Materials and methods for microstereolithography

There is an increasing requirement to fabricate ever smaller components and microdevices and incorporate them within all aspects of our lives. From a Wii controller to a car airbag, micro-technology is employed in a huge spectrum of applications. Within process control and sample analysis, micro-components are making a significant impact, driven by the desire to use smaller volumes, lower concentrations, less reagent, or simply to make the process quicker or cheaper. Currently, methods of fabrication for such devices are based predominantly on silicon processing techniques. While these techniques are suitable for mass manufacture / high volume applications, there are a number of disadvantages for situations requiring lower volumes or where the end system is continually evolving – such as for research applications. The primary drawbacks are cost, turnaround time and the requirement for expensive processing facilities. However, for these situations, additive layer manufacture presents huge promise as an alternative fabrication technology. The field of additive layer manufacture has advanced greatly since its inception 25 years ago. While such technologies are still primarily focused on the field of rapid prototyping of purely mechanical structures, it is clear that their full potential is yet to be realised. This is particularly the case for stereolithography and microstereolithography, the latter of which provides the capability to create complex, true 3D structures (as opposed to pseudo 3D/extruded 2D of silicon techniques), measureable on the micron scale. This thesis shows that microstereolithography has the potential to become an alternative fabrication method for functional micro-devices and structures. This is due to the simplicity of its single-step fabrication process and the significant time/cost savings it presents. Therefore, making it an affordable technique for low volume production where a fast turnaround is required. However, the lack of functional materials compatible with microstereolithography, and hence the lack of examples of the technology being used to produce active components, currently limits it in this respect. This project therefore focused on exploring the possibilities of using microstereolithography as an alternative to traditional silicon based techniques for the direct fabrication of functional micro-devices and sensors. This was achieved through the development of a number of microstereolithography compatible, novel materials, methods and applications. Here, presented for the first time are both conductive and magnetic composite photopolymers compatible with microstereolithography technology. The materials were developed with the use of a custom built, constrained surface system using a parallel projection method. The system used LED technology as a novel exposure source, tuned to the developed materials in an attempt to gain extra control over the curing process and hence achieve higher quality components. These materials were characterised and then used to fabricate exemplar sensing devices using microstereolithography – a method not previously used for creating such devices. Microfluidic flow sensing devices were used to demonstrate the practical application of the magnetic material. One of which, a lab-on-chip type device, was demonstrated to have a working range of 5 to 70 ml/min when tested with a liquid medium. Similarly, a practical application of the conductive material was shown through the fabrication of MSL-printed conductometirc vapour sensors. The sensors showed favourable characteristics working in range of humidites (up to 50% RH) and temperatures (up to 70°C). The sensors also demonstrated a degree of selectivity to different analyte vapours. Finally, the technology was demonstrated as a feasible method of fabricating ultrasonic beam forming apparatus. Acoustic testing of a range of materials also suggested that the composite metal materials could be used to further improve performance. The novel materials and techniques investigated, along with the exemplar devices produced, demonstrate further abilities and a wider range of applications than has been demonstrated with this technology to date. It is hoped that this research will lead to wider use of the technology and encourage further advances in the field of microstereolithography

Using a magnetite/thermoplastic composite in 3D printing of direct replacements for commercially available flow sensors

Flow sensing is an essential technique required for a wide range of application environments ranging from liquid dispensing to utility monitoring. A number of different methodologies and deployment strategies have been devised to cover the diverse range of potential application areas. The ability to easily create new bespoke sensors for new applications is therefore of natural interest. Fused deposition modelling is a 3D printing technology based upon the fabrication of 3D structures in a layer-by-layer fashion using extruded strands of molten thermoplastic. The technology was developed in the late 1980s but has only recently come to more wide-scale attention outside of specialist applications and rapid prototyping due to the advent of low-cost 3D printing platforms such as the RepRap. Due to the relatively low-cost of the printers and feedstock materials, these printers are ideal candidates for wide-scale installation as localized manufacturing platforms to quickly produce replacement parts when components fail. One of the current limitations with the technology is the availability of functional printing materials to facilitate production of complex functional 3D objects and devices beyond mere concept prototypes. This paper presents the formulation of a simple magnetite nanoparticle-loaded thermoplastic composite and its incorporation into a 3D printed flow-sensor in order to mimic the function of a commercially available flow-sensing device. Using the multi-material printing capability of the 3D printer allows a much smaller amount of functional material to be used in comparison to the commercial flow sensor by only placing the material where it is specifically required. Analysis of the printed sensor also revealed a much more linear response to increasing flow rate of water showing that 3D printed devices have the potential to at least perform as well as a conventionally produced sensor

Additively-manufactured piezoelectric devices

A low-cost micro-stereolithography technique with the ability to additively manufacture dense piezoelectric ceramic components is reported. This technique enables the layer-wise production of functional devices with a theoretical in-plane resolution of ∼20 μm and an out-of-plane resolution of <1 μm without suffering a significant reduction in the piezoelectric properties when compared to conventionally produced ceramics of the same composition. The ability to fabricate devices in complex geometries and with different material properties means that conventional limits of manufacturing are not present. A hollow, spherical shell of the piezoelectric material 0.65Pb(Mg⅓Nb⅔)O3–0.35PbTiO3, built without tooling or recourse to additional equipment or processes, is shown generating ultrasound in the MHz range

Additive manufacture of impedance matching layers for air-coupled ultrasonic transducers

A key problem in designing an efficient ultrasonic transducer for operating in a low acoustic impedance medium such as air is the large impedance mismatch between the active piezoceramic material and the load medium. While acoustic matching layers can be added to the face of the piezoceramic, the associated manufacturing difficulties and reliability can impact upon the cost and longevity of the resultant transducer. This paper presents some preliminary investigations conducted using an additive manufacturing technique, to develop a new material system for matching layer fabrication for air-coupled ultrasonic transducers. Results to date are very encouraging, and could result in a robust, reproducible, economical and improved fabrication method for air-coupled transducers

Design and fabrication of 3-D printed conductive polymer structures for THz polarization control

In this paper, we numerically and experimentally demonstrate the inverse polarization effect in three-dimensional (3-D) printed polarizers for the frequency range of 0.5 - 2.7 THz. The polarizers simply consist of 3-D printed strip lines of conductive polylactic acid (CPLA, Proto-Pasta) and do not require a substrate or any further metallic deposition. The experimental and numerical results show that the proposed structure acts as a broadband polarizer between the range of 0.3 THz to 2.7 THz, in which the inverse polarization effect is clearly seen for frequencies above 0.5 THz. In the inverse polarization effect, the transmission of the transverse electric (TE) component exceeds that of the TM component, in contrast to the behavior of a typical wire-grid polarizer. We show how the performance of the polarizers depends on the spacing and thickness of the CPLA structure; extinction ratios higher than 20 dB are achieved. This is the first report using CPLA to fabricate THz polarizers, demonstrating the potential of using conductive polymers to design THz components efficiently and robustly

A simple, low-cost conductive composite material for 3D printing of electronic sensors

3D printing technology can produce complex objects directly from computer aided digital designs. The technology has traditionally been used by large companies to produce fit and form concept prototypes (‘rapid prototyping’) before production. In recent years however there has been a move to adopt the technology as full-scale manufacturing solution. The advent of low-cost, desktop 3D printers such as the RepRap and Fab@Home has meant a wider user base are now able to have access to desktop manufacturing platforms enabling them to produce highly customised products for personal use and sale. This uptake in usage has been coupled with a demand for printing technology and materials able to print functional elements such as electronic sensors. Here we present formulation of a simple conductive thermoplastic composite we term ‘carbomorph’ and demonstrate how it can be used in an unmodified low-cost 3D printer to print electronic sensors able to sense mechanical flexing and capacitance changes. We show how this capability can be used to produce custom sensing devices and user interface devices along with printed objects with embedded sensing capability. This advance in low-cost 3D printing with offer a new paradigm in the 3D printing field with printed sensors and electronics embedded inside 3D printed objects in a single build process without requiring complex or expensive materials incorporating additives such as carbon nanotubes

Glycaemic control in people with type 2 diabetes mellitus during and after cancer treatment: A systematic review and meta-analysis

Background Cancer and Diabetes Mellitus (DM) are leading causes of death worldwide and the prevalence of both is escalating. People with co-morbid cancer and DM have increased morbidity and premature mortality compared with cancer patients with no DM. The reasons for this are likely to be multifaceted but will include the impact of hypo/hyperglycaemia and diabetes therapies on cancer treatment and disease progression. A useful step toward addressing this disparity in treatment outcomes is to establish the impact of cancer treatment on diabetes control. Aim The aim of this review is to identify and analyse current evidence reporting glycaemic control (HbA1c) during and after cancer treatment. Methods Systematic searches of published quantitative research relating to comorbid cancer and type 2 diabetes mellitus were conducted using databases, including Medline, Embase, PsychINFO, CINAHL and Web of Science (February 2017). Full text publications were eligible for inclusion if they: were quantitative, published in English language, investigated the effects of cancer treatment on glycaemic control, reported HbA1c (%/mmols/mol) and included adult populations with diabetes. Means, standard deviations and sample sizes were extracted from each paper; missing standard deviations were imputed. The completed datasets were analysed using a random effects model. A mixed-effects analysis was undertaken to calculate mean HbA1c (%/mmols/mol) change over three time periods compared to baseline. Results The available literature exploring glycaemic control post-diagnosis was mixed. There was increased risk of poor glycaemic control during this time if studies of surgical treatment for gastric cancer are excluded, with significant differences between baseline and 12 months (p < 0.001) and baseline and 24 months (p = 0.002). Conclusion We found some evidence to support the contention that glycaemic control during and/or after non-surgical cancer treatment is worsened, and the reasons are not well defined in individual studies. Future studies should consider the reasons why this is the case

Managing childhood fever and pain – the comfort loop

Parents can transmit their anxiety to their child, and just as children can pick up on parental anxiety, they can also respond to a parent's ability to stay calm in stressful situations. Therefore, when treating children, it is important to address parental anxiety and to improve their understanding of their child's ailment. Parental understanding and management of both pain and fever – common occurrences in childhood – is of utmost importance, not just in terms of children's health and welfare, but also in terms of reducing the economic burden of unnecessary visits to paediatric emergency departments. Allaying parental anxiety reduces the child's anxiety and creates a positive feedback loop, which ultimately affects both the child and parent

Elucidation of the Mode of Action of a New Antibacterial Compound Active against Staphylococcus aureus and Pseudomonas aeruginosa.

Nosocomial and community-acquired infections caused by multidrug resistant bacteria represent a major human health problem. Thus, there is an urgent need for the development of antibiotics with new modes of action. In this study, we investigated the antibacterial characteristics and mode of action of a new antimicrobial compound, SPI031 (N-alkylated 3, 6-dihalogenocarbazol 1-(sec-butylamino)-3-(3,6-dichloro-9H-carbazol-9-yl)propan-2-ol), which was previously identified in our group. This compound exhibits broad-spectrum antibacterial activity, including activity against the human pathogens Staphylococcus aureus and Pseudomonas aeruginosa. We found that SPI031 has rapid bactericidal activity (7-log reduction within 30 min at 4x MIC) and that the frequency of resistance development against SPI031 is low. To elucidate the mode of action of SPI031, we performed a macromolecular synthesis assay, which showed that SPI031 causes non-specific inhibition of macromolecular biosynthesis pathways. Liposome leakage and membrane permeability studies revealed that SPI031 rapidly exerts membrane damage, which is likely the primary cause of its antibacterial activity. These findings were supported by a mutational analysis of SPI031-resistant mutants, a transcriptome analysis and the identification of transposon mutants with altered sensitivity to the compound. In conclusion, our results show that SPI031 exerts its antimicrobial activity by causing membrane damage, making it an interesting starting point for the development of new antibacterial therapies

Review of the efficacy and safety of over-the-counter medicine

Over-the-counter medicines are available without prescription because of their safety and effectiveness, to treat minor ailments and symptoms. The objective of the study was to analyze the availability and quality of systematic reviews published about nonprescription medicines, identifying the groups for which there are gaps in evidence. We identified published articles through the Cochrane Database of Systematic Review and MEDLINE, from the start of the database until May 2012, using the search terms "nonprescription drugs," "over the counter," and "OTC." We searched for articles that describe systematic reviews addressing the efficacy and safety of drugs dispensed without a prescription, according to the lists published by the Association of the European Self-Medication Industry and in Brazil, in the clinical conditions listed in Groups and Specified Therapeutic Indications. We included 49 articles, 18 articles were of moderate quality and 31 of high quality. Of the studies, 74.5% demonstrated efficacy in favor of the use of drugs evaluated. Of the 24 studies that evaluated safety, 21% showed evidence unfavorable to the drug. Overall, the evidence found in the studies included in the overview is favorable to the use of the drugs evaluated. However, there are gaps in evidence for some therapy groups.</p