Tribological evaluation of total shoulder arthroplasty implants : advanced in vitro wear testing and retrieval analysis

PhD ThesisThe glenohumeral joint is subject to dynamic and cyclic loading and motion during activities of daily life (ADLs), which can promote the wear of the articulating surfaces of shoulder joint replacements. The adverse reaction to the generated wear debris can influence the long-term survival of the implant and is considered an issue of contemporary concern. Therefore, it is important to be able to measure the wear and surface characteristics of anatomical and reversed total shoulder replacements in order to understand the complex wear mechanisms that occurs in vivo and predict their performance. To date, there is no consensus in the literature regarding the methods to test the in vitro wear of shoulder replacements. Hence, the aim of this research was to develop a novel protocol based on the loading and motion of relevant ADLs. This protocol subjects the shoulder prosthesis to cyclic loading and intermittent motion in a multi-station shoulder wear simulator. After five million cycles, the polymeric volumetric wear was 58.8 mm3 for reverse shoulder components against metallic glenospheres. The three-dimensional surface roughness (Sa) values of the polyethylene humeral components fell from 692 ± 132 nm to 42 ± 29 nm. Comparison with an earlier wear tests revealed a non-statically significant difference in wear, suggesting that the addition of intermittent loading is unnecessary. This could help those wear testing shoulder implants in future. When an anatomic shoulder design consisting of a PyroCarbon humeral heads (ceramic-like alternative bearing material) and a polyethylene glenoid inserts were tested, the polyethylene wear was 90.6 mm3 . The surface roughness of the polyethylene components fell from 296 ± 28 nm to 32 ± 8 nm. Interestingly, PyroCarbon components did not exhibit a measurable loss in mass or change in the surface roughness. Explant analysis can give key insights into how artificial joints have performed in the body. Therefore, and for the first time, the surface characteristics of retrieved metal– on–polyethylene reverse shoulder prostheses were assessed. From a heterogeneous cohort of thirteen explants with a mean time in vivo of 16 ± 11 months, results indicated - viii - no correlation between the surface roughness and duration of implantation. However, tantalisingly among the metallic components available, low surface roughness values were found (ρ = 0.032) when the bearing material was inverted and used as a humeral component. If shown to be true in larger explant studies, this could suggest that such inverted materials could be associated with a superior tribological performance compared with a conventional arrangement. Predominant surface damage modes observed on most of the conventional reverse total shoulder arthroplasty implants during the analysis of the surface topography were similar to those obtained from the in vitro wear test, and consistent with previous observations on retrieved components; the similitude between these results helped to validate the Newcastle Shoulder Wear Simulator. The collection of results and findings obtained in this research at Newcastle University may help others who test artificial shoulder joints to validate the design of their simulators, improve mathematical wear model predictions, optimize the selection of bearing materials, and contribute to the ongoing efforts to produce the first international standard for in vitro wear testing of shoulder prosthesesNational Council of Science and Technology (CONACYT) of México and The Institute of Innovation and Technology Transfer (I2T2) of Nuevo Leó

The Evolution of Early Christian Theology of Martyrdom in the Pre-Decian Period: Collective Memory and Martyrological Interpretation of the New Testament in Polycarp, Lyon, and Perpetua

Ph. D. Thesis.While early Christian martyrdom accounts had a profound impact on the formation, and success, of the primitive Church, it appears that before 250, the persecutions of Christians were ‘local and sporadic’ (Barnes, 1968). Historical approaches failed to explain these disparities between Christian and pagan sources and to answer questions such as ‘what is martyrdom?’, ‘what are the origins of martyrdom?’ and ‘why were the early Christians persecuted?’. As a result, recent studies have been focusing on more theoretical approaches. Following this trend, this thesis explores the origins of early Christian theology of martyrdom as a discursive creation forged in the collective memory of the first martyrdom accounts as well as in the martyrological interpretation of both New Testament texts and pagan narratives such as Socrates’s death. The first two chapters of the thesis are mostly introductory, the first chapter presenting an overview of the debates and challenges surrounding the study of early Christian martyrdom, and the second covering the methodological approach adopted in this thesis, namely discourse analysis and the collective memory theory. The following three chapters examine three early martyrdom accounts (the Martyrdom of Polycarp, the Martyrs of Lyon and the Passion of Perpetua and Felicity) in order to both highlight the different influences/discourses in the texts and reveal the evolution of the theology of martyrdom. In each case study, both Christian and pagan sources are scrutinised for the rudiments of a concept of martyrdom and its discourse, focusing on possible expressions of collective memory within these martyrdom accounts. This thesis thus contends that the martyrological interpretation of NT texts (Revelation in particular), and assimilation of these interpretations into the communities’ collective memory, provided an eschatological platform in which early Christian authors could inscribe their own experiences, shaping their reality, their narratives and ultimately, their identity

Defining the effector(s) and mechanism(s) by which enteropathogenic E. coli (EPEC) inhibits Akt signalling upstream of PI3 kinase

Ph. D. Thesis.Disease associated with enteropathogenic Escherichia coli (EPEC) depends on a Type 3 Secretion System (T3SS) that delivers ‘effector’ proteins into infected cells. The EPEC E2348/69 strain has approximately 6Mb of horizontally acquired DNA provided, mostly, by 21 prophage (PP) and integrative element (IEs). The T3SS, six effectors and two chaperones - latter aid the export of T3SS substrates - are encoded on an IE named LEE (Locus of Enterocyte Effacement). The remaining effectors are encoded on 7 other IE/PPs. EPEC inhibits the activity of a host kinase, Akt, that regulates important cellular processes, including cell survival, but the responsible effectors and inhibitory mechanism remain undefined. Previous work discounted roles for 17 of 21 known effectors but linked the inactivation process to Akt dephosphorylation in a manner requiring the LEE chaperone, CesT. Here, additional screening strategies undertaken to identify the responsible effector(s) uncovered key but redundant roles for two, previously unexamined, T3SS substrates: LifA (3223 residue, IE6-encoded) and LifA-like (2624 residue, IE2- encoded) proteins. These proteins have putative glycosyltransferase and protease activities with LifA thought to be delivered into host cells. Other studies support CesT dependence of the inhibitory process and, surprisingly, revealed LifA’s inhibitory activity requires IE2-encoded factor(s). Screening IE2-related fragments implicated factor(s) on a cloned 1.7kB region but further studies are needed to confirm the results and provide mechanistic insights. Studies on LifA’s inhibitory mechanism revealed its T3SS- and CesT-dependent accumulation with host membrane proteins with dephosphorylation of Akt not requiring motifs needed for its known glycosyltransferase and protease activities. By contrast, immunoprecipitation studies linked the inhibitory mechanism to O-glycosylation of Akt and revealed infection-induced O-GlcNAc of an Akt-sized band that gradually disappeared in a T3SS-dependent manner. Studies described in this thesis not only identify the EPEC effectors responsible for inhibiting Akt activity, but also provide important insights into the inhibitory mechanism

Progressive Collapse of Ship Structures Under Cyclic Loading

Ph. D. Thesis.Following ultimate limit state philosophy, the structural safety of ships and shiptype floating structures are assessed by ensuring an acceptable margin between their maximum load-carrying capacity and the extreme design load. This ultimate limit state approach is established assuming that the structures are subjected to a monotonic load that leads to an elastoplastic buckling collapse. However, the environmental loads of most marine structures are of a cyclic nature. The evaluation procedure and analysis methodology for ship structures under extreme loads with multiple cycles is currently lacking. Within this context, the aim of this research is to assess the collapse behaviour of ship structures, including plates, stiffened panels and ship hull girders, under combinations of cyclic loads and to investigate the influence of cyclic load on the ultimate strength of ship structures. Overall, four contributions have been achieved in this thesis. A parametric nonlinear finite element study is first performed on a range of ship plates under multiple cycles of compression and tension. The outcomes of this investigation provides a new recognition, for the first time, of the buckling collapse behaviours of unstiffened plates under cyclic compression and tension. In particular the characteristic features that are relevant for ultimate limit state assessment of ship hull structures are demonstrated, such as a progressively reducing but converging compressive strength and stiffness in the reloading regime of structural members under cyclic loads as compared to those under monotonic loads. Using observed response patterns from the numerical study, a response and updating rule methodology is proposed to predict the load-shortening curve of Progressive Collapse of Ship Structures Under Cyclic Loading structural component under cyclic load by updating the critical characteristics. The comparison with equivalent nonlinear finite element results shows an acceptable correlation. This novel method provides an efficient way to represent the cyclic buckling collapse response of structural members and is in an appropriate format for implementing in a Smith-type progressive collapse analysis for estimating the hull girder response. Following the response and updating rule load-shortening curve methodology, an unique extension to the Smith method is introduced for predicting cyclic bending response. Case studies are completed out on several ship-type box girder structures under different combinations of cyclic loads. The validation with nonlinear finite element analysis shows the rationality of the proposed extension, and also demonstrates that the prediction of cyclic response is highly sensitive to structural component’s post-collapse behaviour. An uncertainty evaluation procedure is developed to analyse the effects of critical features of the load-shortening relationship on the hull girder response prediction. The influences of different load-shortening features, including elastic stiffness, ultimate compressive strength, ultimate strain and post-collapse stiffness, are quantified. It is indicated that the post-collapse stiffness of structural components have the largest influence as suggested by a sensitivity index. In addition, this procedure is not only useful for the cyclic response, but also the conventional assessment concerning monotonic load. The outcome of this research work is a validated method which has the potential to improve the safety of ships by considering cyclic load effects

Uncovering the molecular mechanisms behind mycetoma

PhD ThesisMycetoma is a chronic, painless, inflammatory condition, caused by either invading fungi or bacteria. It is one of twenty neglected tropical diseases formally recognised by the World Health Organisation. Following inoculation of the causative organisms into the subcutaneous tissue of a host, they organise into structures called grains. These in turn initiate the formation of granulomas and the development of a large, tumour-like mass. This lesion growth is reported to be painless by the majority of patients. Additionally, through unknown mechanisms, the pathogens appear to be able to persist in the host and evade their immune response. This thesis focuses on actinomycetoma, which is exclusively caused by bacteria of the phylum Actinobacteria. Such bacteria are a major source of specialised metabolites, such as antibiotics, antitumour compounds and immunosuppressants. The central hypothesis of the thesis is that bacterial pathogens produce one or more specialised metabolites that mediate painless lesion development and pathogen persistence. A key aim was therefore to isolate and characterise any such compounds, which may also have therapeutic potential. A new host-pathogen interaction assay was developed and applied to study virulence mechanisms of the actinomycetoma pathogen Streptomyces sudanensis. RNAseq, cytokine ELISAs, an NF-κB activity assay and microscopy were deployed to observe how murine macrophages and S. sudanensis interact. A unique immune profile was observed to be induced within the macrophages, characterised by a mixture of pro- and anti-inflammatory features. Multiple potential virulence factors were also identified within S. sudanensis. Additionally, human tissue culture cells were shown to undergo pyroptosis when interacting with the pathogen. Two related compounds that appear to be responsible for this activity were isolated from the bacteria and identified as 2,5-diketopiperazines. This work provides novel insights into how mycetoma pathogens interact with the immune system and of the molecular mechanisms underlying this disease

The Limits of State Sovereignty: An Exploration of Sardinian Minority Nationalism

PhD ThesisThe concept of sovereignty has been at the heart of discussions in the discipline of International Relations (IR) over the past 30 years, giving way to much-needed interrogations of the exclusionary implications of realist treatments of the term as bound to the territoriality and rationality of unified states. Overlooked in this critical literature, however, have been minority nationalist articulations of sovereignty that do not conform to the neat categorizations of inter/intra-state politics characteristic of realist imaginations of sovereign power. Responding to this lacuna in IR scholarship, this thesis examines the role and significance of sovereignty in Sardinian minority nationalist discourse. Through an analysis of ethnographic fieldnotes and 37 semi-structured interviews with ‘independentists’ conducted in Sardinia between 2017 and 2018, the research draws attention to how the term’s definition constitutes a complex site of political contestation for minority nationalists. Drawing from a Gramscian perspective that emphasises the importance of adopting a relational approach to the study of political discourses as dialectically constructed, the research investigates how activists treated sovereignty as a way of doing politics. Activists used the term in varying ways to contest conditions of economic exploitation and political and cultural marginalization shaped by the unevenness of Italian governance and capitalist development as well as to formulate alternative ‘myths’ of political belonging and credibility. Arguing for an approach that considers sovereignty as shaped by the ongoing effects of political dynamics of ‘revolution/restoration’, the research contributes to ongoing efforts to produce non-essentializing depictions of people’s engagement with sovereignty whilst not losing sight of the structuring effects of social relations of production on perceptions of collective belonging, political legitimacy and the very possibilities of political manoeuvre

A methodology for the quantitative evaluation of attacks and mitigations in IoT systems

PhD ThesisAs we move towards a more distributed and unsupervised internet, namely through the Internet of Things (IoT), the avenues of attack multiply. To compound these issues, whilst attacks are developing, the current security of devices is much lower than for traditional systems. In this thesis I propose a new methodology for white box behaviour intrusion detection in constrained systems. I leverage the characteristics of these types of systems, namely their: heterogeneity, distributed nature, and constrained capabilities; to devise a pipeline, that given a specification of a IoT scenario can generate an actionable intrusion detection system to protect it. I identify key IoT scenarios for which more traditional black box approaches would not suffice, and devise means to bypass these limitations. The contributions include; 1) A survey of intrusion detection for IoT; 2) A modelling technique to observe interactions in IoT deployments; 3) A modelling approach that focuses on the observation of specific attacks on possible configurations of IoT devices; Combining these components: a specification of the system as per contribution 1 and a attack specification as per contribution 2, we can deploy a bespoke behaviour based IDS for the specified system. This one of a kind approach allows for the quick and efficient generation of attack detection from the onset, positioning this approach as particularly suitable to dynamic and constrained IoT environments

Synthetic bacterial communities for plant growth promotion

PhD ThesisIncreasing food demands have driven the adoption of new global strategies to intensify productivity without relying on heavy chemical treatments. In the last decades, plant-growth promoting rhizobacteria (PGPR) have emerged as potential biofertilisers and biopesticides in agriculture. The overall aim of this study was to research and develop approaches to genetically engineer PGPR to improve their beneficial activities toward the plant partner. A simplified PGPR community, a Bacillus consortium of three strains, was adopted to study the complexity of the interactions occurring within the consortium and the plant microbiome. Firstly, the comparative genomic analysis of the consortium highlighted the unique and shared features responsible for plant promotion, microbial interaction and cooperation among the strains (niche partitioning, organisation in biofilms with cooperative mechanisms of quorum sensing, cell density control and antibiotic detoxification). Flux balance analysis identified cross-feeding interactions among the strains and the metabolic capability of the consortium to provide nitrogen to the plant, transforming it into forms available for plant utilisation. The consortium PGP potential was then investigated in vitro (LEAP mesocosm assay) and in vivo (pot experiment) on the vegetable crop Brassica rapa. These tests show increased plant growth when the strains were inoculated together rather than individually and when the consortium was used as a supplement of the natural bulk soil microbiome. The in silico study and the plant experiments highlighted areas for genetic improvement of the consortium genomes. Lastly, this work describes the development of a conjugation system that could be used to efficiently engineer non-domesticated bacteria and bacterial communities, such as rhizobacteria and plant microbiomes. The system, based on the plasmid pLS20, was developed in Bacillus subtilis 168 and successfully tested on twenty-three wild type Bacillus strains and three rhizobacillus communities. The research presented here provides tools and approaches for the genetic manipulation of rhizobacterial communities, with the ultimate aim of generating sustainable agricultural bioformulations and sheds light on the complex interactions that can occur in a model microbial PGPR consortia

The influence of sirtuin-controlled circadian rhythmicity anddiet on lifespan in the honey bee, Apis mellifera

PhD ThesisThis thesis explores the role of sirtuin controlled circadian rhythmicity and diet on honey bee longevity. By manipulating the circadian period of newly emerged honey bees and using qPCR to measure the expression of metabolic and circadian genes, we attempt to understand the effect of non-24 h circadian periods on longevity. We found evidence that altering the circadian period to 20 h or 28 h resulted in reduced longevity and a 1.6-fold increase in mortality, disruption to circadian clockwork and observed that this effect was not additive with that of a high-EAA diet, suggesting a potential shared pathway (Chapter 3). Rapamycin is an inhibitor of the mTOR pathway and has been shown to extend lifespan across species. We investigate the effect of rapamycin on longevity and appetite in the honey bee. We also observe the effects of rapamycin in combination with high-EAA diets. We found no evidence of any life extending effects and in some cases a reduction in longevity as well as polyphagic behaviour common in metabolic diseases (Chapter 4). Methylation plays an important role in sirtuin controlled mediation of lifespan, however the study of methylation in insects is time consuming and costly due to low global methylation levels. In this study we aim to test the viability and suitability of common methods of measuring global and site-specific methylation changes. We determine that methylation levels were too low to effectively measure with generic ELISA-kits in the honey bee and this also made site specific analysis for circadian genes challenging (Chapter 5). In the final chapter we analyse the effect of methionine on longevity and behaviour in the honey bees. By varying the dietary methionine content and analysing key metabolic genes FOXO and Sir2 we attempt to determine the mechanisms controlling these effects. We found that a high methionine diet reduced lifespan, appetite and lead to upregulation of FOXO but not Sir2 (Chapter 6)

Preparation and characterization of silica, reduced graphene oxide and composite aerogels

Ph. D. Thesis.In this thesis, experimental results are reported on the synthesized of waterglass-based silica aerogels monoliths by mixing graphene oxide. The new ambient pressure approach is used to produce aerogels by using a mixture of sodium bicarbonate and water instead of low surface tension solvent. Furthermore, to enhance mechanical properties graphene oxide as nanofillers is added into silica matrix to synthesize composite aerogels based on sol-gel technology. Furthermore, we report a simple method for obtaining reduced graphene oxide aerogels doped with different metal oxide nanoparticles, germanium dioxide (GeO2), cobalt ferrite (CoFe2O4), and iron(III) oxide (Fe3O4) by using supercritical drying method. Firstly, all metal oxide nanoparticles are synthesized. Then metal oxide nanoparticles are added into graphene oxide solution and sodium bisulfide is utilised as a cheap reducing agent. Lastly, prepared aerogels’ properties such as surface area, morphology, the chemical composition, and electrochemical measurements as an anode material for lithium-ion batteries are investigated. Finally, ambient pressure dried graphene-based aerogels are produced with common devices by rewording a partially reduced graphene oxide hydrogel with an ice-template method. This work can be cost effective of high-performance graphene aerogels. Scanning electron microscope (SEM), X-ray diffraction (XRD), uniaxial compression test, fourier transform infrared spectroscopy (FTIR), raman spectroscopy, Brunauer - Emmett - Teller (BET) theory and Barret - Joyner - Halenda (BJH) method are utilised to characterise the produced aerogels.Turkish Governmen