Digital light processing based multimaterial 3D printing: challenges, solutions and perspectives

Multiscale and multimaterial three-dimensional (3D) printing is new frontier in additive manufacturing (AM). It has shown great potential to implement the simultaneous and full control for fabricated object including external geometry, internal architecture, functional surface, material composition and ratio as well as gradient distribution, feature size ranging from nano-, micro-, to macro-scale, embedded components and electrocircuit, etc. Furthermore, it has the ability to construct the heterogeneous and hierarchical structured object with tailored properties and multiple functionalities which cannot be achieved through the existing technologies. That paves the way and may result in great breakthrough in various applications, e.g., functional tissue and organ, functionally graded (FG) material/structure, wearable devices, soft robot, functionally embedded electronics, metamaterial, multifunctionality product, etc. However, very few of the established AM processes have now the capability to implement the multimaterial and multiscale 3D printing. This paper presented a single nozzle-based multiscale and multimaterial 3D printing process by integrating the electrohydrodynamic jet printing and the active mixing multimaterial nozzle. The proposed AM technology has the capability to create multifunctional heterogeneously structured objects with control of the macroscale external geometry and microscale internal structures as well as functional surface features, particularly, the potential to dynamically mix, grade, and vary the ratios of different materials. An active mixing nozzle, as a core functional component of the 3D printer, is systematically investigated by combining with the theoretical analysis, numerical simulation, and experimental verification. The study aims at exploring a feasible solution to implement the multiscale and multimaterial 3D printing at low cost.

There is growing interest in voxelated matter that is designed and fabricated voxel by voxel1-4. Currently, inkjet-based three-dimensional (3D) printing is the only widely adopted method that is capable of creating 3D voxelated materials with high precision1-4, but the physics of droplet formation requires the use of low-viscosity inks to ensure successful printing5. By contrast, direct ink writing, an extrusion-based 3D printing method, is capable of patterning a much broader range of materials6-13. However, it is difficult to generate multimaterial voxelated matter by extruding monolithic cylindrical filaments in a layer-by-layer manner. Here we report the design and fabrication of voxelated soft matter using multimaterial multinozzle 3D (MM3D) printing, in which the composition, function and structure of the materials are programmed at the voxel scale. Our MM3D printheads exploit the diode-like behaviour that arises when multiple viscoelastic materials converge at a junction to enable seamless, high-frequency switching between up to eight different materials to create voxels with a volume approaching that of the nozzle diameter cubed. As exemplars, we fabricate a Miura origami pattern14 and a millipede-like soft robot that locomotes by co-printing multiple epoxy and silicone elastomer inks of stiffness varying by several orders of magnitude. Our method substantially broadens the palette of voxelated materials that can be designed and manufactured in complex motifs.

3D printing has become a powerful technique in electrochemistry for fabricating electrodes, thanks to readily available conductive nanocomposite filaments, such as those based on carbon fillers (i.e., carbon nanotubes (CNTs) or carbon black (CB)) within an insulating polymeric matrix like polylactic acid (PLA). Inspired by inorganic heterostructures that enhance the functional characteristics of nanomaterials, we fabricated hetero-layered 3D printed devices based on carbon allotropes using a layer-by-layer assembly approach. The heterolayers were customised through the alternate integration of different carbon allotrope filaments via a multi-material 3D printing technique, allowing for a time-effective method to enhance electrochemical performance. As a first demonstration of applicability, CNT/PLA and CB/PLA filaments were utilised to construct ordered hetero-layered carbon-based electrodes. This contrasts with conventional methods where various carbon species are mixed in the same composite-based filament used for building electrochemical devices. Multi-material 3D-printed carbon electrodes exhibit improved electrochemical performance in energy conversion (e.g., hydrogen evolution reaction or HER) and sensing applications (e.g., ascorbic acid detection) compared to single-material electrodes. This work paves the way for manufacturing advanced 3D-printed heterolayered electrodes with enhanced electrochemical activity through multi-material 3D printing technology.

Primary and Secondary Recycling of Thermoplastics: A Review

Low-cost 3D desktop printing, although still in its infancy, is rapidly maturing, with a wide range of applications. With its ease of production and affordability, it has led to development of a global maker culture, with the design and manufacture of artefacts by individuals as a collaborative & creative hobbyist practice. This has enabled mass customization of goods with the potential to disrupt conventional manufacturing, giving more people access to traditionally expensive products like prosthetics and medical devices [1], as is the case with e-NABLE, a global community providing open source prosthetics for people with upper limb deficiencies. However one of the major barriers to proliferation of 3D printing as a major manufacturing method is the limitation of compatible materials for use with the technology [2]. This places constraints on the design approach, as well as the complexity & functionality of artefacts that can be produced with 3D printing as compared to traditional manufacturing methods. As a result, devices like the e-NABLE Raptor Reloaded prosthetic hand, which is designed specifically to be produced via a single extruder FDM desktop 3D printer, have limited functionality as compared to conventional prosthetics, leading to low active use and prosthesis abandonment [3]. However, with the advent of multi-material desktop 3D printing, and increasing availability of a broader range of compatible materials (of varying characteristics) [2], there is scope for improving capabilities of low-cost prosthetics through the creation of more sophisticated multi-material functional integrated devices. This work documents the exploration of potential applications of multi-material 3D printing to improve production, capabilities and usability of low-cost open source prosthetics. Various material combinations were initially studied and functional enhancements for current 3D printed prosthetics were prototyped using key material combinations identified. Further, a user-centered design approach was utilized to develop a novel multi-material anthropomorphic prosthetic hand ‘ex_machina’ based on a modular platform architecture, to demonstrate the scope for reduced build complexity and improved dexterity & functional customization enabled by dual extrusion FDM desktop 3D printing. A full prototype was built & tested with a lead user, and results analyzed to determine scope for optimization.

Fabrication and mechanical characterization of 3D printed vertical uniform and gradient scaffolds for bone and osteochondral tissue engineering

Three-dimensional printing is a rapidly developing area of technology and manufacturing in the field of oral surgery. The aim of this study was comparison of presurgical models made by two different types of three-dimensional (3D) printing technology. Digital reference models were printed 10 times using fused deposition modelling (FDM) and digital light processing (DLP) techniques. All 3D printed models were scanned using a technical scanner. The trueness, linear measurements, and printing time were evaluated. The diagnostic models were compared with the reference models using linear and mean deviation for trueness measurements with computer software. Paired t-tests were performed to compare the two types of 3D printing technology. A P value < 0.05 was considered statistically significant. For FDM printing, all average distances between the reference points were smaller than the corresponding distances measured on the reference model. For the DLP models, the average distances in the three measurements were smaller than the original. Only one average distance measurement was greater. The mean deviation for trueness was 0.1775 mm for the FDM group and 0.0861 mm for the DLP group. Mean printing time for a single model was 517.6 minutes in FDM technology and 285.3 minutes in DLP. This study confirms that presurgical models manufactured with FDM and DLP technologies are usable in oral surgery. Our findings will facilitate clinical decision-making regarding the best 3D printing technology to use when planning a surgical procedure.

This study evaluates the accuracy of drill guides fabricated in medical-grade, biocompatible materials for static, computer-aided implant surgery (sCAIS). The virtually planned drill guides of ten completed patient cases were printed (n = 40) using professional (Material Jetting (MJ)) and consumer-level three-dimensional (3D) printing technologies, namely, Stereolithography (SLA), Fused Filament Fabrication (FFF), and Digital Light Processing (DLP). After printing and post-processing, the drill guides were digitized using an optical scanner. Subsequently, the drill guide’s original (reference) data and the surface scans of the digitized 3D-printed drill guide were superimposed to evaluate their incongruencies. The accuracy of the 3D-printed drill guides was calculated by determining the root mean square (RMS) values. Additionally, cast models of the planned cases were used to check that the drill guides fitted manually. The RMS (mean ± SD) values for the accuracy of 3D-printed drill guides were—MJ (0.09 ± 0.01 mm), SLA (0.12 ± 0.02 mm), FFF (0.18 ± 0.04 mm), and DLP (0.25 ± 0.05 mm). Upon a subjective assessment, all drill guides could be mounted on the cast models without hindrance. The results revealed statistically significant differences (p < 0.01) in all except the MJ- and SLA-printed drill guides. Although the measured differences in accuracy were statistically significant, the deviations were negligible from a clinical point of view. Within the limits of this study, we conclude that consumer-level 3D printers can produce surgical guides with a similar accuracy to a high-end, professional 3D printer with reduced costs.

&lt;p&gt;A Percutaneous drain is a medical catheter used by Interventional radiologists to drain abscesses or cysts within the human body. The purpose of drainage is to reduce the need for open surgery, decreasing infections and recovery time. Percutaneous drains were initially designed for irrigation, not drainage; a contributing factor to the current 50% procedural fail rate. Alongside; clogging, kinking and infection.&lt;/p&gt; &lt;p&gt;&lt;br&gt;&lt;/p&gt; &lt;p&gt;The focus of the project is to mitigate failure with a fundamental redesign of the percutaneous drain, utilising a multidisciplinary research team from various organisations that work in conjunction to address this Issue.&lt;/p&gt; &lt;p&gt;&lt;br&gt;&lt;/p&gt; &lt;p&gt;This thesis, while a component of a more significant study, asks the question, ‘how can design research and multi-material 3D printing, provide innovative insights to improve the clinical performance of percutaneous drains?’&lt;/p&gt; &lt;p&gt;&lt;br&gt;&lt;/p&gt; &lt;p&gt;Three elements of the overall drainage procedure are focused on; the efficiency of the drains drainage, the insertion and removal procedure, and simulated anatomy models to provide context to each design. These are explored using multi-material 3D printing as a design tool to investigate new geometries, material combinations and dynamic qualities. Multi-material 3D printing is a design enabler which produces fast and accurate prototypes to explore ideas and communicate intentions to the research team. &lt;/p&gt; &lt;p&gt;The overall aim of this thesis project is to work alongside healthcare professionals cohesively, to develop novel drainage catheter prototypes. This aim will be achieved by utilising multi-material 3D printing for communication, discussion, rapid prototyping, and development. The primary outputs are innovative designs concepts for percutaneous drains, in the form of CAD files and 3D printed prototypes; while the written thesis documents research outcomes, outputs and process &lt;/p&gt;

Compensating the cell-induced light scattering effect in light-based bioprinting using deep learning

A vast majority of utility-scale wind turbine generators in the United States depend on foreign-sourced rare-earth permanent magnets that are vulnerable to supply chain uncertainties. Many small wind original equipment manufacturers are motivated to pursue continuous improvements to the generator design to lower the material and production costs and improve performance by lowering cogging torque and increasing efficiency. Traditional design and manufacturing offer limited opportunities. In this work, we demonstrate advanced design approaches for a 15-kW baseline wind turbine generator by making use of recent progress in three-dimensional (3D) printing of polymer-bonded magnets and electrical and structural steel. We explore three methods of magnet parametrization using Bézier curves resulting insymmetric,asymmetricandmultimaterialmagnet designs. We employ a multiphysics approach combining parametric computer-aided-design modeling, finite-element analysis, and targeted sampling to identify novel designs with more opportunities for reducing rare-earth material, improving efficiency and minimizing cogging torque. The results show that asymmetric-pole design and multimaterial-pole designs offer a greater opportunity to minimize rare-earth magnet materials by up to 35% with similar performance as the baseline generator, suggesting newer opportunities with design freedom beyond traditional limits of symmetry and as allowed by 3D printing.

This study presents the design and fabrication results of an electrothermal micro-electro-mechanical system (MEMS) actuator. Unlike traditional one-directional U-shaped actuators, this bi-directional electrothermal (BET) micro-actuator can produce displacements in two directions as a single device. The BET micro-actuator was fabricated using two-photon polymerization (2PP) and digital light processing (DLP) methods, which are 3D printing techniques. These methods have been compared to see the success of BET micro-actuator fabrication. The compound of these methods and the essential coefficients through the 3D printing operation were applied. Evaluation experiments have demonstrated that in both methods, the 3D printer can print materials smaller than 95.7 μm size features. Though the same design was used for the 2PP and DLP methods, the supporting structures were not produced with the 2PP. The BET micro-actuator was manufactured by removing the supports from the original design in the 2PP. The number of supports, the diameter, and height on the arms of the micro-actuator is 18, 4 μm, and 6 μm, respectively. Although 4 μm diameter supports could be produced with the DLP, it was not possible to produce them with 3D printing device based on 2PP. Besides, the DLP was found to be better than the 2PP for the manufacturing of asymmetrical support structures. The fabrication process has been carried out successfully by two methods. When the fabrication success is compared, the surface quality and fabrication speed of the micro-actuator fabricated with DLP is better than the 2PP. Presented results show the efficiency of the 3D printing technology and the simplicity of fabrication of the micro-actuator via 2PP and DLP. An experimental study was carried out to characterize the relationship between displacement and input voltage for the micro-actuator. Experimental results show that the displacement range of the micro-actuator is 8 μm with DLP, while 6 μm with 2PP.

One of the largest impediments in the development of microfluidic-based smart sensing systems is the manufacturability of integrated, complex devices. Here we propose multimaterial 3D printing for the fabrication of such devices in a single step. A microfluidic device containing an integrated porous membrane and embedded liquid reagents was made by 3D printing and applied for the analysis of nitrate in soil. The manufacture of the integrated, sealed device was realized as a single print within 30 min. The body of the device was printed in transparent acrylonitrile butadiene styrene (ABS) and contained a 400 μm wide structure printed from a commercially available composite filament. The composite filament can be turned into a porous material through dissolution of a water-soluble material. Liquid reagents were integrated by briefly pausing the printing before resuming for sealing the device. The devices were evaluated by the determination of nitrate in a soil slurry containing zinc particles for the reduction of nitrate to nitrite using the Griess reagent. Using a consumer digital camera, the linear range of the detector response ranged from 0 to 60 ppm, covering the normal range of nitrate in soil. To ensure that the sealing of the reagent chamber is maintained, aqueous reagents should be avoided. When using the nonaqueous reagent, the multimaterial device containing the Griess reagent could be stored for over 4 days but increased the detection range to 100-500 ppm. Multimaterial 3D printing is a potentially new approach for the manufacture of microfluidic devices with multiple integrated functional components.

We present development of multi-material Fused deposition modeling (FDM) 3D printer. Most of the FDM type of 3d printers are able to print plastics such as ABS, PLA and Nylon in a single run. In order to overcome this problem, we have developed an affordable multi-material 3D printer that can print an object with a different kind of soft and hard material in a single run. The combination of printing soft and hard materials in a single run will open the doors to various applications such as soft robotics, actuators and sensors. One of the main printing materials for this printer is the conductive based soft filament made by our laboratory "Soft & Wet Matter Engineering Laboratory", along with other different soft filament and hard plastic filament to create a fully functional, multi-material printer to print objects in a single printing run with greater diversity and lower cost than any other single material printer. We have developed a single screw-based extruder 3D printer extruder type 3D printer that can print both soft and hard materials. Instead of using a filament to 3D print objects, we have used pellets of different materials, including carbon-based conductive composites. Such type of single screw base extruder 3D printer will be a new addition to the additive manufacturing process.

Triggered drug delivery devices use external stimulus to trigger the release of the drugs from the device. By controlling the exposure of the stimuli, it would allow for the control over the timing, duration and amount of drug being released from the device, improving drug efficacy. 3D printing uses on-demand deposition and crosslinking of materials to fabricate a product, increasing the customisability of the design and internal structure. By using 3D printing to fabricate triggered drug delivery devices, certain advantages such as complex geometries, gradient compositions, multi-material structures and embedded components can be conferred to the printed devices. In this review paper, triggered drug delivery devices which are fabricated using 3D printing techniques such as vat photopolymerisation and material extrusion are discussed. The advancement in certain areas of 3D printing, such as in multi-material 3D printing and hybrid additive manufacturing, which presents tremendous opportunities for fabricating future triggered drug delivery devices will also be reviewed.