Browsing by Author "Hawi, Sara"

Now showing 1 - 13 of 13
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    Critical review of nanopillar-based mechanobactericidal systems
    (American Chemical Society, 2022-01-05) Hawi, Sara; Goel, Saurav; Kumar, Vinod; Pearce, Oliver; Nishio Ayre, Wayne; Ivanova, Elena P.
    The rise of multidrug-resistant bacteria is the biggest threat to human health globally, as described by the World Health Organization. Mechanobactericidal surfaces provide a sustainable approach to addressing this concern by eradicating pathogens, especially bacteria, “right-at-the-point” of contacting the surface. However, the lack of a “design to manufacture” approach due to our limited understanding of the mechanobactericidal mechanism has impeded engineering optimization to develop scalable exploitation routes in various healthcare applications. It can be argued that the reason, most particularly, is the limitations and uncertainties associated with the current instrumentation and simulation capabilities, which has led to several streams of test protocols. This review highlights the current understanding on the mechanobactericidal mechanisms in light of the contributing factors and various techniques that are used to postulate these mechanisms. The review offers a critique on the variations observed on how nanostructured surfaces found in the literature have been evaluated such that the test protocols and outcomes are incomparable. The review also shows a strong need for developing more accurate models of a bacterium because the currently reported experimental data are insufficient to develop bacterial material models (constitutive equations). The review also alludes to the scarcity of direct experimental evidence of the mechanobactericidal mechanism, suggesting a strong need for further in situ monitoring as a future research direction.
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    Data supporting: 'Mechanical Behavior of 3D Printed Poly(ethylene glycol) Diacrylate Hydrogels in Hydrated Conditions Investigated Using Atomic Force Microscopy'
    (Cranfield University, 2023-03-21 08:49) Hakim Khalili, Mohammad; Panchal, Vishal; Dulebo, Alexander; Hawi, Sara; Zhang, Rujing; Wilson, Sandra; Dossi, Licia; Goel, S.; Impey, Sue; Aria, Indrat
    1. File AFM-Lines: Raw files for all force-distance curves along with excel file summarizing all the indentions on a single line taken at different height on the surface of the hydrogel. 2. File AFM-Maps: Raw files for all force-distance curves along with excel file summarizing all the indentation maps taken at the middle section on the surface of the hydrogel.
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    Data underpinning the paper: 'Development and testing of carbonaceous tin-based solder achieving unprecedented joint performance Item'
    (Cranfield University, 2021-06-21 12:53) Hawi, Sara; Gharavian, Somayeh; Burda, Marek; Goel, Saurav; Lotfian, Saeid; Khaleque, Tasnuva; Yazdani Nezhad, Hamed
    The paper shows that the suitable addition of carbon nanomaterials to a tin-based solder material matrix results in two fold strength of soldered joints.
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    Development of carbonaceous tin-based solder composite achieving unprecedented joint performance
    (Springer, 2021-12-30) Hawi, Sara; Gharavian, Somayeh; Burda, Marek; Goel, Saurav; Lotfan, Saeid; Khaleque, Tasnuva; Yazdani Nezhad, Hamed
    Weight reduction and improved strength are two common engineering goals in the joining sector to benefit transport, aerospace, and nuclear industries amongst others. Here, in this paper, we show that the suitable addition of carbon nanomaterials to a tin-based solder material matrix (C-Solder® supplied by Cametics Ltd.) results in two-fold strength of soldered composite joints. Single-lap shear joint experiments were conducted on soldered aluminium alloy (6082 T6) substrates. The soldering material was reinforced in different mix ratios by carbon black, graphene, and single-walled carbon nanotubes (SWCNT) and benchmarked against the pristine C-solder®. The material characterisation was performed using Vickers micro-indentation, differential scanning calorimetry and nano-indentation, whereas functional testing involved mechanical shear tests using single-lap aluminium soldered joints and creep tests. The hardness was observed to improve in all cases except for the 0.01 wt.% graphene reinforced solders, with 5% and 4% improvements in 0.05 carbon black and SWCNT reinforced solders, respectively. The maximum creep indentation was noted to improve for all solder categories with maximum 11% and 8% improvements in 0.05 wt.% carbon black and SWCNT reinforced ones. In general, the 0.05 wt.% nanomaterial reinforced solders promoted progressive cohesion failure in the joints as opposed to instantaneous fully de-bonded failure observed in pristine soldered joints, which suggests potential application in high-performance structures where no service load induced adhesion failure is permissible (e.g. aerospace assemblies). The novel innovation developed here will pave the way to achieving high-performance solder joining without carrying out extensive surface preparations.
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    Fabrication of functionalised surfaces on gum metal (Ti-30Nb) using micromachining
    (euspen, 2019-06-30) Hawi, Sara; Dickins, Andrew; Pardal, Goncalo; Giusca, Claudiu; Pearce, Oliver; Goel, Saurav
    Structured surfaces are attracting deep interest, as they allow tailoring the functionality via changes in the surface topography. Applications for these surfaces range greatly, including, optical surfaces for antireflective surfaces, thermal structures to assist in heat dispersion and anti-fouling surfaces to reduce micro-organisms from adhering to components. Gum metal is a relatively newer kind of beta titanium alloy that has earmarked its place as the next generation Ortheopedic implant material. In a timely effort, this work investigated the generation of micron level structured surfaces on Gum metal (Ti-30Nb – a beta titanium alloy) to explore micromilling as the robust scalable process to achieve low dimensional surfaces in titanium alloy. During micromilling, the feedrate, spindle speed, axial depth of cut and tool step over were varied to optimise these parameters for achieving superior quality of machining.
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    Magnetic field assisted 3D printing of short carbon fibre-reinforced polymer composites
    (Elsevier, 2022-07-19) Pearson, Celia; Hawi, Sara; Lira, Cristian; Goel, Saurav; Yazdani Nezhad, Hamed
    This paper investigates and discusses the outcomes from an ongoing feasibility research being conducted at Advanced Composites Research Focused Group on 3D printing polymers and carbon composites subjected to localised magnetic field force lines. Magnetic equipped composite processes are starting to become an important new development for structural applications. Specific to this paper, in-situ alignment of short carbon fibres (∼1 mm length) in thermoplastic polymer filaments (Onyx FR, a Nylon base with micro carbon-fibres with a flame retardant additive supplied by Markforged) during a fused deposition modelling (FDM) based 3D printing (MakerBot Replicator 2). An experiment took place in which samples of PLA and onyx were printed, both with and without a magnetic field present. This was done to see what effects, if any, the magnetic field had on the flow orientation of these materials when printed. The results from using a high-resolution optical microscopy and scanning electron microscopy showed that while carbon fibres within the Onyx had aligned in response to the magnetic field, the PLA samples were visibly unchanged by the magnetic field. The observations have been partially supported by theoretical calculations utilizing Multiphysics constitutive equations.
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    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 Indrat
    Three-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.
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    Nature inspired materials: Emerging trends and future prospects
    (Cranfield University, 2020-12-07 00:33) Goel, Saurav; Hawi, Sara; Goel, Gaurav
    Nature inspired materials images
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    Nature-inspired materials: emerging trends and prospects
    (Springer Nature, 2021-07-30) Katiyar, Nirmal Kumar; Goel, Gaurav; Hawi, Sara; Goel, Saurav
    The term ‘Nature-inspired’ is associated with a sequence of efforts to understand, synthesise and imitate any natural object or phenomenon either in the tangible or intangible form which allows us to obtain improved insights into nature. Such inspirations can come through materials, processes, or designs that we see around. Materials as opposed to processes and designs found in nature due to being tangible can readily be used without engineering efforts. One such example is that of an aquaporin which is used to filter water. The scope of this work in Nature-inspired materials is to define, clarify and consolidate the current understanding by probing new insights in the recent developments by reviewing examples from the laboratory to industrial scale while highlighting newer opportunities in this area. A careful analysis of the “nature-inspired materials” shows that they possess specific functionality that relies on our ability to harness peculiar electrical, mechanical, biological, chemical, sustainability or combined gains.
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    Precision laser manufacturing and metrology of nature-inspired bioactive surfaces for antibacterial medical implants
    (Elsevier, 2025-04-01) Hawi, Sara; Goel, Saurav; Kumar, Vinod; Giusca, Claudiu; Pearce, Oliver; Ayre, Wayne Nishio
    Femtosecond laser ablation presents a highly promising method to create bioactive nano/micro-structured metallic surfaces, offering numerous avenues for fabricating diverse types of surface structures. However, the relationship between surface properties and biological functionality, leading to the observed bioactivity remains unclear. This study aimed to investigate the relationship between structured/patterned steel surfaces and bioactivity, identifying key factors that enhance their performance. As opposed to the commonly used controversial parameter, arithmetic surface roughness (Ra), fractal dimension analysis was discovered to be strongly representative in quantifiably evaluating the adhesion of Staphylococcus aureus NCTC 7791 and MG-63 osteoblast-like cells. Surface chemistry and surface energy of structured surfaces showed no significant influence on bacterial adhesion. A specific type of laser-induced periodic structured surfaces with sub-micron wavelengths, high fractal dimension, and high texture aspect ratio demonstrated a 63 % reduction in bacterial adhesion compared to flat surfaces while avoiding cytotoxicity to MG-63 cells. Our findings underline the importance of scale-dependent analysis and the use of fractal analysis in evaluating the effectiveness of laser-structured surfaces for orthopaedic implant applications.
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    Resilient and agile engineering solutions to address societal challenges such as coronavirus pandemic
    (Elsevier, 2020-05-28) Goel, Saurav; Hawi, Sara; Goel, Gaurav; Thakur, Vijay Kumar; Agrawal, Anupam; Hoskins, Clare; Pearce, Oliver; Hussain, Tanvir; Upadhyaya, Hari M.; Cross, Graham; Barber, Asa H.
    The world is witnessing tumultuous times as major economic powers including the US, UK, Russia, India, and most of Europe continue to be in a state of lockdown. The worst-hit sectors due to this lockdown are sales, production (manufacturing), transport (aerospace and automotive) and tourism. Lockdowns became necessary as a preventive measure to avoid the spread of the contagious and infectious “Coronavirus Disease 2019” (COVID-19). This newly identified disease is caused by a new strain of the virus being referred to as Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS CoV-2; formerly called 2019-nCoV). We review the current medical and manufacturing response to COVID-19, including advances in instrumentation, sensing, use of lasers, fumigation chambers and development of novel tools such as lab-on-the-chip using combinatorial additive and subtractive manufacturing techniques and use of molecular modelling and molecular docking in drug and vaccine discovery. We also offer perspectives on future considerations on climate change, outsourced versus indigenous manufacturing, automation, and antimicrobial resistance. Overall, this paper attempts to identify key areas where manufacturing can be employed to address societal challenges such as COVID-19.
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    Shaping the structure and properties of HyTemp using polyethylene glycol diglycidyl ether cross-linkers
    (Wiley, 2024-06-03) Dossi, Eleftheria; Mutele-Nkuna, Khuthadzo Lourate; Wilkinson, Peter; Kister, Guillaume; Patrick, Hugh; Khalili, Mohammad Hakim; Hawi, Sara
    Novel elastomers are made by reaction of hydroxyl-terminated polyacrylic ester (HyTemp) with polyethylene glycol (PEG, number of ethylene glycol units 1, 3, 6, 9) based cross-linkers. The influence of the cross-linker length, the HyTemp/cross-linker (w/w) ratio and the cross-linking accelerator trifluoromethanesulfonate scandium salt (ScTFMS) on the structure and the properties of the materials are studied. The cross-linker length has not influence on the glass transition (Tg) of the products because of the presence of the flexible PEG units that cancels out the cross-linking effect associated to a shift to higher Tg. A two-domain structure is seen by the presence of a dual Tg in samples cured with ScTFMS. Mathematical analysis of the modulated differential scanning calorimetry curves offers for the first time the possibility to identify/confirm structural differences in complex three-dimensional polymeric structures. Scanning electron microscopy and swelling experiments in ethyl acetate respectively reveal an increase in the pore size (1.13 to 5.48 nm) and in the absorption ability of the elastomers cured with different types and quantities of PEG cross-linker. The new elastomeric materials are exhibiting a rubbery state over a wide temperature range and absorptivity for the potential recovery of pollutants in soil and/or water.
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    A testbed for optimal coating selection for micromilling of biomedical grade TI-6AL-4V.
    (Cranfield University, 2019-07) Hawi, Sara; Goel, Saurav; Rodrigues Pardal, Goncalo
    One of the biggest challenges in precision micro-machining of titanium alloys is the tool wear as titanium is characterised as a “difficult to cut” material. Tool coatings provide a promising solution for the problem of tool wear while offering a low cost high value machining route. This project aims to explore the design of engineering material systems along with machining parameters to guide the choice of tool coating while machining biomedical grade Ti-6Al-4V. The overarching aim is to identify a low cost tooling such as WC coated with the right coating composition together with the appropriate machining parameters. The research methodology applied to work towards this aim employs a design of experimental approach using the Taguchi method such that the spindle speed, feed rate and coating would be varied. Both qualitative and quantitative analysis of the machining process was carried out to qualify the machining performance. During the machining trials, data was gathered and analysed to study the effect of cutting parameters on the specific cutting energy, material removal rate and surface roughness.