Printing Platform Research Articles

Embedded 3D Printing of Multimaterial Polymer Lattices via Graph-Based Print Path Planning.

Recent advances in computational design and 3D printing enable the fabrication of polymer lattices with high strength-to-weight ratio and tailored mechanics. To date, 3D lattices composed of monolithic materials have primarily been constructed due to limitations associated with most commercial 3D printing platforms. Here, freeform fabrication of multi-material polymer lattices via embedded three-dimensional (EMB3D) printing is demonstrated. An algorithm is developed first that generates print paths for each target lattice based on graph theory. The effects of ink rheology on filamentary printing and the effects of the print path on resultant mechanical properties are then investigated. By co-printing multiple materials with different mechanical properties, a broad range of periodic and stochastic lattices with tailored mechanical responses can be realized opening new avenues for constructing architected matter.

Numerical-Experimental Analysis toward the Strain Rate Sensitivity of 3D-Printed Nylon Reinforced by Short Carbon Fiber.

Despite the application of the Additive Manufacturing process and the ability of parts' construction directly from a 3D model, particular attention should be taken into account to improve their mechanical characteristics. In this paper, we present the effect of individual process variables and the strain-rate sensitivity of Onyx (Nylon mixed with chopped carbon fiber) manufactured by Fused Filament Fabrication (FFF), using both experimental and simulation manners. The main objective of this paper is to present the effect of the selected printing parameters (print speed and platform temperature) and the sensitivity of the 3D-printed specimen to the strain rate during tensile behavior. A strong variation of tensile behavior for each set of conditions has been observed during the quasi-static tensile test. The variation of 40 °C in the platform temperature results in a 10% and 11% increase in Young's modulus and tensile strength, and 8% decrease in the failure strain, respectively. The variation of 20 mm·s-1 in print speed results in a 14% increase in the tensile strength and 11% decrease in the failure strain. The individual effect of process variables is inevitable and affects the mechanical behavior of the 3D-printed composite, as observed from the SEM micrographs (ductile to brittle fracture). The best condition according to their tensile behavior was chosen to investigate the strain rate sensitivity of the printed specimens both experimentally and using Finite Element (FE) simulations. As observed, the strain rate clearly affects the failure mechanism and the predicted behavior using the FE simulation. Increase in the elongation speed from 1 mm·min-1 to 100 mm·min-1, results in a considerable increase in Young's modulus. SEM micrographs demonstrated that although the mechanical behavior of the material varied by increasing the strain rate, the failure mechanism altered from ductile to brittle failure.

Advances in Photovoltaic Technologies from Atomic to Device Scale

The question of how energy resources can be efficiently used is likewise of fundamental and technological interest. In this opinion, we give a brief overview on developments of harvesting solar energy across different length scales and address some strategies to tackle economic and ecological challenges, in particular with a view to sustainability and toward a circular economy. On the mesoscopic scale, the emergence of thermodynamic laws in open quantum systems is of central importance and how they can be employed for efficient quantum thermal machines and batteries. The broad tunability of band gaps in quantum dot systems makes them attractive for hybrid photovoltaic devices. Complementary, machine learning-aided band gap engineering and the high-throughput screening of novel materials assist with improving absorption characteristics. On the device scale, hybrid concepts of optical control via metasurfaces enable a multitude of functionalities such as a directed re-emission of embedded photoluminescent materials or field enhancement effects from nanostructures. Advanced techniques in computational nanophotonics concern a topology optimization of nanostructured layers together with multiobjective optimization toward specific light management tasks. On the industrial level, modern manufacturers explore 3D printing and flexible solar cell platforms obtained from roll-to-roll technologies. The remote control of solar parks through applications via the Internet of Things opens up new strategies to expand to difficult terrain where human interaction is only required to a limited extent.

LayerLock: Layer-Wise Collision-Free Multi-Robot Additive Manufacturing Using Topologically Interlocked Space-Filling Shapes

We present LayerLock, an approach for synchronous multi-robot additive manufacturing (cooperative 3D printing or C3DP). Our approach is based on Delaunay Lofts, a class of topologically interlocked shapes that are generated by stacking layers of Voronoi partitions of a set of moving Voronoi sites based on wallpaper symmetries. Our approach is based on two key insights. First, each layer of a Delaunay Loft is simply a tessellation of convex polygons allowing for easy division of cells for collision-free simultaneous material deposition. Second, the unique transition of Voronoi cells along the layers naturally leads to topological interlocking, thereby providing better energy absorption ability compensating for the loss of structural strength due to segmented printing. In this work, we constrain our current investigation to a two-robot system and develop the LayerLock algorithm consisting of three steps: (1) a distance-based division of the Voronoi cells at each layer of the Delaunay Loft, (2) a moving-front strategy for determining the sequence of cells for each robot, and (3) print path generation based on the cell sequence, which allows synchronous collaboration. We evaluate our algorithm for a range of geometric parameters such as part orientation and cell resolution. We also demonstrate it practically using a two-robot cooperative 3D printing platform.

Biocomposite fabrication from pilot-scale steam-exploded coconut fiber and PLA/PBS with mechanical and thermal characterizations

Biodegradable fiber-reinforced biocomposites from steam-exploded coconut fibers and polylactic acid (PLA) and polybutylene succinate (PBS) plastic were developed in this study. Biocomposite filaments and samples were produced using a commercial-scale screw extruder and a 3D printer, respectively. In-depth mechanical and thermal analyses were also performed. The results showed that the tensile strengths of PLA mixed with 3% coconut fiber (PLA97/F3) and 6% coconut fiber (PLA94/F6) decreased by approximately 22% and 23%, respectively, compared to the 64% reduction of that of the original PLA after four-week storage. The bending modulus of the PLA/fiber composite was better than that of the original PLA (21–29% higher), whereas a 5–8% improvement was observed for the PLA/PBS/fiber composites. The impact strengths of PLA97/F3 and PLA77/PBS20/F3 were approximately 8.5% and 7.4% higher than those of the original PLA and PLA/PBS, respectively. During the degradation test, both PLA97/F3 and PLA77/PBS20/F3 exhibited higher tensile strengths than the original materials. Finally, this research presents encouraging results for the production of biodegradable fiber-reinforced biocomposites that are applicable to 3D printing platforms. The final products can be used as replacement or aftermarket components of automobiles.

Digital light processing (DLP)‐based (bio)printing strategies for tissue modeling and regeneration

AbstractDigital light processing (DLP)‐based bioprinting technology has recently aroused considerable concerns as a strategy to deliver biomedical materials and/or specific cells to create sophisticated structures for various tissue modeling and regeneration. In this review, we display a concise introduction of DLP bioprinting, and a further discussion on the design and manufacture of DLP (bio)printer with varied bioinks and their biomedical applications toward drug screening, disease modeling, tissue repair, and regenerative medicine. Finally, the advantages, challenges, and perspectives of the DLP printing platforms are detailed. It is believed that DLP bioprinting will play a decisive role in the field of tissue model and regenerative medicine, mainly due to its time‐efficient, higher resolution, and amenability to automation for various tissue needs.

Mechanical and acoustical characterization of elastic properties for additively manufactured polymers

Recent advances in the additive manufacturing of photopolymers has opened new opportunities for the design and realization of novel acoustic materials, such as metamaterials. Despite the significant advantages additive manufacturing offers for photopolymers, a significant lack of characterization data inhibits their use in design for acoustics applications. This work provides characterization data and establishes a relationship between static and dynamic properties: specifically, the mechanically and ultrasonically derived damping factor and loss tangent for additively manufactured photopolymers. To achieve this, a range of stiff and compliant photopolymers are fabricated using a commercially available Polyjet 3-D printing platform. The elastic loss and storage moduli for each material are characterized under static uniaxial loading conditions. Furthermore, shear and compressional phase velocity and attenuation are measured for each material using ultrasound. The damping factor and loss tangent for each material is then calculated for both the static and ultrasonic case using the complex elastic moduli, and a frequency-based relationship is drawn between the two. The presented results are expected to contribute to improved design and broadband characterization of additively manufactured acoustic materials using photopolymers. [Work funded by the Office of Naval Research.]

The Evaluation and Exploration of Piezoelectric Parameter Optimization for Droplet Ejection in Binder Jet 3D Printing Drugs.

Since the first three-dimensional (3D) printed drug was approved by the Food and Drug Administration in 2015, there has been a growing interest in using binder jet 3D printing (BJ-3DP) technology for pharmaceuticals. However, most studies are still at an exploratory stage, lacking micromechanism research, such as the droplet ejection mechanism, the effect of printhead piezoelectric parameters on inkjet smoothness and preparation formability. In this study, based on the inkjet printing and observation platform, the Epson I3200-A1 piezoelectric printhead matched to the self-developed BJ-3DP was selected to analyze the droplet ejection state of self-developed ink at the microlevel with different piezoelectric pulse parameters. The results showed that there was a stable inkjet state with an inkjet pulse width of 3.5 μs, an ink supply pulse width of 4.5 μs, and a jet frequency in the range of 5000-19,000 Hz, ensuring both better droplet pattern and print accuracy, as well as high ejection efficiency. In conclusion, we performed a systematic evaluation of the inkjet behavior under different piezoelectric pulse parameters and provided a good idea and case study for the optimization of printhead piezoelectric parameters when BJ-3DP technology was used in pharmaceuticals.

3D printing of solid-state zinc-ion microbatteries with ultrahigh capacity and high reversibility for wearable integration design

Miniaturized and integrable energy storage systems (MI-ESSs) are highly desired to power portable and wearable electronics. Zinc-ion microbatteries (ZIMBs) are reliable MI-ESS candidates with excellent electrochemical potential; however, the viability and real application of conventional ZIMBs are long stricted by low device capacity/reversibility and challenging device package design. Herein, we report an all-3D-printing design of solid-state ultrahigh-capacity and highly reversible ZIMBs and achieve an advanced wearable integration. Calcium vanadate nanoribbon-based cathode and Zn nanosheet-based anode are rationally constructed by direct ink writing-based 3D printing. With a Cu-modification, dendrite-suppressed anode affords a low polarization and stable voltage profiles during long-term Zn plating/stripping. 3D printed solid-state ZIMBs deliver an outstanding device capacity of 8.9 mAh cm−2, which surpasses previously reported ZIMBs and even lithium-ion microbatteries. Superior rate capability and cycling stability is also achieved. By regulating 3D printing parameters, an ultrahigh device capacity reaches at 14.9 mAh cm−2. Furthermore, vat photopolymerization-enabled microbattery packaging is demonstrated as an efficient 3D printing platform to integrate ZIMBs into wearable monoliths. Such remarkable electrochemical behaviors and wearable integration applications are attributed to advanced 3D printing techniques and sophisticated microelectrode design, paving future roads in manufacturing of state-of-the-art MI-ESSs and powering portable and wearable electronics.

APPLICATION OF TAGUCHI METHOD TO OPTIMIZE ULTRASONIC VIBRATION ASSISTED FUSED DEPOSITION MODELING PROCESS PARAMETERS FOR SURFACE ROUGHNESS

This paper presents the findings on the process parameters for surface roughness optimization of an open-source ultrasonic vibration assisted fused deposition modeling (FDM) printed specimen. Acrylonitrile Butadiene Styrene (ABS) material for the specimens and the printing temperature, layer thickness, and surface layer were determined as the control parameters that influenced the surface roughness. Experimental design with Taguchi level 9 (3*3) Orthogonal Arrays (OA) was designed with nine experimental runs. Three levels of each control factor was identified. In addition, data for multi-responses of build time and surface roughness was obtained by utilizing and conducting the nine-requirement experimental run for Taguchi Method. The specimens were printed using an open-source ultrasonic vibration assisted FDM printer with a 20kHz ultrasonic vibration supplied to the printing platform of the printer. Analysis of variance (ANOVA) was conducted to determine whether p-values are significant with the model or otherwise. The experiments examined the build time and surface roughness, the responses were collected and optimized by using the grey relational grade (GRG). The result shows no correlation between build time and surface roughness in the grey relational grade, and the p-value was higher than 0.05 significant level. However, the surface roughness for optimal level combination setting showed the obvious result, which the settings consist of printing temperature (level 1), layer thickness (level 1), and surface layer (level 1).

Cryoprinting of nanoparticle-enhanced injectable hydrogel with shape-memory properties

Cryogels with interconnected macropores for cell seeding and shape-memory properties for non-invasion injection have shown great potential in tissue engineering. However, traditional manufacturing methods of cryogels are time-consuming and labor-intensive, which has limitations in rapidly fabricating customized cryogels. In this work, we developed a cryoprinting platform that combined 3D printing and cryogelation technologies to fabricate nanoparticle-enhanced injectable and shape-memory cryogels. After cryoprinting, the silk fibroin-based cryogels could be printed to a variety of shapes and sizes and allow rapid volumetric recovery after injection through a needle. These cryogels encapsulating laponite nanoparticles provided enhanced proliferation, spreading, and osteogenic differentiation of the seeded bone marrow-derived mesenchymal stem cells (BMSCs). In addition, the integration of implanted hydrogels with host tissues and the cell invasion within the hydrogel was found with no obvious inflammatory response after subcutaneous injection. These findings showed that the printed nanoparticle-enhanced cryogels could promote the seeded stem cells to actively participate in bone regeneration. In short, this work not only offered a feasible and effective platform to print customized cryogels, but also provided an injectable cryogel for bone tissue engineering via this advanced printing platform.

Inkjet Printing of Structurally Colored Self-Assembled Colloidal Aggregates

Structurally colored materials offer increased stability, high biocompatibility, and a large variety of colors, which can hardly be reached simultaneously using conventional chemical pigments. However, for practical applications, such as inkjet printing, it is vital to compartmentalize these materials in small building blocks (with sizes ideally below 5 μm) and create “ready-to-use” inks. The latter can be achieved by using photonic balls (PB): spherical aggregates of nanoparticles. Here, we demonstrate, for the first time, how photonic ball dispersions can be used as inkjet printing inks. We use solvent drying techniques to manufacture structurally colored colloidal aggregates. The as-fabricated photonic balls are dispersed in pentanol to form ink. A custom-made inkjet printing platform equipped with an industrial printhead and recirculation fluidic system is used to print complex structurally colored patterns. We increase color purity and suppress multiple scattering by introducing carbon black as a broadband light absorber.

3D food printing curing technology based on gellan gum

The fluid state of 3D food printing products greatly limits the customization of the shape. To improve the molding quality, a 3D food printing curing technology based on the temperature-sensitive phase-change characteristics of gellan gum was developed. Corn starch was used as the printing substrate to produce a gel that solidifies during printing. The pre-gelatinized starch slurry containing gellan gum was placed in a barrel with a heating function and extruded onto the printing platform at room temperature. Rheological tests, printing quality evaluations, and low-field nuclear magnetic fields proved that the slurry with gellan gum had good extrusion and printing feasibility. The product supplemented with 4% or 6% gellan gum exhibited significant plastic deformation, which indicated formation of a solid gel. Temperature sweep rheology analyses revealed that gellan gum guided the curing performance by affecting the curing temperature and curing speed of the slurry. Gellan gum improved hardness of the product and destroyed the network structure by self-cooling cross-linking and inhibiting starch gelatinization, which changed product adhesion.

Enhanced Adhesion—Efficient Demolding Integration DLP 3D Printing Device

A novel forming method of enhanced adhesion-efficient demolding integration is proposed to solve the problems of weak adhesion between the initial forming layer and the printing platform as well as the excessive stripping force at the bottom of the liquid tank when the printing platform rises. Therefore, a digital light processing (DLP) 3D printing forming device equipped with a porous replaceable printing platform and a swing mechanism for the liquid tank is manufactured and verified by experiments. The experimental results show that the porous printing platform can enhance the adhesion between the initial forming layer and the printing platform and improve the demolding efficiency of the forming device. In addition, the pull-out design of the printing platform plate reduces the maintenance cost of the forming device. Therefore, the device has a good application prospect.

Partial advances in the diagnosis and treatment of gastrointestinal cancer.

Partial advances in the diagnosis and treatment of gastrointestinal cancer.

High resolution-optical tomography for in-process layerwise monitoring of a laser-powder bed fusion technology

With the implementation of Laser Powder Bed Fusion technologies for industrial production, the need for in-process monitoring has emerged to ensure stable conditions and the process to succeed. Indeed, despite significant technological advances, the rejected parts are still too high if compared to the more conventional manufacturing techniques. Several defects are known to affect the process, more likely when complex geometries are fabricated. Among these, the production of inclined thin walls without support structures is still critical and, in most cases, geometric distortions are observed on the overhanging surfaces. In order to overcome the above mentioned problems and improve the quality of these critical structures, an high resolution monitoring system based on Optical Tomography (OT) was proposed, called High Resolution-Optical Tomography (HR-OT). It uses a very high-resolution sensor, operating in the visible spectrum of light, on a large area of the surface layers comprising the entire printing platform. This very recent technique, typically applied for the detection of volumetric defects, such as porosity or lack of fusion, was successfully applied, in this paper, for the detection of geometric distortions, allowing to avoid onerous pre-processing phases in the image processing workflow. Specific geometric indexes were selected as monitoring outputs and were used for the construction of appropriate control charts in order to carry out statistical process monitoring. Finally, an off-line 3D reconstruction, by means of digital close range photogrammetry, was used to verify the effectiveness of the proposed monitoring solution when applied for in-process detection of geometric distortions.

Physically Entangled Antiswelling Hydrogels with High Stiffness.

Physically cross-linked hydrogels have great potential for tissue engineering because of their excellent biocompatibility and easy fabrication. However, physical cross-linking points are typically weaker compared to chemical ones and therefore cannot form robust hydrogels with excellent water stability, which greatly hinder their further applications. In this work, a novel hydrogel with high stiffness and outstanding antiswelling performance cross-linked by hydrophobic polymer chains entanglements is reported. The hydrophobic polymer polyimide (PI) is mixed with the hydrophilic polymer poly-(vinyl pyrrolidone) (PVP) to form cross-linking points between the chains. At the equilibrium swelling state, tensile modulus of the hydrogel can be up to 22.57 MPa (higher than most existing hydrogels) and the equilibrium water swelling ratio (ESR) can be as low as 125.0%. By decreasing the PI mass ratio, tensile modulus and ESR of the hydrogel can be tuned in a wide range from 22.57 to 0.005 MPa and 125.0% to 765.6%, respectively. Using PVP/PI solutions as inks, uniform structures and multi-material structures are fabricated having mechanical properties close to cartilage through a direct ink writing 3D printing platform. This current work demonstrates that entangled PVP/PI hydrogels have excellent tailoring capabilities and are promising candidates for tissue engineering applications.

Abstract LB110: Twist pan-cancer synthetic reference materials for cell-free DNA (cfDNA) assay development

Abstract Liquid biopsies hold great promise in reducing the burden of the disease of cancer on patients. Early detection of cancer via the cell free DNA represents the broadest vision and requires highly specificity. Ongoing disease monitoring is another important application of liquid biopsy and requires high sensitivity. Assay development requires analytical validation, and assays must be monitored for ongoing performance. These assays demand reference materials at specific variant allele frequencies for the assessment of specificity and sensitivity. Previously, obtaining reference materials was a laborious process of finding or engineering mutant cell lines. Here, we describe the design, manufacture, and quality control of a synthetic reference standard: the Twist Pan-Cancer Reference Standards, developed using Twist’s proprietary DNA printing platform to include a wide selection of both common and rare cancer targets for analytical validation. The reference material closely mimics the size distribution and content of cell-free DNA, with a primary peak at 167 bp and a secondary peak at 334 bp. The background cfDNA is derived from a single donor and highly characterized through NGS. The reference standard includes over 400 variant sites across 84 genes, including literature-curated, clinically-relevant variant sites. Additional panel-wide variants were included to aid in troubleshooting capture panels. The variant DNA is synthetically printed at 167 bp ± 5 bp and tiles over the site with extensive overlap, providing diversity of DNA termini relative to the position of the site of variation. Variant sites were printed and quantified independently so they can be pooled uniformly. NGS quality controls are implemented at multiple steps to ensure quality. The final products are available in a variant allele frequency (VAF) dilution series. The dilution series is quality controlled using droplet digital PCR (ddPCR) to ensure precision of variant allele frequencies. The Twist Pan Cancer Reference Standards provide a valuable solution for NGS-based assay developers seeking reference materials for a wide array of cancer variants, advancing adoption of liquid biopsy tests toward routine clinical practice. Citation Format: Patrick D. Cherry. Twist pan-cancer synthetic reference materials for cell-free DNA (cfDNA) assay development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB110.

Stem Cells-Loaded 3D-Printed Scaffolds for the Reconstruction of Alveolar Cleft.

The advances in the field of tissue engineering and regenerative medicine have opened new vistas for the repair of alveolar clefts. However, the currently available biomaterials used for the repair of alveolar clefts have poor mechanical properties and biocompatibility, which hinders the treatment outcomes. Here, we aimed to develop 3D printed biomimetic scaffolds that fuses β-tricalcium phosphate (β-TCP) and bone marrow mesenchymal stem cells (BMSCs) for improving the repair of alveolar clefts. The methacrylate gelatin (GelMA) was mixed with β-TCP for the preparation of GelMA/β-TCP hybrid scaffolds via 3D printing platform and chemically cross-linking with UV light. The physicochemical properties of the hydrogel scaffolds were characterized. Moreover, the survival state, proliferation ability, morphological characteristics, and osteogenic induction of BMSCs were examined. The prepared hybrid scaffolds showed good biocompatibility and mechanical properties. BMSCs attached well to the scaffolds and proliferated, survived, differentiated, and stimulated osteogenesis for the reconstruction of alveolar clefts. We expect that use of the prepared hybrid hydrogel scaffold can improve the outcomes of alveolar cleft repair in clinic and expand the application of hybrid hydrogel in tissue engineering repair.

Detecting Crystallinity Using Terahertz Spectroscopy in 3D Printed Amorphous Solid Dispersions

This study demonstrates the applicability of terahertz time-domain spectroscopy (THz-TDS) in evaluating the solid-state of the drug in selective laser sintering-based 3D printed dosage forms. Selective laser sintering is a powder bed-based 3D printing platform, which has recently demonstrated applicability in manufacturing amorphous solid dispersions (ASDs) through a layer-by-layer fusion process. When formulating ASDs, it is critical to confirm the final solid state of the drug as residual crystallinity can alter the performance of the formulation. Moreover, SLS 3D printing does not involve the mixing of the components during the process, which can lead to partially amorphous systems causing reproducibility and storage stability problems along with possibilities of unwanted polymorphism. In this study, a previously investigated SLS 3D printed ASD was characterized using THz-TDS and compared with traditionally used solid-state characterization techniques, including differential scanning calorimetry (DSC) and powder X-ray diffractometry (pXRD). THz-TDS provided deeper insights into the solid state of the dosage forms and their properties. Moreover, THz-TDS was able to detect residual crystallinity in granules prepared using twin-screw granulation for the 3D printing process, which was undetectable by the DSC and XRD. THz-TDS can prove to be a useful tool in gaining deeper insights into the solid-state properties and further aid in predicting the stability of amorphous solid dispersions.