Multimaterial Three-dimensional Printing Research Articles

Software for Bioprinting.

The bioprinting of heterogeneous organs is a crucial issue. To reach the complexity of such organs, there is a need for highly specialized software that will meet all requirements such as accuracy, complexity, and others. The primary objective of this review is to consider various software tools that are used in bioprinting and to reveal their capabilities. The sub-objective was to consider different approaches for the model creation using these software tools. Related articles on this topic were analyzed. Software tools are classified based on control tools, general computer-aided design (CAD) tools, tools to convert medical data to CAD formats, and a few highly specialized research-project tools. Different geometry representations are considered, and their advantages and disadvantages are considered applicable to heterogeneous volume modeling and bioprinting. The primary factor for the analysis is suitability of the software for heterogeneous volume modeling and bioprinting or multimaterial three-dimensional printing due to the commonality of these technologies. A shortage of specialized suitable software tools is revealed. There is a need to develop a new application area such as computer science for bioprinting which can contribute significantly in future research work.

Highly dispersed nanomaterials in polymer matrix via aerosol-jet-based multi-material 3D printing

Polymer-based nanocomposites emerged in the 1960s as a groundbreaking approach to advanced materials. By incorporating robust, durable, and multifunctional nanomaterials into a polymer matrix, the performance of nanocomposites has significantly surpassed that of the base polymers. However, over the past six decades, the challenges of achieving uniform nanomaterial dispersion and the resulting non-uniform properties have impeded further progress in this field. Here, we present a polymer-based nanocomposite with highly dispersed nanomaterials, achieved through aerosol-jet-based multi-material three-dimensional (AM3D) printing. This method allows precise programming of the nanocomposite's composition, structure, and dispersity. Numerical simulations in the design of AM3D printing system facilitate the avoidance of interfacial compatibility issue among heterogeneous aerosols, enabling distributed printing without nanomaterial agglomeration. As a result of this high level of dispersion and distribution, the 3D structured nanocomposite exhibits a uniform dielectric constant and low dielectric loss across the entire printed area. This work establishes an engineering framework for defect-free nanocomposites and significantly expands the range of polymer-based multi-material nanocomposite that can be designed and manufactured with complex architectures. One-Sentence SummaryAerosol-jet-based multi-material 3D printing enables highly dispersed nanomaterials in the polymer-based nanocomposite.

Digital Light Processing 3D Printing of Soft Semicrystalline Acrylates with Localized Shape Memory and Stiffness Control.

Multimaterial three-dimensional (3D) printing of objects with spatially tunable thermomechanical properties and shape-memory behavior provides an attractive approach toward programmable "smart" plastics with applications in soft robotics and electronics. To date, digital light processing 3D printing has emerged as one of the fastest manufacturing methods that maintains high precision and resolution. Despite the common utility of semicrystalline polymers in stimuli-responsive materials, few reports exist whereby such polymers have been produced via digital light processing (DLP) 3D printing. Herein, two commodity long-alkyl chain acrylates (C18, stearyl and C12, lauryl) and mixtures therefrom are systematically examined as neat resin components for DLP 3D printing of semicrystalline polymer networks. Tailoring the stearyl/lauryl acrylate ratio results in a wide breadth of thermomechanical properties, including tensile stiffness spanning three orders of magnitude and temperatures from below room temperature (2 °C) to above body temperature (50 °C). This breadth is attributed primarily to changes in the degree of crystallinity. Favorably, the relationship between resin composition and the degree of crystallinity is quadratic, making the thermomechanical properties reproducible and easily programmable. Furthermore, the shape-memory behavior of 3D-printed objects upon thermal cycling is characterized, showing good fatigue resistance and work output. Finally, multimaterial 3D-printed structures with vertical gradation in composition are demonstrated where concomitant localization of thermomechanical properties enables multistage shape-memory and strain-selective behavior. The present platform represents a promising route toward customizable actuators for biomedical applications.

The Inner Complexities of Multimodal Medical Data: Bitmap-Based 3D Printing for Surgical Planning Using Dynamic Physiology.

Motivated by the need to develop more informative and data-rich patient-specific presurgical planning models, we present a high-resolution method that enables the tangible replication of multimodal medical data. By leveraging voxel-level control of multimaterial three-dimensional (3D) printing, our method allows for the digital integration of disparate medical data types, such as functional magnetic resonance imaging, tractography, and four-dimensional flow, overlaid upon traditional magnetic resonance imaging and computed tomography data. While permitting the explicit translation of multimodal medical data into physical objects, this approach also bypasses the need to process data into mesh-based boundary representations, alleviating the potential loss and remodeling of information. After evaluating the optical characteristics of test specimens generated with our correlative data-driven method, we culminate with multimodal real-world 3D-printed examples, thus highlighting current and potential applications for improved surgical planning, communication, and clinical decision-making through this approach.

Multimaterial 4D printing with a tunable bending model

Shape-memory polymer (SMP)-based functional structures may now be produced more efficiently via four-dimensional (4D) printing, benefiting from the recent advances in multi-material three-dimensional printing technologies. Composite material design using 4D printing has opened new possibilities for customizing the shape memory property of smart polymers. This work studies a design strategy to harness desirable morphing by 4D printing multimaterial composites with a focus on the detailed finite element (FE) procedure, experimental results, and soft robotic application. Composites with bilayer laminates consisting of a SMP and a flexible elastomer are constructed with variable thickness ratios to control the self-bending of the composite. FE simulations are used to understand the underlying processes of composite materials and to generate accurate predictions for the experimental results, which reduces cost and development time. The application of 4D printing and multi-material composite programming is demonstrated with a soft robotic gripper for manipulating fragile objects.

Centrifugal multimaterial 3D printing of multifunctional heterogeneous objects

There are growing demands for multimaterial three-dimensional (3D) printing to manufacture 3D object where voxels with different properties and functions are precisely arranged. Digital light processing (DLP) is a high-resolution fast-speed 3D printing technology suitable for various materials. However, multimaterial 3D printing is challenging for DLP as the current multimaterial switching methods require direct contact onto the printed part to remove residual resin. Here we report a DLP-based centrifugal multimaterial (CM) 3D printing method to generate large-volume heterogeneous 3D objects where composition, property and function are programmable at voxel scale. Centrifugal force enables non-contact, high-efficiency multimaterial switching, so that the CM 3D printer can print heterogenous 3D structures in large area (up to 180 mm × 130 mm) made of materials ranging from hydrogels to functional polymers, and even ceramics. Our CM 3D printing method exhibits excellent capability of fabricating digital materials, soft robots, and ceramic devices.

Multimaterial Three-Dimensional Printing of Ultraviolet-Curable Ionic Conductive Elastomers with Diverse Polymers for Multifunctional Flexible Electronics.

Ionic conductive elastomers (ICEs) are emerging stretchable and ionic conductive materials that are solvent-free and thus demonstrate excellent thermal stability. Three-dimensional (3D) printing that creates complex 3D structures in free forms is considered as an ideal approach to manufacture sophisticated ICE-based devices. However, the current technologies constrain 3D printed ICE structures in a single material, which greatly limits functionality and performance of ICE-based devices and machines. Here, we report a digital light processing (DLP)-based multimaterial 3D printing capability to seemly integrate ultraviolet-curable ICE (UV-ICE) with nonconductive materials to create ionic flexible electronic devices in 3D forms with enhanced performance. This unique capability allows us to readily manufacture various 3D flexible electronic devices. To demonstrate this, we printed UV-ICE circuits into polymer substrates with different mechanical properties to create resistive strain and force sensors; we printed flexible capacitive sensors with high sensitivity (2 kPa-1) and a wide range of measured pressures (from 5 Pa to 550 kPa) by creating a complex microstructure in the dielectric layer; we even realized ionic conductor-activated four-dimensional (4D) printing by printing a UV-ICE circuit into a shape memory polymer substrate. The proposed approach paves a new efficient way to realize multifunctional flexible devices and machines by bonding ICEs with other polymers in 3D forms.

Programmable Mechanical Metamaterials with Tailorable Negative Poisson's Ratio and Arbitrary Thermal Expansion in Multiple Thermal Deformation Modes.

Mechanical metamaterials pave a way for designing and optimizing microstructure topology to achieve counterintuitive deformation including negative Poisson's ratio (NPR) and negative thermal expansion (NTE). Previous studies were always limited to single anomalous mechanical or thermal deformation, but current applications for high-precision mechanical or optical equipment always require their combination and customized and anisotropic deformation parameters. This work develops programmable two-dimensional (2D) mechanical metamaterials based on chiral and antichiral structures constructed with curved bimaterial strips to produce tailorable NPR and arbitrary thermal deformation. The coefficient of thermal expansion of the mechanical metamaterials is tunable on a large scale across negative, near-zero, and positive values depending on the bimaterial configurations and geometrical parameters of curved strips, while the value of NPR is mainly determined by the radian. Furthermore, it is programmable by coding the unit cells to exhibit customized and anisotropic thermal deformation combining homogeneous, gradient, and shear modes. The proposed mechanical metamaterials are fabricated by multimaterial three-dimensional (3D) printing, and the unusual deformation modes are verified experimentally, which is well in agreement with the results of finite element analysis. This work demonstrates a feasible approach to achieving customized mechanical and thermal deformation through easy block building for specific engineering applications including eliminating thermal stress, shape morphing, and smart actuators.

Multimaterial powder bed fusion techniques

Purpose This study aims to provide a comprehensive overview of the current state of the art in powder bed fusion (PBF) techniques for additive manufacturing of multiple materials. It reviews the emerging technologies in PBF multimaterial printing and summarizes the latest simulation approaches for modeling them. The topic of “multimaterial PBF techniques” is still very new, undeveloped, and of interest to academia and industry on many levels. Design/methodology/approach This is a review paper. The study approach was to carefully search for and investigate notable works and peer-reviewed publications concerning multimaterial three-dimensional printing using PBF techniques. The current methodologies, as well as their advantages and disadvantages, are cross-compared through a systematic review. Findings The results show that the development of multimaterial PBF techniques is still in its infancy as many fundamental “research” questions have yet to be addressed before production. Experimentation has many limitations and is costly; therefore, modeling and simulation can be very helpful and is, of course, possible; however, it is heavily dependent on the material data and computational power, so it needs further development in future studies. Originality/value This work investigates the multimaterial PBF techniques and discusses the novel printing methods with practical examples. Our literature survey revealed that the number of accounts on the predictive modeling of stresses and optimizing laser scan strategies in multimaterial PBF is low with a (very) limited range of applications. To facilitate future developments in this direction, the key information of the simulation efforts and the state-of-the-art computational models of multimaterial PBF are provided.

Characterization of a 3D Printed Electric Solenoid with Multi-layer Silver Nanoparticle Traces

Multi-material three-dimensional (3D) printing methods that combine conductive and non-conductive materials create new opportunities for the design of electrical circuits as well as electromagnetic actuators. While silver nanoparticle inks have previously been used in 3D printing to enable a wide range of dynamic electromechanical systems, most designs have focused on single-layer and micro-scale devices. In this work, we develop a fully 3D printed, centimeter-scale, 12-layer electric solenoid using conductive silver nanoparticle ink deposited via syringe extrusion and non-conductive polymers manufactured via fused deposition modeling. The design and fabrication techniques for the solenoid are first described. Then, a model for the magnetic force distribution in the solenoid is developed and compared with experimental results. Finally, the mechanical response is analyzed using stochastic system identification techniques. Results show that the solenoid can produce up to 15 mN of force with 6 W of input power. A mechanical bandwidth up to 36 Hz was also observed. After characterization, a 3D printed speaker application is demonstrated using this multi-layer additively manufactured solenoid.

One-Shot 3D-Printed Multimaterial Soft Robotic Jamming Grippers.

Soft gripping provides the potential for high performance in challenging tasks through morphological computing; however, design explorations are limited by a combination of a difficulty in generating useful models and use of laborious fabrication techniques. We focus on a class of grippers based on granular jamming that are particularly difficult to model and introduce a "one shot" technique that exploits multimaterial three-dimensional (3D) printing to create entire grippers, including membrane and grains, in a single print run. This technique fully supports the de facto physical generate-and-test methodology used for this class of grippers, as entire design iterations can be fitted onto a single print bed and fabricated from Computer-Aided Design (CAD) files in a matter of hours. Initial results demonstrate the approach by rapidly prototyping in materio solutions for two challenging problems in unconventional design spaces; a twisting gripper that uses programmed deformations to reliably pick a coin, and a multifunctional legged robot paw that offers the ability for compliant locomotion over rough terrains, as well as being able to pick objects in cluttered natural environments. The technique also allows us to easily characterize the design space of multimaterial printed jamming grippers and provide some useful design rules. The simplicity of our technique encourages and facilitates creativity and innovation. As such, we see our approach as an enabling tool to make informed principled forays into unconventional design spaces and support the creation of a new breed of novel soft actuators.

Sequential Multimaterial Additive Manufacturing of Functionally Graded Biopolymer Composites.

Cellulose, chitin, and pectin are three of the most abundant natural materials on Earth. Despite this, large-scale additive manufacturing with these biopolymers is used only in limited applications and frequently relies on extensive refinement processes or plastic additives. We present novel developments in a digital fabrication and design approach for multimaterial three-dimensional printing of biopolymers. Specifically, our computational and digital fabrication workflow-sequential multimaterial additive manufacturing-enables the construction of biopolymer composites with continuously graded transitional zones using only a single extruder. We apply this method to fabricate structures on length scales ranging from millimeters to meters. Transitional regions between materials created using these methods demonstrated comparable mechanical properties with homogenous mixtures of the same composition. We present a computational workflow and physical system support a novel and flexible form of multimaterial additive manufacturing with a diverse array of potential applications.

Multimaterial three-dimensional printing in brachytherapy: Prototyping teaching tools for interstitial and intracavitary procedures in cervical cancers

PurposeAs the utilization of brachytherapy procedures continues to decline in clinics, a need for accessible training tools is required to help bridge the gap between resident comfort in brachytherapy training and clinical practice. To improve the quality of intracavitary and interstitial high-dose-rate brachytherapy education, a multimaterial, modular, three-dimensionally printed pelvic phantom prototype simulating normal and cervical pathological conditions has been developed. Methods and MaterialsPatient anatomy was derived from pelvic CT and MRI scans from 50 representative patients diagnosed with localized cervical cancer. Dimensions measured from patients’ uterine body and uterine canal sizes were used to construct a variety of uteri based off of the averages and standard deviations of the subjects in our study. Soft-tissue anatomy was three-dimensionally printed using Agilus blends (shore 30 and 70) and modular components using Vero (shore 85). ResultsThe kit consists of four uteri, a standard bladder, a standard rectum, two embedded gross tumor volumes, and four clip-on gross tumor volume attachments. The three anteverted uteri in the kit are based on the smallest, the average, and the largest dimensions from our patient set, whereas the retroverted uterus assumes average dimensions. ConclusionsThis educational high-dose-rate gynecological pelvic phantom is an accessible and cost-effective way to improve radiation oncology resident training in intracavitary/interstitial brachytherapy cases. Implementation of this phantom in resident education will allow for more thorough and comprehensive physician training through its ability to transform the patient scenario. It is expected that this tool will help improve confidence and efficiency when performing brachytherapy procedures in patients.

3D-Printed Column with Porous Monolithic Packing for Online Solid-Phase Extraction of Multiple Trace Metals in Environmental Water Samples

In this study, we used a multimaterial three-dimensional printing (3DP) technology and porous composite filaments (Lay-Fomm, Gel-Lay, and Lay-Felt) to fabricate solid phase extraction (SPE) columns for the enhanced extraction of multiple metal ions. When employed as sample pretreatment devices in an automatic flow injection analysis/inductively coupled plasma mass spectrometry (ICP-MS) system, these 3D-printed SPE columns performed the near-complete extractions of Mn, Co, Ni, Cu, Zn, Cd, and Pb ions from natural water samples prior to ICP-MS determination. After optimizing the column fabrication, the extraction conditions, and the automatic analysis system, the column packed with the porous composite Lay-Fomm 40 was found to provide the highest extraction performance-the extraction efficiencies of the listed metal ions were all greater than 99.2%, and the detection limits of the method ranged from 0.3 to 6.7 ng L-1. The detection of these metal ions in several reference materials (CASS-4, SLEW-3, 1640a, and 1643f) validated the reliability of this method; spike analyses of collected water samples (groundwater, river water, and seawater) demonstrated the applicability of the method. The nature of the printing materials enhanced the analytical performance of 3D-printed sample pretreatment devices. Such approaches will be useful to diversify the range of sample preparation schemes and analytical methods enabled by 3DP technologies.

3D Printing in analytical sample preparation.

In the last 5 years, additive manufacturing (three-dimensional printing) has emerged as a highly valuable technology to advance the field of analytical sample preparation. Three-dimensional printing enabled the cost-effective and rapid fabrication of devices for sample preparation, especially in flow-based mode, opening new possibilities for the development of automated analytical methods. Recent advances involve membrane-based three-dimensional printed separation devices fabricated by print-pause-print and multi-material three-dimensional printing, or improved three-dimensional printed holders for solid-phase extraction containing sorbent bead packings, extraction disks, fibers, and magnetic particles. Other recent developments rely on the direct three-dimensional printing of extraction sorbents, the functionalization of commercial three-dimensional printable resins, or the coating of three-dimensional printed devices with functional micro/nanomaterials. In addition, improved devices for liquid-liquid extraction such as extraction chambers, or phase separators are opening new possibilities for analytical method development combined with high-performance liquid chromatography. The present review outlines the current state-of-the-art of three-dimensional printing in analytical sample preparation.

Multimaterial printing and characterization for mechanical and surface properties of functionally graded prototype

In this work, an effort has been made for multimaterial three-dimensional printing of functionally graded prototypes of polylactic acid matrix (tensile specimens as per ASTM D638 type IV) followed by characterization of mechanical and surface properties. The work is an extension of previous reported studies on twin-screw extrusion process for the preparation of multimaterial wires as feedstock filaments in possible three-dimensional printing applications. The results of the study suggest that the highest peak strength (46.28 MPa) and break strength (41.65 MPa) was obtained for multimaterial three-dimensional printed samples at infill density 100%, infill angle 45°, and infill speed of 90 mm/s on commercial open source fused deposition modeling setup. Further surface hardness measurements performed on two extreme surfaces (top surface comprising magnetite (Fe3O4)-reinforced polylactic acid and bottom with polylactic acid without any reinforcement) revealed that the hardness for the bottom layer was more than the hardness for the top layer. From fractured surface analysis (using photomicrographs), it has been observed that the three-dimensional printed samples with low infill density resulted into more void formation due to which the performance while mechanical testing was poor in comparison to samples printed with higher infill density. The results are also supported by rendered images of photomicrographs, which revealed that high roughness value of samples printed with low infill density was also one of the reasons for poor mechanical performance of multimaterial three-dimensional printed functionally graded prototypes.

Investigations of polylactic acid reinforced composite feedstock filaments for multimaterial three-dimensional printing applications

This paper reports properties of four different filaments prepared from (i) virgin polylactic acid, (ii) polylactic acid reinforced with polyvinyl chloride, (iii) polylactic acid reinforced with wood powder, and (iv) polylactic acid with reinforcement of Fe3O4 prepared with twin-screw extrusion for possible multimaterial three-dimensional printing. The results suggest that the melt flow rate of composite increases with the increase in reinforcements except for wood powder, which has shown a negative trend. Mechanical properties were also reduced with the loading but with the increase in the Fe3O4 content, these properties were improved. It has been observed that with reinforcement of polyvinyl chloride from 10 wt% to 25 wt% peak elongation and break elongation were reduced by 47.61% and 50%, respectively. Further, thermal analysis suggests that all samples were stable but for reinforced samples, the integral energy has decreased significantly in successive cycles. The vibration sample magnetometery of samples suggested that magnetic properties were dependent on the content of Fe3O4 present in the composite.

Design and Computational Modeling of a 3D Printed Pneumatic Toolkit for Soft Robotics.

Soft and compliant robotic systems have the potential to interact with humans and complex environments in more sophisticated ways than rigid robots. The majority of the state-of-the art soft robots are fabricated with silicone casting. This method is able to produce robust robotic parts, yet its results are difficult to quantify and replicate. Silicone casting also limits design complexity as well as customization due to the need to make new molds. As a result, most designs are tailored for simple, individual tasks, that is, bending, gripping, and crawling. To address more complex engineering challenges, this work presents soft robots that are fabricated by using multi-material three-dimensional printing. Instead of monolithic designs, we propose a pneumatic modular toolkit consisting of a bending and an extending appendage, as well as rigid building blocks. They are assembled to achieve different tasks. We show that the performance of both appendages is (1) repeatable, that is, the same internal pressure results in the same rotation or extension across multiple specimens and repetitions, and (2) predictable, that is, the respective deformations can be modeled by using finite element analysis. Using multiple instances of both building blocks, we demonstrate the versatility of this toolkit by assembling and actuating a gripper and a crawling caterpillar. The reliability of the mechanics of the building blocks and the assembled robots show that this simple toolkit can serve as a basis for the next generation of soft robots.

Three-Dimensionally Printed Mechanical Metamaterials With Thermally Tunable Auxetic Behavior

Mechanical metamaterials exhibiting negative Poisson's ratio (expanding, rather than contracting, in the direction perpendicular to an applied force) typically do not retain the ability to behave as typical materials with positive Poisson's ratio, which restricts their application where adaptive behavior is desirable. This work demonstrates dynamic, on-demand regulation of auxetic behaviors in mechanical metamaterials, through a combination of structural design and multimaterial three-dimensional printing. The design principle provides a further degree of freedom for metamaterials exhibiting extraordinary and programmable mechanical behaviors.

A Fully Multi-Material Three-Dimensional Printed Soft Gripper with Variable Stiffness for Robust Grasping.

Multi-material three-dimensional (3D) printing has provided the possibility of direct 3D printing of soft actuators with high complexity and functionality in a fast and easy fabrication process. In this article, we present the design of a multi-material 3D printed variable stiffness soft robotic gripper to ensure grasping robustness during high acceleration. The proposed gripper contains two identical soft fingers, with each finger including a pneumatic actuator and an integrated layer jamming unit. Prototypes of the soft finger, with material hardness transfer from the soft-bodied actuator to the hard pneumatic tubing and layer jamming unit, are fully fabricated by one-step 3D printing. A multi-material 3D printer, Objet350Connex, is used to directly print out the whole finger without the need for an additional casting process. The printed soft finger has a complex inner geometry, which integrates a small, light, and flexible layer jamming unit. The proposed finger can freely deform at low stiffness and maintain its grasping robustness at high stiffness during high acceleration. To demonstrate the effectiveness of the proposed design, the gripper is mounted on a robotic arm to evaluate its grasping robustness. With the aid of the integrated layer jamming unit, grasping robustness can be guaranteed when the robotic arm is moving at acceleration up to 8 m/s2. The results show that the proposed soft gripper is an effective design, which can guarantee grasping robustness during high acceleration.