Chemical and Biomolecular Engineering - Research Publications
Now showing items 1-12 of 531
Electronic spectrum and photodissociation chemistry of the linear methyl propargyl cation H2C4H3+
(AMER INST PHYSICS, 2017-01-28)
The electronic spectrum of the methyl propargyl cation (2-butyn-1-yl cation, H2C4H3+) is measured over the 230-270 nm range by photodissociating the bare cation and its Ar and N2 tagged complexes in a tandem mass spectrometer. The observed A'1←A'1 band system has an origin at 37 753 cm-1 for H2C4H3+, 37738 cm-1 for H2C4H3+-Ar, and 37 658 cm-1 for H2C4H3+-N2. The methyl propargyl cation photodissociates to produce either C2H3++C2H2 (protonated acetylene + acetylene) or H2C4H++H2 (protonated diacetylene + dihydrogen). Photodissociation spectra of H2C4H3+, H2C4H3+-Ar, and H2C4H3+-N2 exhibit similar vibronic structure, with a strong progression of spacing 630 cm-1 corresponding to excitation of the C-C stretch mode. Interpretation of the spectra is aided by ground and excited state calculations using time dependent density functional theory at the ωB97X-D/aug-cc-pVDZ level of theory. Ab initio calculations and master equation simulations were used to interpret the dissociation of H2C4H3+ on the ground state manifold. These calculations support the experimentally observed product branching ratios in which acetylene elimination dominates and also suggests that channel switching occurs at higher energies to favor H2 elimination.
Freeze casting for near-net-shaping of dense zirconium diboride ceramics
Zirconium diboride (ZrB2) was formed into dense complex shapes using freeze casting as a near-net-shaping technique. Aqueous-based formulations were compared with nonaqueous (cyclohexane) based formulations in terms of rheological behavior, particle packing in the green body, sintered density, macroscale porosity, and cracking. The influence of particle solids concentration and freezing rate was investigated. The aqueous formulations were found to be deficient in that they produced macroscale porosity that could not be eliminated during sintering resulting in low density and large pores in the final shaped objects. The nonaqueous-based system was able to produce complex shaped objects with significantly reduced macroscale porosity. The higher concentration of solids in the nonaqueous-based formulations was primarily responsible for the reduced macroscale porosity and enabled higher sintered densities (up to 90%-91.5% of theoretical density for fast freezing). The microstructure of the ZrB2 formed at fast freezing rates and high solids content typically had isolated pores in the order of 5-10 μm in size, mainly found along grain boundaries (grain sizes between 20 and 50 μm). Although this rapid freezing produced denser components, it tended to produce objects with internal cracks. When slower freezing rates were used, intricate complex shaped objects could be produced without cracks but their density was only between 65% and 80% of theoretical density.
Fracture toughness of wet and dry particulate materials comprised of colloidal sized particles: role of plastic deformation
(ROYAL SOC CHEMISTRY, 2017-07-21)
This work demonstrates a method of measuring the fracture toughness of particulate materials comprised of colloidal sized particles over a wide range of saturation. Diametral compression of cylinders containing flaws of controlled length was used to measure the mode I fracture toughness. The effect of degree of saturation on the fracture toughness of slip cast ceramic grade alumina (d50 = 0.7 μm) was investigated. Dry powder compacts have significantly lower fracture toughness than when the powder compact is nearly fully saturated. All observations are consistent with the fracture mechanism being predominantly brittle for the dry samples but predominantly ductile in the nearly saturated samples. The additional dissipation that occurs during the ductile fracture of the nearly saturated samples is due to plastic deformation in front of the crack tip. This well-known mechanism for toughening in metals has been quantified for the first time in soft matter. Analysis of the results indicates that the size of the plastic dissipation zone is more than an order of magnitude larger in the nearly saturated materials compared to the dry material. Understanding the fracture mechanisms that control the propagation of cracks through saturated, partially saturated and dry particulate materials comprised of colloidal sized particles provides additional insight into understanding drying cracks in paint, other coatings, ceramics and water treatment sludge.
Colloidal processing: enabling complex shaped ceramics with unique multiscale structures
Colloidal processing of fine ceramic powders enables the production of complex shaped ceramics with unique micro and macro structures which are not possible to produce via conventional dry processing routes. Because of this enhanced structural control and shaping capabilities, colloidal processing has been exploited to produce ceramic components with ever increasing complexity and functionalities. In this review, we revisit some of the research efforts on this topic to highlight its relevance and growing importance for the advanced manufacturing of functional ceramics. Selected examples of colloidal systems with increasing level of complexity are discussed to showcase the wide range of structures that can be generated through wet processing approaches. The historical development and background knowledge pertaining to colloids and surface interactions is first briefly reviewed. The major colloidal shape forming and additive manufacturing processes that utilize colloidal pastes and inks are then reviewed, highlighting the control of suspension rheology needed in these techniques. Next, methodologies that combine suspended particles with a pore‐forming phase are discussed as a means to produce porous ceramic materials. Further control over the interactions between anisotropic particles and their alignment in suspensions can be gained via externally applied fields (such as magnetic) to produce texturally aligned green bodies. This leads to bioinspired ceramics that can programmably morph into complex shaped objects upon sintering. Hierarchical porous structures with high mechanical efficiency are also shown as an example of the multiscale designs that can be generated through advanced colloidal processing. As drying of ceramic bodies is an inevitable consequence of wet colloidal processing, the current understanding of this critical processing step is reviewed. Finally, the gaps in knowledge in these fields are discussed to provide our perspective on where the field may support advances in ceramics in the future.
Investigation of the Surface of Ga-Sn-Zn Eutectic Alloy by the Characterisation of Oxide Nanofilms Obtained by the Touch-Printing Method
Ga⁻Sn⁻Zn eutectic alloy is a non-toxic liquid metal alloy which could be used in a multitude of applications, including as a heat transfer agent, in gas sensing, and in medicine. Alloys containing gallium readily oxidise in air, forming a thin oxide layer that influences the properties of liquid metals and which has not been studied. In this study, the oxide layer formed on Ga⁻Sn⁻Zn alloy was transferred at room temperature onto three substrates-quartz, glass and silicon. The contact angle between the liquid alloy and different substrates was determined. The obtained thin oxide films were characterised using atomic force microscopy, X-ray photon spectroscopy, and optical and transmission electron microscopy. The contact angle does not influence the deposition of the layers. It was determined that it is possible to obtain nanometric oxide layers of a few micrometres in size. The chemical composition was determined by XPS and EDS independently, and showed that the oxide layer contains about 90 atom % of gallium with some additions of tin and zinc. The oxides obtained from the eutectic Ga⁻Sn⁻Zn liquid alloys appear to be nanocrystalline.
Room temperature CO2 reduction to solid carbon species on liquid metals featuring atomically thin ceria interfaces
(Nature Research (part of Springer Nature), 2019-02-26)
Negative carbon emission technologies are critical for ensuring a future stable climate. However, the gaseous state of CO2 does render the indefinite storage of this greenhouse gas challenging. Herein, we created a liquid metal electrocatalyst that contains metallic elemental cerium nanoparticles, which facilitates the electrochemical reduction of CO2 to layered solid carbonaceous species, at a low onset potential of −310 mV vs CO2/C. We exploited the formation of a cerium oxide catalyst at the liquid metal/electrolyte interface, which together with cerium nanoparticles, promoted the room temperature reduction of CO2. Due to the inhibition of van der Waals adhesion at the liquid interface, the electrode was remarkably resistant to deactivation via coking caused by solid carbonaceous species. The as-produced solid carbonaceous materials could be utilised for the fabrication of high-performance capacitor electrodes. Overall, this liquid metal enabled electrocatalytic process at room temperature may result in a viable negative emission technology.
Wafer-scale two-dimensional semiconductors from printed oxide skin of liquid metals
(NATURE PUBLISHING GROUP, 2017-02-17)
A variety of deposition methods for two-dimensional crystals have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we introduce a technique for depositing and patterning of wafer-scale two-dimensional metal chalcogenide compounds by transforming the native interfacial metal oxide layer of low melting point metal precursors (group III and IV) in liquid form. In an oxygen-containing atmosphere, these metals establish an atomically thin oxide layer in a self-limiting reaction. The layer increases the wettability of the liquid metal placed on oxygen-terminated substrates, leaving the thin oxide layer behind. In the case of liquid gallium, the oxide skin attaches exclusively to a substrate and is then sulfurized via a relatively low temperature process. By controlling the surface chemistry of the substrate, we produce large area two-dimensional semiconducting GaS of unit cell thickness (∼1.5 nm). The presented deposition and patterning method offers great commercial potential for wafer-scale processes.
In vivo three-dimensional evaluation of tumour hypoxia in nasopharyngeal carcinomas using FMT-CT and MSOT.
(Springer Verlag, 2020-05)
PURPOSE: Accurate evaluation of hypoxia is particularly important in patients with nasopharyngeal carcinoma (NPC) undergoing radiotherapy. The aim of this study was to propose a novel imaging strategy for quantitative three-dimensional (3D) evaluation of hypoxia in a small animal model of NPC. METHODS: A carbonic anhydrase IX (CAIX)-specific molecular probe (CAIX-800) was developed for imaging of hypoxia. Mouse models of subcutaneous, orthotopic, and spontaneous lymph node metastasis from NPC (5 mice per group) were established to assess the imaging strategy. A multi-modality imaging method that consisted of a hybrid combination of fluorescence molecular tomography-computed tomography (FMT-CT) and multispectral optoacoustic tomography (MSOT) was used for 3D quantitative evaluation of tumour hypoxia. Magnetic resonance imaging, histological examination, and immunohistochemical analysis were used as references for comparison and validation. RESULTS: In the early stage of NPC (2 weeks after implantation), FMT-CT enabled precise 3D localisation of the hypoxia biomarker with high sensitivity. At the advanced stage (6 weeks after implantation), MSOT allowed multispectral analysis of the biomarker and haemoglobin molecules with high resolution. The combination of high sensitivity and high resolution from FMT-CT and MSOT could not only detect hypoxia in small-sized NPCs but also visualise the heterogeneity of hypoxia in 3D. CONCLUSIONS: Integration of FMT-CT and MSOT could allow comprehensive and quantifiable evaluation of hypoxia in NPC. These findings may potentially benefit patients with NPC undergoing radiotherapy in the future. Graphical abstract A novel multimodality imaging strategy for three-dimensional evaluation of tumour hypoxia in an orthotopic model of nasopharyngeal carcinoma.
Combining Nanomaterials and Developmental Pathways to Design New Treatments for Cardiac Regeneration: The Pulsing Heart of Advanced Therapies
(Frontiers Media, 2020-04-24)
The research for heart therapies is challenged by the limited intrinsic regenerative capacity of the adult heart. Moreover, it has been hampered by the poor results obtained by tissue engineering and regenerative medicine attempts at generating functional beating constructs able to integrate with the host tissue. For this reason, organ transplantation remains the elective treatment for end-stage heart failure, while novel strategies aiming to promote cardiac regeneration or repair lag behind. The recent discovery that adult cardiomyocytes can be ectopically induced to enter the cell cycle and proliferate by a combination of microRNAs and cardioprotective drugs, like anti-oxidant, anti-inflammatory, anti-coagulants and anti-platelets agents, fueled the quest for new strategies suited to foster cardiac repair. While proposing a revolutionary approach for heart regeneration, these studies raised serious issues regarding the efficient controlled delivery of the therapeutic cargo, as well as its timely removal or metabolic inactivation from the site of action. Especially, there is need for innovative treatment because of evidence of severe side effects caused by pleiotropic drugs. Biocompatible nanoparticles possess unique physico-chemical properties that have been extensively exploited for overcoming the limitations of standard medical therapies. Researchers have put great efforts into the optimization of the nanoparticles synthesis and functionalization, to control their interactions with the biological milieu and use as a viable alternative to traditional approaches. Nanoparticles can be used for diagnosis and deliver therapies in a personalized and targeted fashion. Regarding the treatment of cardiovascular diseases, nanoparticles-based strategies have provided very promising outcomes, in preclinical studies, during the last years. Efficient encapsulation of a large variety of cargos, specific release at the desired site and improvement of cardiac function are some of the main achievements reached so far by nanoparticle-based treatments in animal models. This work offers an overview on the recent nanomedical applications for cardiac regeneration and highlights how the versatility of nanomaterials can be combined with the newest molecular biology discoveries to advance cardiac regeneration therapies.
Sulfoxide-Containing Polymer-Coated Nanoparticles Demonstrate Minimal Protein Fouling and Improved Blood Circulation
(Wiley Open Access, 2020-05-17)
Minimizing the interaction of nanomedicines with the mononuclear phagocytic system (MPS) is a critical challenge for their clinical translation. Conjugating polyethylene glycol (PEG) to nanomedicines is regarded as an effective approach to reducing the sequestration of nanomedicines by the MPS. However, recent concerns about the immunogenicity of PEG highlight the demand of alternative low‐fouling polymers as innovative coating materials for nanoparticles. Herein, a highly hydrophilic sulfoxide‐containing polymer—poly(2‐(methylsulfinyl)ethyl acrylate) (PMSEA)—is used for the surface coating of iron oxide nanoparticles (IONPs). It is found that the PMSEA polymer coated IONPs have a more hydrophilic surface than their PEGylated counterparts, and demonstrate remarkably reduced macrophage cellular uptake and much less association with human plasma proteins. In vivo study of biodistribution and pharmacokinetics further reveals a much‐extended blood circulation (≈2.5 times longer in terms of elimination half‐life t 1/2) and reduced accumulation (approximately two times less) in the organs such as the liver and spleen for IONPs coated by PMSEA than those by PEG. It is envisaged that the highly hydrophilic sulfoxide‐containing polymers have huge potential to be employed as an advantageous alternative to PEG for the surface functionalization of a variety of nanoparticles for long circulation and improved delivery.
Review of Membranes for Helium Separation and Purification
Membrane gas separation has potential for the recovery and purification of helium, because the majority of membranes have selectivity for helium. This review reports on the current state of the research and patent literature for membranes undertaking helium separation. This includes direct recovery from natural gas, as an ancillary stage in natural gas processing, as well as niche applications where helium recycling has potential. A review of the available polymeric and inorganic membranes for helium separation is provided. Commercial gas separation membranes in comparable gas industries are discussed in terms of their potential in helium separation. Also presented are the various membrane process designs patented for the recovery and purification of helium from various sources, as these demonstrate that it is viable to separate helium through currently available polymeric membranes. This review places a particular focus on those processes where membranes are combined in series with another separation technology, commonly pressure swing adsorption. These combined processes have the most potential for membranes to produce a high purity helium product. The review demonstrates that membrane gas separation is technically feasible for helium recovery and purification, though membranes are currently only applied in niche applications focused on reusing helium rather than separation from natural sources.
Self-assembling influenza nanoparticle vaccines drive extended germinal center activity and memory B cell maturation.
(American Society for Clinical Investigation, 2020-05-21)
Protein-based, self-assembling nanoparticles elicit superior immunity compared with soluble protein vaccines, but the immune mechanisms underpinning this effect remain poorly defined. Here, we investigated the immunogenicity of a prototypic ferritin-based nanoparticle displaying influenza hemagglutinin (HA) in mice and macaques. Vaccination of mice with HA-ferritin nanoparticles elicited higher serum antibody titers and greater protection against experimental influenza challenge compared with soluble HA protein. Germinal centers in the draining lymph nodes were expanded and persistent following HA-ferritin vaccination, with greater deposition of antigen that colocalized with follicular dendritic cells. Our findings suggest that a highly ordered and repetitive antigen array may directly drive germinal centers through a B cell-intrinsic mechanism that does not rely on ferritin-specific T follicular helper cells. In contrast to mice, enhanced immunogenicity of HA-ferritin was not observed in pigtail macaques, where antibody titers and lymph node immunity were comparable to soluble vaccination. An improved understanding of factors that drive nanoparticle vaccine immunogenicity in small and large animal models will facilitate the clinical development of nanoparticle vaccines for broad and durable protection against diverse pathogens.