ti-6Al-4V). Scaffolds have a network of macropores of diameter between 94 and 546 mm, with struts 20 to 118 mm thick. The structure was dependent on the template from which structures were produced, the number of coats of slurry applied to the template and the sintering temperature. The struts contained numerous micropores, the size of which was increased from 2-5 to 20-30 mm by decreasing the freezing temperature. Whilst the size of individual micropores was independent of the amount of porogen in the slurry, there was some coalescence at higher percentages. Scaffolds exhibited porosities of between 76 and 96%, with porosity consistently decreased by increasing the number of coats from one to five. The mechanical strength of all samples was determined theoretically by the novel incorporation of a shape factor conventially used for microporous structures into an existing equation used to calculate the yield stress of porous structures. In most cases this agreed with the experimentally obtained yield stress. With compressive yield stresses of 0.002 to 0.18MPa and 0.002 to 1.8 MPa respectively, HA and Ti structures are only suitable in non-load bearing situations. However Ti-6Al-4V scaffolds had yield stresses of 0.21-13.7 MPa, within the range of cancellous bone. AFR-fabricated HA scaffold offered greater in-vitro cell viability than a commercially available porous HA disc. Including a porogen offered no improvement in viability compared to structures fabricated without porogen, except at the highest inclusion where a statistically significant increase was observed. The weak compressive strength of scaffolds needs improving, and fabrications require in-vivo analyses. However, AFR could offer a viable alternative to other manufacturing techniques

Automotive to rail : can technologies cross the gap?

There are significant drivers of change in the automotive industry today. Not only is legislation forcing manufacturers to meet ever more stringent emissions standards (particularly in terms of CO2), but customers are also demanding more efficient, safer and more electronically advanced vehicles (both in terms of performance features and interfaces). Manufacturers have responded with dramatic improvements in engine and powertrain efficiencies which have helped address legislative requirements to date. Furthermore they have rapidly moved away from standard steel bodies to multi-material solutions including various advanced grades of steel, aluminium, magnesium and polymer-based materials. Indeed there is currently significant research in the field of composite use for automotive bodies where there are pressing questions about manufacturing times for high volume production, costs and recyclability. The rail industry faces similar pressures as those seen in the automotive sector, driven by needs for lower costs, increased capacities, reduced carbon emissions and higher customer expectations. This paper will discuss the current state-of-the-art in automotive technologies and consider if and how they can be translated into the rail sector. It will consider current research within the WMG High Value Manufacturing Catapult towards implementation of automotive-style technologies in a light rail context

On the effect of anisotropy on the performance and simulation of shrinking tubes used as energy absorbers for railway vehicles

The standard BS EN 15227 requires accurate numerical modelling of railway vehicle energy absorbers that must be correlated against experimental data. Although thin-walled tubes can exhibit anisotropy, such numerical models have traditionally included isotropic material properties. Thus, this work investigates whether anisotropic material models may increase the accuracy of numerical models of shrinking tube energy absorbers. Tensile testing of extruded AW-6082 aluminium alloy shrinking tubes showed the yield strength of the tubes was 10% lower in the hoop direction than in the longitudinal direction. Further, to assess the effect of incorporating anisotropic material behaviour in the numerical model, the tubes were compressed under quasi-static conditions. Numerical models of the shrinking tubes, including isotropic (von Mises yield function) and anisotropic (Hill’s quadratic yield function) material properties, were compared to the experimental data. The isotropic numerical models overestimated the steady-state reaction force, even without the inclusion of friction, indicating that such models do not fulfil the requirements of the standard. Conversely, incorporating anisotropic material models predicted a lower reaction force and enabled the inclusion of energy dissipation by friction, by means of a coefficient of friction μ ¼ 0.03. Although these results demonstrate the need to include anisotropy in the numerical simulation, the friction value was lower than expected due to the methodology of the material characterization and the accuracy of the anisotropic model implemented

Development of a very light rail vehicle

The collaborative very light rail project involves the development of a novel railcar designed to revolutionise the rail industry: a self-powered, Very Light Rail (VLR) vehicle. Each of the two bogies contains a complete diesel-electric series-hybrid drive system, whilst the whole vehicle has undergone significant lightweighting activity to realise a target weight of less than 18 tonnes, or 1 tonne per linear meter. The target cost is £500,000, which is to be achieved through the use of standardised, modular components, and appropriate materials and structural design methodologies. The research covers several aspects of the GB Rail Technical Strategy (RTS) chapter relating to Rolling Stock. Lightweighting leads to a reduction in the propulsion requirements and reduces the infrastructure installation and maintenance costs. The use of higher efficiency drive systems achieved through on-board energy systems enables a reduction in carbon emissions. These hybridisation activities improve the passenger experience through quieter operation, decreased vibration and the possible elimination of exhaust emissions in stations. Combining new drive systems with modular lightweight structures will lead to lower life-cycle costs and thus could enable the economical reopening of lines

A novel route for volume manufacturing of hollow braided composite beam structures

This work investigates the application of a rapid variothermal moulding process for direct processing of a braided thermoplastic commingled yarn. The process uses locally controllable, responsive tooling which provides opportunities for optimum part quality and significantly reduced cycle times compared with conventional processes. The proposed process was used to directly manufacture hollow beam structures from dry commingled braided preforms. It was demonstrated that the cycle time using the rapid process was reduced by more than 90% as compared to a conventional bladder moulding process, resulting in a total cycle time of 14 min. Additionally, initial three point flexure test results indicated an improvement in the mechanical performance of the resultant parts as compared to the benchmark

The Lobby in transition: what the 2009 MPs’ expenses scandal revealed about the changing relationship between politicians and the Westminster Lobby?

The 2009 MPs' expenses scandal was one of the most significant political stories of modern times. It raised questions, not just about the ethics and behaviour of MPs but also about the relationship between politicians at Westminster and the political correspondents who follow them on a daily basis, known as ‘the lobby’. For the significance of this scandal, in media terms, was that the story was not broken by members of the lobby but came from outside the traditional Westminster news gathering process. This paper examines why this was the case and it compares the lobby today with that which was described and analysed by Jeremy Tunstall and Colin Seymour-Ure in their respective studies more than 40 years ago. The article concludes that the lobby missed the story partly because of the nature of the lobby itself and partly as a result of a number of specific changes which have taken place in the media and the political systems over the past 40 years

In-vitro viability of bone scaffolds fabricated using the adaptive foam reticulation technique

The adaptive foam reticulation technique combines the foam reticulation and freeze casting methodologies of fabricating bone reparative scaffolds to offer a potential alternative to autografts. For the first time this paper studies the effect of processing on the mechanical properties and in-vitro cell growth of controllably generating a hierarchical structure of macro- (94 ± 6 to 514 ± 36 μm) and microporosity (2–30 μm) by the inclusion of camphene as a porogen during processing. Scaffolds were produced with porogen additions of 0–25 wt%. Porosity values of the structures of 85–96% were determined using the Archimedes technique and verified using X-ray Computed Tomography. The strength of the hydroxyapatite scaffolds, 5.70 ± 1.0 to 159 ± 61 kPa, correlated to theoretically determined values, 3.71 ± 0.8 to 134 ± 12 kPa, calculated by the novel incorporation of a shape factor into a standard equation. Fibroblast (3T3) and pre-osteoblast (MC3T3) cell growth was found to be significantly (P < 0.005) improved using 25 wt% porogen. This was supported by increased levels of alkaline phosphatase and was thought to result from greater dissolution as quantified by increased calcium levels in incubating media. The combination of these properties renders adaptive foam reticulation-fabricated scaffolds suitable for non-structural bone regenerative applications in non-load bearing bone defects

Heparin versus 0.9% sodium chloride intermittent flushing for prevention of occlusion in central venous catheters in adults

Background Heparin intermittent flushing is a standard practice in the maintenance of patency in central venous catheters. However, we could find no systematic review examining its effectiveness and safety. Objectives To assess the effectiveness of intermittent flushing with heparin versus 0.9% sodium chloride (normal saline) solution in adults with central venous catheters in terms of prevention of occlusion and overall benefits versus harms. Search methods The Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched December 2013) and the Cochrane Central Register of Controlled Trials (CENTRAL) (2013, Issue 11). Searches were also carried out in MEDLINE, EMBASE, CINAHL and clinical trials databases (December 2013). Selection criteria Randomised controlled trials (RCTs) in adults 18 years of age and older with a central venous catheter (CVC) in which intermittent flushing with heparin (any dose with or without other drugs) was compared with 0.9% normal saline were included. No restriction on language was applied. Data collection and analysis Two review authors independently selected trials, assessed trial quality and extracted data. Trial authors were contacted to retrieve additional information, when necessary. Main results Six eligible studies with a total of 1433 participants were included. The heparin concentrations used in these studies were very different (10-5000 IU/mL), and follow-up varied from 20 days to 180 days. The overall risk of bias in the studies was low. The quality of the evidence ranged from very low to moderate for the main outcomes (occlusion of CVC, duration of catheter patency, CVC-related sepsis, mortality and haemorrhage at any site). Combined findings from three trials in which the unit of analysis was the catheter suggest that heparin was associated with reduced CVC occlusion rates (risk ratio (RR) 0.53, 95% confidence interval (CI) 0.29 to 0.94). However, no clear evidence of a similar effect was found when the results of two studies in which the unit of analysis was the participant were combined (RR 0.21, 95% CI 0.03 to 1.70), nor when findings were derived from one study, which considered total line accesses (RR 1.08, 95% CI 0.84 to 1.40). Furthermore, results for other estimated effects were found to be imprecise and compatible with benefit and harm: catheter duration in days (mean difference (MD) 0.41, 95% CI -1.29 to 2.12), CVC-related thrombosis (RR 1.22, 95% CI 0.74 to 1.99), CVC-related sepsis (RR 1.02, 95% CI 0.34 to 3.03), mortality (RR 0.77, 95% CI 0.45 to 1.32) and haemorrhage at any site (RR 1.37, 95% CI 0.49 to 3.85). Authors' conclusions We found no conclusive evidence of important differences when heparin intermittent flushing was compared with 0.9% normal saline flushing for central venous catheter maintenance in terms of efficacy or safety. As heparin is more expensive than normal saline, our findings challenge its continued use in CVC flushing outside the context of clinical trials