Single Printing Research Articles

Organic Ink Multi-Material 3D Printing of Sustainable Soft Systems.

Drawing inspiration from nature, soft materials are at the core of a transformation toward adaptive and responsive engineered systems, capable of conquering demanding terrain and safe when interacting with biological life. Despite recent advances in 3D printing of soft materials, researchers are still far from being able to print complex soft systems where a multitude of different components need to work together symbiotically. Closing this gap necessitates a platform that unites diverse materials into one synergetic process. Here, a multi-material printing system is presented, combining gelatin-based hydrogels with a new biodegradable support material. This organic ink maintains up to 60° overhang and is printable over gaps to structurally support the main biogel body, while triggered dissolution enables its selective removal and the formation of internal cavities. Therefore, the creation of vascular networks, tunable scaffolds, and embedded sensors within a single printing process becomes feasible. Furthermore, a perforation-resistant, joint-like vacuum actuator (VAc) is designed and 3D printed, capable of bending to angles up to 60° at fast response times down to 0.23 s. Combining these approaches in an efficient, streamlined fabrication process with biodegradable materials will unlock new sustainability dimensions for complex and durable soft systems.

Experimental study on buildability and mechanical properties of 3D printing cob

The application of 3D printing technology to earth buildings conforms to the development concept of low carbon, green and intelligent construction. The key issue lies in the development of earth material with both favorable buildability and sufficient mechanical properties. In this study, the printing parameters of mixture for 3D printing with different water contents were optimized. The optimum water content of 3D printing cob was determined based on the buildability. The result shows that when the flow spreading diameter is between 140 mm and 160 mm, 3D printing cob has good buildability performance. The optimum water content is 24.6 %. In addition, anisotropic performance was analyzed by compressive strength tests from three orthogonal directions. In particular, according to the test results of single printing limit height and yield stress, the buildability of 3D printing cob wall was analyzed. The building strategy of the printing divided into multiple times was obtained.

Characterization of Silver Conductive Ink Screen-Printed Textile Circuits: Effects of Substrate, Mesh Density, and Overprinting

This study explores the intricate interaction between the properties of textile substrates and screen-printing parameters in shaping fabric circuits using silver conductive ink. Via analyzing key variables such as fabric type, mesh density, and the number of overprinted layers, the research revealed how the porous structure, large surface area, and fiber morphology of textile substrates influence ink absorption, ultimately enhancing the electrical connectivity of the printed circuits. Notably, the hydrophilic cotton staple fibers fabric effectively absorbed the conductive ink into the fabric substrate, demonstrating superior electrical performance compared with the hydrophobic polyester filament fabric after three overprinting, unlike the results observed after a single print. As mesh density decreased and the number of prints increased, the electrical resistance of the circuit gradually reduced, but ink bleeding on the fabric surface became more pronounced. Cotton fabric, via absorbing the ink deeply, exhibited less surface bleeding, while polyester fabric showed more noticeable ink spreading. These findings provide valuable insights for improving screen printing technology for textile circuits and contribute to the development of advanced fabric circuits that enhance the functionality of smart wearable technology.

Operando visualization of porous metal additive manufacturing with foaming agents through high-speed x-ray imaging

Porous metals find extensive applications in soundproofing, filtration, catalysis, and energy-absorbing structures, thanks to their unique internal pore structure and high specific strength. In recent years, there has been an increasing interest in fabricating porous metals using additive manufacturing (AM), leveraging its unique advantages, including improved design freedom, spatial material control, and cost-effective small-batch production. In this study, we conducted pioneering operando visualization of AM porous metal using a laser powder bed fusion (L-PBF) setup combined with a high-speed synchrotron x-ray imaging system. Single track printing experiments using Ti6Al4V (Ti64) combined with titanium hydride (TiH2) and sodium carbonate (Na2CO3) as foaming agents, with varying mixing ratios were performed under different processing conditions. The results elucidate the dynamic development of porosity formation. The average pore size is significantly influenced by the particle size of foaming agents when pore coalescence is absent. For all foaming agent content tested in the current study, the number of pores is found to be more sensitive to changes in laser power than in laser scanning speed. Increasing linear energy density (increasing laser power or reducing laser scanning speed) promotes the foaming agent activation thereby porosity formation. However, high linear energy density skews pore distribution towards the surface despite forming deeper melt pools. In addition, the impact of additional factors including foaming agent’s laser absorptivity and decomposition kinetics with respect to AM time scales should be carefully considered to avoid ineffective activation of foaming agents during the AM of porous metals.

Optimising Additive Manufacturing to Produce PLA Sandwich Structures by Varying Cell Type and Infill: Effect on Flexural Properties

The objective of this research is to optimize additive manufacturing processes, specifically Fused Filament Fabrication (FFF) techniques, to produce sandwich structures. Mono-material specimens made of polylactic acid (PLA) were produced, where both the skin and core were fabricated in a single print. To optimize the process, variations were made in both the base cell geometry of the core (Tri-Hexagon and Gyroid) and the core infill (5%, 25%, 50%, and 75%), evaluating their effects on static three-point bending behavior. Optical microscopy was employed to assess both the structure generated by additive manufacturing and the fracture modes. The findings reveal that increasing the infill, and thus the core density, enhances the mechanical properties of the structure, although the improvement is such that samples with 50% infill already demonstrate excellent performance. The difference between hexagonal and Gyroid structures is not significant. Based on microscopic analyses, it is believed that the evolution of 3D printers, from open to closed chamber designs, could significantly improve the deposition of the various layers.

Tailoring texture and functionality of vegetable protein meat analogues through 3D printed porous structures

This study presents a comprehensive 3D printing process for plant-based meat alternatives, covering ink formulation, printing, and final product characterization. Traditionally, achieving desired food properties requires extensive exploration of ink components. Here, we demonstrate the potential of manipulating processing parameters instead of ink composition. Two structures were printed, differing only in extrusion temperature. The printed structures exhibited a dimensional accuracy slightly below 100%. We investigated their behavior through simulated food production cycles, including freezing, thawing, dehydration, and rehydration. Rheological measurements revealed that protein denaturation caused a 20% increase in viscosity. Temperature-induced protein denaturation allowed to produce 3D printed samples with a fine porous structure, with pore sizes ranging from 50 to 450 μm. Mechanical characterization showed that a single printing parameter (extrusion temperature) significantly impacts the final product mechanical properties, with an increase of about 50% in the maximum stress for denatured samples after rehydration. This novel approach simplifies 3D-printed protein-based food production, establishing a link between processing parameters and the final product mechanical behavior.

Optimizing polymethyl methacrylate (PMMA)-based stretchable microneedle arrays by vat photopolymerization for efficient drug loading

Advancements in vat photopolymerization printing technology have enabled the fabrication of components with varying mechanical properties within a single print job. Using a digital light projector to cure photopolymer resins layer by layer, it allows the fabrication of parts with both flexibility and rigidity, in different regions. It simplifies the manufacturing process by eliminating the need for multiple steps. Specifically, for applications such as microneedles, printing onto a stretchable substrate is crucial compared to a rigid substrate, as it conforms better to the contours of the skin, ensuring more effective and comfortable drug delivery. However, a notable limitation of vat photopolymerization printing is the current lack of biocompatible materials, which restricts its application for microneedle fabrication. The challenge lies in developing materials that meet biocompatibility standards, while also being compatible with the printing technique and capable to achieve precise microscale structures. Therefore, we have developed an ultraviolet (UV)-curable polymethyl methacrylate (PMMA) suitable for the vat photopolymerization printing and the microneedles were designed to have a hollow side structure, enhancing drug loading efficiency. Comprehensive testing has been conducted, including durability test, drug loading efficiency, and skin penetration capability.

Operando Colorations from Real-Time Growth of 3D-Printed Nanoarchitectures.

While artificial 3D nanostructures can generate precise and flexible coloration, their real-time color changes during 3D nanoprinting remain unexplored owingto the inherent challenges of in situ transient measurements and observations. In this study, a 3D-printing system which supports the operando observation/measurement of the color dynamics of subwavelength metallic nanoarchitectures fabricated in real time is developed and evaluated. During 3D printing, the dimensions and geometries of the 3D nanostructures grow over time, producing a large library of optical spectra associated with real-time color changes. Only a timer is needed to define the expected colors from a single 3D print run. Fin-like nanostructures are used to toggle colors based on the polarization effect and produce color gradients. Based on structural coloration, nanoarchitectures are designed and printed to animate desired color patterns. Moreover, the resulting color dynamics can also serve as an operando identifier for real-time structural information during 3D nanoprinting. A single print run enables the efficient creation of a comprehensive library of desired colorations owing to the flexibility in time-dependent controllability and 3D geometries at the subwavelength scale. 3D nanoprinted plasmonic structures exhibiting time-varying colorations (4D printing of colors) uniquely redefines the coloring stategy,offering considerable potential for numerousapplications.

Enhancement of Scan Strategy for Improving Surface Characteristics of the SLMed Inconel 718 Alloy Component

The technique of selective laser melting has garnered significant interest due to its capacity to fabricate metal parts of any shape using a single printing process. In this study, a scan strategy was proposed for printing the inner structure part based on the varying performance of the Inconel 718 alloy part produced using different scan techniques. The test findings indicated that the surface quality of the printed material along the scan line exhibited significantly superior performance in comparison to that produced in a vertical direction to the scan line. Regarding the scan strategy, it is evident that the zigzag shape scan strategy exhibited superior performance in terms of the microstructure of the printed part. This is attributed to the more consistent cooling rate on each scan track. On the other hand, the square-framed scan strategy demonstrated a relatively optimal condition for the bending deformation of the printed part compared to other scan strategies. This is due to the more appropriate behavior of the molten pool during the outer edge printing process. After considering all of these criteria, a novel scan approach was created that included various scan strategies. The test findings indicated that the component produced using this novel scanning technique exhibited the combined benefits of both the square-shaped and zigzag-shaped scanning strategies.

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.

Fully 3D-Printed Miniature Soft Hydraulic Actuators with Shape Memory Effect for Morphing and Manipulation.

Miniature shape-morphing soft actuators driven by external stimuli and fluidic pressure hold great promise in morphing matter and small-scale soft robotics. However, it remains challenging to achieve both rich shape morphing and shape locking in a fast and controlled way due to the limitations of actuation reversibility and fabrication. Here, fully 3D-printed, sub-millimeter thin-plate-like miniature soft hydraulic actuators with shape memory effect (SME) for programable fast shape morphing and shape locking, are reported. It combines commercial high-resolution multi-material 3D printing of stiff shape memory polymers (SMPs) and soft elastomers and direct printing of microfluidic channels and 2D/3D channel networks embedded in elastomers in a single print run. Leveraging spatial patterning of hybrid compositions and expansion heterogeneity of microfluidic channel networks for versatile hydraulically actuated shape morphing, including circular, wavy, helical, saddle, and warping shapes with various curvatures, are demonstrated. The morphed shapes can be temporarily locked and recover to their original planar forms repeatedly by activating SME of the SMPs. Utilizing the fast shape morphing and locking in the miniature actuators, their potential applications in non-invasive manipulation of small-scale objects and fragile living organisms, multimodal entanglement grasping, and energy-saving manipulators, are demonstrated.

A novel powder sheet laser additive manufacturing method using irregular morphology feedstock

Irregular (i.e. non-spherical) morphology powder is more cost-efficient to produce than spherical shaped powder. However, its reduced levels of flowability limit the wide application ranges of laser beam powder bed fusion (LPBF). To address this issue, a novel powder sheet additive manufacturing concept (MAPS) is proposed. Herein, a pre-manufactured metal particle-polymer binder composite (i.e. powder sheet) feedstock is employed as a raw material. The printability of irregularly shaped powder particles in sheet (MAPS) format was physically investigated using a range of different process parameters. The manufacturing process was observed by high-speed imaging. Microstructural and chemical element characterisations of the irregularly shaped powder particle print were then compared against those prints which were conducted using sheet-based (MAPS) spherical powder morphologies. The results indicated that the geometric accuracy and density of irregular powder morphology sheet printing improved when using a negative defocus strategy of the laser beam. A negative defocusing strategy allowed for the melting mode of the material to be transformed from keyhole to a more favourable conduction state. High speed imaging revealed that more spatter and vapour plume were observed with the increase in the magnitude of the negative defocus. The multi-morphology 304 L stainless steel (SS304) samples were printed in a single printer using an efficient method for the first time, i.e. printing spherical SS304 material on top of irregular SS304. EDX results indicated an insignificant change of chemical elements between the spherical and irregular prints. EBSD results revealed that columnar grains could grow through the irregular-spherical transition zone and similar grain size can form between spherical and irregular prints. The results of this study provide insights into the optimum printing configurations for powder sheet additive manufacturing using a cost-effective solution of irregular morphology material.

A 3D‐Printed Printhead: Custom Inkjet Dispenser for Medium Viscosity Fluids

Inkjet is a versatile non‐contact printing technique that uses droplets of ink jetted from nozzles to print on a variety of substrates. Although some modern piezoelectric printheads support high viscosity fluids (>10 cP), they are currently expensive and may not be suited for many benchtop experiments in research environment. Here, the design, fabrication by 3D‐printing (no cleanroom processes or silicon micromachining are involved) and testing of a multi‐purpose single‐nozzle piezoelectric dispenser/printhead for medium‐viscosity fluids (10–60 cP) is reported. Custom control electronics are developed to drive the printhead. The design features a 200 μm diameter nozzle, suitable for nL drop generation with solutions containing nm sized particles, thus allowing the deposition of μm thick layers of functional inks in a single printing pass. The inkjet dispenser is first tested with glycerol solutions, resulting in drops of 1.9–3.6 nL with typical drop velocity of 0.5–1.3 m s−1. The developed piezoelectric dispensing system is then demonstrated in the printing of a two‐layer capacitive sensor, using silver nanoparticle ink (conductive ink) and a transparent encapsulant ink (dielectric ink). The reported piezoelectric dispenser design can be optimized for many research purposes, allowing the dispensing of functional chemicals, materials, and biomolecules.

Full-composition-gradient in-situ alloying of Cu–Ni through laser powder bed fusion

Multi-material laser powder bed fusion has long been a challenge in additive manufacturing, especially in terms of controlling spatial variations and joining multiple materials. The challenge is even greater when multi-material components have different physical properties (e.g., different thermal expansions, thermal conductivities and laser reflectivities). The aforementioned scenario is applicable to copper–nickel (Cu–Ni) alloy. The simultaneous printing and controllable mixing of pure Cu and pure Ni within a single print have not been accomplished due to the substantial disparity in the physical properties of pure Cu and pure Ni. In this work, a full composition with different mixing proportions (100 % Cu to 100 % Ni) was fabricated in a single printing process through in-situ alloying based on our process of micro laser powder bed fusion. A transition from a columnar grain to a quasi-equiaxed grain morphology with texture variation from <110> to <111> was found in the full–composition–gradient of the Cu–Ni alloy. Microstructural variations, such as fine grain strengthening and grain boundary strengthening, greatly affected the mechanical properties of the alloys: the ultimate tensile strength ranged from 303 to 488 MPa and the yield strength ranged from 231 to 445 MPa. Moreover, the electrical conductivity of the alloys with a compositional gradient ranged from 3.6 % IACS to 96 % IACS due to the electron scattering induced by lattice distortion. In summary, a full-composition Cu–Ni gradient alloy was fabricated through in-situ alloying adopting micro laser powder bed fusion for the first time, enabling the investigation of the evolution of the microstructure and properties of the alloy as the alloy composition varies.

Study of print suitability of environment-friendly plastics using flexography printing

Environmental-friendly plastics (EFP) are new alternatives of fossil-based plastics. The EFP family mainly constitutes bio-plastics/bio-attributed plastics and post-consumer recycled plastics (PCR). EFP contributes around 10% of total plastics production in global plastic production. Presently EFP are mostly used in grocery bags, bin liners, compostable garbage bags and single-use plastics with single or spot color printing. Multi-color printing can add value or open new horizons for these materials, leading to high-value applications. It can also be used for high-speed printing or flexible packaging applications. Plastics available in this category come from both fossil-based and bio-based sources. Fossil-based bioplastics has almost similar degree of print suitability but materials coming from bio-based sources are yet to be explored for print suitability, especially with high-speed multi-color printing machines. Flexographic printing is known for high-quality and high-speed printing on different substrates, including paper, conventional plastics and fossil-based bio-plastics. The advantage of having a common impression cylinder (CIC) arrangement and the requirement of less pressure during printing makes it suitable for consideration for printing on EFP. Hence, this study, print suitability of EFP using flexography printing, is an attempt to explore the mutual compatibility of these substrates and printing process, which will prove to be a boon in the future for establishing EFP as a strong substitute for replacing conventional plastics.

Effect of Core Material Thickness on the Shore Hardness of the Sandwich-Structured Multi-Material 3D-Printed Parts

Fused Filament Fabrication (FFF) continues to experience improvements in terms of its flexibility and functionality, therefore it attracts public attention to use this technology. Multi-Material Additive Manufacturing (MMAM) is an approach in the FFF technology that allows the manufacturing of 3D-printed products composed of two or more materials in a single printing process. MMAM enables the user to apply various configurations to obtain a 3D-printed material with adjustable properties. This study aims to determine the effect of core material on the Shore hardness of the FFF printed parts with the MMAM approach. There were two types of materials combined with the MMAM approach in this work, namely polylactic-acid (PLA) and thermoplastic elastomer (TPE). The Shore hardness test was conducted according to the ASTM D2240-15 standard. The results showed that the thickness of the core material inserted into the printed material had a significant effect on the hardness value of printed multi-material parts. In addition, the hardness value was highly dependent on the modulus of elasticity of the material. Therefore, the hardness value changed following the proportion of the printed material.

Mechanical Performance Comparison of Sandwich Panels with Graded Lattice and Honeycomb Cores.

The design of graded and multifunctional lattice cores is driven by the increasing demand for high-performance components in lightweight engineering. This trend benefits from significant achievements in additive manufacturing, where the lattice core and the face sheets are fabricated simultaneously in a single print job. This work systematically compares the mechanical performance of sandwich panels comprising various graded lattice cores subjected to concentrated loads. In addition to graded lattice cores, uniform lattices and conventional honeycomb cores are analyzed. To obtain an optimized graded lattice core, a fully stressed design method is applied. Stresses and displacements are determined using a linear elastic analytical model that allows grading the core properties in a layerwise manner through the core thickness. The analysis indicates the superior performance of graded lattice cores compared to homogeneous lattice cores. However, conventional honeycombs outperform graded lattice cores in terms of load-to-weight ratio and stiffness-to-weight ratio. This study provides valuable insights for the design of lattice core sandwich panels and the advantages of several design approaches.

Microencapsulation in food processing - A review study

Microencapsulation is one of the efficient, advanced and promising technologies in the field of food processing. The technology involves the protection of different valuable food constituents present in a food product by the use of a suitable covering material on it. Besides, protecting the covering material allows the release of the core material in a controlled way increases shelf life and enhances the sensory qualities. The process of microencapsulation can be done by various methods such as coacervation, polymer-polymer incompatability, solvent evaporation, spray drying, fluidized bed technology, pan coating, spinning disc, extrusion, interfacial polymerization etc. This technology is being used in various fields including pharmaceutical, vectorisation, artificial organs, single dose treatment, agriculture (fungicide, herbicide, insect repellent, artificial insemination), food, printing, cosmetic, textile and defense. No single microencapsulation process is adaptable to all core materials. It is a complicated process and requires skilled person to handle the whole process. As worldwide demands for functional coatings continue to increase, new, cost effective microencapsulation technologies will be developed and the technology will remain at the forefront of future.

Effects of particle damper design parameters on the damping performance of laser powder bed fused structures

Particle dampers (PD), a passive damping technology, absorb energy from particle-particle and particle-cell wall interactions originating from friction and collision. PDs offer advantages such as design simplicity, low cost, applicability in harsh conditions, and flexibility to be used in a wide frequency band range. Additive manufacturing, specifically the powder bed fusion process, can fabricate structures with integrated PDs in a single printing process, eliminating the need to implement external dampers. However, the dynamic behavior of PDs must be determined to utilize their full potential. In this study, we examined 16 cases of integrated PDs by varying specific parameters including size, number, and locations on the structure to understand the effects of these parameters on the dynamic behavior of the first and second modes of the structure. Modal tests were conducted on additively manufactured samples to extract frequency response functions and calculate modal parameters (natural frequency and damping ratio) using the rational fraction polynomial method, studying the effects of PDs. The results showed that the damping performance of the parts was increased by a factor of up to 10 using body-integrated PDs compared with the fully fused specimen. The effectiveness of body-integrated PDs was shown to be strongly dependent on their volume and location. For instance, the damping generally increased as the volume fraction increased, which also reduced the total weight of the specimens by up to 60 g. Furthermore, the damping performance significantly increased for a specific mode when the PDs were located near the maximum displacement regions.

Additive Manufacturing of Multi‐Metal Microstructures by Localized Electrochemical Deposition Under Hydrodynamic Confinement

AbstractThis study presents a device and method for multi‐metal printing of microscale structures. The method is based on combining hydrodynamic confinement of electrolytes with localized electrochemical deposition (HLECD), allowing rapid switching of the deposited metal. The device used in HLECD integrates a micro‐anode on a vertical microfluidic chip containing two open‐ended channels that control the flow of electrolytes surrounding the anode. When placed on top of a conducting surface, a localized electrochemical reaction is initiated, wherein the deposited metal composition is dictated by the electrolyte in the confinement. A range of electrolytes, which are used to deposit copper, tin, silver, and nickel, are used to fabricate multiple structures involving more than 60 material changes within a single printing process. The structures are analyzed using electron microscopy, showing the ability to achieve sharp transitions between pure metals. The constant replenishment of electrolytes also eliminates the problem of ion depletion commonly occurring in localized electrochemical deposition, and enables printing rates that are nearly an order of magnitude greater.