Low-cost Printing Research Articles

A virtual visualization method for improving the manufacturing accuracy based VPP 3D printers

Compared to traditional vat photopolymerization 3D printing methods, pixel blending technique provides greater freedom in terms of user-defined lighting sources. Based on this technology, scientists have conducted research on 3D printing manufacturing for elastic materials, biologically inert materials, and materials with high transparency, making significant contributions to the fields of portable healthcare and specialty material processing. However, there has been a lack of a universal and simple algorithm to facilitate low-cost printing experiments for researchers not in the 3D printing industry. Here, we propose a mathematical approach based on morphology to simulate the light dose distribution and virtual visualization of parts produced using grayscale mask vat photopolymerization 3D printing technology. Based on this simulation, we develop an auto-correction method inspired by circle packing to modify the grayscale values of projection images, thereby improving the dimensional accuracy of printed devices. This method can significantly improve printing accuracy with just a single parameter adjustment. We conducted experimental validation of this method on a vat photopolymerization printer using common commercial resins, demonstrating its feasibility for printing high precision structures. The parameters utilized in this method are comparatively simpler to acquire compared to conventional techniques for obtaining optical parameters. For researchers in non-vat photopolymerization 3D printing industry, it is relatively user-friendly.

Electroplating Additively Manufactured Honeycomb Structures to Increase Energy Absorption Under Quasi-Static Crush

Honeycomb (HC) has been used in energy absorption applications due to its high stiffness and low density. Metallic HC are used for energy absorption applications, however, these metallic structures can be challenging to manufacture if complex geometric features designed to improve energy absorption are used, which motivates the use of additive manufacturing (AM). Metal AM methods include powder bed fusion (PBF) and direct energy deposition (DED). In addition to capital equipment cost, these processes possess challenges that include a required inert environment, powder handling, final part porosity, residual stresses, and nonuniform surface finish. These concerns can be alleviated through the use of polymer AM, however, polymeric parts exhibit brittle failure and have a lower stiffness than metallic HC structures. In this study, a low-cost 3D polymer printing method, stereolithography (SLA), is combined with a conventional electroplating process to fabricate a metal-plastic composite HC structure with energy absorption capability much greater than of a plastic HC structures of the same nominal volume. SLA parts have a smooth surface, so that the surface finish is at least as uniform after electroplating as the SLA part. The energy absorption characteristics of the electroplated HC is studied to determine how these energy absorbing materials can be manufactured at reduced cost. Our study confirms that the metal-plastic composite HC increases both the crush strain range and the mean crush stress of these samples, resulting in metal-plastic composite HC structures with substantially increased energy absorption. This study also examines how buckling initiators (BIs), or diamond shaped holes located at 50, 75, and 100% of the height of the hexagonal cell vertices, can influence energy absorption performance. This study shows that it is feasible to fabricate electroplated HCs, using an SLA preform, to achieve a substantial increase in energy absorption over using SLA alone.

Development of a 3D printer for long fiber-reinforced plastic and evaluation of the mechanical properties of printed parts

The field of three-dimensional (3D) printing, a technology that allows low-cost printing of complex 3D shapes with a high degree of modeling freedom, has exhibited significant growth over the last few years. This paper proposes a new 3D printing mechanism for long fiber-reinforced plastic as part of an effort to realize 3D-printed shapes with favorable mechanical properties and describes how prototype parts were printed using the new method. We also devise a method for modifying the fiber surface and other techniques for improving adhesion of fibers and UV resin. Mechanical testing of prototype parts printed using the proposed method indicates that the parts exhibit excellent mechanical properties as a result of filling with long fibers, indicating that the method yields a material with few voids and a high fiber volume fraction.

Customizable Fabrication of Photothermal Microneedles with Plasmonic Nanoparticles Using Low-Cost Stereolithography Three-Dimensional Printing.

Photothermal microneedle (MN) arrays have the potential to improve the treatment of various skin conditions such as bacterial skin infections. However, the fabrication of photothermal MN arrays relies on time-consuming and potentially expensive microfabrication and molding techniques, which limits their size and translation to clinical application. Furthermore, the traditional mold-and-casting method is often limited in terms of the size customizability of the photothermal array. To overcome these challenges, we fabricated photothermal MN arrays directly via 3D-printing using plasmonic Ag/SiO2 (2 wt % SiO2) nanoaggregates dispersed in ultraviolet photocurable resin on a commercial low-cost liquid crystal display stereolithography printer. We successfully printed MN arrays in a single print with a translucent, nanoparticle-free support layer and photothermal MNs incorporating plasmonic nanoaggregates in a selective fashion. The photothermal MN arrays showed sufficient mechanical strength and heating efficiency to increase the intradermal temperature to clinically relevant temperatures. Finally, we explored the potential of photothermal MN arrays to improve antibacterial therapy by killing two bacterial species commonly found in skin infections. To the best of our knowledge, this is the first time describing the printing of photothermal MNs in a single step. The process introduced here allows for the translatable fabrication of photothermal MN arrays with customizable dimensions that can be applied to the treatment of various skin conditions such as bacterial infections.

Carbon Nanotube-Based Printed All-Organic Microelectrode Arrays for Neural Stimulation and Recording.

In this paper, we report a low-cost printing process of carbon nanotube (CNT)-based, all-organic microelectrode arrays (MEAs) suitable for in vitro neural stimulation and recording. Conventional MEAs have been mainly composed of expensive metals and manufactured through high-cost and complex lithographic processes, which have limited their accessibility for neuroscience experiments and their application in various studies. Here, we demonstrate a printing-based fabrication method for microelectrodes using organic CNT/paraffin ink, coupled with the deposition of an insulating layer featuring single-cell-sized sensing apertures. The simple microfabrication processes utilizing the economic and readily available ink offer potential for cost reduction and improved accessibility of MEAs. Biocompatibility of the fabricated microelectrode was suggested through a live/dead assay of cultured neural cells, and its large electric double layer capacitance was revealed by cyclic voltammetry that was crucial for preventing cytotoxic electrolysis during electric neural stimulation. Furthermore, the electrode exhibited sufficiently low electric impedance of 2.49 Ω·cm2 for high signal-to-noise ratio neural recording, and successfully captured model electric waves in physiological saline solution. These results suggest the easily producible and low-cost printed all-organic microelectrodes are available for neural stimulation and recording, and we believe that they can expand the application of MEA in various neuroscience research.

OpenStax Revisited

OpenStax (<ext-link ext-link-type="uri" xlink:href="https://openstax.org">https://openstax.org</ext-link>) is a nonprofit publisher of peer-reviewed and open-licensed college textbooks. It is part of Rice University with funding support from philanthropic foundations. OpenStax delivers on its promise of providing quality no-cost online textbooks and low-cost print textbooks for popular college and K‐12 subjects. Additionally, its provision of a variety of ancillary materials for instructors as well as helpful resources for students greatly enhances the user’s open-resource experience.

Conductivity enhancement of Ag nanowire ink by decorating in situ formed Ag particles under low-temperature sintering

Silver nanowires (AgNWs) have attractive applications in the fabrication of flexible electronics because of their adequate electrical conductivity, mechanical properties, and oxidation resistance. However, the film produced by AgNW ink needs to be sintered at temperatures above 200 °C to obtain high electrical conductivity, which is incompatible with commonly used flexible substrates such as paper or polymer materials. In this study, the AgNW network was decorated by in situ reduced Ag particles (AgPs) to improve the structural integrity and conductivity of the film. After sintering at 80 °C, the pores and voids within the AgNW network were filled with Ag particles smaller than 200 nm, and the porosity of the film was markedly reduced. The lowest resistivity value was 3.9 × 10–5 Ω cm after sintering at 100 °C, only 10.8% and 8.5% of the resistivity values of the films produced from AgNW and ion inks, respectively. During sintering, Ag nucleated on the surface of AgNWs, and its growth and agglomeration resulted in interconnections between the AgNWs and Ag particles. Thereafter, the bridging and filling effect of the Ag particles facilitated the formation of a compact and firm network, improving the film conductivity. The line film printed from the composite ink with 10 layers exhibited a low resistivity of 7.3 × 10–7 Ω·m. Even after 5000 bending cycles, the resistivity of the line only increased by 4.47 × 10–6 Ω·cm from the initial value. The composite ink reported in this study is a promising candidate for the low-cost printing of ultralow-power-consumption wearable electronic devices.

Stretchable triboelectric sensor array for real-time tactile sensing based on coaxial printing

With the rapid development of flexible and wearable electronics, tactile sensor array has shown great potential to detect diverse external stimuli in human–machine interactions and robotic intelligence. In this study, we developed triboelectric sensor array (TSA) with cross-laminated electrode via low-cost coaxial printing technique with the advantages of high precision, high efficiency and excellent uniformity. The results show that the proposed cross-laminated electrode based TSA possesses the characteristics of easy-fabrication process, high-sensitivity, long-term mechanical endurance and real-time trajectory sensing capacity. It can generate the maximum output voltage of 15.98 V at a frequency 4 Hz and vertical force 5 N in single electrode mode, and the maximum power is about 3.9 μW. Besides, TSA shows excellent stability under harsh mechanical bending, twisting and stretching deformation and even waterproof capability. This work offers a previously unexplored strategy for shortening individual design and fabrication cycle of flexible electronics, and promoting the potential application for stretchable sensor array in electronic skin, tactile detection and human–machine interactions.

Design of Low-Cost Full W-Band 8th Harmonic Mixers for Frequency Extension of Spectrum Analyzer

High-order harmonic mixer is popular for frequency extension of spectrum analyzer (SA) from microwave to millimeter-wave or even terahertz band. The manufactures of SA usually offer expensive harmonic mixers where frequency extension is needed. In this work, low-cost designs of 2-port and 3-port W-band 8th harmonic mixers covering 75–110 GHz are proposed, and design method of two port mixer without frequency diplexer to separate local oscillator (LO) and intermediate frequency (IF) signals are first presented. These two kinds of mixers are compatible with almost all the current SAs with frequency extension options, which provides LO for the external harmonic mixer. The mixers are designed with planar microstrip lines and antiparallel Schottky diodes. The circuit of 2-port mixer includes the input broadband bandpass filter, diodes, output lowpass filter, and matching circuits. As for 3-port mixer, only an extra diplexer is needed to separate the IF signal and LO signal. The diplexer is composed of a planar semi-lumped lowpass and a highpass filter. The planar circuits are easily fabricated with low-cost print circuit board process on polytetrafluoroethylene substrate. The measured conversion loss of 2-port 8th harmonic mixer is from 20 to 26 dB, and 23 to 28 dB for 3-port mixer at full W-band. The good measured results indicate the proposed mixers are simple and effective.

3-D printed membrane-type acoustic metamaterials with tailored performance

While traditional membrane-type acoustic metamaterials act as effective lightweight sound insulation materials, their geometries can neither be easily customized nor incorporated into other acoustic designs in a single workflow. Here, we leverage our established techniques at 3-D printing thin membranes to create custom acoustic metamaterials with tailored performance that can be easily implemented into other acoustic designs without any post-processing. In this study, we present the workflow to additively manufacture flexible membranes with added textural features using low-cost extrusion-based printing methods. Using a custom G-code, we print membranes with controlled mass, stiffness, and porosity while superimposing various surface pattern designs. Using a four-microphone normal-incidence impedance tube setup, we demonstrate the effect of each parameter on the membrane’s sound transmission loss behavior and compare the results against traditional acoustic mass law.

AeroFeathers: Feathered airfoils inspired by the quiet flight of owls

Owls are well-known as the quietest flying birds. Recent studies show that they achieve noise-less flight because of their specialized feather design. Their feathers have three important components: a velvety surface texture, comb-like hooks on their leading edge, and jagged fibrous fringes on their trailing edges. Some researchers have attempted to imitate these design features within airfoil designs to reduce aeroacoustic noise emitted by fixed wing and vertical lift vehicles; however, such features cannot be easily fabricated using traditional manufacturing processes. In this student-led project funded by NASA’s University Student Research Challenge, we leverage our established success at additively manufacturing fibrous structures to introduce a new method to 3-D print velvety textures, fibrous fringes, and flexible edge serration using low-cost material extrusion-based printing methods. By altering the printer’s G-code, we create customized feathered airfoils with individual design parameters, including serration thickness and fringe density. We conduct acoustic tests in an anechoic chamber and aeroacoustic tests in an acoustic wind tunnel to determine the effect of each parameter on the overall acoustic signature of the airfoil. We analyze the data and explain the role of owl feather-like features on the noise reduction performance of propeller blades and scaled fixed-wing airfoils.

Numerical Simulation and Experimental Study Regarding the Cross-Sectional Morphology of PEEK Monofilament Deposition During FDM-Based 3D Printing.

Polyether-ether-ketone (PEEK) is widely used in the field of biomedical engineering because of its excellent mechanical properties, chemical stability, and biocompatibility. Fused deposition modeling (FDM), which is a typical 3D printing process, can achieve low-cost and high-efficiency printing of complex PEEK structures. However, poor monofilament deposition quality leads to rough surfaces on macroscopic printed parts, low dimensional accuracy, and weak interlayer bonding, which are urgent problems to be solved. In this study, considering the shear thinning characteristic of PEEK, a numerical model for monofilament deposition was constructed by using the finite volume method. This model revealed the influences of process parameters on the monofilament cross-sectional profiles and achieved predictions of monofilament cross-sectional profiles during FDM-based 3D printing of PEEK. The average relative error of the monofilament cross-sectional area predictions was 7.68%. The average relative error of the monofilament cross-sectional aspect ratio predictions was 12.06%. It was also found that there are three typical deposited monofilament cross-sectional profile shapes, i.e., a capsule shape, a bread shape, and a circular shape. These three shapes occurred because of the combined effect of the layer thickness and the extrusion width during the extrusion and deposition of PEEK. These revealed monofilament cross-sectional profiles provide the basis for accurate nozzle motion trajectory planning, and they lay a foundation for surface roughness predictions and dimensional accuracy control during the FDM-based 3D printing of PEEK.

(Invited) inkjet-Printed Soft Electronic Devices and Sensors for Wearable Health Monitoring Applications

Stretchable electronic devices and sensors built on thin elastomer substrates may find a wide range of applications in wearable health monitoring devices owing to their ability to conformably adapt to human skin for long-term and comfortable wearing. In this talk, I will present our work on developing intrinsically-stretchable electronic materials that are formulated as electronic inks and patterend using a highly scalable and low-cost inkjet printing process. A variety of soft sensors including silver nanoparticle based ultrasensitive resistive strain sensor and pressure sensor, porous elastomer dielectric based capacitive pressure sensor, and multimodal sensor that can differentiate pressure, strain, and temperature stimuli have all been demonstrated on ultrathin polydimethylsiloxane (PDMS) substrate by printing. These devices have been used in applications including motion and gesture tracking, voice recognition, arterial pulse waveform and photoplethysmogram monitoring. In addition, I will also report our work on the development of a unique porous PDMS sponge electrode as a gel-free dry interface for motion-artifact tolerant recording of electrophysiological signals. The porous structure of the soft electrode significantly increases the effective contact area and lowers the electrode-skin impedance, which result in improved signal-to-noise ratio. Compared to commercial rigid electrodes, the soft and thin form factor also makes the spongy electrode well-suited for long-term recording of high quality biopotential signals including electrocardiogram (ECG) and electromyography (EMG) on ambulatory patients. As a demonstration of its clinical usage with a focus on maternal and fetal health monitoring, I will show an array of such soft electrodes integrated on a printed patch of textile-based interconnections, and used for recording and spatiotemporal mapping of the uterine contraction patterns from patients in active labor.

Microstructure Design of Semi-Solid Slurry for Metal Direct Writing

Metal direct writing in semi-solid slurry is an innovative technology to realize low-cost printing of load-bearing parts in contrast to laser-based additive manufacturing. However, it is challenging to achieve near net-forming of 3D parts in the current stage because of the out of controlled microstructure and hence the unstable macro extrusion of the used semi-solid slurry. Here, mixed powder remelting (MPR) is introduced to actively design the characteristics of solid phases, i.e., solid fraction, shape factor, and size distribution. Specifically, high-melting-point pure Al powder served as the dispersed solid phases in the liquid phase that transformed from Al-Si alloy powder after remelting, leading to hypoeutectic Al-Si semi-solid slurry. The effectiveness of this approach was experimentally examined and kinetically modelled, to prepare semi-solid slurry with pre-set microstructure. The improved extrusion stability of semi-solid slurry can be anticipated, and it is universal for manufacturing of metal matrix composites slurry.

A Novel Method for the Low-detectable Dihedral Corner Utilizing Phase Gradient Metasurface based on Phase Cancellation Mechanism

In this paper, a phase gradient metasurface (PGM) is proposed to reduce the radar cross-section (RCS) of the dihedral corner based on phase cancellation mechanism. The phase cancellation mechanism is used to derive the formula of the low-detectable dihedral corner for the first time, which is directly used to deal with the wave path difference problem that introduced by the dihedral corner. According to the formula, six sub-cells are designed with a 60∘ phase difference, which is arranged by sub-array along the y-axis. The reflection coefficients of the selected sub-cells are all above 0.8. The RCS reduction of the dihedral corner achieves over 10 dB from 4.9 GHz to 5.14 GHz under an incident angle of 45∘. In particular, the RCS reduction of the low-detectable dihedral corner is 13.97 dB at 5 GHz. Meanwhile, the proposed dihedral corner with PGM also has an excellent performance of angle insensitivity ranging from 0∘ to 75∘. To further verify our design, the dihedral corner with PGM is manufactured by a low-cost printing circuit board technique. The measured results agreed well with the simulations, and both of them show an excellent performance of RCS reduction in the operating frequency band, regardless of any angle within 75∘. Overall, the dihedral corner with PGM that we proposed has the advantages of being low-detectable, low-profile, low-cost, lightweight, and it is easy to design and manufacture. It has wide application prospects in the future.

Aerosol Jet Printing-Enabled Dual-Function Electrochemical and Colorimetric Biosensor for SARS-CoV-2 Detection.

An aerosol jet printing-enabled dual-function biosensor for the sensitive detection of pathogens using SARS-CoV-2 RNA as an example has been developed. A CRISPR-Cas13:guide-RNA complex is activated in the presence of a target RNA, leading to the collateral trans-cleavage of ssRNA probes that contain a horseradish peroxidase (HRP) tag. This, in turn, catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by HRP, resulting in a color change and electrochemical signal change. The colorimetric and electrochemical sensing protocol does not require complicated target amplification and probe immobilization and exhibits a detection sensitivity in the femtomolar range. Additionally, our biosensor demonstrates a wide dynamic range of 5 orders of magnitude. This low-cost aerosol inkjet printing technique allows for an amplification-free and integrated dual-function biosensor platform, which operates at physiological temperature and is designed for simple, rapid, and accurate point-of-care (POC) diagnostics in either low-resource settings or hospitals.

Breaking Boundaries in LED Technology: Exploring the Revolutionary Diode Characteristics of Screen Printed (TiO2)1−x (CuO)x Thick Films

A thick TiO2-CuO composite film is deposited on a Si substrate by a low-cost screen printing method. Both anatase and CuO-doped TiO2 are characterized for diode applications. X-ray Diffraction (XRD) confirms that the composite film exists as an anatase phase of TiO2 and a monoclinic phase of CuO with a maximum diffraction of (101) plane. SEM images depict the less severe agglomeration of particles for the doped TiO2 as compared to the anatase TiO2. The UV–visible spectra reveal a direct band gap shift of 3.35 eV (pure TiO2) to 3.26 eV (doped TiO2). From the PL study, the blue shaded emission is perfectly derived for anatase TiO2 while the color is seen to change to the white zone supporting TiO2-CuO composite formation as depicted by the CIE diagram. The diode parameters such as ideality factor (n) and barrier height (Φb) are calculated with the help of I–V characteristics. This only reported novel effort on screen-printed TiO2-CuO thick film may help in manufacturing possible LEDs for optoelectronic applications.

Inkjet-Printed Ferrite Substrate-Based Vialess Waveguide Phase Shifter

Magnetically controlled waveguide-based phase shifters are desirable for their high performance, but are bulky and heavy, thus cannot be easily integrated with printed circuit board (PCB) based circuits. To tackle this, substrate-integrated waveguide (SIW) technology has been utilized, which brings the waveguide to a standard PCB, but requires large numbers of vias as well as multiple cavities in the substrate for ferrite slab placement. This implementation technique involves complex fabrication and yields a relatively low figure of merit (FoM). To alleviate this, we present the first completely vialess ferrite substrate-based waveguide phase shifter realized through low-cost inkjet printing technique. All the four sides of a yttrium iron garnet (YIG) substrate have been metalized through inkjet printing, allowing the fabrication of a conventional rectangular waveguide on a standard magnetic substrate. The prototype has been tested in symmetric as well as antisymmetric modes of biasing and peak FoMs of 160°/dB at 7.22 GHz and 332°/dB at 7.46 GHz have been measured, which are higher than those of the previously reported designs. This all-around inkjet printing approach can open the door to low-cost, integrable magnetic phase shifters with excellent RF performances.

Low-cost and open-source three-dimensional (3D) printing in neurosurgery: A pilot experiment using direct drive modification to produce multi-material neuroanatomical models

Background3-dimensional (3D) printing carries a genuine potential for pre-operative planning in neurosurgery. Entry-level 3D printers offer practicality in low resource settings, but are often limited by the range of filament materials as well as the capability of open-source segmentation software. ObjectiveWe intended to demonstrate that 3D printing of neuroanatomical structures is possible using an entry-level 3D printer equipped with the direct drive (DD) modification, which supported flexible filaments, with the models segmented using an open-source software. MethodsA DD system was installed onto the Ender 3 Pro printer. An attempt to print neurosurgical models using a low-cost 3D printer was conducted, where four patient-based neuroanatomical models were printed: skull base-vasculature, skull base-tumour, cervical spine, and ventricular system. The results were discussed and compared to similar endeavours in past literature. ResultsAlthough DD installation was challenging and led to vibration and longer print time, which ultimately warranted an inferior printing speed, DD system enabled the printing with thermoplastic polyurethane (TPU), a versatile elastomer; in addition to producing equal amount of detail to those printed with high-end printers and advanced image segmentation software. Fitting the frame well, changing infill type, and avoiding warping and stringing will improve print quality with the DD system. Conclusion3D printing with entry-level 3D printers equipped with DD system has been proven to be a reliable way of accurately reproducing patient-specific neuroanatomical constructs. Follow-up studies are necessary to implement 3D printing for neurosurgical planning in low-resource settings.

Highly durable machine-learned waterproof electronic glove based on low-cost thermal transfer printing for amphibious wearable applications

Highly durable machine-learned waterproof electronic glove based on low-cost thermal transfer printing for amphibious wearable applications