Using large-scale additive manufacturing (LSAM) as a bridge manufacturing process in response to shortages in PPE during the COVID-19 outbreak

The global COVID-19 pandemic has led to an international shortage of Personal Protective Equipment (PPE), with traditional supply chains unable to cope with the significant demand leading to critical shortfalls. A number of open and crowd sourced initiatives have sought to address this shortfall by producing equipment such as protective face shields using additive manufacturing techniques such as Fused Filament Fabrication (FFF). This paper reports the process of designing and manufacturing protective face shields using Large-scale Additive Manufacturing (LSAM) to produce the major thermoplastic components of the face shield. LSAM offers significant advantages over other Additive Manufacturing (AM) technologies in bridge manufacturing scenarios as a true transition between prototypes and mass production techniques such as injection moulding. In the context of production of COVID-19 face shields, the ability to produce the optimised components in under five minutes compared to what would typically take one to two hours using another AM technologies meant that significant production volume could be achieved rapidly with minimal staffing

Multiscale patterning of nanocomposite polyelectrolyte/nanoparticle films using inkjet printing and AFM scratching

The fabrication of structured polymer/nanoparticle composite films through a combination of additive, subtractive and self-assembly methodologies is investigated. Consumer grade inkjet printing hardware is employed to deposit cationic polyelectrolytes on (i) hydrophilic and (ii) hydrophobised glass substrates. The hydrophobisation process controls the spreading of the droplets and hence the lateral size of printed features. The printed cationic polyelectrolyte regions are used as a template to direct the self-assembly of negatively charged gold nanoparticles onto the surface. Micro-scale features are created in the polyelectrolyte/nanoparticle films using AFM scratching to selectively displace material. The effect of substrate wettability on film morphology is discussed

A physical investigation of wear and thermal characteristics of 3D printed nylon spur gears

For particular applications such as automotive and aerospace engineering, polymer gears have unique advantages over metal gears, such as: low cost and weight; high efficiency; quietness of operation; functioning without external lubrication; etc. The characteristics of wear and thermal behaviour of injection moulded gears have previously been studied [1], however, additive manufacturing (AM) and 3D printing processes have become increasingly popular for production of polymer components. It is generally understood that 3D printing is cost effective if production volumes are below 1000 units in comparison with plastic injection moulding [2]. The technology has been applied in wide range of industries, including the automotive, aerospace, medical and architectural industries [3]. The nature of 3D printing means that the process is inherently linked to the materials used and each 3D printing technology has a subset of materials that it is compatible with. For Fused Deposition Modelling (FDM) for instance there are many different materials available on the market including polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polycarbonate (PC), nylon and many others [4]. Due to the increased interest in 3D printing there is an increasing amount of research regarding the direct mechanical properties and thermal properties of 3D printed materials and their modification. Leigh et al. [5] introduced a low-cost conductive composite material for 3D printing of electronic sensosr. Christ et al. [6] increased the elastic strain of polyurethane through addition of multi wall carbon nanotubes. Blok et al. [7] claimed that adding continuous fibers could further increasing the tensile strength compared with carbon fibre nylon composites. Kalin et al. [8] Claimed that gear performance and durability could be affected by thermal properties with the result showing an increase in operating temperature could decreasing the life cycle of the gear. Hu and Mao [9] investigated misalignment effects on acetal gears together with wear behaviour, with the results demonstrating that acetal gears were most sensitive to pitch misalignment

In-line evanescent-field-coupled THz bandpass mux/demux fabricated by additive layer manufacturing technology

In this research, we present the design, fabrication, and experimental validation of 3D printed bandpass filters and mux/demux elements for terahertz frequencies. The filters consist of a set of in-line polystyrene (PS) rectangular waveguides, separated by 100 µm, 200 µm, and 400 µm air gaps. The principle of operation for the proposed filters resides in coupled-mode theory. Q-factors of up to 3.4 are observed, and additionally, the experimental evidence demonstrates that the Q-factor of the filters can be improved by adding fiber elements to the design. Finally, using two independent THz broadband channels, we demonstrate the first mux/demux device based on 3D printed in-line filters for the THz range. This approach represents a fast, robust, and low-cost solution for the next generation of THz devices for communications

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

Quantum Dot Imaging Agents: Haematopoietic Cell Interactions and Biocompatibility

Quantum dots (QDs) are semi-conducting nanoparticles that have been developed for a range of biological and non-biological functions. They can be tuned to multiple different emission wavelengths and can have significant benefits over other fluorescent systems. Many studies have utilised QDs with a cadmium-based core; however, these QDs have since been shown to have poor biological compatibility. Therefore, other QDs, such as indium phosphide QDs, have been developed. These QDs retain excellent fluorescent intensity and tunability but are thought to have elevated biological compatibility. Herein we discuss the applicability of a range of QDs to the cardiovascular system. Key disease states such as myocardial infarction and stroke are associated with cardiovascular disease (CVD), and there is an opportunity to improve clinical imaging to aide clinical outcomes for these disease states. QDs offer potential clinical benefits given their ability to perform multiple functions, such as carry an imaging agent, a therapy, and a targeting motif. Two key cell types associated with CVD are platelets and immune cells. Both cell types play key roles in establishing an inflammatory environment within CVD, and as such aid the formation of pathological thrombi. However, it is unclear at present how and with which cell types QDs interact, and if they potentially drive unwanted changes or activation of these cell types. Therefore, although QDs show great promise for boosting imaging capability, further work needs to be completed to fully understand their biological compatibility

Molecular epidemiology of Streptococcus uberis clinical mastitis in dairy herds: strain heterogeneity and transmission

Multi Locus Sequence Typing was successfully completed on 494 isolates of S. uberis from clinical mastitis cases in a study of 52 commercial dairy herds over a 12 month period. In total, 195 sequence types (STs) were identified. S. uberis mastitis cases occurring in different cows within the same herd and attributed to a common ST were classified as 'potential transmission events' (PTE). Clinical cases attributed to 35 of the 195 STs identified in this study were classified PTE. PTE were identified in 63% of herds. PTE associated cases, which include the first recorded occurrence of that ST in that herd (Index case) and all persistent infections with that PTE ST represented 40% of all the clinical mastitis cases and occurred in 63% of herds. PTE associated cases accounted for over 50% of all S. uberis clinical mastitis cases in 33% of herds. Nine sequence types (ST 5, 6, 20, 22, 24, 35, 233, 361, and 512), eight of which grouped within a clonal complex (sharing at least four alleles), were statistically overrepresented (OVR STs). The findings indicate that 38% of all clinical mastitis cases and 63% of the potential transmission events attributed to S. uberis in dairy herds may be caused by the nine most prevalent strains. The findings suggest that to a small subset of sequence types are disproportionally important in the epidemiology of S. uberis mastitis in the UK with cow to cow transmission of S. uberis potentially occurring in the majority of UK herds and may be the most important route of infection in many herds

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