Direct Printing Research Articles

Additive manufacturing of interconnected hierarchically porous zirconia: Utilizing both microspherical and filamentary pore-forming agents via direct ink printing

Osteogenic differentiation and bone regeneration can be effectively aided by porous scaffolds with multiscale cellular structures, making it easier to repair defects in bone tissue. Due to the scarcity of pore-forming agents, it is extremely challenging to fabricate interconnected hierarchically porous zirconia at multi-scale. This work described a novel and straightforward method for directly imprinting a slurry containing two pore-forming agents (microspherical and filamentary) to produce strong and highly porous zirconia (ZrO2) ceramics with four levels of porosity ranging from nanometers to millimeters. The concentration of hemp fibers significantly affected printability when the rheological behavior of a zirconia slurry was examined. Utilizing a scanning electron microscope (SEM) to monitor the development of powder interstices under various sintering techniques. The permeability performance was assessed when simulated plasma had fully filled the scaffolds. The structure had a high compressive strength of 24.18 MPa, a porosity of 80.9 %, an apparent porosity of 55.7 %, and took just 1.11 s to fill a scaffold that was 15 mm high. It is anticipated that the proposed route will be expanded to include various engineering materials for structural and practical applications.

Evaluation on Surface Characteristics, Accuracy, and Dimensional Stability of Tooth Preparation Dies Fabricated by Conventional Gypsum and 3D-Printed Workflows.

To evaluate the surface characteristics, accuracy (trueness and precision), and dimensional stability of tooth preparation dies fabricated using conventional gypsum and direct light processing (DLP), stereolithography (SLA), and polymer jetting printing (PJP) techniques. Gypsum preparation dies were replicated according to the reference data and imported into DLP, SLA, and PJP printers, and the test data were obtained by scanning after 0, 1, 3, 7, 14, 28, and 42 days. After analyzing the surface characteristics, a best-fit algorithm between the test and the reference data was used to evaluate the accuracy and dimensional stability of the preparation dies. The data were analyzed by one-way analysis of variance and Tukey test or Kruskal-Wallis H test (α = .05). Compared with the gypsum group (3.61 ± 0.59 μm), the root mean square error (RMSE) values of the SLA group (5.33 ± 0.48 μm) was rougher (P < .05), the PJP group (2.43 ± 0.37 μm) was smoother (P < .05), and the DLP group (2.92 ± 0.91 μm) had no significant difference (P > .05). For trueness, the RMSE was greater in the PJP (34.90 ± 4.91 μm) and SLA (19.01 ± 0.95 μm) groups than in the gypsum (16.47 ± 0.47 μm) group (P < .05), and no significant difference was found between the DLP (17.10 Å} 1.77 μm) and gypsum groups. Regarding precision, the RMSE ranking was gypsum = DLP = SLA < PJP group. The RMSE ranges in the gypsum, DLP, PJP, and SLA groups at different times were 6.79 to 8.86 μm, 5.44 to 10.17 μm, 10.16 to 11.28 μm, and 10.94 to 32.74 μm, respectively. Although gypsum and printed preparation dies showed statistically significant differences in surface characteristics, accuracy, and dimensional stability, all tooth preparation dies were clinically tolerated and used to produce fixed restorations.

Fit and Strength of a Three-Unit Temporary Prosthesis Made by Different Manufacturing Techniques: An In Vitro Study.

To compare the fit and fracture load of temporary fixed partial prostheses fabricated by means of a conventional direct technique, milling, or 3D printing. A maxillary right first premolar and molar were prepared on a Frasaco cast, which was then duplicated 40 times. In total, 10 provisional three-unit fixed prostheses (Protemp 4, 3M) were made using the conventional technique with a putty mold. The 30 remaining casts were scanned to design a provisional restoration using CAD software. A total of 10 designs were milled (CEREC MC X5/shaded PMMA Disk, Dentsply Sirona), while the other 20 were 3D printed with one of the two 3D printers (Asiga UV MAX or Nextdent 5100, C&B, Nextdent). Internal and marginal fit were examined using the replica technique. Next, the restorations were cemented on their respective casts and loaded until fracture using a universal testing machine. The location and propagation of the fracture were also evaluated. 3D printing demonstrated the best internal fit. Nextdent (median internal fit: 132 μm) was significantly better compared to the milled (median internal fit: 185 μm; P = .006) and conventional restorations (median internal fit: 215 μm; P < .001), while the fit of Asiga (median internal fit: 152 μm) was only significantly better than the conventional restorations (P < .012). The lowest marginal discrepancy was found for the milled restorations (median marginal fit: 96 μm), but this was only significant when compared to the conventional group (median internal fit: 163 μm; P < .001). The conventional restorations demonstrated the lowest fracture load (median fracture load: 536 N), which was only significant when compared to Asiga (median fracture load: 892 N; P = .003). Within the present in vitro study's limitations, CAD/CAM demonstrated superior fit and strength compared to the conventional technique.

Artifact suppression and improved signal-to-noise ratio by phase-locked multiplexed coherent imaging.

Laser additive manufacturing (AM) promises direct metal 3D printing, but is held back by defects and process instabilities, giving rise to a need for in situ process monitoring. Inline coherent imaging (ICI) has proven effective for in situ, direct measurements of vapor depression depth and shape in AM and laser welding but struggles to track turbulent interfaces due to poor coupling back into a single-mode fiber and the presence of artifacts. By z-domain multiplexing, we achieve phase-sensitive image consolidation, automatically attenuating autocorrelation artifacts and improving interface tracking rates by 58% in signal-starved applications.

3D printed microfluidic valve on PCB for flow control applications using liquid metal

Direct 3D printing of active microfluidic elements on PCB substrates enables high-speed fabrication of stand-alone microdevices for a variety of health and energy applications. Microvalves are key components of microfluidic devices and liquid metal (LM) microvalves exhibit promising flow control in microsystems integrated with PCBs. In this paper, we demonstrate LM microvalves directly 3D printed on PCB using advanced digital light processing (DLP). Electrodes on PCB are coated by carbon ink to prevent alloying between gallium-based LM plug and copper electrodes. We used DLP 3D printers with in-house developed acrylic-based resins, Isobornyl Acrylate, and Diurethane Dimethacrylate (DUDMA) and functionalized PCB surface with acrylic-based resin for strong bonding. Valving seats are printed in a 3D caterpillar geometry with chamber diameter of 700 µm. We successfully printed channels and nozzles down to 90 µm. Aiming for microvalves for low-power applications, we applied square-wave voltage of 2 Vpp at a range of frequencies between 5 to 35 Hz. The results show precise control of the bistable valving mechanism based on electrochemical actuation of LMs.

Direct 4D printing of ceramics driven by hydrogel dehydration

4D printing technology combines 3D printing and stimulus-responsive materials, enabling construction of complex 3D objects efficiently. However, unlike smart soft materials, 4D printing of ceramics is a great challenge due to the extremely weak deformability of ceramics. Here, we report a feasible and efficient manufacturing and design approach to realize direct 4D printing of ceramics. Photocurable ceramic elastomer slurry and hydrogel precursor are developed for the fabrication of hydrogel-ceramic laminates via multimaterial digital light processing 3D printing. Flat patterned laminates evolve into complex 3D structures driven by hydrogel dehydration, and then turn into pure ceramics after sintering. Considering the dehydration-induced deformation and sintering-induced shape retraction, we develop a theoretical model to calculate the curvatures of bent laminate and sintered ceramic part. Then, we build a design flow for direct 4D printing of various complex ceramic objects. This approach opens a new avenue for the development of ceramic 4D printing technology.

Direct Printing of Flexible Multilayer Composite Electrodes Based on Electrohydrodynamic Printing

Direct Printing of Flexible Multilayer Composite Electrodes Based on Electrohydrodynamic Printing

Direct Pellet Three-Dimensional Printing of Polybutylene Adipate-co-Terephthalate for a Greener Future.

The widespread use of conventional plastics in various industries has resulted in increased oil consumption and environmental pollution. To address these issues, a combination of plastic recycling and the use of biodegradable plastics is essential. Among biodegradable polymers, poly butylene adipate-co-terephthalate (PBAT) has attracted significant attention due to its favorable mechanical properties and biodegradability. In this study, we investigated the potential of using PBAT for direct pellet printing, eliminating the need for filament conversion. To determine the optimal printing temperature, three sets of tensile specimens were 3D-printed at varying nozzle temperatures, and their mechanical properties and microstructure were analyzed. Additionally, dynamic mechanical thermal analysis (DMTA) was conducted to evaluate the thermal behavior of the printed PBAT. Furthermore, we designed and printed two structures with different infill percentages (40% and 60%) to assess their compressive strength and energy absorption properties. DMTA revealed that PBAT's glass-rubber transition temperature is approximately -25 °C. Our findings demonstrate that increasing the nozzle temperature enhances the mechanical properties of PBAT. Notably, the highest nozzle temperature of 200 °C yielded remarkable results, with an elongation of 1379% and a tensile strength of 7.5 MPa. Moreover, specimens with a 60% infill density exhibited superior compressive strength (1338 KPa) and energy absorption compared with those with 40% infill density (1306 KPa). The SEM images showed that with an increase in the nozzle temperature, the quality of the print was greatly improved, and it was difficult to find microholes or even a layered structure for the sample printed at 200 °C.

Versatile cost-effective fabrication of large-area nanotube arrays with highly ordered periodicity

Nanomaterials typically exhibit physical and chemical properties that differ from those of conventional bulk materials owing to their nanometer-scale structures. Among them, nanotube arrays are characterized by their ability to exhibit remarkably aligned larger surface areas than those of existing arrays. Consequently, they have been used to increase efficiency in various fields such as sensing, energy storage and conversion, and optical communication. Processes such as anodic-aluminum-oxide templating, secondary sputtering, and sputtering are generally used to manufacture nanotube arrays. However, these methods have limitations in creating periodically aligned structures and precisely controlling nanotube characteristics such as diameter, period, and height. Therefore, a method combining direct printing and oblique-angle deposition (OAD) performed by e-beam evaporation is reported in this study for generating nanotubes with a highly ordered periodicity. Using this approach, nanotube arrays of various shapes and specifications can be manufactured by adjusting the type of master stamp used in the direct printing and the OAD parameters. Additionally, this scheme can be leveraged to produce nanotube arrays with metals, inorganic compounds, multilayer structures, and core–shell configurations.

Direct 4D printing of functionally graded hydrogel networks for biodegradable, untethered, and multimorphic soft robots

Recent advances in functionally graded additive manufacturing (FGAM) technology have enabled the seamless hybridization of multiple functionalities in a single structure. Soft robotics can become one of the largest beneficiaries of these advances, through the design of a facile four-dimensional (4D) FGAM process that can grant an intelligent stimuli-responsive mechanical functionality to the printed objects. Herein, we present a simple binder jetting approach for the 4D printing of functionally graded porous multi-materials (FGMM) by introducing rationally designed graded multiphase feeder beds. Compositionally graded cross-linking agents gradually form stable porous network structures within aqueous polymer particles, enabling programmable hygroscopic deformation without complex mechanical designs. Furthermore, a systematic bed design incorporating additional functional agents enables a multi-stimuli-responsive and untethered soft robot with stark stimulus selectivity. The biodegradability of the proposed 4D-printed soft robot further ensures the sustainability of our approach, with immediate degradation rates of 96.6% within 72 h. The proposed 4D printing concept for FGMMs can create new opportunities for intelligent and sustainable additive manufacturing in soft robotics.

Planar-thick panels and 3D-printed gap fillers: A hybrid digital fabrication approach to curved surface approximations

Curved surfaces may be approximated using polygonal panels to simplify complex architectural designs, yet their constructions can be expensive due to single-use moulds producing unique panels. To reduce costs, strategies like planarizing and reducing the number of different panels have been suggested, which are increasingly achievable with advancing digital fabrication technologies. However, current subtractive and additive manufacturing techniques face challenges in producing complex 3D shapes and large volumes, respectively. Combining these two techniques has been attempted, mainly with small 3D-printed nodes, leaving the direct realization of curved surface approximations unexplored. This paper extends the thick-panel origami theory to introduce planar-thick panels and 3D-printed gap fillers for cost-effective constructions. It presents a computational workflow to transform meshes into non-intersecting panels while preserving edge connectivity and frame-like gap fillers with minimized volumes. Physical prototypes demonstrate significant cost savings compared to direct 3D printing. All prototypes are accurate within a 10 mm material thickness due to the guidance of the gap fillers. The finite element analysis shows that structural performance is greatly influenced by the material properties, especially of panels, due to their relatively larger volume. Numerical examples are also presented using the k-means clustering-optimization method to reduce the number of different panels.

Enhancement of hydrophilicity and color strength in plasma treated PET with water vapor post-exposure using a new in-line pilot scale DBD plasma

Due to its low hydrophilicity, direct sublimation inkjet printing on woven polyester fabric surfaces is challenging. This research experimentally studies the efficacy of dielectric barrier discharge (DBD) roll-to-roll plasma treatment with or without water vapor post-exposure as a novel method to modify polyethylene terephthalate (PET) surfaces to enhance hydrophilicity, color performance, and printing quality. The Response Surface Methodology (RSM) was used to design experiments, and the optimum conditions were analyzed through statistical calculations. Their results were examined using Optical Emission Spectroscopy (OES), Atomic Force Microscopy (AFM), field emission scanning electron microscopy (FESEM), Energy Dispersive X-ray (EDX), X-ray Photoelectron Spectroscopy (XPS), and Attenuated Total Reflectance Fourier Transform Infra-Red spectroscopy (ATR-FTIR) tests. Qualitative and quantitative tests for color performance and wicking test used for hydrophilicity assessment confirms the effectiveness of this Green inline pretreatment for industries to enhance direct sublimation inkjet printing quality on PET by a decrease in absorption time from 12051 to 202 s and an increase in the color depth to 12.49%, 25.89 and 18.07% for Cyan, Magenta and Key (black) respectively. One of the stable optimum conditions in which three printed colors: Cyan, Magenta, and Black (Key), show high-quality color performance is at 15 processing rounds, 2 m/min velocity in the absence or presence of water vapor post-exposure. Water vapor post-exposure exhibits a beneficial, economic effect along with plasma treatment. The results show that the chemical modification aspect of this treatment plays a more significant role in printing quality enhancement than its morphological modification.

Additive manufacturing via protein denaturation

Application of patterned photothermal transduction enables direct vat-based 3D printing of unmodified proteins from aqueous formulations.

Direct laser writing-enabled 3D printing strategies for microfluidic applications.

Over the past decade, additive manufacturing-or "three-dimensional (3D) printing"-has attracted increasing attention in the Lab on a Chip community as a pathway to achieve sophisticated system architectures that are difficult or infeasible to fabricate via conventional means. One particularly promising 3D manufacturing technology is "direct laser writing (DLW)", which leverages two-photon (or multi-photon) polymerization (2PP) phenomena to enable high geometric versatility, print speeds, and precision at length scales down to the 100 nm range. Although researchers have demonstrated the potential of using DLW for microfluidic applications ranging from organ on a chip and drug delivery to micro/nanoparticle processing and soft microrobotics, such scenarios present unique challenges for DLW. Specifically, microfluidic systems typically require macro-to-micro fluidic interfaces (e.g., inlet and outlet ports) to facilitate fluidic loading, control, and retrieval operations; however, DLW-based 3D printing relies on a micron-to-submicron-sized 2PP volume element (i.e., "voxel") that is poorly suited for manufacturing these larger-scale fluidic interfaces. In this Tutorial Review, we highlight and discuss the four most prominent strategies that researchers have developed to circumvent this trade-off and realize macro-to-micro interfaces for DLW-enabled microfluidic components and systems. In addition, we consider the possibility that-with the advent of next-generation commercial DLW printers equipped with new dynamic voxel tuning, print field, and laser power capabilities-the overall utility of DLW strategies for Lab on a Chip fields may soon expand dramatically.

Coatable strain sensors for nonplanar surfaces.

Rapidly fabricating flexible and stretchable sensors on nonplanar surfaces is crucial for wearable device applications. We employed a novel fabrication method, incorporating molds and gels into electroless plating, to enable direct printing of sensors on a wide array of surfaces, from those with up to 100 μm profile heights to hydrogels with a Young's modulus of 100 kPa. This coatable strain (CS) sensor offers several potential advantages. Firstly, it is designed to circumvent the typical limitations of limited flexibility, plastic deformation, and low repeatability found in viscoelastic polymers by being directly coated onto the surface without requiring a substrate. Secondly, it potentially increases the effective contact area and signal-to-noise ratio by eliminating voids between the sensor and the surface. Finally, the CS sensor can obtain any desired patterning at room temperature in a matter of minutes, significantly reducing energy and time consumption. In this study, we demonstrated the versatility of the CS sensor by applying it to a range of substrates, showcasing its adaptability to diverse materials, surface roughness levels, and Young's modulus values. Our primary focus was on plant growth monitoring, a challenging application that showcased the sensor's efficacy on surfaces like needles, hairy leaves, and fruits. These applications, traditionally difficult for conventional polymer-based sensors, serve to illustrate the CS sensor's potential in a range of complex environmental contexts. The successful deployment of the CS sensor in these settings suggests its broader applicability in various scientific and technological fields, potentially contributing to significant developments in the area of wearable devices and beyond.

Mechanical properties of materials for 3D printed orthodontic retainers.

The purpose of this study was to compare the mechanical properties of materials used for orthodontic retainers made by direct 3D printing and thermoforming.

Electro-Codeposition of Composite Materials for Enhanced Thermal and Electrical Properties

State of the art cryocoolers, high powered electronic systems, semiconductor backplanes, and space platforms require next generation high conductivity composite materials that can reduce product weight while improving performance. To meet this need, Faraday Technology with the help of Universities, National Labs, and industrial partners is developing a scalable electro-codeposition method to produce high conductivity hybrid graphene/copper composite materials. Specifically, this talk will highlight two activities ongoing at Faraday and demonstrate the feasibility of fabricating either composite or laminated graphene-copper hybrid foils or direct printed composite nanowires via a pulse electro-codeposition approach. These activities indicated these composite materials can achieve a greater than 50% reduction in sheet resistance, a ~50% increase in mechanical strain, and a 100% increase in thermal conductivity compared to Cu foils. We will also discuss the opportunity to produce a wide range of material shapes by enabling a direct print apparatus that combines x,y,z control methods with an electro-codeposition printhead. If successful we envision that method to print next generation composite materials like ‘covetics’ that have the potential to meet many of the electronics and space community’s needs by enabling in space structural repairs, fabrication of new electronic components or sensors, or be utilized as heat exchanger composite materials. Finally, this activity also identified commercial partners interested in integrating these next generation into high powered electronics like laser diodes or invertors for electric vehicles.Acknowledgements: Faraday Technology acknowledges the Department of Energy and NASA SBIR activities under Contract No. DE-SC0021676 (DOE Phase II) and 80NSSC22CA099 (NASA Phase II).

Facile Fabrication of Flexible and High-Performing Thermoelectrics by Direct Laser Printing on Plastic Foil.

The emerging fields of wearables and the Internet of Things introduce the need for electronics and power sources with unconventional form factors: large area, customizable shape, and flexibility. Thermoelectric (TE) generators can power those systems by converting abundant waste heat into electricity, whereas the versatility of additive manufacturing suits heterogeneous form factors. Here, additive manufacturing of high-performing flexible TEs is proposed. Maskless and large-area patterning of Bi2Te3-based films is performed by laser powder bed fusion directly on plastic foil. Mechanical interlocking allows simultaneous patterning, sintering, and attachment of the films to the substrate without using organic binders that jeopardize the final performance. Material waste could be minimized by recycling the unexposed powder. The particular microstructure of the laser-printed material renders the-otherwise brittle-Bi2Te3 films highly flexible despite their high thickness. The films survive 500 extreme-bending cycles to a 0.76mm radius. Power factors above 1500 µW m-1K-2 and a record-low sheet resistance for flexible TEs of 0.4 Ω sq-1 are achieved, leading to unprecedented potential for power generation. This versatile fabrication route enables innovative implementations, such as cuttable arrays adapting to specific applications inself-powered sensing, and energy harvesting from unusual scenarios like human skin and curved hot surfaces.

(Invited) Case Studies for in-Space Electrochemical Operations

Faraday Technology Inc. is a research, development and electrochemical engineering firm developing electrochemical innovations for terrestrial and space system.[1,2] With that founding basis Faraday has been able to bridge the gap between academic understanding and small-scale demonstrations to commercialization of practical components for over 32 years of operation.This presentation will discuss a broad range of electrochemical approaches to improve the performance of components used in space or to be used for in-space production. We will provide insight into case studies, performed at Faraday, from our four business units of electrodeposition, electrochemical surface finishing, electrochemical conversion, and electrochemical system design. For instances, we will discuss direct print electrodeposition, electrophoretic application of coatings for glare resistance, surface finishing of rocket components, bioelectrochemical treatment of urine, and the generation of peroxide. Each electrochemical process has applications on earth and in space; additionally, each program had to overcome specific challenges that only space can present.

High-performance and selective semi-transparent perovskite solar cells using 3D-structured FTO

Perovskite solar cells (PSCs) have been in the spotlight as a promising next-generation solar cell. With the tremendous development of power conversion efficiency (PCE) over the past decades, a considerable amount of research has focused on semi-transparent perovskite solar cells for applications. However, the short-circuit current density (JSC) greatly decreases in semi-transparent PSCs with an increase in transmittance, and this results in a significant decrease in PCE. In this study, semi-transparent PSCs were fabricated by controlling the absorption layer thickness and aperture ratio using a 3D-structured FTO manufactured via processes that can work large areas (direct printing and mist-CVD). This strategy has an advantage in that the aperture ratio (transmission/entire area) can be controlled easily by adjusting pattern specification. The effect of a 3D-structured FTO enhanced the diffuse transmittance and shortened the carrier travel distance; further, it minimized the decrease in PCE because of an increase in transmittance. Our fully semi-transparent PSCs (F–PSCs) with the ITO cathode achieved a PCE of 12.0 %–14.6 %, and an average visible transmittance (AVT) of 13.4 %–17.0 %. These results demonstrate that the parameter of semi-transparent PSCs (transmittance and PCE) can be easily tailored to the application by controlling the specification of the pattern.