3D Printing Process Research Articles

Microdeformation and strengthening mechanism of 3D printed TC4/TC11 gradient titanium alloy subjected to tensile loading

3D printing of heterogeneous alloys holds promising application potentials in industry, especially in the field of aerospace. However, the relationship between the microstructure and mechanical properties of heterogeneous gradient titanium alloys produced by this technique, especially the micromechanical properties and mechanisms within the gradient zones, remains largely unexplored. In this study, we investigated the tensile micromechanical properties and deformation mechanism of 3D printed TC4/TC11 titanium alloy using the digital image correlation method in combination with scanning electron microscopy. The results show that this heterogeneous gradient titanium alloy possesses superior tensile properties. Furthermore, we elucidated the influence of microstructure and grain size on the alloy’s mechanical properties. Notably, an increased presence of secondary α phases and refined grain size were found to reduce the likelihood of microcrack initiation and propagation. Interestingly, all samples fractured on the TC4 side, with the microcracks predominantly extending at a 45° angle to the tensile direction. This observation underscores the necessity for optimizing the fabrication process of the TC4 alloy. Additionally, the strengthening mechanism of the gradient-bonded region of the alloy was also explored. The heterogeneous deformation-induced strengthening was identified as a key factor enhancing the strength of the dual alloyed zone. Collectively, this study provides valuable insights for optimizing the 3D printing process of heterogeneous gradient titanium alloys. It also lays a solid foundation for future investigation in this burgeoning field.

3D printing of active mechanical metamaterials: A critical review

The emergence of mechanical metamaterials from 4D printing has paved the way for developing advanced hierarchical structures with superior multifunctionalities. In particular, 4D-printed mechanical metamaterials exhibit extraordinary mechanical performance by integrating multiphysics stimuli with advanced structures when actuated by external factors, thereby altering their shapes, properties, and functionalities. This critical review offers readers a comprehensive overview of the rapidly growing 4D printing technology for developing novel mechanical metamaterials. It provides essential information about the multifunctionalities of 4D-printed mechanical metamaterials, including energy absorption and shape-morphing behavior in response to physical, chemical, or mechanical stimuli. These capabilities are key to developing smart and intelligent structures for multifunctional applications such as biomedical, photonics, acoustics, energy storage, and thermal insulation. The primary focus of this review is to describe the structural and functional applications of mechanical metamaterials developed through 4D printing. This technology leverages the shape-shifting functions of smart materials in applications such as micro-grippers, soft robots, biomedical devices, and self-deployable structures. Additionally, the review addresses current progress and challenges in the field of 4D-printed mechanical metamaterials. In conclusion, recent developments in 4D-printed mechanical metamaterials could establish a new paradigm for applications in engineering and science.

Mechanics guided design of programmable bilayer for aortic valve stent

Transcatheter aortic valve replacement (TAVR) has emerged as a promising treatment option for aortic stenosis. However, the prevalent stent used for valve placement restricts the post-release adjustment or movement of the artificial valve, increasing the potential risk to patients once accidental mispositioning occurs. Herein, we propose a 4D printing strategy to realize a proof-of-concept thermal-activated transcatheter aortic valve (TAV) stent that allows for programmable manipulation. Polylactic acid/polyurethane composites are directly printed to perform as the active units that tailor the configuration of the programmable TAV stent, accommodating to different tasks such as blood vessel navigation and topological fixation with cardiac cavity. A theoretical model is developed to explore the curvature evolutions of the active composite, realizing good agreement with experimental observations. Guided by the model, we seek out the optimized programming and activation conditions that allow for desired transformations to realize permanent fixation under intra-annular release and thermal-activated retraction under infra-annular release, inspiring the future development of TAV stents with shape memory principle.

Numerical and experimental investigation of 3D printed tunable stiffness metamaterial with real-time response using digital light processing technology

A tunable mechanical metamaterial is a type that can be altered or manipulated to change its physical properties in various situations. This study introduces a novel type of metamaterial, hydro-tunable metamaterials (HTMs), which can be dynamically adjusted in real-time by filling or draining it with water. The development of HTMs has significant implications for various fields, including mechanical engineering, biomedical applications, and energy absorption. The study involves designing and manufacturing HTMs using a Digital Light Processing (DLP) 3D printing process. The design process involves modifying an initial basic auxetic structure to create a closed and sealed structure accommodating fluid. The printed samples are then characterized using mechanical testing and finite element analysis (FEA). Experiments and simulations have found that a sample containing water behaves differently from a sample without water, resulting in an increase in stiffness. This difference can be leveraged to modify the stiffness and strength of the structure. This phenomenon is attributed to the incompressibility of water within the structure. Water exerts a hydrostatic pressure on the auxetic material, resulting in increased stiffness and resistance to compression. This technique highlights the potential of HTMs to be dynamically adjusted in real-time, leading to enhanced energy absorption and improved performance. An additional FEA was conducted to examine the impact of water pressure on the mechanical behavior of the structure. The results indicate that applying pressure or temperature to the water can significantly enhance the mechanical properties of the water-filled sample.

Tailoring the Thermoelectric Properties of 3D-Printed n-Type Bi1.7Sb0.3Te3 with Incorporated Edge-Oxidized Graphene.

Using three-dimensional (3D) printing technology to fabricate Bi2Te3-based thermoelectric (TE) generators opens a potential way to create shape-conformable devices capable of recovering waste heat from thermal energy sources with diverse surface morphologies. However, pores formed in 3D-printed Bi2Te3-based materials by the removal of the organic ink binder result in unsatisfactory performance compared to the bulk materials, which has limited the widespread application of the ink-based 3D printing process. Furthermore, managing the volatile Se element in the n-type materials poses significant technological challenges compared to the p-type counterparts, resulting in a scarcity of research on 3D printing of n-type Bi2Te3. Here, we synthesized edge-oxidized graphene (EOG)-incorporated Se-free n-type Bi1.7Sb0.3Te3 (BST) using a direct ink writing (DIW) process with a binder-free novel ink. The incorporated EOG provides connectivity between small BST grains separated by pores and induces a bimodal-like grain structure during the DIW and sintering process. The optimal EOG content of 0.1 wt % in 3D-printed n-type BST simultaneously achieved both carrier transport control and active phonon scattering, due to its unique microstructure. A maximum ZT of 0.71 was obtained in the 0.1 wt % EOG/BST materials at 448 K, comparable to commercial bulk n-type Bi2Te3-based materials. Further, a single-element device composed of the EOG-BST material exhibited a 2-fold improvement in performance compared to pure-BST. These results open a technological route for the application of 3D printing technology for ink-based TE materials.

Exploring the Adaptability of 4D Printed Shape Memory Polymer Featuring Dynamic Covalent Bonds.

4D printing (4DP) of high-performance shape memory polymers (SMPs), particularly using digital light processing (DLP), has garnered intense global attention due to its capability for rapid and high-precision fabrication of complex configurations, meeting diverse application requirements. However, the development of high-performance dynamic shape memory polymers (DSMPs) for DLP printing remains a significant challenge due to the inherent incompatibilities between the photopolymerization process and the curing/polymerization of high-strength polymers. Here, a mechanically robust DSMP compatible is developed with DLP printing, which incorporates dynamic covalent bonds of imine linking polyimide rigid segments, exhibiting remarkable mechanical performance (tensile strength ≈41.7MPa, modulus ≈1.63GPa) and thermal stability (Tg ∼ 113°C, Td ∼ 208°C). More importantly, benefiting from the solid-state plasticity conferred by dynamic covalent bonds, 4D printed structures demonstrate rapid network adaptiveness, enabling effortless realization of reconfiguration, self-healing, and recycling. Meanwhile, the extensive π-π conjugated structures bestow DSMP with an intrinsic photothermal effect, allowing controllable morphing of the 4D configuration through dual-mode triggering. This work not only greatly enriches the application scope of high-performance personalized configurations but also provides a reliable approach to addressing environmental pollution and energy crises.

In situ foam 3D printed microcellular multifunctional nanocomposites of thermoplastic polyurethane and carbon nanotube

Electrically conductive and mechanically robust thermoplastic polyurethane (TPU)/carbon nanotube (CNT) foams were achieved using a novel in situ foam 3D printing (F-3DP) process. Thermally expandable microspheres (TEMs), as blowing agent, were incorporated into the TPU/CNT filaments and fed to the F-3DP process. Foams with uniform morphologies and repeatable properties were achieved in a wide density range by solely regulating the nozzle temperature and its correlated flow rate. Overall, the degree of foaming increased substantially with an increase in the temperature, providing a density range of 0.96 to 0.17 g/cm3. It was interestingly found that a small amount of CNT (1 wt%) increased the expansion ratio. A further increase of CNT (to 3 and 5 wt%), however, caused a reduction in the expansion ratio. These opposing trends were attributed to the competing effects of CNT on the melt's thermal conductivity and viscosity. Both CNT content and nozzle temperature exhibited significant impacts on the tensile properties and electrical conductivity. This resulted in foams with diverse Young's modulus and strain at break in the range of 3.9–29.5 MPa and 260 to 52 %, respectively. More importantly, the electrical conductivity increased up to several orders of magnitude, as the foam expansion was increased due to temperature rise. This interesting finding was thoroughly discussed in terms of the enhanced inter-bead adhesion, vanishing inter-bead gaps, and realignment of CNTs around the growing TEMs. The results demonstrate a great potential of F-3DP to produce functional foams with controllable density and performance in a wide range.

Tailoring texture and functionality of vegetable protein meat analogues through 3D printed porous structures

This study presents a comprehensive 3D printing process for plant-based meat alternatives, covering ink formulation, printing, and final product characterization. Traditionally, achieving desired food properties requires extensive exploration of ink components. Here, we demonstrate the potential of manipulating processing parameters instead of ink composition. Two structures were printed, differing only in extrusion temperature. The printed structures exhibited a dimensional accuracy slightly below 100%. We investigated their behavior through simulated food production cycles, including freezing, thawing, dehydration, and rehydration. Rheological measurements revealed that protein denaturation caused a 20% increase in viscosity. Temperature-induced protein denaturation allowed to produce 3D printed samples with a fine porous structure, with pore sizes ranging from 50 to 450 μm. Mechanical characterization showed that a single printing parameter (extrusion temperature) significantly impacts the final product mechanical properties, with an increase of about 50% in the maximum stress for denatured samples after rehydration. This novel approach simplifies 3D-printed protein-based food production, establishing a link between processing parameters and the final product mechanical behavior.

Novel 4D-printed multi-stable metamaterials: programmability of force-displacement behaviour and deformation sequence.

The unique properties of metamaterials are determined by the configuration and spatial arrangement of artificially designed unit structures. However, the configuration and mechanical properties of conventional metamaterials are challenging to reverse and adjust. Based on curved beams, two types of novel three-dimensional (3D) multi-stable metamaterials with reconfigurable deformation and tunable mechanical properties are designed and fabricated using a four-dimensional (4D) printing method. The effects of temperature and curved-beam thickness on the force-displacement curves and multi-stable snapping sequence of the 3D multi-stable metamaterials are investigated by finite-element analysis (FEA) and experiments. In addition, based on the designed four-branch multi-stable metamaterials, three- and six-branched multi-stable structures are designed by changing the number of curved-beam branches. It is shown that, owing to shape memory effects, the 3D multi-stable metamaterials can realize mechanical programmability, and the multi-stable deformation sequence can be precisely regulated by varying the temperature and curved-beam thickness. These 4D-printed multi-stable metamaterials provide valuable contributions to the design of programmable multi-stable metamaterials and their applications in soft robots and intelligent structures. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'.

Influence of Printing Interval on the Imbibition Behavior of 3D-Printed Foam Concrete for Sustainable and Green Building Applications

Foam concrete is highly valued as a sustainable cement-based material, but the development of 3D-printed foam concrete (3DPFC) has remained constrained. This study investigated the influence of printing interval on the microstructure and imbibition behavior of 3DPFC. The results revealed that horizontal interlayers are broader compared to vertical interlayers, leading to more significant imbibition. For X-oriented 3DPFC, the vertical interlayer was rapidly occupied by water after imbibition, forming an elliptical moisture profile. For Y-oriented 3DPFC, the moisture profile appeared more convoluted, mainly surrounding the horizontal interlayers but shifting at intersections with the vertical interlayers. In Z-oriented 3DPFC, where only tight horizontal interlayers were present, interlayer imbibition was almost negligible. Additionally, when the printing interval was less than 15 min, imbibition was primarily restricted to the top filament since the bottom filament was compacted by the filament above. Conversely, with a printing interval longer than 15 min, the bottom filament hardened before the setting of the top filament. This allowed the surface of the bottom filament to be compacted by the top filament, resulting in a dense interlayer that offers better resistance against imbibition compared to the matrix of 3DPFC. This work contributes to the advancement of green building technologies by providing insights into optimizing the 3D printing process for foam concrete, thereby enhancing its structural performance without compromising the designated air content and consistency of the foam concrete, facilitating a more efficient utilization of materials and a reduction in overall material consumption.

Digital Twins in 3D Printing Processes Using Artificial Intelligence

Digital twins (DTs) provide accurate, data-driven, real-time modeling to create a digital representation of the physical world. The integration of new technologies, such as virtual/mixed reality, artificial intelligence, and DTs, enables modeling and research into ways to achieve better sustainability, greater efficiency, and improved safety in Industry 4.0/5.0 technologies. This paper discusses concepts, limitations, future trends, and potential research directions to provide the infrastructure and underlying intelligence for large-scale semi-automated DT building environments. Grouping these technologies along these lines allows for a better consideration of their individual risk factors and use of available data, resulting in an approach to generate holistic virtual representations (DTs) to facilitate predictive analyses in industrial practices. Artificial intelligence-based DTs are becoming a new tool for monitoring, simulating, and optimizing systems, and the widespread implementation and mastery of this technology will lead to significant improvements in performance, reliability, and profitability. Despite advances, the aforementioned technology still requires research, improvement, and investment. This article’s contribution is a concept that, if adopted instead of the traditional approach, can become standard practice rather than an advanced operation and can accelerate this development.

4D printing of magneto-responsive shape memory nano-composite for stents

Abstract This study focuses on the 4D printing simulation technique of magneto-responsive shape memory nanocomposite stents. A nanocomposite material was created by incorporating polycaprolactone, a shape memory material, with Fe3O4 to enhance magnetic responsiveness and stiffness. Tensile tests were conducted, and the material properties were applied to finite element analysis. Shape memory experiments were also performed to measure the temperature at which shape memory progression occurs due to magnetic response. In the 4D printing simulation, different coefficients of thermal expansion and the measured temperatures were reflected in the sections where shape memory is activated to implement shape memory behavior. The specimen simulation confirmed shape memory behavior progressing from 145 degrees to 3 degrees, while the stent simulation demonstrated satisfactory expansion to a radius of 3 mm. This study proposes a controllable method for implementing shape memory considering temperatures induced by magnetic response, showing potential for various medical device applications.

Integration of Sustainable and Net-Zero Concepts in Shape-Memory Polymer Composites to Enhance Environmental Performance.

This review research aims to enhance the sustainability and functionality of shape-memory polymer composites (SMPCs) by integrating advanced 4D printing technologies and sustainable manufacturing practices. The primary objectives are to reduce environmental impact, improve material efficiency, and expand the design capabilities of SMPCs. The methodology involved incorporating recycled materials, bio-based additives, and smart materials into 4D printing processes, and conducting a comprehensive environmental impact and performance metrics analysis. Significant findings include a 30% reduction in material waste, a 25% decrease in energy consumption during production, and a 20% improvement in shape-memory recovery with a margin of error of ±3%. Notably, the study highlights the potential use of these SMPCs as biomimetic structural biomaterials and scaffolds, particularly in tissue engineering and regenerative medicine. The ability of SMPCs to undergo shape transformations in response to external stimuli makes them ideal for creating dynamic scaffolds that mimic the mechanical properties of natural tissues. This increased design flexibility, enabled by 4D printing, opens new avenues for developing complex, adaptive structures that support cell growth and tissue regeneration. In conclusion, the research demonstrates the potential of combining sustainable practices with 4D printing to achieve significant environmental, performance, and biomedical advancements in SMPC manufacturing.

NIR-II light-encoded 4D-printed magnetic shape memory composite for real-time reprogrammable soft actuator

For the intelligent 4D-printed actuators, the excellent performance, including quickly reversible spatial-shape transformation and locking, digital and precise shape manipulation in real-time, and remote actuation in special spaces or harsh environments, is significantly desirable but still challenging. Here, using a UV-curable system containing the shape memory polymer (SMP) and NdFeB particles, namely the magSMP composite, we fabricate a real-time reprogrammable soft actuator via high-resolution Digital Light Processing (DLP)-based 4D printing. The printed structure is composed of an array of physical binary magSMP composite elements (m-bits), analogous to digital bits. Owing to the NdFeB's photothermal effect, each m-bit can be independently and reversibly switched between unlocking or locking states (allowing or prohibiting responsive shape-morphing) in response to the on/off state of NIR-II light. Through projecting NIR-II light patterns for encoding a set of binary instructions onto 4D-printed actuators, the real-time light-programmed deformations are induced precisely under an actuation magnetic field due to the NdFeB's huge coercivity. Thus, the synergistic magnetic and light field-manipulated multimodal deformations of actuators, including mimosa shape changing, grasping, and wire guiding, are achieved. This study shines lights on the fabrication of soft structures of arbitrary sizes and provides their future perspectives in soft robot design.

3D Bioprinting of Engineered Living Materials with Extracellular Electron Transfer Capability for Water Purification.

Attention is widely drawn to the extracellular electron transfer (EET) process of electroactive bacteria (EAB) for water purification, but its efficacy is often hindered in complex environmental matrices. In this study, the engineered living materials with EET capability (e-ELMs) were for the first time created with customized geometric configurations for pollutant removal using three-dimensional (3D) bioprinting platform. By combining EAB and tailored viscoelastic matrix, a biocompatible and tunable electroactive bioink for 3D bioprinting was initially developed with tuned rheological properties, enabling meticulous manipulation of microbial spatial arrangement and density. e-ELMs with different spatial microstructures were then designed and constructed by adjusting the filament diameter and orientation during the 3D printing process. Simulations of diffusion and fluid dynamics collectively showcase internal mass transfer rates and EET efficiency of e-ELMs with different spatial microstructures, contributing to the outstanding decontamination performances. Our research propels 3D bioprinting technology into the environmental realm, enabling the creation of intricately designed e-ELMs and providing promising routes to address the emerging water pollution concerns.

4D printing of the ferrite permanent magnet BaFe12O19 and its intelligent shape memory effect

4D printing of the barium ferrite permanent magnets provides new opportunities for intelligent structure and process innovation of permanent magnets. In this paper, the preparation, filament manufacture, and intelligent printing methods with shape memory/recovery effect are studied for the barium ferrite permanent magnet. Firstly, the PLA/TPU/BaFe12O19 composite materials are developed by adding different contents of ferrite permanent magnet BaFe12O19 powders into the PLA/TPU (polylactic acid/thermoplastic polyurethane) matrix. The weight percentage of the BaFe12O19 is 10–40 wt% with an interval of 10 wt%. Secondly, the composites are pelletized and further extruded to manufacture composite filaments with different BaFe12O19 contents. Scanning electron microscope (SEM) is used for the microstructural analysis. The BaFe12O19 particles are uniformly distributed in the PLA/TPU matrix, and the slight particle agglomeration phenomenon occurs in the composite filaments with 30 and 40 wt% BaFe12O19. The thermal properties of PLA/TPU/BaFe12O19 composite filaments are analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). After adding the barium ferrite particles, the glass transition temperature of the composite filaments changes within a small range from 53.5 °C to 55 °C. Thirdly, the filaments are successfully manufactured to magnet parts by the fused deposition modeling (FDM) 3D printing for the tests of mechanical, magnetic, and shape recovery properties. With the increase of the barium ferrite content, the magnetic properties show a rising trend, proving the feasibility of using 3D printing technology to make magnets. The shape memory effects of the printed parts are excellent and the shape recovery ratios show a rising trend, from 85.6 % to 88.9 % under heat contact stimulus and from 88.9 % to 97.8 % under electromagnetic induction non-contact stimulus. Relatively, the parts hold fast response speed due to direct contact with the heat source under the heat stimulus, and the parts hold higher shape recovery ratios due to more heats produced under the electromagnetic induction stimulus. The addition of magnetic particles is helpful to improve the heat transfer ability and provide the possibility of non-contact heat transfer. The magnetic parts with complex structure and intelligent shape memory/recovery effect can be achieved for special application requirements. As a result, the research of this paper expands preparation methods of new magnetic composite materials, explores the manufacture process for intelligent magnets and lays a solid foundation for the development of new permanent magnet devices.

4D printing of Nd-Fe-B composites with both shape memory and permanent magnet excitation deformation

Novel composite filaments are developed by mixing PLA, TPU, and Nd-Fe-B components and utilizing melt extrusion for 4D printing. The results reveal that the Nd-Fe-B magnetic particles are uniformly dispersed in the PLA/TPU polymer matrix, and the composite filaments meet the requirements of high-precision printing. Increasing the proportion of Nd-Fe-B magnetic particles in the composite contributes to higher remanence, coercivity, and magnetic energy product for the printed magnets. Under the 70 °C thermal stimulus, it has a high shape fixed ratio (>99 %), a high shape recovery ratio (>90 %), and a rapid response time (≤6.55 s). The magnetic particles accelerate the shape recovery process. Moreover, the petal-like structure and the hollow ball structure are designed and printed. After deformation, each structure can nearly fully recover its initial shape. This recovery is achieved through a non-contact stimulus response based on ’thermal-magnetic’ coupling. The grippers printed by the developed composite show comprehensive properties of shape memory and magnetically controlled smart gripping.

Slicing on the Tessellated Model for the 3D Printing Process based on the Variable Thickness Layers

Additive Manufacturing (AM) is a modern technology that enhances manufacturing by building thin layers of material from digitized (3D) designs, entirely constructed using advanced CAD software. This method facilitates the creation of new types of objects with unique material properties. However, while AM is often hailed as the next industrial revolution, significant challenges remain for its successful commercialization. This project focuses on the microstructural aspects and the dimensional accuracy of the product. Additionally, the paper discusses the slicing algorithm and the material extrusion process in detail.

Investigating the Use of 3D Printing and the Integration of BIM in Manufacturing Furniture Units

Abstract 3D printing is an emerging technology and one of the main aspects that can help in its success is BIM (Building Information Modelling). Despite recent interest in this topic, research indicates that to date no framework is in place that highlights the integration of BIM with 3D printing technology in the furniture design and production industry. This research delves deep into the use of 3D printing with the aid of BIM tools to produce furniture units. Through an analytical and experimental approach, this study aims to develop a conceptual framework that integrates BIM within the 3D printing process of small-scale furniture units. To gather data, the existing literature has been reviewed thoroughly and a framework was developed and adopted in the experimental study; where a BIM software was used to simulate a piece of furniture and measure the printing process against a set of criteria such as cost, material, and energy consumption. Results of the experiment were analysed and validated by applying comparative analysis between the interview with an expert in the interior 3D printing field and the results of the simulation. The research provided key aspects to be considered in the 3D printing of interior furniture pieces in addition to outlining the relevant limitations as well as the possible opportunities for further research.

The development of a smart thermoresponsive macroporous 4D structure using 4D printing of Pickering‐high internal phase emulsions stabilized by plasmafunctionalized starch nanomaterials

The development of a smart thermoresponsive macroporous 4D structure using 4D printing of Pickering‐high internal phase emulsions stabilized by plasmafunctionalized starch nanomaterials