Printability Characteristics Research Articles

Effects of cellulose nanofibrils on rheological and mechanical properties of 3D printable cement composites

This study explores the effects of cellulose nanofibrils (CNF), a relatively new type of nanocellulose material, on the rheological and printability characteristics of cementitious mixtures, and the mechanical properties of 3D printed specimens. The rheology of the mortar mixtures with varying ratios of CNF is thoroughly assessed first. Two testing protocols, stress growth test and ramp test, are followed for rotational measurements using a shear rheometer with a building cell and vane motor. Stress growth tests are carried out to quantify the static yield stress of the cementitious mixtures. Ramp tests are conducted to determine dynamic yield stress and plastic viscosity of the mixes using the Bingham visco-plastic material model. As oscillatory measurements, amplitude sweep tests are carried out to determine the viscoelastic properties of the mortar mixes, including storage modulus and critical strain that are found to be essential for buildability. Thermogravimetric analysis (TGA) is conducted to assess the effects of CNF on the hydration characteristics of the mixtures. The printability and the buildability of the mortar mixtures incorporating CNF are assessed using a 3D concrete printer equipped with a 10 mm diameter nozzle and screw pump mechanism. Tensile, flexural, and compressive strength tests are conducted to determine the mechanical properties of 3D printed specimens with varying ratios of CNFs. Scanning electron microscopy (SEM) is used to conduct the microstructural analysis on fractured surfaces of the mechanically tested specimens. Results indicate that adding CNF at least 0.3 wt% of cement has a favorable effect on the rheological properties of cement composites.

Impact of build location on dimensional accuracy of 316L parts using SLM

The objective of this study is to comprehensively investigate the printability characteristics of a selective laser melting (SLM) system, which will be achieved through the development of a benchmark test part. In addition, the effect of the build location on the dimensional accuracy and precision of 316 L stainless steel parts produced by SLM was thoroughly evaluated.

Assessment of the sustainability and producibility of adobe constructions reinforced with Ca-based binders: Environmental life cycle analysis (LCA) and 3D printability

This study investigated the usability of adobe samples reinforced with calcium-based binders in a 3D-printed technique. These adobe samples' physical, mechanical, durability and microstructure characteristics were investigated and their 3D printability characteristics experimentally. In the case of adobe production by 3D-printing method, the compressive strength decreased by 9–33 % compared to mold casting. While the thermal conductivity coefficient of adobe samples varied between 0.833 and 1.421 W/mK, the thermal conductivity was reduced by 43 % thanks to the preference for gypsum. Within the scope of the LCA analysis, the slightest effect in terms of environmental damage was observed in mixtures containing gypsum compared to cement and slaked lime mixtures. As a result, it was determined that adobe's physical and mechanical characteristics could be improved by using gypsum, lime and cement, and these mixtures can be used in 3D-printing. It was determined that more sustainable adobe production is possible with gypsum and lime.

3D-Printable PLA/Mg Composite Filaments for Potential Bone Tissue Engineering Applications.

Magnesium (Mg) is a promising material for bone tissue engineering applications due to it having similar mechanical properties to bones, biocompatibility, and biodegradability. The primary goal of this study is to investigate the potential of using solvent-casted polylactic acid (PLA) loaded Mg (WE43) composites as filament feedstock for fused deposition modeling (FDM) 3D Printing. Four PLA/Magnesium (WE43) compositions (5, 10, 15, 20 wt%) are synthesized and produced into filaments, then used to print test samples on an FDM 3D printer. Assessments are made on how Mg incorporation affected PLA's thermal, physicochemical, and printability characteristics. The SEM study of the films shows that the Mg particles are uniformly distributed in all the compositions. The FTIR results indicate that the Mg particles blend well with the polymer matrix and there is no chemical reaction between the PLA and the Mg particles during the blending process. The thermal studies show that the addition of Mg leads to a small increase in the melting peak reaching a maximum of 172.8 °C for 20% Mg samples. However, there are no dramatic variations in the degree of crystallinity among the Mg-loaded samples. The filament cross-section images show that the distribution of Mg particles is uniform up to a concentration of 15% Mg. Beyond that, non-uniform distribution and an increase in pores in the vicinity of the Mg particles is shown to affect their printability. Overall, 5% and 10% Mg composite filaments were printable and have the potential to be used as composite biomaterials for 3D-printed bone implants.

High resolution and fidelity 3D printing of Laponite and alginate ink hydrogels for tunable biomedical applications

The formulation of hydrogels that meet the necessary flow characteristics for their extrusion-based 3D printing while providing good printability, resolution, accuracy and stability, requires long development processes. This work presents the technological development of a hydrogel-based ink of Laponite and alginate and evaluates its printing capacity. As a novelty, this article reports a standardizable protocol to quantitatively define the best printing parameters for the development of novel inks, providing new printability evaluation parameters such as the Printing Accuracy Escalation Index. As a result, this research develops a printable Laponite-Alginate hydrogel that presents printability characteristics. This ink is employed for the reproducible manufacture of 3D printed scaffolds with versatile and complex straight or curved printing patterns for a better adaptation to different final applications. Obtained constructs prove to be stable over time thanks to the optimization of a curing process. In addition, the study of the swelling and degradation behavior of the Laponite and alginate 3D printed scaffolds in different culture media allows the prediction of their behavior in future in vitro or in vivo developments. Finally, this study demonstrates the absence of cytotoxicity of the printed formulations, hence, setting the stage for their use in the field of biomedicine.

Effects of viscosity modifying admixture and nanoclay on fresh and rheo-viscoelastic properties and printability characteristics of cementitious composites

This study explores the effects of a viscosity modifying admixture (VMA) and attapulgite nanoclay (ANC) on rheological and viscoelastic properties as well as printability characteristics of mortar mixtures used for 3D printing. A total of sixteen mortar mixtures with varying dosages of VMA and ANC are prepared using a factorial design of experiments. Rheological properties of each mixture including static yield stress, plastic viscosity, and dynamic yield stress are evaluated through rotational rheometry tests such as ramp test and stress growth test. Then, the viscoelastic properties such as storage modulus, loss modulus and linear viscoelastic range are determined using oscillatory rheology tests. A thermogravimetric analysis (TGA) is conducted to assess the effects of VMA and ANC on hydration characteristics of mortar mixtures. A statistical analysis is performed to further evaluate the individual and joint effects of VMA and ANC on key performance parameters. An unsupervised clustering algorithm is used to group the mixtures into three clusters based on the obtained rheological and viscoelastic properties. A direct printing test using a screw type 3D concrete printing is conducted to assess the printability and buildability of the mortar mixtures selected from each cluster. Results indicate that the ANC can more effectively alter both rheological and viscoelastic properties of mortar composites for 3D printing compared with VMA. However, the combined use of VMA and ANC in printable mortar mixtures leads to a high static yield stress and storage modulus and the resulted mixture exhibits good buildability without any plastic collapse.

Characterization of rice flour and pastes with different sweeteners for extrusion-based 3D food printing.

This work aims at investigating the impact of commonly used sweeteners-sugar and jaggery on 3D printability of rice flour (RF) paste. The physicochemical characteristics of rice flour suitable for 3D food printing have been investigated. Three mixes, rice flour with water (M1 : RF-50.86%, water-49.14%), rice flour with sugar and water (M2 : RF-36.75%, sugar-14.10%, water-49.14%) and rice flour with jaggery and water (M3 : RF-36.75%, jaggery-14.10%, water-49.14%) were compared on 3D printability based on visual inspection and properties supporting 3D printability and shape retention. The effect of the three mixes was characterized on color, rheological, thixotropic, and handling properties. Out of the three mixes, M3 is found to have the best printability characteristics with shear thinning behavior, yield stress of 157 Pa, flow stress of 121 Pa, and extrusion force of 6.62 kg.

Physico-chemical modification of gelatine for the improvement of 3D printability of oxidized alginate-gelatine hydrogels towards cartilage tissue engineering

This work explored 3D printing to mimic the intrinsic hierarchical structure of natural articular cartilage. Alginate di-aldehyde- gelatine (ADA-GEL) hydrogel was used as ink to create hierarchically ordered scaffolds. In comparison to previously reported ADA-GEL compositions, we introduce a modified formulation featuring increased amounts of thermally modified gelatine. Gelatine was degraded by hydrolysis which resulted in tailorable printability characteristics further substantiated by rheological analysis. ADA (3.75 %w/v)-GEL (7.5 %w/v) with gelatine modified at 80 °C for 3 h could be printed in hierarchical complex structures reaching scaffold heights of over 1 cm. The hierarchical structure of the scaffolds was confirmed via µCT analysis. To examine mechanical properties as well as the suitability of the hydrogel as a proper matrix for cell seeding and encapsulation, nanoindentation was performed. Elastic moduli in the range of ~ 5 kPa were measured. Gelatine heat pre-treatment resulted in modifiable mechanical and rheological characteristics of ADA-GEL. In summary, this study demonstrates the possibility to enhance the printability of ADA-GEL hydrogels to fabricate hierarchical scaffold structures with shape stability and fidelity, without the necessity to change the initial hydrogel chemistry by the use of additives or crosslinkers, providing a valuable approach for fabrication of designed scaffolds for cartilage tissue engineering.

Hyaluronic Acid/Laponite Clay Nanocomposites‐Based Hydrogels for 3D Bioprinting Applications

Hyaluronic acid (HA) is a glycosaminoglycan with excellent physicochemical and biological properties and represents a potential component to constitute inks used in tissues and organs 3D bioprinting process. On the other hand, it does not have an adequate degree of rigidity necessary for the structural maintenance of printed components. Laponite (Lap) is a synthetic nanoclay capable of increasing the rheological properties of polymeric hydrogels. The present study aimed to develop and characterize HA/Lap clay nanocomposites-based hydrogels for the constitution of inks for 3D bioprinting, considering the Lap potential to improve the rheological characteristics of HA. For this, HA (12 mg/mL) and Laponite-XLG (50 mg/mL) hydrogels were initially produced. Three additional hydrogels, composed from the association of different percentages of HA and Lap samples (w/w), were manufactured (HA/Lap 75:25%, 50:50%, and 25:75%). After constitution, all hydrogels samples were characterized by rheological and spectrophotometric analysis (Fourier-Transform Infrared Spectroscopy-FTIR). Finally, they were submitted to an in vitro cytotoxicity test, with cell viability (human fibroblasts-GM07492) established by a spectrophotometric Resazurin/Resorufin method. The rheological analysis results demonstrate a directly proportional increase in hydrogel viscosity concerning the increase in Lap percentage. The values of HA, Lap, and experimental HA/Lap clay nanocomposites-based hydrogels samples (75:25%, 50:50%, and 25:75%) were 4.9, 12.7, 4.0, 9.4, and 12.0 Pa.s, respectively. In FTIR analysis, bands (wavenumber 1000.7 cm-1) were identified in the Lap and HA/Lap samples, corresponding to the stretching of the Si-O interaction of Lap's tetrahedral layer. The viability tests demonstrated the non-toxic profile of the HA, Lap, and the hydrogels resulting from their associations. Such results demonstrate the biological safety of HA/Lap samples and the rheological modifying role from Lap on developed hydrogels. The viscosity levels achieved, especially in the proportions of HA/Lap of 50:50% and 25:75%, demonstrate its potential in the constitution of inks for use in 3D bioprinting. Further research should contribute to establishing the ideal composition (percentage of HA and Lap) and the printability characteristics of the HA/Lap clay nanocomposites-based hydrogels.

Ag-Coated Cu/Polylactic Acid Composite Filament for Lithium and Sodium-Ion Battery Current Collector Three-Dimensional Printing via Thermoplastic Material Extrusion

This article focuses on the development of polylactic acid– (PLA-) based thermoplastic composite filament for its use, once 3D printed via thermoplastic material extrusion (TME), as current collector at the negative electrode side of a lithium-ion battery or sodium-ion battery. High electronic conductivity is achieved through the introduction of Ag-coated Cu charges, while appropriate mechanical performance to allow printability was maintained through the incorporation of poly(ethylene glycol) dimethyl ether average Mn ∼ 500 (PEGDME500) as a plasticizer into the PLA polymer matrix. Herein, thermal, electrical, morphological, electrochemical, and printability characteristics are discussed thoroughly. While Ag-Li alloy formation is reported at 0.1V upon cycling, its use with active materials such as Li4Ti5O12 (LTO) or Li2-terephthalate (Li2TP) operating at a plateau at higher potential is demonstrated. Furthermore, its ability to be used with negative electrode active material of sodium-ion battery technology in a wide potential window is demonstrated.

Environmentally Friendly Lithium-Terephthalate/Polylactic Acid Composite Filament Formulation for Lithium-Ion Battery 3D-Printing via Fused Deposition Modeling

In this paper, the development of an environmentally-friendly lithium-terephtalate/polylactic acid (Li2TP/PLA) composite filament, for its use, once 3D-printed via Fused Deposition Modeling (FDM), as negative electrode of a lithium-ion battery is reported. Solvent-free formulation of the 3D-printable filament is achieved through the direct introduction of synthesized Li2TP particles and PLA polymer powder within an extruder. Printability is improved through the incorporation of poly(ethylene glycol) dimethyl ether average Mn∼500 (PEGDME500) as plasticizer, while electrical performances are enhanced through the introduction of carbon black (CB). Thermal, electrical, morphological, electrochemical and printability characteristics are discussed thoroughly. By taking advantage of the 3D-printing slicer software capabilities, an innovative route is proposed to improve the liquid electrolyte impregnation within the 3D-printed electrodes.

Flame Retardant Hybrid Paper Coatings with PVA - Melamine / Zinc Borat

Papers are raw materials with high flammability. Some of the products produced in the printing industry are used in places requiring high heat resistance. High-tech papers can be produced by adding a flame retardant to the paper coating formulation or pulp. In this study, it is aimed to prepare polyvinyl alcohol (PVA )- zinc borate / melamine / zinc boratemelamine paper coating formulations and to produce flame retardant paper by coating on paper.For this purpose, primarily zinc borate is produced by boric acid and zinc carbonate reaction . In the second part of the study, four different coating formulations were prepared by adding zinc borate, melamine and their double mixtures to the main formulation, where PVA polymer matrix was used as binder, and coatings were made on an 80g/m2 paper surface. Limiting oxygen index (LOI ), gloss, color, surface energy and contact angles properties of the produced papers were determined. Offset printing was done onto coated papers with IGT C1 test printing machine. All produced flame retardant papers have good printability characteristics

Hybrid additive manufacturing of the modified electrolyte‐electrode surface of planar solid oxide fuel cells

AbstractDigital Control of the surface patterning of functional layers of solid oxide fuel cells (SOFCs), via the inkjet printing technique, offers better efficiency in performance. A combination of inkjet printing and tape casting in a single machine system defines as hybrid additive manufacturing, facilitates printing complex structures. Also, implementing this idea removes the blocking of the print head nozzle orifice issue.In this paper, a highly dispersed and long‐term stable colloidal zirconia‐based suspension, with optimal printability characteristics, is designed to be prepared in approximately three hours to fabricate the macro patterned structure of the SOFC electrolyte. Hybrid Additive Manufacturing is successfully employed to make a symmetric cathode side cell with a modified electrolyte‐electrode surface to reduce the electron resistivity.

Silk-Reinforced Collagen Hydrogels with Raised Multiscale Stiffness for Mesenchymal Cells 3D Culture.

Type I collagen hydrogels are of high interest in tissue engineering. With the evolution of 3D bioprinting technologies, a high number of collagen-based scaffolds have been reported for the development of 3D cell cultures. A recent proposal was to mix collagen with silk fibroin derived from Bombyx mori silkworm. Nevertheless, due to the difficulties in the preparation and the characteristics of the protein, several problems such as phase separation and collagen denaturation appear during the procedure. Therefore, the common solution is to diminish the concentration of collagen although in that way the most biologically relevant component is reduced. In this study, we present a new, simple, and effective method to develop a collagen-silk hybrid hydrogel with high collagen concentration and with increased stiffness approaching that of natural tissues, which could be of high interest for the development of cardiac patches for myocardial regeneration and for preconditioning of mesenchymal stem cells (MSCs) to improve their therapeutic potential. Sericin in the silk was preserved by using a physical solubilizing procedure that results in a preserved fibrous structure of type I collagen, as shown by ultrastructural imaging. The macro- and micromechanical properties of the hybrid hydrogels measured by tensile stretch and atomic force microscopy, respectively, showed a more than twofold stiffening than the collagen-only hydrogels. Rheological measurements showed improved printability properties for the developed biomaterial. The suitability of the hydrogels for 3D cell culture was assessed by 3D bioprinting bone marrow-derived MSCs cultured within the scaffolds. The result was a biomaterial with improved printability characteristics that better resembled the mechanical properties of natural soft tissues while preserving biocompatibility owing to the high concentration of collagen. Impact statement In this study, we report the development of silk microfiber-reinforced type I collagen hydrogels for 3D bioprinting and cell culture. In contrast with previously reported studies, a novel physical method allowed the preservation of the silk sericin protein. Hydrogels were stable, showed no phase separation between the biomaterials, and they presented improved printability. An increase between two- and threefold of the multiscale stiffness of the scaffolds was achieved with no need of using additional crosslinkers or complex methods, which could be of high relevance for cardiac patches development and for preconditioning mesenchymal stem cells (MSCs) for therapeutic applications. We demonstrate that bone marrow-derived MSCs can be effectively bioprinted and 3D cultured within the stiffened structures.

Printability of Methacrylated Gelatin upon Inclusion of a Chloride Salt and Hydroxyapatite Nano‐Particles

Abstract3D biomaterial printing requires an ink to have suitable printability characteristics, as well as creating a final construct of controllable swelling and stiffness. To tune such properties, the impact of adding different levels of chloride salts (NaCl and CaCl2) and hydroxyapatite nano‐particles (nHA) to a highly concentrated and photo‐crosslinkable methacrylated gelatin (GelMA) is investigated. By adding up to 100 mmCaCl2or 1.11mNaCl, the GelMA viscosity decreases from that of control GelMA (no salt). Interestingly, a 25G needle and strong photo‐polymerization kinetics are able to overcome the low viscosity of the 50CaG ink during printing. Adding further CaCl2increases GelMA viscosity, while decreasing both the swelling and dynamic modulus of the UV‐cured construct observed in water. As all UV‐cured constructs have a dynamic modulus greater than 1 MPa, this novel system is able to match the dynamic modulus of articular cartilage—a feat not previously reported for a GelMA‐based system. Lastly, nHA inclusion improves ink printability, as well as decreases swelling and increases dynamic modulus of the final construct. Overall, this study leads to the successful development of a new advanced functional ink which will be beneficial in the 3D printing of biomaterials toward tissue engineering applications.

Printability, accuracy and strength of geopolymer made using powder-based 3D printing for construction applications

Abstract The authors of this study have recently succeeded to develop geopolymer materials using slag only formulations for the requirements and demands of commercially available powder-based 3D printers. In this study, the formulation is extended to fly ash and slag combinations so that to expand the scope of geopolymer materials that can be used in the commercially available powder-based 3D printers for construction applications. The quantitative influence of fly ash content on the printability characteristics (i.e., depositability and wettability) of the geopolymer powder, as well as the linear dimensional accuracy and compressive strength of the printed specimens were investigated. The effect of type of alkaline solution used for post-processing on the linear dimensional accuracy and compressive strength of the post-processed specimens were also evaluated. The results indicated that the increase in fly ash content had no effect on the powder depositability, but adversely affected the powder wettability, linear dimensional accuracy and compressive strength of the printed specimens. The minimum slag content required to prepare fly ash/slag blended geopolymer powder for powder-based 3D concrete printing process is 50 wt%. The post-processing significantly increased the compressive strength. The post-processed specimens printed with 50 wt% slag/50 wt% fly ash powder exhibited a 7-day compressive strength of up to 25 MPa, which is sufficiently high for many construction applications.

On the Feasibility of Printing 3D Composite Objects Based on Polypropylene/Multi-walled Carbon Nanotubes

In this paper, the feasibility of 3D printing polypropylene/ multi-walled carbon nanotube (PP/MWCNT) composites by fused deposition modeling. First, the rheological behavior of PP with 0.3, 0.5 and 1 wt.% of MWCNT was investigated in order to determine the printability in terms of melt shear viscosity and flow activation energy. Second, the filament extrusion process was optimized by the trial-and-error method in order to obtain round and constant filaments. Finally, tensile specimens were printed and tested in order to determine the mechanical properties at various printing direction. Experimental results show that the PP/MWCNT composite filaments with MWCNT loading up to 1 wt.% have good printability characteristics and can be successfully 3D printed with good mechanical performance.

Fabrication of thin yttria-stabilized-zirconia dense electrolyte layers by inkjet printing for high performing solid oxide fuel cells

In this work, we present how a low-cost HP Deskjet 1000 inkjet printer was used to fabricate a 1.2 μm thin, dense and gas tight 16 cm2 solid oxide fuel cells (SOFC) electrolyte. The electrolyte was printed using an ink made of highly diluted (<4 vol.%) nanometric yttria stabilized zirconia (YSZ) powders (50 nm in size) in an aqueous medium. The ink was designed to be a highly dispersed, long term stable colloidal suspension, with optimal printability characteristics. The electrolyte was made by a multiple printing procedure, which ensures coverage of the several flaws occurring in a single printing pass. Together with an optimized sintering procedure this resulted in good adhesion and densification of the electrolyte. The SOFC exhibited a close-to-theoretical open circuit voltage and a remarkable peak power density above 1.5 W cm−2 at 800 °C.

Physical Properties and Printability Characteristics of Mechanical Printing Paper with LWC

Acrylic styrene latex was used in combination with nanoclay at two different loading levels and calcium carbonate at four loading levels to improve printability characteristics of mechanical printing paper. SEM micrographs indicated filling of the voids and covering of the printing paper surface. Different rheological behavior of the coating that contained two coating pigments, in addition to their different viscosity, was clearly evident. Calcium carbonate was more advantageous due to the reduction in pumping costs. Paper coating improved roughness and air-permeability properties. Water absorption of the coated paper was decreased by at least 50% which significantly affects the dimensional stability of the paper during web offset printing. Specular gloss and print density were significantly increased at a 1% probability level by coating the surface of the paper. Contrary to the control sample, picking of the paper (which is of great importance after printing and for linting on the printing cylinder) did not occur.

Absorption Properties of Coatings: A Selected Overview of Absorption Criteria Derived from Recent Pore Network Modelling

Absorption of fluids into porous media controls the printability characteristics of coated papers in respect to ink setting rate and phenomena such as wicking and bleeding. The dynamic of absorption is related to the runnability on printing presses. Pore structure, size distribution, and surface chemistry are the parameters which can be used to design structures for optimal absorption. To achieve a working understanding it has been necessary to develop the theory of absorption to encompass the short timescale fast absorption occurring during wetting of the fluid ink onto the surface of the paper. The phenomena of fluid spread and absorption are studied and shown to depend on the observed pore size distribution rather than porosity alone. This finding calls into question the traditional acceptance of the Lucas–Washburn relationship for such porous networks as the hydraulic absorption radius determined from experimental absorption rate measurements fails to follow the actual measured pore size trend. It is necessary to invoke the concept of a preferred pathway of absorption in which only selected groups within the finest connecting pores or throats of the network in combination with intermediate pore reservoirs contribute maximally to the transmission of fluid through the coating structure as porosity increases. By defining the pore size range involved in this mechanism using an inertial wetting term, found in the short time solution to the Bosanquet equation, it is possible for the first time to identify the connective structures responsible for the important time dependent absorption properties of coatings and their relationship to the ink tackification and/or setting rates for a range of printing ink solvents and diluents, including offset, rotogravure, flexographic, and ink jet inks. Additionally, the differential chromatographic effect of coatings and associated binder systems results in further time dependent offset ink setting phenomena in which miscible ink oils of different natures separate within the coating pores and between the pores and synthetic latex binders. In situ determination of the viscosity and solids content of an offset ink via static ink tack measurements allows the dynamic of ink setting to be studied on real coating systems. Combining these criteria, the necessary steps can be followed to design the coating pigment structures required for optimising existing and future fluid‐based printing technologies.