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•Successfully imaged H concentrations in δ phase and carbonitrides, and at their interfaces with the matrix using NanoSIMS in alloy 718.•δ attracts a higher concentration of H than ...the matrix while carbonitrides adsorb much less. No H segregation was observed at the interfaces.•The higher vulnerability of δ in H induced cracking is attributed to its higher capacity in H adsorption, and vice versa for carbonitrides.
Here we report imaging of hydrogen/deuterium concentrations in δ phase and carbonitrides, and at their interfaces with the matrix in a nickel-based superalloy using Nanoscale Secondary Ion Mass Spectrometry. It is found that δ phase attracts a higher concentration of hydrogen than the matrix during cathodic charging, while carbonitrides adsorb much less. No hydrogen segregation was observed at the interfaces. Detailed electron microscopy analysis of the H-charged samples after tensioning to failure demonstrates that the higher vulnerability of δ in hydrogen induced cracking is largely attributed to its higher capacity in hydrogen adsorption, and vice versa for carbonitrides.
Previously we demonstrated that heparin administration during carotid endarterectomy (CEA) caused a marked, but transient increase in platelet aggregation to arachidonic acid (AA) and adenosine ...diphosphate (ADP), despite effective platelet cyclo-oxygenase-1 (COX-1) inhibition with aspirin. Here we investigated the metabolism of AA via platelet 12-lipoxygenase (12-LOX) as a possible mediator of the observed transient aspirin resistance, and compared the effects of unfractionated (UFH) and low-molecular-weight (LMWH) heparin. A total of 43 aspirinated patients undergoing CEA were randomised in the trial to 5,000 IU UFH (n=22) or 2,500 IU LMWH (dalteparin, n=21). Platelet aggregation to AA (4x10⁻³) and ADP (3x10⁻⁶) was determined, and the products of the COX-1 and 12-LOX pathways; thromboxane B₂ (TXB₂) and 12-hydroxyeicosatretraenoic acid (12-HETE) were measured in plasma, and in material released from aggregating platelets.Aggregation to AA increased significantly (~10-fold) following heparinisation (p<0.0001), irrespective of heparin type (p=0.33). Significant, but smaller (~2-fold) increases in aggregation to ADP were also seen, which were significantly lower in the platelets of patients randomised to LMWH (p<0.0001). Plasma levels of TxB2 did not rise following heparinisation (p=0.93), but 12-HETE increased significantly in the patients' plasma, and released from platelets stimulated in vitro withADP, with both heparin types (p<0.0001). The magnitude of aggregation to ADP correlated with 12-HETE generation (p=0.03). Heparin administration during CEA generates AA that is metabolised to 12-HETE via the 12-LOX pathway, possibly explaining the phenomenon of transient heparin-induced platelet activation. LMWH has less effect on aggregation and 12-HETE generation than UFH when the platelets are stimulated with ADP.
Abstract It is irrefutable that the presence of hydrogen reduces the mechanical performance of many metals and alloys used for structural components. Several mechanisms of hydrogen-assisted cracking ...(HAC) of steels have been postulated. The direct evidence of the mechanisms by which hydrogen embrittles these materials has remained elusive. This is by virtue of our difficulty to directly observe the hydrogen distribution at spatial resolutions less than 100 nm and analysis volumes greater than 1 × 10 9 atoms at microstructural features such as grain boundaries, dislocations, twins, stacking faults and sub-micron inclusions that are all potential hydrogen trapping sites postulated to be responsible for the degradation of mechanical performance. Here, we report on an experimental methodology combining an elaborate fatigue testing protocol in an enriched gaseous deuterium environment with NanoSIMS (secondary ion mass spectrometry) imaging for detection of deuterium at spatial resolutions as low as 100 nm and accompanying TEM analysis. Type 316 stainless steel compact tension specimens were precharged in deuterium followed by fatigue testing at high stress ratio (0.7), low delta K (~11 MPa √m), and a frequency of 1 cycle per minute using a sawtooth waveform with a rise time of 30 s in high pressure (68.9 MPa) gaseous deuterium (99.999% purity) environment at room temperature. High resolution NanoSIMS imaging was then used to measure the deuterium distribution at the tip of and in the wake of secondary and tertiary fatigue cracks as well as at MnS inclusions. The use of deuterium eliminates the difficulties of interpreting hydrogen measurements by SIMS relating to the ubiquitous presence of hydrogen in all high vacuum systems and guarantees that deuterium measured by the NanoSIMS must be attributed to the fatigue testing protocol. This methodology has allowed us to directly observe the distribution of hydrogen in dislocation tangles ahead and in the wake of fatigue crack tips and at the interface of MnS inclusions. The protocol provides an avenue by which the path and speed with which hydrogen proceeds along its embrittling course of action may be directly followed through modifications of the fatigue testing parameters and/or alloy type and allows a means to validate at least qualitatively recently published models of enhanced hydrogen transport by dislocations.
IntroductionSevere limb ischaemia (SLI) is the end stage of peripheral arterial occlusive disease where the viability of the limb is threatened. Around 25% of patients with SLI will ultimately ...require a major lower limb amputation, which has a substantial adverse impact on quality of life. A newly established rapid-access vascular limb salvage clinic and modern revascularisation techniques may reduce amputation rate. The aim of this study was to investigate the 12-month amputation rate in a contemporary cohort of patients and compare this to a historical cohort. Secondary aims are to investigate the use of frailty and cognitive assessments, and cardiac MRI in risk-stratifying patients with SLI undergoing intervention and establish a biobank for future biomarker analyses.Methods and analysisThis single-centre prospective cohort study will recruit patients aged 18–110 years presenting with SLI. Those undergoing intervention will be eligible to undergo additional venepuncture (for biomarker analysis) and/or cardiac MRI. Those aged ≥65 years and undergoing intervention will also be eligible to undergo additional frailty and cognitive assessments. Follow-up will be at 12 and 24 months and subsequently via data linkage with NHS Digital to 10 years postrecruitment. Those undergoing cardiac MRI and/or frailty assessments will receive additional follow-up during the first 12 months to investigate for perioperative myocardial infarction and frailty-related outcomes, respectively. A sample size of 420 patients will be required to detect a 10% reduction in amputation rate in comparison to a similar sized historical cohort, with 90% power and 5% type I error rate. Statistical analysis of this comparison will be by adjusted and unadjusted logistic regression analyses.Ethics and disseminationEthical approval for this study has been granted by the UK National Research Ethics Service (19/LO/0132). Results will be disseminated to participants via scientific meetings, peer-reviewed medical journals and social media.Trial registration number NCT04027244.
Secondary-ion mass spectrometry (SIMS) is an important tool for investigating isotopic composition in the chemical and materials sciences, but its use in biology has been limited by technical ...considerations. Multi-isotope imaging mass spectrometry (MIMS), which combines a new generation of SIMS instrument with sophisticated ion optics, labeling with stable isotopes, and quantitative image-analysis software, was developed to study biological materials.
The new instrument allows the production of mass images of high lateral resolution (down to 33 nm), as well as the counting or imaging of several isotopes simultaneously. As MIMS can distinguish between ions of very similar mass, such as 12C15N- and 13C14N-, it enables the precise and reproducible measurement of isotope ratios, and thus of the levels of enrichment in specific isotopic labels, within volumes of less than a cubic micrometer. The sensitivity of MIMS is at least 1,000 times that of 14C autoradiography. The depth resolution can be smaller than 1 nm because only a few atomic layers are needed to create an atomic mass image. We illustrate the use of MIMS to image unlabeled mammalian cultured cells and tissue sections; to analyze fatty-acid transport in adipocyte lipid droplets using 13C-oleic acid; to examine nitrogen fixation in bacteria using 15N gaseous nitrogen; to measure levels of protein renewal in the cochlea and in post-ischemic kidney cells using 15N-leucine; to study DNA and RNA co-distribution and uridine incorporation in the nucleolus using 15N-uridine and 81Br of bromodeoxyuridine or 14C-thymidine; to reveal domains in cultured endothelial cells using the native isotopes 12C, 16O, 14N and 31P; and to track a few 15N-labeled donor spleen cells in the lymph nodes of the host mouse.
MIMS makes it possible for the first time to both image and quantify molecules labeled with stable or radioactive isotopes within subcellular compartments.
A 32 year old female patient underwent laparoscopic cholecystectomy and in the post-operative phase was investigated after developing obstructive jaundice. ERCP revealed a stenosis at the junction of ...the cystic and common hepatic ducts and this was seen to be directly adjacent to the clips which had been used to ligate the cystic duct. The stricture was easily dilated with a balloon and all her symptoms improved and her liver function tests returned to normal. Eight years later she represented with a mid-common bile duct calculus. An ERCP was performed but the stone could not be dislodged or retrieved and when removed subsequently at open exploration it was found to have precipitated around two metal clips, which had migrated into the lumen of the common bile duct. We propose that the risk of this rare, yet previously reported complication, could be reduced by heeding the longstanding recommendation that only absorbable material be used in biliary surgery, and particularly when there is a short cystic duct.
Simultaneous open surgery has been advocated in the elective management of abdominal aortic aneurysm patients with significant ischemic heart disease, as staged procedures risk worsening myocardial ...ischemia or aortic rupture, depending on which is the first intervention. The argument for combined aneurysm and valve repair is less established. We describe the case of a 70-year-old female who while awaiting aortic valve replacement suffered rupture of an abdominal aortic aneurysm. The patient was successfully managed with emergency combined open abdominal aortic aneurysm repair and open aortic valve replacement. We would advocate that such a strategy be considered as a salvage technique in similarly difficult management dilemmas.
There is no single methodology that can map the distribution of hydrogen and relate it to specific crystallographic phases or defect structures. Here, we present a case study demonstrating two ...methodologies towards achieving this goal: Correlating nanoscale secondary ion mass spectrometry (NanoSIMS) deuterium maps with electron backscattered diffraction (EBSD) data ahead of crack tips in a 304 stainless steel sample fatigue tested in deuterated water, and secondly correlating NanoSIMS deuterium maps with (scanning) transmission electron microscopy ((S)TEM) data from focused ion beam (FIB) lift-out samples. Correlating NanoSIMS/EBSD images, we confirmed an association of deuterium with martensitic lath structures. Furthermore, we discovered localized enrichments of deuterium along the martensitic laths, with a higher associative preponderance to ε−martensite. Applying correlative NanoSIMS/(S)TEM imaging of the fracture surface, we found deuterium accumulation at the metal oxide interface. However, in the pre-crack region, the deuterium was clearly concentrated underneath the oxide layer.
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•Correlative imaging shows associations of 2H and BCC phases in stainless steel.•Deuterium localizes at ε-martensite in stainless steel fatigue tested in D2O.•2H is co-located with a Ni-enriched layer formed below the surface oxide.
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