The Covid-19 global pandemic has reshaped the requirements of healthcare sectors worldwide. Following the exposure risks associated with Covid-19, this paper aims to design, optimise, and validate a wearable medical device that reduces the risk of transmission of contagious droplets from infected patients in a hospital setting. This study specifically focuses on those receiving high-flow nasal oxygen therapy. The design process consisted of optimising the geometry of the visor to ensure that the maximum possible percentage of harmful droplets exhaled by the patient can be successfully captured by a vacuum tube attached to the visor. This has been completed by deriving a number of concept designs and assessing their effectiveness, based on numerical analysis, computational fluid dynamics (CFD) simulations and experimental testing. The CFD results are validated using various experimental methods such as Schlieren imaging, particle measurement testing and laser sheet visualisation. Droplet capturing efficiency of the visor was measured through CFD and validated through experimental particle measurement testing. The results presented a 5% deviation between CFD and experimental results. Also, the modifications based on the validated CFD results improved the visor effectiveness by 47% and 38% for breathing and coughing events, respectively.

Seafood has often been implicated in outbreaks of food-borne illness caused by Listeria monocytogenes but the source of contamination is usually not known. In this study we investigated the possibility that this pathogen could survive in seawater for an extended time period. Freshly collected seawater samples were inoculated with 1x10(8)CFU per ml of L. monocytogenes EGD-e and survival was monitored by plate counting for up to 25days. When incubated in the dark, either at ambient temperatures (4-14 degrees C) or at 16 degrees C, >10(4)CFU per ml survivors were present after 25days. However, when the seawater cell suspensions were exposed to ambient light (solar irradiation) and temperatures, L. monocytogenes lost viability rapidly and no survivors could be detected after the 80h time point. Both UV-A and visible light in the blue region of the spectrum (470nm) were found to contribute to this effect. The stress inducible sigma factor sigma(B) was found to play a role in survival of L. monocytogenes in seawater. Together these data demonstrate that solar irradiation is a critical determinant of L. monocytogenes survival in marine environments. The data further suggest the possibility of controlling this food-borne pathogen in food-processing environments using visible light. Significance and Impact of the StudyListeria monocytogenes is a food-borne bacterial pathogen capable of causing the life-threatening infection, listeriosis. In seafood the route of contamination from the environment is often not well understood as this pathogen is not generally thought to survive well in seawater. Here we provide evidence that L. monocytogenes is capable of surviving for long periods of time in seawater when light is excluded. Sunlight is demonstrated to have a significant effect on the survival of this pathogen in seawater, and both visible (470nm) and UV-A light are shown to contribute to this effect.

Catheter-associated urinary tract infections are the most common hospital-acquired infection, for which Escherichia coli is the leading cause. This study investigated the efficacy of 385 nm and 420 nm light for inactivation of E. coli attached to the silicone matrix of a urinary catheter. Using urine mucin media, inactivation of planktonic bacteria and biofilm formation was monitored using silicone coupons. Continuous irradiance with both 385 nm and 420 nm wavelengths with starting cell density population 103 CFU ml− 1 reduced planktonic suspensions of E. coli to below the detection level after 2 h and 6 h, respectively. Bacterial attachment to silicone was successfully prevented during the same treatment. Inactivation by 385 nm and 420 nm was found to be dependent on media, cell density and oxygen, with less inhibition on planktonic suspensions when higher starting cell densities were used. In contrast to planktonic suspensions in PBS, continuous irradiance of pre-established biofilms showed a greater reduction in survival compared to urine mucin media after 24 h. Enhanced inhibition for 385 nm and 420 nm light in urine mucin media was associated with increased production of reactive oxygen species. These findings suggest 385 nm and 420 nm light as a promising antimicrobial technology for the prevention of biofilm formation on urethral catheters.

Side-emitting polymer optical fibres are commonly used for applications in fibre-optical sensing, dosimetry and medical phototherapy. This paper describes the fabrication of a side emitting fibre using UV picosecond laser micromachining to deliver uniform light in medical devices for antimicrobial applications. The side emission is achieved by creating an array of optical imperfections with varying spatial densities along the required length of polymer optic fibre. This disturbs the light propagation at scattering sites along the active side-emitting region of the fibre. LED and laser diodes of various wavelengths were successfully coupled into the optical fibre using paired aspheric condenser lenses. Each side emitting fibre was irradiance mapped along its length and the process optimised for uniformity. This is to ensure that consistency is achieved as the inhibitory effect of the light exposure is proportional to the light irradiance.Violet-Blue light was targeted as is has been shown to possess antimicrobial properties against a wide collection of bacterial pathogens. Its germicidal efficacy is lower than UV Light but the safety advantage of this visible light allows it to be used for a vast range of medical applications. It also allows a selection of light sources to be investigated and a higher irradiance value to be achieved that may be required for various medical applications.

ABSTRACT Listeria monocytogenes senses blue light via the flavin mononucleotide-containing sensory protein Lmo0799, leading to activation of the general stress response sigma factor SigB (σ B ). In this study, we investigated the physiological response of this foodborne pathogen to blue light. We show that blue light (460 to 470 nm) doses of 1.5 to 2 mW cm −2 cause inhibition of growth on agar-based and liquid culture media. The inhibitory effects are dependent on cell density, with reduced effects evident when high cell numbers are present. The addition of 20 mM dimethylthiourea, a scavenger of reactive oxygen species, or catalase to the medium reverses the inhibitory effects of blue light, suggesting that growth inhibition is mediated by the formation of reactive oxygen species. A mutant strain lacking σ B (Δ sigB ) was found to be less inhibited by blue light than the wild type, likely indicating the energetic cost of deploying the general stress response. When a lethal dose of light (8 mW cm −2 ) was applied to cells, the Δ sigB mutant displayed a marked increase in sensitivity to light compared to the wild type. To investigate the role of the blue-light sensor Lmo0799, mutants were constructed that either had a deletion of the gene (Δ lmo0799 ) or alteration in a conserved cysteine residue at position 56, which is predicted to play a pivotal role in the photocycle of the protein ( lmo0799 C56A). Both mutants displayed phenotypes similar to the Δ sigB mutant in the presence of blue light, providing genetic evidence that residue 56 is critical for light sensing in L. monocytogenes . Taken together, these results demonstrate that L. monocytogenes is inhibited by blue light in a manner that depends on reactive oxygen species, and they demonstrate clear light-dependent phenotypes associated with σ B and the blue-light sensor Lmo0799. IMPORTANCE Listeria monocytogenes is a bacterial foodborne pathogen that can cause life-threatening infections in humans. It is known to be able to sense and respond to visible light. In this study, we examine the effects of blue light on the growth and survival of this pathogen. We show that growth can be inhibited at comparatively low doses of blue light, and that at higher doses, L. monocytogenes cells are killed. We present evidence suggesting that blue light inhibits this organism by causing the production of reactive oxygen species, such as hydrogen peroxide. We help clarify the mechanism of light sensing by constructing a “blind” version of the blue-light sensor protein. Finally, we show that activation of the general stress response by light has a negative effect on growth, probably because cellular resources are diverted into protective mechanisms rather than growth.

The use of contactless payment methods for consumer transactions is becoming increasingly popular - 1.1 billion contactless transactions were made by Visa cardholders across Europe in the 12 months to July 2015 (€12.6 billion total value). Typically the contactless payment process uses a Radio Frequency (RF) enabled smartcard or a Near Field Communication (NFC) enabled smartphone. In order to ensure continued market acceptance and repeat usage the contactless operation must be robust, quick and efficient. This paper describes the development of an inductively coupled contactless smartcard utilising UV DPSS laser micromachining to fabricate the novel antenna structures from copper laminated epoxy tape. The design of the antenna modules was supported by device modelling using electromagnetic simulation software. Iterative laser ablated antenna prototypes were tested using a Vector Network Analyser to determine the optimum resonant frequency in the 13.56 MHz RFID range and a commercial automated RF test station to measure contactless functionality to EMVCO and ISO14443 standards. An antenna design toolkit was developed based on parameters such as kerf width, number of antenna loops, track width, pitch, antenna DC resistance, etc.The translation of the laser ablated antenna designs from smartcards to wearable objects, such as wristbands, is also presented.

The corrosion rate of magnesium alloys is generally too high for biodegradable implant applications. This work explored combinations of anodizing and picosecond laser surface treatments to modify the corrosion response of magnesium alloy AZ31. Anodizing of the AZ31 in NaOH solutions produced porous oxide layer structures. Shallow laser treatment of these anodized surfaces, using low pulse powers, resulted mainly in oxide ablation and impaired corrosion resistance. Higher pulse power, resulting in rapid melting and resolidification into the substrate, provided an improved corrosion response. The refined grain structure produced is approximately only 5 µm deep and therefore has minimal influence on bulk mechanical properties. It is therefore a suitable process for surface modifications on small medical device structures. Controlling the initial point of degradation has been demonstrated by the use of selective laser treatment of the AZ31 surface.

Lasers are widely used to slit and perforate thin polymer films (< 200 µm) in applications such as food packaging and consumer products. In this paper the results of an investigation of the optimal CO2 laser wavelength for the micro-slitting of an acoustic absorber polymer film for thermal mass buildings are presented. The CO2 laser is the most commonly used laser for the machining of polymer films in low-value high-throughput applications as the CO2 laser provides the most cost effective solution (lowest $ per Watt of laser power). As the cutting efficiency is a key process factor this paper presents the results of a study of the impact of the CO2 laser wavelength in relation to polymer absorption and cutting efficiency. This paper investigates the effect of 10.6 µm and 10.2 µm CO2 laser wavelengths for various configurations of Polypropylene (PP) and Polyethylene (PE) films. The polymer films range in thickness from 30 µm to 180 µm and are both Machine Direction Oriented and nonoriented. The impact of the laser polarization state (Linear and Circular) is also considered. Results show that significant increases in cutting efficiency can be achieved by selecting the optimal laser wavelength and polymer material. It is shown that the 10.2 µm wavelength is up to 3 times more efficient than 10.6 µm for cutting PP of 50 µm thickness. There is no significant enhancement of the cutting efficiency of PE with 10.2 µm wavelength compared to 10.6 µm.

Laser ablation is a significant industrial tool for material structuring; however, the quality of such physical processes is often hindered by the redeposition of ablated matter in the laser interaction zone. Laser-induced liquefaction (LIL) offers a novel approach to minimizing material redeposition by irradiating the target in a dry ambient and transporting the material away in a liquid medium. SEM, EDX, and real-time imaging provided evidence of the decomposition of the assist gases, tetrafluoroethane (C2H2F4) and sulfur hexafluoride (SF6), during nanosecond laser ablation of silicon and confirmed the presence of a transient liquid phase in the vicinity of the trench during laser ablation. The elemental composition and spatial characteristics of the redeposited ablated matter indicate that the liquefied species and chemistry of the ablated matter are important in the enhancement of the material removal processes. As a result, high aspect ratio trenches with low redeposition of material in the ablated feature were achieved. The identification of the LIL process now has potentially interesting applications in nanoparticle generation during laser ablation and to the improved understanding of silicon microstructures formed in these gases.

In FDA regulated medical device manufacturing, real time inspection of manufactured product is limited by the requirement to destructively test random samples of the product post production. Infra Red thermography offers the ability to non-destructively test, key critical to quality attributes of medical devices during laser welding and facilitates real time statistical process control for enhanced product quality and yield. This paper will present results of research work focused on non-destructive methods using Infra Red Thermography to potentially replace destructive methods of assessment for laser welded joints in stent delivery catheters. The approach utilizes designed experiments in conjunction with IR assessment and also identifies some limitations of the proposed method.

The use of short and ultrashort pulse lasers for laser micromachining of silicon is now a well advanced manufacturing technique. Applications include semiconductor wafer dicing, inkjet printhead slotting, and substrate structuring for solar cell production. A key element of the laser machining process is the role of the ambient or assist media in relation to enhancing the ablation rate, minimising the negative impact of debris generation, and functionalising the laser generated particulate. This paper will present results of research work focused on the impact of assist media, in particular the use of water, non-polar liquids, and halocarbon gases, in laser micromachining of silicon. Novel observations related to the laser induced liquefaction of assist gases will also be presented.

The development of femtosecond lasers with high repetition rates combined with high average power is making this technology more relevant to the needs of the manufacturing community particularly in the field of micromachining. Although the scientific community has extensively studied the interaction of femtosecond laser pulses with materials, there remain aspects of the machining process that merit further study, particularly in relation to hybrid and assisted laser processes. This paper reviews the implementation of a multi-functional femtosecond laser and diagnostic system designed to allow a comprehensive analysis of ultrafast machining processes. The laser system is based on a diode-pumped Ytterbium laser with a sub 500 fs pulse width at 1030 nm, 515 nm, and 343 nm with repetition rates up to 300 kHz. Shorter pulse durations (sub 100 fs) at these wavelengths are achieved using spectral broadening in a Photonic Crystal Fiber and subsequent pulse compression. Oscillator laser output at 29 MHz is also available. The process diagnostic system includes online Raman spectroscopy, Schlieren imaging, and high speed video analysis.

High power fiber lasers offer several advantages for industrial use; high power with stable output, parameter flexibility, low maintenance costs, high efficiency and small footprint. A 200W SPI / Rofin fiber laser system was used to study the potential for high speed remote cutting and welding using a galvo scanner. Metallurgical analysis of the weld quality, cut edge quality and the throughput of fiber laser welding for a variety of materials and applications are presented.

Gallium Nitride (GaN) is an important semiconductor material as GaN based devices have revolutionised the optoelectronics and high power electronics sectors. A great deal of attention has been focused on developing methods to fabricate semiconductor nanostructures with uniform size distributions. We report the formation of Excimer laser induced periodic surface structures. The ablation threshold of GaN with the 193 nm excimer laser was determined empirically. The surface structures were produced using a phase mask with a 668.2 nm periodicity. The features produced on the surface of the GaN were regular and of uniform periodicity, however, a significant amount of debris was generated during the machining of GaN. In order to try and reduce the debris generated further trials were carried out on both process optimisation and also on the use of a variety of assist gases. It is concluded that fluence does not have a significant impact on debris generation and Helium was found to be the most successful assist gas reducing the debris significantly.

Gallium Nitride (GaN) free-standing substrate material has attracted considerable attention recently for high quality LED and Laser fabrication due to their better lattice and thermal match with the LED/Laser epi-layers than existing substrates (Sapphire or SiC). However there is still scope for the further development of both the substrate material and the epi-layer LED structures. Here we report on a preliminary investigation of the shaping capabilities of a laser-machining system on GaN LED wafer substrates. The pieces were scribed and shaped using a Nd:YVO4 diode pumped solid state AVIA 355-7000 laser (Coherent). Finally the machining of 2-dimensional scribing patterns in the free-standing wafer materials is discussed.

The use of a water assist has been shown to improve machining efficiency and feature cleanliness for the laser micro machining of features in silicon. However, the water assist has been shown to have some disadvantages, including the fact that it dissolves protective coatings on semiconductor wafers and it tends to cause blockages in the debris extract system. Protective coatings dissolve because they are typically water-based in order to facilitate their removal after machining and therefore they are not compatible with the water assist process. Blockages in the extract system are due to the deposition of silicon debris, which does not remain adequately entrained in the water flowing through the extract system. This paper describes the use of oil assist instead of water assist to solve these problems while maintaining the advantages of water assist. Unlike water, which is polar in nature, oil does not dissolve the water-based coating. Due to the properties of the oil assist, the debris does not tend to deposit on the surfaces of the extract system so blockages are avoided. Suitable oils include industrial oils like Castrol Carecut and common vegetable oils like grape seed oil or olive oil.

We report on pulsed laser ablation for dicing/scribing monocrystalline silicon with a frequency tripled DPSS Q-switched nanosecond laser (355nm, AVIA, Coherent). Using a Galvanometer scanhead, a laser beam (repetition rate 30kHz, 143µJ per pulse maximum) was focused down to a 30µm diameter spot on silicon wafer and scanned in single-line mode. The trenches were machined by applying different number of laser scan passes and different laser powers. The cross-section and the side-wall of the trenches were examined using optical and scanning electron microscopes. The laser machining throughput was evaluated by measuring the trench depth and the results show as the trench deepens with repetitive scans the effective ablation rate decreased and maximum depth of 500µm was achieved (aspect ratio 17 approximately). The debris generation and transport is known to be critical in optimising throughput of laser ablative processes. Study of the debris reveals that instead of being removed from the trench part of the debris generated from laser ablation re-deposits in the trench and on the side-walls and forms a recast layer. The formation of such features narrow the open space inside the trenches, which made laser beam delivery and debris transport more difficult.

Gallium nitride (GaN) and related alloys are important semiconductor materials for fabricating novel photonic devices such as ultraviolet (UV) light-emitting diodes (LEDs) and vertical cavity surface-emitting lasers (VCSELs). Recent technical advances have made free-standing GaN substrates available and affordable. However, these materials are strongly resistant to wet chemical etching and also, low etch rates restrict the use of dry etching. Thus, to develop alternative high-resolution processing for these materials is increasingly important. In this paper, we report the fabrication of microstructures in free-standing GaN using pulsed UV lasers. An effective method was first developed to remove the re-deposited materials due to the laser machining. In order to achieve controllable machining and high resolution in GaN, machining parameters were carefully optimised. Under the optimised conditions, precision features such as holes (through holes, blind or tapered holes) on a tens of micrometer length scale have been machined. To fabricate micro-trenches in GaN with vertical sidewalls and a flat bottom, different process strategies of laser machining were tested and optimised. Using this technique, we have successfully fabricated high-quality micro-trenches in free-standing GaN with various widths and depths. The approach combining UV laser micromachining and other processes is also discussed. Our results demonstrate that the pulsed UV laser is a powerful tool for fabricating precision microstructures and devices in gallium nitride.

We present theoretical calculations and experimental measurements of silicon micromachining rates, efficiency of laser pulse utilization, and morphology changes under UV nanosecond pulses with intensities ranging from 0.5 GW/cm(2) to 150 GW/cm(2). Three distinct irradiance regimes are identified based on laser intensity. At low intensity, proper gas dynamics and ablation vapor plume kinetics are taken into account in our theoretical modeling. At medium high intensity, we incorporate the proper plasma dynamics, and predict the effects of the laser generated vapor plasma and the electron hole plasma on the laser-matter interaction. At even higher intensity, we attribute the observed increased ablation rate to energy re-radiation from the laser heated hot plasma, the strong shock wave, and the accompanied strong shock wave heating effects. Experimentally measured data in these regimes agree well with our calculations, without changing parameters in the calculations used for the three regimes. Our results can be applied toward quantitatively characterize the behavior of ablation results under different laser parameters to achieve optimal results for micromachining of slots and vias on silicon wafers.