Printing Properties Research Articles

Effect of Cu2O nanosphere size on femtosecond laser reductive sintering/melting for Cu printing

In this study, the size effect of Cu2O nanospheres on femtosecond laser reductive sintering/melting properties for Cu printing is investigated. First, two types of monodispersed Cu2O nanospheres (average sizes of 110 and 250 nm) are prepared using the polyol method. The particle size is significantly affected by the amount of polyvinylpyrrolidone because of the capping of initially-precipitated nanospheres and their aggregations. Both the prepared inks containing nanospheres and reducing agents exhibit the same reaction temperature in thermogravimetry and differential thermal analyses. These results indicate that the size of the nanospheres does not affect the reaction temperature. The small Cu2O nanospheres are well-sintered, whereas the large nanospheres are easily melted by irradiation with femtosecond laser pulses. As both inks possess the same reaction temperature, their printing properties depend on their thermal conductivity. The low thermal conductivity of the large nanosphere ink owing to their small reduced surfaces against volume induces local heating and subsequent melting, and the high thermal conductivity of the small nanosphere ink owing to their large reduced surfaces against volume increases sintering area. The sintered patterns fabricated using the small nanospheres exhibited an electrical conductivity of ∼1.1 × 106 S/m, which is 1/50 of pure Cu. These strong size effects of the nanospheres on direct writing demonstrate that mixed sizes of the nanospheres can improve the electrical conductivity of the patterns because of their high density and sufficient thickness.

The effects of nozzle diameter and length on the resulting strand properties for shotcrete 3D printing

Additive manufacturing in construction (AMC) enables new design methods and strategies within the construction industry. In particular, Shotcrete 3D Printing (SC3DP) offers a high degree of design freedom by enabling the deposition of concrete at variable layer orientation based on a wet-mix shotcrete process. However, the mechanical properties and geometry of the printed layers are dependent on the material and process parameters used. In this context, the effects of air and concrete flow rates, path planning parameters, and material parameters have been investigated in previous research. The presented study investigates the influence of the nozzle geometry on the resulting strand properties, e.g. strand geometry, layer bond strength, and compressive strength, to evaluate nozzle diameter and length as control parameters for the SC3DP process. Experimental investigations were performed with fixed nozzle diameters between 10 and 30 mm and nozzle lengths ranging from 100 to 200 mm. The results show a significant influence of the nozzle diameter on the resulting strand geometry as well as the mechanical properties. Finally, concepts for a nozzle with a controllable outlet diameter were developed and evaluated.

3D-bioprintable endothelial cell-laden sacrificial ink for fabrication of microvessel networks

Although various research efforts have been made to produce a vascular-like network structure as scaffolds for tissue engineering, there are still several limitations. Meanwhile, no articles have been published on the direct embedding of cells within a glucose sensitive sacrificial hydrogel followed by three-dimensional (3D) bioprinting to fabricate vascular structures. In this study, the hydrogel composed of reversibly crosslinked poly(ethylene glycol) diacrylate and dithiothreitol with borax and branched polyethylenimine was used as the sacrificial hydrogel to fabricate vascular-like network structure. The component proportion ratio of the sacrificial hydrogel was optimized to achieve proper self-healing, injectable, glucose-sensitive, and 3D printing properties through the balance of boronate ester bond, hydrogen bond, and steric hinderance effect. The endothelial cells (ECs) can be directly embedded into sacrificial hydrogel and then bioprinted through a 110 μm nozzle into the neural stem cell (NSC)-laden non-sacrificial hydrogel, forming the customized EC-laden vascularized microchannel (one-step). The EC-laden sacrificial hydrogel was dissolved immediately in the medium while cells kept growing. The ECs proliferated well within the vascularized microchannel structure and were able to migrate to the non-sacrificial hydrogel in one day. ECs and NSCs interacted around the vascularized microchannel to form capillary-like structure and vascular-like structure expressing CD31 in 14 d. The sacrificial hydrogel conveniently prepared from commercially available chemicals through simple mixing can be used in 3D bioprinting to create customized and complex but easily removable vascularized structure for tissue engineering applications.

Medical-Grade PLA Nanocomposites with Optimized Tungsten Carbide Nanofiller Content in MEX Additive Manufacturing: A Rheological, Morphological, and Thermomechanical Evaluation.

The goal of this paper is to investigate tungsten carbide (WC) as a reinforcement in the popular material extrusion (MEX) additive manufacturing (AM) procedure. The impressive characteristics of WC demonstrate its potential as a valuable additive for commonly used polymeric matrices in MEX 3D printing, offering reinforcement and stabilization properties. The mechanical properties of hybrid polymer/ceramic nanocomposites made up of various filler loadings (0-10 wt. %) of medical-grade polylactic acid (PLA) and WC were studied. The mechanical characteristics, structure, and thermomechanical properties of the resulting compounds were fully characterized following the respective standards. The fracture mechanisms were revealed with Scanning Electron Microscopy. Overall, a laborious effort was implemented with fifteen different tests to fully characterize the nanocomposites prepared. In comparison to the raw PLA material, the tensile strength of the 4.0 wt. % WC PLA/WC nanocomposite was improved by 42.5% and the flexural strength by 41.9%. In the microhardness test, a 120.4% improvement was achieved, justifying the properties of WC ceramic. According to these findings, PLA nanocomposites reach high-performance polymer specifications, expanding their potential use, especially in wear-related applications.

Effect of Hydroxypropyl methyl cellulose (HPMC) on rheology and printability of the first printed layer of cement activated slag-based 3D printing concrete

Nowadays, Ground Granulated Blast Furnace Slag (GGBFS) is generally used to replace cement for reducing carbon emissions, but due to its low hydration activity and unstable working performance in the early stage, it is difficult to apply in 3D printed concrete (3DPC) as the main binder. In this study, a combination of ordinary Portland cement and calcium sulfoaluminate cement was used to activate GGBFS. In the presence of 0.2 wt% polycarboxylate superplasticizer (PCE), in order to achieve high-precision printing, hydroxypropyl methyl cellulose (HPMC) was used. The rheological properties of mortar were evaluated by the slugs-test and a rotational rheometer. The results show that the yield stress and thixotropy of slag cement-based 3D printing concrete are significantly increased, with addition of HPMC. The slugs-test shows its advantages in measuring rheological properties, such as superior repeatability of rheological data and a better association with 3D printing performance. Pumpability, extrudability, and buildability of the first printed layer of slag cement-based 3DPC were evaluated using pumping pressure, horizontal printing, and vertical printing. The results show that, with a 0.15 wt% HPMC, the 3D printing properties of the first layer are greatly improved, a stable and high-precision slag cement-based 3DPC can be developed, and the relationship between rheological properties and 3D printing performance can be established.

Influences of engineering spoil on the properties and microstructure of 3D printable magnesium cement

Using magnesium cement to solidify engineering spoil (ES) is an eco-friendly option for disposing of solid waste. This paper proposes a novel type of magnesium cement for 3D printing (MC-3DP) using ES as an additive to magnesium oxychloride cement (MOC). The effect of the ES on the mechanical properties and water resistance of the MC-3DP paste and mortar were investigated. The MC-3DP paste was subjected to a hydration heat test and microscopic tests (X-ray diffraction and scanning electron microscopy). The 3D printing properties of the MC-3DP paste were evaluated, including the open time, flowability, extrudability, buildability, and hardened properties. The results showed that the ES improved the MC-3DP’s mechanical properties and water resistance. The results of the hydration heat test, XRD analysis, and SEM analysis revealed that the addition of ES did not result in new hydration products in the MC-3DP paste. Instead, the ES served as a filler and improved the performance of MC-3DP. Additionally, the ES addition significantly improved the printing properties of the MC-3DP paste, and the degree of improvement increased with the ES content. Our results provide new insights into developing methods to upcycle ES.

3D printable strain hardening cementitious composites (3DP-SHCC), tailoring fresh and hardened state properties

With the introduction of 3D concrete printing, research started on how to include reinforcement in 3D printed structures. Initial studies on the implementation of strain hardening cementitious composites (SHCC) as self-reinforcing printable mortars have shown promising results. The development of this new type of SHCC comes with additional challenges. Where SHCC by itself is already a complex material engineered to achieve specific micromechanical behaviour under tensile loading, its application in 3D printing techniques imposes even more requirements - the so-called ‘printability’ requirements. The question that rises for the development of this new material is how to achieve printability without losing strain hardening capacity. This paper investigates the influence of raw materials and additives, such as silica fume, limestone powder, viscosity modifying agents and water, on the fresh and hardened mechanical properties of printable SHCC, by improving on a previously developed mixture. The fresh material mixtures were subjected to slump flow tests to analyse their applicability for 3D printing. In hardened state, the mixtures were tested on their compressive strength and flexural strength to assess their potential for strain hardening capacity. Finally, two mixtures were selected for printing. The mixtures were assessed on print quality and buildability by the deployment of a buildability test. Furthermore, the printed elements were mechanically tested at 28 days, on compressive strength, flexural strength and uniaxial tensile strength and strain. It was concluded that the silica fume content and water to solid ratio are relevant variables for 3DP-SHCC optimization. The study has yielded two 3DP-SHCC mix designs that display significant strain hardening capacity and good printability properties.

Rheo-fermentation properties of bread dough with different gluten contents processed by 3D printing

The rheological properties of dough closely correlate to a dough’s ability to be three-dimensionally (3D) printed, but only weakly characterize its fermentation and baking process. This study aimed to use rheo-fermentation properties to predict rheological properties of dough, thereby obtaining indirect information on both 3D printing properties and post-processing characteristics. The 3D printing behavior and baking quality of the dough were measured. A gluten content of 13% was found to be the most suitable for 3D printing and exhibited desirable performance during fermentation and baking. Pearson correlation analysis revealed a strong correlation between rheological properties and rheo-fermentation properties. Using partial least squares regression-based models, the coefficients of determination of the prediction for rheological parameters (G′, G″, η*) were 0.920, 0.854 and 0.863, respectively, with corresponding residual prediction deviation values of 3.063, 3.774, and 4.773. These findings suggest that 3D printing of bread dough products can be easily and successfully accomplished.

Enhanced fresh-keeping capacity of printed surimi by Ca2+-nano starch-lutein and its nondestructive freshness monitoring based on 4D printed anthocyanin

To solve undiscernible freshness changes of printed functional surimi while maintaining printed shape, 4D printable color-changing material were prepared. Firstly, based on results of printing properties and fresh-keeping of Ca2+-NS-L-surimi, it showed better printing effects (enhanced mechanical strength) and good preservation (inhibition of amino acids decomposition, bacterial growth). However, freshness changes of printed Ca2+-NS-L-surimi were not distinguished directly. To avoid that, 4D printable color-changing material—anthocyanin-hydroxypropyl methyl cellulose-xanthan gum-carrageenan (AHXK) was prepared for indicating freshness through discoloration. Printing results showed AHX with 5 % K had the most suitable mechanical strength (appropriate gel strength, texture, rheology) for printing. Based on that, AHXK had stable color (ΔE fluctuation <5) and was sensitive to pH and ammonia (obvious discoloration; ΔE > 10). Actual freshness monitoring results (co-printing of AHXK-surimi) exhibited significant discolorations, especially for HXK with 0.75 % A. It became green during refrigeration of 3–5 d (keeping fresh, ΔE < 4), brighter green at 7 d (decreased freshness, ΔE > 6), turned yellow at 9 d (spoilage, ΔE > 16), which were distinguished significantly with naked eyes rather than traditional freshness determining. In conclusion, printed AHXK-functional surimi exhibited good printing, preservation and nondestructive freshness monitoring, facilitating application of 3D printed functional surimi.

A biobased epoxy vitrimer/cellulose composite for 3D printing by Liquid Deposition Modelling

Conventional epoxy polymers are obtained from oil-based resources and their structure is formed by permanent covalent crosslinks. Therefore, this class of materials is now considered non environmentally friendly as they are neither renewable nor reprocessable and recyclable. In this study, we prepared a vitrimeric material based on an epoxy-functionalised cardanol cured with a biobased polycarboxylic acid. In the presence of a zinc-containing catalyst, a soft polyester with a Tg = −13 °C was obtained; its reprocessability by a chemical method was demonstrated to be feasible without any relevant change in properties once a second curing cycle was completed. The vitrimeric polyester was then used in combination with cellulose powder for the preparation of a sustainable and biobased composite. The matrix/filler mass fraction was tailored to obtain a composite paste with suitable rheological properties for 3D printing via Liquid Deposition Modelling (LDM). Preliminary printing tests were successful, and the vitrimeric printed parts were then thermally cured retaining the shape. The suitability of the vitrimeric composite for additive manufacturing was thus confirmed: the new material can provide a solution to 3D printing of recyclable thermosetting biobased polymers.

An Innovative Approach to Fabrication With Photo-Cured Resins by Shell-Printed-Core-Casting

Abstract Modified LCD-based method was used to print three-dimensional (3D) elements. This innovative method combines printing the external shell and filling, thus obtaining mould by casting resin. In order to compare the properties of prints obtained with this method with the ones fabricated in a standard procedure, we conducted bending tests of vertically/horizontally printed and shell-printed cast specimens. The shell-cast samples showed higher flexural strength and larger values of apparent Young’s modulus. The presented results also concern the kinetics of curing samples obtained with different fabrication routes.

Dynamically Cross-Linked Granular Hydrogels for 3D Printing and Therapeutic Delivery.

Granular hydrogels have recently emerged as promising biomaterials for tissue engineering and 3D-printing applications, addressing the limitations of bulk hydrogels while exhibiting desirable properties such as injectability and high porosity. However, their structural stability can be improved with post-injection interparticle cross-linking. In this study, we developed granular hydrogels with interparticle cross-linking through reversible and dynamic covalent bonds. We fragmented photo-cross-linked bulk hydrogels to produce aldehyde or hydrazide-functionalized microgels using chondroitin sulfate. Mixing these microgels facilitated interparticle cross-linking through reversible hydrazone bonds, providing shear-thinning and self-healing properties for injectability and 3D printing. The resulting granular hydrogels displayed high mechanical stability without the need for secondary cross-linking. Furthermore, the porosity and sustained release of growth factors from these hydrogels synergistically enhanced cell recruitment. Our study highlights the potential of reversible interparticle cross-linking for designing injectable and 3D printable therapeutic delivery scaffolds using granular hydrogels. Overall, our study highlights the potential of reversible interparticle cross-linking to improve the structural stability of granular hydrogels, making them an effective biomaterial for use in tissue engineering and 3D-printing applications.

Aqueous Calcium Phosphate Cement Inks for 3D Printing

Mimicking the native properties and architecture of natural bone is a remaining challenge within the field of regenerative medicine. Due to the chemical similarity of calcium phosphate cements (CPCs) to bone mineral, these cements are well studied as potential bone replacement material. Nevertheless, the processing and handling of CPCs into prefabricated pastes with adequate properties for 3D printing has drawbacks due to slow reaction times, limited design freedom, as well as fabrication issues such as filter pressing during ejection through thin nozzles. Herein, an aqueous cement paste containing α‐tricalcium phosphate powder is proposed, which is stabilized by sodium pyrophosphate (Na4P2O7·10H2O) as additive. Since high powder loadings within pastes can result in filter pressing during extrusion, various concentrations and molecular weights of hyaluronic acid (HyAc) are added to the cement paste, resulting in reduced filter pressing during 3D extrusion‐based printing. These cement pastes are investigated regarding their setting reaction after activation with orthophosphate solution by isothermal calorimetry and X‐ray diffraction, as well as their hardening performance using Imeter measurements, while the processability is assessed by extrusion through 1.2 and 0.8 mm cannulas. The 3D‐printed structures with appropriate HyAc molecular weight and concentration demonstrate suitable mechanical properties and resolution for clinical application.

UV-Curing Additive Manufacturing of Bio-Based Thermosets: Effect of Diluent Concentration on Printing and Material Properties of Itaconic Acid-Based Materials.

In the quest toward sustainable thermosets, research has been conducted on various polymer classes like epoxy, benzoxazines, acryl-/methacrylates, etc. One particular group that can also be utilized as sustainable inks for additive manufacturing is itaconic acid-based unsaturated polyester resins. However, due to increased viscosity of the resins, the use of reactive diluents is required to increase their processability. While research has focused on creating different polymeric structures to expand the possible applications, the required amount of diluent has not received equal attention. In this work, a group of itaconic acid-based polyesters was synthesized to create a series of formulations with different reactive diluent contents. The physicochemical properties of the prepared formulations, along with their reactivity toward UV light, were assessed via photo-differential scanning calorimetry (photo-DSC), real-time attenuated total reflectance (RT-ATR), and photorheology measurements. The same formulations were then used to fabricate test specimens via digital light processing (DLP) three-dimensional (3D) printing, which were examined as to their thermomechanical properties by means of dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) measurements.

Analysis of the Changes in the Mechanical Properties of the 3D Printed Polymer rPET-G with Different Types of Post-Processing Treatments

The paper deals with the actual topic of mechanical properties of 3D prints made from the polymer material rPET-G and its changes. Using this material in additive technology has great potential in the automotive industry. The research evaluates five different post-processing modifications of 3D prints from rPET-G (recycled polyethylene terephthalate-glycol) material produced by the Fused Filament Fabrication technology. The post-processing included the chemical smoothing of the samples using dichloromethane vapors and heat treatment in an annealing furnace. An epoxy resin, a synthetic coating, and a water-based coating were also applied. The standard was represented by samples without post-processing modifications, both in the form of recycled material and in the form of virgin PET-G. The texture of the samples was evaluated according to EN ISO 4287. Furthermore, the moisture absorption of the samples was evaluated using the gravimetric method according to EN ISO 62. The mechanical testing of the samples was carried out using a tensile test (EN ISO 527-2), a three-point bending test (EN ISO 178), impact strength (EN ISO 179-2), and a cupping test (EN ISO 1520). Degradation of the coatings took place using cyclic tests, which used a combination of exposure in a salt fog environment and in a climate chamber. The results of the experiments indicate that heat treatment appears to be a universal post-processing technology, as this method statistically improves not only the mechanical properties but also significantly reduces moisture absorption.

Investigation and Prediction of the Impact of FDM Process Parameters on Mechanical Properties of PLA Prints

Investigation and Prediction of the Impact of FDM Process Parameters on Mechanical Properties of PLA Prints

Prediction of the mechanical properties of heat-treated fused filament fabrication thermoplastics using adaptive neuro-fuzzy inference system

The requirement for post-processing methods in 3D printing has increased due to its major limitations such as poor mechanical and surface properties. Thermal annealing, a heat-treatment procedure, has proven to be an excellent approach for increasing the mechanical strength of additive manufactured thermoplastics. The optimized thermal annealing parameters for maximum tensile strength are identified. The Adaptive Neuro-fuzzy Inference System (ANFIS) methodology is employed in this study to forecast the tensile strength of thermal annealed fused filament fabricated polylactic acid (PLA), carbon fiber filled polylactic acid (PLA-CF), and polycarbonate acrylonitrile butadiene styrene (PC-ABS). The root mean square error (RMSE) of the predicted tensile strength of PLA, PLA-CF, and PC-ABS are obtained as 1.012, 0.5, and 0.835 respectively. The coefficient of determination for the predicted model of thermoplastics PLA, PLA-CF, and PC-ABS is determined as 0.98, 0.99, and 0.89 respectively. The ANFIS model developed is successful in determining the tensile strength of annealed 3D printed thermoplastics at various annealing conditions of temperature and duration. Further, the study investigates the effect of heat treatment on the compressive, impact, and flexural properties of PLA prints.

Antibacterial Azo Dyes Containing Sulfa Drug Moieties and Their Colour Assessment on Printing Polyester Fabric

AbstractSynthesis of a new series of biologically active dyes containing the sulfa drug nucleus and its use in polyester silk screen printing were presented. Synthesis was performed via azo coupling with C and N Nucleophiles. Spectroscopic tools were used to characterize the synthesized azo derivatives. Also, testing of their printing properties, including fastness to washing, light, rubbing, perspiration, and sublimation were evaluated. The new dyes showed respectable fastness and good antibacterial resistance to the growth of certain species of gram‐positive and gram‐negative bacteria. These low‐cost facile synthesized biologically active dyes could be used for sterilizing textiles.

Comprehensive investigations on the relationship between the 3D concrete printing failure criterion and properties of fresh-state cementitious materials

Comprehensive investigations on the relationship between the 3D concrete printing failure criterion and properties of fresh-state cementitious materials

High internal phase emulsion stabilized by whey protein isolate-gum Arabic Maillard conjugate: Characterization and application in 3D printing

High internal phase emulsions (HIPEs) stabilized by protein-polysaccharide are attracting considerable attention in the food industry and have been used in the emerging 3D printing. However, research on protein-polysaccharide Maillard conjugates with health-promoting effects used in HIPEs and 3D printing is limited. Developing HIPEs with enhanced stability, printability, and desirable functional properties remains a challenge. This study was aimed to investigate the potential of whey protein isolate-gum Arabic Maillard conjugates (WPI-GA-C) as emulsifiers for stabilizing HIPEs and to prepare HIPEs with improved properties for personalized functional foods and 3D printing. The effects of WPI-GA-C concentration and oil mass fraction on the properties of HIPEs were systematically characterized. The results showed that the WPI-GA-C concentration and oil mass fraction had significant effects on the particle size, processability, and textural, rheological and 3D printing properties of HIPEs. The HIPEs stabilized with 3% WPI-GA-C and 80% oil mass fraction exhibited better self-supporting properties, higher viscosity, higher storage modulus, and lower frequency dependence compared with HIPEs prepared with lower WPI-GA-C concentrations (1% and 2%) and lower oil mass fractions (74% and 77%). The prepared HIPEs could be used as food-grade 3D printing inks to print models with good dimensional printing accuracy. In conclusion, WPI-GA-C could be used to prepare stable HIPEs as potential inks for 3D printing. These results provided new insights into personalized functional food applications with protein-polysaccharide Maillard conjugate stabilized emulsions.