Browsing by Author "Impey, Susan A."
Now showing 1 - 20 of 26
Results Per Page
Sort Options
Item Open Access 3D characterisation of tool wear whilst diamond turning silicon(Elsevier Science B.V., Amsterdam., 2006-07-24T00:00:00Z) Durazo-Cardenas, Isidro; Shore, Paul; Luo, X.; Jacklin, T.; Impey, Susan A.; Cox, A.Nanometrically smooth infrared silicon optics can be manufactured by the diamond turning process. Due to its relatively low density, silicon is an ideal optical material for weight sensitive infrared (IR) applications. However, rapid diamond tool edge degradation and the effect on the achieved surface have prevented significant exploitation. With the aim of developing a process model to optimise the diamond turning of silicon optics, a series of experimental trials were devised using two ultra-precision diamond turning machines. Single crystal silicon specimens (1 1 1) were repeatedly machined using diamond tools of the same specification until the onset of surface brittle fracture. Two cutting fluids were tested. The cutting forces were monitored and the wear morphology of the tool edge was studied by scanning electron microscopy (SEM). The most significant result showed the performance of one particular tool was consistently superior when compared with other diamond tools of the same specification. This remarkable tool performance resulted in doubling the cutting distance exhibited by the other diamond tools. Another significant result was associated with coolant type. In all cases, tool life was prolonged by as much as 300% by using a specific fluid type. Further testing led to the development of a novel method for assessing the progression of diamond tool wear. In this technique, the diamond tools gradual recession profile is measured by performing a series of plunging cuts. Tool shape changes used in conjunction with flank wear SEM measurements enable the calculation of the volumetric tool wear rate.Item Open Access Additive manufacturing and physicomechanical characteristics of PEGDA hydrogels: recent advances and perspective for tissue engineering(MDPI, 2023-05-17) Khalili, Mohammad Hakim; Zhang, Rujing; Wilson, Sandra; Goel, Saurav; Impey, Susan A.; Aria, Adrianus IndratIn this brief review, we discuss the recent advancements in using poly(ethylene glycol) diacrylate (PEGDA) hydrogels for tissue engineering applications. PEGDA hydrogels are highly attractive in biomedical and biotechnology fields due to their soft and hydrated properties that can replicate living tissues. These hydrogels can be manipulated using light, heat, and cross-linkers to achieve desirable functionalities. Unlike previous reviews that focused solely on material design and fabrication of bioactive hydrogels and their cell viability and interactions with the extracellular matrix (ECM), we compare the traditional bulk photo-crosslinking method with the latest three-dimensional (3D) printing of PEGDA hydrogels. We present detailed evidence combining the physical, chemical, bulk, and localized mechanical characteristics, including their composition, fabrication methods, experimental conditions, and reported mechanical properties of bulk and 3D printed PEGDA hydrogels. Furthermore, we highlight the current state of biomedical applications of 3D PEGDA hydrogels in tissue engineering and organ-on-chip devices over the last 20 years. Finally, we delve into the current obstacles and future possibilities in the field of engineering 3D layer-by-layer (LbL) PEGDA hydrogels for tissue engineering and organ-on-chip devices.Item Open Access Analysis of infrared optical polishing effluents and reduction of COD and TSS levels by ultrafiltration and coagulation/flocculation(Taylor & Francis, 2014-01-27) Durazo-Cardenas, Isidro; Noguera-Sagrera, Albert; Impey, Susan A.Samples of polishing effluent produced during infrared optics manufacture were analyzed. Their particle size, composition, Zeta potential, chemical oxygen demand (COD), total suspended solids (TSS), and settleable solids were determined. Feasibility of treatment methods such as ultrafiltration (UF) and coagulation/flocculation was investigated to reduce both COD and TSS. It was found that effluents consisted of a suspension of micro- and nanoparticles. Effluent particle size distribution reflected the removal rate of the originating polishing process. Their composition was primarily germanium and other polished substrates as well as polishing abrasives. The effluent Zeta potential was highly negative and prevented particle settling. COD of all specimens was very high, which prevented sewage discharge. Laboratory-scale trials using UF showed substantial COD abatement of up to 74.1%. TSS was reduced to zero after UF. Comparable coagulation/flocculation COD abatement was demonstrated for the highest COD sample.Item Open Access Best practice indicators for new product development at universities(Cranfield University, 2014-02) Iglesias Bares, Belen; Williams, Leon; Impey, Susan A.It is public domain that the development of new products is a crucial activity for business success. Since new product development (NPD) is only conceived as a process within the industry environment, nearly all of the studies on this topic are empirically driven. The most important, and common ones, are based on surveys that look for the habits, methods, and approaches of the best performers, in order to distil NPD best practice. Academics and practitioners generally agree that the environment at small new ventures may differ significantly from the NPD environment at large and medium sized firms. Nevertheless, the advantages attributed to the NPD best practice at large and medium sized companies may also benefit small organisations, including university projects. However, the application of this best practice within university projects needs more exploration. This gap in the knowledge should be investigated since cooperating with external partners a key trend in NPD. Here, the scientist’s expertise and the extensive resources of research universities can make them excellent partners. This study aspires to answer the question “Is new product development at universities performed properly?”. It addresses this debate by carrying out a systematic review, a content analysis, and a benchmarking performance in order to identify six indicators that are associated with higher degree of NPD success in the university environment. Subsequently, empirical data regarding the use of those practices at universities is collected using a questionnaire, then the data is analysed statistically. The results report an alignment of the NPD executed at universities with the NPD best practice indicators. The fulfillment is also compared with industry execution. Finally, the NPD best practice indicators, particularly those that universities perform noticeably better or worse than industry, are discussed. The study provides a tool-questionnaire to organisations interested in assessing outsourced NPD processes (particularly those performed at universities). The results obtained with this tool can be benchmarked with the industry and universities’ data. This study also allows teams engaged in NPDs at universities to determine the weaknesses (i.e. methods and practices that are not usually applied) in this specific environment.Item Open Access Characterising flow with continuous aeration in an oscillatory baffle flow reactor using residence time distribution(Royal Society of Chemistry, 2023-08-30) Cox, Rylan; Salonitis, Konstantinos; Impey, Susan A.; Rebrov, EvgenyMulti-phase flow occurs in many reactions with gas, an integral part of the reaction. This study assesses the synergistic impact of continuous aeration and velocity ratio on mixing conditions within an oscillatory baffled flow reactor to enhance the degree of plug flow, quantified by a tanks-in-series (TiS) model. A bubbly flow regime is shown in all experiments. In most cases, the TiS value was reduced with gas flow, and a maximum TiS value of 23.6 was achieved at a velocity ratio of 3.8 at 225 ml min−1 in a counter-current direction. Single-phase runs and co-current multi-phase runs produced maximum TiS values of 23.5 and 18.2 respectively at a velocity ratio of 2.2. Regardless of the gas flow rate, the velocity ratio was found to be the most influential factor that dictates the level of plug flow within the OBR. A predictive model is developed and used to maximise the mixing efficiency by determining the level of plug flow within the OBR at selected amplitudes, frequencies, and gas flow rates.Item Open Access Control of Magnesium Alloy Corrosion through the Use of Engineered Intermetallics(Cranfield University, 2014-12) Pidcock, Andrew; Robinson, M. J.; Impey, Susan A.The low density and high relative strength of Mg alloys means they can offer engineering benefits over steels or Al alloys. However, the susceptibility of Mg alloys to corrosion has limited their exploitation and restricted their use to more benign environments. An Mg-Al intermetallic surface layer is a good candidate for a robust corrosion protection method. This work demonstrates their development by using a novel ionic liquid electroplating process to deposit Al on to Mg substrates that when heat treated diffuses to form discrete intermetallic layers. Examination of three Mg-Al-Zn alloys showed that the amount Mg-Al intermetallic phases in their microstructures was linked to the quantity of Al they contained. Subsequent self-corrosion measurements using electrochemical impedance spectroscopy demonstrated that their performance was connected to the amount of intermetallic present, and in particular the strength of the micro-galvanic couples generated between the anodic and cathodic phases. Measurements of the self-corrosion behaviour of manufactured samples of the Mg-Al intermetallics confirmed that they could provide significant improvements, but it was acknowledged that their noble nature compared to an Mg substrate would encourage galvanic corrosion if a surface layer was damaged. As such the galvanic activity of the Mg-Al-Zn alloys and Mg-Al intermetallics was compared against a pure Mg standard using zero resistance ammetry and the resistance box technique. Galvanic models of alloy self-corrosion and a damaged intermetallic surface layer were also used to assess the potential problem. These measurements demonstrated that the intermetallics could act as strong cathodes, but further discussion on the nature of the behaviour suggested means by which galvanic corrosion might self-limit or self-repair. The galvanic corrosion experiments also revealed how the combination of current flow and a solution saturated with Mg2+ ions could lead to the formation of a highly protective Mg(OH)2 film with promising characteristics.Item Open Access Corrosion behaviour of wire plus arc additive manufacturing (WAAM) built high strength pipeline steels(2022-03-01) Shehu, Najib Usman; Impey, Susan A.; Ganguly, SupriyoWire and Arc Additive Manufacturing (WAAM) is of interest for many industries that requires parts with complex geometries via metal 3D printing. WAAM is capable of producing metal components with high deposition rates, large build volumes, minimum material waste and lead times and good structural integrity. Previous research in this field has focused on achieving correct geometrical and defect free deposition, while maintaining good mechanical properties when compared with wrought alloy. This is the first investigated study devoted to the corrosion behaviour of WAAM pipeline steels in artificial seawater. The corrosion rate of electrode rod 90 solid (ER90S-G) WAAM deposited low alloy steel (as deposited and heat-treated conditions) were compared to F22 wrought alloy of similar chemical composition. Corrosion behaviour of the low alloy steels were assessed using mass loss and electrochemical characterisation and correlated to the microstructural characteristics and hardness. The experimental results showed improved corrosion resistance and strength in ER90 WAAM built low alloy as compared to the wrought. Optical micrographs and hardness measurements confirmed that a martensitic structure was formed under air cooled condition in as deposited ER90, while tempered-martensitic structures were observed in heat treated ER90 and F22 wrought alloy steels. This research is the first step in creation of corrosion data of WAAM built structures and compare to their wrought version. This underpinning correlation between microstructural variation and corrosion pattern would allow modification of the WAAM process in a suitable manner for successful commercial applications.Item Open Access Corrosion of high strength pipeline steel weldment using submerged jet impingement.(2019-03) Nofrizal; Impey, Susan A.; Georgarakis, KonstantinosThe aim of this research is to evaluate submerged jet impingement (SJI) as a tool for assessing the effect of flow and the associated corrosion behaviour across an X65 high strength pipeline weldment. The focus is corrosion caused by turbulent artificial sea water at different velocities impinging onto the weldment. An SJI target consisting of 3 rings (centre, inner and outer) based on a previous design [13], was constructed from an X65 pipeline steel weldment. Parent material (PM), heat affected zone (HAZ) and weld metal (WM) are analysed together in a high shear stress environment and changes in the weldment in a range of hydrodynamic conditions evaluated. Electrochemical measurements were performed with X65 pipeline steel with stagnant and flowing artificial seawater saturated with carbon dioxide at 1 bar at 0 -10 m/s at 25˚C and pH 4. The behaviour with and without an inhibitor was also examined. Galvanic current characteristics between coupled weldment regions were recorded using a zero-resistance ammeter (ZRA), and self-corrosion analysed using linear polarisation resistance (LPR) measurements. Computational fluid dynamic (CFD) analysis was undertaken to understand the hydrodynamic effects and velocity changes across the SJI target in flowing conditions. The velocity distribution across the target varied in each weld region where the centre, outer and inner electrodes are 25, 33 and 50% of the impinging jet velocity respectively. The inner electrodes of the SJI target experience 30% of the expected wall shear stress calculated from the impinging jet velocity. Alternative SJI target configurations are proposed to represent a wide range of shear stress and fluid velocities across the target with good precision and accuracy. For low turbulence, the target centre electrode is minimised or placed at the target edge. To achieve maximum turbulence, an electrode 4 mm from the target centre is proposed. To achieve 10 m/s on the suggested target, a jet velocity of just over 15 m/s is required.Item Open Access Effects of long-term exposure to the low-earth orbit environment on drag augmentation systems(IAF, 2020-10-14) Serfontein, Zaria; Kingston, Jennifer; Hobbs, Stephen; Holbrough, Ian E.; Beck, James C.; Impey, Susan A.; Aria, Adrianus IndratSpacecraft in low-Earth orbit are exposed to environmental threats which can lead to material degradation and component failures. The presence of atomic oxygen and collisions from orbital debris have detrimental effects on the structures, thus affecting their performance. Cranfield University has developed a family of drag augmentation systems (DAS), for end-of-life de-orbit of satellites, addressing the space debris challenge and ensuring that satellites operate responsibly and sustainably. Deorbit devices are stowed on-orbit for the duration of the mission lifetime and, once deployed, the devices must withstand this harsh low-Earth environment until re-entry; a process which can take several years. The DAS’ deployable aluminised Kapton sails are particularly susceptible to undercutting by atomic oxygen. In preparation for commercialising the DAS, Cranfield University and Belstead Research Ltd. have submitted several joint proposals to better understand the degradation process of the drag sail materials and to qualify the materials for the specific application of drag sails in low Earth Orbit (LEO). This paper will outline the proposals and the expected benefits from the projects. Additionally, collisions with debris could accelerate the degradation of the system and generate additional debris. This paper will discuss a future ESABASE2 risk assessment study, aiming to quantifying the probability of collisions between the deployed drag sail and orbital debris. The atmospheric models required to simulate the aforementioned risks are complex and often fail to accurately predict performance or degradation observed in the space environment. A previous UKSA Pathfinder project highlighted this issue when different atmospheric models with varying levels of solar activity yielded drastically different re-entry times. Since Cranfield University has two deployed drag sails in orbit, previous de-orbit analysis performed using STELA and DRAMA will be updated and the simulations will be compared to actual data. This paper will conclude in a summation of the different on-going research projects at Cranfield University related to commercialising the DAS family. This research will benefit the wider space community by expanding the understanding of the effects of long-term exposure on certain materials, as well as improving the validity of future low Earth atmospheric models.Item Open Access Effects of long-term exposure to the low-earth orbit environment on drag augmentation systems(Elsevier, 2021-06-10) Serfontein, Zaria; Kingston, Jennifer; Hobbs, Stephen; Impey, Susan A.; Aria, Adrianus Indrat; Holbrough, Ian E.; Beck, James C.Spacecraft in low-Earth orbit are exposed to environmental threats which can lead to material degradation and component failures. The presence of atomic oxygen and collisions from orbital debris have detrimental effects on the structures, thus affecting their performance. Cranfield University has developed a family of drag augmentation systems (DAS), for end-of-life de-orbit of satellites, addressing the space debris challenge and ensuring that satellites operate responsibly and sustainably. De-orbit devices are stowed on-orbit for the duration of the mission lifetime and, once deployed, the devices must withstand the harsh low Earth environment until re-entry; a process which can take several years. The DAS’ deployable aluminised Kapton sails are particularly susceptible to undercutting by atomic oxygen. In preparation for commercialising the DAS, Cranfield University are investigating the degradation process of the drag sail materials, with the end goal of qualifying the materials for the specific application of drag sails in low Earth orbit (LEO). This paper will outline the proposed research and the expected benefits from the projects. This paper will conclude in a summation of the different on-going research projects at Cranfield University related to commercialising the DAS family. This research will benefit the wider space community by expanding the understanding of the effects of long-term exposure on certain materials, as well as improving the validity of future low Earth atmospheric models.Item Open Access Flow accelerated preferential weld corrosion of X65 steel in brine(Cranfield University, 2014-04) Adegbite, Michael Adedokun; Robinson, M. J.; Impey, Susan A.Preferential weld corrosion (PWC) remains a major operational challenge that jeopardizes the integrity of oil and gas production facilities. It is the selective dissolution of metal associated with welds, such that the weld metal (WM) and / or the adjacent heat-affected zone (HAZ) corrode rather than the parent metal (PM). Corrosion inhibition is conventionally used to mitigate this problem however several indications suggest that some corrosion inhibitors may increase PWC. Furthermore, it is not possible to detect systems that are susceptible to PWC and or to understand the apparent ineffectiveness of some corrosion inhibitors at high flow rates. Consequently, the aim of this research is to assess the suitability of submerged jet impingement method to study flow accelerated preferential weld corrosion, which is critical to safe and economic operations of offshore oil and gas facilities. In this research, a submerged jet-impingement flow loop was used to investigate corrosion control of X65 steel weldment in flowing brine, saturated with carbon dioxide at 1 bar, and containing a typical oilfield corrosion inhibitor. A novel jet-impingement target was constructed from samples of parent material, heat affected zone and weld metal, and subjected to flowing brine at velocities up to 10 ms- 1 , to give a range of hydrodynamic conditions from stagnation to high turbulence. The galvanic currents between the electrodes in each hydrodynamic zone were recorded using zero-resistance ammeters and their self-corrosion rates were measured using the linear polarisation technique. At low flow rates, the galvanic currents were small and in some cases the weld metal and heat affected zone were partially protected by the sacrificial corrosion of the parent material. However, at higher flow rates the galvanic currents increased but some current reversals were observed, leading to accelerated corrosion of the weld region. The most severe corrosion occurred when oxygen was deliberately admitted into the flow loop to simulate typical oilfield conditions. The results are explained in terms of the selective removal of the inhibitor film from different regions of the weldment at high flow rates and the corrosion mechanism in the presence of oxygen is discussed.Item Open Access The impact of process variables and wear characteristics on the cutting tool performance using Finite Element Analysis(Cranfield University, 2016-09) Jiang, Xiaoheng; Salonitis, Konstantinos; Impey, Susan A.The frequent failure of cutting tool in the cutting process may cause a huge loss of money and time especially for hard to machine materials such as titanium alloys. Thus this study is mainly focused on the impact of wear characteristics and process variables on the cutting tool which is ignored by most of researchers. A thermo-mechanical finite element model of orthogonal metal cutting with segment chip formation is presented. This model can be used to predict the process performance in the form of cutting force, temperature distribution and stress distribution as a function of process parameters. Ls-dyna is adopted as the finite element package due to its ability in solving dynamic problems. Ti-6Al-4V is the workpiece material due to its excellent physical property and very hard to machine. This thesis uses the Johnson-Cook constitutive model to represent the flow stress of workpiece material and the Johnson-Cook damage model to simulate the failure of the workpiece elements. The impacts of process variables and tool wear are investigated through changing the value of the variables and tool geometry. It is found that flank wear length has a linear relationship with the cutting force which is useful for predicting the cutting tool performance. Increasing the crater wear will in some degree diminishes the cutting force and temperature. A chip breakage will also happen in some cases of crater wear. Through these findings, the relationship between flank wear and cutting power is established which can be used as the guidance in the workshop for changing the tools. The distribution of temperature and stress on the cutting tool in different cutting conditions can be adopted to predict the most possible position forming cutting tool wear.Item Open Access Investigation of pre and post plating surface roughness of electroless nickel phosphorus coated substrate for diamond turning application(European Society for Precision Engineering and Nanotechnology, 2016-06-30) Xia, Peter; Almond, Heather; Impey, Susan A.In an overarching project to reduce the number of defects found in electroless nickel phosphorus alloy (EN-P) coatings on large diamond-turned components used in the next generation of reel-to-reel (R2R) printing stations, the significance of the coating surface on achieving a wear resistant and optically smooth surface has been investigated. This paper presents an investigation that focuses on the substrate roughness variation achieved through different pre-treatment methods prior to coating using a commercial plating solution. It looks at the number of features observed pre and post plating. The results provide some suggestions with respect to the diamond machining of a 100 micron thick EN-P coating.Item Open Access Low temperature ITO thin film deposition for solar cells(Cranfield University, 2008-09) Seraffon, Maud; Impey, Susan A.; Lawson, K. J.; Rao, JeffThe electrical and optical properties as well as the microstructure of indium tin oxide thin films deposited on glass and flexible substrates is demonstrated in this project report. This project is a part of an MSc in Advanced Materials at Cranfield University. The understanding and improvement of indium tin oxide coatings deposited by magnetron sputtering on both glass and polymer substrates has been an area of extensive research in the last decade. This technology appears to be very interesting in terms of money saving and efficiency in the solar cell domains where the coatings are used in thin film solar cells. Research into the thin film solar cells mechanism, the sputtering process and ITO coatings is reported, along with detailed consideration of the best results obtained in the past in terms of ITO films’ electrical and optical properties. ITO thin films were deposited on glass and different sputtering parameters were changed in order to investigate their influence on the coatings properties: film thickness, chamber pressure, rotation, oxygen amount and sputtering power. A decision was made to establish the best sputtering parameters. These parameters were set to deposit ITO on polyethylene terephthalate (flexible substrate). The samples were also annealed at 150°C and 370°C. An ITO thin film with a resistivity of 1x10-4 Ωcm and a 90% transmissivity was obtained. An Energy Dispersive Spectrometry analysis was finally made on samples showing a substoichiometric composition of the ITO films.Item Open Access Mechanical behavior of 3d printed poly(ethylene glycol) diacrylate hydrogels in hydrated conditions investigated using atomic force microscopy(American Chemical Society, 2023-04-05) Hakim Khalili, Mohammad; Panchal, Vishal; Dulebo, Alexander; Hawi, Sara; Zhang, Rujing; Wilson, Sandra; Dossi, Eleftheria; Goel, Saurav; Impey, Susan A.; Aria, Adrianus IndratThree-dimensional (3D) printed hydrogels fabricated using light processing techniques are poised to replace conventional processing methods used in tissue engineering and organ-on-chip devices. An intrinsic potential problem remains related to structural heterogeneity translated in the degree of cross-linking of the printed layers. Poly(ethylene glycol) diacrylate (PEGDA) hydrogels were used to fabricate both 3D printed multilayer and control monolithic samples, which were then analyzed using atomic force microscopy (AFM) to assess their nanomechanical properties. The fabrication of the hydrogel samples involved layer-by-layer (LbL) projection lithography and bulk cross-linking processes. We evaluated the nanomechanical properties of both hydrogel types in a hydrated environment using the elastic modulus (E) as a measure to gain insight into their mechanical properties. We observed that E increases by 4-fold from 2.8 to 11.9 kPa transitioning from bottom to the top of a single printed layer in a multilayer sample. Such variations could not be seen in control monolithic sample. The variation within the printed layers is ascribed to heterogeneities caused by the photo-cross-linking process. This behavior was rationalized by spatial variation of the polymer cross-link density related to variations of light absorption within the layers attributed to spatial decay of light intensity during the photo-cross-linking process. More importantly, we observed a significant 44% increase in E, from 9.1 to 13.1 kPa, as the indentation advanced from the bottom to the top of the multilayer sample. This finding implies that mechanical heterogeneity is present throughout the entire structure, rather than being limited to each layer individually. These findings are critical for design, fabrication, and application engineers intending to use 3D printed multilayer PEGDA hydrogels for in vitro tissue engineering and organ-on-chip devices.Item Open Access Nano and microhardness testing of aged EB PVD TBCs(Elsevier Science B.V., Amsterdam., 2004-11-01T00:00:00Z) Wellman, R. G.; Tourmente, H.; Impey, Susan A.; Nicholls, John R.Previous studies on the erosion of electron beam physical vapour deposited thermal barrier coatings (EB PVD TBCs) has shown that aging the coatings at between 1100 and 1500 à °C before erosion increases the erosion rate. These changes in the erosion rate were attributed to a number of factors including changes to the nanoporosity within the coatings as well as phase changes within the coatings. Such changes in the morphology of the coatings should be measurable as changes in their hardness. Thus, it was decided to ascertain the effect that the aging had on the hardness of the coatings. Since, during erosion, the size of the interaction zone between the impacting particle and the coating is in the same range as the size of the individual columns of the coating, it was decided to measure the change in the hardness of the columns as well as the coating as a whole. It was found that the aging increased the hardness of both the coating as a whole and the individual columns of the coatings. The microhardness of the coating was found to increase from 2.5â  3.5 GPa in the as-received condition to 4.5â  6 GPa after 100 h at 1100 à °C and to 7.5â  8 GPa after 24 h at 1500 à °C. The nanohardness of the individual columns on the other hand was found to increase from 18 GPa in the as-received condition to 35 GPa after aging. This paper discusses the increases in hardness due to aging in terms of the sintering and morphological changes that occur in the coating. The difference in the nano- and microhardness results are discussed in terms of the relative size of the indents and column size and the associated interactions that occur under the different indenter heads aItem Open Access Nanoindentation response of 3D printed PEGDA hydrogels in hydrated environment(American Chemical Society, 2023-01-20) Hakim Khalili, Mohammad; Williams, Craig J.; Micallef, Christian; Duarte-Martinez, Fabian; Afsar, Ashfaq; Zhang, Rujing; Wilson, Sandra; Dossi, Eleftheria; Impey, Susan A.; Goel, Saurav; Aria, Adrianus IndratHydrogels are commonly used materials in tissue engineering and organ-on-chip devices. This study investigated the nanomechanical properties of monolithic and multilayered poly(ethylene glycol) diacrylate (PEGDA) hydrogels manufactured using bulk polymerization and layer-by-layer projection lithography processes, respectively. An increase in the number of layers (or reduction in layer thickness) from 1 to 8 and further to 60 results in a reduction in the elastic modulus from 5.53 to 1.69 and further to 0.67 MPa, respectively. It was found that a decrease in the number of layers induces a lower creep index (CIT) in three-dimensional (3D) printed PEGDA hydrogels. This reduction is attributed to mesoscale imperfections that appear as pockets of voids at the interfaces of the multilayered hydrogels attributed to localized regions of unreacted prepolymers, resulting in variations in defect density in the samples examined. An increase in the degree of cross-linking introduced by a higher dosage of ultraviolet (UV) exposure leads to a higher elastic modulus. This implies that the elastic modulus and creep behavior of hydrogels are governed and influenced by the degree of cross-linking and defect density of the layers and interfaces. These findings can guide an optimal manufacturing pathway to obtain the desirable nanomechanical properties in 3D printed PEGDA hydrogels, critical for the performance of living cells and tissues, which can be engineered through control of the fabrication parameters.Item Open Access Novel nanocomposite automotive temperature sensing technology(Cranfield University Press, 2013-09-19) Kelly, Andrew; Impey, Susan A.; Mitsev, Petar; Nicholls, John R.In recent years, automotive emissions legislation has been introduced and is rapidly becoming more stringent. With alternative vehicular propulsion methods far from becoming mainstream reality, leading automotive providers have intensified efforts in the direction of reducing the harmful footprint of their products. This is being accomplished via smaller, more optimally designed internal-combustion engines. A crucial means to that end is exhaust gas temperature monitoring and control. To enable such control, a mass-produced sensor, capable of operating reliably in the harsh automotive combustion environment, comprising a broad spectrum of high temperatures, severe shocks and a chemically aggressive ambient, has been used widely in the past decade, with performance demands growing constantly in line with advances in engine performance. This paper presents a technology overview of the potential of novel nano composite sensor design and manufacture using materials in an innovative way towards industrialising such a sensing solution. The presented sensor design implements the state-of-the-art in thick and thin film technology incorporating nano materials for improved strength, fabrication and performance properties.Item Open Access Particle distribution, film formation and wear performance of brush plated Ni/WC(Electrochemical Society, 2018-06-16) Isern, Luis; Impey, Susan A.; Clouser, S. J.; Milosevic, D.; Endrino, José L.Nickel-matrix composite coatings with tungsten carbide particles were produced by brush electroplating using different current densities and materials of the brush. Non-abrasive materials and high current densities produce coatings with high particle content and non-uniform dispersion. Abrasive wear testing showed premature coating failure in areas with high particle concentrations (>21.3 at.% of W). Changes to the solution flow direction were undertaken to decrease ‘solution pooling’, as it was related to areas with excessive particle content. This, together with the use of abrasive brushes at lower current densities, gives Ni/WC coatings with a low and narrow composition range (from 13.2 ± 4.8 to 2.8 ± 0.8 at.% of W). Such optimized coatings minimized premature coating failure and improved the wear resistance to 1.8–4.4 times that of the original nickel matrix, achieving values similar to hard chrome coatings tested under the same conditions. Unlike other brush plated composite coatings, changes in coating morphology are not heavily influenced by processing parameters, but are sensitive to the presence of WC particles.Item Open Access Physicochemical and nanomechanical behaviour of 3d printed pegda hydrogel structures for tissue engineering applications(Cranfield University, 2023-03) Hakim Khalili, Mohammad; Impey, Susan A.; Aria, Adrianus Indrat; Goel, SauravPoly(ethylene glycol) diacrylate (PEGDA) hydrogels are well established in tissue engineering and organ-on-chip applications as scaffolds for 3D templates in aqueous environments due to their high water content, biocompatibility and low toxicity. The versatility of PEGDA hydrogels as a platform for cell encapsulation and tissue engineering is attributed to their ability to be modified in various ways, including concentration, molecular weight, and polymerisation technique. Since properties of the PEGDA host material will affect the functionality of the cells and tissues, and vice versa, a key missing feature of the currently developed screening solutions is the lack of proper understanding of the behaviour of the 3D printed PEGDA soft support structures holding living tissues in a dynamic human like tissue microenvironment. Thus, the aim of this research is to demonstrate repeatability and reliability in the measurement of physicochemical and nanomechanical properties of multilayer 3D printed UV crosslinked PEGDA hydrogels for use in organ-on-chip devices. The research offers insights into long term stability of hydrogels through studying how changes in both environmental and printing parameters can be extrapolated to other biomaterials for benefit of other tissue engineering applications. Recent advancements in the use of PEGDA hydrogels for tissue engineering are reviewed, with a focus on bulk cross-linking and 3D printing synthesis methods. Characterisation methods for 3D printed PEGDA hydrogels are also discussed. The current state of development of biomedical applications, particularly in organ on-chip devices, is highlighted. The thermal response of multilayer PEGDA hydrogels made using in-house projection lithography was compared to monolithic hydrogels created through bulk photo-cross-linking. The results indicated that the volume of multilayer PEGDA hydrogels changes in response to the temperature with dimensional change between +10% and -11.5%, and also displaying an anisotropic characteristic where the axial dimensional change was higher than the lateral dimension. The results also confirmed the swelling behaviour to be reversible between 8 and 45 °C. The nanomechanical properties of monolithic and multilayer PEGDA hydrogels fabricated through bulk cross linking and layer-by-layer projection lithography were studied. The findings showed that an increase in the number of layers results variation in axial elastic modulus between 1.69 and 0.67 MPa. Additionally, the research examines the structural heterogeneity of 3D printed hydrogels which is linked to the degree of cross-linking of the printed layers and showed variations in lateral elastic modulus between 2.8 and 11.9 kPa. The results suggest that by controlling the cross linking throughout the 3D printed structure, the surface nanomechanical properties of the hydrogels can be manipulated to direct cell attachment and adhesion in specific regions within the structure, offering potential for future improvement in the reproducibility and reliability of 3D printed hydrogels for tissue engineering and organ-on-chip applications.