Conventional Manufacturing Techniques Research Articles

Assessing the suitability of fused deposition modeling to produce acrylic removable denture bases.

To study the feasibility of using poly methyl methacrylate(PMMA) filament and fused deposition modeling (FDM) to manufacture denture bases via the development of a study that considers both conventional and additive-based manufacturing techniques. Five sample groups were compared: heat and cold cured acrylic resins, CAD/CAM milled PMMA, 3D-printed PMMA (via FDM), and 3D-printed methacrylate resin (via stereolithography, SLA). All groups were subjected to mechanical testing (flexural strength, impact strength, and hardness), water sorption and solubility tests, a tooth bonding test, microbiological assessment, and accuracy of fit measurements. The performance of sample groups wasreferred to ISO 20795-1 and ISO/TS 19736. The data was analyzed using one-way ANOVA. Samples manufactured using FDM performed within ISO specifications for mechanical testing, water sorption, and solubility tests. However, the FDM group failed to achieve the ISO requirements for the tooth bonding test. FDM samples presented a rough surface finish which could ultimately encourage an undesirable high level of microbial adhesion. For accuracy of fit, FDM samples showed a lower degree of accuracy than existing materials. Although FDM samples were a cost-effective option and were able to be quickly manufactured in a reproducible manner, the results demonstrated that current recommended testing regimes for conventionally manufactured denture-based polymers are not directly applicable to additive-manufactured denture base polymers. Therefore, new standards should be developed to ensure the correct implementation of additive manufacturing techniques within denture-based fabrication workflow.

Single-Step Fabrication of Highly Tunable Blazed Gratings Using Triangular-Shaped Femtosecond Laser Pulses

Blazed gratings are periodic surface structures of great interest for applications such as friction control, light trapping, and spectrometry. While different laser processing methods have been explored to produce these elements, they have not yet surpassed conventional surface manufacturing techniques, often based on lithography processes or mechanical ruling. This work introduces a new approach based on the combination of ultrashort pulses and triangular beam shaping, which enables the generation of asymmetrical grooves in a single step. The main advantage of this strategy is that by simply changing the laser processing direction we can induce a significant modification in the ratio of asymmetry between the sidewall angles of the machined channels. The paper includes a comprehensive study, which has been supported by statistical tools, of the effect of this and other experimental parameters on the morphology of grooves machined on stainless steel. As a result, we achieved a wide range of geometries, with asymmetry ratios spanning from 1 to 5 and channel depths between 3 and 15 µm. Furthermore, we demonstrate the validity of the approach through the successful manufacture of blazed gratings of various slopes. The results reflect the versatility and cost-efficiency of the proposed fabrication strategy, and thus its potential to streamline the production of sawtooth gratings and other devices that are based on asymmetrical features.

Recent Advancements in Material Waste Recycling: Conventional, Direct Conversion, and Additive Manufacturing Techniques

To improve the microstructure and mechanical properties of fundamental materials including aluminum, stainless steel, superalloys, and titanium alloys, traditional manufacturing techniques have for years been utilized in critical sectors including the aerospace and nuclear industries. However, additive manufacturing has become an efficient and effective means for fabricating these materials with superior mechanical attributes, making it easier to develop complex parts with relative ease compared to conventional processes. The waste generated in additive manufacturing processes are usually in the form of powders, while that of conventional processes come in the form of chips. The current study focuses on the features and uses of various typical recycling methods for traditional and additive manufacturing that are presently utilized to recycle material waste from both processes. Additionally, the main factors impacting the microstructural features and density of the chip-unified components are discussed. Moreover, it recommends a novel approach for recycling chips, while improving the process of development, bonding quality of the chips, microstructure, overall mechanical properties, and fostering sustainable and environmentally friendly engineering.

Continuous additive manufacturing of hemp yarn-reinforced biocomposites with improved impregnation method

This study was motivated by the development of new additively manufactured bio-based materials with high performance. Hemp yarn was used in continuous material extrusion additive manufacturing to produce novel hemp yarn-reinforced biocomposites. The hemp yarn was compared to an original hemp/poly(lactic acid) hybrid yarn prepared by commingling before printing as an improved impregnation method. In X-ray micro-computed tomography, the hybrid yarn-based biocomposite exhibited a higher impregnation rate accompanied by a reduced void content, more aligned fibers, and a more homogeneous distribution of the different constituents, resulting in significantly higher mechanical properties during tensile loading with a more brittle behavior compared to the additively manufactured biocomposite based on pure hemp yarn. In addition, superior mechanical performance was obtained while having lower fiber fraction with the use of hybrid yarns, raising awareness about the importance of improving the impregnation of the plant fibers as well as the fiber volume fraction. This original preparation method can provide bio-based materials with enhanced quality and performance, close to those obtained with conventional manufacturing techniques, while making the most of additive manufacturing for sustainable, lightweight, and high-end applications in health or aerospace.

Mechanical, metallurgical, and corrosion investigations on wire arc additively manufactured low carbon steel

Current global 3D metal printing research is focused on powder bed fusion and direct energy deposition. Several materials are presently under research to assess their post-additive manufacturing properties, and to process them in industries using advanced manufacturing techniques. This study investigates the electrochemical, mechanical, and metallurgical properties of wire arc additively manufactured (WAAM) ER70S-6 alloy walls on AISI S235 plates, emphasizing ship component fabrication. The corrosion resistance of both materials is assessed through Electrochemical Impedance Spectroscopy and Potentiodynamic Polarization testing in a 3.5% NaCl solution. Surface and cross-sectional morphologies are analyzed using optical microscopy and scanning electron microscopy, while energy dispersive spectroscopy is employed to study the chemical composition of the corrosion products. Moreover, the hardness of the WAAM-deposited ER70S6 wall is found to be highest in the uppermost layers of deposition due to the presence of acicular ferrite and ferritic-bainite microstructure. Tensile and Charpy impact strength for AISI S235 and WAAM-deposited ER70S-6 exhibit similar performance at room and low temperatures. Interestingly, the WAAM sample demonstrates a 60% higher elongation than the AISI S235 sample. Hence, the findings from this experimental work suggest that WAAM-deposited carbon steel exhibits favourable corrosion resistance and comparable mechanical properties to AISI S235. Consequently, WAAM is emerging as a promising alternative to conventional manufacturing techniques for fabricating ship components, repairing and modifying hull structures, manufacturing nozzles, propeller blades, fin-like structures, structural components, and more.

Parametric Study of Die Sinking EDM of H13 Steel using Taguchi Techniques

As for H13 die steel, it is distinguished by a high hardness and a unique surface characteristics that must be created during machining using non-standard methods. One of such non conventional manufacturing techniques involving the use of Electrical Discharge Machining (EDM) for machining complex or hard material parts. It indicates that EDM has progressed from a series of a tool and die process to an alternative micro-scale application machining process. The paper is aimed at elaborating mathematical models defining the link between the MRR and SR to measured input parameters (current, pulse-on time, pulse-off time, and Reference voltage) in hot work steel EDM. With a L9 orthogonal involving four variables at three levels were used. The values of the model quality factors analyzed by the ANOVA procedure show that the selected mathematical models describe the process performance within successfully studied range with high level of precision. To determine the optimal condition, Taguchi method was used to measure the performance impact of different process parameters and find out best mixing. Minitab V 21 software has been used for the analysis and explanations. A good agreement between experimental value and the predicted one was found.

Improving the processability and grain structures of additively manufactured Al-Fe-Cu-xZr alloy: Experiment and high-fidelity simulation

Additive manufacturing (AM) offers significant advantages over conventional manufacturing techniques in processing Al alloys, however, high-strength Al alloys produced by AM commonly encounter a few challenges including poor processability and undesirable microstructures with coarse columnar grains and even micro-cracks, leading to poor mechanical properties of the resultant Al alloys. Here, we demonstrate that these issues can be largely resolved by micro-alloying of Zr element in the Al-based alloys. In this study, a series of novel Al-1Fe-0.6Cu-xZr alloys with different content of Zr (x=0.3, 0.6, 0.8, 1.3 at%) are designed and then subjected to laser powder bed fusion (LPBF). It is found that, with increasing Zr content, the processability of Al alloys is significantly improved, as evidenced by the gradual reduction of melt splashing and defects (including pores, balling, necking and discontinuity) during LPBF, which eventually leads to decrease of surface roughness and improvement of processability. High-fidelity simulation reveals that the processability is closely related to the melt velocity gradient (MVG) in melt pools. Increasing Zr content results in a more uniform distribution of MVG and decreased Marangoni convection, which favors the stability of melt pool and good processability. On the other hand, Zr content also plays an important role in microstructure. Although the four LPBF Al alloys all exhibit notably heterogeneous structures with alternate distribution of coarse grain zones (CGZs) and fine grain zones (FGZs) in the whole samples, with increasing Zr content, the coarse columnar grain structure in CGZs is suppressed and transforms to the fine equiaxial grain structure. The occurrence of columnar-to-equiaxed transition (CET) is attributed to the decreased ratio between temperature gradient (G) and solidification rate (R) at the solid-liquid interface with increasing Zr content. In addition, the increase in Zr content also leads to a gradual refinement of the grain size in both CGZs and FGZs due to the increased cooling rate. Beneficial from the good processability and fully refined equiaxial gain structure, nearly full-dense and high-strength Al alloys with 0.8 and 1.3 at% Zr are successfully fabricated, which show a good combination of high strength and ductility. The findings in this work provide a guild for design of novel Al alloys with good processability and advanced mechanical properties for additive manufacturing.

Microfluidics-mediated Liposomal Nanoparticles for Cancer Therapy: Recent Developments on Advanced Devices and Technologies.

Liposomes, spherical particles with phospholipid double layers, have been extensively studied over the years as a means of drug administration. Conventional manufacturing techniques like thin-film hydration and extrusion have limitations in controlling liposome size and distribution. Microfluidics enables superior tuning of parameters during the self-assembly of liposomes, producing uniform populations. This review summarizes microfluidic methods for engineering liposomes, including hydrodynamic flow focusing, jetting, micro mixing, and double emulsions. The precise control over size and lamellarity afforded by microfluidics has advantages for cancer therapy. Liposomes created through microfluidics and designed to encapsulate chemotherapy drugs have exhibited several advantageous properties in cancer treatment. They showcase enhanced permeability and retention effects, allowing them to accumulate specifically in tumor tissues passively. This passive targeting of tumors results in improved drug delivery and efficacy while reducing systemic toxicity. Promising results have been observed in pancreatic, lung, breast, and ovarian cancer models, making them a potential breakthrough in cancer therapy. Surface-modified liposomes, like antibodies or carbohydrates, also achieve active targeting. Overall, microfluidic fabrication improves reproducibility and scalability compared to traditional methods while maintaining drug loading and biological efficacy. Microfluidics-engineered liposomal formulations hold significant potential to overcome challenges in nanomedicine-based cancer treatment.

Combined Soft Grasping and Crawling Locomotor Robot for Exterior Navigation of Tubular Structures

This paper presents the design, development, and testing of a robot that combines soft-body grasping and crawling locomotion to navigate tubular objects. Inspired by the natural snakes’ climbing locomotion of tubular objects, the soft robot includes proximal and distal modules with radial expansion/contraction for grasping around the objects and a longitudinal contractile–expandable driving module in-between for providing a bi-directional crawling movement along the length of the object. The robot’s grasping modules are made of fabrics, and the crawling module is made of an extensible pneumatic soft actuator (ePSA). Conceptual designs and CAD models of the robot parts, textile-based inflatable structures, and pneumatic driving mechanisms were developed. The mechanical parts were fabricated using advanced and conventional manufacturing techniques. An Arduino-based electro-pneumatic control board was developed for generating cyclic patterns of grasping and locomotion. Different reinforcing patterns and materials characterize the locomotor actuators’ dynamical responses to the varying input pressures. The robot was tested in a laboratory setting to navigate a cable, and the collected data were used to modify the designs and control software and hardware. The capability of the soft robot for navigating cables in vertical, horizontal, and curved path scenarios was successfully demonstrated. Compared to the initial design, the forward speed is improved three-fold.

Designing and experimental validation of single-layer mixed foil resonator acoustic membrane to enhance sound transmission loss (STL) within low to medium frequency range

This study presents a novel design for an acoustic membrane structure that employs a parallel-arrangement of mixed foil sound resonators to improve sound absorption and insulation capabilities in the low to medium frequency range. The structure is composed of a single layer of parallel-arranged mixed foil wedge-shaped coffers and a bottom flat panel separated by an air cavity. The mixed thickness-based foil resonators are treated as a combination of independent resonators with unique resonance frequency, resulting in improved sound insulation with broadband efficacy. A comprehensive parametric analysis was carried out using the Finite Element Method (FEM) based COMSOL Multiphysics, yielding the anticipated outcomes. The study revealed that the broadband Sound Transmission Loss (STL) can be tailored by varying the thickness of the top and side walls, the bottom plate thickness, and the depth of the rear air cavity. The findings suggest that existing acoustic membrane design can be highly efficient, achieving, and average STL of over 40 dB ∼ 45 dB across the low to medium frequency range of 500 Hz to 3000 Hz. The experimental validation was conducted in an anechoic chamber, and the results were found to be in close agreement with the FEM simulation results. In comparison to conventional uniform foil sound resonator based acoustic membrane structure, this mixed single-layer square wedge-shaped foil resonator based acoustic membrane exhibits outstanding sound insulation performances in the low to medium frequency range, owing to its lightweight structure and availability of conventional manufacturing techniques. This advanced version of the foil sound resonator based acoustic membrane holds immense promise for the use in acoustics and noise control applications across domestic, commercial, and industrial environments.

Design Optimisation for Hybrid Metal Additive Manufacturing for Sustainable Construction

Wire arc additive manufacturing (WAAM) enables the manufacturing of efficient and lightweight structural elements in which material can be utilised wherever needed in an optimised shape, in contrast to standard prismatic profiles used in construction. However, the specific energy consumption (SEC) of WAAM is higher than that of conventional manufacturing (CM) techniques (i.e., hot-rolling) for standard profiles. Therefore, it is an open question whether the material savings through computational design realised through WAAM is environmentally beneficial or not. This systematic study aims to provide a better understanding of the environmental impact of hybrid manufacturing, which is defined as the combination of WAAM and CM rather than using any of them alone. Topology optimisation (TO) is used to design a series of beams with an identical performance (i.e., stiffness) but with a reduced material consumption depending on the hybrid ratio. The environmental impact of the designs has been used to determine when and how hybridisation can become advantageous. The results show that although the optimal proportions of WAAM and CM are dependent on their relative SEC, the hybrid solutions have always been environmentally superior compared to that of WAAM or CM alone for the realistic SEC values. The results showed that the hybrid beams can exhibit up to a 60% reduction in environmental impact compared to that of CM.

Wafer‐Scale Manufacturing of Near‐Infrared Metalenses

AbstractMetalenses have revolutionized optical technologies with their superior ability to manipulate light and the potential to replace conventional, bulky optical components. However, their commercialization is hindered by limitations in conventional manufacturing techniques, such as small patterning areas, low throughput, and high cost. In this study, two methods are introduced for scalable and wafer‐scale manufacturing of metalenses operating in the near‐infrared region, aimed at overcoming the abovementioned challenges. The first type of metalens is polarization‐independent and constructed using hydrogenated amorphous silicon cylindrical structures fabricated through direct photolithography. This metalens has a diameter of 1 cm and numerical aperture (NA) of 0.53. The focusing efficiency is confirmed at a 940 nm wavelength, and the focal spot profile approaches the diffraction limit. The second metalens is polarization‐dependent and fabricated using silicon nanoparticle‐embedded‐resin rectangular structures through a cost‐effective nanoimprinting method. This process can produce metalenses with a diameter of 5 mm and an NA of 0.53. Both types of metalenses demonstrate high‐resolution capabilities when imaging a 1951 USAF resolution test target and bioimaging. This research offers innovative pathways for the mass production and large‐scale fabrication of metalenses. It is believed that the work will accelerate the industrialization of metalenses, fostering further advances in optical technology.

Effect of Hirtisation treatment on surface quality and mechanical properties of AlSi10Mg samples produced by laser powder bed fusion

Laser Powder Bed Fusion (L-PBF) provides a larger design freedom than conventional manufacturing techniques. Surface post-processing is widely investigated to improve the roughness of as built L-PBF parts by reducing powder sintered to the surface and the staircase effect, but it becomes even more important to guarantee a smooth surface if support structures are included for tilted overhanging structures. This study focuses on L-PBF AlSi10Mg samples with a building angle of 30° with respect to the baseplate. This building angle inevitably requires support structures. The study investigates if a hybrid surface treatment combining chemical and electrochemical polishing, called Hirtisation®, removes the support structure and to what extent it improves the surface roughness of samples with a 30° building angle. Currently, the results of surface treatments are mostly reported on vertically built samples while down-facing areas of samples with a lower building angle are typically the roughest areas of the samples causing crack initiation in fatigue. Roughness, defect population, residual stresses, microstructure, fatigue, and tensile properties are studied to investigate correlations with the physical effect of Hirtisation. A porous zone is observed in the down-facing area close to the support structures of as built samples. Hirtisation removed successfully the support and the porous area. In the down-facing roughest area, the average values of the average roughness, mean roughness depth and deepest valley depth are reduced by respectively 56,5%, 58,7% and 51,5% by Hirtisation compared to the as built state. The deepest valley measured reduced from 155,5 µm to 74,4 µm. Hirtisation combined with annealing increased the fatigue resistance at a stress amplitude of 120 MPa with a factor 3,1 compared to the as built state and with a factor 2,7 compared to the annealing state. The improved fatigue resistance is linked to halving the deepest valley depth as well as a change in the residual stress at the outer surface from tensile stresses after annealing to a small compressive stress after Hirtisation which counteracts the tensile load in fatigue. Hence, Hirtisation reduces roughness, inverses a tensile residual stress at the outer surface to a small compressive residual stress. In addition, the chemical-electrochemical process allows to access areas which are impossible to post-process with e.g. sandblasting or vibratory polishing. These conclusions make Hirtisation interesting for further investigations for future applications, however the deepest valley depth could be reduced more by increasing the material removal in the process to improve the fatigue life more.

Experimental validation of auxetic stent designs: three-point bending of 3D printed Titanium prototypes.

Numerical simulations have demonstrated the superior bending flexibility of auxetic stents compared to conventional stent designs for endovascular procedures. However, conventional stent manufacturing techniques struggle to produce complex auxetic stent designs, fueling the adoption of additive manufacturing techniques. In this study, we employed DMLS additive manufacturing to create Titanium Ti64 alloy stent prototypes based on auxetic stent designs investigated in a previous study. These prototypes were then subjected to experimental three-point bending tests. The experimental results were replicated using a finite element model, which showed remarkable accuracy in predicting the bending flexibility of four auxetic stents and two conventional stents. Although this validation study demonstrates the promising potential of DMLS and other additive manufacturing methods for fabricating auxetic stents, further optimization of current stent design limitations and the incorporation of post-processing techniques are essential to enhance the reliability of these additive manufacturing processes.

Enhanced tribological performance of laser directed energy deposited Inconel 625 achieved through laser surface remelting

Inconel 625 (IN625) is an essential material for the manufacture of turbine blades and seals, aircraft ducting systems, engine components, and pressure valves. Laser Directed Energy Deposition (LDED) process has shown the potential to fabricate IN625 parts with superior mechanical properties and higher corrosion resistance when compared to those fabricated using conventional manufacturing techniques. However, the poor surface quality limits the practical application of LDED fabricated parts, especially in sectors that demand high tribological performance. To this end, this study focuses on improving the surface quality and tribological performance of LDED fabricated IN625 components using Laser Surface Remelting (LSR) as a postprocessing operation. The tribological performance was evaluated using a linear reciprocating ball-on-flat wear test setup. The surface roughness, remelting depth (RD), microstructure, hardness, and tribological performance (coefficient of friction and wear rate) of the remelted (RM) samples were compared with that of as-deposited (AD) samples. Microstructural characterization revealed that LSR resulted in grain refinement, reduced dendrite size, and primary dendritic arm spacing (PDAS). Laser scanning speed effects RD, dendrite size and PDAS via its effect on cooling rates. SEM + EDS analysis confirmed the presence of Laves phase in both AD and RM samples. XRD analysis of RM samples showed an increase in the amount of Laves phase. The refinement in microstructural features and the increased amount of Laves phase among the RM samples led to improvement in microhardness when compared to AD samples. Wear test results revealed a reduction in the coefficient of friction (COF) and wear rate after LSR with wear mechanism being either abrasive or delamination. Reduction in the size of dendrites and refinement in grain size are attributed to the enhanced tribological performance after LSR.

Innovative Fabrication Design for In Situ Martensite Decomposition and Enhanced Mechanical Properties in Laser Powder Bed Fused Ti6Al4V Alloy

Ti6Al4V alloy (Ti64) is a popular material used in the aerospace, medical, and automotive industries due to its excellent mechanical properties. Laser Powder Bed Fusion (LPBF) is a promising manufacturing technique that can produce complex and net-shaped components with comparable mechanical properties to those produced using conventional manufacturing techniques. However, during LPBF, the rapid cooling of the material can limit its ductility, making it difficult to achieve high levels of ductility while maintaining the required tensile strength for critical applications. To address this challenge, this study presents a novel approach to controlling the microstructure of Ti64 during LPBF by using a border design surrounding the main parts. It is hypothesized that the design induces in situ martensitic decomposition at different levels during the fabrication process, which can enhance the ductility of the material without compromising its tensile strength. To achieve this aim, a series of Ti64 samples were fabricated using LPBF with varying border designs, including those without borders and with gaps from 0.5 to 4 mm. The microstructure, composition, and mechanical properties of the Reference sample were compared with those of the samples fabricated with the surrounding border design. It was found that the latter had a more homogenized microstructure, a higher density, and improvements in both ductility and tensile strength. Moreover, it was discovered that the level of property improvement and martensitic transformation can be controlled by adjusting the gap space between the border and the main part, providing flexibility in the fabrication process. Overall, this study presents a promising approach for enhancing the mechanical properties of Ti64 produced via LPBF, making it more suitable for critical applications in various industries.

Soft Kirigami Composites for Form‐Finding of Fully Flexible Deployables

AbstractA new class of thin flexible structures is introduced that morph from flat into prescribed 3D shapes through strain mismatch between layers of a composite plate. To achieve control over the target shape, two different concepts are coupled. First, motivated by biological growth, strain mismatch is applied between the flat composite layers to transform it into a 3D shape. Depending on the amount of the applied strain mismatch, the transformation involves buckling into one of the available finite number of deformation modes. Second, inspired by kirigami, portions of the material are removed from one of the layers according to a specific pattern. This dramatically increases the number of possible 3D shapes and allows us to attain specific topologies. An experimental apparatus that allows precise control of the strain mismatch is devised. An inverse problem is posed, where starting from a given target shape, the physical parameters that make these shapes possible are determined. To show how the concept works, it focuses on circular composite plates and designs a kirigami pattern that yields a hemispherical structure. The analysis combines a theoretical approach with numerical simulations and physical experiments to understand and predict the shape transition from 2D to 3D. The tools developed here can be extended to attain arbitrary 3D shapes. The initially flat shape suggests that conventional additive manufacturing techniques can be used to functionalize the soft kirigami composite to fabricate, for example, deployable 3D structures, smart skins, and soft electromagnetic metasurfaces.

Additive manufacturing for ultra-high vacuum components: Leveraging photo-polymer resin technologies

Over the past two decades, Additive Manufacturing (AM) technologies, commonly known as 3D printing, have witnessed exponential advancements, transforming the paradigms of instrument design and fabrication across an array of scientific and engineering disciplines. The utilization of Computer-Aided Design (CAD) and monolithic machining within the AM framework offers unprecedented levels of flexibility, precision, and mechanical stability. These attributes not only facilitate complex geometrical constructions but also substantially streamline the overall fabrication workflows. In this study, we provide experimental evidence to substantiate the viability of employing Masked Stereolithography Additive Manufacturing (MSLA) technology in concert with commercially available photo-polymer resins for the fabrication of components that are compatible with Ultra-High Vacuum (UHV) conditions. Utilizing high-temperature photo-polymer resins and specialized post-printing treatments—including an approximate 24-h vacuum bake—we have achieved a vacuum level of approximately 1 × 10−9 torr for a solid component encompassing a volume up to 16 cm3. This methodology paves the way for the expedited and cost-effective production of complex, UHV-compatible devices, thereby offering a substantial departure from conventional manufacturing techniques. The wide-ranging applicability of this technology holds considerable potential for transformative impacts across diverse sectors of research and development. By leveraging UHV-compatible MSLA technology, both academic researchers and industrial professionals are poised to benefit from an efficient and adaptable fabrication methodology, consequently catalyzing cutting-edge advancements in their respective fields of inquiry.

A novel approach to the manufacture of dissolving microneedles arrays using aerosol jet printing

Despite much research over the last few decades, microneedle arrays for the transdermal delivery of drugs have failed to live up to their initial promise. This may be changing however as companies close in on the commercial delivery of vaccines via this technology. These breakthroughs will undoubtably increase the interest in the use of microneedles arrays for the delivery of biopharmaceuticals but will also drive research into the development of scalable manufacturing processes for their fabrication. While 3D printing is an exciting development in this field, conventional Additive Manufacturing (AM) techniques are unsuitable for biopharmaceuticals due to the harsh processing conditions which can cause degradation of the active ingredient.In this paper we report the first use of Aerosol Jet Printing (AJP) as an AM technique for the fabrication of dissolving microneedle arrays. A formulation of poly(vinyl pyrrolidone), trehalose and glycerol dissolved in water was prepared and characterised. The formulation was aerosolised using ultrasonication and deposited onto a silicon substrate. Critical process parameters such as Computer Aided Design (CAD) design, flow rate, temperature, print speed and focussing ratio were studied to determine their impact on the microneedle quality attributes. 4 × 4 microneedle arrays were printed, with needle heights > 500 µm achieved with print times of 30 mins or less. The resulting needles had sufficient strength and sharpness to penetrate porcine skin samples. Importantly, the microneedles can be fabricated under benign conditions which should be suitable for the processing and subsequent delivery of biopharmaceuticals across the skin.

Heat Transfer in an Injector-Scaled Additively Manufactured Fuel Passage

Abstract Knowledge of heat transfer in fuel wetted passages is important for informing injector design and life estimates due to the effects of temperature on fuel degradation. Future injectors will be manufactured using additive methods in an effort to reduce production costs and time, while also facilitating more agile design practices. Additive manufacturing (AM) is known to result in increased surface roughness compared to conventional manufacturing techniques, however limited data exist on how this roughness impacts heat transfer, particularly in liquid flows. This paper solves the inverse heat conduction problem for heat transfer coefficient in liquid flows through rough 90 deg channel bends typical of the pilot gallery in a lean direct-injection fuel spray nozzle. Heat transfer distributions across two rough surfaces are compared to an equivalent smooth surface. The two rough surfaces have different morphologies but have the same relative effective sand grain roughness which is matched to a prototype AM fuel injector. The sand grain roughness is predicted from a correlation that has been adapted for the high relative roughness scales characteristic of additively manufactured fuel passages. The effective sand grain roughness estimated from surface measurements of a prototype AM fuel gallery was ∼13% of the passage hydraulic diameter. For the two rough surfaces, the heat transfer enhancement is up to three times the smooth surface value for the straight section preceding the bend and up to four times around the bend. Heat transfer distributions across the two rough surfaces are similar, but the magnitudes differ by ∼17% depending on the surface morphology. This highlights the importance of the heat transfer effectiveness of surface features, which unlike the sand grain roughness is not matched for the two surfaces considered. Adjusting the data for differences in heat transfer effectiveness corrects the average heat transfer for the rough surfaces to within 7%.