Fluid, solid and fluid-structure interaction simulations on patient-based abdominal aortic aneurysm models

This article describes the use of fluid, solid and fluid-structure interaction simulations on three patient-based abdominal aortic aneurysm geometries. All simulations were carried out using OpenFOAM, which uses the finite volume method to solve both fluid and solid equations. Initially a fluid-only simulation was carried out on a single patient-based geometry and results from this simulation were compared with experimental results. There was good qualitative and quantitative agreement between the experimental and numerical results, suggesting that OpenFOAM is capable of predicting the main features of unsteady flow through a complex patient-based abdominal aortic aneurysm geometry. The intraluminal thrombus and arterial wall were then included, and solid stress and fluid-structure interaction simulations were performed on this, and two other patient-based abdominal aortic aneurysm geometries. It was found that the solid stress simulations resulted in an under-estimation of the maximum stress by up to 5.9% when compared with the fluid-structure interaction simulations. In the fluid-structure interaction simulations, flow induced pressure within the aneurysm was found to be up to 4.8% higher than the value of peak systolic pressure imposed in the solid stress simulations, which is likely to be the cause of the variation in the stress results. In comparing the results from the initial fluid-only simulation with results from the fluid-structure interaction simulation on the same patient, it was found that wall shear stress values varied by up to 35% between the two simulation methods. It was concluded that solid stress simulations are adequate to predict the maximum stress in an aneurysm wall, while fluid-structure interaction simulations should be performed if accurate prediction of the fluid wall shear stress is necessary. Therefore, the decision to perform fluid-structure interaction simulations should be based on the particular variables of interest in a given study.     

Interventions targeting child undernutrition in developing countries may be undermined by dietary exposure to aflatoxin

Child undernutrition, a form of malnutrition, is a major public health burden in developing countries. Supplementation interventions targeting the major micronutrient deficiencies have only reduced the burden of child undernutrition to a certain extent, indicating that there are other underlying determinants that need to be addressed. Aflatoxin exposure, which is also highly prevalent in developing countries, may be considered an aggravating factor for child undernutrition. Increasing evidence suggests that aflatoxin exposure can occur in any stage of life, including in utero through a trans-placental pathway and in early childhood (through contaminated weaning food and family food). Early life exposure to aflatoxin is associated with adverse effects on low birth weight, stunting, immune suppression, and the liver function damage. The mechanisms underlying impaired growth and aflatoxin exposure are still unclear but intestinal function damage, reduced immune function, and alteration in the insulin-like growth factor axis caused by the liver damage are the suggested hypotheses. Given the fact that both aflatoxin and child undernutrition are common in sub-Saharan Africa, effective interventions aimed at reducing undernutrition cannot be satisfactorily achieved until the interactive relationship between aflatoxin and child undernutrition is clearly understood, and an aflatoxin mitigation strategy takes effect in those vulnerable mothers and children.     

The synthesis,swelling behaviour and rheological properties of chemically crosslinked thermosensitive copolymers based on <Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide

In this contribution thermosensitive polymer matrices based on N-isopropylacrylamide have been developed. The hydrogels were prepared by photopolymerisation of N-isopropylacrylamide and 1-vinyl-2-pyrrolidinone in appropriate amounts of distilled water. The monomers were cured using a UV-light sensitive initiator called 1-hydroxycyclohexylphenylketone. These copolymers were crosslinked using ethylene glycol dimethacrylate and poly(ethylene glycol) dimethacrylate with molecular weights 600 and 1,000, at 0.1 wt% of the total monomer content. The chemical structure of the xerogels was characterised by means of Fourier transform infrared spectroscopy (FTIR) and the transition temperature of the hydrogels was determined using modulated differential scanning calorimetry (MDSC). By altering the feed ratio, hydrogels were synthesised to have lower critical solution temperatures (LCST) around 37 °C. This ability to shift the phase transition temperature of the gels provides excellent flexibility in tailoring transitions for specific uses. The samples synthesised with PEG1000DMA crosslinking agents absorbed over 18 times their weight in water, while maintaining good gel integrity thus falling marginally short of being characterised as superabsorbent. Each of the samples showed similar deswelling behaviour at 37 °C. Rheological studies showed that increasing the molecular weight of the crosslinking agent caused an increase in hydrogel strength.     

Partially observed epidemics in wildlife hosts: modelling an outbreak of dolphin morbillivirus in the northwestern Atlantic,June 2013–2014

Morbilliviruses cause major mortality in marine mammals, but the dynamics of transmission and persistence are ill understood compared to terrestrial counterparts such as measles; this is especially true for epidemics in cetaceans. However, the recent outbreak of dolphin morbillivirus in the northwestern Atlantic Ocean can provide new insights into the epidemiology and spatio-temporal spread of this pathogen. To deal with uncertainties surrounding the ecology of this system (only stranded animals were observed), we develop a statistical framework that can extract key information about the underlying transmission process given only sparse data. Our self-exciting Poisson process model suggests that individuals are infectious for at most 24 days and can transfer infection up to two latitude degrees (220 km) within this time. In addition, the effective reproduction number is generally below one, but reaches 2.6 during a period of heightened stranding numbers near Virginia Beach, Virginia, in summer 2013. Network analysis suggests local movements dominate spatial spread, with seasonal migration facilitating wider dissemination along the coast. Finally, a low virus transmission rate or high levels of pre-existing immunity can explain the lack of viral spread into the Gulf of Mexico. More generally, our approach illustrates novel methodologies for analysing very indirectly observed epidemics.     

Effect of using internal teat sealant with or without antibiotic therapy at dry-off on subsequent somatic cell count and milk production

The objective of this study was to assess the effect of treating cows with teat sealant only compared with antibiotic plus teat sealant at drying off on weekly somatic cell count, potential intramammary infection, and milk production across the entire subsequent lactation. In 3 research herds in the south of Ireland, cows with SCC that did not exceed 200,000 cells/mL in the previous lactation (LowSCC) were randomly assigned to 1 of 2 treatments at drying off: internal teat sealant alone (ITS) or antibiotic plus teat sealant (AB+ITS). Cows with SCC that exceeded 200,000 cells/mL in the previous lactation were treated with AB+ITS and included in the analyses as a separate group (HighSCC). Weekly individual animal composite SCC records were available for 654 cow lactations and were transformed to somatic cell scores (SCS) for the purpose of analysis. Data were divided into 3 data sets to represent records obtained (1) up to 35 DIM, (2) up to 120 DIM, and (3) across the lactation. Foremilk secretions were taken from all quarters at drying off, at calving, 2 wk after calving, and in mid-lactation and were cultured to detect the presence of bacteria. The LowSCC cows treated with ITS alone had higher daily milk yield (0.67 kg/d) across lactation compared with LowSCC cows treated with AB+ITS. The LowSCC cows treated with ITS alone had higher SCS in early, up to mid, and across lactation compared with LowSCC cows treated with AB+ITS. We detected no difference in weekly SCS of LowSCC cows treated with ITS alone and SCS of HighSCC cows. The least squares means back-transformed SCC across lactation of the LowSCC cows treated with ITS alone, LowSCC cows treated with AB+ITS, and HighSCC cows were 41,523, 34,001, and 38,939 cells/mL respectively. The odds of LowSCC cows treated with ITS alone having bacteria present in their foremilk across lactation was 2.7 (95% confidence interval: 1.91 to 3.85) and 1.6 (1.22 to 2.03) times the odds of LowSCC cows treated with AB+ITS and of HighSCC cows treated with AB+ITS, respectively. In this study, Staphylococcus aureus was the most prevalent pathogen isolated from the population. Recategorizing the threshold for LowSCC cows as ≤150,000 cells/mL or ≤100,000 cells/mL in the previous lactation had no effect on the results. The results indicate that herds with good mastitis control programs may use ITS alone at dry-off in cows with SCC <200,000 cells/mL across lactation with only a small effect on herd SCC.     

An investigation of the relationship between hemodynamics and thrombus deposition within patient-specific models of abdominal aortic aneurysm

The relationship between hemodynamics and thrombus deposition in abdominal aortic aneurysm is investigated for three patients (A, B and C), each with mature fusiform aneurysms. Our methodology utilises initial and follow-up computerised tomography scans for each patient to identify regions of mural thrombus growth and to provide patient-specific models for hemodynamic analysis using computational fluid dynamics. The intervals between scans for patients A, B and C were 17, 15 and 3 months, respectively. The simulations were performed using physiologically realistic boundary conditions. The hemodynamic features of the flow considered include the velocity field, the shear strain rate field, the time averaged wall shear stress and the oscillatory shear index. The parameter that showed best correlation with the location of thrombus growth was the oscillatory shear index. In particular, in the case of patient C where the interval between scans was the shortest, thrombus growth was observed at regions of low oscillatory shear index (OSI < 0.1).     

Copper Sulfide (CuxS) Nanowire‐in‐Carbon Composites Formed from Direct Sulfurization of the Metal‐Organic Framework HKUST‐1 and Their Use as Li‐Ion Battery Cathodes

Li‐ion batteries containing cost‐effective, environmentally benign cathode materials with high specific capacities are in critical demand to deliver the energy density requirements of electric vehicles and next‐generation electronic devices. Here, the phase‐controlled synthesis of copper sulfide (Cu_xS) composites by the temperature‐controlled sulfurization of a prototypal Cu metal‐organic framework (MOF), HKUST‐1 is reported. The tunable formation of different Cu_xS phases within a carbon network represents a simple method for the production of effective composite cathode materials for Li‐ion batteries. A direct link between the sulfurization temperature of the MOF and the resultant Cu_xS phase formed with more Cu‐rich phases favored at higher temperatures is further shown. The Cu_xS/C samples are characterized through X‐ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy, and energy dispersive X‐ray spectroscopy (EDX) in addition to testing as Li‐ion cathodes. It is shown that the performance is dependent on both the Cu_xS phase and the crystal morphology with the Cu_1.8S/C‐500 material as a nanowire composite exhibiting the best performance, showing a specific capacity of 220 mAh g^?1 after 200 charge/discharge cycles.     

Effective hydrodynamic shaping of sample streams in a microfluidic parallel-plate flow-assay device: matching whole blood dynamic viscosity

We report the development of an aqueous buffer system tailored to the fluidic and hemodynamic requirements of our recently reported microfluidic platelet dynamic assay device, which uses hydrodynamic focusing to "shape" a blood sample into a thin flowing layer adjacent to its protein-functionalized surface. By matching the dynamic viscosity of whole blood (3.13 ± 0.08 mPa·s, from healthy donors), the selected buffer minimizes interfacial fluid mixing and better controls shear rate within the device, permitting platelet/protein-surface interaction assays with as little as 50 μL of whole blood. Buffers containing the viscosity-enhancing components bovine serum albumin (BSA), gelofusine/glycine, or histopaque (Ficoll gradient solution) were found not to activate platelets when incubated with blood at concentrations up to 50%, as assessed by flow cytometry quantitation of P-selectin expression and αIIbβ (3) activation. In contrast, glycerol-based buffer activated platelets (two-fold increase in P-selectin levels) at concentrations as low as 10% by volume. BSA- and gelofusine/glycine-based buffers were problematic in preparation and use, and therefore, were not used beyond initial characterization. The histopaque solution selected as the best choice for flow studies stabilizes sample contact with the device's thrombogenic surface, does not activate platelets, and does not interfere with the action of agonists added to deliberately activate platelets.