Digital Light Processing 3D Printing Research Articles

Top-down digital light processing 3D printing of composite structures using carbon fiber modified UV curable resin

Top-down digital light processing 3D printing of composite structures using carbon fiber modified UV curable resin

Methacrylated wood flour-reinforced “all-wood” derived resin for digital light processing (DLP) 3D printing

Additive manufacturing (AM) has led to the immense design freedom and fast production rates of wood-polymer composites (WPCs). However, vat photopolymerization-based AM techniques such as digital light processing (DLP) have yet to be exploited for the fabrication of complex and high resolution WPCs. This work demonstrates a microwave-assisted strategy for the rapid hydrophobization and functionalization of wood flour with methacrylate groups, in order to enhance its compatibility and interfacial interaction with novel wood-monomer derived photopolymer resins. The efficiency of this approach was exemplified in the inclusion of a high loading amount (10 wt%) of methacrylated wood flour to a biobased resin consisting of methacrylated eugenol and vanillin, without compromising the resin's dispersion stability and printability. Ultimately, the development of the resin culminated in the successful DLP 3D printing of wood flour-reinforced biobased composites that exhibited increases of 617%, 482%, and 31% in tensile strength, Young's modulus, and elongation at break, respectively, compared to resins without wood flour.

Cost-effective recycled resin for digital light processing 3D printing

In this study, a new method was established to repeatedly recycle/reuse photocured acrylic resins in 3D printed products. Discarded 3D-printed dental models were ground into micrometer-size recycled powder by the ball milling process. The recycled resin prepared through planetary mixing can be printed into accurate models under low solid content (<30 per hundred kilograms of resin, phr), yet the poor reflowing property of higher solid content limits the amount of recovery. Further blending and de-aggregation by a high-shear-force three roller mill make the recycled resins exhibit great suspension stability over 3 days and in addition to low viscosity (<5 Pa s) for fine DLP printing. The recycled-resin-printed samples showed excellent accuracy (variation: x-y direction<1%, thickness<3%) with low roughness (<1 μm). In Comparing with printed objects from pristine resin, objects from 50 phr recycled resin possess a similar tensile strength of 30 MPa and a better compressive strength performance of 153 MPa. Moreover, the products from recycling studies using 50 phr resin retained great printing accuracy and preserved the same mechanical properties. The prepared recycled resin can also be directly used for the production of customized, detailed, and low-roughness dental models, demonstrating the potential of this recycling method for practical applications.

3D printing of alumina ceramic heat sink with mini‐channels for thermal management

AbstractThermal management has become one of the most challenging issues for high‐power, integrated, and miniaturized electronic devices. In this paper, an alumina ceramic heat sink with mini‐channels was fabricated using a digital light processing 3D printing technology. Microstructures of the ceramic were investigated by scanning electron microscopy. A proper flow rate of water in the mini‐channels was figured out for efficient cooling by infrared thermal imaging and micro‐thermocouple characterizations. The ceramic heat sink was further integrated with a high‐power laser diode module; cooling performance was evaluated by investigating the thermal resistance of the ceramic heat sink and the optoelectronic property of the laser diode module. Results indicated that the laser diode module could be operated at high driving power of 115.6 W. This study provided a new strategy for a highly efficient thermal management of electronic devices and highlighted the technical potential of ceramic heat sink with more compact coolant channels.

3D printing of octopi-inspired hydrogel suckers with underwater adaptation for reversible adhesion

Biological structures with reversible adhesion can be widely observed in nature. The current biomimetic adhesion system has attracted extensive interest yet remains the fundamental challenge in the reversible high-adhesion with good environment compatibility, especially underwater. Herein, inspired with octopus, we propose the hydrogel-based suckers with favorable mechanical performance achieved readily by digital light processing 3D printing of the Zr4+-coordinated hydrogels, leading to the excellent underwater adaptation due to the water permeability. In this case, hydrogel, as the typical soft material infilled with water, can effectively enhance the adhesion and stability by the interfacial water sealing in comparison with the traditional hydrophobic and dry materials. The optimized hydrogel sucker with the radius of 5 mm, inclination of 30°, and wall thickness of 1 mm exhibits the highest adhesive strength of 48.46 ± 3.93 kPa in air, and 57.19 ± 1.93 kPa under water by experimental and numerical demonstration. The hydrogel suckers also display good adhesion versatility to different materials, including metal, ceramic, plastic and tissue etc. Finally, a pneumatic hydrogel gripper integrated with the bioinspired suckers can efficiently capture objects under water and in air. This research provides a novel path to develop the intelligent adhesion systems and mobile devices/robots.

Design and fabrication of biomimicking radially graded scaffolds via digital light processing 3D printing for bone regeneration.

Scaffolds are an essential component in bone tissue engineering (BTE). However, most of the current BTE scaffolds are homogeneous structures and do not resemble the graded architectures of native bone. In the current study, four types of biomimicking scaffold designs based on gyroid (G) and primitive (P) units with radially graded pore sizes were devised, and scaffolds of these designs with two porosity groups (65 vol% and 75 vol%) were fabricated via digital light processing (DLP) 3D printing using biphasic calcium phosphate (BCP). Scaffolds of the gyroid-gyroid (G-G) design displayed better dimensional accuracy, compressive property, and cell proliferation rate than gyroid-primitive (G-P), primitive-gyroid (P-G), and primitive-primitive (P-P) scaffolds. Subsequently, graded G-G scaffolds with different porosities were fabricated and the relationship between compressive strength and porosity was determined. Furthermore, the sintered BCP bioceramics fabricated via current manufacturing process exhibited excellent biocompatibility and bioactivity, indicating their high potential for BTE.

Digital light processing 3D printing of dynamic magneto-responsive thiol-acrylate composites.

Additive manufacturing is one of the most promising processing techniques for fabricating customized 3D objects. For the 3D printing of functional and stimuli-triggered devices, interest is steadily growing in processing materials with magnetic properties. Synthesis routes for magneto-responsive soft materials typically involve the dispersion of (nano)particles into a non-magnetic polymer matrix. Above their glass transition temperature, the shape of such composites can be conveniently adjusted by applying an external magnetic field. With their rapid response time, facile controllability, and reversible actuation, magnetically responsive soft materials can be used in the biomedical field (e.g. drug delivery, minimally invasive surgery), soft robotics or in electronic applications. Herein, we combine the magnetic response with thermo-activated healability by introducing magnetic Fe3O4 nanoparticles into a dynamic photopolymer network, which undergoes thermo-activated bond exchange reactions. The resin is based on a radically curable thiol-acrylate system, whose composition is optimized towards processability via digital light processing 3D printing. A mono-functional methacrylate phosphate is applied as a stabilizer to increase the resins' shelf life by preventing thiol-Michael reactions. Once photocured, the organic phosphate further acts as a transesterification catalyst and activates bond exchange reactions at elevated temperature, which render the magneto-active composites mendable and malleable. The healing performance is demonstrated by recovering magnetic and mechanical properties after the thermally triggered mending of 3D-printed structures. We further demonstrate the magnetically driven movement of 3D-printed samples, which gives rise to the potential use of these materials in healable soft devices activated by external magnetic fields.

Class I Biocompatible DLP-Printed Acrylate Impairs Adhesion and Proliferation of Human Mesenchymal Stromal Cells in Indirect Cytotoxicity Assay.

The popular method of digital light processing 3D printing (DLP) for complex and individual laboratory equipment requires materials that are as inert as possible for use in contact with cells for subsequent investigations. However, the per se incomplete curing of acrylate resins by UV light leaves residuals that are not suitable for cell culture application. Therefore, we evaluated the cytotoxicity of four commercially available acrylate resins with bone marrow-derived human mesenchymal stromal cells (BM-hMSC) in an indirect cytotoxicity test. This involved incubating the printed cylinders in Transwell™ inserts for 7 days. While the degree of crosslinking did not increase significantly between freshly printed and stored samples (3 weeks in ambient conditions), the storage improved the material's performance in terms of cytocompatibility. The DNA amount and LDH activity showed a direct influence of the resin residuals on cell adhesion. The class I acrylate Surgical Guide™ left no adherent cells after 7 days, regardless of previous storage. In comparison, the Basic Ivory™ resin after storage allowed same amount of adherent cells after 7 days as the polystyrene reference. We conclude that resin residuals of certain materials are released, which allows the use of the resins in indirect contact with cells thereafter.

Spatially resolved photoactivation of dynamic exchange reactions in 3D-printed thiol–ene vitrimers

On-demand photoactivation of dynamic transesterification in cross-linked thiol–ene polymers manufactured by digital light processing 3D printing.

Photocuring and digital light processing 3D printing of vitrimer composed of 2-hydroxy-2-phenoxypropyl acrylate and acrylated epoxidized soybean oil

Photocuring and digital light processing 3D printing of vitrimer composed of 2-hydroxy-2-phenoxypropyl acrylate and acrylated epoxidized soybean oil

Effects of heat-treatment methods on cytocompatibility and mechanical properties of dental products 3D-printed using photopolymerized resin.

The purpose of this study was to test heat-treatment methods for improving the cytocompatibility of dental 3D printable photopolymer resins. Nextdent C&B resin and a digital light processing 3D printer were used to print all specimens, which were divided into seven groups as follows: 1-month storage at controlled room temperature, 20 to 25 °C (RT), 24-hour storage at RT, 24-hour storage in RT water, 1-min immersion in 80 °C water, 1-min immersion in 100 °C water, 5-min immersion in 100 °C water, and autoclaving. Cell viability tests, cytotoxicity tests, and confocal laser scanning microscopy were performed to analyze the cytocompatibility of the 3D-printed resin. Fourier-transform infrared spectroscopy was performed after heat-treatment to determine the degree of conversion (DC). Immersing printed resin samples in 100 °C water for 1 or 5 min after the curing process was an effective method for increasing cytocompatibility by inducing the preleaching of toxic substances such as unpolymerized monomers, photoinitiators, and additives. Moreover, the DC can be increased by additional polymerization without affecting the mechanical properties of the material. Immersing the printed photosensitive dental resins in 100 °C water for 5 min is a suitable method for increasing cytocompatibility and the DC.

Design and Applications of Soft Actuators Based on Digital Light Processing (DLP) 3D Printing

Design and Applications of Soft Actuators Based on Digital Light Processing (DLP) 3D Printing

Guided Endodontic Access Cavity of Maxillary Obliterated Pulp Canal Lateral Incisor

Background: Managing severe calcified teeth in endodontics seems to be challenging for clinical, so static and dynamic guided endodontics ware developed to reduce the professional stress, increasing the patient\&amp;apos;s comfort, gives shorter clinical or procedural sessions with minimal invasive approach, and predictable canal location to avoid iatrogenic mishaps to be happened. Case Presentation: Preoperative investigations were conducted, tooth #12 had calcified chamber. Cone beam computed tomography (CBCT) was taken (Sirona GALILEOS Comfort CBCT scanner) showed that the coronal third of root canal is obliterated. For Guide planning, maxillary alginate impression was taken and scanned by digital scanner (smart optics - Vinyl High Resolution). Digital planning was done by 3Shape Implant Studio Software using sleeve size 3.5 mm (external diameter). Guided was printed by Digital Light Processing (DLP) 3d printing machine (NextDent 5100 3D printer). Enamel drilling by diamond round bur, guide was adapted to mouth and drill through until reach to 10 mm, periapical radiograph was taken to confirm the drilling depth. Conclusion: Guided treatment modality is not only used for anterior teeth or initial endodontic treatment, for posterior teeth and re-treatment endodontic cases as well. Finally, guided endodontic should be considered as mandatory treatment modality for pulp canal obliteration.

Customizable single-layer hydrogel robot with programmable NIR-triggered responsiveness.

Hydrogel robots are widely used in biomedical fields due to their excellent biocompatibility and response to external stimuli. However, traditional processing methods cannot rapidly fabricate complex structures, and smart response strategies often rely on double-layer structures fabricated from two materials with significantly different swelling properties. In this study, we present a single-layer hydrogel robot that can be fabricated in one step using a high-precision digital light processing (H-P DLP) 3D printing system. The robot has structural differences and the ability to maintain a repetitive response. Additionally, we fabricated several robot grippers to demonstrate their potential for customization and programming, as well as their potential applications in cargo delivery. Our work provides a new approach to achieve the formation and response of various irregular hydrogels, which is expected to advance the development of biomedical applications.

Fun-shaped oral dosage forms for the pediatric population fabricated by digital light processing (DLP) 3D printing technique

Fun-shaped oral dosage forms for the pediatric population fabricated by digital light processing (DLP) 3D printing technique

A novel photocurable pullulan-based bioink for digital light processing 3D printing.

Digital light processing has significant advantages, such as high repeatability, low failure rate, and no extrusion shear force. To make it possible to print complex structures with high resolution, the consecutive development of photocurable ink materials is indispensable. In this work, photo-functionalized pullulan (Pul-NB) was prepared by introducing norbornene groups into pullulan chains, and an ink material suitable for photocurable printing was prepared by thiol-ene click reaction. The rheology, water absorption, and mechanical properties of the Pul-NB precursor solution and photocurable hydrogel were investigated. The optimal composition of Pul-NB ink for three-dimensional (3D) printing was obtained by adjusting the degree of substitution, Pul-NB concentration, and thiol crosslinking agent. This novel bioink for digital light processing 3D printing showed good printability and high shape fidelity. This ink material provides an excellent alternative for printing biomimetic soft tissue organs, high-throughput tissue models, soft robots, etc.

Light-Mediated 3D Printing of Micro-Pyramid-Decorated Tailorable Wound Dressings with Endogenous Growth Factor Sequestration for Improved Wound Healing.

Medical dressings play an important role in the field of tissue engineering owing to their ability to accelerate the process of wound healing. Great efforts have been made to fabricate wound dressings with distinctive features for promoting wound healing. However, most of the current synthesis methods either generate dressings of uniform size or involve complex fabrication techniques, thus limiting their commercialization for the personalized dressings. We report here a dressing, which presents a paradigm shift in the design of the dressing from uniform films to a micro-patterned film. The hypothesis driving the design is the ability of the 3D patterns to provide an efficient transient matrix filling the depth of the wound rather than just providing a barrier and slight re-epithelialization. We demonstrate the use of the digital light processing 3D printing technique to generate micro-pyramid-decorated wound healing dressings with individualized design and with bio-compatible gelatin methacryloyl to contact the wounded areas. In addition to providing better adhesion to the migratory cells, the micro-pyramids also enable covalent conjugation of heparin, providing capability to sequester endogenous growth factors (GFs). Based on these advantages, the developed dressing not only adheres strongly to the wound bed but also promotes the treatment of a rat wound model by utilizing the power of endogenous GFs for tissue regeneration. Thus, it is believed that the developed dressing can break through the limitation of traditional wound treatment and be an ideal candidate for wound healing.

BIOMIMETIC CELLULAR STRUCTURES FOR TURBINE SYSTEM COMPONENTS

The research aim is to investigate cellular structures inspired from nature, in order to improve the internal structural resistance of turbine system components (e.g. hydroelectric and gas turbine blades, OGV-Outer Guide Vanes, nacelles, gearboxes) with reduced mass. The investigations were conducted at laboratory level, utilizing two 3D printing technologies to acquire the desired cellular structures which were further tested for tensile, bending and impact resistance. The first selected technology was Fused Deposition Modelling with Continuous Filament Fabrication to obtain 3D printed parts, which can be reinforced with continuous carbon, glass, or Kevlar fibers. The second technology used is Digital Light Processing 3D printing, which uses photopolymer liquid resin that cures under digital light source. The main motivation of utilizing the 3D printing technologies is the desire of implementing rapid prototyping in the final manufacturing of the turbine system components with structural topological optimization and improved structural and dynamic efficiency through biomimetic inspired structures. Conventional polymeric composite manufacturing technologies are sometimes restrictive in the geometries they can produce, and there is a chance that additive manufacturing can step in and help create internal structures that could not be obtained through conventional manufacturing methods. New developed structural architectures could be manufactured for a specific application through 3D printing which allows for a high level of customization parameters, including the possibility to use continuous carbon, glass and Kevlar fiber to create the geometrical pattern. All these, combined with conventional composite manufacturing technologies, could lead to obtain better end results.

An Approach to Improve the Resolution of DLP 3D Printing by Parallel Mechanism

For 3D printing based on Digital Light Processing (DLP) technology, the tradeoff of size and resolution remains challenging due to the limitations of the existing techniques. Therefore, we propose an approach to improve the feature resolution without sacrificing the part size. It is achieved by changing the projection distance and then adjusting the projection resolution and format, which is different from the previous printing principle of fixed resolution. To achieve this process, the tripteron 3-Degree-of-Freedom (3-DoF) parallel mechanism is innovatively applied to the DLP 3D printing structure, which simplifies the control process. Since the projection is fixed on the motion platform, the projection distance changes as the platform moves in space. Then the PLC-based program is developed according to the motion process, which successfully runs on the established prototype. Finally, the experiments are designed through the orthogonal method to optimize the molding process parameters. The effectiveness of the approach is verified by the feature forming comparison experiment. The results show that it can reduce the size of features by about 1.3 times through adjusting the projection resolution under the same size parts. Our method provides a new way for solving the contradiction, but more research needs to be done.

Vat Photopolymerization 3D-Printing of Dynamic Thiol-Acrylate Photopolymers Using Bio-Derived Building Blocks.

As an energy-efficient additive manufacturing process, vat photopolymerization 3D-printing has become a convenient technology to fabricate functional devices with high resolution and freedom in design. However, due to their permanently crosslinked network structure, photopolymers are not easily reprocessed or repaired. To improve the environmental footprint of 3D-printed objects, herein, we combine the dynamic nature of hydroxyl ester links, undergoing a catalyzed transesterification at elevated temperature, with an acrylate monomer derived from renewable resources. As a sustainable building block, we synthesized an acrylated linseed oil and mixed it with selected thiol crosslinkers. By careful selection of the transesterification catalyst, we obtained dynamic thiol-acrylate resins with a high cure rate and decent storage stability, which enabled the digital light processing (DLP) 3D-printing of objects with a structure size of 550 µm. Owing to their dynamic covalent bonds, the thiol-acrylate networks were able to relax 63% of their initial stress within 22 min at 180 °C and showed enhanced toughness after thermal annealing. We exploited the thermo-activated reflow of the dynamic networks to heal and re-shape the 3D-printed objects. The dynamic thiol-acrylate photopolymers also demonstrated promising healing, shape memory, and re-shaping properties, thus offering great potential for various industrial fields such as soft robotics and electronics.