CERES :: Browsing by Author "Aria, Adrianus Indrat"

Browsing by Author "Aria, Adrianus Indrat"

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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 Indrat
In 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.
Open Access
Atomic layer deposited oxide films as protective interface layers for integrated graphene transfer
(IOP Publishing: Hybrid Open Access, 2017-10-17) Cabrero-Vilatela, Andrea; Alexander-Webber, Jack; Sagade, Abhay; Aria, Adrianus Indrat; Braeuninger-Weimer, Philipp; Martin, Marie-Blandine; Weatherup, Robert; Hofmann, Stephan
The transfer of chemical vapour deposited (CVD) graphene from its parent growth catalyst has become a bottleneck for many of its emerging applications. The sacrificial polymer layers that are typically deposited onto graphene for mechanical support during transfer are challenging to fully remove and hence leave graphene and subsequent device interfaces contaminated. Here, we report on the use of atomic layer deposited (ALD) oxide films as protective interface and support layers during graphene transfer. The method avoids any direct contact of the graphene with polymers and through the use of thicker ALD layers (≥100nm), polymers can be eliminated from the transfer-process altogether. The ALD film can be kept as a functional device layer, facilitating integrated device manufacturing. We demonstrate back-gated field effect devices based on single-layer graphene transferred with a protective Al2O3 film onto SiO2 that show significantly reduced charge trap and residual carrier densities. We critically discuss the advantages and challenges of processing graphene/ALD bilayer structures.
Open Access
Bolometric detection of terahertz quantum cascade laser radiation with graphene-plasmonic antenna arrays
(IOP Publishing, 2017-03-27) Degl'Innocenti, Riccardo; Xiao, Long; Kindness, Stephen J.; Kamboj, Varun S.; Wei, Binbin; Braeuninger-Weimer, Philipp; Nakanishi, Kenichi; Aria, Adrianus Indrat; Hofmann, Stephan; Beere, Harvey E.; Ritchie, David A.
We present a fast room temperature terahertz detector based on graphene loaded plasmonic antenna arrays. The antenna elements, which are arranged in series and are shorted by graphene, are contacting source and drain metallic pads, thus providing both the optical resonant element and the electrodes. The distance between the antenna’s arms of approximately 300 nm allows a strong field enhancement in the graphene region, when the incident radiation is resonant with the antennas. The current passing through the source and drain is dependent on the graphene’s conductivity, which is modified by the power impinging onto the detector as well as from the biasing back-gate voltage. The incident radiation power is thus translated into a current modification, with the main detection mechanism being attributed to the bolometric effect. The device has been characterized and tested with two bound to continuum terahertz quantum cascade lasers emitting at a single frequency around 2 THz and 2.7 THz yielding a maximum responsivity of ~2 mA W−1.
Open Access
Chemical vapour deposition of freestanding sub-60 nm graphene gyroids
(AIP Publishing, 2017-12-18) Cebo, Tomasz; Aria, Adrianus Indrat; Dolan, James A.; Weatherup, Robert S.; Nakanishi, Kenichi; Kidambi, Piran R.; Divitini, Giorgio; Ducati, Caterina; Steiner, Ullrich; Hofmann, Stephan
The direct chemical vapour deposition of freestanding graphene gyroids with controlled sub-60 nm unit cell sizes is demonstrated. Three-dimensional (3D) nickel templates were fabricated through electrodeposition into a selectively voided triblock terpolymer. The high temperature instability of sub-micron unit cell structures was effectively addressed through the early introduction of the carbon precursor, which stabilizes the metallized gyroidal templates. The as-grown graphene gyroids are self-supporting and can be transferred onto a variety of substrates. Furthermore, they represent the smallest free standing periodic graphene 3D structures yet produced with a pore size of tens of nm, as analysed by electron microscopy and optical spectroscopy. We discuss generality of our methodology for the synthesis of other types of nanoscale, 3D graphene assemblies, and the transferability of this approach to other 2D materials.
Open Access
Compressive behavior and failure mechanisms of freestanding and composite 3D graphitic foams
(Elsevier, 2018-08-09) Nakanishi, Kenichi; Aria, Adrianus Indrat; Berwind, Matthew; Weatherup, Robert S.; Eberl, Christoph; Hofmann, Stephan; Fleck, Norman A.
Open-cell graphitic foams were fabricated by chemical vapor deposition using nickel templates and their compressive responses were measured over a range of relative densities. The mechanical response required an interpretation in terms of a hierarchical micromechanical model, spanning 3 distinct length scales. The power law scaling of elastic modulus and yield strength versus relative density suggests that the cell walls of the graphitic foam deform by bending. The length scale of the unit cell of the foam is set by the length of the struts comprising the cell wall, and is termed level I. The cell walls comprise hollow triangular tubes, and bending of these strut-like tubes involves axial stretching of the tube walls. This length scale is termed level II. In turn, the tube walls form a wavy stack of graphitic layers, and this waviness induces interlayer shear of the graphitic layers when the tube walls are subjected to axial stretch. The thickness of the tube wall defines the third length scale, termed level III. We show that the addition of a thin, flexible ceramic Al2O3 scaffold stiffens and strengthens the foam, yet preserves the power law scaling. The hierarchical model gives fresh insight into the mechanical properties of foams with cell walls made from emergent 2D layered solids.
Open Access
Development of NI3AL corrosion resistant coatings for SS347 heat storage components in presence of molten nitrate salt.
(Cranfield University, 2020-07) Yasir, Sarah; Aria, Adrianus Indrat; Endrino, José L.
Climate change is an inevitable global issue with long term consequences for the sustainable development. It is a crucial time to review this climate issue with ensured determination. There is a need and demand for alternative sources to generate power rather than the conventional burning of fuels due to impact on environment. Renewable energy sources are those natural reserves that are refilled continually, including wind, solar, biomass and geothermal. A number of technologies have been developed to use solar energy for power generation. Among them, an important feature of concentrated solar power plants is the potential to incorporate thermal storage. Thermal energy storage allows generation beyond sunset and in times of cloud cover. Several possibilities for heat transfer fluid and thermal energy storage have been identified. From a wide range of materials, molten nitrate salt is selected because of adequate heat storage and transfer capability. Different approaches to prolong life by suppressing corrosion have been suggested in the literature, coating is a promising option because coatings are believed to provide shield to suppress corrosion. Among different coatings, nickel aluminide has been claimed to possess high-temperature mechanical strength and it has a remarkable oxidation resistance performance as substrate component. Moreover, nickel aluminide has low solubility in the molten nitrate salt. Ni₃Al coatings are much preferred to be used as corrosion resistant coatings as they possess strength at high temperature, oxidation protection and creep properties. Among different deposition techniques, plasma spray has been identified as most applicable because it is versatile, adaptable, cost effective. It also has high deposition rate, deposition efficiency and less environmental impact, more importantly it is easy to scale up. Corrosion behaviour of stainless steel 347 (SS347) and Ni₃Al coated SS347 was investigated in molten nitrate salt (60wt% NaNO₃ + 40wt% KNO₃) immersion at 565oC for 500 hours intervals up to 3000 hours. A growth of stratified oxide layers was observed on SS347 sample surface comprising of NaFeO₂ , Fe₂ O₃ and Fe₃O₄ . The Ni₃Al coated SS347 samples were observed to undergo rapid oxidation within first 500 hours. Apparent Mass change for bare SS347 was 4 mg/cm²/yr, equivalent to oxide growth rate of ~ 5 µm/yr. Mass change for Ni₃Al coated SS347 was 29.8 mg/cm²/yr, equivalent to oxide growth rate of ~ 44.6 μm/yr for first 500 hours and 0.5 mg/cm²/yr, equivalent to oxide growth rate of ~ 0.7 μm/yr for 500 to 3000 hours. The results presented in this study suggest that Ni3Al coating supresses the formation of oxide layers on the surface of stainless- steel substrates and can be used to suppress corrosion in presence of molten nitrate salts. The fact, that Ni₃Al coated SS347 gives mass change of one order of magnitude lower than the bare SS347, it means that these coatings can be used to prolong the lifetime of bare SS347 in molten nitrate salt at 565oC, which is of relevance to thermal energy storage applications. The Engineering Doctorate portfolio is structured as an innovation report and five submissions. A personal profile and a report on international industrial placement are also included in the portfolio.
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.
Open Access
Effects of long-term exposure to the low-earth orbit environment on drag augmentation systems
(International Astronautical Federation (IAF), 2020-10-14) Serfontein, Zaria; Kingston, Jennifer; Hobbs, Stephen; Holbrough, Ian E.; Beck, James C.; Impey, Susan A.; Aria, Adrianus Indrat
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. 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.
Open Access
External amplitude and frequency modulation of a terahertz quantum cascade laser using metamaterial/graphene devices
(Nature Publishing Group, 2017-08-09) Kindness, S. J.; Jessop, D. S.; Wei, B.; Wallis, R.; Kamboj, Varun S.; Xiao, L.; Ren, Y.; Braeuninger-Weimer, P.; Aria, Adrianus Indrat; Hofmann, S.; Beere, H. E.; Ritchie, David A.; Degl’Innocenti, R.
Active control of the amplitude and frequency of terahertz sources is an essential prerequisite for exploiting a myriad of terahertz applications in imaging, spectroscopy, and communications. Here we present a optoelectronic, external modulation technique applied to a terahertz quantum cascade laser which holds the promise of addressing a number of important challenges in this research area. A hybrid metamaterial/graphene device is implemented into an external cavity set-up allowing for optoelectronic tuning of feedback into a quantum cascade laser. We demonstrate powerful, all-electronic, control over the amplitude and frequency of the laser output. Full laser switching is performed by electrostatic gating of the metamaterial/graphene device, demonstrating a modulation depth of 100%. External control of the emission spectrum is also achieved, highlighting the flexibility of this feedback method. By taking advantage of the frequency dispersive reflectivity of the metamaterial array, different modes of the QCL output are selectively suppressed using lithographic tuning and single mode operation of the multi-mode laser is enforced. Side mode suppression is electrically modulated from ~6 dB to ~21 dB, demonstrating active, optoelectronic modulation of the laser frequency content between multi-mode and single mode operation.
Open Access
From growth surface to device interface: preserving metallic Fe under monolayer hexagonal boron nitride
(American Chemical Society, 2017-08-08) Caneva, Sabina; Martin, Marie-Blandine; D'Arsie, Lorenzo; Aria, Adrianus Indrat; Sezen, Hikmet; Amati, Matteo; Gregoratti, Luca; Sugime, Hisashi; Esconjauregui, Santiago; Robertson, John; Hofmann, Stephan; Weatherup, Robert S.
We investigate the interfacial chemistry between Fe catalyst foils and monolayer hexagonal boron nitride (h-BN) following chemical vapor deposition and during subsequent atmospheric exposure, using scanning electron microscopy, X-ray photoemission spectroscopy, and scanning photoelectron microscopy. We show that regions of the Fe surface covered by h-BN remain in a metallic state during exposure to moist air for ∼40 h at room temperature. This protection is attributed to the strong interfacial interaction between h-BN and Fe, which prevents the rapid intercalation of oxidizing species. Local Fe oxidation is observed on bare Fe regions and close to defects in the h-BN film (e.g., domain boundaries, wrinkles, and edges), which over the longer-term provide pathways for slow bulk oxidation of Fe. We further confirm that the interface between h-BN and metallic Fe can be recovered by vacuum annealing at ∼600 °C, although this is accompanied by the creation of defects within the h-BN film. We discuss the importance of these findings in the context of integrated manufacturing and transfer-free device integration of h-BN, particularly for technologically important applications where h-BN has potential as a tunnel barrier such as magnetic tunnel junctions.
Open Access
Graphene-based nanolaminates as ultra-high permeation barriers
(Nature Publishing Group, 2017-10-23) Sagade, Abhay A.; Aria, Adrianus Indrat; Edge, Steven; Melgari, Paolo; Gieseking, Bjoern; Bayer, Bernhard C.; Meyer, Jannik C.; Bird, David; Brewer, Paul; Hofmann, Stephan
Permeation barrier films are critical to a wide range of applications. In particular, for organic electronics and photovoltaics not only ultra-low permeation values are required but also optical transparency. A laminate structure thereby allows synergistic effects between different materials. Here, we report on a combination of chemical vapor deposition (CVD) and atomic layer deposition (ALD) to create in scalable fashion few-layer graphene/aluminium oxide-based nanolaminates. The resulting ~10 nm contiguous, flexible graphene-based films are >90% optically transparent and show water vapor transmission rates below 7 × 10−3 g/m2/day measured over areas of 5 × 5 cm2. We deploy these films to provide effective encapsulation for organic light-emitting diodes (OLEDs) with measured half-life times of 880 h in ambient.
Open Access
Graphene-passivated nickel as an efficient hole-injecting electrode for large area organic semiconductor devices
(AIP Publishing, 2020-04-20) Di Nuzzo, Daniele; Mizuta, Ryo; Nakanishi, Kenichi; Martin, Marie-Blandine; Aria, Adrianus Indrat; Weatherup, Robert; Friend, Richard H.; Hofmann, Stephan; Alexander-Webber, Jack
Efficient injection of charge from metal electrodes into semiconductors is of paramount importance to obtain high performance optoelectronic devices. The quality of the interface between the electrode and the semiconductor must, therefore, be carefully controlled. The case of organic semiconductors presents specific problems: ambient deposition techniques, such as solution processing, restrict the choice of electrodes to those not prone to oxidation, limiting potential applications. Additionally, damage to the semiconductor in sputter coating or high temperature thermal evaporation poses an obstacle to the use of many device-relevant metals as top electrodes in vertical metal–semiconductor–metal structures, making it preferable to use them as bottom electrodes. Here, we propose a possible solution to these problems by implementing graphene-passivated nickel as an air stable bottom electrode in vertical devices comprising organic semiconductors. We use these passivated layers as hole-injecting bottom electrodes, and we show that efficient charge injection can be achieved into standard organic semiconducting polymers, owing to an oxide free nickel/graphene/polymer interface. Crucially, we fabricate our electrodes with low roughness, which, in turn, allows us to produce large area devices (of the order of millimeter squares) without electrical shorts occurring. Our results make these graphene-passivated ferromagnetic electrodes a promising approach for large area organic optoelectronic and spintronic devices. Organic semiconductors serve as a platform for (opto)electronic devices with tunable characteristics by molecular design, enabling versatile device integration, and processing strategies.1 However, ambient processing techniques such as solution processing can facilitate oxidation of metal contacts, resulting in an uncontrolled electronic interface, which is deleterious to performance in semiconductor devices.2,3 New techniques are, therefore, required to control the interface between organic semiconductors and oxidizing metals while maintaining the possibility of solution processing. Graphene has been shown to act as an atomically thin permeation barrier.4–6 Graphene grown via chemical vapor deposition (CVD) directly on the surface of strongly interacting7 catalytic metals, such as Ni, Co, or Fe, acts as a barrier layer to prevent oxidation.8–11 These oxide-free ferromagnetic interfaces have been shown to hold significant benefits within the field of spintronics,12,13 as they enable oxidative fabrication processes, such as solution processing9,10 or atomic layer deposition,14 to be used to fabricate devices with a wider range of relevant materials. One appealing possibility would be to develop graphene-passivated ferromagnets as electrodes9,10 for organic semiconductor spintronics,15–18 where the quality of the electronic interface between the ferromagnetic electrode and the organic semiconductor is of paramount importance.19,20 Another important advantage of an ambient-stable ferromagnetic layer is that it can be used as a bottom electrode in vertical metal-organic semiconductor–metal structures, allowing one to employ techniques such as sputtering to obtain high quality and thickness-controlled metal layers or multi-layers; note that sputtering cannot be used for top-electrodes as it would destroy21 the organic semiconductor. Previous reports using graphene passivated ferromagnets as electrodes for organic semiconductor devices have studied the spin injection properties10 as well as charge injection in lateral organic semiconductor field effect transistors.9 In this work, we investigate few-layer graphene-passivated nickel (Ni/FLG) as a bottom electrode for injection of holes into organic semiconducting polymers in a vertical device structure, demonstrating efficient injection into two standard semiconducting polymers deposited from solution and in air, directly on top of Ni/FLG. Compared to previous reports on graphene-passivated ferromagnetic electrodes, where lithographic techniques had to be used in order to produce micrometer-sized features,8–10,12,14 here, we were able to produce working devices with several orders of magnitude larger active area (4.5 mm2). Our results are, thus, encouraging for the further development of organic optoelectronic and spintronic devices processed from solution under ambient conditions. Nickel was initially sputtered on thermally oxidized silicon wafers, producing films with a thickness of 150 nm. FLG domains were grown on such sputtered Ni films in a custom low-pressure Chemical Vapor Deposition (CVD) reactor (base pressure ∼1 × 10−6 mbar). All substrates were cleaned by sonicating in acetone followed by isopropyl alcohol and blow-dried with a nitrogen gun before loading. Samples were heated to approximately 450 °C using a resistive heater (temperature measurements by a K-type thermocouple) with a rapid ramp rate of 100 °C/min and annealed at ∼1 mbar of H2 for 10 min. This reduces the native oxide prior to graphene growth. After annealing, the H2 flow was stopped and the chamber was evacuated back to approximately base pressure over a period of 5 min. For graphene growth, C2H2 gas was gradually introduced into the reactor via a mass flow controller by incrementally increasing the flow rate over 5 min to achieve a partial pressure of C2H2 of 2.5 × 10−4 mbar. Subsequently, the samples were held at 450 °C in 2.5 × 10−4 mbar of C2H2 for a further 25 min, before rapid cooling (initially ∼300 °C/min) while maintaining the C2H2 flow. All gases were stopped once room temperature had been reached. Upon graphene growth, a roughening of the Ni sputtered on thermally oxidized Si was observed, with an RMS = 67 nm [Fig. 1(a)]. The roughness was found to increase with increasing growth temperature. The roughening of Ni upon graphene growth is explained by grain growth in the sputtered Ni films, occurring at high temperatures during the CVD process: under these conditions, the internal forces in the film are larger than those between the film and the substrate, and diffusion of the film material is appreciable.
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 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.
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 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.
Open Access
Numerical Analysis of Reduced Frequency on Flapping Tandem Foils
(Praise Worthy Prize, 2023-06-30) Joevian, Michael; Tobing, Sheila; Surjadi, Rainer Louis; Timothy, Kenneth; Aria, Adrianus Indrat
Numerous investigations on flapping wing motion have been conducted over the last two decades. The study of flapping wing motion was inspired by the possibility of using it to design and develop micro air vehicles. The application of flapping wing motion in power generation systems has attracted attention recently because of the growing need to replace fossil fuels with renewable energy sources. This research examines the effect of pitch oscillation frequency on the propulsion of a tandem flapping foils power generation system. Herein, the 2D models of tandem foils pitching with reduced frequencies f* of 0.04, 0.14, and 0.18 are used for parametric investigation. The results reveal that f* = 0.18 offers the optimal lift force among other reduced frequencies and 2.91% lower drag force compared to f* = 0.14.
Open Access
Parameter space of atomic layer deposition of ultra-thin oxides on graphene
(American Chemical Society , 2016-10-10) Aria, Adrianus Indrat; Nakanishi, Kenichi; Xiao, Long; Braeuninger-Weimer, Philipp; Sagade, Abhay A.; Alexander-Webber, Jack; Hofmann, Stephan
Atomic layer deposition (ALD) of ultrathin aluminum oxide (AlOx) films was systematically studied on supported chemical vapor deposition (CVD) graphene. We show that by extending the precursor residence time, using either a multiple-pulse sequence or a soaking period, ultrathin continuous AlOx films can be achieved directly on graphene using standard H2O and trimethylaluminum (TMA) precursors even at a high deposition temperature of 200 °C, without the use of surfactants or other additional graphene surface modifications. To obtain conformal nucleation, a precursor residence time of >2s is needed, which is not prohibitively long but sufficient to account for the slow adsorption kinetics of the graphene surface. In contrast, a shorter residence time results in heterogeneous nucleation that is preferential to defect/selective sites on the graphene. These findings demonstrate that careful control of the ALD parameter space is imperative in governing the nucleation behavior of AlOx on CVD graphene. We consider our results to have model system character for rational two-dimensional (2D)/non-2D material process integration, relevant also to the interfacing and device integration of the many other emerging 2D materials.
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, 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.
Open Access
Piezoelectic Materials for energy harvesting and sensing applications: roadmap for future smart materials
(Wiley, 2021-07-13) Mahapatra, Susmriti Das; Mohapatra, Preetam Chandan; Aria, Adrianus Indrat; Christie, Graham; Mishra, Yogendra Kumar; Hofmann, Stephan; Thakur, Vijay Kumar
Piezoelectric materials are widely referred to as “smart” materials because they can transduce mechanical pressure acting on them to electrical signals and vice versa. They are extensively utilized in harvesting mechanical energy from vibrations, human motion, mechanical loads, etc., and converting them into electrical energy for low power devices. Piezoelectric transduction offers high scalability, simple device designs, and high-power densities compared to electro-magnetic/static and triboelectric transducers. This review aims to give a holistic overview of recent developments in piezoelectric nanostructured materials, polymers, polymer nanocomposites, and piezoelectric films for implementation in energy harvesting. The progress in fabrication techniques, morphology, piezoelectric properties, energy harvesting performance, and underpinning fundamental mechanisms for each class of materials, including polymer nanocomposites using conducting, non-conducting, and hybrid fillers are discussed. The emergent application horizon of piezoelectric energy harvesters particularly for wireless devices and self-powered sensors is highlighted, and the current challenges and future prospects are critically discussed.
Open Access
Rapid surface finishing of chemical vapour deposited tungsten carbide hard coatings by electropolishing
(Elsevier, 2021-11-15) Micallef, Christian; Chiu, Cheng-Wei; Zhuk, Yuri; Aria, Adrianus Indrat
Tungsten/tungsten carbide (W/WC) coatings deposited through chemical vapour deposition (CVD) exhibit favourable mechanical properties and are widely used to extend the working life and performance of engineering parts which operate in high wear and corrosive environments. Following the coating deposition process, the coated parts must adhere to low surface roughness and geometrical tolerance specifications necessitating the need of a machining or surface finishing operation. Unlike monolithic materials, hard W/WC coatings have low machinability due to their high hardness and superior mechanical properties. In this study, electropolishing, which is independent of the material's hardness and capable of processing parts with complex geometries has been studied as a prospective noncontact machining and surface finishing technique for CVD W/WC coatings. Here we report the electropolishing behaviour of W/WC coatings with an average thickness of 50 ± 15 μm and 1300 ± 50 HV hardness. Optimal electropolishing parameters using 5 wt% sodium hydroxide (NaOH) electrolyte concentration at 21 °C allow a mirror-like surface finish with Ra of less than 50 nm and a change in coating thickness of up to 18 μm to be achieved within 5 min. The change in electrolyte temperature from 21 °C to 40 °C was found to have a significant effect on the electropolishing behaviour due to the formation of a thin and unstable viscous film. The electrolyte concertation of 5 wt% was more stable when compare to 3 wt%, giving an overall better surface finish. EBSD analysis revealed that grains with a {111} orientation were preferentially etched in NaOH.
Open Access
Recent progress in precision machining and surface finishing of tungsten carbide hard composite coatings
(MDPI, 2020-07-25) Micallef, Christian; Zhuk, Yuri; Aria, Adrianus Indrat
Owing to their high hardness, fracture toughness and oxidation resistance, tungsten carbide (WC) coatings are extensively deposited on parts that operate in demanding applications, necessitating wear, erosion, and corrosion resistance. The application of thick and hard WC coatings has an inevitable effect on the original dimensions of the parts, affecting the geometrical tolerances and surface roughness. The capability of achieving a sub-micron surface finish and adhere to tight geometrical tolerances accurately and repeatably is an important requirement, particularly with components that operate in high-precision sliding motion. Meeting such requirements through conventional surface finishing methods, however, can be challenging due to the superior mechanical and tribological properties of WC coatings. A brief review into the synthesis techniques of cemented and binderless WC coatings is presented together with a comprehensive review into the available techniques which are used to surface finish WC-based coatings with reference to their fundamental mechanisms and capabilities to process parts with intricate and internal features. The binderless WC/W coating considered in this work is deposited through chemical vapour deposition (CVD) and unlike traditional cemented carbide coatings, it has a homogenous coating structure. This distinctive characteristic has the potential of eliminating key issues commonly encountered with machining and finishing of WC-based coatings. Here, six contact and non-contact surface finishing techniques, include diamond turning, precision grinding, superfinishing, vibratory polishing, electrical discharge machining, and electropolishing are discussed along with their current use in industry and limitations. Key challenges in the field are highlighted and potential directions for future investigation, particularly on binderless WC coatings, are proposed herein