3D-printed Structures Research Articles

Fabrication of hierarchically porous trabecular bone replicas via 3D printing with high internal phase emulsions (HIPEs).

Combining emulsion templating with additive manufacturing enables the production of inherently porous scaffolds with multiscale porosity. This approach incorporates interconnected porous materials, providing a structure that supports cell ingrowth. However, 3D printing hierarchical porous structures that combine semi-micropores and micropores remains a challenging task. Previous studies have demonstrated that using a carefully adjusted combination of light absorbers and photoinitiators in the resin can produce open surface porosity, sponge-like internal structures, and a printing resolution of about 150 µm. In this study, we explored how varying concentrations of tartrazine (0, 0.02, 0.04, and 0.08 wt%) as a light absorber affect the porous structure of acrylate-based polymerized Medium Internal Phase Emulsions (polyMIPEs) fabricated via vat photopolymerization. Given the importance of a porous and interconnected structure for tissue engineering and regenerative medicine, we tested cell behavior on these 3D-printed disk samples using MG-63 cells, examining metabolic activity, adhesion, and morphology. The 0.08 wt% tartrazine-containing 3D-printed sample (008T) demonstrated the best cell proliferation and adhesion. To show that this HIPE resin can be used to create complex structures for biomedical applications, we 3D-printed trabecular bone structures based on microCT imaging. These structures were further evaluated for cell behaviour and migration, followed by microCT analysis after 60 days of cell culture. This research demonstrates that HIPEs can be used as a resin to print trabecular bone mimics using additive manufacturing, which could be further developed for lab-on-a-chip models of healthy and diseased bone.

Sustainable and Recyclable Acrylate Resins for Liquid-Crystal Display 3D Printing Based on Lipoic Acid.

The development of renewable vinyl-based photopolymer resins offers a promising solution to reducing the environmental impact associated with 3D printed materials. This study introduces a bifunctional lipoate cross-linker containing a dynamic disulfide bond, which is combined with acrylic monomers (n-butyl acrylate) and conventional photoinitiators to develop photopolymer resins that are compatible with commercial stereolithography 3D printing. The incorporation of disulfide bonds within the polymer network's backbone imparts the 3D printed objects with self-healing capabilities and complete degradability. Remarkably, the degraded resin can be fully recycled and reused for high-resolution reprinting of complex structures while preserving mechanical properties that are comparable to the original material. This proof-of-concept study not only presents a sustainable strategy for advancing acrylate-based 3D printing materials, but also introduces a novel approach for fabricating fully recyclable 3D-printed structures. This method paves the way for reducing the environmental impact while enhancing material reusability, offering significant potential for the development of eco-friendly additive manufacturing.

Biomimetic toughening design of 3D-printed polymeric structures: Enhancing toughness through sacrificial bonds and hidden lengths

Spider silk is known for its excellent strength and fracture resistance properties due to its molecular design structure, characterized by sacrificial bonds and hidden lengths. These structures have inspired reinforcements of synthetic polymer materials to enhance toughness. In this study, we mimic these natural toughening mechanisms by designing and manufacturing 3D-printed polymeric structures incorporating overlapping curls consisting of coiling fiber with sacrificial bonds and hidden lengths. Utilizing the liquid rope coiling effect, we manufactured overlapping curls using three polymers: polylactic acid (PLA), liquid crystal polymer (LCP), and polyamide 6 (PA6). Uniaxial tensile tests were performed to characterize the mechanical properties of overlapping curl as a function of geometries, post-treatments, and material constitutive parameters. Our results show that single-sided overlapping curls can fully unfold while double-sided curls are prone to premature failure. Heat-pressure post-treatment was found to significantly increase the load-capacity of the sacrificial bonds by up to ▪ due to increased contact area. However, the defects introduced in the fibre after the break of the sacrificial bonds, make the structure more susceptible to premature failure, limit the complete unfolding of the hidden length, and lead to a decrease up to ▪ of the toughness. To guarantee the complete unfolding of the hidden lengths and improve the toughness, we demonstrate that selecting a polymer material with either high fracture strength (e.g., LCP, ▪) or high fracture strain (e.g., PA6, >2) is crucial, and increase toughness up to ▪ and ▪, respectively.

Continuous Material Deposition on Filaments in Fused Deposition Modeling.

A novel approach, i.e., Continuous Material Deposition on Filaments (CMDF), for the incorporation of active materials within 3D-printed structures is presented. It is based on passing a filament through a solution in which the active material is dissolved together with the polymer from which the filament is made. This enables the fabrication of a variety of functional 3D-printed objects by fused deposition modeling (FDM) using commercial filaments without post-treatment processes. This generic approach has been demonstrated in objects using three different types of materials, Rhodamine B, ZnO nanoparticles (NPs), and Ciprofloxacin (Cip). The functionality of these objects is demonstrated through strong antibacterial activity in ZnO NPs and the controlled release of the antibiotic Cip. CMDF does not alter the mechanical properties of FDM-printed structures, can be applied with any type of FDM printer, and is, therefore, expected to have applications in a wide variety of fields.

Investigating the delamination frequency in 3D-printed PLA-TPU bi-material composite structures under cyclic bending fatigue testing

Investigating the delamination frequency in 3D-printed PLA-TPU bi-material composite structures under cyclic bending fatigue testing

Osteochondral Regeneration With Anatomical Scaffold 3D-Printing-Design Considerations for Interface Integration.

There is a clinical need for osteochondral scaffolds with complex geometries for restoring articulating joint surfaces. To address that need, 3D-printing has enabled scaffolds to be created with anatomically shaped geometries and interconnected internal architectures, going beyond simple plug-shaped scaffolds that are limited to small, cylindrical, focal defects. A key challenge for restoring articulating joint surfaces with 3D-printed constructs is the mechanical loading environment, particularly to withstand delamination or mechanical failure. Although the mechanical performance of interfacial scaffolds is essential, interface strength testing has rarely been emphasized in prior studies with stratified scaffolds. In the pioneering studies where interface strength was assessed, varying methods were employed, which has made direct comparisons difficult. Therefore, the current review focused on 3D-printed scaffolds for osteochondral applications with an emphasis on interface integration and biomechanical evaluation. This 3D-printing focus included both multiphasic cylindrical scaffolds and anatomically shaped scaffolds. Combinations of different 3D-printing methods (e.g., fused deposition modeling, stereolithography, bioprinting with pneumatic extrusion of cell-laden hydrogels) have been employed in a handful of studies to integrate osteoinductive and chondroinductive regions into a single scaffold. Most 3D-printed multiphasic structures utilized either an interdigitating or a mechanical interlocking design to strengthen the construct interface and to prevent delamination during function. The most effective approach to combine phases may be to infill a robust 3D-printed osteal polymer with an interlocking chondral phase hydrogel. Mechanical interlocking is therefore recommended for scaling up multiphasic scaffold applications to larger anatomically shaped joint surface regeneration. For the evaluation of layer integration, the interface shear test is recommended to avoid artifacts or variability that may be associated with alternative approaches that require adhesives or mechanical grips. The 3D-printing literature with interfacial scaffolds provides a compelling foundation for continued work toward successful regeneration of injured or diseased osteochondral tissues in load-bearing joints such as the knee, hip, or temporomandibular joint.

Characterization of PLA/LW-PLA Composite Materials Manufactured by Dual-Nozzle FDM 3D-Printing Processes.

This study investigates the properties of 3D-printed composite structures made from polylactic acid (PLA) and lightweight-polylactic acid (LW-PLA) filaments using dual-nozzle fused-deposition modeling (FDM) 3D printing. Composite structures were modeled by creating three types of cubes: (i) ST4-built with a total of four alternating layers of the two filaments in the z-axis, (ii) ST8-eight alternating layers of the two filaments, and (iii) CH4-a checkered pattern with four alternating divisions along the x, y, and z axes. Each composite structure was analyzed for printing time and weight, morphology, and compressive properties under varying nozzle temperatures and infill densities. Results indicated that higher nozzle temperatures (230 °C and 240 °C) activate foaming, particularly in ST4 and ST8 at 100% infill density. These structures were 103.5% larger on one side than the modeled dimensions and up to 9.25% lighter. The 100% infill density of ST4-Com-PLA/LW-PLA-240 improved toughness by 246.5% due to better pore compression. The ST4 and ST8 cubes exhibited decreased stiffness with increasing temperatures, while CH4 maintained consistent compressive properties across different conditions. This study confirmed that the characteristics of LW-PLA become more pronounced as the material is printed continuously, with ST4 showing the strongest effect, followed by ST8 and CH4. It highlights the importance of adjusting nozzle temperature and infill density to control foaming, density, and mechanical properties. Overall optimal conditions are 230 °C and 50% infill density, which provide a balance of strength and toughness for applications.

Impact response of 3D printed cornstalk-inspired structures: The effect of indenter shape on penetration

This paper reports the mechanical response and damage tolerance of 3D-printed cornstalk-inspired structures subjected to impact loading. Specimens were subjected to dynamic indentation tests at multiple impact energies with flat, hemispherical, and conical indenters. The mechanical properties of the base material (ABS) were measured across varying strain rates using a Shimadzu® Universal Testing Machine and a Split Hopkinson Pressure Bar. The effect of geometrical variations of the constituents on energy-absorbing capability was also investigated. Damage characteristics were interrogated through X-ray CT scans and provided detailed failure modes associated with each indenter shapes. Further, finite element simulations provided insights into the penetration mechanisms associated with the different indenter shapes. The results demonstrated that test specimens impacted by flat indenters absorbed ∼25 % less energy than those impacted by hemispherical and conical indenters. Among the various indenters, the conical shape had the highest duration of contact force within the specimen before experiencing failure by matrix cracking and complete perforation.

ASSESSMENT OF GEOMETRIC DISTORTION OF CANTILEVERS PRINTED WITH DIFFERENT INTERNAL STRUCTURES AFTER DIFFERENT POST-PROCESSES

This study assesses the geometric distortion of cantilevers fabricated from stainless steel 316L with varying internal structures using Selective Laser Melting (SLM) technology. The cantilevers were printed under identical conditions and subsequently post-processed with Wire Electrical Discharge Machining (WEDM) and heat treatment. The geometric deviations were evaluated using a micrometer and a Coordinate-Measuring Machine (CMM). This research underscores the importance of internal structure selection and post-processing in enhancing the geometric accuracy and mechanical stability of 3D-printed slender structures from stainless steel. By demonstrating that internal geometries can significantly influence the end product's structural performance, the findings provide valuable insights for the design and engineering of Additive Manufactured (AM) components, particularly in applications that involve bending.

Effect of 3D printing accuracy by wheat starch gel combined with canola oil

This study investigated the impact of canola oil (CO) on wheat starch (WS) in 3D printing, focusing on intermolecular interactions and gel characteristics. 3D printing performance, microstructure, rheology, texture, proton distribution, thermal properties, molecular structures, and crystal structure were used to analyze the properties of starch gels. The results showed that adding CO improved the similarity between printed products and their models, and facilitated smoother extrusion by enhancing the cohesiveness and adhesiveness of the WS-CO complex. Moreover, adding >6 % CO to the starch gels destabilized the 3D-printed structure, causing the top layer to collapse, which affected the aesthetics and printing accuracy. The WS-4%CO complex demonstrated superior printing performance and enhanced accuracy. FTIR (Fourier Transform Infrared) and NMR (Nuclear Magnetic Resonance) results indicated that the interaction between WS and CO involved non-covalent interactions, primarily hydrophobic interactions. SEM (scanning electron microscope) results further revealed the molecular structure, CO hindered the interaction between amylose and amylopectin, disrupting the ordered structure and increasing lamellar formation, thereby affecting the stability of the 3D printing structure. This experiment provides valuable insights for enriching the nutrition and improving the accuracy of 3D-printed food.

Direct Ink Writing 3D Printing Elastomeric Polyurethane Aided by Cellulose Nanofibrils.

3D printing of a flexible polyurethane elastomer is highly demandable for its potential to revolutionize industries ranging from footwear to soft robotics thanks to its exceptional design flexibility and elasticity performance. Nevertheless, conventional methods like fused deposition modeling (FDM) and vat photopolymerization (VPP) polyurethane 3D printing typically limit material options to thermoplastic or photocurable polyurethanes. In this research, a water-borne polyurethane ink was synthesized for direct ink writing (DIW) 3D printing through the incorporation of cellulose nanofibrils (CNFs), enabling direct printing of complex, monolithic elastomeric structures at room temperature that can maintain the designed structure. Additionally, a solvent-induced fast solidification (SIFS) method was introduced to facilitate room-temperature curing and enhance mechanical properties. The 3D-printed WPU structures demonstrated strong interfacial adhesion, exhibiting high ultimate tensile strength of up to 22 MPa and an elongation at break of 951%. The 3D-printed WPU structures also demonstrated outstanding resilience and durability, capable of enduring more than 100 cycles of compression and tension as well as withstanding vehicle crushing and heavy lifting. This method also shows suitability for 3D printing complex structures such as a vase and an octopus.

3D-Printing Functional Ceramic for One-Step Fabrication of Pd/C Catalytic Reactor

Catalysts are widely used in the chemical industry because of their environmental friendliness and low energy consumption. However, integrated fabrication of catalytic reactors (CRs) remains challenging. In this study, we propose the integrated manufacturing of a palladium-carbon (Pd/C) CR for the first time. The outer shell ink comprises Al2O3 powder and aluminum dihydrogen phosphate (AP), whereas the inner core ink consists of activated carbon powder, AP, and polymethylmethacrylate (PMMA). By integrating with the coaxial 3D printing strategy, the Pd/C CR can be freeform-designed with different core thicknesses, lengths, and shapes (W-type, L-type, and U-type). Based on this, a CR with excellent catalytic properties was further developed by loading palladium (Pd) particles. Typically, the resultant Pd/C CR with a length of 2.5 cm exhibits a catalytic efficiency of up to 97.6% after 60 min. This method of preparing Pd/C CR using coaxial 3D printing combines multimaterial 3D printing, integrated molding, and complex biomimetic structure fabrication. This offers a feasible and cost-effective solution that uses a simple fabrication process.

Nonlinear mechanics of horseshoe microstructure-based lattice design

Enhancing buffering capacity, flexibility, and energy absorption to withstand large deformations in structure remains a challenge. Bio-inspired horseshoe lattice structures, with their curved trusses, exhibit distinct mechanical characteristics compared to conventional metamaterials. However, their mechanical properties under in-plane compression have been rarely explored. This study characterised and modelled three types of novel 3D-printed horseshoe lattice structures, totalling 12 configurations, with unit cell geometry varying based on cell-wall angles ranging from 120°to 210°. The implementation of the FE simulation based on the three-network viscoplastic (TNV) model showed good agreement with the experiments. The results demonstrated that the cell-wall angle in the geometry and the cross-lap joint topology were significantly associated with the failure mechanism of the unit cell and the overall non-linear mechanical behaviour. Increasing the cell-wall angles can prevent beams from failing due to bending and buckling fractures, facilitate the initiation of internal contacts and stretching during in-plane compression. This reveals a configurable mechanism where the flexibility and stability of the lattice structure can trigger strain hardening, resulting in an increase in load-bearing capacity. The sensitivity to strain hardening varies depending on the order of cross-laps within the topology. A colour-pattern tracking method was employed to monitor the progressive stabilisation of lattice structures, and offering a novel approach for the future design of flexible, configurable, and programmable horseshoe-based lattice structures.

Mechanical Property Characterization of 3D-Printed Carbon Fiber Honeycomb Core Composite Sandwich Structures

Mechanical Property Characterization of 3D-Printed Carbon Fiber Honeycomb Core Composite Sandwich Structures

3D-printed gradient conductivity and porosity structure for enhanced absorption-dominant electromagnetic interference shielding

The application of 3D printing for the development of electromagnetic interference (EMI) shielding materials is currently constrained by a limited range of material options and design schemes. In this work, we developed conductivity-modulated polylactic acid (PLA)-MXene composite filaments for fused deposition modeling (FDM) 3D printing, demonstrating excellent printability and durability. Utilizing these filaments, we propose a design scheme focused on absorption-dominant EMI shielding materials. Our design features non-conductive PLA with larger pores at the incident surface, transitioning to layers with increasing conductivity and decreasing pore sizes. This gradient structure minimizes reflection by providing impedance matching and enhances absorption by extending the propagation path of EM waves through multiple reflections and scattering within the pores. Additionally, interfacial polarization effects between air, PLA, and MXene nanoflakes strengthen the absorption mechanisms. Both simulation and experimental results confirm that the combined gradient conductivity and pore size structures significantly improve EMI shielding effectiveness (EMI SE) and absorptivity, achieving an EMI SE of 65 dB and an absorptivity of 0.76 in the X-band. Our findings underscore its potential to create adaptable, high-performance EMI shields suitable for complex geometries and reducing secondary interference.

Energy Absorption Properties of 3D-Printed Polymeric Gyroid Structures for an Aircraft Wing Leading Edge

Laminar flow offers significant potential for increasing the energy efficiency of future transport aircraft. At the Cluster of Excellence SE2A—Sustainable and Energy-Efficient Aviation—the laminarization of the wing by means of hybrid laminar flow control (HLFC) is being investigated. The aim is to maintain the boundary layer as laminar for up to 80% of the chord length of the wing. This is achieved by active suction on the leading edge and the rear part of the wing. The suction panels are constructed with a thin micro-perforated skin and a supporting open-cellular core structure. The mechanical requirements for this kind of sandwich structure vary depending on its position of usage. The suction panel on the leading edge must be able to sustain bird strikes, while the suction panel on the rear part must sustain bending loads from the deformation of the wing. The objective of this study was to investigate the energy absorption properties of a triply periodic minimal surface (TPMS) structure that can be used as a bird strike-resistant core in the wing leading edge. To this end, cubic-sheet-based gyroid specimens of different polymeric materials and different geometric dimensions were manufactured using additive manufacturing processes. The specimens were then tested under quasi-static compression and dynamic crushing loading until failure. It was found that the mechanical behavior was dependent on the material, the unit cell size, the relative density, and the loading rate. In general, the weight-specific energy absorption (SEA) at 50% compaction increased with increasing relative density. Polyurethane specimens exhibited an increase in SEA with increasing loading rate, as opposed to the specimens of the other investigated polymers. A smaller unit cell size induced a more consistent energy absorption, due to the higher plateau force.

Eco-Friendly 3D-Printed Concrete Using Steel Slag Aggregate: Buildability, Printability and Mechanical Properties

Utilizing steel slag aggregate (SA) as a substitute for river sand in 3D concrete printing (3DCP) has emerged as a new technique as natural resources become increasingly scarce. This study investigates the feasibility of using steel slag (SS) as fine aggregate for 3DCP. Ninety mixtures with varying steel slag aggregate-to-cement ratios (SA/C), water-to-cement ratios (W/C), and silica fume (SF) contents were designed to study the workability and compressive strength of the 3D-printed concrete. Additionally, the actual components were printed to evaluate the printability of these mixtures. The experimental results indicate that it is feasible to fully employ SA in concrete for 3D printing. Mixtures with slump values ranging from 40 to 80 mm and slump flow values varying from 190 to 210 mm are recommended for 3D printing. The optimal mix is determined to have SA/C and W/C ratios of 1.0 and 0.51, respectively, and an SF content of 10% by cement weight. A statistical approach was utilized to construct the prediction models for slump and slump flow. Moreover, to predict the plastic failure of the 3D-printed concrete structure, the modified prediction model with an SA roughness coefficient of 4 was found to fit well with the experimental data. This research provides new insights into using eco-friendly materials for 3D concrete printing.

Designs and mechanical responses of 3D-printed Ti6Al4V porous structures based on triply periodic minimal surfaces with different iso-values

With the increasing applications of additive manufacturing in orthopaedic implants and numerous designs of porous structures available, there is a strong need and opportunity to optimize the structure designs for improved bone integration. Here we created a unique group of sheet structures based on triply periodic minimal surface (TPMS) by varying the iso-value and systematically examined how iso-value influences the mechanical performance of sheet diamond TPMS structures compared to the Octet truss structure. Four iso-values (C) 0, 0.25, 0.5, and 0.75 were designed for sheet Diamond (OSD) TPMS with varying porosity, and Ti6Al4V powder bed fusion was used to produce the porous structures. Compressive tests revealed that iso-value C significantly affected mechanical performance, and interestingly, the impact was porosity-dependent. At high relative density (>0.25), OSD0 (C = 0) displayed the highest elastic modulus and yield strength, whereas at low relative density (<0.25), OSD0.5 showed the highest among all OSD structures. Regarding failure mechanisms, OSD0, OSD0.25, and OSD0.75 showed a mixed domination of stretching and bending, while OSD0.5 was predominantly stretching-dominated. Finite Element Analysis (FEA) found that local yielding initiated at cell nodes upon loading, followed by surface bending and the formation of single or multiple shear bands near the cell nodes. This work demonstrated the feasibility of improving the mechanical performance of porous TPMS structures by simple adjustments in their governing trigonometric functions, serving as a starting point to customize porous structures for specific applications.

Uncertainty quantification for damage detection in 3D-printed auxetic structures using ultrasonic guided waves and a probabilistic neural network

Auxetic structures hold significant potential for applications due to their outstanding properties. Ultrasonic waves and neural networks are the popular technologies used for structural health monitoring (SHM). To increase the reliability of the neural network output for SHM, comprehensive uncertainty quantification is needed for damage detection in unknown areas of auxetic structures. This paper presents the first comprehensive framework for health diagnosis and uncertainty quantification based on ultrasonic guided waves in two 3D-printed star hourglass honeycomb auxetic structures. The proposed framework integrates in-plane compression with simultaneous ultrasonic testing to receive ultrasonic signals across various deformation states. Additionally, fully elastic and elasto-plastic finite element simulations are conducted to analyze wave energy variations and mechanical responses in auxetic structure. Critical damage deformation is identified based on observed deformation patterns and variations in signal energy. The Hilbert transform is used to extract two damage-sensitive features, namely envelope and phase. These features serve as input data for the Flipout probabilistic convolutional neural network (FPCNN) model, which integrates pseudo-independent weight perturbations and a Gaussian probabilistic layer within the visual geometry group 13 architecture to predict structural deformations and associated uncertainties. The UQ framework effectively separates and quantifies the predictive variance of the FPCNN model into aleatoric and epistemic uncertainty. The framework’s effectiveness is demonstrated through the comprehensive approach, combining compression and ultrasonic tests, finite element simulation, and the FPCNN technique.

The preparation and axial compressive properties of 3D-printed polymer lattice-reinforced cementitious composite columns

Research on the mechanical properties of 3D-printed lattice-reinforced cementitious materials is becoming increasingly widespread. The bending and compression performances of such materials have been studied from the perspectives of the lattice preparation materials, structural forms, gradient design, and cement-based material types. The extant research has primarily focused on the bending performance of lattice-reinforced specimens, while little research has been conducted on the compressive properties. In addition, the reinforcing effect of the lattice on cementitious materials under lateral constraints has not been considered. This article investigates the compressive performance of cement mortar reinforced by 3D-printed spiral lattices or skin structures with different volume reinforcement ratios (different grid constraint layers). Multi Jet Fusion (MJF) technology was used to print four types of spiral lattices, and six specimens, including a control group, were prepared. The experiment considered the performance differences of polymer-reinforced mortars with different volume reinforcement ratios, bonding performance, and skin reinforcement. The load, displacement, stress, strain and other data of the specimen were measured, and combined with the full field strain measured by DIC technology, the strength, energy absorption performance, ductility, elastic modulus, constraint effect, deformation mechanism, and failure mode of the specimen were comprehensively analyzed. The experimental results indicate that 3D-printed spiral or skin lattices can improve the ductility and energy absorption capacity of cementitious materials. However, the elastic modulus of the raw materials used to reinforce the structure is lower than that of cementitious materials, which will reduce the compressive strength and elastic modulus. In addition, the lateral deformation constraint effect of the lattice or skin structure on the cement mortar under axial compression is not significant. All cementitious specimens were found to exhibit the shear failure of the inclined section under axial compression. This article reveals that 3D printed spiral lattices can improve the deformation ability of cementitious composite materials under compression, providing new ideas for the ideal replacement of stirrups and the development of building energy conservation and emission reduction.