3D-printed Structures Research Articles

Three-dimensional printing with waste acrylonitrile butadiene styrene: Processing and characterization

Three-dimensional (3D) printing of waste plastic such as acrylonitrile butadiene styrene (ABS) is challenging because multiple heating cycles and irregular cooling cause accumulation of stress in 3D-printed structures, which significantly affects mesostructured and fiber-to-fiber bond strength. Hence, this study demonstrates the ability to print high-quality parts via 3D printing using ABS waste. The different weight proportions (100, 90/10, 80/20, 70/30, 60/40, 50/50) of recycled ABS (RABS)/virgin ABS (VABS) are selected for experimentation. It is found that increasing VABS content in RABS significantly improved the physical properties of samples. Due to VABS blending in RABS, the average enhancement in flexural strength (Sf), flex modulus (Ef), and work of fracture (WOF) are 11.49%, 5.45%, and 17.31%, respectively, when compared with 100% RABS samples. Similarly, the average increase in Young’s modulus (E), tensile strength at yield (Ty), and ultimate tensile strength (UTS) are 7.71%, 5.19%, and 3.51%, respectively. The samples printed with 50% RABS/50% VABS blends show superior mechanical properties than others, also the properties of 90% RABS/10% VABS and 80% RABS/20% VABS are very close to 100% VABS samples. Hence, this study provides unique opportunities for the sustainable use of waste ABS using 3D printing technology.

Engineering 3D-printed carbon structures with atomic layer deposition coatings as photoelectrocatalysts for water splitting

3D-printed carbon structures are lightweight, conductive, and durable in harsh conditions. A straightforward surface treatment allows for functional ALD coatings, enhancing light-driven hydrogen and oxygen evolution reactions.

Synthesis of TiO2 Nanotube Arrays on 3D-Printed Structures for Application as Fischer-Tropsch Synthesis Catalysts

In this work, 3D-printed Ti6Al4V structures are used as substrates to synthesize TiO2 nanotube arrays by electrochemical anodization. These nanostructured materials are used as supports for bimetallic FeCo catalysts in...

Addressing bioprinting challenges in tissue engineering

This paper discusses the current challenges and potential solutions in the field of bioprinting tissues and organs. It highlights that most bioprinted tissues are small, composed of few cell types, lack vascular systems, and have limited functionality. This paper emphasizes the need to develop methods to obtain various functional cell types, create vascular systems for nutrient delivery, and enhance the size and capabilities of 3D-printed tissue structures. Additionally, it explores the advancements in nanorobots in the medical field, focusing on their unique properties and applications in various medical areas like cancer, cardiology, and neurology.

Combination of nanofibers with 3D-printed or 4D-printed structures

Combination of nanofibers with 3D-printed or 4D-printed structures

3D printing of polyvinyl alcohol hydrogels enabled by aqueous two-phase system.

The synthesis of PVA hydrogels (PVA-Hy) requires a highly basic environment (e.g., an aqueous solution of sodium hydroxide, NaOH, 14% w/w, 4.2 M), but the rapid crosslinking of PVA due to high pH makes it challenging to perform layer-by-layer three-dimensional (3D) printing of PVA-Hy. This work demonstrated 3D printing of PVA-Hy in moderate alkaline conditions (e.g., NaOH, 1% w/w, 0.3 M) assisted by aqueous two-phase system (ATPS). Salting out of PVA to form ATPS allowed temporal shape retention of a 3D-printed PVA structure while it was physically crosslinked in moderate alkaline conditions. Crucially, the layer-to-layer adhesion of PVA was facilitated by delayed crosslinking of PVA that required additional reaction time and overlapping between the layers. To verify this principle, we studied the feasibility of direct ink write (DIW) 3D printing of PVA inks (5-25% w/w, μ = 0.1-20 Pa s, and MW = 22 000 and 74 800) in aqueous embedding media offering three distinct chemical environments: (1) salts for salting out (e.g., Na2SO4), (2) alkali hydroxides for physical crosslinking (e.g., NaOH), and (3) a mixture of salt and alkali hydroxide. Our study suggested the feasibility of 3D-printed PVA-Hy using the mixture of salt and alkali hydroxide, demonstrating a unique concept of embedded 3D printing enabled by ATPS for temporary stabilization of the printed structures to facilitate 3D fabrication.

Design and development of a small-scale cement-based 3D printing robot extrusion nozzle

Additive manufacturing (AM), also known as three-dimensional (3D) printing, offers great potential to create complex structures layer by layer from computer-aided design (CAD) models. Despite advancements in printable concrete technology, controlling printing quality remains a challenge associated with both the geometric and materials design of the printer nozzle, especially for small-scale printing that may be required by small and medium-sized enterprises (SMEs). Therefore, this study explored the design and development of a robot nozzle system, optimised for a small-scale 3D printing of cement-based structures. Key design considerations included weight, nozzle diameter/shape, material compatibility, flow control, mixing mechanism, temperature resistance, cost-effectiveness, adaptability, safety, and ease of maintenance. Iterative designs were developed, focusing on stress concentration mitigation and material flow optimisation. The challenge of incorporating mixing mechanisms during nozzle designs was discussed, leading to the adoption of an on-demand accelerator spraying system. This method involved a micro-peristaltic pump connected to an accelerator tank, spraying accelerator onto the surface of the deposited material, as the robot moved along its programmed path. Evidently, both the nozzle design and the spraying approach improved the buildability and print quality of the extrusion-based 3D-printed cement-based structures.

Modelling and bending analysis of a 3D-printed sandwich structure with an auxetic star-4 core

Quasi-static 3-point bending of additive manufactured sandwich components with auxetic star-4 cores was investigated to obtain information on the influence of geometry parameters of the auxetic structure on the stress distribution of the face sheets. Experiments were carried out on specimens manufactured by fused deposition modelling from a PLA polymer to verify a simulation model for analyses. A hyperelastic material model was used in the finite element models to describe the elastic material behaviour and a hardening model to consider plasticity. Nanoindentation tests on the printed structures were conducted to identify the material parameters with modelling the nanoindentation procedure using the finite element method and applying automated optimisation techniques. This approach enabled an accurate reproduction of the nanoindentation tests in the simulations. The derived models for analysing the auxetic geometry have shown that the stress distribution in the face sheets of the sandwich components can be noticeably influenced with targeted changing the wall thicknesses of the auxetic star-4 structure. The simulations have also made it apparent that more effort is required to take into account the influences of the printing process on the deformation behaviour of the sandwich structure in the simulation model.

Energy Absorption by 3D-Printed Mesh Structures with a Negative Poisson’s Ratio

Energy Absorption by 3D-Printed Mesh Structures with a Negative Poisson’s Ratio

Optic-Fiber-Based Optogenetic Stimulator With μLED and 3D-Printed Structures for Brain Stimulation

Optic-Fiber-Based Optogenetic Stimulator With μLED and 3D-Printed Structures for Brain Stimulation

Double-crosslinkable poly(urethane)-based hydrogels relying on supramolecular interactions and light-initiated polymerization: promising tools for advanced applications in drug delivery.

Physical and chemical hydrogels are promising platforms for tissue engineering/regenerative medicine (TERM). In particular, physical hydrogels are suitable for use in the design of drug delivery systems owing to their reversibility and responsiveness to applied stimuli and external environment. Alternatively, the use of chemical hydrogels represents a better strategy to produce stable 3D constructs in the TERM field. In this work, these two strategies were combined to develop multi-functional formulations integrating both drug delivery potential and TERM approaches in a single device. Specifically, a novel photo-sensitive poly(ether urethane) (PEU) was developed to form supramolecular networks with α-cyclodextrins (α-CDs). The PEU was successfully synthesized using Poloxamer® 407, 1,6-diisocyanatohexane and 2-hydroxyethyl methacrylate, as assessed by infrared spectroscopy, size exclusion chromatography and proton nuclear magnetic resonance (1H NMR) spectroscopy. Subsequently, PEU thermo-responsiveness was characterized through critical micelle temperature evaluation and dynamic light scattering analyses, which suggested the achievement of a good balance between molecular mass and overall hydrophobicity. Consequently, the formation of supramolecular domains with α-CDs was demonstrated through X-ray diffraction and 1H NMR spectroscopy. Supramolecular hydrogels with remarkably fast gelation kinetics (i.e., few minutes) were designed using a low PEU concentration (≤5% w/v). All formulations were found to be cytocompatible according to the ISO 10993-5 regulation. Notably, the hydrogels were observed to possess mechanical properties and self-healing ability, according to rheological tests, and their fast photo-crosslinking was evidenced (<60 s) by photo-rheology. A high curcumin payload (570 μg mL-1) was encapsulated in the hydrogels, which was released with highly tunable and progressive kinetics in a physiological-simulated environment for up to 5 weeks. Finally, a preliminary evaluation of hydrogel extrudability was performed using an extrusion-based bioprinter, obtaining 3D-printed structures showing good morphological fidelity to the original design. Overall, the developed hydrogel platform showed promising properties for application in the emerging field of regenerative pharmacology as (i) easily injectable drug-loaded formulations suitable for post-application stabilization through light irradiation, and (ii) biomaterial inks for the fabrication of patient-specific drug-loaded patches.

A high-performance design of tubular lattice structure having zero Poisson’s ratio

In this work, novel zero Poisson’s ratio (ZPR) tubular lattice structures, named as strut-reinforced semi-reentrant honeycomb (SR-SRH), were designed. Finite element simulations of quasi-static compression were conducted, and Design of Experiments (DoE) technique was used to study the effects of geometric parameters of the tubular lattices on the mechanical properties. One of the proposed designs of SR-SRH tubular lattices (SR-SRH-1) exhibited remarkably higher ZPR strain limit and energy absorption ability compared to previously studied ZPR tubular lattices. Another design (SR-SRH-2) demonstrated excellent compressive strength and elastic modulus. These 3D-printed structures were tested under quasi-static compression to corroborate the numerical simulations.

Surface-Wetting Characteristics of DLP-Based 3D Printing Outcomes under Various Printing Conditions for Microfluidic Device Fabrication.

In recent times, the utilization of three-dimensional (3D) printing technology, particularly a variant using digital light processing (DLP), has gained increasing fascination in the realm of microfluidic research because it has proven advantageous and expedient for constructing microscale 3D structures. The surface wetting characteristics (e.g., contact angle and contact angle hysteresis) of 3D-printed microstructures are crucial factors influencing the operational effectiveness of 3D-printed microfluidic devices. Therefore, this study systematically examines the surface wetting characteristics of DLP-based 3D printing objects, focusing on various printing conditions such as lamination (or layer) thickness and direction. We preferentially examine the impact of lamination thickness on the surface roughness of 3D-printed structures through a quantitative assessment using a confocal laser scanning microscope. The influence of lamination thicknesses and lamination direction on the contact angle and contact angle hysteresis of both aqueous and oil droplets on the surfaces of 3D-printed outputs is then quantified. Finally, the performance of a DLP 3D-printed microfluidic device under various printing conditions is assessed. Current research indicates a connection between printing parameters, surface roughness, wetting properties, and capillary movement in 3D-printed microchannels. This correlation will greatly aid in the progress of microfluidic devices produced using DLP-based 3D printing technology.

Metal-Plastic Hybrid Additive Manufacturing to Realize Small-Scale Self-Propelled Catalytic Engines.

Microengines driven by catalytic decomposition of a fuel have been an interesting research area recently due to their diverse applications, such as environmental monitoring and drug delivery. Literature reports a number of studies on this topic where researchers have made various attempts to manufacture such microengines. Some such methods are deposition of catalytic metal layers on sacrificial photoresists, electrochemical deposition of metal layers on polymeric structures, or 3D printing of structures followed by multi-step loading of structures with catalysts. These methods, even though proven to be effective, are tedious, time-consuming, and expensive. To address these issues, herein we report a 3D printing technique to realize microengines in a simple, rapid, and inexpensive single-step process. The printing of various shapes of microengines is achieved using digital light processing printing of a catalyst resin, where Pd(II) acts as a catalyst resin. The proposed integrated molding process can achieve cost-effective preparation of high-efficiency microengines. We demonstrate the locomotion of these microengines in 30% (w/w) H2O2 through the decomposition of H2O2 to generate oxygen to facilitate the self-propelled locomotion. The study characterizes the microengine based on several factors, such as the role of H2O2, Pd, shape, and design of the microengine, to get a full picture of the self-locomotion of microengines. The study shows that the developed method is feasible to manufacture microengines in a simple, rapid, and inexpensive manner to be suitable for numerous applications such as environmental monitoring, remediation, drug delivery, diagnosis, etc., through the modification of the catalyst resin and fuel, as desired.

3D-printed multilayer structures for high-numerical aperture achromatic metalenses.

Flat optics consisting of nanostructures of high-refractive index materials produce lenses with thin form factors that tend to operate only at specific wavelengths. Recent attempts to achieve achromatic lenses uncover a trade-off between the numerical aperture (NA) and bandwidth, which limits performance. Here, we propose a new approach to design high-NA, broadband, and polarization-insensitive multilayer achromatic metalenses (MAMs). We combine topology optimization and full-wave simulations to inversely design MAMs and fabricate the structures in low-refractive index materials by two-photon polymerization lithography. MAMs measuring 20 μm in diameter operating in the visible range of 400 to 800 nm with 0.5 and 0.7 NA were achieved with efficiencies of up to 42%. We demonstrate broadband imaging performance of the fabricated MAM under white light and RGB narrowband illuminations. These results highlight the potential of the 3D-printed multilayer structures for realizing broadband and multifunctional meta-devices with inverse design.

Design and Fabrication of Flexible Woodpile Structured Nanocomposite for Microwave Absorption Using Material Extrusion Additive Technique

The explosive growth of electronics and the widespread use of transient power sources have given rise to an undesirable and uncontrolled consequence of electromagnetic interference (EMI). It is crucial to address and mitigate the issues caused by EMI by developing effective shielding techniques. The material extrusion additive technique provides a solution through its versatile 3D printing of polymeric ink, offering advantages such as design flexibility, structural complexity, and environmental sustainability. The primary objective of this study is to investigate the rheological properties, electromagnetic properties, and thermal stability of nanocomposites consisting of Polydimethylsiloxane (PDMS) and Multi-Walled Carbon Nanotubes (CNTs). The aim is to utilize these findings for the design and 3D printing of a microwave absorber with high efficiency. Composite inks containing 50 vol% (C50) and 60 vol% (C60) of CNTs exhibit favorable shear-thinning behavior and shape retention. On the other hand, lower CNT percentages result in inconsistent viscosity, rendering the inks non-printable. Thermogravimetry analysis reveals that an increase in CNT vol% leads to a decrease in the thermal stability of 3D-printed PDMS-CNT nanocomposites. Higher CNT proportion enhances electric polarization, and attenuation capacity, as evidenced by measurements of complex permittivity and dielectric loss tangent. X-Ray Diffraction analysis was employed to examine the effect of CNT inclusion in the composites. A woodpile-structured metamaterial microwave absorber based on gradient index (GWMMA) was designed by manipulating geometric parameters and CNT vol%. Fifteen unit cell configurations were generated and subsequently chosen based on their exceptional attenuation capabilities, low impedance, and narrower filament width for simulations. The GWMMA demonstrates exceptional absorption performance, surpassing reflection loss values of −10dB. Incorporating a third filament stacking into the woodpile structure augments its efficacy, yet further additions of stackings result in diminishing returns. Experimental validation of a selected 3D-printed GWMMA structure of C60 with a width of 0.75 mm confirms its absorption capabilities, closely aligning with the simulated results. The GWMMA exhibits promising performance for microwave absorption, with absorption values exceeding 90%. Simulations indicate the adjustability of the GWMMA's bandwidth and absorption capabilities through alterations in array periodicity and cell size. Its spatial scale aligns with sub-wavelength structures, establishing it as a representative Metamaterial Absorber (MMA).

Optical fiber Bragg grating (FBG)-based strain sensor embedded in different 3D-printed materials: A comparison of performance

A compact fiber Bragg grating (FBG)-based strain sensor has been developed by embedding an FBG inside a 3D-printed structure, allowing the comparison of FBG responses across different filaments such as polylactic acid (PLA), thermoplastic polyurethane (TPU), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and nylon. Results have shown that FBG embedded in TPU can be effective in the measurements of mechanical strain, giving a responsivity value of 17.70 pm/cm with outstanding linearity of 98 %. Furthermore, small-scale field testing conducted in below-ground environments has shown that strain sensors based on FBG embedded in TPU are the most effective. They offer a responsivity of 13.9 pm/kg with a small standard deviation and high linearity. Additionally, they have the highest temperature sensitivity value of 15.4 pm/°C compared to the other embedded FBGs. Therefore, for most industrial applications, the FBG embedded in TPU can be considered as an alternative to existing embedment methods for strain sensing applications.

Effect of Topology Parameters on Physical–Mechanical Properties of Magnetic PLA 3D-Printed Structures

This work aims to characterize 3D-printed structures composed of a thermoplastic material (polylactic acid (PLA)) containing a combination of magnetic particles composed of iron(III) oxide (hematite) and iron(II)–iron (III) oxide (magnetite) with various infill densities and print orientations in regard to their possible processing by Fused Filament Fabrication additive technology. The correct processing temperatures have been determined using thermal analysis, and the paramagnetic and mechanical properties of the samples have been tested. The relative permeability has been identified to be strongly dependent on the topology parameters of the tested samples. The results of the inductance values for the samples without magnetic additives (infill densities 50% and 100%) have been detected to be comparable; nonetheless, the magnetic samples with 100% infill density has been found to be about 50% higher. A similar trend has been observed in the case of the values of the relative permeability, where the magnetic samples with 100% infill density have been measured as having an about 40% increased relative permeability in the comparison with the samples without magnetic additives (infill densities 20–100%). Finite Element Modelling (FEM) simulations have been applied to determine the magnetic field distributions and, moreover, to calculate the holding forces of all the printed samples. The maximum value of the holding force for the minimum distance of the plastic plate has been found to reach a value of almost 300 N (magnetic sample with 100% infill density). The obtained comprehensive characterization of the printed samples may be utilized for designing and tuning the desired properties of the samples needed in various industrial applications.

Life cycle assessment on fabrication and characterization techniques for additively manufactured polymers and polymer composites

Life cycle assessment (LCA) is a powerful tool to evaluate the environmental impacts of any domestic or industrial activity consuming goods and services. There has been an increasing interest in recycling polymers and polymer composites for circular economy and sustainability; however, the widespread use of polymers should be avoided upfront, especially for research and development. LCA is performed to evaluate the environmental impact of two characterization approaches (numerical modeling and experimentation) used for additively manufactured polymers and composites. The current study was conducted using GaBi software, per the International Organization for Standardization (ISO) 14040 and 14044 guidelines. Five different environmental impacts, namely global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), ozone layer depletion (ODP), and fossil fuel depletion (FFD), were evaluated and compared for numerical modeling and experimental characterization approaches. Electrical energy used during the filament fabrication, 3DP process, and mechanical testing was identified as a hotspot in the environmental impacts (GWP, AP, EP, and FFD) for experimental design. However, the materials consumed during the experimental characterization contributed considerably to ODP. Results concluded that using the numerical modeling approach could significantly reduce the environmental impact caused due to extensive resource utilization in experiments. The numerical modeling approach can help promote sustainability as these tools can adequately predict the response of 3D-printed structures; therefore, they should be explored and improved further.

Nanomaterials Function in Additive Manufacturing

Nanomaterials are substances that have at least one dimension that falls within the three-dimensional nanoscale range or fundamental structural components made of substances that fall inside this range. Micro-nano 3D printing technology can realize the processing of 3D micro-nano structures with nanometer precision and has broad application prospects in many fields. Metals and polymers can be easily connected through bonding reactions to obtain metal-metal or covalent bonds in 3D printing. These potent chemical bonds make 3D-printed structures stable, and 3D printing of metals and plastics is developing rapidly. The review focuses on the latest developments in unique composite nanomaterials for different field applications, comprising nanomaterials and 3D printing technology. A summary of the mechanisms, functional characteristics, benefits, drawbacks, and applications of various nanomaterials used in scientific 3D printing includes metal-based nanomaterials, metal-organic frameworks, upconversion nanoparticles, and lipid-based nanoparticles. Finally, this study presents an overview and highlights the issues that need to be resolved for nanomaterials to continue to be developed for the advantages of 3D printing.