Approach Of Printing Research Articles

Solid Knitting

We introduce solid knitting, a new fabrication technique that combines the layer-by-layer volumetric approach of 3D printing with the topologically-entwined stitch structure of knitting to produce solid 3D objects. We define the basic building blocks of solid knitting and demonstrate a working prototype of a solid knitting machine controlled by a low-level instruction language, along with a volumetric design tool for creating machine-knittable patterns. Solid knitting uses a course-wale-layer structure, where every loop in a solid-knit object passes through both a loop from the previous layer and a loop from the previous course. Our machine uses two beds of latch needles to create stitches like a conventional V-bed knitting machine, but augments these needles with a pair of rotating hook arrays to provide storage locations for all of the loops in one layer of the object. It can autonomously produce solid-knit prisms of arbitrary length, although it requires manual intervention to cast on the first layer and bind off the final row. Our design tool allows users to create solid knitting patterns by connecting elementary stitches; objects designed in our interface can---after basic topological checks and constraint propagation---be exported as a sequence of instructions for fabrication on the solid knitting machine. We validate our solid knitting hardware and software on prism examples, detail the mechanical errors which we have encountered, and discuss potential extensions to the capability of our solid knitting machine.

Multi-material 4D printing to realize two-phase morphing in self-actuating structures

4D printing has garnered significant attention within the field of engineering due to its capacity to introduce novel functionalities in printed structures through shape-morphing. Nevertheless, there persist challenges in the design and fabrication of intricate structures, primarily stemming from the intricate task of controlling variables that impact morphing characteristics. In order to surmount these hurdles, the approach of multi-material 4D printing is employed, underpinned by parametric studies, to actualize complex structures through a two-phase morphing process. This study specifically investigates the utilization of acrylonitrile butadiene styrene (ABS) and polycarbonate/ABS. The distinction in glass transition temperatures within these materials enables the realization of two distinct morphing phases. The research delves into the impact of structural parameters on morphing properties. Finite element analyses are subsequently conducted, leveraging the insights gained from parametric studies, to facilitate the accurate prediction of a diverse array of shape alterations in response to temperature fluctuations. Several structural models are both simulated and fabricated to experimentally validate the precise forecasting of desired morphing phases. The culmination of this study manifests in the design and fabrication of multiple multi-material structures, exemplifying both their functionality and intricate geometric complexity.

Periodic and aperiodic Ti lattices additively manufactured under reactive atmosphere: Mechanical and biological properties

Porous Ti materials can reduce the so-called stress shielding effect and are widely regarded as superior biomedical materials. In this study, commercially-pure Ti (CP-Ti) with five different porous structures, namely Dodecahedron, Diamond, Gyroid, Fischer Koch S, and Voronoi, have been printed using Powder Bed Fusion Laser Beam (PBF-LM) and under a reactive atmosphere (97%Ar+3%N2). Compressive tests and in vitro bio tests including osteogenic mineralization and cytotoxicity have been conducted to evaluate their mechanical and biomedical performances. Analytical means such as laser confocal microscopy have been used and radar properties maps have been built to compare overall properties of these different lattices. Results show that some of the porous CP-Ti lattices (with Gyroid and Fischer Koch S arrangement) can achieve engineering fracture strength above 1000 MPa, while maintaining their low Young’s modulus (<20 GPa) and good biocompatibility. For the lattices, relationships between Young’s modulus and relative density are discussed under the scheme of the Gibson and Ashby model (G-A model) with C constant as 0.1–4. Energy absorption data for the lattices are provided, showing high values due to the excellent combination of strength and ductility. The study implies that a good selection of the lattice type together with the approach of printing under reactive atmosphere can lead to advanced Ti lattices for biomedical applications.

In vitro vascularization of hydrogel-based tissue constructs via a combined approach of cell sheet engineering and dynamic perfusion cell culture

The bioengineering of artificial tissue constructs requires special attention to their fast vascularization to provide cells with sufficient nutrients and oxygen. We addressed the challenge of in vitro vascularization by employing a combined approach of cell sheet engineering, 3D printing, and cellular self-organization in dynamic maturation culture. A confluent cell sheet of human umbilical vein endothelial cells (HUVECs) was detached from a thermoresponsive cell culture substrate and transferred onto a 3D-printed, perfusable tubular scaffold using a custom-made cell sheet rolling device. Under indirect co-culture conditions with human dermal fibroblasts (HDFs), the cell sheet-covered vessel mimic embedded in a collagen gel together with additional singularized HUVECs started sprouting into the surrounding gel, while the suspended cells around the tube self-organized and formed a dense lumen-containing 3D vascular network throughout the gel. The HDFs cultured below the HUVEC-containing cell culture insert provided angiogenic support to the HUVECs via molecular crosstalk without competing for space with the HUVECs or inducing rapid collagen matrix remodeling. The resulting vascular network remained viable under these conditions throughout the 3 week cell culture period. This static indirect co-culture setup was further transferred to dynamic flow conditions, where the medium perfusion was enabled via two independently addressable perfusion circuits equipped with two different cell culture chambers, one hosting the HDFs and the other hosting the HUVEC-laden collagen gel. Using this system, we successfully connected the collagen-embedded HUVEC culture to a dynamic medium flow, and within 1 week of the dynamic cell culture, we detected angiogenic sprouting and dense microvascular network formation via HUVEC self-organization in the hydrogel. Our approach of combining a 3D-printed and cell sheet-covered vascular precursor that retained its sprouting capacity together with the self-assembling HUVECs in a dynamic perfusion culture resulted in a vascular-like 3D network, which is a critical step toward the long-term vascularization of bioengineered in vitro tissue constructs.

Synthesis of disc-shaped copper flakes by mechanical milling: Green laser-sintered, highly conductive printed Cu features

Recently, a digital fabrication technique has been recognized as one of requisite processing methods that can realize large-area, low-cost, form-factor free optoelectronics applications. Digitally printed conductive layers are implemented in practical device layouts for electrically interconnecting active/passive components. In terms of high conductivity, printing processability, and cost-effectiveness, printable Cu fluids are most appropriate to generate highly conductive printed features. To resolve critical issues in printed Cu conductors, we propose a selective green-laser-sintering process with a usage of a mixture of Cu nanoparticles and flakes. Surface oxide-free Cu nanoparticles and sub-micron Cu particles are synthesized through highly concentrated solvothermal synthetic methods. Sub-micron spherical Cu particles are transformed into disc-shaped Cu flakes by a subsequent mechanical milling process. The printable Cu fluids including the mixed particles and a photo-reactive polymer, enable the formation of printed particle assemblies that can be sintered by highly energetic green-wavelength photons. It is demonstrated that highly conductive printed layers are generated with values in resistivity and resistance as low as 16μΩcm and 1.9 Ω/cm, respectively, by the combined approach of mask-free printing and selective green-laser sintering processes.

3D-Printed Energy Storage Devices

The increasing demand for multifunctional portable/wearable electronic devices, including wireless sensors and implantable medical devices is continuously growing. Such devices need rechargeable batteries with dimensions on the scale of 1–10 mm3 (few to tens mm2 footprint area of substrate) including all the components and all the associated packing. Thus, in the past decade, along with the developments in battery materials, the focus has been shifting more and more towards innovative fabrication processes, unconventional configurations, and designs with multi-functional components. 3D printing technologies enable a well-controlled creation of functional materials with three-dimensional architectures, representing a promising approach for fabrication of next-generation electrochemical energy storage (EES) devices with high performance due to a higher electrode/electrolyte interfacial area.In this work, we demonstrate a novel design and a novel approach of 3D printing of batteries of different shapes and size by using filaments composed of active electrode materials bound with polymers. The electrodes were printed by fused-filament fabrication (FFF) method. We demonstrated a reversible electrochemical cycling of 3D printed lithium iron phosphate (LFP) and lithium titanate (LTO) composite polymer electrodes vs. lithium metal anode with high performance and capacity in cells containing both conventional non-aqueous and ionic-liquid electrolytes.In addition, the development and fabrication of a novel 3D-printed solid-state or quasi-solid electrolyte by FFF has been accomplished. The electrolytes are composed primarily of polyethylene oxide (PEO) and polyethylene glycol (PEG) which are known ionic conductors, and polylactic acid (PLA) for enhanced mechanical properties and high temperature durability.Our research introduces novel thick-layer 3D batteries, thus reducing cost related to high mass loading per battery footprint of smart 3D structures with the help of low-cost fabrication method.

4D Printing of a Light-Driven Soft Actuator with Programmed Printing Density.

There is a growing interest in the concept of four-dimensional (4D) printing that combines a three-dimensional (3D) manufacturing process with dynamic modulation for bioinspired soft materials exhibiting more complex functionality. However, conventional approaches have drawbacks of low resolution, control of internal micro/nanostructure, and creation of fast, complex actuation due to a lack of high-resolution fabrication technology and suitable photoresist for soft materials. Here, we report an approach of 4D printing that develops a bioinspired soft actuator with a defined 3D geometry and programmed printing density. Multiphoton lithography (MPL) allows for controlling printing density in gels at pixel-by-pixel with a resolution of a few hundreds of nanometers, which tune swelling behaviors of gels in response to external stimuli. We printed a 3D soft actuator composed of thermoresponsive poly(N-isopropylacrylamide) (PNIPAm) and gold nanorods (AuNRs). To improve the resolution of printing, we synthesized a functional, thermoresponsive macrocrosslinker. Through plasmonic heating by AuNRs, nanocomposite-based soft actuators undergo nonequilibrium, programmed, and fast actuation. Light-mediated manufacture and manipulation (MPL and photothermal effect) offer the feasibility of 4D printing toward adaptive bioinspired soft materials.

Screen printing directed synthesis of covalent organic framework membranes with water sieving property

Screen printing is introduced to direct the synthesis of crack-free and thickness-tunable TpPa(OH)2 covalent organic framework membranes. A smooth precursor layer is firstly screen printed and then fully crystallised into the TpPa(OH)2 membrane. Molecular-scale pores endow the membrane with a fast water-sieving property, which is promising in water desalination.

LayerCode

With the advance of personal and customized fabrication techniques, the capability to embed information in physical objects becomes evermore crucial. We present LayerCode , a tagging scheme that embeds a carefully designed barcode pattern in 3D printed objects as a deliberate byproduct of the 3D printing process. The LayerCode concept is inspired by the structural resemblance between the parallel black and white bars of the standard barcode and the universal layer-by-layer approach of 3D printing. We introduce an encoding algorithm that enables the 3D printing layers to carry information without altering the object geometry. We also introduce a decoding algorithm that reads the LayerCode tag of a physical object by just taking a photo. The physical deployment of LayerCode tags is realized on various types of 3D printers, including Fused Deposition Modeling printers as well as Stereolithography based printers. Each offers its own advantages and tradeoffs. We show that LayerCode tags can work on complex, nontrivial shapes, on which all previous tagging mechanisms may fail. To evaluate LayerCode thoroughly, we further stress test it with a large dataset of complex shapes using virtual rendering. Among 4,835 tested shapes, we successfully encode and decode on more than 99% of the shapes.

Space Truss Masonry Walls With Robotic Mortar Extrusion

This work presents a generalized method for robotic mortar extrusion, allowing the fabrication of structural-insulating walls of novel performances. It involves two distinct steps that are to be simultaneously automated: extrusion of a specifically formulated mortar, and assembly of adequately shaped insulating blocks. Here, the layer by layer approach of concrete printing is renewed by using insulating blocks as support for the extrusion. The volumetric space of the wall is divided by an adequate space tessellation, dividing it in polyhedra. They become insulating blocks, on the edges of which mortar is extruded. The set of edges then forms a space truss, of great mechanical efficiency. “Printable” mortar is crucial to the system for the blocks could not withstand the hydrostatic pressure of fresh mortar without additional form-work features, once a few meters height has been reached. This approach renews traditional confined masonry, allowing for geometric complexity and automation.

Novel solvent bonding method for creation of a three-dimensional, non-planar, hybrid PLA/PMMA microfluidic chip

Fused deposition modeling (FDM) is an approach of 3D printing and has been used in the fabrication of microfluidic systems. Unfortunately, the poor optical transparency of the resulting microfluidic devices makes the characterization and quantification of experiment results difficult. In this study, we developed a method of solvent bonding PMMA and poly(lactic acid) (PLA) thermoplastic materials for the creation of hybrid microfluidic chips. The benefits of the proposed method are as follows: (1) simplified fabrication of complex 3D microfluidic chips; (2) optical characterization and quantification of fabrication results; and (3) the ability to print and embed tubing connectors within the microfluidic chip to facilitate assembly. Three experiments were conducted to evaluate the efficacy of the proposed scheme. We fabricated one microfluidic chip with an S-microchannel to examine the fundamental fabrication results. We also fabricated two application-oriented microfluidic chips respectively featuring a 3D non-planar micromixer and a double emulsion generator. Our experiment results demonstrate the efficacy of this bonding method in the rapid formation of strong bonds (exceeding 13 bars) between PLA and PMMA substrates. The two application examples further demonstrate that the proposed scheme is applicable to the fabrication of complex microfluidic chips quickly and easily without sacrificing their intended functionalities.

3D sand mould printing: a review and a new approach

PurposeThe purpose of this paper is to review available technologies, analyse their features, propose a new approach of 3D sand mould printing based on line forming, introduce the manufacturing principle and show advantages of this approach, especially for larger parts with large Z steps in the build, such as 2 mm stepwise.Design/methodology/approachThis paper introduces 3D sand mould printing, compares and analyses technological process and existing fabrication approaches among available technologies first. Then, a new approach of 3D sand mould printing is proposed to improve build speed. In addition, the proposed system will be analysed or benchmarked against existing systems.FindingsA new approach based on line forming of sand mould printing is put forward by reviewing and analysing available technologies, to improve build speed from the aspect of basic moulding movement instead of optimization of moulding methods and process parameters. The theoretical calculation and analysis shows that build speed can be improved greatly, and it is more suitable for the manufacture of large-scale casting’s sand mould when considering dimensional accuracy and printing error, as well as uniformity of each layer.Research limitations/implicationsThe specific implement scheme of line forming and nozzle’s specific structure of this new approach need further study.Practical implicationsMuch higher build speed of 3D sand mould printing with new approach brings evident implication for moulds companies and manufacturing industry, having a far-reaching influence on the development of national economy.Originality/valueThis paper reviews available technologies and presents a new approach of 3D sand mould printing for the first time. Analysis of the new approach shows that this new method of sand mould printing can boost build speed greatly. So, its application prospect is great.

The Effect of Carbon Nanotubes on the Mechanical Properties of Wood Plastic Composites by Selective Laser Sintering.

Wood-plastic composites (WPCs) made by selective laser sintering (SLS) approach of 3D printing offer many advantages over single polymer materials, such as low cost, sustainability, and better sintering accuracy. However, WPCs made via SLS are too weak to have widespread applications. In order to increase the mechanical properties of WPCs, a novel type of WPCs containing 0, 0.05, 0.1 and 0.15 wt % carbon nanotubes (CNT), 14 wt % wood fibers, 86 wt % polyether sulfone (PES) was manufactured via SLS. The experimental results showed that the addition of small amount of CNTs can significantly increase the mechanical properties of the wood/PES composite material. The tensile strength, bending strength, and elasticity modulus were 76.3%, 227.9%, and 128.7% higher with 0.1 wt % CNTs than those without CNTs. The mechanical properties of specimens first increased and then decreased with the addition of CNTs. The SEM results of the specimens’ fracture morphology indicate that the preferable bonding interfaces between wood flour grains and PES grains were achieved by adding CNTs to the composites. There are two reasons why the composites possessed superior mechanical properties: CNTs facilitate the laser sintering process of WPCs due to their thermal conductivities, and CNTs directly reinforce WPCs.

Research on color 3D printing based on color adherence

PurposeThis paper aims to present a method of color three-dimensional (3D) printing based on color adherence.Design/methodology/approachFirst, experiments of the color effects of 3D printings using different carriers and different printing methods were performed. Second, the color of a specific point could be calculated through a theory of dimension-reducing, and the color distribution of 3D model was transformed from 3D to 1D color line corresponding with 3D print sequence. At last, the color lines, which were printed on a PE film by silk-screen printing, was carried by a filament and then printed through a fused deposition modeling 3D printer.FindingsThe printing ink and PE film are suitable as the pigment and carrier under this investigation, respectively. Based on an idea of reducing dimension, the method of 3D color printing through adhering color to a filament is realized. The color saturation of the sample was relatively high through the method.Research limitations/implicationsIt is hard to avoid that there may be some residual color in the nozzle through this method, and the purity of following color will be affected. As a result, continuous improvements should be made to perfect the method.Practical implicationsAn approach of 3D color printing is described in detail, and what kind of model is more applicable is discussed particularly.Originality/valueThis approach is implemented to print color 3D objects with just one nozzle by means of color adherence. That is, printing the 3D objects using the filament is carried out with 1D color line, which is printed by a traditional printing method.

3D Printing of Polymers with Hierarchical Continuous Porosity

AbstractCellular thermoplastic structures with multiscale porosity (1–300 µm microporosity to 0.3–10 mm macroporosity) are produced from an integrated approach of 3D printing by Fused Deposition Modeling printing and Supercritical CO2 Foaming. Porous strands and related hierarchical structures are processed in one continuous step. Influence of printing parameters (e.g., deposition temperature and speed) on foam porosity and pores distribution is described for a semicrystalline food grade Poly‐Lactide Acid. The process is then applied to other thermoplastics filament with different mechanical properties. In particular, a composite blend of Poly‐l‐Lactide and βTCP (90–10) ceramic particles and a soft copolymer Poly‐Lactide‐co‐Caprolactone are processed to print foamed strands with various internal cellular microstructures. The dynamic material transformation phenomena controlling the microstructure upon deposition and foaming are determined. This new additive manufacturing method introduces for the first time the possibility to tune cellular morphology in situ and on line, offering an unmatched freedom to design anisotropy in 3D.

Hierarchically self-morphing structure through 4D printing

ABSTRACTHierarchical self-morphing refers to the concurrent global and local changes in shape or structure. Previous research works have demonstrated 3D printed self-morphing structures and the sequential folding/unfolding behaviours. However, the shape change events occurred mainly at the global level in a water environment either through absorbing moisture or through heating. Concurrent global and local shape changes in an ambient environment have not been reported. In this paper, we report a hierarchically blooming flower that blossoms in an ambient environment. Our design considers the strain limit through understanding the effect of thickness on the local strain to avoid fracture and the appropriate allocation of multiple materials to achieve predefined global and local shape changes. This design approach of hierarchical 4D printing may be useful for a variety of applications that involve controlled self-morphing structures with complex geometries.

One Copy on Japanese Paper

One of the essential characteristics of the private press working on the principles laid down by William Morris was the use of hand-made paper, and in practice a proprietary paper with a distinctive watermark, such as those that were manufactured for De Zilverdistel and De Heuvelpers. Morris’s rules were published in ‘The Ideal Book’, and could be checked from his Kelmscott Press books. They were initially followed to the letter by Dutch private presses, and prospectuses and publisher’s lists attest to this. The lack of information about paper in the colophons was copied after Morris’s example. However, a practical approach of printing implied that the ideal of hand-made paper was silently abandoned, when so-called hand-made Japanese papers were selected for some books, and for financial reasons papers with obsolete watermarks were used. In his printing studio, the idealistically inclined printer turned into a pragmatic artisan.

Formability of Porous Tantalum Sheet-Metal

Over the past 10 years, a novel cellular solid, Trabecular MetalTM (TM), has been developed for use in the orthopedics industry as an ingrowth scaffold. Manufactured using chemical vapor deposition (CVD) on top of a graphite foam substrate, this material has a regular matrix of interconnecting pores, high strength, and high porosity. Manufacturing difficulties encourage the application of stamping and forming technologies to increase CVD reactor throughput and reduce materials wastes. In this study, the formability of TM was evaluated using a novel camera-based system for measuring surface strains, since the conventional approach of printing or etching gridded patterns was not feasible. A forming limit diagram was then obtained using specially fabricated 1.65 mm thick sheets. No lubricant was used due to the cleanliness requirements for orthopedic implants.

Formability of porous tantalum sheet-metal

Over the past ten years, a novel cellular solid, Trabecular Metal™, has been developed for use in the orthopaedics industry as an ingrowth scaffold. Manufactured using chemical vapour deposition (CVD) on top of a graphite foam substrate, this material has a regular matrix of interconnecting pores, high strength, and high porosity. Manufacturing difficulties encourage the application of bending, stamping and forming technologies to increase CVD reactor throughput and reduce material wastes. In this study, the bending and forming behaviour of Trabecular Metal™ was evaluated using a novel camera-based system for measuring surface strains, since the conventional approach of printing or etching gridded patterns was not feasible. A forming limit diagram was obtained using specially fabricated 1.65 mm thick sheets. A springback coefficient was measured and modeled using effective hexagonal cell arrangements.

Reactive μCP on Ultrathin Block Copolymer Films: Investigation of the μCP Mechanism and Application to Sub-μm (Bio)molecular Patterning

In this paper, the mechanism of the recently introduced soft lithographic patterning approach of reactive microcontact printing on thin substrate-supported polystyrene-block-poly(tert-butyl acrylate) (PS690-b-PtBA1210) films using trifluoroacetic acid (TFA)-inked elastomeric poly(dimethylsiloxane) (PDMS) stamps is investigated in detail. In this approach, solventless deprotection reactions are carried out with very high spatial definition using TFA as a volatile reagent that partitions into the PtBA skin layer. On the basis of a systematic investigation of the process, ink loading was identified as a crucial parameter for obtaining faithful pattern transfer. Using optimized conditions, submicrometer-sized patterns were successfully fabricated. In combination with subsequent wet chemical covalent coupling of various (bio)molecules, reactive microCP is established as an approach to afford positive, as well as negative, images of the features of the stamps used. In addition, the size of the patterned areas was manipulated by exploiting the controlled spreading of the ink; thus, stamps with identical features yield patterns with different sizes, yet identical periodicity, as shown for bovine serum albumin (BSA)-poly(ethylene glycol) patterns. The reactive microCP methodology affords new pathways for submicrometer-scale patterning of bioreactive surfaces.