Digital Light Processing 3D Printing Research Articles

Meniscal transplantation and regeneration using functionalized polyurethane bionic scaffold and digital light processing 3D printing

Owing to the limited healing ability, the repair of meniscal injury and prevention of secondary osteoarthritis pose considerable challenges for clinicians and researchers. While tissue engineering technology is a promising method, many difficulties, including the construction of the meniscus scaffold with appropriate mechanical properties and its functionalization to promote the regeneration of meniscus tissue, remain to be addressed. In this study, a novel structurally and functionally optimized tissue engineering meniscus scaffold with mechanical properties and spatial structure similar to those of a natural meniscus is prepared using digital light processing 3D printing technology. Kartogenin-loaded polyurethane scaffolds with a specific structure designed using finite element analysis are printed, and their surface is modified using polydopamine. The optimized scaffolds exhibit superior performance in promoting meniscus regeneration, protecting articular cartilage, and mitigating the development of osteoarthritis. Moreover, this study addresses challenges posed by polyurethane, which is found in most widely used commercial meniscus grafts, including unsatisfactory biocompatibility with stem cells and unavailability of a fine 3D structure. Although further research in preclinical applications is required, the results of this study in terms of a next-generation clinical meniscus biomaterial repair strategy are promising.

Photosensitive thiol–ene composition for DLP 3D printing of thermally stable polymer materials

N-allylated derivatives with a modification degree of 80% were obtained by reacting poly[N,N′-(1,3-phenylene)isophthalamide] with allyl bromide in the presence of a strong base. Using the obtained functionalized polyamide and pentaerythritol tetrakis(3-mercaptopropionate), we formulated new photo- sensitive compositions capable of forming crosslinked structures due to UV-initiated thiol–ene polymerization. High-resolution 3D objects that are heat resistant up to 380 °C were formed using digital light processing (DLP) 3D printing

Photo curable resin for 3D printed conductive structures

In this study, a new resin formulation method was developed to fabricate 3D printed conductive structures via digital light processing (DLP) 3D printing technology. Metal fillers, such as silver-coated copper flakes (AgCu) and silver nanoparticles (AgNP), were tested for conductive resin formulation. With low UV shielding and printing derivation, AgCu was selected as the conductive filler, and mixed with a photo curable acrylic resin. To resolve the sedimentation problem of metal fillers, carbon nanotubes (CNT) were added as a thickening agent to provide a supportive network to stop the metal fillers from settling. With the CNT addition, AgCu up to 70 wt% can be well dispersed in the acrylic resin with both fluidity and suspension stability. The resin can be printed into 3D metal circuitry structures with a conductivity up to 1000 S/cm without sintering. Multi-material stereolithography was also performed to produce conductive circuitry within insulation materials. The sectional view showed great connections between multiple layers of printed conductive tracks. Through-hole vias and blind vias were also built with great quality to demonstrate the capability of this conductive resin formulation.

A novel UV-curable acryl-polyurethane for flexural 3D printing architectures

An acryl-functionalized urethane prepolymer series with various compositions were synthesized using polyethylene glycol (PEG) and hexamethylene diisocyanate (HDI). A novel acryl-urethane resin (AU) was designed by the addition of 2-hydroxyethyl methacrylate (2-HEMA) as a suitable material for digital light processing (DLP) 3D printing. The optimizing photo-initiator and additive were selected by UV-spectroscopy. The formulation containing the UV-curable AU resin and photo-curable additives was exposed to 405 nm UV radiation to produce the flexible 3D architectures. The effects of the photo-initiator/multifunctional acrylate value and UV absorptive power on the 3D printing performance were evaluated in terms of the mechanical properties and dimensional resolution. When the acryl-urethane resin/base acrylate ratio was 1/9, the UV-cured APU formulations had the excellent mechanical properties and highest resolution. The surface properties of the 3D architectures were tuned by controlling the photo-initiator type and composition in the AU resin. Overall, this novel UV-curable AU resin can be a promising prepolymer for the DLP printing of flexible photo-resin for biocompatible and photo-curable applications. © 2001 Elsevier Science. All rights reserved

Balancing flexural strength and porosity in DLP-3D printing Al2O3 cores for hollow turbine blades

High porosity and high strength are usually mutually exclusive in the preparation of ceramic materials. However, high porosity and flexural strength are required for the preparation of complex ceramic cores for hollow turbine blades. In this study, Al2O3 cores with high porosity and high flexural strength were successfully prepared using digital light processing (DLP) 3D printing technology. The influence of sintering temperature on the microstructure, pore evolution, and flexural strength of the cores were investigated. With an increase in the sintering temperature, the porosity of the ceramic cores first increased and then decreased, reaching a maximum value of 35% at 1400 °C. The flexural strength increased with the increase in sintering temperature, but at 1400°C the incremental enhancement of flexural strength was greatest. Combined with the core service requirements and core performance, this study selected 1400 °C (open porosity of 35.1% and flexural strength of 20.3 MPa) as the optimal sintering temperature for the DLP-3D printed Al2O3 core.

3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization.

3D printing provides facile access to geometrically complex materials. However, these materials have intrinsically linked bulk and interfacial properties dependent on the chemical composition of the resin. In the current work, 3D printed materials are post-functionalized using the 3D printer hardware via a secondary surface-initiated polymerization process, thus providing independent control over the bulk and interfacial material properties. This process begins with preparing liquid resins, which contain a monofunctional monomer, a crosslinking multifunctional monomer, a photochemically labile species that enables initiation of polymerization, and critically, a thiocarbonylthio compound which facilitates reversible addition-fragmentation chain transfer (RAFT) polymerization. The thiocarbonylthio compound, known commonly as a RAFT agent, mediates the chain growth polymerization process and provides polymeric materials with more homogeneous network structures. The liquid resin is cured in a layer-by-layer fashion using a commercially available digital light processing 3D printer to give three-dimensional materials having spatially controlled geometries. The initial resin is removed and replaced with a new mixture containing functional monomers and photoinitiating species. The 3D printed material is then exposed to light from the 3D printer in the presence of the new functional monomer mixture. This allows photoinduced surface-initiated polymerization to occur from the latent RAFT agent groups on the surface of the 3D printed material. Given the chemical flexibility of both resins, this process allows a wide range of 3D printed materials to be produced with tailorable bulk and interfacial properties.

Digital Light Processing 3D Printing of Enhanced Polymers via Interlayer Welding.

Digital light processing (DLP) 3D printing is advantageous in high printing efficiency and printing resolution for fabricating complex structures across various applications. However, the layer-by-layer curing manner of DLP leads to weak interlayer adhesion and the anisotropic mechanical properties of printed objects. Here, linear polymers are introduced into commercial resins to weld the interlayer by the diffusion and entanglement of linear polymers after DLP printing via heat treatment. This introduction of linear polymers not only shows a strengthening and toughening effect on the printed objects, but also has no negative impact on the DLP printability. The tensile strengths of objects containing 4.7wt% polycaprolactone can reach up to ≈500% of that of neat samples in any printing direction. This simple strategy by adding linear polymers into printing resins provides an effective access to prepare DLP printed objects with improved mechanical properties as well as ensure printing resolution and printing efficiency.

Preparation of porous SnO2-based ceramics with lattice structure by DLP

Porous tin oxide-based (SnO2-based) ceramics with lattice structures were prepared by digital light processing (DLP) 3D printing technology. A 57 wt% SnO2-based DLP slurry was prepared by rheological experiments. By optimizing the exposure time, the DLP process for preparing SnO2 based ceramics had better molding accuracy. The printing size error could be controlled at about 1.8%. The degreasing and sintering curves were obtained by thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, and the SnO2-based porous ceramics with porosity of 50%–71% were prepared. The SnO2-based ceramics with high densification could be obtained by sintering at 1300 °C for 2 h. The relative density of printed SnO2-based ceramics was about 92%. In this paper, zinc oxide (ZnO) was selected as a sintering additive to promote the densification of SnO2 ceramics. According to the characterization methods of scanning electron microscopy(SEM), X-ray diffraction(XRD), Energy dispersive spectrometer (EDS) and relative density, the optimum doping amount of ZnO was 9 wt%. The influence of pore structure on compressive strength was analyzed by finite element simulation and compressive test. The compressive strength of porous ceramics could be reduced from 1.56 MPa to 0.27 MPa by controlling the porosity of the porous lattice from 50% to 71%. The compressive strength of the solid block was 160 MPa. In this study, the porous SnO2-based ceramics prepared can be used in porous electrodes, lithium-ion batteries, supercapacitors, catalysts, sensors and other fields in the future.

Three-dimensional printing of gyroid-structured composite bioceramic scaffolds with tuneable degradability

Customisation of bioactivity and degradability of porous bioceramic scaffolds is a formidable challenge in the field of regenerative medicine. In this study, we developed gyroid-structured ternary composite scaffolds (biphasic calcium phosphate (BCP) and 45S5 bioglass® (BG)) using digital light processing 3D printing technology based on material and structural design. Additionally, the mechanical strength, bioactivity, degradability, and biocompatibility of the composite ceramic scaffolds were evaluated. The results revealed that BG reacted with BCP to generate major active crystalline phases of CaSiO3 and Na3Ca6(PO4)5. These active crystalline phases accelerated the exchange rate of Si4+, Ca2+, and PO43− with HCO3− in simulated body fluids and resulted in the rapid formation of carbonated hydroxyapatite (CHA), analogous to the formation of natural bone tissue. Interestingly, the precipitated CHA showed petal- and needle-like morphologies, which provided a large surface area to promote cell adhesion and proliferation. Furthermore, an increase in the BG content improved the degradability of ternary composite scaffolds after soaking in Tris-HCl solution. The tuneable degradability increased by three times at 30 wt% BG and sharply increased by 6.8 times at 40 wt% BG. This study provides a promising strategy to design scaffolds with improved bioactivity and tuneable degradability to assist a diverse population suffering from orthopedic conditions.

Characterization and prediction of the nonlinear creep behavior of 3D-printed polyurethane acrylate

While the potential application of 3D-printed polymers is remarkable because of the favorable mechanical properties of these materials and their feasibility for producing customized structural components, 3D-printed polymer materials are rarely used in load-bearing structures due to a lack of understanding of the mechanical behaviors of a printed part over a long service life. In this study, the creep behaviors of ultraviolet-curable polyurethane acrylate (UV-PUA) fabricated by using a digital light processing 3D printer was investigated through experimental testing and finite element simulations. Digital image correlation was used to monitor the creep deformations under various thermomechanical conditions. A one-dimensional creep constitutive model was developed to characterize the nonlinear viscoelastic responses of the 3D-printed UV-PUA by decoupling temperature and stress effects. The constitutive model was further implemented in an ABAQUS UMAT subroutine. The simulation results show that the numerical creep model describes well the creep deformations and predicts a reasonable creep life at low temperatures. The sensitivity of the creep behavior of the printed specimens to various types of initial damage was also studied using the developed constitutive model, and the model results were validated by the tensile test results. The results are in good agreement, which verifies the feasibility of numerical method implemented in UMAT for studying the mechanical properties of 3D printed polymers. • Creep behavior of a 3D-printed polymer was monitored using DIC technology. • A nonlinear temperature-dependent viscoelastic model was developed. • 3D constitutive models were developed and implemented in finite element analysis. • The developed model predicts well the creep behavior of the 3D-printed polymer.

4D printed thermochromic Fresnel lenses for sensing applications

The conventional manufacturing processes for optical sensors fabrication have limitations in terms of ease of fabrication, design freedom, mechanical flexibility, cost requirements, etc. Therefore, adapting additive manufacturing (3D printing) is highly desirable because it opens up a variety of design and manufacturing possibilities. We have demonstrated that the 3D fabrication process using computer-aided design may be used to fabricate 4D functionalized photonic devices such as Fresnel lenses. We have introduced spectral color variation as the fourth dimension to 3D printed lenses in response to temperature as an external stimulus. The digital light processing (DLP) 3D printing process parameters were optimized to print the needed features with precise geometric dimensions of the lenses. Thermochromic pigment powders were mixed in the liquid monomer resins to print tinted Fresnel lenses used for selective color focusing and temperature sensing applications. The focusing ability and thermal sensing of printed lenses were assessed using customized setups that included normalized power intensity and transmission spectra measurements. Contact angle measurements were used to determine surface wettability, revealing the hydrophilic nature of the lens material. 3D printing offers custom-built optical devices and the ability to optimize the materials for both active and passive optical sensing applications, making them more promising than traditional Fresnel lenses.

"Invisible" Digital Light Processing 3D Printing with Near Infrared Light.

The ability to 3D print structures with low-intensity, long-wavelength light will broaden the materials scope to facilitate inclusion of biological components and nanoparticles. Current materials limitations arise from the pervasive absorption, scattering, and/or degradation that occurs upon exposure to high-intensity, short-wavelength (ultraviolet) light, which is the present-day standard used in light-based 3D printers. State-of-the-art techniques have recently extended printability to orange/red light. However, as the wavelength of light increases, so do the inherent challenges to match the speed and resolution of traditional UV light-induced solidification processes (i.e., photocuring). Herein, a photosystem is demonstrated to enable low-intensity (<5 mW/cm2), long-wavelength (∼850 nm) near-infrared (NIR) light-driven 3D printing, "invisible" to the human eye. The combination of a NIR absorbing cyanine dye with electron-rich and -deficient redox pairs was required for rapid photocuring in a catalytic manner. The rate of polymerization and time to solidification upon exposure to NIR light were characterized via in situ spectroscopic and rheological monitoring. Translation to NIR digital light processing (projection-based) 3D printing was accomplished through rigorous optimization of resin composition and printing parameters to balance the speed (<60 s/layer) and resolution (<300 μm features). As a proof-of-concept, composite 3D printing with nanoparticle-infused resins was accomplished. Preliminary analysis showed improved feature fidelity for structures produced with NIR relative to UV light. The present report provides key insight that will inform next-generation light-based photocuring technology, such as wavelength-selective multimaterial 3D bio- and composite-printing.

Preparation and characterization of customized bone grafting hydroxyapatite models obtained by digital light processing 3D printing

Preparation and characterization of customized bone grafting hydroxyapatite models obtained by digital light processing 3D printing

Nano-Hydroxyapatite Bone Scaffolds with Different Porous Structures Processed by Digital Light Processing 3D Printing.

The morphologies and structures of the scaffold have a significant influence on their mechanical and biological properties. In this work, different types of porous structures: Triply periodic minimal surface-Schwarz primitive (P), body-centered cubic, and cubic pore-shaped (CPS) hydroxyapatite scaffolds with ~70% porosity were fabricated through digital light processing (DLP) 3D printing technology. The compressive properties and in vitro cell evaluations such as cell proliferation and attachment morphology of these scaffolds were systematically compared. The results showed that the CPS scaffolds exhibited the highest compressive strength (~22.5 MPa) and modulus (~400 MPa). In addition, the CPS scaffolds also performed the most active cell metabolisms as compared to other two structures, which may account for the larger pore size and smaller curvature of the substrate. This study provides a general guidance for the fabrication and selection of porous bone scaffolds processed by DLP 3D printing.

Digital light processing 3D printing of multi-materials with improved adhesion using resins containing low functional acrylates

Digital light processing 3D printing of multi-materials with improved adhesion using resins containing low functional acrylates

Digital light processing 3D printing of surface-oxidized Si3N4 coated by silane coupling agent

ABSTRACT Due to high light absorption and high refractive index of silicon nitride (Si3N4) ceramic, it is difficult to prepare Si3N4 slurry with favorable curing ability, high solid loading and low viscosity at the same time, and thus the high-quality Si3N4 parts are hard to fabricate via Digital Light Processing (DLP). In this paper, the oxidation process was used to enhance the curing behavior of Si3N4 slurry, and then silane coupling agent (KH560) was used to improve the rheological properties of the oxidized Si3N4 slurry. The effect of Si3N4 slurry with oxidation and modification on its rheological behavior, light absorption, curing ability and stability have been systematically investigated. A Si3N4 slurry with abundant photocuring ability, high solid loading, low viscosity and reliable stability was fabricated by the oxidized (1 h) and KH560 (1 wt.%) modified Si3N4 powders, and the dense Si3N4 ceramic parts were produced by this slurry via DLP 3D printing. Subsequently, the influence of oxidation and modification on microstructure, mechanical properties and thermal conductivity have been investigated. Finally, the microstructure and performances of Si3N4 ceramic were compared between different forming processes (including: DLP and cool isostatic pressing).

Additively Manufactured Amplitude Tapered Slotted Waveguide Array Antenna With Horn Aperture for 77 GHz

In this work, a combined frontend of horn and slotted waveguide array antenna serving as feeding subsystem is presented. This setup allows to implement an amplitude taper in one plane while using the horn aperture to shape the far field radiation characteristics in the perpendicular plane independently and tailored to the individual demand of the application. Moreover, the feeding system is implemented as a loop resulting in a standing wave distribution for a wide frequency range in order to increase the antenna bandwidth. Two specimens with different horn apertures are additively manufactured in slotted waveguide technology from UV curable photopolymer resin using a digital light processing 3D printer and subsequently metal coated by electroless silver plating. A relatively large bandwidth of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{B}_{-10\text {dB}} = 7.2$ </tex-math></inline-formula> GHz and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{B}_{-15\,\text {dB}}$ </tex-math></inline-formula> of 4.9 GHz is achieved in measurements indicating a relative bandwidth of 9 % and 6 % respectively. Antenna Gain is characterized as 17.5 and 20.17 dBi in measurements while maintaining a sidelobe level of 20–22.5 dB at 77 GHz and exhibiting a radiation efficiency of 78.9 and 79.4 %. The proposed antenna architecture provides a flexible approach for beam shaping in applications where azimuth and elevation planes exhibit different or contrary requirements, e.g. broad vs. narrow field of view - especially suitable for automotive MIMO-radar sensors.

Recyclable and Reprintable Biobased Photopolymers for Digital Light Processing 3d Printing

Recyclable and Reprintable Biobased Photopolymers for Digital Light Processing 3d Printing

Construction of Photoresponsive 3D Structures Based on Triphenylethylene Photochromic Building Blocks.

Photoresponsive materials have been widely used in sensing, bioimaging, molecular switches, information storage, and encryption nowadays. Although a large amount of photoresponsive materials have been reported, the construction of these smart materials into precisely prescribed complex 3D geometries is rarely studied. Here we designed a novel photoresponsive material methyl methacrylate containing triphenylethylene (TrPEF2-MA) that can be directly used for digital light processing (DLP) 3D printing. Based on TrPEF2-MA, a series of photoresponsive 3D structures with reversible color switching under ultraviolet/visible light irradiations were fabricated. These complex photoresponsive 3D structures show high resolutions (50 μm), excellent repeatability (25 cycles without fatigue), and tunable saturate color degrees. Multicomponent DLP 3D printing processes were also carried out to demonstrate their great properties in information hiding and information-carrying properties. This design strategy for constructing photoresponsive 3D structures is attractive in the area of adaptive camouflage, information hiding, information storage, and flexible electronics.

WITHDRAWN: Comparative evaluation of internal and marginal fit of interim crowns fabricated by CAD/CAM milling and two different 3D printing systems - An in vitro study

The aim of the present study is to compare and evaluate the internal and marginal fit of interim crowns fabricated by CAD/CAM milling and two different 3D printing systems. Fabrication of the metal master model was done by Selective Laser Melting Unit after preparing and scanning a typhodont tooth. A designing software was used to design crowns onto the metal master model after scanning it. The STL (Stereolithography) file of designed crowns is then sent to CAD/CAM milling machine and two different 3D printing systems namely Stereolithography (SLA) and digital light processing (DLP) for fabrication of 15 crowns each. Internal and marginal fit was measured with the help of silicon replica technique and obtained data was analysed with one way ANOVA which was followed by Tukey’s post-hoc analysis test for verifying the statistical significance. The smallest discrepancy of 96.7 μm was observed in DLP 3D Printing group followed by 131.1 μm in SLA 3D printing group and lastly CAD/CAM group stood with the discrepancy of 179.6 μm. A significant difference was seen for discrepancy values of the 3 groups and it was observed that DLP 3D Printing was able to manufacture crowns with better marginal and internal fit than SLA 3D Printing and SLA 3D Printing was better than CAD/CAM Milling group.