Multi-material Deposition Research Articles

Integrating Robotics in Bioprinting: Advancements in 3D-Printed Tissue and Organ Engineering

The integration of robotics in bioprinting is revolutionizing the field of tissue and organ engineering, enabling unprecedented precision, scalability, and complexity in 3D-printed biological structures. This research explores the advancements brought about by robotic systems in bioprinting processes, focusing on their role in enhancing the fabrication of tissues and organs with intricate architectures and functional properties. Key areas of investigation include robotic-assisted multi-material deposition, real-time process monitoring, and adaptive printing techniques that ensure high fidelity and cell viability. The study also examines the incorporation of robotics into scalable bioprinting workflows for large-scale tissue engineering and transplantable organ production. Ethical considerations, such as regulatory challenges and equitable access, are addressed to highlight the societal implications of these innovations. By bridging robotics, bioengineering, and regenerative medicine, this research underscores the transformative potential of robotic-assisted bioprinting in addressing critical healthcare challenges, including organ shortages and personalized medicine. With advancements in precision and adaptability, robotic systems are poised to reshape the future of bioprinting, paving the way for breakthroughs in tissue engineering and regenerative therapies.

Additive manufacturing of functionally graded stellite6/17-4 PH fabricated via direct laser deposition

Multi-material structures with variable functionalities can lead to unique solutions for engineering problems compared to single-material structures. Additive manufacturing of Functionally Graded Materials (FGMs) using Direct Laser Deposition for the multi-material deposition of Stellite6 and 17–4 PH stainless steel has been investigated in this study. Process parameter design was successfully applied to achieve FGM structures with expected composition ratio and defect free. Results revealed that clads with insufficient laser power had unmelted 17-4 PH powders, while those with excessive power resulted in micro-cracks and disrupting the expected composition for the previous layer. Energy Dispersive Spectroscopy analysis results showed that the composition was almost as expected, with less than 10% deviation. The Stellite6 composition in FGM exhibits a minimum ratio near the substrate due to the penetration of 17-4 PH elements. Meanwhile, in multi-track clads, the Stellite6% decreases along the transverse direction due to increased heat input, multiple cladding tracks, higher dilution, and slower solidification rate. The results of the micro-hardness tests illustrated the gradual evolution of micro-hardness along the build direction starting from the base metal, which had a hardness of approximately 300 HV for 17-4 PH and for the compositions of 25%, 50%, 75%, and 100% Stellite6 showed increases of 10%, 39%, 43%, and 63% respectively, reaching up to 490 HV for fully Stellite6 at the top of the specimen.

Multi-material deposition of Inconel 718 and Ti–6Al–4V using the Ti–Nb–Cr–V–Ni high entropy alloy intermediate layer

Multi-materials are required in high-tech industries that require different properties at different locations in the same structure. The successful utilization of multi-materials can be economical, space-saving, and easy to maintain in engineering applications. Regardless of the technique used, the multi-material deposition (MMD) of Ti and Ni alloys presents some unique challenges. In this study, MMD of Ti–6Al–4V and Ni–20Cr using a high-entropy alloy (HEA) intermediate layer was performed, and deposition failure causes were analyzed. Deposition failures were found to be caused by the immiscibility between materials, differences in thermal properties, and interface due to the formation of brittle intermetallic compounds (IMC). HEA causes lattice distortion owing to the difference in the size of the elements constituting the solid solution and has excellent mechanical properties owing to the lattice distortion and the unique microstructure caused by the formation of a single-phase solid solution. In addition, HEAs do not form IMC because they exhibit slow diffusion rates. Therefore, HEA could be used as an effective interlayer to inhibit IMC formation. In this study, Inconel 718 and Ti–6Al–4V were successfully deposited by applying a Ti–Nb–Cr–V–Ni HEA intermediate layer to MMD. In addition, microstructure analysis and hardness measurements were performed to analyze whether IMC inhibition and successful deposition occurred.

A Need for New Standards: Communicating Shape Transformations in the Technical Documentation of Products

Abstract Advances in additive manufacturing have enabled functional grading and multi-material deposition to produce “4D printed” parts that are net or near net shape; creating highly complex features that are difficult to produce with conventional manufacturing processes. This article addresses the fundamental challenge of how to ensure that the design, manufacturing, and functional intent for 4D printed parts can be accurately and unambiguously communicated across the design, manufacturing, inspection, and supply value chain. The use case of a generic mini-gripper sheds light on the benefits that a new standard could bring to the engineering and design of shape memory materials.

A Review on Multiplicity in Multi-Material Additive Manufacturing: Process, Capability, Scale, and Structure.

Additive manufacturing (AM) has experienced exponential growth over the past two decades and now stands on the cusp of a transformative paradigm shift into the realm of multi-functional component manufacturing, known as multi-material AM (MMAM). While progress in MMAM has been more gradual compared to single-material AM, significant strides have been made in exploring the scientific and technological possibilities of this emerging field. Researchers have conducted feasibility studies and investigated various processes for multi-material deposition, encompassing polymeric, metallic, and bio-materials. To facilitate further advancements, this review paper addresses the pressing need for a consolidated document on MMAM that can serve as a comprehensive guide to the state of the art. Previous reviews have tended to focus on specific processes or materials, overlooking the overall picture of MMAM. Thus, this pioneering review endeavors to synthesize the collective knowledge and provide a holistic understanding of the multiplicity of materials and multiscale processes employed in MMAM. The review commences with an analysis of the implications of multiplicity, delving into its advantages, applications, challenges, and issues. Subsequently, it offers a detailed examination of MMAM with respect to processes, materials, capabilities, scales, and structural aspects. Seven standard AM processes and hybrid AM processes are thoroughly scrutinized in the context of their adaptation for MMAM, accompanied by specific examples, merits, and demerits. The scope of the review encompasses material combinations in polymers, composites, metals-ceramics, metal alloys, and biomaterials. Furthermore, it explores MMAM's capabilities in fabricating bi-metallic structures and functionally/compositionally graded materials, providing insights into various scale and structural aspects. The review culminates by outlining future research directions in MMAM and offering an overall outlook on the vast potential of multiplicity in this field. By presenting a comprehensive and integrated perspective, this paper aims to catalyze further breakthroughs in MMAM, thus propelling the next generation of multi-functional component manufacturing to new heights by capitalizing on the unprecedented possibilities of MMAM.

Prototype Design for Grading Structures in Powder Bed Fusion Processes.

While targeted alignment in certain additive manufacturing (AM) methods such as material extrusion (MEX) and stereolithography (SLA) has been well documented in the research community, a method for targeted alignment of added fillers or fibrous materials in powder bed fusion (PBF) AM devices has yet to be successfully achieved. Similarly, incorporation of multimaterials does not work easily with any of the AM technologies. This study creates a prototype design that could be integrated into a PBF system to allow for multimaterial layer deposition and alignment of powders and powder blends. The rheological properties of polyamide powder and a range of polyamide composite blends (incorporating milled carbon fibre, graphite flakes, polytetrafluoroethylene, and glass microspheres) in different concentrations were studied, and together with the particle size distribution and particle morphology analysis were applied for the design of a prototype hopper for incorporation in the PBF system to create targeted multimaterial deposition. Different concept designs, multichambered and multi-hopper with hopper angles calculated specifically for the composite blend powders selected, were proposed. Initial deposition trials outside a PBF process were tested, and the deposited layers were measured.

Machining Strategy Determination for Single- and Multi-Material Wire and Arc Additive Manufactured Thin-Walled Parts

Wire and arc additive manufacturing (WAAM) technology has recently become attractive due to the fact of its high production capacity and flexible deposition strategy. One of the most prominent drawbacks of WAAM is surface irregularity. Therefore, WAAMed parts cannot be used as built; they require secondary machining operations. However, performing such operations is challenging due to the fact of high waviness. Selecting an appropriate cutting strategy is also challenging, because surface irregularity makes cutting forces unstable. The present research determines the most suitable machining strategy by assessing the specific cutting energy and local machined volume. Up- and down-milling are evaluated by calculating the removed volume and specific cutting energy for creep-resistant steel, stainless steel, and their combination. It is shown that the main factors that affect the machinability of WAAMed parts are the machined volume and specific cutting energy rather than the axial and radial depths of the cut due to the fact of high surface irregularity. Even though the results were unstable, a surface roughness of 0.1 µm was obtained with up-milling. Despite a two-fold difference in the hardness between the two materials in the multi-material deposition, it is found that hardness should not be used as a criterion for as-built surface processing. In addition, the results show no machinability difference between multi- and single-material components for a low machined volume and low surface irregularity.

Design for multi-material 4D printing: Development of an algorithm for interlocking blocks assembly generation

4D printing involves smart materials (SMs) that can respond to stimulation energy by changing their shape/property. Current advances in digital materials require addressing heterogeneous (multi-material deposition) 4D printing to attain targeted shape-changes. However, innovative structures embedding inert and SMs simultaneously are yet difficult to build. To overcome this challenge, we propose a genuine computational design approach addressed to heterogeneous additive manufacturing (AM). The main idea is to resort to an efficient algorithm capable of converting a computed digital multi-material distribution in a voxel-based 3D/4D structure to interlocking blocks intended to be printed separately with different AM techniques and then assembled.

Multimaterial direct energy deposition: From three-dimensionally graded components to rapid alloy development for advanced materials

Laser-based direct energy deposition (L-DED) with blown powder enables the simultaneous or sequential processing of different powder materials within one component and, thus, offers the possibility of additive multimaterial manufacturing. Therefore, the process allows a spatially resolved material allocation and fabrication of sharp or even graded material transitions. Within this contribution, the latest results from two major research fields in multimaterial L-DED—(I) automation and (II) rapid alloy development of high entropy alloys (HEAs) by in situ synthesis—shall be presented. First, an automated multimaterial deposition process was developed, which enables the automated manufacturing of three-dimensionally graded specimens. For this, a characterization of the deposition system regarding powder feeding dynamics and resulting powder mixtures in the process zone was conducted. The obtained system characteristics were used to achieve a three-dimensional deposition of specified powder mixtures. The fabricated specimens were analyzed by energy-dispersive x-ray spectroscopy, scanning electron microscopy, and micro hardness measurement. The research demonstrates the increasing readiness of L-DED for the fabrication of multimaterial components. Second, the latest results from rapid alloy development for HEAs by DED are presented. By the simultaneous usage of up to four powder feeders, a vast range of alloy compositions within the Al–Ti–Co–Cr–Fe–Ni HEA system was investigated. For this, tailored measurement systems such as an in-house developed powder sensor were beneficially used. The study shows the influence of a variation of Al on the phase formation and resulting mechanical properties and demonstrates the potential of L-DED for reducing development times for new alloys.

Research progress in multi-material laser-powder bed fusion additive manufacturing: A review of the state-of-the-art techniques for depositing multiple powders with spatial selectivity in a single layer

Additive manufacturing offers great potential and versatility for manufacturing high-quality and geometrically complex components. Multi-material laser-powder bed fusion is an emerging additive manufacturing approach where multiple materials are combined in order to manufacture multi-material components with new possibilities in product design and spatially tailored properties. Several multi-material delivery systems have been developed and a broad spectrum of applications have been demonstrated using multi-material laser-powder bed fusion. This work provides an overview in terms of architecture, construction and applications of all existing multi-material delivery systems developed for multi-material laser-powder bed fusion. Numerous challenges related to the deposition and processing of multi-materials which have been reported are discussed and potentials, which emerged through the use of multi-material laser-powder bed fusion are discussed together with the future perspectives.

Normalized hardness prediction of L-DED metal matrix composite coatings for wear-resistant applications

In the present work, a Finite Element (FE) model is developed to predict the normalized hardness of Metal Matrix Composite (MMC) coatings manufactured by laser Directed Energy Deposition (L-DED).L-DED has gained significant attention lately, both in industry and research. This technology is primarily focused on repair and coating applications. In conjunction with its tight control over the energy input, which renders L-DED technology highly suitable for coating applications, the multi-material deposition capability has unlocked the development of high-performance coatings. Analytical solutions have been developed in the past, where a broad spectrum of values is defined. However, the precise determination of their hardness still poses a challenge.To that end, a FE Model has been developed to predict the hardness of particulate reinforced composites, which is compared with both analytical solutions in the literature and experimental results. The simulated results agree well with experimental results, with an error of less than 5%. Hence, the suitability of FE modelling for the estimation of the normalized hardness of MMCs is proven.

Characterization of the Functional Properties of Polycaprolactone Bone Scaffolds Fabricated Using Pneumatic Micro-Extrusion

Abstract Pneumatic micro-extrusion (PME) is a direct-write additive manufacturing process, which has emerged as a robust, high-resolution method for the fabrication of a broad spectrum of biological tissues and organs. PME allows for noncontact multimaterial deposition of functional inks for tissue engineering applications. In spite of the advantages and engendered potential applications, the PME process is inherently complex, governed not only by complex physical phenomena but also by material–process interactions. Consequently, investigation of the influence of PME process parameters as well as the underlying physical phenomena behind material transport and deposition in PME would be inevitably a need. The overarching goal of this research work is to fabricate biocompatible, porous bone tissue scaffolds for the treatment of osseous fractures, defects, and diseases. In pursuit of this goal, the objectives of the work are: (i) to investigate the influence of seven consequential scaffold design factors and PME process parameters on the mechanical properties of fabricated bone tissue scaffolds and (ii) to explore the underlying dynamics behind material transport in the PME process, using a three-dimensional computational fluid dynamics (CFD) model. To investigate the effects of the design and process parameters, a series of experiments were designed and conducted. Layer height was identified as the most significant factor in this study. An increase in the layer height led to less overlap between subsequent layers, which allowed for more shrinkage and ultimately a reduction in scaffold diameter. In addition, print speed appeared as an influential factor in this study. An increase in the print speed resulted in a decline in linear mass density and thus in the extent of fusion between subsequent deposited layers. Besides, it was observed that there was a strong correlation between deposition mass and compression modulus. Overall, the results of this study pave the way for future investigation of PME-deposited polycaprolactone (PCL) scaffolds with optimal functional and medical properties for incorporation of stem cells toward the treatment of osseous fractures and defects.

Microstructural and mechanical characterization of stainless steel 420 and Inconel 718 multi-material structures fabricated using laser directed energy deposition

Varying material properties are required for components designed to withstand harsh environments with simultaneous thermal and mechanical loading. This has been traditionally achieved by using multiple materials fabricated by traditional processes, followed by permanent or non-permanent joining techniques to realize a full, multi-material and multi-functional component. A potential simpler approach to this is to develop multi-material structures fabricated using additive manufacturing (AM). Additionally, many existing structures in can also be simplified by incorporating multi-material and multi-functional structures. Laser directed energy deposition (laser-DED) AM technique is suitable for fabricating multi-material structures using powdered feedstock material with high material flexibility. However, the fabrication of multi-material structures requires careful investigation into the compatibility and behavior of the constituent material systems. This remains a crucial task for multi-material deposition because there is relatively less knowledge available currently on the optimal multi-material mixtures for achieving adequate structural integrity and mechanical performance. In this study, multi-material structures of stainless steel 420 (SS420) and Inconel 718 (IN718) alloys were studied. These alloys were chose due to their applications in gas turbine components such as shaft assemblies, exhaust components and in the energy industry for fabricating various high strength, corrosion resistant devices. The specific compositions of the multi-materials structures investigated were: 100% SS420, 100% IN718, 75% SS420 + 25% IN718, 50% SS420 + 50% IN718 and 75% IN718 + 25% SS420. These samples were characterized for their microstructural, phase, and mechanical properties in the as-fabricated condition and compared with conventionally fabricated alloys. Significant differences in the microstructure and properties were observed between the laser-DED fabricated 100% alloys and mixtures of the two alloys. The laser-DED fabricated SS420 and IN718 alloys showed rapidly solidified microstructures typical to laser processes and properties comparable or better than the conventionally fabricated alloys. The three mixtures of SS420 and IN718 alloys showed microstructure and phases that were intermediate between the two unmixed alloys, as well as a higher amount of metallic carbide and Laves phases. Hardness and tensile tests indicated that the three mixtures of SS420 and IN718 were weaker than the unmixed laser-DED fabricated alloys due to the brittle carbide and Laves phases. Amongst the mixture, the mixture composition of 25%SS420 + 75%IN718 has showed highest strength and ductility.

A numerical Approach to design and develop freestanding porous structures through cold spray multi-material deposition

Cold spray is a solid-state particle deposition technique with a wide range of applications for coating, repair and additive manufacturing. Cold spray parameters are normally tuned to obtain deposits with minimal porosity and thus highest strength. However, there are specific applications such as biomedical prostheses, heat sinks and energy absorbing products, where a higher exposed surface area can lead to enhanced performance, rendering porosity a desirable feature. Few recent studies have experimentally evaluated the potential of cold spray technology for obtaining porous deposits. To enhance the efficiency of these approaches, here we developed a detailed numerical framework that can determine the topological and mechanical features of cold spray porous deposits. A series of combined Eulerian-Lagrangian finite element models were developed considering a multi-material feedstock, one constituent of which served as a porogen. Different powder blends of pure Ti mixed with either Al or Cu, as the sacrificial powder, with varying volumetric fractions were analysed. A novel post-processing approach was developed to remove the sacrificial powder and extract distinct characteristic indicators from the simulations' output; these indices include porosity and structural connectivity of the remaining Ti structure. Equivalent plastic strain was considered as an index to assess the strength of the resultant deposit. The obtained data regarding particle deformation were in agreement with preliminary experimental tests. The numerical results revealed that Ti-Cu combinations can yield deposits with higher Ti particle deformation compared to the Ti-Al blend and hence, lead to a better inter-particle bonding. This study presents a robust numerical approach for selection of cold spray process parameters towards obtaining coatings and freestanding porous metal parts with modulated porosity, connectivity and strength.

Inkjet-/3D-/4D-Printed Perpetual Electronics and Modules: RF and mm-Wave Devices for 5G+, IoT, Smart Agriculture, and Smart Cities Applications

With the revolutionary developments in the fields of millimeter-wave (mm-wave) and Internet of Things (IoT) technologies and the billion devices promised to be implemented by the end of the decade, the realization of inexpensive, low-power, and intelligent systems is highly desirable. Additive manufacturing (AM) is a technology seeing widespread adoption due to its ability to enable rapid prototyping for iterative design; its reduced setup costs, facilitating economic small-batch production; and its ability to significantly reduce waste by-products, resulting in both environmental benefits as well as lower manufacturing costs. On the other hand, current lithography-based manufacturing technologies-a huge contributor to the growing RF and 5G wireless electronics industry-require extensive design verification, have longer turnaround times, and produce harmful byproducts. Although AM can offer time and cost benefits under the correct conditions, among the more impactful demonstrations of the manufacturing technology are the novel topologies enabled by design rules that allow feature sets, including nonorthogonal planes, conformal surfaces, multimaterial deposition, simultaneous thick- and thin-film deposition [1], complex 3D structures, integrated voids, and gradient index materials.

Nanotribological Printing: A Nanoscale Additive Manufacturing Method.

Additive manufacturing methods are transforming the way components and devices are fabricated, which in turn is opening up completely new vistas for conceiving and designing products and engineered systems. Small-scale (submicrometer) additive manufacturing methods are largely in their infancy. While a number of methods exist, a particular challenge lies in finding methods that can produce a range of materials while obtaining sufficiently robust mechanical properties. In this paper, we describe a novel nanoscale additive manufacturing technique deemed "Nanotribological Printing" (NTP), which creates structures through tribomechanical and tribochemical surface interactions at the contact between a substrate and an atomic force microscope probe, where material pattern formation is driven by normal and shear contact stresses. The "ink" consists of nanoparticles or molecules dispersed in a carrier fluid surrounding the atomic force microscope (AFM) probe, which are entrained into the contact during sliding. Being stress-driven, patterning only occurs locally within regions which experience contact and sufficiently high stresses. Thus, imaging and measurement to characterize the morphology and properties of the deposited structures can be conducted in situ during the manufacturing process. Moreover, using local mechanical energy as the kinetic driver activating the solidification process, the method is compact and does not require application of a bias voltage or laser exposure and can be performed at ambient temperatures. We demonstrate (1) control of pattern dimensions with sub-100 nm lateral and sub-5 nm thickness control through variations in contact size and applied stress, (2) creation of amorphous, polycrystalline, and nanocomposite structures including sequential multimaterial deposition, and (3) formation of manufactured structures which exhibit mechanical properties approaching those of bulk counterparts. The ability to create nanoscale patterns using standard AFM cantilever probes and operation modes (contact mode scanning in fluid) with commercial AFM instruments, independent of substrate, establishes NTP as a versatile and easily accessible method for nanoscale additive manufacturing.

Multi-Material Deposition of Polymer Powders with Vibrating Nozzles for a New Approach of Laser Sintering

Multi-Material Deposition of Polymer Powders with Vibrating Nozzles for a New Approach of Laser Sintering

Microfluidics: A New Layer of Control for Extrusion-Based 3D Printing.

Advances in 3D printing have enabled the use of this technology in a growing number of fields, and have started to spark the interest of biologists. Having the particularity of being cell friendly and allowing multimaterial deposition, extrusion-based 3D printing has been shown to be the method of choice for bioprinting. However as biologically relevant constructs often need to be of high resolution and high complexity, new methods are needed, to provide an improved level of control on the deposited biomaterials. In this paper, we demonstrate how microfluidics can be used to add functions to extrusion 3D printers, which widens their field of application. Micromixers can be added to print heads to perform the last-second mixing of multiple components just before resin dispensing, which can be used for the deposition of new polymeric or composite materials, as well as for bioprinting new materials with tailored properties. The integration of micro-concentrators in the print heads allows a significant increase in cell concentration in bioprinting. The addition of rapid microfluidic switching as well as resolution increase through flow focusing are also demonstrated. Those elementary implementations of microfluidic functions for 3D printing pave the way for more complex applications enabling new prospects in 3D printing.

Multifunctional 3D printing of heterogeneous hydrogel structures.

Multimaterial additive manufacturing or three-dimensional (3D) printing of hydrogel structures provides the opportunity to engineer geometrically dependent functionalities. However, current fabrication methods are mostly limited to one type of material or only provide one type of functionality. In this paper, we report a novel method of multimaterial deposition of hydrogel structures based on an aspiration-on-demand protocol, in which the constitutive multimaterial segments of extruded filaments were first assembled in liquid state by sequential aspiration of inks into a glass capillary, followed by in situ gel formation. We printed different patterned objects with varying chemical, electrical, mechanical, and biological properties by tuning process and material related parameters, to demonstrate the abilities of this method in producing heterogeneous and multi-functional hydrogel structures. Our results show the potential of proposed method in producing heterogeneous objects with spatially controlled functionalities while preserving structural integrity at the switching interface between different segments. We anticipate that this method would introduce new opportunities in multimaterial additive manufacturing of hydrogels for diverse applications such as biosensors, flexible electronics, tissue engineering and organ printing.

Spreading of the nanofluid triple line in ink jet printed electronics tracks

One of the next avenues for Additive Manufacturing to develop is that of multi-material deposition in order to add functionality to the already complex geometries that are capable of being manufactured. However, for electronic applications the fidelity of the deposited electronic tracks is of utmost importance. The purpose of this study was to investigate the effects of solid surface tensions, σsg−σsl, on the quality of printed lines, using 30–40nm silver nanofluid ink. The solid surface tensions of silver ink on glass and polytetrofluoroethylene (PTFE) substrates were determined theoretically, knowing characteristics of droplet. Meanwhile, a Dimatix printer with nozzles of size of 21.5μm was used to print conductive lines on smooth glass and PTFE substrates. The printed lines on glass were observed to be continuous with high quality of triple line, which was attributed to the high solid surface tensions of silver nanofluid ink on glass substrates. The solid surface tensions of silver nanofluid ink were relatively low on PTFE, as results the printed lines were discontinuous. The solid surface tensions were introduced as a reliable criterion to predict the printability of nanofluids. The distribution of silver nanoparticles and layering phenomenon in silver nanofluid triple region on glass substrate was clearly observed, using environmental scanning electron microscopy (ESEM) for the first time. In addition to disjoining pressure, the size of droplet and affinity of nanofluid for substrate were observed to have important influences on spreading of nanoparticles in triple region.