5,336 research outputs found

    Multifunctional liquid metal polymer composites

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    Liquid metals are fast becoming a new class of materials and additives for composites synthesis. In particular, gallium (Ga) and Ga-based liquid metal and alloys exhibit fluidity and frictionless behaviours along with metallic conductivity properties. Liquid metals based on Ga also present low-toxicity and can be readily formed into micro and nanodroplets or utilised in the bulk as conductive liquid substrates. The resulting Ga-based composites present novel physio-chemical behaviours and multifunctional properties that remain to be explored for a range of applications. In this PhD thesis, the author investigates three liquid metal/polymer composite systems synthesised with low toxicity input materials for remote magnetic actuation, ionic sensing and separation, and cell electrostimulation capabilities. In the first project, the author aims to develop conductive and magnetic liquid metal polymeric gels. Electrically and magnetic conductive nanodroplets of Ga-based alloys are in-situ synthesised in a polyvinyl alcohol (PVA) solution using mild mechanical agitation methods. The resulting conductive and magnetic gels show additional self-healing properties and demonstrate great potential for the design of soft electronic systems and robotics. For the second project, Ga-based composites are investigated for the sensing and separation of alkali metal ions. Nanodroplets of Ga-based alloys embedded into a crosslinked PVA flat-sheet composite provide selectivity and sensing capability and stability in mixed ionic alkali metal solutions. The Ga-based flat-sheet composite has implications for the efficient and low-energy recovery of lithium ions from brines. In the third project, conductive liquid metal polymer composites are prepared for cell culture and electrostimulation. The composite substrates are composed of bulk Ga coated with polydopamine (PDA) to enhance cell adhesion capability. The Ga/PDA composites surfaces show high biocompatibility for cell culture. With added electrical stimulation protocols, the proliferation of mouse embryonic fibroblast cells is promoted. The conductive and biocompatible substrates lead to the use of liquid metals in regenerative medicine and tissue engineering. Collectively, the findings presented in this thesis provide deep insights and scientific findings for future research directions in the field of liquid metal-based composites for multifunctional materials in soft electronics, separation and sensing, and biomaterials

    UMSL Bulletin 2022-2023

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    The 2022-2023 Bulletin and Course Catalog for the University of Missouri St. Louis.https://irl.umsl.edu/bulletin/1087/thumbnail.jp

    Two-dimensional metal halide perovskites and their heterostructures: from synthesis to applications

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    Size- and shape- dependent unique properties of the metal halide perovskite nanocrystals make them promising building blocks for constructing various electronic and optoelectronic devices. These unique properties together with their easy colloidal synthesis render them efficient nanoscale functional components for multiple applications ranging from light emission devices to energy conversion and storage devices. Recently, two-dimensional (2D) metal halide perovskites in the form of nanosheets (NSs) or nanoplatelets (NPls) are being intensively studied due to their promising 2D geometry which is more compatible with the conventional electronic and optoelectronic device structures where film-like components are employed. In particular, 2D perovskites exhibit unique thickness-dependent properties due to the strong quantum confinement effect, while enabling the bandgap tuning in a wide spectral range. In this review the synthesis procedures of 2D perovskite nanostructures will be summarized, while the application-related properties together with the corresponding applications will be extensively discussed. In addition, perovskite nanocrystals/2D material heterostructures will be reviewed in detail. Finally, the wide application range of the 2D perovskite-based structures developed to date, including pure perovskites and their heterostructures, will be presented while the improved synergetic properties of the multifunctional materials will be discussed in a comprehensive way.Comment: 83 pages, 38 Figure

    The electrofabrication of di- and tripeptide hydrogels and their subsequent material properties

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    In this thesis, we report the ability to fabricate hydrogels using low molecular weight gelators (LMWGs) and the subsequent characterisation of their mechanical properties over a variety of different length scales. These materials have been investigated due to their potential use in a wide range of biomedical applications including drug delivery, tissue engineering, cell culture and wound healing. We describe the localised gelation of LMWGs on electrode surfaces via electrochemically generated pH gradients. The electrofabrication of hydrogels on electrode surfaces has shown great potential in the field of biomedicine, with applications ranging from antimicrobial wound dressings, tissue engineering scaffolds and biomimetic materials. First, we describe the largest reported di- and tri-peptide-based hydrogels on electrode surfaces via the electrochemical oxidation of hydroquinone. Expanding upon previous work which focuses on the fabrication of hydrogels on the nanometre to millimetre scale, we deposit hydrogels around 3 cm3 in size. Furthermore, we demonstrate that there is an upper limit to how large the hydrogels can grow which is determined by the size of the pH gradient from the electrode surface. To grow hydrogels of this size, much longer deposition times of two to five hours are required than in previous reports. When the gelator/hydroquinone solution is left exposed to the open atmosphere for this amount of time, the hydroquinone in solution oxidises to benzoquinone/quinhydrone before it can be consumed electrochemically. This inhibits the electrochemical reaction and reduces gelation efficiency. To prevent this, we build a system that can perform the fabrication process under an inert nitrogen atmosphere. Using this system, we show how the choice of gelator affects the mechanical properties of the hydrogel and the resulting material phenomena that cause these changes. As well as this, we show how this approach can be used to grow multi-layered hydrogels, with each layer presenting different chemical and mechanical properties. Secondly, we report the first known example of electrodeposition for a LMWG molecule using an electrochemically generated basic pH gradient at electrode surfaces. This approach has previously been used to fabricate hydrogels of the biopolymer chitosan using the galvanostatic reduction of hydrogen peroxide. During the electrochemical reduction of hydrogen peroxide, hydroxide ions are produced. As a result, a basic pH zone is generated at the electrode, triggering solutions of chitosan to form immobilised hydrogels on the electrode surface. Using this approach, we show how electrodeposition at high pH can be applied to our LMWG system. We then show that we can electrochemically form hydrogels at high pH, with the gel properties being greatly improved by the addition and increased concentration of hydrogen peroxide. Following from this, we then show the simultaneous formation of two low molecular weight hydrogels at acidic and basic pH extremes. To achieve this, we couple the electrochemical reduction of hydrogen peroxide and the electrochemical oxidation of hydroquinone described in the previous chapter. Finally, we report the electrodeposition of five carbazole-protected amino acid hydrogels on electrode surfaces via the electrochemical oxidation of hydroquinone. As well as this, we report the full to partial electropolymerisation of the pre-assembled hydrogels in perchloric acid. For the less bulky carbazole-protected amino acids, the full collapse of the hydrogel to form electrochromic polymers on the electrode surface is achieved. However, for the bulkier gelators, little to no evidence of polymerisation occurs. We believe this is due to the bulky side chain on the gelator backbone preventing the molecular reorganization required for polymerization to occur. To probe the primary self-assembled structures of the carbazole-based hydrogels growing in-situ and their full to partial electropolymerisation in perchloric acid, a first-of-its-kind experiment was performed using small-angle X-ray scattering (SAXS) at Diamond Light Source (I22 beamline, Oxfordshire, UK). We present the novel SAXS set-up discussed as a tool to open up new opportunities to probe and analyse soft materials in realtime

    Phosphate-based glass microspheres for bone repair and localised chemotherapy and radiotherapy treatment of bone cancers

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    Phosphate-based glasses (PBGs) are hugely promising materials for bone repair and regeneration as they can be formulated to be compositionally similar to the inorganic component of bone. Alterations to PBG formulations can be made to tailor their degradation rates and subsequent release of biotherapeutic ions to induce cellular responses, such as osteogenesis. In this work, novel invert-PBGs in the series xP2O5·(56-x)CaO·24MgO·20Na2O (mol%), where x is 40, 35, 32.5 and 30, were formulated to contain pyro (Q1) and orthophosphate (Q0) species. These PBGs were then processed into highly porous microspheres (PMS) via a flame spheroidisation process developed within the research group. Compositional and structural analysis using EDX and 31P-MAS NMR analysis revealed significant depolymerisation had occurred with reducing phosphate content, which increased further when PBGs were processed into PMS. A decrease from 50% to 0% of Q2 species and increase from 6% to 35% of Q0 species was observed for the PMS when the phosphate content decreased from 40 to 30 mol%. Ion release studies also revealed up to a 4-fold decrease in cations and an 8-fold decrease in phosphate anions released with decreasing phosphate content. In vitro bioactivity studies revealed that the orthophosphate rich PMS had favourable bioactivity responses after 28 days of immersion in SBF. Indirect and direct cell culture studies confirmed that the PMS were cytocompatible and supported cell growth and proliferation over 7 days of culture. The P30 PMS with ~65% pyro and ~35% ortho phosphate content revealed the most favourable properties and was proposed to be highly suitable for bone repair and regeneration, especially for orthobiologic applications owing to their highly porous morphology. Doxorubicin (DOX) was used as a model drug to assess its loading and release kinetics from porous phosphate-based glass microspheres to ascertain their suitability for localised drug delivery for the treatment of bone cancers. P40 PMS revealed a DOX loading efficiency of 55%, which was significantly greater than P30 PMS at 29.1%. Both P40 and P30 PMS released more DOX in phosphate buffered saline (PBS) at pH 5 as compared to release at pH 7.4. P40 PMS released 57% of DOX at pH 5 over a 48-hour period, whereas P30 PMS only released 15% of DOX. A pH-responsive DOX release in a more acidic environment suggests that the chemotherapeutic delivery and efficacy properties may lead to increased drug release within tumour tissues. Internal radiotherapy has been shown to be an effective treatment modality to destroy cancerous tissues and is usually achieved by the placement of radioactive sources at the tumour site. In this work, a novel processing method was established to combine yttrium oxide (Y2O3) with P40 phosphate glass particles to form uniform, solid microspheres containing very high yttrium levels via our flame spheroidisation process. The 30Y (~15 mol% Y2O3) and 50Y microspheres (~39 mol% Y2O3) had equivalent and superior yttrium content in comparison to clinically available microspheres used for internal radiotherapy (i.e., Therasphere®). The yttrium-containing microspheres formed were shown to be glass-ceramics, with crystalline phases present but with all elements homogenously distributed throughout the microspheres. Increasing yttrium addition resulted in increased durability of the microspheres, with 50Y microspheres revealing a 10-fold decrease in the release rate of some ions compared to P40 solid microspheres. Indirect and direct cell culture studies confirmed that the 30Y and 50Y microspheres were cytocompatible and supported cell growth and proliferation over 7 days of culture. No significant difference was observed in the metabolic and ALP activity for MG63s for both 30Y and 50Y microspheres from both indirect and direct cell culture studies. Yttrium was incorporated into the phosphate-based microspheres at a level that had not previously been achieved or observed from the literature studies and were shown to support bone cell attachment and growth. A high yttrium content could enable more radiation to be delivered per dose of microspheres, resulting in shorter neutron activation times which could prove beneficial for logistical issues associated with transportation of the biomaterials following nuclear activation. The radionuclide holmium-166 (166Ho) which is comparable to yttrium-90 (90Y) in that it emits β-radiation with a similar tissue penetration range and a significantly reduced half-life of 26.8 hours, was also investigated. The beneficial paramagnetic properties and density of 166Ho indicates that 166Ho-doped materials could be visualised through clinical imaging techniques, whilst simultaneously delivering a therapeutic dose of radiation. In this work, solid holmium-containing microspheres were similarly produced via the flame spheroidisation process using holmium oxide (Ho2O3) and P40 phosphate glass particles. The glass-ceramic microspheres produced had equivalent (30H: ~17mol% Ho2O3) and superior (50H: ~30mol% Ho2O3) holmium content in comparison to clinically used yttrium-doped microspheres (i.e. Therasphere®). Analogous to yttrium containing microspheres, elevated holmium content resulted in topographically unique features on the surface of some 50H microspheres. This increased holmium content resulted in significantly reduced ion release rates for all the ions and the holmium-microspheres did not show evidence of bioactivity. However, in vitro indirect and direct cell culture studies demonstrated their cytocompatibility. No significant difference was observed in the metabolic and ALP activity of MG63 cells for 30H and 50H microspheres in both the indirect and direct cell culture methods. This study appears to be the first to demonstrate microspheres containing high levels of holmium content that can also facilitate direct cell growth and proliferation of human osteoblast-like cells. The microspheres developed are therefore hugely promising biomaterials for both drug delivery and internal radiotherapy applications, as well as for promoting bone repair and regeneration at damaged sites. High holmium content could also result in higher specific activity per microsphere to increase radiotherapy delivery whilst also promoting higher visibility via imaging modalities

    Lanthanide-doped upconversion nanoparticles (UCNPs) for biomedical applications

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    This thesis examines the need for new antibacterial materials to treat small colony variants (SCVs) of Staphylococcus (S.) aureus bacteria and their parental strains. While ZnO-based nanoparticles (NPs) activated by ultraviolet (UV) and short wavelength visible light have been researched for their antibacterial properties, the potential benefits of incorporating UCNPs to allow activation by near-infrared (NIR) light have been overlooked. This study aims to fill this research gap by comprehensively investigating the synthesis and performance of ZnO-coated lanthanide-doped upconversion nanoparticle (UCNP) composites activated by NIR light against S. aureus SCVs and parental strains. Furthermore, this research addresses the limited understanding of the potential risks associated with UV emission from UCNPs used as fluorescent probes in super-resolution microscopy (SRM). Despite extensive research on the usage of UCNPs as fluorescent probes for SRMs, the potential cytotoxic effects of UV emission from UCNPs have not been thoroughly studied. To advance cellular imaging techniques and ensure cellular viability, a comprehensive investigation of UV emission from UCNPs is necessary. This thesis aims to identify and quantify UV emission by UCNPs used in SRM and develop strategies to minimise UV emission and mitigate potential cytotoxic effects. These two main aims are addressed in three results chapters. The first aim, the focus of chapters 2 and 3, focuses on the synthesis UCNP@ZnO composites that can be activated by NIR light for antimicrobial photodynamic therapy (aPDT) applications against S. aureus SCVs and parental strains. Chapter 2 reports the synthesis and performance of these composites, showing these materials to be effective antibacterial therapies against S. aureus SCVs, while chapter 3 improves upon the performance of these composites by careful tuning of the UCNP core and provides enhancements to the ZnO shell composition to improve reactive oxygen species generation and add a second mode of action in the form of silver nanoparticles. The second aim of this research is covered in chapter 4, which reports an investigation into the UV emission from UCNPs used as fluorescent probes in SRM. The work posits the need to understand the UV emission properties of these UCNPs as knowledge of these and the potential for cytotoxic effects are crucial for optimizing cellular imaging experiments and ensuring accurate and reliable results. Chapter 4 identifies design features and compositions that can limit UV emission, thereby minimizing the risk of phototoxicity and advancing the field of cellular imaging. Overall, the findings from this research have the potential to contribute to the development of safer and more effective targeted antibacterial therapies and enhance the understanding of UV emissions in cellular imaging techniques.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 202

    Cardiovascular health: from cardiomyocyte electrostimulation to miRNA detection

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    Current methods of cell culture where electrical stimulation is applied during culture require a wired connection to a power supply to generate an electric field with which to stimulate the cells. This method is intrusive in a lab setting and does not conveniently allow for traditional cell culture techniques during stimulation, hence it is frequently omitted from cell culture protocols. The aim of this work is to demonstrate a novel method of electrical stimulation of cardiomyocytes using wireless bipolar electrochemical techniques. The work describes the design and characterisation of a wireless bipolar electrode and wireless bipolar electrochemical cell to facilitate wireless bipolar electrostimulation. By using a wireless connection more versatile experiments can be conducted on cells in culture while mitigating the contamination risk of a traditional wired stimulation platform. Using a polypyrrole based conducting film doped with fibronectin molecules to facilitate the adherence and growth of cardiomyocytes on the bipolar electrode surface. Cell culture on a conductive film opens the possibility of future applications in electroceuticals by providing a wireless platform to deliver and electric field to cells in culture. Demonstrating cell culture on conductive polymer with the application of electric fields allows for the study of healthy and disease cell populations in the presence of electrical stimuli. Biomarker monitoring during this work is important to characterise and understand the impact of stimuli on the cells in culture. As such, an electrochemical miRNA biosensor was also explored in this work. The assay was based on the detection of miRNA through hydrogen peroxide degradation. The assay was built of screen-printed electrodes as a method to characterise cell cultures. The ability to monitor biomarkers both in vitro and in vivo is important in generating an understanding of disease models and in the development of point-of-care testing capabilities

    The 2023 wearable photoplethysmography roadmap

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    Photoplethysmography is a key sensing technology which is used in wearable devices such as smartwatches and fitness trackers. Currently, photoplethysmography sensors are used to monitor physiological parameters including heart rate and heart rhythm, and to track activities like sleep and exercise. Yet, wearable photoplethysmography has potential to provide much more information on health and wellbeing, which could inform clinical decision making. This Roadmap outlines directions for research and development to realise the full potential of wearable photoplethysmography. Experts discuss key topics within the areas of sensor design, signal processing, clinical applications, and research directions. Their perspectives provide valuable guidance to researchers developing wearable photoplethysmography technology
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