Extrusion-based Additive Manufacturing Technique Research Articles

Thermal Weathering of 3D-Printed Lunar Regolith Simulant Composites.

The production of lunar regolith composites is a promising venture, especially when enabled by extrusion-based additive manufacturing techniques such as direct ink write. However, both three-dimensional (3D) printing production and usage of polymer composites containing regolish on the lunar surface are challenges due to harsh environmental conditions such as severe thermal cycling. While thermal degradation in polymer composites under thermal cycling has been studied, there is limited understanding of how polymer properties impact the mechanical performance of lunar regolith composites when both printing and usage are carried out under extreme thermal conditions. Here, we aim to bridge that gap through the creation of composites containing a lunar Highlands regolith simulant suspended in an ultraviolet (UV) curable binder, which were printed at -30 °C and thermally cycled between weekly lunar day (127 °C) and weekly night (-190 °C) temperatures. We validate that thermal stresses cause both physical and chemical degradation since the regolith simulant composites become stiffer, more porous, and show yellowing after exposure to thermal cycling. Moreover, we indicate that chemical degradation mechanisms seem to compete with residual polymerization in certain formulations. We attribute this phenomenon to partial crystallization of monomer species during printing at -30 °C, resulting in low vinyl bond conversion during initial curing. The results presented here shed light on the intricate interplay between thermal stresses, uncured polymer properties, and degradation mechanisms, which can help guide future use cases of regolith composites for lunar infrastructure needs.

Probabilistic analysis of homogenized elastic property for resin products fabricated by additive manufacturing based on three-dimensional random field modeling of microstructure

Additive manufacturing (AM) techniques have been used in several fields of science and industry, and fabrication techniques are being updated. For this fact, especially, for industrial use, mechanical property evaluation methodologies for AM products and standards for product quality assessment should also be well established. In this paper, a probabilistic evaluation of the homogenized elastic properties of a resin product fabricated by a material extrusion-based AM technique is attempted by considering the randomness of both material and microscopic geometrical quantities. This AM method fabricates a resin structure by piling up melted resin, and to decrease consumed material and influence of thermal deformation, the inner structure of the fabricated products will include many pores and its geometry is difficult to be well controlled. From this fact, the products will be regarded as a heterogeneous material with complex random microstructure. This will cause difficulty in the evaluation of its apparent material properties and therefore a probabilistic homogenization analysis is attempted for their quantitative estimation in this study. In particular, to investigate probabilistic properties of microscopic geometry, a random field modeling technique is employed for the evaluation of autocorrelation of the microscopic geometrical parameter, and the results of the autocorrelation identified by experimental observation are introduced to the probabilistic homogenization analysis. The two-dimensional or three-dimensional random field modeling is attempted, and the effectiveness of this approach is investigated by comparing it with the experimental result.

3D Printing Direct Powder Extrusion in the Production of Drug Delivery Systems: State of the Art and Future Perspectives.

The production of tailored, on-demand drug delivery systems has gained attention in pharmaceutical development over the last few years, thanks to the application of 3D printing technology in the pharmaceutical field. Recently, direct powder extrusion (DPE) has emerged among the extrusion-based additive manufacturing techniques. It is a one-step procedure that allows the direct processing of powdered formulations. The aim of this systematic literature review is to analyze the production of drug delivery systems using DPE. A total of 27 articles have been identified through scientific databases (Scopus, PubMed, and ScienceDirect). The main characteristics of the three types of 3D printers based on DPE have been discussed. The selection of polymers and auxiliary excipients, as well as the flowability of the powder mixture, the rheological properties of the molten material, and the printing temperatures have been identified as the main critical parameters for successful printing. A wide range of drug delivery systems with varied geometries and different drug release profiles intended for oral, buccal, parenteral, and transdermal routes have been produced. The ability of this technique to manufacture personalized, on-demand drug delivery systems has been proven. For all these reasons, its implementation in hospital settings in the near future seems promising.

Micro-Architected Lithium Cobalt Oxide Electrodes Via Hydrogel Infusion Additive Manufacturing

Additive manufacturing frees up the structural design of battery electrode materials from traditional slurry electrodes, enabling three-dimensional free-standing structures with micro-architected features, which provides a promising pathway toward 3D solid-state batteries with high power and high energy density. In this work, lithium cobalt oxide (LCO) is fabricated into 3D micro-lattice through a novel hydrogel infusion additive manufacturing (HIAM) process. A blank 3D architected organogel is fabricated through photopolymerization-based 3D printing and soaked in water to form a blank hydrogel micro-lattice, where lithium and cobalt ions in an aqueous solution are then swelled into the hydrogel. A free-standing LCO micro-lattice is synthesized from the ion-containing hydrogel during the post-printing calcination process. 50 μm beam diameter is obtained, giving a crucial lithium-ion diffusion length of 25 μm into LCO lattice beams. Structural, electrochemical, and mechanical properties of the LCO microlattice are investigated. HIAM technique utilizes photopolymerization of a UV-curable photoresin to create 3D structures with well-controlled form factors. Compared to traditional extrusion-based additive manufacturing techniques, photopolymerization stands out for its ability to fabricate materials with higher resolution. The main challenge with photopolymerization to fabricate non-polymeric functional materials is the complex photoresin design. A standard approach is to introduce active material nanoparticles into the photoresin, which often sacrifices print resolution due to the presence of light-scattering nanoparticles. HIAM technique overcomes the difficulties during the resin design by using a single photoresin to fabricate a large variety of functional materials. Without presence of nanoparticles, even higher resolution can be achieved. With this technique, LCO cathodes can be flexibly architected into 3D geometries for optimization of their electrochemical performance. It also enables the fabrication of various electrode materials into 3D structures with well-controlled form factors, and their incorporation into customizable batteries and microbatteries of any shape.

Production and mechanical characterization of Titanium Carbide ISOL target disks fabricated by direct ink writing

Titanium carbide boasts a large variety of high-temperature applications from aerospace to electronics and is also employed as Isotope Separation On-Line target for the production of Radioactive Ion Beams, which are employed in numerous research and technological fields, ranging from nuclear physics to medical applications. High working temperature, open and tailored porosity and resistance to thermal stresses are fundamental characteristics for this kind of targets. In this work, an extrusion-based additive manufacturing technique (Direct Ink Writing) was used for the fabrication of complex three-dimensional macro-porous structures in the shape of disks with dimensions compatible for their use as targets. An ink containing a suspension of TiC powders with solid loading of 47.5 vol% was prepared and its rheological properties were investigated. Afterwards, single filaments with an average diameter of 0.36 mm were produced and characterized with four-point bending tests to determine the bulk material tensile strength and Young's modulus. TiC targets were then manufactured and their mechanical properties were characterized with the Ball on Three Balls approach, a biaxial flexural test suitable for disk-shaped samples. For both flexural tests, a Finite Element model was developed representatively reproducing the experimental results. The calculated tensile strength values for both filaments and disks were analyzed with Weibull's statistical approach to provide reference stress limit, corresponding to a survival probability of 99.9%.

Influence of material extrusion parameters on fracture mechanisms of polylactic acid under three-point bending

In this work, a thorough fracture assessment of additive manufactured specimens made by 3D printed polylactic acid (PLA) under three-point bending is presented. This polymer is widely used in additive manufacturing for numerous applications, gaining prominence in fields such as biomechanics. Prismatic fully dense specimens and lattice structure specimens with different raster orientations and densities were fabricated using the material extrusion-based additive manufacturing technique. The objective is to analyse the effect of relevant process parameters on the fracture mechanism of short beam specimens tested under three-point bending. Digital image correlation and computed tomography have been used to measure the full field displacement and internal defects, respectively. Furthermore, the theory of critical distances was applied to assess the mechanical strength of lattice structure specimens. The results have shown the strong influence of raster orientation on the mechanical strength and fracture patterns even for negative air gap values. The transition from brittle to ductile failure was observed when changing density and raster orientation. Lastly, neck-shaped defects were detected in knots of specimens manufactured with a grid pattern. Defects in grid pattern specimens appear due to the prescribed path followed by the extruder during the building process. They were the main source causing a decrease in the mechanical strength and fracture trajectories. The objective of this research is to enhance the knowledge on the mechanical response of 3D printed components and to give an in-depth failure assessment.

Melt Electrowriting of Liquid Crystal Elastomer Scaffolds with Programmed Mechanical Response.

Recently, significant advances have been achieved to precisely program the response of liquid crystal elastomers (LCEs) through extrusion-based additive manufacturing techniques; however, important challenges remain, especially when well-defined scaffolds based on ultrafine fibers are required. Here the melt electrowriting of reactive liquid crystalline inks, leading, after ultraviolet-light-induced crosslinking, to digitally positioned uniform LCE fibers with diameters ranging from hundreds of nanometers to tens of micrometers is presented, whichishardly accessible with conventional extrusion-based printing techniques. The electrowriting process induces the preferential alignment of the mesogens parallel to the fiber's axis. Such an alignment, defined by the printing path, determines the mechanical response of the crosslinked material upon stimulation. This manufacturing platform allows the preparation of open square lattice scaffolds with ultrafine fibers (afew micrometers in diameter), periods as small as 90µm, and well-defined morphology. Additionally, the combination of accurate fiber stacking (up to 50 layers) and fiber fusion between layers leads to unprecedented microstructures composed of high-aspect-ratio LCE thin walls. The possibility of digitally controlling the printing of fibers allows the preparation complex fiber-based scaffolds with programmed and reversible shape-morphing, thus opening new avenues to prepare miniaturized actuators and smart structures for soft robotics and biomedical applications.

Microwave sintering and characterization of robocasted HA, CNT-HA scaffold structures for bone regeneration applications

The application of additive manufacturing in the field of biomedical medical research is being widely explored, in the development of bone scaffolds with different architectures and desired properties. Robocasting, an extrusion-based additive manufacturing technique that can print a wide range of materials at a relatively lower cost has been adopted in this study. The 3D structure was realized by robocasting of hydroxyapatite (HA) incorporated with different loading percentages (0.5, 1, and 2 wt%) of multiwalled carbon nanotubes (MWCNTs). Carboxymethyl cellulose (CMC) is used as a binder for the development of ceramic slurries with desired viscoelastic properties. Microwave sintering of the developed scaffold structures in the argon (Ar) atmosphere was performed at different sintering temperatures, with a 5 min soaking time, and 3 LPM Ar flow rate. FESEM/EDS imaging and Raman spectroscopy analysis confirmed the retention of incorporated MWCNTs post-sintering. With an increase in sintering temperature, physical properties of the developed scaffold structures such as density and shrinkage were observed to increase whereas porosity was reduced. The better compressive strength was observed in samples sintered at 1100 °C. And a maximum compressive strength of 21.86 MPa was recorded for 0.5HAIF100 scaffold structures in comparison to other reported groups. The in vitro cell studies confirmed that the adopted percentages of MWCNTs were biocompatible and also capable of promoting osteogenic differentiation. The developed scaffolds also remained stable for about 28 days without undergoing degradation.

Three-Dimensional Printing of Highly Conducting PEDOT: PSS-Based Polymers

Abstract Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most successful conducting polymers for electronic applications. Most commonly, the spin coating process is used to fabricate PEDOT:PSS thin films from an aqueous solution, yet it is unsuitable for fabricating complicated two-dimensional (2D) structures. Extrusion-based additive manufacturing (AM) processes have been investigated for 3D printing PEDOT:PSS-based polymers with free-form architecture. However, such methods imply strict requirements on the rheological properties of materials and, as a result, have limited choices of appropriate materials. In the past, additives have been added to improve the 3D printing processability of PEDOT:PSS materials, which, however, usually deteriorate the electrical conductivity. This article reports a new type of PEDOT:PSS material capable of addressing the previously listed challenges and characterized by high processability and electrical conductivity (72 S/cm). In addition, a novel extrusion-based AM technology, electrostatically-assisted direct ink writing (eDIW), is investigated for printing materials containing PEDOT:PSS. The eDIW method prints lines at micro-scale resolution at an ultra-high speed (1.72 m/s). This combination is often deemed impossible in the framework of classical extrusion-based AM techniques. This work lays the foundation for future explorations of applications of PEDOT:PSS-based conducting polymers in fields that require superb properties and custom geometry, which were conventionally impossible.

Characterization of micro-sandwich structures via direct ink writing epoxy based cores

Sandwich structured (SS) composites demonstrate considerable flexural stiffness and high strength-to-weight ratios and can be tailored as functional materials. Historically they have been constrained to specific material types and geometry due to limitations in manufacturing methods. However, employing additive manufacturing (AM), specifically direct ink writing (DIW), can provide an alternative method for making SS composites with complex and controllable micro and mesostructures with multifunctionality targeted at desired mechanical, thermal, and electrical properties. DIW, an extrusion-based AM technique, uses a viscous and thixotropic ink with desired components that, once printed, is cured to obtain the final complex net shape parts. In this paper, a novel hybrid AM technique is employed to manufacture SS composite materials containing bisphenol A-based epoxy core and carbon fiber reinforced polymer (CFRP) face sheets that are fabricated via DIW and vacuum infusion process (VIP), respectfully. We demonstrate that the fabrication of these SS composites can be tailored from a thermosetting material, from which additives and/or various lattice structures can be manufactured to achieve enhanced and desirable mechanical integrity with functional properties. Surface topology and mechanical testing techniques are used to characterize the fabricated hybrid SS composites to study and assess mechanical stability. A rheo-kinetic cure model was developed for the core material to allow for additive manufacturing process requirements while ensuring complete cross-linking for the thermoset-based core material. Because of the ability to obtain relatively small core-thickness and controlled architecture, this method now allows for fabricating layered micro-sandwich structures for realizing further light-weighting in relevant applications.

Extrusion-based additive manufacturing of Mg-Zn/bioceramic composite scaffolds

The treatment of femoral nonunion with large segmental bone defect is still challenging. Although magnesium alloys have been considered potential materials for such a treatment, their application is limited by their fast degradation. Adding bioceramic particles into magnesium to form Mg-matrix composites is a promising strategy to adjust their biodegradation rates and to improve their mechanical properties and cytocompatibility further. Here, we developed an extrusion-based additive manufacturing technique to fabricate biodegradable Mg-Zn/bioceramic composite scaffolds ex-situ. Inks carrying a Mg-Zn powder and 5, 10 and 15% β-tricalcium phosphate (TCP) powder particles were investigated regarding the dispersion of β-TCP particles in the inks and viscoelastic properties. Optimally formulated inks were then employed for subsequent 3D printing of porous composite scaffolds. The in vitro biodegradation rate of the scaffolds containing 5% β-TCP decreased to 0.5mm/y, which falls within the range desired for critical-sized bone substitution. As compared to the monolithic Mg-Zn scaffolds, the elastic moduli and yield strengths of the composite scaffolds were much enhanced, which remained in the range of the cancellous bone properties even after 28 d of in vitro degradation. The Mg-Zn/5TCP and Mg-Zn/10TCP scaffolds also exhibited improved biocompatibility when cultured with preosteoblasts, as compared to Mg-Zn scaffolds. In addition, the ALP activity and mineralization level of the composite scaffolds were much enhanced in the extracts of the composite scaffolds. Taken together, this research marks a great breakthrough in fabricating porous Mg-matrix composite scaffolds that meet several design criteria in terms of appropriate biodegradation rate, mechanical properties, and bioactivity. STATEMENT OF SIGNIFICANCE: The treatment of posttraumatic femoral nonunion with large segmental bone defect is still challenging. In this study, we developed a multi-material extrusion-based additive technique to fabricate porous Mg/bioceramic composite scaffolds for such a treatment. The technique allowed for the fine-tuning of printable inks to optimize the dispersion of micro-sized particles. The relative densities of the struts of the fabricated composite scaffolds reached 99%. The added bioceramic particles (β-TCP) exhibited proper interfacial bonding with the Mg alloy matrix. The porous Mg-based composite possessed desired biodegradability, bone-mimicking mechanical properties throughout thein vitrobiodegradation period and improved bioactivity to bone cells. These results demonstrated great prospects of extrusion-based 3D printed porous Mg materials to be developed further as ideal biodegradable bone-substituting materials.

Developing a novel technique for the fabrication of PLA-graphite composite filaments using FDM 3D printing process

Developing a uniform polymer-based composite filament is a critical factor for a successful 3D printing process. In this regard, a novel technique for the fabrication of PLA-graphite filament with the potential to be applied to other PLA-based composite filaments was proposed and compared to the solvent casting method. This modified mixing technique involves partial dissolution of the PLA pellets surface by dichloromethane (DCM), which creates a sticky surface for the strong adhesion of reinforcement powders. The manufactured composite filament by this method exhibited excellent structural features, while the solvent casting method yielded a heterogeneous filament with a non-uniform diameter and numerous voids. In addition, graphite, as a cost-effective carbon-based filler for polymer matrix composites, could effectively act as a reinforcement phase, leading to noticeable mechanical strength enhancement of PLA. Furthermore, significantly enhanced printability and mechanical properties of 3D-printed PLA-graphite composite specimens indicate the efficiency of the modified mixing method as a practical and time-saving technique for developing uniform PLA-based composite filaments for the extrusion-based additive manufacturing techniques such as FDM.

Compounding a High-Permittivity Thermoplastic Material and Its Applicability in Manufacturing of Microwave Photonic Crystals.

Additive Manufacturing (AM) techniques allow the production of complex geometries unattainable through other traditional technologies. This advantage lends itself well to rapidly iterating and improving upon the design of microwave photonic crystals, which are structures with intricate, repeating features. The issue tackled by this work involves compounding a high-permittivity material that can be used to produce 3D microwave photonic structures using polymer extrusion-based AM techniques. This material was acrylonitrile butadiene styrene (ABS)-based and used barium titanate (BaTiO3) ceramic as the high-permittivity component of the composite and involved the use of a surfactant and a plasticizer to facilitate processing. Initial small amounts of the material were compounded using an internal batch mixer and studied using polymer thermal analysis techniques, such as thermogravimetric analysis, rheometry, and differential scanning calorimetry to determine the proper processing conditions. The production of the material was then scaled up using a twin-screw extruder system, producing homogeneous pellets. Finally, the thermoplastic composite was used with a screw-based, material extrusion additive manufacturing technique to produce a slab for measuring the relative permittivity of the material, as well as a preliminary 3D photonic crystal. The real part of the permittivity was measured to be 12.85 (loss tangent = 0.046) in the range of 10 to 12 GHz, representing the highest permittivity ever demonstrated for a thermoplastic AM composite at microwave frequencies.

Investigating the effect of cooling rate on strength of Fused Filament Fabrication parts using differential scanning calorimetry technique

Desired mechanical properties are major area of interest within the field of Additive Manufacturing (AM) technologies. Fused Filament Fabrication (FFF) is an extrusion-based AM technique. In FFF process, the primary concern of strength is bonding between strands,and it is greatly influenced by the heat transfer during the manufacturing process. The extent of bonding not only influences the strength, but also the structural integrity of the part. To study the bonding between the extruded polymer strands of FFF process, investigation must be done to understand the influence of rate of cooling during FFF process. The present study focuses on investigation of cooling rate effects on FFF-ABS (Acrylonitrile Butadiene Styrene) parts over their tensile strength. Since glass transition temperature plays a key role in understanding the history of the thermal behavior, it is hence important to estimate its value for various extrusion temperatures. To understand this, glass transition temperature is estimated through Differential Scanning Calorimetry (DSC) experimentation technique as it records the thermal history of the polymer and hence this test is applied at different cooling rate. Additionally, to support the DSC graphs, tensile testing of FFF made parts is done on the parts manufactured at two extreme extruder temperatures namely 230° C and 250° C. Better bond formation between the strands contributes to higher strength and hence neck growth is estimated by capturing the scanning electron microscope graphs. The higher strength (as obtained for higher neck growth)is due to higher or proper cooling process. The results also show that the parts cooled at higher cooling rate have better bonding in terms of neck growth which proves a good agreement among the cooling rate, strength, and neck growth. The novelty of this work lies in polymer characterization to provide more insights in FFF layer deposition process (effect of different cooling rate on FFF process) using DSC and mechanical testing/analysis.

Improvement of part strength prediction modelling by artificial neural networks for filament and pellet based additively manufactured parts

ABSTRACT Nowadays, extrusion-based additive manufacturing techniques have been utilised from domestic to industrial end-product fabrications. However, parts fabricated through these techniques are facing poorer part strength issues due to its high nature of anisotropic fabrication strategies. Moreover, it may be improved if it can be predicted in the initial stage of fabrication through part strength modelling technique. In this direction, many researchers have attempted to model part strength estimation models that could be utilised for prediction purposes and hence controlled and improved the part strength. However, due to the anisotropic nature of 3D printed parts, models developed in the existing literature are showing more prediction errors, which can affect the final part strength. To overcome this issue, a new part strength modelling technique based on ANN technique has been defined in this study, which reduces the prediction error significantly. For the validation of the developed model, a comparative study has been performed by considering previously developed models and corresponding data available in the existing literature. Results obtained from the proposed ANN model show that prediction errors reduced significantly and it can be one of the possible alternatives to predict part strength of anisotropic behaviour of 3D printed parts.

Toughening robocast chitosan/biphasic calcium phosphate composite scaffolds with silk fibroin: Tuning printable inks and scaffold structure for bone regeneration

The present work aims the production of composite bioceramic scaffolds by robocasting suppressing sintering as post printing process. To achieve this purpose, extrudable ink compositions containing a high concentration of bioceramic powders (hydroxyapatite and β-tricalcium phosphate) embedded in aqueous polymeric solutions of chitosan and silk fibroin were fine-tuned. Polymeric solutions of chitosan/silk fibroin with different ratios were tested, maintaining the total amount of bioceramic solids at 30 vol%. The inks were characterized by rheological studies in viscometry and oscillatory modes, being the printable ones selected to produce scaffolds with different macropore sizes (300 μm and 500 μm). The scaffolds were characterized by mechanical properties (dry and wet conditions) and morphological features, as well as its degradability. In vitro studies were also evaluated in the scaffolds that presented the best structural performance.The addition of 2 wt% silk fibroin to a 5 wt% chitosan matrix allows to significantly improve the mechanical performance of the printed composite scaffolds, reflected in high values for Young's modulus and maximum compressive strength. This trend was continued in wet scaffolds with a concomitant reduction of mechanical properties. Regarding degradability, the scaffolds in general presented a weight loss in the range of 14–18% after 28 days incubation in HEPES solution at two different pH values at 37 °C, with an associated release of calcium and phosphorus ions. The scaffold with 300 μm porosity comprising the both polymers in its composition presented the less rate degradation when compared to the scaffolds with similar porosity and containing only chitosan as base matrix. Moreover, the combined natural polymers gave rise to a significant increase in the metabolic activity of human osteoblasts grown on the scaffolds with both macropore' size, being in line with the full cellular filling of their surfaces, demonstrated by SEM and confocal imaging. The advances presented in this work are a promising path in the ink's development for extrusion-based additive manufacturing techniques and subsequent biomaterials, encompassing suitable physical and chemical characteristics with high potential to be used as bone substitutes.

Benchmarking analysis of digital light processing resins in terms of dimensional accuracy and geometric tolerances

Additive Manufacturing (AM) is a groundbreaking fabrication technology that is revolutionizing traditional manufacturing processes. Generally, following a layer-by-layer approach, in AM the final shape of the product is built through the progressive deposition of one or more materials. The most common extrusion-based AM technique for thermoplastic polymers is Fused Filament Fabrication (FFF), whilst for photopolymer resins, Digital Light Processing (DLP) and Stereolithography (SLA) are widely used. In the last years, DLP has spread rapidly, due to its low average cost and simple use. Moreover, a lower layer thickness can be used in DLP if compared to the FFF process. Therefore, hobbyists or amateur end users and many companies use DLP to achieve high dimensional accuracy and smooth surfaces for small products.This work aims to evaluate the performance of three different DLP resins in terms of dimensional and geometrical accuracy. A benchmarking activity is carried out using a Rover printer by Sharebot to produce replicas of a reference part using Sharebot resins. After production, the replicas were inspected using a Coordinate Measuring Machine (CMM) for comparing the dimensional accuracy of the geometric features according to ISO IT grades and tolerances of the GD&T system. The results of this study are also compared with previous works from the literature in the conclusions.

Can filaments, pellets and powder be used as feedstock to produce highly drug-loaded ethylene-vinyl acetate 3D printed tablets using extrusion-based additive manufacturing?

Personalized medicine, produced through 3D printing, is a promising approach for delivering the required drug dose based on the patient's profile. The primary purpose of this study was to investigate the potential of two different extrusion-based additive manufacturing techniques – fused filament fabrication (FFF) and screw-based 3D printing, also known as direct extrusion additive manufacturing (DEAM). Different ethylene-vinyl acetate (EVA) copolymers (9 %VA, 12 %VA, 16 %VA, 18 %VA, 25 %VA, 28 %VA, and 40 %VA) were selected and loaded with 50% (w/w) metoprolol tartrate (MPT). Hot-melt extrusion was performed to produce the drug-loaded filaments. These filaments were used for FFF in which the mechanical and rheological properties were rate-limiting steps. The drug-loaded filament based on the 18 %VA polymer was the only printable formulation due to its appropriate mechanical and rheological properties. As for the highest VA content (40 %VA), the feeding pinch rolls cause buckling of the filaments due to insufficient stiffness, while other filaments were successfully feedable towards the extrusion nozzle. However, poor flowability out of the extrusion nozzle due to the rheological limitation excluded these formulations from the initial printing trials. Filaments were also pelletized and used for pellets-DEAM. This method showed freedom in formulation selection because the screw rotation drives the material flow with less dependence on their mechanical properties. All drug-loaded pellets were successfully printed via DEAM, as sufficient pressure was built up towards the nozzle due to single screw extrusion processing method. In contrast, filaments were used as a piston to build up the pressure required for extrusion in filament-based printing, which highly depends on the filament's mechanical properties. Moreover, printing trials using a physical mixture in powder form were also investigated and showed promising results. In vitro drug release showed similar release patterns for MPT-loaded 3D printed tablets regardless of the printing technique. Additionally, pellets-DEAM enabled the production of tablets with the highest VA content, which failed in FFF 3D printing but showed an interesting delayed release profile.

Optimized preceramic polymer for 3D structured ceramics via fused deposition modeling

3D structured ceramics stemmed from preceramic polymers via additive manufacturing have attracted much attention recently. However, these polymers with high ceramic yield are so brittle that extrusion-based additive manufacturing techniques are hardly able to be utilized for assembling 3D structures. Herein, we developed a strategy to prepare feedstocks for these manufacturing techniques, i.e., utilizing a small amount of thermal-plastic polymer to optimize the preceramic polymer while good compatibility is required between the two polymers to ensure a homogeneous mixture. Polycarbosilane and polypropylene were selected as the representative materials. Polypropylene occupied a small proportion (≤5wt.%) and significantly improved the formability of the precursor. Three-dimensional SiC were obtained via fused deposition modeling combined with crosslinking and pyrolysis. The SiC ceramic filaments showed a mean tensile strength of 471 MPa. The strategy is also applicable to a large field of ceramic systems with corresponding precursor, such as sialon ceramic and multicomponent Si-based ceramics.

Numerical study of texture in material extrusion: Orientation in a multicomponent system of spheres and ellipsoids

Abstract Extrusion-based Additive Manufacturing techniques, such as Robocasting, produce continuous filaments to create layer-wise structures. The material properties of these structures depend on the orientation of suspended particles within the filament. This orientation can be predicted by analytical models, but those models do not exist for the paste specifically regarded in this work: A multicomponent paste that consists of two types of particles having either spherical and ellipsoidal shape, respectively. To improve understanding of the texture evolution within such a suspension, we use experimentally validated particle-level simulations to address the following three questions: First, how strong do the spheres affect the alignment of ellipsoids under various deformations in terms of shear and/or elongation? Second, to which extend does an analytical orientation prediction model match the numerical simulations although the model ignores the presence of spheres? Third, which means exist to improve alignment of the ellipsoids in such a multicomponent system?