Multi-material 3D Research Articles

Hyaluronic Acid-Based 3D Bioprinted Hydrogel Structure for Directed Axonal Guidance and Modeling Innervation In Vitro.

Neurons form predefined connections and innervate target tissues through elongating axons, which are crucial for the development, maturation, and function of these tissues. However, innervation is often overlooked in tissue engineering (TE) applications. Here, multimaterial 3D bioprinting is used to develop a novel 3D axonal guidance structure in vitro. The approach uses the stiffness difference of acellular hyaluronic acid-based bioink printed as two alternating, parallel-aligned filaments. The structure has soft passages incorporated with guidance cues for axonal elongation while the stiff bioink acts as a structural support and contact guidance. The mechanical properties and viscosity differences of the bioinks are confirmed. Additionally, human pluripotent stem cell (hPSC) -derived neurons form a 3D neuronal network in the softer bioink supplemented with guidance cues whereas the stiffer restricts the network formation. Successful 3D multimaterial bioprinting of the axonal structure enables complete innervation by peripheral neurons via soft passages within 14 days of culture. This model provides a novel, stable, and long-term platform for studies of 3D innervation and axonal dynamics in health and disease.

Four-Dimensional Printing of Multi-Material Origami and Kirigami-Inspired Hydrogel Self-Folding Structures.

Four-dimensional printing refers to a process through which a 3D printed object transforms from one structure into another through the influence of an external energy input. Self-folding structures have been extensively studied to advance 3D printing technology into 4D using stimuli-responsive polymers. Designing and applying self-folding structures requires an understanding of the material properties so that the structural designs can be tailored to the targeted applications. Poly(N-iso-propylacrylamide) (PNIPAM) was used as the thermo-responsive material in this study to 3D print hydrogel samples that can bend or fold with temperature changes. A double-layer printed structure, with PNIPAM as the self-folding layer and polyethylene glycol (PEG) as the supporting layer, provided the mechanical robustness and overall flexibility to accommodate geometric changes. The mechanical properties of the multi-material 3D printing were tested to confirm the contribution of the PEG support to the double-layer system. The desired folding of the structures, as a response to temperature changes, was obtained by adding kirigami-inspired cuts to the design. An excellent shape-shifting capability was obtained by tuning the design. The experimental observations were supported by COMSOL Multiphysics® software simulations, predicting the control over the folding of the double-layer systems.

Multi-material 3D printing of functionally graded soft-hard interfaces for enhancing mandibular kinematics of temporomandibular joint replacement prostheses

Temporomandibular joint (TMJ) replacement prostheses often face limitations in accommodating translational movements, leading to unnatural kinematics and loading conditions, which affect functionality and longevity. Here, we investigate the potential of functionally graded materials (FGMs) in TMJ prostheses to enhance mandibular kinematics and reduce joint reaction forces. We develop a functionally graded artificial cartilage for the TMJ implant and evaluate five FGM designs: hard, hard-soft, and three FGM gradients with gradual transitions from 90% hard material to 0%, 10%, and 20%. These designs are 3D printed, mechanically tested under quasi-static compression, and simulated under physiological conditions. Results from computational modeling and experiments are compared to an intact mandible during incisal clenching and left group biting. The FGM design with a transition from 90% to 0% hard material improves kinematics by 19% and decreases perfomance by 3%, reduces joint reaction forces by 8% and 10%, and increases mandibular movement by 20% and 88% during incisal clenching and left group biting, respectively. These findings provide valuable insights for next-generation TMJ implants.

Genetic algorithm-enabled mechanical metamaterials for vibration isolation with different payloads

Mechanical vibration isolation with adaptable payloads has always been one of the most challenging topics in mechanical engineering. In this study, we address this problem by introducing machine learning method to search for quasi-zero stiffness metamaterials with arbitrarily predetermined payloads and by employing multi-material 3D printing technology to fabricate them as an integrated part. Dynamic tests demonstrate that both the single- and multi-payload metamaterials can effectively isolate mechanical vibration in low frequency domain. Importantly, the payload of the metamaterial could be arbitrarily designed according to the application scenario and could function at multiple payloads. This design strategy opens new avenues for mechanical energy shielding under various scenarios and under variable loading conditions.

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.

3D-Printed Transducers for Solid Contact Potentiometric Ion Sensors: Improving Reproducibility by Fabrication Automation.

3D printing technology has become attractive in the development of electrochemical sensors as it offers automation in fabrication, customization on-demand, and reproducibility, among other features. Nonetheless, to date, solid contact potentiometric ion sensors have remained overlooked using this technology. Thus, the novelty of this work relies on demonstrating for the first time the usefulness of the multimaterial 3D printing approach to manufacture potentiometric ion-selective electrodes. The significance is indeed twofold. First, we discovered that by using the polyethylene terephthalate glycol (PETg) and polylactic acid-carbon black (PLA-CB) filaments together with a rational electrode design containing a well to accommodate the ion-selective membrane, a tight seal among all of the sensing materials is obtained. Importantly, this has mainly impacted the electrode-to-electrode reproducibility (ERSD0 ± 3 mV). Second, 75 ready-to-use electrodes can be printed in less than 3.5 h in a completely automated manner at a cost of ∼0.32 €/sensor. This feature may positively impact the suitability of further scaled-up production as well as the possibility of application in low-resource contexts. Overall, the presented outcomes are expected to encourage certain research directions to adopt using multimaterial 3D-printing approaches for producing highly reproducible solid contact potentiometric ion-selective electrodes, but are not restricted to them.

Multi-material fused deposition modelling of structural–functional integrated absorber with multi-scale structure possessing tunable broadband microwave absorption

Designing and manufacturing advanced structural microwave absorbers is one of the most feasible methods to address the growing electromagnetic stealth and protection challenges in both military and civilian domains. To this end, under the application context of structural–functional integration, a series of nanocomposites with varying ratios were prepared using multi-walled carbon nanotubes (MWCNTs) and inexpensive thermoplastic polypropylene as raw materials. The dispersion of nanofillers, rheological properties, thermal properties, and mechanical properties were evaluated. The research found that the impedance matching factor of the electromagnetic wave absorbers plays a more critical role in determining the material’s absorption capacity compared to the loss factor. Simple structural layering by changing the composition and design can effectively increase the effective absorption bandwidth (EAB) of the absorbers, with microwave attenuation primarily arising from conductive loss, interfacial polarization, dipole polarization, and multiple reflections. Finally, a multi-scale quasi-honeycomb absorber was fabricated using multi-material 3D printing with a structured design. Both simulation and experimental results showed consistent trends, demonstrating low sensitivity to the incident azimuth angle. This research features simplicity, low cost, and strong design capability, providing a new strategy for the preparation of functionally graded materials with potential applications in electromagnetic wave absorption.

Experimental and theoretical studies on 3D printed short and continuous carbon fiber hybrid reinforced composites

3D-printed carbon fiber composites hold significant potential in aerospace applications because of their lightweight, high strength and complex structure fabrication capabilities. However, additive manufacturing characteristics such as high porosity, anisotropy and continuous fiber content significantly affect the mechanical properties of printed parts. The aim of this study is to investigate the influence of hybrid printing of short and continuous carbon fibers on the mechanical properties and failure mechanisms of composites and to develop a model to predict elastic properties considering porosity. First, mechanical testing and characterization of short and continuous fiber reinforced polyamide (nylon) print filaments are performed. The results indicate that the elastic modulus and ultimate strength of continuous carbon fiber filaments reach 60 GPa and 1500 MPa, respectively, while the strength and elastic modulus of short carbon fiber filaments reach 60 MPa and 1 GPa, respectively. Then tensile specimens with different continuous fiber orientations and different continuous fiber placement sequences are printed and tested using a multi-material 3D printing technique. The specimens are characterized before and after testing using scanning electron microscopy and microscopy to assess the porosity and failure mechanisms of specimens with different configurations. The results show that the mechanical properties of the printed parts are much lower than those of the print filaments, which proves the serious negative impact of the material extrusion process on the mechanical properties of the printed structural parts. Finally, an analytical method for predicting the elastic behavior of printed composites is developed by introducing the porosity factor in the volume-averaged stiffness model. For continuous and short fiber filled composites with different fiber contents and printing orientations, the predicted results are in agreement with the experiments, and the prediction error is greatly reduced from 30 % to <5 %.

Multi-material 3D printed multiple state sensor units: design and materialization of a command joystick set

Multi-material 3D printed multiple state sensor units: design and materialization of a command joystick set

Multifunctional seamless meta-sandwich composite as lightweight, load-bearing, and broadband-electromagnetic-wave-absorbing structure

Engineered porous geometries composed of low-density lossy materials are promising as broadband absorbers due to their tunable structural attenuation that can selectively manipulate electromagnetic (EM) waves. However, the exposed cellular architectures require mechanical reinforcement and additional packaging. Here, we present a multifunctional meta-sandwich structure as one seamlessly integrated component composed of functional faceplates and dielectric lossy material-based octet-truss geometries toward a lightweight, load-bearing, and high-performance broadband EM wave absorber. EM responses are explored in the 4–18 GHz range by varying material combinations and multilayers of the upper-lower faceplates and the octet-truss core, elucidating the absorbing mechanisms of meta-sandwich structures. Multi-material 3D printing that streamlines the production of the seamless meta-sandwich composite into a single step implements the devised design that simultaneously excel in EM wave absorption and mechanical functionalities. The fabricated composite in a thin, single-layer structure comprising a transmitting upper faceplate, a dielectric lossy core, and a reflecting lower faceplate, achieves an average absorption rate of 95.0 % and a broadband reflection loss (≤-10 dB) over the entire measured bandwidth. Furthermore, flexural testing confirms superior bending resistance compared to conventional honeycomb structures. The multi-materials meta-sandwich design will inspire versatile multifunctionalities enabled by rationally combining mechanical metamaterials and functional housing.

Explosively welded SLM-AlSi10Mg/SLM-SUS316L: Unveiling superiority of interlayer welding for enhanced mechanical properties

Following the advent of three-dimensional (3D) printing technology, multi-material 3D printing has garnered significant attention due to its potential to enhance the flexibility and development of high-performance 3D printing materials. This study investigated the application of explosive welding to create multi-material 3D printed structures. Specifically, we explored the use of direct and interlayer explosive welding to fabricate SLM-AlSi10Mg/SLM-SUS316L explosive composites with the aim of further improving material properties. Our primary objective was to explore the unique interfaces and mechanical characteristics of 3D printed materials subjected to explosive impact loading. This study provides a new idea of 3D printing multi-materials, which is of great significance for the development of both explosive welding and 3D printing. The results demonstrated the feasibility of using explosive welding to create multi-material composites from 3D printed metals, including both direct and interlayer welding of SLM-AlSi10Mg/SLM-SUS316L. Interlayer welding exhibited superior mechanical performance compared to direct welding, with a 70%–250% increase in strength observed in the macro tensile shear test. Additionally, samples fabricated with a 40 mm explosive thickness displayed more stable and exceptional performance in the micro tensile test. Corrosion testing and X-ray computed tomography (XCT) analysis were employed to investigate the distribution of pores within the 3D printed materials.

Multi-material 3D nanoprinting for structures to functional micro/nanosystems

Multi-material 3D fabrication at the nanoscale has been a long-sought goal in additive manufacturing, with great potential for the direct construction of functional micro/nanosystems rather than just arbitrary 3D structures. To achieve this goal, researchers have introduced several nanoscale 3D printing principles, explored various multi-material switching and combination strategies, and demonstrated their potential applications in 3D integrated circuits, optoelectronics, biological devices, micro/nanorobots, etc. Although some progress has been made, it is still at the primary stage, and a serious breakthrough is needed to directly construct functional micro/nano systems. In this perspective, the development, current status and prospects of multi-material 3D nanoprinting are presented. We envision that this 3D printing will unlock innovative solutions and make significant contributions to various technologies and industries in the near future.

Material extrusion fabrication of continuous metal wire-reinforced polymer–matrix composites

3D printing via material extrusion is capable of using polymeric materials for a large range of applications. They are generally used, however, for prototyping as opposed to creating functional parts due to their lower mechanical properties in comparison to other materials, such as metals or epoxies, and processing methods, such as compression molding or injection molding. Carbon fiber, glass fiber, and kevlar have been used as reinforcement materials with very positive results in terms of creating functional parts. However, little focus has been placed on metallic wire reinforcement. In this investigation, a novel strategy to manufacture continuous metallic wire-reinforced polymer–matrix composites with increased mechanical properties by material extrusion is presented. A customized multimaterial 3D printer was built and used to fabricate coupons of unidirectionally reinforced Al wire/PLA matrix composites with either 15% or 25% wire volume fraction. The microstructure of the composites was analyzed to understand the formation of porosity during processing. These results also showed the potential of the manufacturing technique to precisely control the wire location and orientation. Incorporation of a volume fraction 25% of Al wires led to a 600% increase in elastic modulus and a 63% increase in tensile strength compared to pure PLA. These results indicate an efficient load transfer between the polymer matrix and the incorporated wires, despite exhibiting a relatively low interface strength. Overall, the novel strategy opens the possibility to manufacture high volume fraction composite laminates of thermoplastic polymers reinforced with metallic wires by material extrusion.

Effects of Topology Optimization in Multimaterial 3D Bioprinting of Soft Actuators

Recently, there has been a proliferation of soft robots and actuators that exhibit improved capabilities and adaptability through three-dimensional (3D) bioprinting. Flexibility and shape recovery attributes of stimuli-responsive polymers as the main components in the production of these dynamic structures enable soft manipulations in fragile environments, with potential applications in biomedical and food sectors. Topology optimization (TO), when used in conjunction with 3D bioprinting with optimal design features, offers new capabilities for efficient performance in compliant mechanisms. In this paper, multimaterial TO analysis is used to improve and control the bending performance of a bioprinted soft actuator with electrolytic stimulation. The multimaterial actuator performance is evaluated by the amplitude and rate of bending motion and compared with the single material printed actuator. The results demonstrated the efficacy of multimaterial 3D bioprinting optimization for the rate of actuation and bending.

Development of a Multi-Material 3D Printer for Functional Anatomic Models.

Anatomic models are important in medical education and pre-operative planning as they help students or doctors prepare for real scenarios in a risk-free way. Several experimental anatomic models were made with additive manufacturing techniques to improve geometric, radiological, or mechanical realism. However, reproducing the mechanical behavior of soft tissues remains a challenge. To solve this problem, multi-material structuring of soft and hard materials was proposed in this study, and a three-dimensional (3D) printer was built to make such structuring possible. The printer relies on extrusion to deposit certain thermoplastic and silicone rubber materials. Various objects were successfully printed for testing the feasibility of geometric features such as thin walls, infill structuring, overhangs, and multi-material interfaces. Finally, a small medical image-based ribcage model was printed as a proof of concept for anatomic model printing. The features enabled by this printer offer a promising outlook on mimicking the mechanical properties of various soft tissues.

Integrated 3D printing of reconfigurable soft machines with magnetically actuated crease-assisted pixelated structures

Reconfigurable magnetic soft machines have a wide range of applications in soft robotics, aerospace, medical devices and flexible electronics. However, the high-precision reconfiguration of magnetically actuated soft machines is hindered by the absence of rational structural design and integrated manufacturing techniques. Here, we report an innovative design and manufacturing approach to realize magnetically actuated high-precision reconfigurability. We present a crease-assisted pixelated design using a mixture of magnetic particles and phase-change medium as the pixel points, with an elastomer as the crease to connect the pixel points, simulating origami. The design of elastomer creases improves pixel stiffness without loss of reconfigurable accuracy, thereby significantly improves the magnetic particle concentration in the pixel. An effective multi-material 3D printing technique is used to achieve the integrated printing of the designed structure. The resulting magnetically actuated soft machines exhibit remarkable capabilities, achieving small curvature bending and precise reconfiguration with weaker actuating magnetic fields (100mT). The superior performance of this design has been confirmed through demonstrations of crawling and rolling machines, magnetically controlled switches, and logic circuits. The work enhances the reconfiguration accuracy of magnetically actuated soft machines, increasing their potential for soft robotics and flexible electronics applications.

Material Compatibility in 4D Printing: Identifying the Optimal Combination for Programmable Multi-Material Structures.

This study identifies the optimal combination of active and passive thermoplastic materials for producing multi-material programmable 3D structures. These structures can undergo shape changes with varying radii of curvature over time when exposed to hot water. The research focuses on examining the thermal, thermomechanical, and mechanical properties of active (PLA) and passive (PRO-PLA, ABS, and TPU) materials. It also includes the experimental determination of the radius of curvature of the programmed 3D structures. The pairing of active PLA with passive PRO-PLA was found to be the most effective for creating complex programmable 3D structures capable of two-sided transformation. This efficacy is attributed to the adequate apparent shear strength, significant differences in thermomechanical shrinkage between the two materials, identical printing parameters for both materials, and the lowest bending storage modulus of PRO-PLA among the passive materials within the activation temperature range. Multi-material 3D printing has also proven to be a suitable method for producing programmable 3D structures for practical applications such as phone stands, phone cases, door hangers, etc. It facilitates the programming of the active material and ensures the dimensional stability of the passive components of programmable 3D structures during thermal activation.

Feasibility of continuous switching 3D printing on surimi

Continuous switching 3D printing that allows multiple materials printed in a single nozzle was introduced to verify its applicability to the food system, which aims to improve the switching ability and manufacturing precision of multi-material 3D printed food. By integrating a self-developed 3D printing platform with logical adjustments of extrusion pressure and 3D motion, the feasible continuous switching of surimi was achieved. Moreover, employing a dual-channel continuous switching extrusion nozzle, the study elucidated the influence of surimi rheological properties on the interface behavior between pastes during extrusion. Through the analysis of fluid dynamics behavior of channel flow and utilization of simulation technology, a channel extension solution was formulated. Extending the length of the non-extrusion channel to 15 mm effectively prevented intrusion over 4 mm at an extrusion speed of 40 mm/s. This study managed to repetitively switch between two kinds of surimi pastes within a 2 mm unit length. Meanwhile, three types of 3D printing modes were established based on the control of Gcode, and the corresponding model offset correction enabled precise deposition of 2 mm × 1 mm units. The research also succeeded in 3D printing complex structures, such as meat-fat structure of beef based on surimi.

Direction-dependent bending resistance of 3D printed bio-inspired composites with asymmetric 3D articulated tiles

Inspired by the protective armors in nature, composites with asymmetric 3D articulated tiles attached to a soft layer are designed and fabricated via a multi-material 3D printer. The bending resistance of the new designs are characterized via three-point bending experiments. Bending rigidity, strength, and final deflection of the designs are quantified and compared when loaded in two different in-plane and two different out-of-plane directions. It is found that in general, the designs with articulated tiles show direction-dependent bending behaviors with significantly increased bending rigidity, strength, and deflection to final failure in certain loading directions, as is attributed to the asymmetric tile articulation (asymmetric about the mid-plane of tiles) and an interesting sliding-induced auxetic effect. Analytical, numerical, and experimental analyses are conducted to unveil the underlying mechanisms.

Mechanical response of 3D printed irregular sutural tessellations with Voronoi tile patterns under tension

The mechanical response of bio-inspired irregular sutural tessellations with Voronoi tile patterns are designed and fabricated via multi-material 3D printing. The effective mechanical properties of the designs were characterized via uni-axial tension mechanical experiments on the 3D printed specimens. Systematic nonlinear finite element simulations are conducted to explore the damage initiation and evolution of the designs. The influences of important design parameters, including tile length aspect ratio R, tile size irregularity Cstd, suture amplitude irregularity Astd, and stiffness ratio between the soft and hard phases, were evaluated. The effective stiffness, Poisson’s ratio, strength, toughness, and failure mechanisms are systematically quantified. The results demonstrate that an optimized level of suture irregularity exists for maximizing the modulus of toughness. The results provide a general design guideline for designing functionally graded two-phase tessellations with high mechanical performance.