3D Printability Research Articles

Rheological properties and 3D printability of tomato-starch paste with different types of starch

In this study, the effect of different types of starch (potato, wheat, corn, tapioca, and mung bean) on the quality of three-dimensional (3D) printed food products containing tomato-starch paste (TSP) was investigated. The printability of TSP was evaluated by examining its rheological and textural properties and the microstructure of 3D printed products. The results showed that the tomato starch paste containing wheat starch had the best printing accuracy and print quality compared to the other samples, which had an extruded line width of 0.93 mm and centre heights and diameters of 18.56 mm and 20.15 mm. The macrorheological and microrheological analysis results showed that the apparent viscosity, loss modulus, storage modulus, and viscoelasticity of the TSP containing wheat starch were significantly higher than those of the other samples (P < 0.05). Low-field nuclear magnetic resonance (LF-NMR) results showed that T21 and T22 of TSP containing wheat starch significantly decreased, thereby improving the retention of printed shapes and deposition of 3D-printed TSP. The analysis of textural properties showed that TSP containing wheat starch had significantly higher strength in terms of hardness, elasticity, cohesion and chewiness, which were 9.58 N, 0.58, 0.31 and 2.13 N, respectively (P < 0.05). Thus, the pseudoplastic gel formed by TSP containing wheat starch exhibited a higher fluidity and structural density than the other samples, which improved the extrudability and shape stability of the printed product as well as the self-supporting properties of TSP.

3D Printable Alginate-Chitosan Hydrogel Loaded With Ketoconazole Exhibits Anticryptococcal Activity.

Natural polymers have recently been investigated for various applications, such as 3D printing and healthcare, including treating infections. Among microbial infections, fungal diseases remain overlooked, with limited therapeutic options and high recurrence. Cutaneous cryptococcosis is an opportunistic fungal infection triggered by mechanical inoculation or hematogenous dissemination of the yeast that causes cryptococcal pneumonia and meningitis. Every year, Cryptococcus neoformans endanger the lives of immunosuppressed hosts, resulting in 180,000 deaths per year. Nonetheless, healthy individuals can also be affected by this fungal infection. Cryptococcosis has a restricted and expensive therapeutic regimen with no topical approach to skin manifestations. This study sought to create a 3D printable biodegradable polymeric hydrogel carrying ketoconazole, a low-cost antifungal drug with reported anticryptococcal activity. The developed hydrogel exhibited good 3D printability and rheological properties, including a pseudoplastic behavior. The FTIR spectra of cross-linked hydrogels revealed interactions between alginate and Ca+2, referred to as the egg-box model, indicated by the decrease in peaks at 1600 and 1410 cm-1. Furthermore, the hydrogel loaded with ketoconazole showed remarkable antifungal activity against C. neoformans strains indicated by inhibition zones, which cross-linking did not seem to affect its antifungal performance. The developed material remained structurally stable for up to 12 days (288 h) in swelling studies, and preliminary cytotoxicity performed with V79 cells indicates potential for invivo studies and topical application.

3D Printable Polymeric Composite Material with Enhanced Conductivity Achieved by Affinity Matching.

Polymer-based conductive composites are lightweight, low-cost, and easily processable materials with important applications in various fields. However, achieving highly conductive and 3D printable polymer-based conductive composites remains challenging. In this study, we successfully developed a highly conductive composite suitable for direct ink writing 3D printing using unsaturated polyester resin as the polymer matrix and graphene nanosheets as conductive fillers and rheological modifiers. Due to the well-matched affinity between graphene nanosheets and unsaturated polyester, the graphene nanosheets aggregate within the unsaturated polyester, forming a 3D conductive network. Moreover, the shearing force during direct ink writing 3D printing induces the orientation of the 2D graphene nanosheets, significantly enhancing their conductivity along the printing direction. At room temperature, the unsaturated polyester resin/graphene composite shows a high conductivity of 69.9 S m-1 while maintaining excellent 3D printability. Structures printed using this material exhibit improved heat dissipation and electromagnetic shielding performance. The reported unsaturated polyester resin/graphene nanosheet composites demonstrate outstanding electrical and heat conductivity and excellent processability, making them promising candidates for applications in electromagnetic shielding, printed electronics, and other fields.

On-demand imidazolidinyl urea-based tissue-like, self-healable, and antibacterial hydrogels for infectious wound care

Bacterial wound infections are a growing challenge in healthcare, posing severe risks like systemic infection, organ failure, and sepsis, with projections predicting over 10 million deaths annually by 2050. Antibacterial hydrogels, with adaptable extracellular matrix-like features, are emerging as promising solutions for treating infectious wounds. However, the antibacterial properties of most of these hydrogels are largely attributed to extrinsic agents, and their mechanisms of action remain poorly understood. Herein we introduce for the first time, modified imidazolidinyl urea (IU) as the polymeric backbone for developing tissue-like antibacterial hydrogels. As-designed hydrogels behave tissue-like mechanical features, outstanding antifreeze behavior, and rapid self-healing capabilities. Molecular dynamics (MD) simulation and density functional theory (DFT) calculation were employed to well-understand the extent of H-bonding and metal-ligand coordination to finetune hydrogels’ properties. In vitro studies suggest good biocompatibility of hydrogels against mouse fibroblasts & human skin, lung, and red blood cells, with potential wound healing capacity. Additionally, the hydrogels exhibit good 3D printability and remarkable antibacterial activity, attributed to concentration dependent ROS generation, oxidative stress induction, and subsequent disruption of bacterial membrane. On top of that, in vitro biofilm studies confirmed that developed hydrogels are effective in preventing biofilm formation. Therefore, these tissue-mimetic hydrogels present a promising and effective platform for accelerating wound healing while simultaneously controlling bacterial infections, offering hope for the future of wound care.

High Self‐Supporting Chitosan‐Based Hydrogel Ink for In Situ 3D Printed Diabetic Wound Dressing

AbstractCustomizable 3D‐printed biopolymer hydrogels, highly sought after for diabetic wound management, face challenges in clinical application due to weak physical crosslinking within their constituent inks. In this study, a novel chitosan‐based hydrogel ink with a dense yet reversible physical crosslinking network is subtly designed for the rapid in situ fabrication of personalized diabetic wound dressing. This robust network is established through multiple electrostatic and hydrogen bonding interactions between unique carboxymethyl chitosan and nanoclay, further reinforced by the introduction of amide bonds, which act as double hydrogen bond donors/acceptors. Benefiting from this network, the ink with low nanoclay content exhibits remarkable self‐supporting properties, enabling high‐fidelity, large‐scale, and complex 3D printability without additional processing, while substantially retaining its inherent rheological properties after autoclave sterilization and the incorporation of active components. Given these advantages, this multifunctional 3D printable hydrogel can be rapidly in situ constructed on diabetic wounds. Simultaneously, the 3D‐printed hydrogel demonstrates biodegradability, anti‐swelling, and appropriate mechanical properties, along with remarkable in vitro antibacterial and pro‐angiogenic capabilities, leading to effective diabetic wound healing in vivo. This work offers a new strategy for creating highly self‐supporting biopolymer inks and paves the way for developing advanced personalized wound dressings.

3D-Printable Gelatin Methacrylate-Xanthan Gum Hydrogel Bioink Enabling Human Induced Pluripotent Stem Cell Differentiation into Cardiomyocytes.

We describe the development of a bioink to bioprint human induced pluripotent stem cells (hiPSCs) for possible cardiac tissue engineering using a gelatin methacrylate (GelMA)-based hydrogel. While previous studies have shown that GelMA at a low concentration (5% w/v) allows for the growth of diverse cells, its 3D printability has been found to be limited by its low viscosity. To overcome that drawback, making the hydrogel both compatible with hiPSCs and 3D-printable, we developed an extrudable GelMA-based bioink by adding xanthan gum (XG). The GelMA-XG composite hydrogel had an elastic modulus (~9 kPa) comparable to that of cardiac tissue, and enabled 3D printing with high values of printing accuracy (83%) and printability (0.98). Tests with hiPSCs showed the hydrogel's ability to promote their proliferation within both 2D and 3D cell cultures. The tests also showed that hiPSCs inside hemispheres of the hydrogel were able to differentiate into cardiomyocytes, capable of spontaneous contractions (average frequency of ~0.5 Hz and amplitude of ~2%). Furthermore, bioprinting tests proved the possibility of fabricating 3D constructs of the hiPSC-laden hydrogel, with well-defined line widths (~800 μm).

Facile fabrication of 3D-printed cellulosic fiber/polylactic acid composites as low-cost and sustainable acoustic panels

This work presents a green, cost-effective and eco-friendly strategy to reduce noise pollution by developing biopolymer-based 3D-printed acoustic panels. We successfully fabricated two series of composites by varying the weight percentage (wt%) of cellulose fibers of water hyacinth (WH) and pineapple leaf (PAL), with polylactic acid (PLA) as the matrix via the heat-press method. All samples were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Physico-mechanical properties, including hardness, tensile, and impact strength, were improved with increasing fiber loading. Filaments of 1 wt% water hyacinth fibers (WHFs) in PLA (1 WHF/PLA) and 1 wt% pineapple leaf fibers (PALFs) in PLA (1 PALF/PLA) were prepared and tested for 3D printability. The sound absorption coefficients (α) of the 3D-printed panels were investigated from 500 to 5000 Hz sound frequency range. The 3D-printed 1 WHF/PLA and 1 PALF/PLA acoustic panels achieve a maximum α (α-max) of 0.55 and 0.83 at 5000 and 4000 Hz, respectively, featuring the first work to report α-max > 0.5 at low fiber loadings in the high-frequency sound range. The tensile strength of the 3D-printed versions is significantly higher than non-3D-printed counterparts and commercial acoustic absorbers. Our data suggest the prepared 3D-printed panels are excellent candidates for acoustic applications at high-frequency noises. This study exhibits a facile, environmentally benign and sustainable approach to construct highly efficient and mechanically robust biopolymer-based 3D-printed sound-proof panels, which have promising potential as green engineering materials. Interestingly, this research also proposes a mitigation technology for the freshwater invader, Eichhornia crassipes (water hyacinths).

Mechanistic understanding of enhancing bioactivity via bio-ionic liquid functionalization of biomaterials

The selection of biomaterials is a pivotal criterion for designing tissue engineering scaffolds, crucial for diverse biomedical applications. While natural biomaterials offer inherent bioactivity and biocompatibility, fine-tuning their properties for specific applications poses challenges. Conversely, synthetic biomaterials, while highly customizable, are often bio-inert. Functionalizing materials with bioactive molecules can improve cell-material interactions. Prevailing approaches utilizing RGD peptides or natural/synthetic composites have drawbacks including cost and immunogenicity. Bio-ionic liquids (BILs), a class of biocompatible ionic liquids derived from natural or synthetic biomolecules, offer a potential alternative. Herein, we present the biofunctionalization of a bio-inert polyethylene glycol diacrylate (PEGDA) with an acrylated choline-based BIL (“BioPEG”) as a method for enhancing the bioactivity of biomaterials. Cell studies using mouse myoblast C2C12 and human mesenchymal stem cells (hMSCs) revealed the excellence of BioPEG hydrogels in promoting cell attachment, growth, proliferation, and differentiation. Computational molecular dynamics (MD) simulations elucidated the mechanism by which BIL facilitates cell interaction with PEGDA. 3D printability of BioPEG hydrogel was showcased using a digital light processing (DLP) bioprinter, with printed scaffolds demonstrating excellent cytocompatibility. Collectively, these findings present BIL as a versatile bioactive agent for augmenting cell adhesion to materials, thus enriching the repertoire of biomaterials for advanced tissue engineering.

Citrus fibers improve rheology of OSA starch-based high internal phase emulsion for 3D printed elderly foods

3D printing ready-to-eat emulsions using trans-fat-free edible oil, presents a significant challenge due to the complexities involved in achieving the necessary material structure, rheological properties, and stability. This study fabricated High Internal Phase Emulsions (HIPEs) stabilized with citrus fibers and octenyl succinic anhydride (OSA) modified waxy starch, serving as the printable inks for 3D-printable elderly foods. These printable inks exhibited a pseudoplastic gel structure, which provided enhanced extrudability and improved shape retention. The incorporation of citrus fiber, water, OSA starch, sunflower oil at a concentration of 0.3 wt%, 22.7 % wt %, 2 % wt%, 75 wt% in the 3D-printed HIPEs resulted in optimal addition, yielding the highest level of shape accuracy. Compared to the addition of OSA-modified starch, microstructural analysis and rheological testing (using Lissajous-Bowditch plots) indicated that the addition of citrus fiber had a greater impact on the rheological and textural properties of the HIPEs, which improved shape retention and fluidity of the HIPEs, and ensure the stability of continuous extrusion printing. Additionally, bionic tribological properties demonstrated that tribological properties of the prepared HIPEs were very close to the ones of mayonnaise, which indicating that the prepared HIPEs had smooth texture and easy-to-chew properties for the elderly. These findings offered a comprehensive understanding of the structure–function relationship between the molecular structures of HIPEs and their 3D printability, providing technical insights for the development of 3D-printed emulsion-based ready-to-eat elderly food products. This study provided a good industrialized method for HIPEs stabilized with only fruit dietary fiber and modified starch, and facilitated the development of emulsion-based ready-to-eat food products with 3D printability.

Polymer microsphere inks for semi-solid extrusion 3D printing at ambient conditions

Extrusion-based 3D printing methods have great potential for manufacturing of personalized polymer-based drug-releasing systems. However, traditional melt-based extrusion techniques are often unsuitable for processing thermally labile molecules. Consequently, methods that utilize the extrusion of semi-solid inks under mild conditions are frequently employed. The rheological properties of the semi-solid inks have a substantial impact on the 3D printability, making it necessary to evaluate and tailor these properties. Here, we report a novel semi-solid extrusion 3D printing method based on utilization of a Carbopol gel matrix containing various concentrations of polymeric microspheres. We also demonstrate the use of a solvent vapor-based post-processing method for enhancing the mechanical strength of the printed objects. As our approach enables room-temperature processing of polymers typically used in the pharmaceutical industry, it may also facilitate the broader application of 3D printing and microsphere technologies in preparation of personalized medicine.

Regulation of tapioca starch 3D printability by yeast protein: Rheological, textural evaluation, and machine learning prediction

This article investigated the effects of yeast protein (YP) on gel rheology, texture, and 3D printability of tapioca starch and the feasibility of Principal component analysis (PCA) and support vector machine (SVM) algorithms for classification and prediction of printability. The results indicated that increasing YP content enhanced the viscosity, storage and loss moduli, and hardness, thereby improving extrudability and supportability of 3D printing. The addition of 15% YP exhibited the best 3D printing performance, but excessively high YP addition hindered ink extrusion. PCA analysis based on rheological and texture indices categorized the ink's 3D printing performance into four classes: poor support and low printing accuracy; good support but low printing accuracy; good support and high printing accuracy; and non-smooth extrusion. Furthermore, SVM algorithm used texture data to predict printability classification, with the highest prediction accuracy (91.67%) achieved at polynomial kernel among four different kernel functions. These results confirm that YP can serve as a potential ink for 3D printing and underscore SVM's efficacy in predicting ink's 3D printing performance.

Prediction of 3D printability and rheological properties of different pineapple gel formulations based on LF-NMR

In this study, a pineapple-starch-xanthan gum system was prepared using fresh pineapple juice, maize starch, and xanthan gum (XG). The feasibility of using low-field nuclear magnetic resonance (LF-NMR) to predict pineapple gels' rheological properties and printability was evaluated. Results indicated that as maize starch and XG increased, the gel transformed from unable to support printed models to a stable shape, eventually becoming too viscous for printing. Principal component analysis and Fisher discriminant analysis classified the gels into four categories based on their rheological properties, aligning with the actual printing results. Pearson correlation analysis showed a strong correlation between the LF-NMR parameters and the rheological properties of gels. The partial least squares (PLS) and back-propagation artificial neural network (BP-ANN) models constructed using the LF-NMR parameters can effectively predict the rheological properties of pineapple gels. Therefore, LF-NMR is a valuable, non-destructive method for quickly assessing pineapple gels' 3D printing suitability.

Enhancing alginate dialdehyde-gelatin (ADA-GEL) based hydrogels for biofabrication by addition of phytotherapeutics and mesoporous bioactive glass nanoparticles (MBGNs)

This study explores the 3D printing of alginate dialdehyde-gelatin (ADA-GEL) inks incorporating phytotherapeutic agents, such as ferulic acid (FA), and silicate mesoporous bioactive glass nanoparticles (MBGNs) at two different concentrations. 3D scaffolds with bioactive properties suitable for bone tissue engineering (TE) were obtained. The degradation and swelling behaviour of films and 3D printed scaffolds indicated an accelerated trend with increasing MBGN content, while FA appeared to stabilize the samples. Determination of the degree of crosslinking validated the increased stability of hydrogels due to the addition of FA and 0.1% (w/v) MBGNs. The incorporation of MBGNs not only improved the effective moduli and conferred bioactive properties through the formation of hydroxyapatite (HAp) on the surface of ADA-GEL-based samples but also enhanced VEGF-A expression of MC3T3-E1 cells. The beneficial impact of FA and low concentrations of MBGNs in ADA-GEL-based inks for 3D (bio)printing applications was corroborated through various printing experiments, resulting in higher printing resolution, as also confirmed by rheological measurements. Cytocompatibility investigations revealed enhanced MC3T3-E1 cell activity and viability. Furthermore, the presence of mineral phases, as confirmed by an in vitro biomineralization assay, and increased ALP activity after 21 days, attributed to the addition of FA and MBGNs, were demonstrated. Considering the acquired structural and biological properties, along with efficient drug delivery capability, enhanced biological activity, and improved 3D printability, the newly developed inks exhibit promising potential for biofabrication and bone TE.

3D Bioprinting Using Universal Fugitive Network Bioinks.

Three-dimensional (3D) bioprinting has emerged with potential for creating functional 3D tissues with customized geometries. However, the limited availability of bioinks capable of printing 3D structures with both high-shape fidelity and desired biological environments for encapsulated cells remains a key challenge. Here, we present a 3D bioprinting approach that uses universal fugitive network bioinks prepared by loading cells and hydrogel precursors (bioink base materials) into a 3D printable fugitive carrier. This approach constructs 3D structures of cell-encapsulated hydrogels by printing 3D structures using fugitive network bioinks, followed by cross-linking printed structures and removing the carrier from them. The use of the fugitive carrier decouples the 3D printability of bioinks from the material properties of bioink base materials, making this approach readily applicable to a range of hydrogel systems. The decoupling also enables the design of bioinks for the biological functionality of the final printed constructs without compromising the 3D printability. We demonstrate the generalizable 3D printability by printing self-supporting 3D structures of various hydrogels, including conventionally non-3D printable hydrogels and those with a low polymer content. We conduct preprinting screening of bioink base materials through 3D cell culture to select bioinks with high cell compatibility. The selected bioinks produce 3D constructs of cell-encapsulated hydrogels with both high-shape fidelity and high cell viability and proliferation. The universal fugitive network bioink platform could significantly expand 3D printable bioinks with customizable biological functionalities and the adoption of 3D bioprinting in diverse research and applied settings.

Indirect prediction of the 3D printability of polysaccharide gels using multiple machine learning (ML) models

In this paper, the capabilities of NIR spectroscopy and LF-NMR data were compared for rapidly predicting the rheological properties of polysaccharide gels and assessing their printability. Seven machine learning (ML) models were established for rheological property prediction based on partial least squares regression (PLSR), support vector regression (SVR), back propagation artificial neural network (BPANN), one-dimensional convolutional neural network (1D CNN), recurrent neural network (RNN), long short-term memory (LSTM), and Transformer. The results showed that among the seven models, the SVR, BPANN, and 1D CNN models based on NIR spectroscopy effectively predicted the rheological parameters of polysaccharide gels, with the highest R2 in the prediction set reaching 0.9796 and the highest RPD reaching 7.0708. For most polysaccharide gels, using the LF-NMR relaxation time distribution curves provided better predictions of rheological properties than using transverse relaxation time and peak area. Among the seven models, the PLSR, SVR, 1D CNN, and Transformer models effectively predicted the rheological characteristics based on LF-NMR parameters, with the highest R2 in the prediction set reaching 0.9869 and the highest RPD reaching 8.7220. This study successfully established a prediction system for the rheological behaviors and 3D printing performance of polysaccharide gels using NIR spectroscopy and LF-NMR data combined with ML methods, achieving an intelligent assessment of the 3D printing behavior of polysaccharide gels.

Regulating emulsion properties through tannin acid-mediated gelatin/cellulose nanocrystal complexes: From low-oil emulsion to high internal phase emulsion gel for 3D printing

In this study, a stabilized low-oil emulsion and high internal phase emulsion gels (HIPE gels) integrated preparation method is proposed. Highly stable low-oil emulsions, prepared using tight ternary complexes formed by incorporating tannic acid (TA) into gelatin/cellulose nanocrystals (GLT/CNC) complexes mainly through strengthening hydrogen-bonding interaction. The subsequent heating-centrifugation process was used to enable the conversion of GLT/CNC/TA stabilized low-oil emulsions to stabilized HIPE gels, and systematically investigated the regulation of emulsion properties by TA concentrations. The ternary complexes formed by appropriate concentration of TA (0.6 %) can form stable low-oil emulsions with smallest average particle (36.1 ± 0.25 μm) size and best rheological properties, while the rheological properties of HIPE gels were similarly regulated by the TA concentration (0 %, 0.2 %, 0.6 %, 1.0 %, 1.2 %). Heating induced flocculation of low-oil emulsions without causing demulsification, allowed for the subsequent centrifugation to yield stable HIPE gels, significantly superior to the GLT/CNC/TA-stabilized HIPE gels prepared by conventional methods that typically exhibit thermal instability. TA effectively promoted the interfacial adsorption of GLT/CNC and tight stacking of oil droplets to build a more stable network structure in the continuous phase. HIPE gels with 0.6 % TA demonstrated excellent 3D printability with optimal dimensional resolution and surface quality, presenting a novel strategy for HIPE gel preparation and versatile emulsion applications.

The impact of dietary fibers on the construction and molecular network of extrusion-based 3D-printed chicken noodles: Unlocking the potential of specialized functional food

3D printing technology is promising in creating specialized functional foods, such as high-protein and high dietary fiber noodles. In this study, chicken breast-based noodles with varying proportions of oat bran and konjac flour were developed. The research analyzed the physicochemical, digestive properties, and 3D printability of these chicken-based doughs and noodles. The results indicated that the inclusion of fiber-rich flours notably enhanced dough viscosity and viscoelasticity. However, exceeding 4 % konjac flour negatively affected cooking quality and texture due to its strong water absorption capacity. The experimental group with fiber-rich flours exhibited prolonged starch/protein digestion time compared to the Control group. The increased ability to bind water in the fiber rich formula likely restricted water mobility, affecting mass transition in the “water channel”. Notably, chicken noodles fortified with 6 % oat bran and 2 % konjac flour displayed the highest 3D printability. These results offer valuable insights for the industry in selecting appropriate dietary fiber sources for the development of nutritionally balanced 3D-printed meal options.

Exploring gelation properties and structural features on 3D printability of compound proteins emulsion gels: Emphasizing pH-regulated non-covalent interactions with xanthan gum

Rational regulation of pH and xanthan gum (XG) concentration has the potential to modulate interactions among macromolecules and enhance 3D printability. This study investigated non-covalent interactions between XG and other components within compound proteins emulsion gel systems across varying pH values (4.0–8.0) and XG concentrations (0–1 wt%) and systematically explored impacts of gelation properties and structural features on 3D printability. The results of rheological and structural features indicated that pH-regulated non-covalent interactions were crucial for maintaining structural stability of emulsion gels with the addition of XG. The 3D printability of emulsion gels would be significantly improved through moderate depletion flocculation produced when XG concentration was 0.75 wt% at the pH 6.0. Mechanical properties like viscosity exhibited a strongly negative correlation with 3D printability, whereas structural stability showed a significantly positive correlation. Overall, this study provided theoretical insights for the development of emulsion gels for 3D printing by regulating non-covalent interactions.

Effects of coarse aggregates on 3D printability and mechanical properties of ultra high performance fiber reinforced concrete

3D printing of ultra high performance fiber reinforced concrete (UHPFRC) suffers from high shrinkage and poor interlayer properties. To mitigate these problems, this study develops new mixtures of UHPFRC materials containing coarse aggregates (CA), and critically examines their suitability for 3D printing (3DP). Totally 90 mould-cast and 3DP cylinder and beam specimens with different CA sizes (5–15 mm) and CA-binder ratios (0.3–0.5) were tested under compression and bending in three directions. The internal distribution and volume fractions of steel fibers and pores and the crack trajectories were characterized and analysed by micro X-ray CT scanned 3D images with 37 μm voxel resolution. The results show that adding more and bigger CAs into UHPFRC reduced the flowability but enhanced the buildability with desired extrudability achieved by adjusting 3D printing velocity. Although the compressive strength of the 3DP cylinders was 15–42 % lower than that of the mould-cast ones due to higher porosities, over 100 MPa strength was still achieved for all the 3DP cylinders with less than 10 % anisotropy. The CT images did not show evident interlayers and interlayer delamination under compression, indicating the new 3DP mixtures and printing parameters may have highly promoted cement hydration. The flexural strength of 3DP beams was 3–34 % higher than that of the cast ones, because most fibres were oriented in the printing or beam axis direction as represented by overall orientation indices calculated from CT images, thereby providing significant crack-bridging effects. The developed new mixtures are therefore well suited for 3D printing, particularly for fabrication of structural members with preferred fibre orientation, such as beams, slabs and shells.

3D Printed Concrete: Fresh and Hardened Properties

3D concrete printing (3D CP) is an advanced form of additive manufacturing (AM), that allows for the creation of complex geometrical structures using concrete. This technology has the potential to reduce construction time and labour costs while minimizing material waste. However, there are also challenges related to material properties, structural integrity, and standardization of construction practices. The primary challenge in developing 3D printable cementitious materials lies in engineering specific fresh properties that enable extrusion-based printing. Unlike cast concrete, where formwork provides dimensional stability during the printing process, the absence of formwork in 3D printing necessitates fresh mixtures with low-slump and high-thixotropy to be suitable for concrete 3D printing. Additionally, the orthotropic nature of the resulting 3D printed object due to the extrusion process impacts its mechanical properties. Therefore, this research aims to study the effect of water content and loading directions on 3D printed concrete. A pre-mix material from Sika was used in this study. Three mixes were prepared by using three different water to dry material (w/d) ratios, 0.140 l/kg, 0.145 l/kg and 0.150 l/kg. The experiments focused on analysing flowability, green strength, mechanical properties (compressive strength, flexural strength, and modulus of elasticity), water absorption, porosity, and chemical transformations at high temperatures through thermoanalytical measurement. The results showed that the mixture containing 0.145 l/kg (w/d) exhibited satisfactory 3D printability, optimal mechanical performance, lower porosities compared with mixtures 0.140 and 0.150, and same total porosity compared with cast specimen.