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Preparation of a fibre optic sensor based on AgNp/silica composite for pH measurement
Full text linkThe measurement of hydrogen ion concentration in a solution, commonly referred to as pH, holds significant importance in various industries. However, measuring pH under high-temperature and high-pressure (HTHP) conditions has posed a formidable challenge due to the lack of reliable sensors and instrumentation. Recent research has demonstrated the potential of utilising the localised surface plasmon resonance (LSPR) phenomenon seen by gold nanoparticles deposited on optical fibres for pH detection under varying temperature and pressure conditions. Usingthis reported stability of optical fibres in HTHP conditions, this project aimed to create an optical fibre-based pH sensor using silver nanoparticles (AgNp) embedded within a silica matrix, which is suitable for use under HTHP conditions. In this work, a AgNp/silica coating is applied on a glass optical fibre to create an optical pH sensor. The initial stage of the project involved the preparation of colloidal silver nanoparticles and silica gel as separate entities, with a focus on stabilising the colloidal solution and optimising silica gel production. Subsequently, setbacks were overcome in creating the AgNp/silica coating, refining the sol-gel method, and enhancing adhesion through careful adjustments of gelation temperature and heat treatment procedures. The project optimised the gelation process to achieve goodadhesion on the glass while maintaining sufficient silver nanoparticles for pH sensitivity. Characterisation through UV-Vis spectroscopy indicated an extinction peak at 400 nm, which confirms the presence of silver nanoparticles. Afterwards, the AgNp/silica coating was applied to the optical fibres. In the preparation of the optical fibre, the fibre was etched using 7 M sodium hydroxide (NaOH). This marked a successful milestone in utilising NaOH as an etchant for optical fibres. The coated optical fibre reached an ideal core diameter of 104 ± 1 microns, which was required for pH sensitivity. Extensive experimentation led to fine-tuning the sensor setup, ensuring optimal sensitivity while emphasising the delicate balance between light source voltage and detector integration time. Durability testing revealed susceptibility to acidic environments, underscoring theneed for coating improvement. The project explored pH measurement under ambient conditions, demonstrating the sensor's accuracy and stability in various chemical conditions. A calibration curve was constructed, and the coating's reproducibility and repeatability were thoroughly analysed, further validating its reliability as a pH sensing tool. The calibration curve provided insights into pH measurement using theoptical method. Additionally, the performance and sensitivity of the sensor were investigated and compared between sensors prepared in the same batch and those from batch-to-batch production, offering insights into the sensor's characteristics. Furthermore, an evaluation was conducted to assess the accuracy of the sensor in comparison to the potentiometric pH measurement technique. The project's most challenging phase involved testing the sensor in HTHP conditions, revealing issues related to the stability of the AgNp/silica coating at higher temperatures and pressures. It was observed that the pH decreased as the temperature of the solution increased. The experimental apparatus was constructed, which allowed experiments up to a gauge pressure of 5 bar, equivalent to 156 °Ctemperature, where a higher dissolution of the coating was observed. Nonetheless, the sensor was stable at lower gauge pressures, such as 2 bar, even during multiple heating and cooling cycles. Despite these challenges, the inclusion of silver nanoparticles showed promise in improving the sensor's consistency and stability. In conclusion, this project represents a significant effort in developing a robust opticalpH sensor with potential applications in industries such as oil and gas, chemicals, and environmental monitoring. The work underscores the ongoing challenge of maintaining sensor integrity under HTHP conditions, showing the need for further research to enhance coating resilience and a more robust calibration technique. Despite these challenges, this project pushes the boundaries of pH measurement technology and contributes substantially to the field of optical pH sensing. It is an exciting step towards overcoming the limitations of pH measurement in extremeenvironments, opening new avenues for precise monitoring and control in critical industries.The measurement of hydrogen ion concentration in a solution, commonly referred to as pH, holds significant importance in various industries. However, measuring pH under high-temperature and high-pressure (HTHP) conditions has posed a formidable challenge due to the lack of reliable sensors and instrumentation. Recent research has demonstrated the potential of utilising the localised surface plasmon resonance (LSPR) phenomenon seen by gold nanoparticles deposited on optical fibres for pH detection under varying temperature and pressure conditions. Usingthis reported stability of optical fibres in HTHP conditions, this project aimed to create an optical fibre-based pH sensor using silver nanoparticles (AgNp) embedded within a silica matrix, which is suitable for use under HTHP conditions. In this work, a AgNp/silica coating is applied on a glass optical fibre to create an optical pH sensor. The initial stage of the project involved the preparation of colloidal silver nanoparticles and silica gel as separate entities, with a focus on stabilising the colloidal solution and optimising silica gel production. Subsequently, setbacks were overcome in creating the AgNp/silica coating, refining the sol-gel method, and enhancing adhesion through careful adjustments of gelation temperature and heat treatment procedures. The project optimised the gelation process to achieve goodadhesion on the glass while maintaining sufficient silver nanoparticles for pH sensitivity. Characterisation through UV-Vis spectroscopy indicated an extinction peak at 400 nm, which confirms the presence of silver nanoparticles. Afterwards, the AgNp/silica coating was applied to the optical fibres. In the preparation of the optical fibre, the fibre was etched using 7 M sodium hydroxide (NaOH). This marked a successful milestone in utilising NaOH as an etchant for optical fibres. The coated optical fibre reached an ideal core diameter of 104 ± 1 microns, which was required for pH sensitivity. Extensive experimentation led to fine-tuning the sensor setup, ensuring optimal sensitivity while emphasising the delicate balance between light source voltage and detector integration time. Durability testing revealed susceptibility to acidic environments, underscoring theneed for coating improvement. The project explored pH measurement under ambient conditions, demonstrating the sensor's accuracy and stability in various chemical conditions. A calibration curve was constructed, and the coating's reproducibility and repeatability were thoroughly analysed, further validating its reliability as a pH sensing tool. The calibration curve provided insights into pH measurement using theoptical method. Additionally, the performance and sensitivity of the sensor were investigated and compared between sensors prepared in the same batch and those from batch-to-batch production, offering insights into the sensor's characteristics. Furthermore, an evaluation was conducted to assess the accuracy of the sensor in comparison to the potentiometric pH measurement technique. The project's most challenging phase involved testing the sensor in HTHP conditions, revealing issues related to the stability of the AgNp/silica coating at higher temperatures and pressures. It was observed that the pH decreased as the temperature of the solution increased. The experimental apparatus was constructed, which allowed experiments up to a gauge pressure of 5 bar, equivalent to 156 °Ctemperature, where a higher dissolution of the coating was observed. Nonetheless, the sensor was stable at lower gauge pressures, such as 2 bar, even during multiple heating and cooling cycles. Despite these challenges, the inclusion of silver nanoparticles showed promise in improving the sensor's consistency and stability. In conclusion, this project represents a significant effort in developing a robust opticalpH sensor with potential applications in industries such as oil and gas, chemicals, and environmental monitoring. The work underscores the ongoing challenge of maintaining sensor integrity under HTHP conditions, showing the need for further research to enhance coating resilience and a more robust calibration technique. Despite these challenges, this project pushes the boundaries of pH measurement technology and contributes substantially to the field of optical pH sensing. It is an exciting step towards overcoming the limitations of pH measurement in extremeenvironments, opening new avenues for precise monitoring and control in critical industries
Response surface methodology for chemical activation of peanut shells : synthesis and application of activated carbon for wastewater treatment
Full text linkModern society has undergone rapid industrialization, which has led to various
environmental and health challenges on a global level. Some of the main contributors to these challenges are the industrial discharge of organic dyes, oils, solvents, metal ions etc. and this situation constitutes a serious global concern. Industrial and agricultural effluents are abundant and feasible sources of water; however, these require treatment to protect the ecosystem and enable their reuse. Among various methods employed in the treatment of wastewater, adsorption is one of the most feasible and effective methods. Adsorption processes employ solid materials, known as adsorbents, to facilitate the removal of contaminants from water. Activated carbon (AC) is a widely used adsorbent that has high porosity and adsorption capacity for various contaminants. However, the production of commercial AC faces the challenges of high cost and scarcity of raw materials, due to the high demand of commercial ACs for multiple purposes. Therefore, there is a need to develop low-cost and alternative AC materials by exploring the use of renewable and abundant resources, such as biomass. This work aims to synthesise AC materials from peanut shells, which are an agricultural by-product with high carbon content and potential as a low-cost and renewable precursor for AC production, and to optimise the activation variables (temperature, hold-time, and impregnation ratio, i.e., activating agent weight / precursor weight), to obtain AC materials with high surface areas and yields. Previous studies on peanut shells have lacked a focus in identifying the controlling activation variables to enhance the properties of peanut derived carbon materials. To bridge this gap, the current work employs a single stage chemical activation process, using ZnCl2 as an activating agent, and investigates the effects of activation variables on the properties of AC derived from peanut shells. A design of experiment (DoE) is used to generate a set of experimental design points and obtain a response surface of the results, to visualise the relationship between the responses (surface area and yield) and the independent variables, demonstrating how to model the synthesis of AC from
biomass. The work characterises the AC materials synthesised from peanut shells using various techniques, such as Brunauer-Emmett-Teller (BET) analysis of nitrogen adsorption data, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Textural analysis revealed that the synthesised AC materials have relatively high surface areas and porosities, indicating the effectiveness of the chemical activation method, using ZnCl2 as an activating agent. Response surface analysis revealed that temperature and impregnation ratio were the most significant variables in determining the characteristics of the AC materials derived from peanut shells. As revealed, by both textural and surface chemistry analyses, the synthesised AC materials show heterogeneous characteristics.
Furthermore, the work provided a screening analysis to select the most effective
candidate among the synthesised AC materials, allowing its performance for the
removal of ionic dyes (methyl orange, MO and methylene blue, MB) from water to be evaluated. The most effective candidate, denoted as PNTS2-600-15, was obtained under the following activated conditions: temperature of 600 °C, hold time of 15 min and an impregnation ratio of 2. PNTS2-600-15 showed low moisture and ash contents, indicating the high quality of the sample. The adsorption performance of PNTS2-600-15 for MO and MB dyes was investigated by varying the contact time, solution pH, and initial dye concentration. The experimental data were fitted using a number of kinetic and isotherm models to elucidate the adsorption mechanism, and capacity of the carbon material. The results indicate that a pseudo-second-order kinetic model, and the Freundlich and Sips isotherm models, provided the best fit for the adsorption data of both dyes. The Sips model estimated the maximum adsorption capacities of
PNTS2-600-15 for MO and MB to be 4584 mg g-1 and 1769 mg g-1
, respectively. These show outstanding capacities in comparison with other AC materials reported in the literature. Finally, the mechanism of adsorption involved in the adsorption processes for MO and MB dyes on PNTS2-600-15 was further investigated, using several experimental techniques, such as post-adsorption characterisation of the textural and surface properties of the carbon material, and desorption studies of the adsorbed dyes. The adsorption mechanism was mainly attributed to π–π interactions, n–π electron donor-acceptor (EDA) interactions, and pore filling. The AC material exhibited good reusability and stability, achieving over 90% dye removal, after five cycles of regeneration.
This work demonstrates that peanut shells can be used as a low-cost and effective precursor for AC production, and that the properties and performance of the AC materials can be tuned and tailored by manipulating the activation variables. The work contributes to the development of sustainable and alternative AC materials for water remediation applications.Modern society has undergone rapid industrialization, which has led to various
environmental and health challenges on a global level. Some of the main contributors to these challenges are the industrial discharge of organic dyes, oils, solvents, metal ions etc. and this situation constitutes a serious global concern. Industrial and agricultural effluents are abundant and feasible sources of water; however, these require treatment to protect the ecosystem and enable their reuse. Among various methods employed in the treatment of wastewater, adsorption is one of the most feasible and effective methods. Adsorption processes employ solid materials, known as adsorbents, to facilitate the removal of contaminants from water. Activated carbon (AC) is a widely used adsorbent that has high porosity and adsorption capacity for various contaminants. However, the production of commercial AC faces the challenges of high cost and scarcity of raw materials, due to the high demand of commercial ACs for multiple purposes. Therefore, there is a need to develop low-cost and alternative AC materials by exploring the use of renewable and abundant resources, such as biomass. This work aims to synthesise AC materials from peanut shells, which are an agricultural by-product with high carbon content and potential as a low-cost and renewable precursor for AC production, and to optimise the activation variables (temperature, hold-time, and impregnation ratio, i.e., activating agent weight / precursor weight), to obtain AC materials with high surface areas and yields. Previous studies on peanut shells have lacked a focus in identifying the controlling activation variables to enhance the properties of peanut derived carbon materials. To bridge this gap, the current work employs a single stage chemical activation process, using ZnCl2 as an activating agent, and investigates the effects of activation variables on the properties of AC derived from peanut shells. A design of experiment (DoE) is used to generate a set of experimental design points and obtain a response surface of the results, to visualise the relationship between the responses (surface area and yield) and the independent variables, demonstrating how to model the synthesis of AC from
biomass. The work characterises the AC materials synthesised from peanut shells using various techniques, such as Brunauer-Emmett-Teller (BET) analysis of nitrogen adsorption data, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Textural analysis revealed that the synthesised AC materials have relatively high surface areas and porosities, indicating the effectiveness of the chemical activation method, using ZnCl2 as an activating agent. Response surface analysis revealed that temperature and impregnation ratio were the most significant variables in determining the characteristics of the AC materials derived from peanut shells. As revealed, by both textural and surface chemistry analyses, the synthesised AC materials show heterogeneous characteristics.
Furthermore, the work provided a screening analysis to select the most effective
candidate among the synthesised AC materials, allowing its performance for the
removal of ionic dyes (methyl orange, MO and methylene blue, MB) from water to be evaluated. The most effective candidate, denoted as PNTS2-600-15, was obtained under the following activated conditions: temperature of 600 °C, hold time of 15 min and an impregnation ratio of 2. PNTS2-600-15 showed low moisture and ash contents, indicating the high quality of the sample. The adsorption performance of PNTS2-600-15 for MO and MB dyes was investigated by varying the contact time, solution pH, and initial dye concentration. The experimental data were fitted using a number of kinetic and isotherm models to elucidate the adsorption mechanism, and capacity of the carbon material. The results indicate that a pseudo-second-order kinetic model, and the Freundlich and Sips isotherm models, provided the best fit for the adsorption data of both dyes. The Sips model estimated the maximum adsorption capacities of
PNTS2-600-15 for MO and MB to be 4584 mg g-1 and 1769 mg g-1
, respectively. These show outstanding capacities in comparison with other AC materials reported in the literature. Finally, the mechanism of adsorption involved in the adsorption processes for MO and MB dyes on PNTS2-600-15 was further investigated, using several experimental techniques, such as post-adsorption characterisation of the textural and surface properties of the carbon material, and desorption studies of the adsorbed dyes. The adsorption mechanism was mainly attributed to π–π interactions, n–π electron donor-acceptor (EDA) interactions, and pore filling. The AC material exhibited good reusability and stability, achieving over 90% dye removal, after five cycles of regeneration.
This work demonstrates that peanut shells can be used as a low-cost and effective precursor for AC production, and that the properties and performance of the AC materials can be tuned and tailored by manipulating the activation variables. The work contributes to the development of sustainable and alternative AC materials for water remediation applications
Work, Health, and Wellbeing WE908 Exam papers
No full textNo papers available.PAST EXAM PAPERS ARE NO LONGER BEING ADDED TO STAX. PLEASE VISIT SUPRIMO TO ACCESS AN UP-TO-DATE COLLECTION OF PAST EXAM PAPERS: https://suprimo.lib.strath.ac.uk
Functionalised gelatin for vascular graft sealant applications
No full textGelatin is one of the most widely used biopolymers with many desirable properties including: it is biodegradable, non-toxic, biocompatible, non-immunogenic, easily modified and exhibits good cell adhesion. These characteristics are often tailored and applied in the food, biomedical and pharmaceutical industries. Gelatin hydrogels are often used in the medical field for tissue engineering, drug delivery and as sealants in medical devices. Gelatin is formed by the partial hydrolysis of collagen. The resulting gelatin material is naturally polyampholytic, dissolves readily in water and forms a thermoreversible sol-gel upon cooling. The behaviour of these hydrogels is influenced by the charges located on the amino acid side chains throughout the gelatin molecules.
The presence and distribution of ionisable side chains influences the surface activity of gelatin and ultimately determines the material properties. Side chain modifications can also be performed to achieve the optimum hydrogel properties. Physical gelatin hydrogels are held together by non-covalent interactions which can easily be broken down above 30 °C. Therefore, chemical crosslinking is often carried out to introduce strong covalent interactions into the gelatin network, improving the material mechanical properties and thermal stability. When acting as a vascular graft sealant, the role of gelatin is to decrease the permeability of the graft upon implantation and to serve as a temporary scaffold for cell attachment. The sealant is gradually resorbed by the patient during healing and replaced with human tissue. The infiltration of human tissue is dependent on the extent of crosslinking within the sealant. Therefore, the
sealant and its degree of crosslinking influence the patient healing process.
The initial aim of this research was to develop a greater understanding of gelatin
modifications, with a primary focus on the succinylation modification at the ε-amino group of lysine. The reaction conditions were investigated by altering the pH and mass of reagents. When strict pH was maintained throughout the duration of the reaction, consistently high levels of modification were achieved. Once optimised at the laboratory scale, these reaction parameters were implemented in a series of development runs at pilot scale for company material validation studies. The succinylation reaction was also successful at this scale and subsequent development work focussed on material purification solutions. The ionisable side chains present throughout gelatin influences the material properties of the hydrogel and makes them susceptible to changes at various pH values and salt concentrations. The influence of pH and salt species on the mechanical properties and underlying material morphology were investigated. When adjusted to more acidic or alkaline pH values, larger swelling ratios and softer gelatin blocks were observed due to unbalanced surface charges and increased electrostatic repulsion. Conversely, at pH values close to the isoelectric point, the materials exhibited lower swelling ratios and firmer gelatin blocks due to balanced surface charges and minimised electrostatic repulsion. These Coulombic interactions dictate the hydrogel properties. The presence
of salt species of different concentrations and valency were also found to have an influence on gelatin properties. The ionic species had the largest influence on material swelling, while gelatin block firmness and gelling temperatures were only notably impacted at the highest salt concentration tested. It was very difficult to discern any distinct trends from the data as the values fluctuated. However, it was observed that divalent salt species had more of an impact on the hydrogel properties compared to the monovalent salts. The multivalent salt species displayed crosslinking abilities that limited gelatin solubility. Alternative side chain modifications were performed and optimised to study the influence of different side chain chemistries on the hydrogel properties. As with the succinylation reaction, the modifications were reproducible when strict pH was maintained and high degrees of modification were achieved. As a result of different side chain hydrophilicity and steric bulk, the materials exhibited different swelling behaviour, mechanical properties and specific rotation. Glyoxal crosslinking was explored as an alternative to formaldehyde. However, after glyoxal crosslinking the materials exhibited different trends in terms of material swelling and firmness. Inverse swelling behaviour was observed, while hydrogel softening was exhibited by all samples. To satisfy the manufacturing element of this PhD, vascular grafts were made using laboratory succinylated gelatin. The 50:50 blend of non-succinylated and laboratory succinylated gelatin was an effective sealant for the Terumo Aortic Gelweave™ vascular grafts. The sealant blend showed excellent properties, preventing blood leakage while degrading within the required timeframe.Gelatin is one of the most widely used biopolymers with many desirable properties including: it is biodegradable, non-toxic, biocompatible, non-immunogenic, easily modified and exhibits good cell adhesion. These characteristics are often tailored and applied in the food, biomedical and pharmaceutical industries. Gelatin hydrogels are often used in the medical field for tissue engineering, drug delivery and as sealants in medical devices. Gelatin is formed by the partial hydrolysis of collagen. The resulting gelatin material is naturally polyampholytic, dissolves readily in water and forms a thermoreversible sol-gel upon cooling. The behaviour of these hydrogels is influenced by the charges located on the amino acid side chains throughout the gelatin molecules.
The presence and distribution of ionisable side chains influences the surface activity of gelatin and ultimately determines the material properties. Side chain modifications can also be performed to achieve the optimum hydrogel properties. Physical gelatin hydrogels are held together by non-covalent interactions which can easily be broken down above 30 °C. Therefore, chemical crosslinking is often carried out to introduce strong covalent interactions into the gelatin network, improving the material mechanical properties and thermal stability. When acting as a vascular graft sealant, the role of gelatin is to decrease the permeability of the graft upon implantation and to serve as a temporary scaffold for cell attachment. The sealant is gradually resorbed by the patient during healing and replaced with human tissue. The infiltration of human tissue is dependent on the extent of crosslinking within the sealant. Therefore, the
sealant and its degree of crosslinking influence the patient healing process.
The initial aim of this research was to develop a greater understanding of gelatin
modifications, with a primary focus on the succinylation modification at the ε-amino group of lysine. The reaction conditions were investigated by altering the pH and mass of reagents. When strict pH was maintained throughout the duration of the reaction, consistently high levels of modification were achieved. Once optimised at the laboratory scale, these reaction parameters were implemented in a series of development runs at pilot scale for company material validation studies. The succinylation reaction was also successful at this scale and subsequent development work focussed on material purification solutions. The ionisable side chains present throughout gelatin influences the material properties of the hydrogel and makes them susceptible to changes at various pH values and salt concentrations. The influence of pH and salt species on the mechanical properties and underlying material morphology were investigated. When adjusted to more acidic or alkaline pH values, larger swelling ratios and softer gelatin blocks were observed due to unbalanced surface charges and increased electrostatic repulsion. Conversely, at pH values close to the isoelectric point, the materials exhibited lower swelling ratios and firmer gelatin blocks due to balanced surface charges and minimised electrostatic repulsion. These Coulombic interactions dictate the hydrogel properties. The presence
of salt species of different concentrations and valency were also found to have an influence on gelatin properties. The ionic species had the largest influence on material swelling, while gelatin block firmness and gelling temperatures were only notably impacted at the highest salt concentration tested. It was very difficult to discern any distinct trends from the data as the values fluctuated. However, it was observed that divalent salt species had more of an impact on the hydrogel properties compared to the monovalent salts. The multivalent salt species displayed crosslinking abilities that limited gelatin solubility. Alternative side chain modifications were performed and optimised to study the influence of different side chain chemistries on the hydrogel properties. As with the succinylation reaction, the modifications were reproducible when strict pH was maintained and high degrees of modification were achieved. As a result of different side chain hydrophilicity and steric bulk, the materials exhibited different swelling behaviour, mechanical properties and specific rotation. Glyoxal crosslinking was explored as an alternative to formaldehyde. However, after glyoxal crosslinking the materials exhibited different trends in terms of material swelling and firmness. Inverse swelling behaviour was observed, while hydrogel softening was exhibited by all samples. To satisfy the manufacturing element of this PhD, vascular grafts were made using laboratory succinylated gelatin. The 50:50 blend of non-succinylated and laboratory succinylated gelatin was an effective sealant for the Terumo Aortic Gelweave™ vascular grafts. The sealant blend showed excellent properties, preventing blood leakage while degrading within the required timeframe
In Silico size effects in cancellous bone
Full text linkCancellous bone is a heterogeneous material with a complex lattice microstructure. The description of this microstructure in terms of the mechanical properties of cancellous bone exhibited on the macroscopic scale is important in the understanding of periprosthetic stress concentrations which eventually lead to aseptic loosening or radiolucency in implants. Micropolar elasticity is a higher order continuum theory which could potentially used to describe the influence of the microstructure of cancellous bone on its mechanical behaviour at a macroscopic scale. This theory predicts a size effect behaviour in bending and torsion while predicted no size effect behaviour in compression. This has been investigated computationally and validated experimentally using bovine distal femoral trabecular bone. Computational models of various idealised lattice models have also been analysed and compared to priorly investigated models. It was observed that the idealised lattice models exhibited size effect behaviour as predicted by micropolar theory whilst the experimental models and the computational models of cancellous bone exhibited a size effect behaviour that was opposite to that predicted by micropolar theory. The ramifications of this are that micropolar theory may not be suitable to model the size effect behaviour of trabecular bone and that further mathematical models and/or idealised lattice arrays may need to be further investigated to create a more accurate representation of trabecular bone. These findings are important because they in silico testing has been validated through experimental testing. Analysis of the stress and strain distributions also provides insight as to why size effects that are opposite to those predicted by micropolar theory have been observed both in silico and experimentally.Cancellous bone is a heterogeneous material with a complex lattice microstructure. The description of this microstructure in terms of the mechanical properties of cancellous bone exhibited on the macroscopic scale is important in the understanding of periprosthetic stress concentrations which eventually lead to aseptic loosening or radiolucency in implants. Micropolar elasticity is a higher order continuum theory which could potentially used to describe the influence of the microstructure of cancellous bone on its mechanical behaviour at a macroscopic scale. This theory predicts a size effect behaviour in bending and torsion while predicted no size effect behaviour in compression. This has been investigated computationally and validated experimentally using bovine distal femoral trabecular bone. Computational models of various idealised lattice models have also been analysed and compared to priorly investigated models. It was observed that the idealised lattice models exhibited size effect behaviour as predicted by micropolar theory whilst the experimental models and the computational models of cancellous bone exhibited a size effect behaviour that was opposite to that predicted by micropolar theory. The ramifications of this are that micropolar theory may not be suitable to model the size effect behaviour of trabecular bone and that further mathematical models and/or idealised lattice arrays may need to be further investigated to create a more accurate representation of trabecular bone. These findings are important because they in silico testing has been validated through experimental testing. Analysis of the stress and strain distributions also provides insight as to why size effects that are opposite to those predicted by micropolar theory have been observed both in silico and experimentally
Iridium-catalysed hydrogen isotope exchange of n-heterocycles and nucleosides
No full textThe investigation of ADMET properties plays a crucial role in the development of any new chemical entity (NCE), with hydrogen isotope exchange heavily utilised for the late-stage labelling of target compounds. Iridium-catalysed methods, which have been extensively developed by Kerr and co-workers, have largely proceeded via directed metallacyclic intermediates with a wide range of directing groups well tolerated. This thesis describes the development of new iridium-catalysed methodologies specifically designed to label the αnitrogen position of pyridines and other heterocycles. The labelling of pyridines has been extensively optimised and explored, with methodologies developed to encompass pyridines with a variety of substitution patterns. High deuterium incorporations have been obtained across a wide range pyridine substrates and positions, with the methodologies expanded to include other N-heteroaromatics. In addition, a range of drug molecules have been subjected to both deuteration and tritiation, with a high degree of reactivity. An initial mechanistic investigation has additionally been carried out, utilising both experimental and computational studies to provide evidence towards a mechanistic proposal. Additionally, as part of a modernisation program to prior computational mechanistic studies, new insights into the nature of hydrogen fluxionality have been realised. Using a variety of computational methods, a new transition state for hydrogen fluxionality has been identified and new factors, including quantum tunnelling and relativistic effects, have been explored. In addition to the ongoing DFT studies, experimental investigations into kinetic isotope effect have revealednew considerations, such as the rate of gas exchange with reaction stirring speeds playing a particularly important role. Finally, an initial investigation has been conducted to examine hydrogen isotope exchange in nucleosides. This area of research is relatively underexplored; however, an extensive catalyst screen has permitted the development of a methodology which affords modest incorporationsacross a range of unprotected nucleosides. This provides an excellent starting platform for further development which shall continue in the future.The investigation of ADMET properties plays a crucial role in the development of any new chemical entity (NCE), with hydrogen isotope exchange heavily utilised for the late-stage labelling of target compounds. Iridium-catalysed methods, which have been extensively developed by Kerr and co-workers, have largely proceeded via directed metallacyclic intermediates with a wide range of directing groups well tolerated. This thesis describes the development of new iridium-catalysed methodologies specifically designed to label the αnitrogen position of pyridines and other heterocycles. The labelling of pyridines has been extensively optimised and explored, with methodologies developed to encompass pyridines with a variety of substitution patterns. High deuterium incorporations have been obtained across a wide range pyridine substrates and positions, with the methodologies expanded to include other N-heteroaromatics. In addition, a range of drug molecules have been subjected to both deuteration and tritiation, with a high degree of reactivity. An initial mechanistic investigation has additionally been carried out, utilising both experimental and computational studies to provide evidence towards a mechanistic proposal. Additionally, as part of a modernisation program to prior computational mechanistic studies, new insights into the nature of hydrogen fluxionality have been realised. Using a variety of computational methods, a new transition state for hydrogen fluxionality has been identified and new factors, including quantum tunnelling and relativistic effects, have been explored. In addition to the ongoing DFT studies, experimental investigations into kinetic isotope effect have revealednew considerations, such as the rate of gas exchange with reaction stirring speeds playing a particularly important role. Finally, an initial investigation has been conducted to examine hydrogen isotope exchange in nucleosides. This area of research is relatively underexplored; however, an extensive catalyst screen has permitted the development of a methodology which affords modest incorporationsacross a range of unprotected nucleosides. This provides an excellent starting platform for further development which shall continue in the future
Heterogeneous integration of ZnCdSe/ZnCdMgSe vertical-external-cavity surface-emitting laser heterostructures
Full text linkThe wide bandgap ZnCdMgSe-on-InP material system offers the opportunity to develop vertical-external-cavity surface-emitting lasers (VECSELs) with a fundamental emission at typically hard to reach visible wavelengths (540 nm – 590 nm). This thesis reports the progress towards the development of this novel laser system.The material parameters of the ZnCdMgSe-on-InP material system are less studied than their more mature III-V counterparts and so in this work a literature review is conducted and a list of all parameters necessary to design a ZnCdMgSe-based VECSEL are summarized. A simple model of the material gain of a ZnCdSe/ZnCdMgSe quantum well (QW) is assessed and used to inform an analysis, based on that proposed by Kuznetsov for infrared VECSELs [1], to calculate the optimum gain structure design for a 565 nm emitting ZnCdMgSe-based distributed-Bragg-reflector-free (DBR-free) VECSEL. The optimum structure consisted of 4 pairs of ZnCdSe/ZnCdMgSe QWs, spaced with a resonant periodic gain arrangement. The molecular beam epitaxial growth of this structure is completed and multiple growth campaigns are used to iteratively improve the material quality by varying the thicknesses of the II-VI and InGaAs buffer layers that are required for growth on InP substrates.ZnCdMgSe DBR-free VECSEL structures need to undergo epitaxial lift off from their native (001) InP substrate, as it is opaque at visible wavelengths. The resulting ZnCdMgSe membranes need to be transferred onto single crystal, high thermal conductivity, intra cavity, transparent heatspreaders such as diamond or silicon carbide (SiC) to achieve efficient thermal management. A full substrate removal method is developed to yield cm2 sized QW membranes, which are subsequently broken into pieces and bonded to diamond. The low quality membranes produced by the full substrate removal method did not reach the laser threshold. The low membrane quality is attributed to damage induced by the HCl based wet etching of the InP substrate and the handling of membranes in liquid suspension.Due to the poor results of the full substrate removal a suspension and transfer printing method was developed for the ZnCdMgSe-on-InP material system: 100-μm-sided square membranes held by anchors to rails were patterned into a ZnCdMgSe layer, had sidewall protection applied and were under-etched using a three step wet etch to liberate them from the InP substrate and remove the InGaAs buffer layer. The resulting ZnCdMgSe membranes exhibit nm-scale root mean quare surface roughness and are transfer printed onto diamond, a result which highlights promise for the future heterogeneous integration of the ZnCdMgSe. The same suspension and transfer printing method is adapted to a GaInP/AlGaInP, DBR-free VECSEL structure and used to transfer print DBR-free VECSEL membranes onto diamond. The ZnCdMgSe and GaInP/AlGaInP membranes undergo surface roughness, photoluminescence and Raman spectroscopy characterization, which reveals that sidewall protection and under-etch chemistry improvements are required for transfer printed DBR-free VECSEL membranes to reach threshold.The wide bandgap ZnCdMgSe-on-InP material system offers the opportunity to develop vertical-external-cavity surface-emitting lasers (VECSELs) with a fundamental emission at typically hard to reach visible wavelengths (540 nm – 590 nm). This thesis reports the progress towards the development of this novel laser system.The material parameters of the ZnCdMgSe-on-InP material system are less studied than their more mature III-V counterparts and so in this work a literature review is conducted and a list of all parameters necessary to design a ZnCdMgSe-based VECSEL are summarized. A simple model of the material gain of a ZnCdSe/ZnCdMgSe quantum well (QW) is assessed and used to inform an analysis, based on that proposed by Kuznetsov for infrared VECSELs [1], to calculate the optimum gain structure design for a 565 nm emitting ZnCdMgSe-based distributed-Bragg-reflector-free (DBR-free) VECSEL. The optimum structure consisted of 4 pairs of ZnCdSe/ZnCdMgSe QWs, spaced with a resonant periodic gain arrangement. The molecular beam epitaxial growth of this structure is completed and multiple growth campaigns are used to iteratively improve the material quality by varying the thicknesses of the II-VI and InGaAs buffer layers that are required for growth on InP substrates.ZnCdMgSe DBR-free VECSEL structures need to undergo epitaxial lift off from their native (001) InP substrate, as it is opaque at visible wavelengths. The resulting ZnCdMgSe membranes need to be transferred onto single crystal, high thermal conductivity, intra cavity, transparent heatspreaders such as diamond or silicon carbide (SiC) to achieve efficient thermal management. A full substrate removal method is developed to yield cm2 sized QW membranes, which are subsequently broken into pieces and bonded to diamond. The low quality membranes produced by the full substrate removal method did not reach the laser threshold. The low membrane quality is attributed to damage induced by the HCl based wet etching of the InP substrate and the handling of membranes in liquid suspension.Due to the poor results of the full substrate removal a suspension and transfer printing method was developed for the ZnCdMgSe-on-InP material system: 100-μm-sided square membranes held by anchors to rails were patterned into a ZnCdMgSe layer, had sidewall protection applied and were under-etched using a three step wet etch to liberate them from the InP substrate and remove the InGaAs buffer layer. The resulting ZnCdMgSe membranes exhibit nm-scale root mean quare surface roughness and are transfer printed onto diamond, a result which highlights promise for the future heterogeneous integration of the ZnCdMgSe. The same suspension and transfer printing method is adapted to a GaInP/AlGaInP, DBR-free VECSEL structure and used to transfer print DBR-free VECSEL membranes onto diamond. The ZnCdMgSe and GaInP/AlGaInP membranes undergo surface roughness, photoluminescence and Raman spectroscopy characterization, which reveals that sidewall protection and under-etch chemistry improvements are required for transfer printed DBR-free VECSEL membranes to reach threshold
Identification and quantification of antibiofilm metabolite extracts using electrochemical techniques
Full text linkCurrently 2.29% of deaths worldwide are caused by antimicrobial resistance (AMR), this is compared to 1.16% caused by malaria, and 1.55% caused by human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDs). Furthermore, deaths from AMR are projected to increase to more than 10 million per annum by 2050. Bacteria within biofilms have shown resistance to 1000-fold higher concentrations of antibiotics than planktonic cells. This is due to the bacteria entering a dormant-like state, reducing their growth rate. As many antibiotics target mechanisms of active metabolism, these are less effective. New antibiofilm-metabolites are needed to inhibit biofilm formation and target established biofilms. Bacteria from the marine environment are a rich, untapped source of novel bioactive metabolites, many of which have not been tested for antibiofilm properties. However, the current methods of screening for antibiofilm activity and quantification of biofilms are slow, and do not provide crucial information, such as time to eradication. This thesis aims to tap into this rich marine biodiversity. To fulfil this, strains were isolated from Scottish marine sediments, and screened these for their antibiotic and antibiofilm potential. Their metabolites were subsequently extracted and analysed using tandem mass spectrometry to identify the bioactive compound. Alongside this, we aimed to develop a method for biofilm quantification which could be translated into the clinical setting, as well as used in the screening of antibiofilm agents. This was carried out alongside crystal violet staining, as a published point of reference. The developed electrochemical techniques, electrochemical impedance spectroscopy and square wave voltammetry, were able to detect P. aeruginosa biofilm formation within an hour after seeding P. aeruginosa on the sensor. This showed that there was a 40% decrease in impedance modulus when P. aeruginosa biofilm had formed, compared to the media only control. This was also compared to a non-biofilm forming mutant, which showed only a 9% decrease in impedance modulus also compared to the media only control. As such, this thesis offers a starting point for the development of real-time biofilm sensing technologies, which can be translated into implantable materials.Currently 2.29% of deaths worldwide are caused by antimicrobial resistance (AMR), this is compared to 1.16% caused by malaria, and 1.55% caused by human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDs). Furthermore, deaths from AMR are projected to increase to more than 10 million per annum by 2050. Bacteria within biofilms have shown resistance to 1000-fold higher concentrations of antibiotics than planktonic cells. This is due to the bacteria entering a dormant-like state, reducing their growth rate. As many antibiotics target mechanisms of active metabolism, these are less effective. New antibiofilm-metabolites are needed to inhibit biofilm formation and target established biofilms. Bacteria from the marine environment are a rich, untapped source of novel bioactive metabolites, many of which have not been tested for antibiofilm properties. However, the current methods of screening for antibiofilm activity and quantification of biofilms are slow, and do not provide crucial information, such as time to eradication. This thesis aims to tap into this rich marine biodiversity. To fulfil this, strains were isolated from Scottish marine sediments, and screened these for their antibiotic and antibiofilm potential. Their metabolites were subsequently extracted and analysed using tandem mass spectrometry to identify the bioactive compound. Alongside this, we aimed to develop a method for biofilm quantification which could be translated into the clinical setting, as well as used in the screening of antibiofilm agents. This was carried out alongside crystal violet staining, as a published point of reference. The developed electrochemical techniques, electrochemical impedance spectroscopy and square wave voltammetry, were able to detect P. aeruginosa biofilm formation within an hour after seeding P. aeruginosa on the sensor. This showed that there was a 40% decrease in impedance modulus when P. aeruginosa biofilm had formed, compared to the media only control. This was also compared to a non-biofilm forming mutant, which showed only a 9% decrease in impedance modulus also compared to the media only control. As such, this thesis offers a starting point for the development of real-time biofilm sensing technologies, which can be translated into implantable materials
A collaborative framework to regulate arbitrator practice in investor-state arbitration : the case of oil and gas disputes
Full text linkInvestor-state arbitration comes under increasing criticism regarding arbitrators’ integrity, suggesting that arbitrators favour investors in their decisions in oil and gas disputes. This constitutes a great challenge for the legitimacy of the investor-state arbitration. Accordingly, some oil and gas countries have withdrawn from the system and (ICSID) membership. In view of that issue, this thesis represented a comprehensive analysis of the disqualifications to the independence and impartiality of arbitrators in oil and gas investment disputes. This analysis asserted that from the total of (34) arbitrators’ disqualifications in oil and gas disputes there were (25) disqualifications submitted by respondents’ states. The disqualifications were based on repeated appointments, arbitrator professional relationships and deciding similar legal issues in prior cases in oil and gas disputes. This indicated that there was a small elite number of arbitrators were selected often. Also, the thesis analysed the regulatory framework that governs such disqualifications and confirmed that there were inequities in the disqualification standards of arbitration rules applied to determine the disqualification of arbitrators. Indeed, successful arbitrators’ disqualifications were higher under the (UNCITRAL) rules than under the (ICSID) rules. From the total (34) disqualifications requests in oil and gas disputes only (4) successful disqualifications requests were under the (ICSID) cases and (19) disqualifications were rejected. These findings support the aim of research for developing a collaborative framework to regulate arbitrator practice in investor-state arbitration that will be used as a guide to identify more professional arbitrators for oil and gas disputes in investor-state arbitration.
Thus, the primary objective of this thesis was to propose the creation of an independent third-party certifier body based on transitional private regulation (TPR). Establishing a certification scheme for arbitrators could combat the concerns of states and investors about arbitrators’ integrity and strengthen the regulatory legal framework, improve arbitrators’ selection and appointment, and enlarge the arbitrators’ pool in oil and gas disputes. The thesis proposal aligned with the recent movement of (ICSID) and (UNCITRAL) toward professional regulation by introducing a collaborative code of conduct for arbitrators in investment arbitration. Finally, this thesis hoped to influence these efforts and encourage states and the investor-state arbitration community to take steps to create professional certifications to maintain the legitimacy of the regime and resort confidence in the system and continue to promote the growth of the global economy.Investor-state arbitration comes under increasing criticism regarding arbitrators’ integrity, suggesting that arbitrators favour investors in their decisions in oil and gas disputes. This constitutes a great challenge for the legitimacy of the investor-state arbitration. Accordingly, some oil and gas countries have withdrawn from the system and (ICSID) membership. In view of that issue, this thesis represented a comprehensive analysis of the disqualifications to the independence and impartiality of arbitrators in oil and gas investment disputes. This analysis asserted that from the total of (34) arbitrators’ disqualifications in oil and gas disputes there were (25) disqualifications submitted by respondents’ states. The disqualifications were based on repeated appointments, arbitrator professional relationships and deciding similar legal issues in prior cases in oil and gas disputes. This indicated that there was a small elite number of arbitrators were selected often. Also, the thesis analysed the regulatory framework that governs such disqualifications and confirmed that there were inequities in the disqualification standards of arbitration rules applied to determine the disqualification of arbitrators. Indeed, successful arbitrators’ disqualifications were higher under the (UNCITRAL) rules than under the (ICSID) rules. From the total (34) disqualifications requests in oil and gas disputes only (4) successful disqualifications requests were under the (ICSID) cases and (19) disqualifications were rejected. These findings support the aim of research for developing a collaborative framework to regulate arbitrator practice in investor-state arbitration that will be used as a guide to identify more professional arbitrators for oil and gas disputes in investor-state arbitration.
Thus, the primary objective of this thesis was to propose the creation of an independent third-party certifier body based on transitional private regulation (TPR). Establishing a certification scheme for arbitrators could combat the concerns of states and investors about arbitrators’ integrity and strengthen the regulatory legal framework, improve arbitrators’ selection and appointment, and enlarge the arbitrators’ pool in oil and gas disputes. The thesis proposal aligned with the recent movement of (ICSID) and (UNCITRAL) toward professional regulation by introducing a collaborative code of conduct for arbitrators in investment arbitration. Finally, this thesis hoped to influence these efforts and encourage states and the investor-state arbitration community to take steps to create professional certifications to maintain the legitimacy of the regime and resort confidence in the system and continue to promote the growth of the global economy
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