Browsing by Author "Hakim Khalili, Mohammad"

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    Broad band anti-reflection 2-16μm coatings on diamond and ZnSe.
    (2018-08) Hakim Khalili, Mohammad; Endrino Armenteros, Jose
    In this project, Thin Metal Films an optical coating company is requiring the upgrade of a desktop research type radio frequency magnetron sputtering machine which was custom made for a European funded project and was gifted to it after the project completion. As the machine had no usage history, it had to be investigated and its capabilities and characteristics identified. The first part of the project, focused on restoring the machine using a systematic approach by utilising a technique called Plan Do Check Act, where a continuous feedback loop is used to identify problems and finding solution to them. Within the restoration process the aim was to improve the coating uniformity and machine’s repeatability. The restoration of the machine consumed almost the entire project duration leaving a little time for second part of the project. The second part was to use the restored machine, to develop single and multilayer Broad Band Anti-Reflective Coatings for Zinc Selenide and diamond optics. The optics are to be used in Attenuated Total Reflectance accessory units for Infrared spectroscopy. Based on the literature review and multiple decision criteria, yttria and ytterbia were showing promising results in adhering very well to a diamond surface and improving its transmission. Therefore, using Macleod software, a single layer quarter wavelength coating was designed and theoretically examined. It was found that a quarter wavelength ytteria at 5000 nm and a quarter wavelength ytterbia at 3370 nm can increase the transmission on both ZnSe and diamond optics to maximum of 98% and 95% accordingly. The coatings have not actually been deposited on the optics due to both targets breaking before conducting the actual experiments.
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    Data for: Nanoindentation Response of 3D Printed PEGDA Hydrogels in a Hydrated Environment
    (Cranfield University, 2023-01-27 09:40) Hakim Khalili, Mohammad; J. Williams, Craig; Zhang, Rujing; Wilson, Sandra; Impey, Sue; Aria, Indrat; Goel, Saurav; Dossi, Licia; Afsar, Ashfaq; Duarte martinez, Fabian; Micallef, Christian
    Raw and processed data sets from nanoidentation response of 3D printed hydrogels. 1. Raw data of nanoindentation response. 2. Representative load-displacement curves for each type of hydrogel. 3. Representative data for creep for different types of hydrogels. 4. Representative data for NMR spectras of different types of hydrogels. 5. Representative data for glass transition of different types of hydrogels.
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    Data supporting 'Thermal response of multi-layer UV crosslinked PEGDA hydrogels'
    (Cranfield University, 2023-02-16 11:15) Hakim Khalili, Mohammad; Afsar, Ashfaq; Zhang, Rujing; Wilson, Sandra; Goel, Saurav; Impey, Sue; Aria, Adrianus
    All data sets are raw data from thermoresponse behaviour of hydrogels. 1. Swelling test for multi-150 um hydrogels with 1.8 mg/ml of photoabsorber.2. Swelling test for mono-5 mm hydrogels with 0 mg/ml of photoabsorber.3. Swelling test for multi-20 um hydrogels with 9 mg/ml of photoabsorber.4. Swelling test for mono-3 mm and mono-1.5 mm hydrogels with 0 mg/ml of photoabsorber.5. Cyclic test for multi-150 um hydrogels.6. Dried weight and solid residue weight of all hydrogels samples7. EWC, NWF, NVF-summary for all hydrogel samples8. DSC-TG-Thermogram-All sample types
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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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    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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    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 Indrat
    Hydrogels 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.
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    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, Saurav
    Poly(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.