Computational modelling of blood flow through sutured and coupled microvascular anastomoses

The research presented in this thesis uses Computational Fluid Dynamics (CFD) to model blood flow through idealised sutured and coupled microvascular Anastomoses to investigate the affect of each surgical technique on the flow within the vessel. Local flow phenomena are examined in detail around suture and coupler sites to study characteristics that could potentially initiate thrombus formation; for example, changes in velocity profile, wall shear stress or recirculating flow (vorticity). Idealised geometries of sutured and coupled blood vessels were created using CFD software with dimensions identical to microvascular suture material and coupling devices. Vessels were modelled as non‐compliant 1mm diameter ducts, and blood was simulated as a Newtonian fluid, in keeping with previous similar studies. All analyses were steady-state and performed on arteries. Comparison of the sutured and coupled techniques in the simulated microarterial anastomoses revealed a reduced boundary velocity profile; high Wall Shear Stress (WSS); high Shear StrainRate(SSR);and elevated vorticity at the suturesites. The coupled anastomosis simulation showed a small increase in maximum WSS at the anastomotic region compared to a pristine vessel. However, this was less than half that of the sutured model. The coupled vessel displayed an average WSS equal to a pristine vessel. Taken together, these observations demonstrate an increased thrombogenic profile in the sutured anastomosis when compared to a pristine, or indeed a coupled vessel. Data from the simulations on a coupled anastomosis reveal a profile that is less thrombogenic than that of the sutured anastomosis, and one that is nearly equivalent to that of a pristine vessel. Overall, it can be concluded that, within the limits of CFD simulations and the assumptions taken in this study, a sutured anastomosis is potentially more likely to generate an intravascular thrombosis than a coupled anastomosis

Observation of substituent effects in the electrochemical adsorption and hydrogenation of alkynes on Pt{hkl} using SHINERS

By combining cyclic voltammetry (CV) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), the adsorption behavior of two alkynes, propargyl alcohol (PA) and 2-methyl-3-butyn-2-ol (MeByOH), undergoing hydrogenation on Pt basal plane single-crystal electrodes is investigated. It is found that PA and MeByOH give rise to strong surface sensitivities in relation to both hydrogenation activity and molecular fragmentation into adsorbed species such as CO. For PA, irreversible adsorption is strongly favored for Pt{100} and Pt{110} but is weak in the case of Pt{111}. It is suggested that the presence of the primary alcohol substituent is key to this behavior, with the order of surface reactivity being Pt{100} > Pt{110} > Pt{111}. In contrast, for MeByOH, strong irreversible adsorption is observed on all three basal plane Pt surfaces and we propose that this reflects the enhanced activity of the alkyne moiety arising from the inductive effect of the two methyl groups, coupled with the decreased activity of the tertiary alcohol substituent toward fragmentation. Pt{111} also exhibits singular behavior in relation to MeByOH hydrogenation in that a sharp Raman band at 1590 cm–1 is observed corresponding to the formation of a di-σ/π-bonded surface complex as the alkyne adsorbs. This band frequency is some 20 cm–1 higher than the analogous broadband observed for PA and MeByOH adsorbed on all other basal plane Pt surfaces and may be viewed as a fingerprint of Pt{111} terraces being present at a catalyst surface undergoing hydrogenation. Insights into the hydrogenation activity of different Pt{hkl} surfaces are obtained using quantitative comparisons between Raman bands at hydrogenation potentials and at 0.4 V vs Pd/H, the beginning of the double-layer potential region, and it is asserted (with support from CV) that Pt{110} is the most active plane for hydrogenation due to the presence of surface defects generated via the lifting of the (1 × 2) to (1 × 1) clean surface reconstruction following flame annealing and hydrogen cooling. Our findings are also consistent with the hypothesis that Pt{111} planes are most likely to provide semihydrogenation selectivity of alkynes to alkenes, as reported previously

Identification and characterisation of enteroaggregative Escherichia coli subtypes associated with human disease

Enteroaggregative E. coli (EAEC) are a major cause of diarrhoea worldwide. Due to their heterogeneity and carriage in healthy individuals, identification of diagnostic virulence markers for pathogenic strains has been difficult. In this study, we have determined phenotypic and genotypic differences between EAEC strains of sequence types (STs) epidemiologically associated with asymptomatic carriage (ST31) and diarrhoeal disease (ST40). ST40 strains demonstrated significantly enhanced intestinal adherence, biofilm formation, and pro-inflammatory interleukin-8 secretion compared with ST31 isolates. This was independent of whether strains were derived from diarrhoea patients or healthy controls. Whole genome sequencing revealed differences in putative virulence genes encoding aggregative adherence fimbriae, E. coli common pilus, flagellin and EAEC heat-stable enterotoxin 1. Our results indicate that ST40 strains have a higher intrinsic potential of human pathogenesis due to a specific combination of virulence-related factors which promote host cell colonization and inflammation. These findings may contribute to the development of genotypic and/or phenotypic markers for EAEC strains of high virulence

Exploratory Study of Incubator Tenant Firm Social Capital through Network Analysis

This paper looks to explore the degree of social capital possessed by incubator tenant firms that being the resource accrued from their networks and constituent relations. It analyses how networks, and the social capital within, are leveraged to access resources and isolate which toes of networks are more important than others. Findings show that different types of networks are utilised different in terms of resource acquisition and that social capital is an important factor in this dynamic

Computational Non-Newtonian Hemodynamics of Small Vessels

The significance of non-Newtonian hemodynamics of small blood vessels is addressed via the description and critical discussion of cogent models within Computational Fluid Dynamics (CFD) software, in this case ANSYS-CFX. Several applicable hemodynamical shear-thinning models are presented and the relevance with respect to prediction of Shear Strain Rate (SSR) rigorously examined, in order to critically evaluate salient literature. It is found that the small vessels explored, in line with the aforementioned literature, that non-Newtionian evaluation of the fluid behavior is indeed negligible. The work presented herein is a precursor to investigation of more complex geometries and hemodynamic simulations, which are being actively researched. This is a technical note which attempts to address the significance of Newtonian/non-Newtonian flows in small blood vessels