Tribological properties of duplex plasma oxidised, nitrided and PVD coated Ti-6Al-4V

The authors gratefully acknowledge financial support from the UK Technology Strategy Board under Technology Programme project TP/22076, for underpinning research carried out at Sheffield University, on which the work presented in this paper was partially based.Sequential triode plasma oxidation and nitriding have been used to provide enhanced load support for physical vapour deposited (PVD) hard coatings. The diffusion process has been designed to maximise process efficiency and coating adhesion, thereby significantly improving the tribological properties of the Ti–6Al–4V alloy — particularly at high contact pressures. This has been demonstrated using unlubricated linear reciprocating-sliding ball-on-plate wear tests and micro-scratch adhesion testing. Also, surface micro- profilometry, nano/micro-indentation hardness testing, scanning electron microscopy (SEM), energy- dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and glow-discharge optical emission spectroscopy (GDOES) data are presented to corroborate the effect of the several plasma diffusion processes and duplex diffusion/coating combinations discussed here. The results presented show that the novel processing technique developed permits the use of oxygen diffusion in order to obtain relatively large case depths in shorter treatment times without compromising the adhesion strength of subsequently deposited PVD layers.peer-reviewe

An investigation into the effect of Triode Plasma Oxidation (TPO) on the tribological properties of Ti6Al4V

The authors gratefully acknowledge the UK Technology Strategy Board for financial support under the collaborative project LIB-TEC, project No TP 22076.Improving the tribological properties of titanium alloys has been the subject of extensive research for many years. A number of thermochemical processes have been developed for that purpose. In this study, surface hardening of Ti6Al4V is achieved by Triode Plasma Oxidation (TPO) which differs from conventional diode plasma treatments through the use of a third electrode; a negatively biased tungsten filament to enhance the ionisation levels in the plasma. The resultant surface generally consists of a top oxide layer with an oxy- gen diffusion zone lying immediately underneath it. The effects of process parameters such as substrate tem- perature, current density and oxygen partial pressure have been investigated. Surface hardness measurements at various indentation loads were carried out to assess the changes in hardness with depth across the diffusion layer. The hardness profiles obtained confirmed the gradual decrease in hardness with treatment depth and provided an indication of the thickness of the hardened layer produced. Ball-on-plate reciprocating sliding wear data and glancing angle XRD analyses of the oxidised samples are also presented. The results indicate that a harder and deeper case is achieved at both high substrate temperature and high oxygen partial pressure. Furthermore, XRD data show that the substrate temperature strongly affects the structure of the oxide layer produced. All TPO-treated samples exhibit significantly better wear performance compared to the untreated material.peer-reviewe

Improved detection of synthetic lethal interactions in Drosophila cells using Variable Dose Analysis (VDA)

This is the author accepted manuscript. The final version is available from National Academy of Sciences via the DOI in this record.Synthetic sick or synthetic lethal (SS/L) screens are a powerful way to identify candidate drug targets to specifically kill tumor cells, but this approach generally suffers from low consistency between screens. We found that many SS/L interactions involve essential genes and are therefore detectable within a limited range of knockdown efficiency. Such interactions are often missed by overly efficient RNAi reagents. We therefore developed an assay that measures viability over a range of knockdown efficiency within a cell population. This method, called Variable Dose Analysis (VDA), is highly sensitive to viability phenotypes and reproducibly detects SS/L interactions. We applied the VDA method to search for SS/L interactions with TSC1 and TSC2, the two tumor suppressors underlying tuberous sclerosis complex (TSC), and generated a SS/L network for TSC. Using this network, we identified four Food and Drug Administration-approved drugs that selectively affect viability of TSC-deficient cells, representing promising candidates for repurposing to treat TSC-related tumors.This work was supported by NIH Grant P01CA120964; University of Pennsylvania Orphan Disease Program Grant MDBR-15-103-LAM; and Department of Defense Grant W81XWH-16-1-0127. N.P. is a Howard Hughes Medical Institute Investigator

Structural and biophysical analysis of nuclease protein antibiotics

© 2016 The Author(s); published by Portland Press Limited on behalf of the Biochemical Society. Protein antibiotics (bacteriocins) are a large and diverse family of multidomain toxins that kill specific Gram-negative bacteria during intraspecies competition for resources. Our understanding of the mechanism of import of such potent toxins has increased significantly in recent years, especially with the reporting of several structures of bacteriocin domains. Less well understood is the structural biochemistry of intact bacteriocins and how these compare across bacterial species. Here, we focus on endonuclease (DNase) bacteriocins that target the genomes of Escherichia coli and Pseudomonas aeruginosa, known as E-Type colicins and S-Type pyocins, respectively, bound to their specific immunity (Im) proteins. First, we report the 3.2 Å structure of the DNase colicin ColE9 in complex with its ultra-high affinity Im protein, Im9. In contrast with Im3, which when bound to the ribonuclease domain of the homologous colicin ColE3 makes contact with the translocation (T) domain of the toxin, we find that Im9 makes no such contact and only interactions with the ColE9 cytotoxic domain are observed. Second, we report small-Angle X-ray scattering data for two S-Type DNase pyocins, S2 and AP41, into which are fitted recently determined X-ray structures for isolated domains. We find that DNase pyocins and colicins are both highly elongated molecules, even though the order of their constituent domains differs. We discuss the implications of these architectural similarities and differences in the context of the translocation mechanism of protein antibiotics through the cell envelope of Gram-negative bacteria

Evaluating the effects of PIRAC nitrogen-diffusion treatments on the mechanical performance of Ti-6Al-4V alloy

The authors would like to thank the European Regional Development Fund (Malta) for research equipment funded through the application of the project “Developing an Interdisciplinary Material Testing and Rapid Prototyping R&D Facility (Ref. no. 012)”. The authors are also greatly indebted to MATERAþ/ERA-NET Plus for funding support for this research (Project ESM-1935).Powder Immersion Reaction Assisted Coating (PIRAC) is a relatively simple nitrogen diffusion based process which has been proposed as a technique capable of considerable improvements in the tribological performance of ceramics and metals alike; however, the necessary exposure of the substrate material to high temperatures for several hours may have an adverse effect on the bulk properties of materials such as titanium alloys. The effect of PIRAC treatments on the bulk metallography and mechanical properties of Ti–6Al–4V has been studied. Following PIRAC nitrogen-diffusion treatment, studies using X-ray diffraction and cross-sectional microscopy have shown evidence of the formation of a thin (1.4 mm) TiN/Ti2N layer, together with the presence of some Ti3Al intermetallic phase. Semi- logarithmic S–N plots show a deleterious effect after PIRAC treatment in terms of material cyclic fatigue strength, particularly at higher treatment temperatures. Samples processed at 800 1C for 4 h however exhibit better fatigue performance than others treated at lower temperatures for longer nitriding times. Fractographic inspection has shown that fatigue cracks originate at (or near) the surface for the untreated Ti-alloy and from the subsurface regions following diffusion treatment, owing to the build-up of compressive stresses in the latter, which hinder crack propagation.peer-reviewe

Enabling lightweight, high load aero-bearings

Environmental and commercial considerations are strongly driving research into weight saving in aircraft. In this research, innovative manufacturing processes were developed to produce lightweight titanium alloy bearings capable of withstanding high bearing pressures. This will enable the replacement of heavier conventional bearing materials with titanium alloy bearings of the same size thereby saving weight. Plasma processing and PVD coating techniques were refined and combined and a sound scientific understanding of the resulting novel processes developed to assure high performance, reliability and repeatability. These techniques were applied to test discs and small bearing (bush) samples, which were tested under progressively greater loads (pressures). FEA was also used to evaluate pressure distribution in a bush test assembly. The novel treatment has potential applications for many bearings and bearing surfaces throughout aircraft.peer-reviewe

Image-based view-angle independent cardiorespiratory motion gating and coronary sinus catheter tracking for x-ray-guided cardiac electrophysiology procedures

Determination of the cardiorespiratory phase of the heart has numerous applications during cardiac imaging. In this article we propose a novel view-angle independent near-real time cardiorespiratory motion gating and coronary sinus (CS) catheter tracking technique for x-ray fluoroscopy images that are used to guide cardiac electrophysiology procedures. The method is based on learning CS catheter motion using principal component analysis and then applying the derived motion model to unseen images taken at arbitrary projections, using the epipolar constraint. This method is also able to track the CS catheter throughout the x-ray images in any arbitrary subsequent view. We also demonstrate the clinical application of our model on rotational angiography sequences. We validated our technique in normal and very low dose phantom and clinical datasets. For the normal dose clinical images we established average systole, end-expiration and end-inspiration gating success rates of 100%, 85.7%, and 92.3%, respectively. For very low dose applications, the technique was able to track the CS catheter with median errors not exceeding 1 mm for all tracked electrodes. Average gating success rates of 80.3%, 71.4%, and 69.2% were established for the application of the technique on clinical datasets, even with a dose reduction of more than 10 times. In rotational sequences at normal dose, CS tracking median errors were within 1.2 mm for all electrodes, and the gating success rate was 100%, for view angles from RAO 90° to LAO 90°. This view-angle independent technique can extract clinically useful cardiorespiratory motion information using x-ray doses significantly lower than those currently used in clinical practice

Surface flattening of the human left atrium and proof-of-concept clinical applications

Surface flattening in medical imaging has seen widespread use in neurology and more recently in cardiology to describe the left ventricle using the bull's-eye plot. The method is particularly useful to standardize the display of functional information derived from medical imaging and catheter-based measurements. We hypothesized that a similar approach could be possible for the more complex shape of the left atrium (LA) and that the surface flattening could be useful for the management of patients with atrial fibrillation (AF). We implemented an existing surface mesh parameterization approach to flatten and unfold 3D LA models. Mapping errors going from 2D to 3D and the inverse were investigated both qualitatively and quantitatively using synthetic data of regular shapes and computer tomography scans of an anthropomorphic phantom. Testing of the approach was carried out using data from 14 patients undergoing ablation treatment for AF. 3D LA meshes were obtained from magnetic resonance imaging and electroanatomical mapping systems. These were unfolded using the developed approach and used to demonstrate proof-of-concept applications, such as the display of scar information, electrical information and catheter position. The work carried out shows that the unfolding of complex cardiac structures, such as the LA, is feasible and has several potential clinical uses for the management of patients with AF.</p

Pyocin S5 import into Pseudomonas aeruginosa reveals a generic mode of bacteriocin transport

Pyocin S5 (PyoS5) is a potent protein bacteriocin that eradicates the human pathogen Pseudomonas aeruginosa in animal infection models, but its import mechanism is poorly understood. Here, using crystallography, biophysical and biochemical analyses, and live-cell imaging, we define the entry process of PyoS5 and reveal links to the transport mechanisms of other bacteriocins. In addition to its C-terminal pore-forming domain, elongated PyoS5 comprises two novel tandemly repeated kinked 3-helix bundle domains that structure-based alignments identify as key import domains in other pyocins. The central domain binds the lipid-bound common polysaccharide antigen, allowing the pyocin to accumulate on the cell surface. The N-terminal domain binds the ferric pyochelin transporter FptA while its associated disordered region binds the inner membrane protein TonB1, which together drive import of the bacteriocin across the outer membrane. Finally, we identify the minimal requirements for sensitizing Escherichia coli toward PyoS5, as well as other pyocins, and suggest that a generic pathway likely underpins the import of all TonB-dependent bacteriocins across the outer membrane of Gram-negative bacteria

Discovery, characterization and in vivo activity of pyocin SD2, a protein antibiotic from Pseudomonas aeruginosa

Increasing rates of antibiotic resistance among Gram-negative pathogens such as Pseudomonas aeruginosa means alternative approaches to antibiotic development are urgently required. Pyocins, produced by P. aeruginosa for intraspecies competition, are highly potent protein antibiotics known to actively translocate across the outer membrane of P. aeruginosa. Understanding and exploiting the mechanisms by which pyocins target, penetrate and kill P. aeruginosa is a promising approach to antibiotic development. In this work we show the therapeutic potential of a newly identified tRNase pyocin, pyocin SD2, by demonstrating its activity in vivo in a murine model of P. aeruginosa lung infection. In addition, we propose a mechanism of cell targeting and translocation for pyocin SD2 across the P. aeruginosa outer membrane. Pyocin SD2 is concentrated at the cell surface, via binding to the common polysaccharide antigen (CPA) of P. aeruginosa lipopolysaccharide (LPS), from where it can efficiently locate its outer membrane receptor FpvAI. This strategy of utilizing both the CPA and a protein receptor for cell targeting is common among pyocins as we show that pyocins S2, S5 and SD3 also bind to the CPA. Additional data indicate a key role for an unstructured N-terminal region of pyocin SD2 in the subsequent translocation of the pyocin into the cell. These results greatly improve our understanding of how pyocins target and translocate across the outer membrane of P. aeruginosa. This knowledge could be useful for the development of novel anti-pseudomonal therapeutics and will also support the development of pyocin SD2 as a therapeutic in its own right