Digital Light Processing 3D Printing Research Articles

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.

Silicone Elastomer with High Elongation at Break Used in Digital Light Processing 3D Printing

Silicone Elastomer with High Elongation at Break Used in Digital Light Processing 3D Printing

3D printable resin/carbon nanotube composites for wearable strain sensors: Enhancing mechanical and electrical properties

Electrically conductive composite materials are widely used for several applications, particularly flexible strain sensors for wearable electronic devices to detect human motions or apply to soft robotic technologies. Among the carbon nanotube (CNT) composites for strain sensors, the CNT composites with polypyrrole (PPy) have been scarcely found for electromechanical property improvement via digital light processing (DLP) 3D printing. Thus, this research presents a 3D printing fabrication of flexible polyurethane/CNT/PPy (FPU/CNT/PPy) composites for high complexity and model specifications, particularly strain sensing. The FPU/CNT/PPy composites were prepared as photopolymer resin with various proportions of the three components. The composites successfully achieved a gauge factor of 91.9 at 20 percent strain with high durability in 100 stretching-releasing cycles. More than 85% of printing accuracy was also found under the DLP 3D printing method. The small deformation of the composites could be detected during the stretching-releasing process during time-dependent testing. Examples of simple human activity and complex spring motion could be successfully detected due to the high responsibility and reproducibility of the finger motion. The composites mentioned in this study could reach the field of strain sensing and can further be applied to other fields such as healthcare and soft robotics.

Low‐Temperature Resistant Stretchable Micro‐Supercapacitor Based on 3D Printed Octet‐Truss Design (Small 23/2023)

Micro-Supercapacitors In article number 2207634, Hui Ying Yang and co-workers develop an innovative stretchable micro-supercapacitor with excellent resistance to freezing. Using digital light processing (DLP) 3D printing technology, an interdigital electrode with octet-truss lattice structure has been designed to enhance the electrochemical performance of the micro-supercapacitor. It is anticipated that the proposed design concept will be applicable for next-generation stretchable electronics.

Digital light processing 3D printing of porous ceramics based on multi-materials additive manufacturing

Digital light processing 3D printing of porous ceramics based on multi-materials additive manufacturing

Study of Forming Performance and Characterization of DLP 3D Printed Parts.

In order to explore the effect of printing parameter configurations on the forming performance of Digital Light Processing (DLP) 3D printed samples, printing experiments were carried out on the enhanced adhesion and efficient demolding of DLP 3D printing devices. The molding accuracy and mechanical properties of the printed samples with different thickness configurations were tested. The test results show that when the layer thickness increases from 0.02 mm to 0.22 mm, the dimensional accuracy in the X and Y directions increases first and then decreases, while the dimensional accuracy in the Z direction decreases, and the dimensional accuracy is the highest when the layer thickness is 0.1 mm. The mechanical properties of the samples decline with an increasing layer thickness of the samples. The mechanical properties of the 0.08 mm layer thickness are the best, and the tensile, bending, and impact properties are 22.86 Mpa, 48.4 Mpa, and 35.467 KJ/m2, respectively. Under the condition of ensuring molding accuracy, the optimal layer thickness of the printing device is determined to be 0.1 mm. The analysis of the section morphology of samples with different thicknesses illustrates that the fracture of the sample is a river-like brittle fracture, and there are no defects such as pores in the section of samples.

Lignin nanoparticle-enhanced biobased resins for digital light processing 3D printing: Towards high resolution and tunable mechanical properties

The more widespread applicability of photopolymerization-based three-dimensional (3D) printing is limited by the availability of light-curable resins, most of which are based on fossil-derived compounds. We developed a biobased lignin-derivable resin by utilizing methacrylated derivatives of vanillin, vanillyl alcohol, and eugenol as aromatic monomers. Lignin nanoparticles (LNPs) were incorporated as functional fillers that enhance print resolution and material properties. The crosslinking degree, and thereby the tensile properties, was modulated through the use of mono- or dimethacrylated vanillin derivatives in the resin formulation. The LNPs acted as UV absorbers, conferring better control of the photopolymerization process by preventing light penetration across unintended layers, leading to enhanced print resolution. The LNPs showed excellent dispersion stability due to their size and morphology. The inclusion of up to 2 wt% of LNPs improved the ductility of the 3D printed nanocomposites through toughening mechanisms enabled by the rigid nanoparticles. Finally, exploiting the differences in crosslinking degree of the resin formulations, a multi-material model featuring both soft and rigid domains was fabricated. This study demonstrates a simple but effective strategy for the design of biobased photocurable resins with tailorable mechanical properties that are suitable for high-resolution and multi-material 3D printing.

Design, manufacturing, and elastic analysis of digital light processing 3D printed fiber reinforced sandwich beams with thermosetting polymer matrix

For the first time, a digital light processing (DLP) three-dimensional (3D) printer is implemented for additive manufacturing of sandwich beams with fiber reinforced facesheets and different core types without using adhesives. After characterizing the formulated thermosetting resin, sandwich beams with honeycomb and square core unit cells were printed in out-of-plane (OP) and in-plane (IP) arrangements, with and without woven glass fiber reinforcement in the facesheets. Meanwhile, using theoretical, micromechanical, and finite element (FE) approaches, the elastic properties and stiffness of sandwich beams were predicted. The stiffness measured from flex tests showed reliable agreement with predictions from analytical and finite element analysis (FEA) for most cases. Additionally, fiber reinforcement significantly increased specific stiffness of these structures, but did not affect the trends for different core geometries. The novel methodology presented here can open new doors for manufacturing advanced structures using DLP 3D printing technology.

Effect of substitution on light-curable properties in diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide: DFT and TD-DFT calculations

Acylphosphine oxide-based photoinitiators have been used in digital light processing (DLP) 3D printing slurry to prepare ceramic materials. However, the limitation is how to improve the absorption efficiency of photoinitiator in UV–Vis light and its initiation efficiency. In this study, through the DMol3 module of Materials Studio, the hydrogen atom is substituted by different electron-donating substituents (-NH2, -OCH3, -OH), substitution positions (ortho, meta, para) and tri-substitutions positions (2,4,6 and 3,4,5) were systematically studied respectively, including the change from the ground state to the first excited state, energy gap, ultraviolet-visible spectrum, the excitation energy, absorption wavelength, and oscillator strength. These results show that the order of electron-donating ability of these four groups is as follows: -NH2 > -OCH3 > -OH> -H. When the initiation wavelength λ≤ 425 nm, enhancing the electron-donating ability of the substituent and substitute para-substitution position can improve the oscillator strength and cause a blue-shift of the absorption peak. 4-TPO-NH2 which has the strongest electron-donating ability group substituted in para position shows the highest oscillator strength (21.5%) and blue shift (22 nm) compared with unsubstituted TPO. When the initiation wavelength λ≥ 425 nm, enhancing the electron-donating ability of the substituent, substitute para-substitution or ortho-substitution position, and tri-substituents of 2,4,6 positions, is the most beneficial to improve the oscillator strength and the red-shift of the absorption peak. Compared to unsubstituted TPO, 2,4,6-TPO-NH2 has 9.00 times increase in oscillator strength with 122 nm red-shift, and 2-TPO-NH2 has 134 nm red-shift with 2.53 times increase in oscillator strength. Furthermore, these studies can improve the development of acylphosphine oxide-based photoinitiators, and will also help to expand the application of DLP 3D printing in ceramic fields.

Construction of superhydrophobic surfaces via dual-scale modified particles and digital light processing 3D printing techniques

This article reports a method of Construction of superhydrophobic surfaces via digital light processing (DLP) and a low-cost, clean, and non-fluoride calcium sulfate particle (CSP) modification method with stearyl chloride. Modified micron-scale CSP and nano-scale hydrophobic fumed silica (HFS) were added into photocurable resin as fillers to prepare 3D printing ink. Relying on the manufacturing features of DLP 3D printing layer-by-layer curing and layer-by-layer stacking. The nano-scale HFS and micro-scale CSP are uniformly assembled to the surface and form a superhydrophobic layer with a dual-scale structure, so 3D objects with superhydrophobic surfaces were successfully prepared. The contact angle (CA) of superhydrophobic surfaces reached 157°, and the sliding angle (SA) reached 2.64°. Relying on the advantages of high precision of DLP 3D printing technology, different 3D samples were printed, whose surfaces also exhibited excellent superhydrophobic, which makes 3D objects expected to be applied in the fields of liquid transportation, micro-reactor, etc.

A Sensitivity-Enhanced Fiber Optic Fabry-Perot Acoustic Sensor Based on Grooved Diaphragm

A novel fiber optic Fabry-Perot acoustic sensor based on a grooved diaphragm has been proposed, avoiding the decrease of resonant frequency due to the enhanced sensitivity of the sensor based on conventional circular diaphragm. The effect of the structural parameters on sensitivity and resonant frequency is investigated by finite element simulation, and the designed diaphragm is fabricated by a digital light processing 3D printer. Experimental results indicate that the sensor based on the grooved diaphragm has an acoustic pressure sensitivity of 37.44 mV/Pa @2 kHz and a resonant frequency of 2.12 kHz, where the sensitivity is about 2.07 times that of the sensor based on the conventional circular diaphragm and the resonant frequency is almost unchanged. It is shown that the proposed sensor has the advantages of simple fabrication process, high consistency, and excellent applicability for weak acoustic signal detection.

Sustained-Drug-Release, Strong, and Anti-Swelling Water-Lipid Biphasic Hydrogels Prepared via Digital Light Processing 3D Printing for Protection against Osteoarthritis: Demonstration in a Porcine Model.

Osteoarthritis is a serious disease affecting joint cartilage. Owing to poor blood supply, the meniscus and acetabular labrum of joints heal poorly after injury. However, the development of artificial alternatives to these components that have similar mechanical properties and cartilage-protection ability is challenging. In this study, a strong hydrogel with a biomimetic microstructure is prepared with an emulsion-type photosensitive resin, where both hydrophilic and hydrophobic monomers, photo-initiator, and drugs can be adopted. In this system, the hydrophobic monomer forms uniformly dispersed aggregates after curing, improving the mechanical properties of the hydrogel significantly. Furthermore, the coordination bonds between nontoxic Zr4+ cations and sulfonic acid groups prevent hydrogel swelling. In addition, the water-oil biphasic hydrogel ink enables the loading of water- and lipid-soluble drugs, yielding hydrogel scaffolds with sustained dual-drug release ability. Crucially, hydrogel scaffolds having excellent mechanical properties, low swelling, and sustained biphasic drug release ability can be prepared using digital light processing 3D printing technology, owing to the high curing rate of the hydrophobic photo-initiator. These hydrogel scaffolds are applied as meniscal and labral replacements in a porcine model and show great promise for the prevention of secondary osteoarthritis, demonstrating the broad potential clinical applications of this material.

Piezoresistive behavior of DLP 3D printed CNT/polymer nanocomposites under monotonic and cyclic loading

This study examines the piezoresistive behavior of MWCNT/polymer composites fabricated by the digital light processing (DLP) technique. A photocurable nanocomposite resin feedstock possessing low viscosity with excellent printability and high conductivity was developed for DLP 3D printing of bulk and cellular geometries. By optimizing the resin composition and synthesis route, electrical percolation was achieved at an ultra-low MWCNT loading of 0.01 phr (parts per hundred resin), providing a conductivity of 3.5 × 10−5 S m−1, which is significantly higher than the values reported in the extant works for similar nanocomposites. Reducing the MWCNT content also enhanced the piezoresistivity of the nanocomposite due to longer inter-MWCNT distances in the percolating conductive network. Under quasi-static tensile loading, the nanocomposite with 0.01 phr MWCNT loading showed gauge factors of 2.40 and 4.78, corresponding to the elastic and inelastic regime, respectively. Quasi-static cyclic tensile tests with constant strain amplitudes (within elastic regime) revealed that the response of the nanocomposite was affected by viscoelastic deformation, which caused significant changes in the material’s strain sensing performance between consecutive load cycles. Finally, the developed resin was used to realize a self-sensing gyroid lattice structure, and its strain and damage sensing capabilities were demonstrated.

Grayscale Digital Light Processing Gradient Printing for Stress Concentration Reduction and Material Toughness Enhancement

Abstract Avoiding stress concentrations is essential to achieve robust parts since failure tends to originate at such concentrations. With recent advances in multimaterial additive manufacturing, it is possible to alter the stress (or strain) distribution by adjusting the material properties in selected locations. Here, we investigate the use of grayscale digital light processing (g-DLP) 3D printing to create modulus gradients around areas of high stress. These gradients prevent failure by redistributing high stresses (or strains) to the neighboring material. The improved material distributions are calculated using finite element analysis. The much-enhanced properties are demonstrated experimentally for thin plates with circular, triangular, and elliptical holes. This work suggests that multimaterial additive manufacturing techniques like g-DLP printing provide a unique opportunity to create tougher engineering materials and parts.