Digital Light Processing 3D Printing Research Articles

Ceramic bodies without warping using epoxide–acrylate hybrid ceramic slurry for photopolymerization‐based 3D printing

AbstractTo be able to produce ceramic bodies with complex shapes without interlayer delamination and warping through vat photopolymerization‐based 3D printing techniques, photosensitive ceramic slurries should be studied to prepare 3D printed green and sintered bodies. In this study, we developed dual curable acrylate–epoxide ceramic slurries for digital light processing (DLP) 3D ceramic printing. The dual curing process of the slurries is a combination of photo‐radical polymerization of acrylate and thermal cationic polymerization of cyclo‐aliphatic epoxide. The green bodies prepared by dual curing of the slurries showed higher fracture strength and better adhesion between layers and between starting particles and binder polymer in comparison to acrylate‐based green body. These advantages were due to higher crosslinking density of the binder matrix and hydrogen bonding by hydroxyl groups from epoxide ring opening. The green and sintered bodies printed with improved slurry and DLP 3D printer had flat shape without warping unlike those from acrylate‐based bodies. Moreover, the distribution of inter‐particle necking in the sintered body was uniform and the interface boundary between layers was not observed. This is because of excellent uniformity of the dual cured acrylate–epoxide polymer matrix (uniform crosslinking density in layers) in the green body and hydroxyl groups generated by epoxy ring opening.

Biobased vitrimer synthesized from 2-hydroxy-3-phenoxypropyl acrylate, tetrahydrofurfuryl methacrylate and acrylated epoxidized soybean oil for digital light processing 3D printing

The development of sustainable biobased vitrimeric materials is critical for the environment. Herein, UV-curable resins composed of the monomers derived from glycerol, soybean oil, and hemicellulose have been designed and applied in digital light processing (DLP) 3D printing. The use of hemicellulose-derived monomer tetrahydrofurfuryl methacrylate for resins can increase the tensile strength that is used to calculate the reprocessability efficiency. The vitrimeric properties of the resulting polymers such as shape memory, weldability, repairability, and reprocessability have been investigated. The most suitable resin for DLP 3D printing containing a sufficient amount of hydroxyl and ester groups that are essential in transesterification reactions has been selected according to the results of the real-time Fourier transform infrared spectroscopy and real-time photorheometry measurements. By activating dynamic transesterification reactions at elevated temperatures, the 3D printed samples exhibited shape memory, repairability, and reprocessability properties. A recovery ratio of 100 %, repairability with improved tensile strength by 2 times, and a recycling efficiency of 344 % was reached by incorporating tetrahydrofurfuryl methacrylate into the resins. The recycling efficiency achieved is 10 times higher compared to a similar vitrimer based on glycerol and soybean oil.

Digital light processing 3D printing of Hydrochlorothiazide with modified release

Digital light processing 3D printing of Hydrochlorothiazide with modified release

3D-printed polyacrylamide-based hydrogel polymer electrolytes for flexible zinc-ion battery

Zinc ion batteries (ZIBs) are a highly cost-effective and safe option for electrochemical energy storage, particularly suited for flexible wearable devices. However, the development of hydrogel polymer electrolytes (HPEs) for ZIBs using 3D printing technology presents challenges in terms of performance, stability, and durability. The purpose of this study is to address these challenges by creating 3D-printed flexible HPEs with varying porosity from polyacrylamide (PAM) using digital light processing (DLP) 3D printing. The electrochemical properties of the 3D-printed HPEs were compared to conventional casted HPEs. The 3D printed HPEs exhibited improved electrochemical performance, especially in ionic conductivity (28.10 mS cm−1, equivalent to the current conventional HPEs). Higher porosity in the 3D printed HPEs enhanced electrolyte absorption and facilitated Zn2+ ions diffusion, as confirmed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results. Furthermore, galvanostatic charge-discharge (GCD) measurements demonstrated that the 3D-printed PAM hydrogel electrolyte with 40% porosity achieved a specific capacity of 161.4 mAh g−1 at 0.1 A g−1. The findings validate the potential of the 3D-printed PAM hydrogel as a flexible HPE for ZIBs. The customized design structure of the 3D-printed HPEs enabled improved electrochemical properties, surpassing the limitations of conventional casted HPEs.

Development and Digital Light Processing 3D Printing of a Vitrimer Composed of Glycerol 1,3-Diglycerolate Diacrylate and Tetrahydrofurfuryl Methacrylate.

The development of biobased reshapable and repairable vitrimers has received extensive attention due to the growing focus on an environmentally friendly society. Therefore, the objective of this research was to synthesize sustainable polymers with an environmentally friendly strategy combining the benefits of renewable resources, UV curing, and vitrimers. Two biobased monomers, glycerol 1,3-diglycerolate diacrylate and tetrahydrofurfuryl methacrylate, were chosen for the preparation of UV-curable resins and tested by real-time photorheometry and RT-FTIR spectroscopy to determine their suitability for digital light processing (DLP) 3D printing. DLP 3D-printed polymer showed shape memory, weldability, and repairability capabilities by triggering the dynamic transesterification process at high temperatures. The vitrimer with a weight ratio of 60:40 of glycerol 1,3-diglycerolate diacrylate and tetrahydrofurfuryl methacrylate showed shape memory properties with a recovery ratio of 100% and a 7-fold improved tensile strength compared to the original sample, confirming efficient weldability and repairability.

A digital light processing 3D printing approach for tuning the interfacial properties of pore forming agents for porous ceramics

The utilization of pore forming agents (PFAs) in digital light processing (DLP) 3D printing to manufacture porous ceramics through their thermal decomposition has received a great deal of attention. Nevertheless, even though the inner PFA microstructure of a green body is an essential precondition for tailoring the properties of porous ceramics, the approaches established to date have only focused on post-processing. To address this gap, the present study demonstrates a novel DLP approach to elucidate how PFAs are formed in green bodies during DLP 3D printing. Specifically, complex UV light scattering patterns that are common in composite DLP 3D printing and often detrimental were exploited to modify the interface between PFA and the ceramic-polymer matrix. This was done through modulation of the size difference between ceramics and PFAs as well as the DLP's process parameters. Additionally, a method for inferring the interfacial properties of PFAs embedded in a green body through surface characterization is proposed.

Digital light processing 3D printing for microfluidic chips with enhanced resolution via dosing- and zoning-controlled vat photopolymerization

Conventional manufacturing techniques to fabricate microfluidic chips, such as soft lithography and hot embossing process, have limitations that include difficulty in preparing multiple-layered structures, cost- and labor-consuming fabrication process, and low productivity. Digital light processing (DLP) technology has recently emerged as a cost-efficient microfabrication approach for the 3D printing of microfluidic chips; however, the fabrication resolution for microchannels is still limited to sub-100 microns at best. Here, we developed an innovative DLP printing strategy for high resolution and scalable microchannel fabrication by dosing- and zoning-controlled vat photopolymerization (DZC-VPP). Specifically, we proposed a modified mathematical model to precisely predict the accumulated UV irradiance for resin photopolymerization, thereby providing guidance for the fabrication of microchannels with enhanced resolution. By fine-tuning the printing parameters, including optical irradiance, exposure time, projection region, and step distance, we can precisely tailor the penetration irradiance stemming from the photopolymerization of the neighboring resin layers, thereby preventing channel blockage due to UV overexposure or compromised bonding stability owing to insufficient resin curing. Remarkably, this strategy can allow the preparation of microchannels with cross-sectional dimensions of 20 μm × 20 μm using a commercial printer with a pixel size of 10 μm × 10 μm; this is significantly higher resolution than previous reports. In addition, this method can enable the scalable and biocompatible fabrication of microfluidic drop-maker units that can be used for cell encapsulation. In general, the current DZC-VPP method can enable major advances in precise and scalable microchannel fabrication and represents a significant step forward for widespread applications of microfluidics-based techniques in biomedical fields.

4D printing of biodegradable elastomers with tailorable thermal response at physiological temperature

4D printing has a great potential for the manufacturing of soft robotics and medical devices. The alliance of digital light processing (DLP) 3D printing and novel shape-memory photopolymers allows for the fabrication of smart 4D-printed medical devices in high resolution and with tailorable functionalities. However, most of the reported 4D-printed materials are nondegradable, which limits their clinical applications. On the other hand, 4D printing of biodegradable shape-memory elastomers is highly challenging, especially when transition points close to physiological temperature and shape fixation under ambient conditions are required. Here, we report the 4D printing of biodegradable shape-memory elastomers with tailorable transition points covering physiological temperature, by using poly(D,L-lactide-co-trimethylene carbonate) methacrylates at various monomer feed ratios. After the programming step, the high-resolution DLP printed stents preserved their folded shape at room temperature, and showed efficient shape recovery at 37 °C. The materials were cytocompatible and readily degradable under physiological conditions. Furthermore, drug-loaded devices with tuneable release kinetics were realized by DLP-printing with resins containing polymers and levofloxacin or nintedanib. This study offers a new perspective for the development of next-generation 4D-printed medical devices.

Unexpected self-assembly of carbon dots during digital light processing 3D printing of vanillin Schiff-base resin

Bio-based and recyclable composite thermosets were obtained through digital light processing (DLP) 3D printing by dispersing cellulose-derived carbon dots (CDs) in a photocurable vanillin Schiff-base resin. The exposure of CDs to DLP induced a partial reduction of the oxygen functionalities and a self-assembly of CDs into micrometric fibers embedded in the thermoset matrix. A comparison with the vanillin Schiff-base thermoset, illustrated lower transition temperature from the glassy to the rubbery state and inferior shape memory properties for the CD containing thermoset. This is ascribed to a lower crosslinking density due to the replacement of the covalent interactions of the thermosets with supramolecular interactions generated inside the microfibers and between the microfibers and the surrounding matrix. This can also explain the inferior mechanical rigidity of the composites with respect to the single component thermosets. However, the supramolecular interactions endow the composites with better mechanical and chemical recyclability with an almost complete preservation of the original mechanical properties.

One-Step Method for Direct Acrylation of Vegetable Oils: A Biobased Material for 3D Printing.

The substitution of fossil resources by alternatives derived from biomass is a reality that is taking on a growing relevance in the chemical and energy industries. In this sense, fats, oils, and their derived products have become indispensable inputs due to their broad functional attributes, stable price and sustainable character. Acrylated vegetable oils are considered to be very versatile materials for very broad applications (such as in adhesives, coatings or inks) since, in the presence of photoinitiators, they can be polymerized by means of UV-initiated free radical polymerizations. The usual process for the synthesis of acrylate vegetable oils consists in reacting epoxidized oils derivatives with acrylic acid. Here, the influence of different catalysts on the activity and selectivity of the process of acrylation of epoxidized soybean oil is studied. In addition, a novel one-step method for direct acrylation of vegetable oils is also explored. This new approach advantageously uses the original vegetable resource and eliminates intermediate reactions, thus being more environmentally efficient. This study offers a simple and low-cost option for synthesizing a biomass-derived monomer and studies the potential for the 3D printing of complex structures via digital light processing (DLP) 3D printing of the thus-obtained novel sustainable formulations.

The Effects of Polyaniline Nanofibers and Graphene Flakes on the Electrical Properties and Mechanical Properties of ABS-like Resin Composites Obtained by DLP 3D Printing.

Three-dimensional printing is regarded as a future-oriented additive manufacturing technology that is making significant contributions to the field of polymer processing. Among the 3D printing methods, the DLP (digital light processing) technique has attracted great interest because it requires a short printing time and enables high-quality printing through selective light curing of polymeric materials. In this study, we report a fabrication method for ABS-like resin composites containing polyaniline (PANI) nanofibers and graphene flakes suitable for DLP 3D printing. As-prepared ABS-like resin composite inks employing PANI nanofibers and graphene flakes as co-fillers were successfully printed, obtaining highly conductive and mechanically robust products with the desired shapes and different sizes through DLP 3D printing. The sheet resistance of the 3D-printed composites was reduced from 2.50 × 1015 ohm/sq (sheet resistance of pristine ABS-like resin) to 1.61 × 106 ohm/sq by adding 3.0 wt.% of PANI nanofibers and 1.5 wt.% of graphene flakes. Furthermore, the AP3.0G1.5 sample (the 3D-printed composite containing 3.0 wt.% of PANI nanofibers and 1.5 wt.% of graphene flakes) exhibited 2.63 times (22.23 MPa) higher tensile strength, 1.47 times (553.8 MPa) higher Young's modulus, and 5.07 times (25.83%) higher elongation at break values compared to the pristine ABS-like resin with a tensile strength of 8.46 MPa, a Young's modulus of 376.6 MPa, and an elongation at break of 5.09%. Our work suggests the potential use of highly conductive and mechanically robust ABS-like resin composites in the 3D printing industry. This article not only provides optimized DLP 3D printing conditions for the ABS-like resin, which has both the advantages of the ABS resin and the advantages of a thermoplastic elastomer (TPE), but also presents the effective manufacturing process of ABS-like resin composites with significantly improved conductivity and mechanical properties.

Effect of reactive diluent concentration on rheological and curing behavior of zirconia ceramic slurry for DLP printing

AbstractA series of photosensitive zirconia ceramic slurry with adjustable viscosity and cured depth have been presented for the construction of high‐quality zirconia ceramic fabricated by digital light processing 3D printing. The rheological and curing behavior of the slurry can be flexibly optimized by tuning the reactive diluent concentration and category, since the change of dominant position of diluent on viscosity and the different curing mode. Monofunctional reactive diluent (HEA, hydroxyethyl acrylate) exhibits an enhanced dilution effect compared with that of bifunctional reactive diluent (HDDA, 1,6‐hexamethylene diacrylate) due to the lower molecular mass of monofunctional diluent. As a result, the viscosity reaches lower than 2000 mPa·s when the concentration of both HEA and HDDA exceeds 50 wt.%. At the same time, the non‐Newtonian properties of the slurry are also changed, which facilitates the printing process. However, excessive addition of diluent may generate more defects in ceramic green body. Consequently, the cured depth of zirconia slurry can reach 55 and 50 µm, respectively, at the curing time of 3 s while introducing the HEA or HDDA with the concentration below 70 wt.%, and the modified feedstock is promising for high‐quality and low‐defect zirconia ceramic components printing for biomedical applications.

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.

Mechanical characterization of Al2O3 twisted honeycomb structures fabricated by digital light processing 3D printing

Inspired by the double-helix structure of biological DNA, low-volume fraction and high-strength Al2O3 twisted honeycomb structures with characteristics similar to those of helical structures in the z-axis were prepared by digital light processing 3D printing technology. As the twist angle increased, the compressive strength of the fabricated Al2O3 structure decreased, and the deformation mechanism of the Al2O3 structures gradually changed from stretching-dominated to bending-dominated, which can be predicted by the Gibson–Ashby model. The relationship between the effective elastic modulus and the volume fraction that can be modified by varying the wall thickness was described by the Pabst–Gregorova exponential relationship. The compressive strength of the Al2O3 structure with a twist angle of 0° can reach 62.4 MPa at a volume fraction of 13.3%, providing guidance to optimize lightweight structures of ceramics.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials

3D‐Printed Inherently Porous Structures with Tetrahedral Lattice Architecture: Experimental and Computational Study of Their Mechanical Behavior

AbstractIncreasing demand in automotive, construction, and medical industries for materials with reduced weight and high mechanical durability has given rise to porous materials and composites. Materials combining nano‐ and microporosity and a well‐defined cellular macroporous architecture offer great potential weight reduction while maintaining mechanical durability. To achieve predictable mechanical performance, it is essential to apply experimental and computational efforts to precisely describe material structure–properties relationships. This study explores polymer structures with polymerization‐inherited porosity and well‐defined macroporous geometry, fabricated via digital light processing (DLP) 3Dprinting. Pore size and relative density are varied by ink composition and printing parameters to track their influence on the structure stiffness. Simulated stiffness values for the base polymer correspond to the experimentally determined elastic properties, showing Young's moduli of 554–722 MPa depending on the cosolvent ratio, which confirms the structure–properties relationship. Macroporosity is introduced in the form of a 3D tetrahedral bending‐dominated architecture with the resulting specific Young's moduli of 79.5 MPa cm3 g−1, comparable to foams. To merge the gap in stiffnesses, further investigation of structure–property relationships of various 3D–printed lattice architectures, as well as its application to other stereolithography methods to eliminate the negative effects from printing artifacts and resolution limit of the DLP 3D‐printing, are envisioned.

3D Printing Transparent γ‐Alumina Porous Structures Based on Photopolymerizable Sol–Gel Inks

AbstractA novel method for fabricating transparent porous γ‐alumina 3D structures by printing at high resolution is presented. The process is based on combining digital light processing 3D printing (DLP) and sol–gel reactions, all performed in transparent solutions, resulting in ceramic monolithic porous structures. The aqueous printing solution contains mainly aluminum chloride, propylene oxide (PO), ethanol, and acrylic acid (AA). The printed polymerized structures are aged, followed by supercritical drying (SCD), and sintered at high temperatures. During aging and sintering, the printed objects shrink, thus enabling a final printing resolution far beyond the nominal value of the used printer. The resulting structures are crystalline γ‐Al2O3, with a very high surface area, above 1800 m2 g−1, and optical transmission above 80% at 600 nm. In addition, SCD enables precise control of pores’ dimensions and total surface area, which are essential for applications including thermal insulation and catalyst support and for obtaining heat‐resistant transparent optical devices.

Preparation of large-size alumina ceramic parts by DLP 3D printing using high-solid-loading paste and optimizing the debinding process

Digital light processing (DLP) is a promising additive manufacturing method for creating complex structural alumina ceramic with high precision, high efficiency, and low cost. However, printing large-size parts with high feature resolution by DLP, obtaining high-performance pastes, and optimizing the debinding process are challenges that still need to be overcome. In this study, an advanced top-down Matrix-DLP technology that seamlessly connects two high-definition-resolution DLP projectors, with high resolution and a large projection area, was used to achieve fine-structured large-size alumina green bodies. The homogeneous and stable non-self-levelling alumina pastes suitable for the DLP technology were developed, with a high solid loading up to 55 vol%, viscosity of 35.0 Pa s at 30 s−1, and good rheological properties by innovatively using 2.5 wt% P5318 as surface modifiers of alumina powders and with only a 0.244% volume of bubble residue by using 0.5 wt% BYK-066N defoamer in combination with a vacuum planetary stirring defoaming process. The debinding processes were designed based on TG-DSC analysis and then optimized, and it was proved that the segmented-atmosphere debinding process was the best approach and can obtain defect- and carbon residue-free bodies with uniform grain distribution, and can also achieve non-destructive debinding for the thick-walled parts with thickness greater than 10 mm. The effects of the debinding residual carbon and the solid loading on the microstructure and properties after sintering were also investigated. Consequently, the high-precision large-size alumina ceramic with good interlayer bonding, dense microstructure, and high microhardness of 17.92 GPa was obtained.

Development of polymeric/MXenes composites towards 3D printable electronics

3D printing is an emerging technology for many applications, including electronics. On the other hand, to gather the applications’ requirements with the possibility to produce complex 3-dimensional structures, the development of novel 3D printable materials is necessary. In this context, herein it is reported the synthesis of 3D printable photocurable resins embedding Ti3C2Tz-MXenes, a class of 2D layered materials with outstanding electrical and electronic properties. Stable inks suitable for Digital Light Processing 3D printing technology have been successfully synthesized and employed to fabricate complex 3D composite structures with high printing fidelity. To enhance the electrical conductivity of the material, annealing treatments have been performed, followed by a complete characterization of the so obtained materials. The results show that objects with improved electrical conductivity have been successfully obtained, opening new perspectives in towards the development of complex 3 dimensional electronic.

Fabrication of Chemotaxis Microfluidic Device Mould Using Digital Light Processing 3D Printing Method

Chemotaxis microfluidic devices are one type of lab-on-a-chip (LOC) devices that functions to minimize the volume of sample used and the testing time by conducting an analysis on a smaller scale. Chemotaxis microfluidic devices consist of micro-scale features that are delicate to be produced using conventional manufacturing methods. Chemotaxis microfluidic devices are generally manufactured using soft lithography. This study attempts to apply hot embossing process to replace soft lithography process, in which the hot embossing mould was fabricated using 3D printing, especially digital light processing (DLP) methods. This project investigates the challenges of fabricating the hot embossing mould of chemotaxis microfluidic device using DLP 3D printing. Three printed orientations for the moulds were produced and compared. The three moulds are subsequently used in the hot embossing process to produce chemotaxis microfluidic devices on poly(methyl methacrylate) (PMMA) substrate. The performance of the moulds is compared to the mould produced by micro-milling process using qualitative (visual analysis) and quantitative (dimensional analysis) methods. The analysis shows that DLP 3D printed moulds have comparable quality with those produced by micro-milling. The printing orientation has significant effect on the dimensional differences between the mould and design with mould WT (area of width and thickness attached to the platform) has the smallest dimensional differences.