Digital Light Processing 3D Printing Research Articles

Experimental investigation and optimization of process parameters on digital light processing (DLP) 3D printing process based on Taguchi-grey relational analysis

Additive manufacturing technology, specifically Digital Light Processing (DLP), offers a unique approach to fabricating intricate objects without the need for traditional molds or machining. The technique described entails the incremental construction of layers through the curing process polymer, facilitated by a projection light source. Digital Light Processing 3D printing is particularly suited for creating complex structures with small cross-sections, requiring high surface polish and durability. In this study, DLP-printed test coupons were produced using an Ultraviolet-sensitive resin, and the investigation focused on examining the impact of surface quality and toughness, adhering to guidelines outlined by the ASTM specifications. To optimize the DLP printing process, Taguchi and Grey relational optimization techniques were employed to find the best values for multiple factors. The parameters considered in this study were speed, layer thickness, orientation, and pattern type. By employing these techniques, the optimal parameters were identified as follows: The printing process is conducted at a speed of 3 mm per second, with each layer being 0.05 mm thick and the orientation of the printed object is set at 90 degrees, and the pattern employed is of the square type. Experimental results revealed that utilizing these parameters yielded a surface roughness of 2.58 µm and an impact strength of 9.1J. The results showed that the Grey relational grade improved from 0.6244 to 0.7974, with a deviation of 0.173 and 27.71%, indicating a significant enhancement in the optimization process. Additionally, contour plots depicting the relationships between speed and orientation, speed and layer thickness, and orientation and layer thickness were generated for surface roughness, impact strength, and the Grey relational grade. This research offers valuable insights into optimizing DLP 3D printing processes to achieve enhanced surface quality, toughness, and material efficiency while reducing costs and production time.

Multiscale design and digital light processing preparation of high-strength SiOC ceramic metastructures for tuning microwave absorption properties

Silicon oxycarbide (SiOC) ceramics have been used to fabricate microwave-absorbing metastructures, demonstrating impressive absorption capabilities. However, SiOC ceramic metastructures with excellent performance require simple fabrication processes and appropriate mechanical and electromagnetic properties. In this study, a solvent-free photosensitive polysiloxane preceramic was developed by blending methoxy/hydroxy polysiloxanes with acrylates, with a ceramic yield of over 60% after curing using a novel two-step ultraviolet (UV)/thermal method. The composition and microstructure of SiOC ceramics can be designed by controlling the preceramic composition. Dense, crack-free gyroid-shellular shaped triple periodic minimal surface (GS-TPMS) electromagnetic metastructures were fabricated using digital light processing (DLP) 3D printing technology. By designing the porosity of the GS-TPMS structure to 51%, an effective absorption bandwidth that covers the X-band can be achieved at a thickness of 3.1 mm. The honeycomb structure, with a geometric density of 0.69 g/cm3, exhibited a high compressive strength of 107.05 MPa. This paper presents an efficient approach for the prompt and customized fabrication of lightweight ceramic metastructures with outstanding microwave absorption properties.

Flame Retardant Additives in Polylactic Acid (PLA) Photopolymer Resin for 3D Printing Digital Light Processing (DLP)

Digital light processing (DLP) technology has been developed based on stereolithography (SLA) 3D-printing principle. The biodegradable and low-cost polylactic-acid (PLA) has so far been used as polymeric material for photopolymer resin in SLA and DLP. To achieve functional SLA-processed product, the properties of such PLA has been improved, with the aim to make it flame retardant, less viscous, and having light transmittance characteristics. In this study, the liquid raw PLA photopolymer was changed by adding different contents of Ammonium Phosphate (APP), melamine cyanurate (MCA), Aluminum Tri-hydroxide (Al2O3) and Nano-silicon dioxide (SiO2) additives. The solid PLA nanocomposite specimens were printed by using DLP device according to the standard geometry for burning test UL-94 to evaluate its flame-retardant property. In addition, the printing product and residue after burning test was analyzed for their morphological characteristic by using SEM. The results showed that the low weight fraction of MCA showed excellent performance. PLA/MCA successfully kept green body form until the sintering temperature of stainless steel was achieved. It can become a reference for application DLP 3D printing products in the casting and sintering process.

Digital light processing 3D printing of microfluidic devices targeting high-pressure liquid-phase separations.

This paper focuses on 3D printing using digital light processing (DLP) to create microchannel devices with inner diameters of100, 200, and 500 µm and cater flow-through applications within the realm of analytical chemistry, in particular high-pressure liquid chromatographic separations. Effects of layer thickness and exposure time on channel dimensions and surface roughness were systematically investigated. Utilizing a commercially accessible 3D printer and acrylate resin formulation, we fabricated 100-500 µm i.d. squared and circular channel designs minimizing average surface roughness (< 20%) by applying a 20-µm layer thickness and exposure times ranging from 1.1 to 0.7s. Pressure resistance was measured by encasing microdevices in an aluminum chip holder that integrated flat-bottom polyetheretherketon (PEEK)nanoports allowing to establish the micro-to-macro interface to the HPLC instrument. After thermal post-curing and finetuning the clamping force of the chip holder, a maximum pressure resistance of 650bar (1.5% RSD) was reached (n = 3). A polymer monolithic support structure was successfully synthesized in situ with the confines of a 500 µm i.d. 3D printed microchannel. A proof-of-concept of a reversed-phase chromatographic gradient separation of intact proteins is demonstrated using an aqueous-organic mobile-phase with isopropanol as organic modifier.

Digital light 3D printing of artificial bone with star-shaped polycaprolactone-based polyurethane acrylate

Advanced medical materials and manufacturing technologies are highly in demand in artificial bones. Herein, a four-arm star-shaped polycaprolactone polyurethane acrylate (FPCLA) was designed and synthesized. The photosensitive character of FPCLA contributed to the rapid prototyping and personalized customization under digital light processing (DLP) 3D printing technology. The FPCLA was prepared by introducing unsaturated double bonds into polycaprolactone tetraethyl alcohol (PCLT). We characterized the physico-chemical properties of the material through FTIR, H-NMR, GPC, DSC and SEM. Cell behaviors on material were observed in vitro. In addition, we employed a DLP 3D printer to evaluate the feasibility of FPCLA to fabricate artificial bone model. The photocuring star polycaprolactone was confirmed in detail by detection method. SEM analyses demonstrated that FPCLA has good tenacity. The material can be used to fabricated artificial bone with a diameter of 3.02 mm at its narrowest by DLP 3D printing technology. The cell survival rates of CCK-8 and Live/Dead fluorescence staining experiments were both above 90%, which indicated safety and feasibility of such new-generation artificial bone made of synthetic polymers.

Evonik launches new flame retardant photopolymer resin and high-performance phosphate methacrylate

On February 8, 2024, Evonik announced the launch of a new photopolymer resin that is claimed to be both flame retardant and mechanically durable when cured. Designed for use with DLP (digital light processing) 3D printers, INFINAM® FR 4100L is claimed to be pourable at room temperature and printable and further processable to achieve a desired surface feel.

Digital Light Processing 4D Printing of Poloxamer Micelles for Facile Fabrication of Multifunctional Biocompatible Hydrogels as Tailored Wearable Sensors.

The lack of both digital light processing (DLP) compatible and biocompatible photopolymers, along with inappropriate material properties required for wearable sensor applications, substantially hinders the employment of DLP 3D printing in the fabrication of multifunctional hydrogels. Herein, we discovered and implemented a photoreactive poloxamer derivative, Pluronic F-127 diacrylate, which overcomes these limitations and is optimized to achieve DLP 3D printed micelle-based hydrogels with high structural complexity, resolution, and precision. In addition, the dehydrated hydrogels exhibit a shape-memory effect and are conformally attached to the geometry of the detection point after rehydration, which implies the 4D printing characteristic of the fabrication process and is beneficial for the storage and application of the device. The excellent cytocompatibility and in vivo biocompatibility further strengthen the potential application of the poloxamer micelle-based hydrogels as a platform for multifunctional wearable systems. After processing them with a lithium chloride (LiCl) solution, multifunctional conductive ionic hydrogels with antifreezing and antiswelling properties along with good transparency and water retention are easily prepared. As capacitive flexible sensors, the DLP 3D printed micelle-based hydrogel devices exhibit excellent sensitivity, cycling stability, and durability in detecting multimodal deformations. Moreover, the DLP 3D printed conductive hydrogels are successfully applied as real-time human motion and tactile sensors with satisfactory sensing performances even in a -20 °C low-temperature environment.

Rapid tooling for rubber extrusion molding by digital light processing 3D printing with dual curable vitrimers

AbstractFor the manufacture of extrusion dies, three‐dimensional (3D) printing with photopolymers offers numerous advantages including flexibility, high surface quality, decent build speed, low costs and a reduced amount of waste. However, the majority of photocurable resins used in vat photopolymerization 3D printing rely on acrylates, which entail 3D‐printed objects with poor mechanical properties. In particular, the high brittleness limits their application in rapid tooling, for which tough materials with high glass transition temperatures (Tg) are required. In the present study, we highlight the use of dual curable acrylate‐epoxy resins with dynamic covalent bonds for the direct fabrication of extrusion dies. During digital light processing (DLP) 3D printing the acrylate network is formed, whose toughness and thermal stability are significantly enhanced by the thermoactivated formation of a second network. By following a postbaking procedure, aminoglycidiyl monomers are cured with an anhydride hardener bearing bulky norbornene groups yielding interpenetrating polymer networks with a Tg &gt; 100°C. The tertiary amine groups present in the structure of the aminoglycidyl derivatives do not only accelerate the ring‐opening reaction but also act as internal catalysts and activate bond exchange reactions between free –OH groups and ester moieties available in the photopolymer. This is confirmed by rheometer studies showing a distinctive stress relaxation at elevated temperature and giving rise to a possible reprocessability of the 3D‐printed dies. With a selected resin formulation, a set of dies is printed by DLP 3D printing, with which a highly filled rubber compound is successfully extruded. The results clearly show that dual curable resins with dynamic covalent bonds are a promising class of material for rapid tooling and pave the way towards a customized and convenient fabrication of extrusion dies for rubber processing.

Effect of functionality of diluents on digital light processing (DLP) based three‐dimensional (3D) printing of UV‐curable bisphenol A‐based epoxy acrylate resin

AbstractDigital light processing (DLP) based three‐dimensional (3D) printing technology which uses photocurable resin has been a center of interest due to its printing accuracy and printing speed. In our research, we have synthesized and modified the bisphenol A‐based epoxy acrylate resin for the DLP 3D printer having a printing accuracy of 50 μm. As the viscosity plays an important role in printing accuracy, the resin was modified with mono‐functional, di‐functional, tri‐functional, and combination of di‐tri functional acrylate diluents as well as with photoinitiator to achieve the desired level of viscosity. The process parameters like curing time and intensity were optimized using the DLP 3D printer. The uncured and UV‐cured samples were characterized using FTIR‐ATR, 1HNMR, UV–VISIBLE, and TGA techniques. The analysis of the uncured and UV‐cured samples was carried out using viscosity, gel content, water absorption, and chemical resistance test. The mechanical properties of the UV‐cured samples were determined using hardness and tensile strength test. The 3D‐printed samples were observed under high‐resolution microscope to confirm the printing quality and resolution. The resulting outcome confirmed that the proper selection of diluents is an important parameter for achieving the good quality and resolution of samples printed using the DLP 3D printer technology.Highlights Synthesis and modification of UV‐curable resin Selection of diluents for controlling the processablility of UV‐curable resin Optimization of process parameters for DLP based 3D printer 3D printing of samples having good quality, resolution and feature size.

DLP‐Printable Porous Cryogels for 3D Soft Tactile Sensing

AbstractThree‐Dimensional (3D) printed porous materials hold the potential for various soft sensing applications due to their remarkable flexibility, low density, and customizable geometries. However, developing versatile and efficient fabrication methods is crucial to unlock their full potential. A novel approach is introduced by combining Digital Light Processing (DLP) 3D printing and freeze‐drying to manufacture deformable cryogels featuring intricate morphologies. Photocurable hydrogels based on Poly(3,4‐ethylenedioxythiophene)Polystyrene sulfonate (PEDOT:PSS), Polyethylene glycol Diacrylate (PEGDA) and Ethylene Glycol (EG) are successfully printed and lyophilized. In this way, porous cryogels with tailorable properties are achieved. Microporosity varies from 68% to 96%, according to the chemical composition. Ultra‐soft cryogels with a compressive modulus of 0.13MPa are fabricated by adding a reactive diluent. As a result of the cryogelation process, which effectively removes water from the hydrogels, microporous structures with details as fine as 100 µm are obtained. The achieved freedom of design is exploited to fabricate resistive force sensors with a honeycomb lattice morphology. The sensitivity and the working range of the sensors can be tailored by tuning the size of the cells, paving the way for sensors with programmable architectures that can meet diverse requirements.

DLP Fabrication of Multiple Hierarchical Biomimetic GelMA/SilMA/HAp Scaffolds for Enhancing Bone Regeneration.

Severe bone defects resulting from trauma and diseases remain a persistent clinical challenge. In this study, a hierarchical biomimetic microporous hydrogel composite scaffold was constructed by mimicking the hierarchical structure of bone. Initially, gelatin methacrylamide (GelMA) and methacrylic anhydride silk fibroin (SilMA) were synthesized, and GelMA/SilMA inks with suitable rheological and mechanical properties were prepared. Biomimetic micropores were then generated by using an aqueous two-phase emulsification method. Subsequently, biomimetic microporous GelMA/SilMA was mixed with hydroxyapatite (HAp) to prepare biomimetic microporous GelMA/SilMA/HAp ink. Hierarchical biomimetic microporous GelMA/SilMA/HAp (M-GSH) scaffolds were then fabricated through digital light processing (DLP) 3D printing. Finally, in vitro experiments were conducted to investigate cell adhesion, proliferation, and inward migration as well as osteogenic differentiation and vascular regeneration effects. In vivo experiments indicated that the biomimetic microporous scaffold significantly promoted tissue integration and bone regeneration after 12 weeks of implantation, achieving 42.39% bone volume fraction regeneration. In summary, this hierarchical biomimetic microporous scaffold provides a promising strategy for the repair and treatment of bone defects.

3D printed microfluidic valve on PCB for flow control applications using liquid metal

Direct 3D printing of active microfluidic elements on PCB substrates enables high-speed fabrication of stand-alone microdevices for a variety of health and energy applications. Microvalves are key components of microfluidic devices and liquid metal (LM) microvalves exhibit promising flow control in microsystems integrated with PCBs. In this paper, we demonstrate LM microvalves directly 3D printed on PCB using advanced digital light processing (DLP). Electrodes on PCB are coated by carbon ink to prevent alloying between gallium-based LM plug and copper electrodes. We used DLP 3D printers with in-house developed acrylic-based resins, Isobornyl Acrylate, and Diurethane Dimethacrylate (DUDMA) and functionalized PCB surface with acrylic-based resin for strong bonding. Valving seats are printed in a 3D caterpillar geometry with chamber diameter of 700 µm. We successfully printed channels and nozzles down to 90 µm. Aiming for microvalves for low-power applications, we applied square-wave voltage of 2 Vpp at a range of frequencies between 5 to 35 Hz. The results show precise control of the bistable valving mechanism based on electrochemical actuation of LMs.

Direct 4D printing of ceramics driven by hydrogel dehydration

4D printing technology combines 3D printing and stimulus-responsive materials, enabling construction of complex 3D objects efficiently. However, unlike smart soft materials, 4D printing of ceramics is a great challenge due to the extremely weak deformability of ceramics. Here, we report a feasible and efficient manufacturing and design approach to realize direct 4D printing of ceramics. Photocurable ceramic elastomer slurry and hydrogel precursor are developed for the fabrication of hydrogel-ceramic laminates via multimaterial digital light processing 3D printing. Flat patterned laminates evolve into complex 3D structures driven by hydrogel dehydration, and then turn into pure ceramics after sintering. Considering the dehydration-induced deformation and sintering-induced shape retraction, we develop a theoretical model to calculate the curvatures of bent laminate and sintered ceramic part. Then, we build a design flow for direct 4D printing of various complex ceramic objects. This approach opens a new avenue for the development of ceramic 4D printing technology.

Preparation of excellent performance ZTA ceramics and complex shaped components using digital light processing 3D printing technology

Complex cellular structured Al2O3 ceramics is difficult to fabricate due to its poor toughness. To overcome this limitation, La2O3 and ZrO2 were introduced into Al2O3 ceramics in digital light processing (DLP) 3D printing. The toughening of ZrO2 and in-situ formation of platelet grains by La2O3 addition dramatically increased the performance of printed ceramics (flexural strength of 556.6 MPa, fracture toughness of 6.94 MPa·m1/2, Vickers hardness of 18.88 GPa, and an apparent porosity of 0.09%), which exceeds most of those fabricated by traditional process. Furthermore, four different cellular structures were successfully fabricated with a Diamond-structure being the best (compressive strength of 40.62 MPa, Young’s modulus of 2.41 GPa, energy absorption of 0.45 MJ/m3, cellular density of 1.70 g/cm3, and specific strength of 23.83 MPa/(g/cm3)). This study presents a novel strategy for using DLP 3D printing technology in the fabrication of lightweight, high-strength and complex shaped ceramic components. It aims to expedite the rapid application of DLP 3D printing technology in various fields such as aerospace and medical.

Antiviral and Antibacterial 3D-Printed Products Functionalised with Poly(hexamethylene biguanide).

Infection prevention and public health are a vital concern worldwide, especially during pandemics such as COVID-19 and seasonal influenza. Frequent manual disinfection and use of chemical spray coatings at public facilities are the typical measures taken to protect people from coronaviruses and other pathogens. However, limitations of human resources and coating durability, as well as the safety of disinfectants used are the major concerns in society during a pandemic. Non-leachable antimicrobial agent poly(hexamethylene biguanide) (PHMB) was mixed into photocurable liquid resins to produce novel and tailor-made covers for public facilities via digital light processing, which is a popular 3D printing technique for satisfactory printing resolution. Potent efficacies of the 3D-printed plastics were achieved in standard antibacterial assessments against S. aureus, E. coli and K. pneumoniae. A total of 99.9% of Human coronavirus 229E was killed after being in contact with the 3D-printed samples (containing the promising PHMB formulation) for two hours. In an eight-week field test in Hong Kong Wetland Park, antibacterial performances of the specially designed 3D-printed covers analysed by environmental swabbing were also found to be satisfactory. With these remarkable outcomes, antimicrobial products prepared by digital light processing 3D printing can be regarded as a reliable solution to long-term infection prevention and control.

4D-printed microneedles from dual-sensitive chitosan for non-transdermal drug delivery

Microneedles are a promising micro-scale drug delivery platform that has been under development for over two decades. While 3D printing technology has been applied to fabricate these systems, the challenge of achieving needle sharpness remains. In this study, we present an innovative approach for microneedle fabrication using digital light processing (DLP) 3D printing and smart chitosan biomaterial. For the first time, we used hydroxybutyl methacrylated chitosan (HBCMA), which possesses dual temperature- and photo-sensitive properties, to create microneedles. The DLP approach enabled a quick generation of HBCMA-based microneedles with a high resolution. The microneedles exhibited 4D properties with a change in needle dimensions upon exposure to temperature, which enhances resolution, sharpens needles, and improves mechanical strength. We demonstrated the ability of these microneedles to load, deliver, sustained release small molecular drugs and penetrate soft tissue. Overall, the HBCMA-based microneedles show promising potential in non-dermal drug delivery applications.

Triplet Upconversion under Ambient Conditions Enables Digital Light Processing 3D Printing.

The rapid photochemical conversion of materials from liquid to solid (i.e., curing) has enabled the fabrication of modern plastics used in microelectronics, dentistry, and medicine. However, industrialized photocurables remain restricted to unimolecular bond homolysis reactions (Type I photoinitiations) that are driven by high-energy UV light. This narrow mechanistic scope both challenges the production of high-resolution objects and restricts the materials that can be produced using emergent manufacturing technologies (e.g., 3D printing). Herein we develop a photosystem based on triplet-triplet annihilation upconversion (TTA-UC) that efficiently drives a Type I photocuring process using green light at low power density (<10 mW/cm2) and in the presence of ambient oxygen. This system also exhibits a superlinear dependence of its cure depth on the light exposure intensity, which enhances spatial resolution. This enables for the first-time integration of TTA-UC in an inexpensive, rapid, and high-resolution manufacturing process, digital light processing (DLP) 3D printing. Moreover, relative to traditional Type I and Type II (photoredox) strategies, the present TTA-UC photoinitiation method results in improved cure depth confinement and resin shelf stability. This report provides a user-friendly avenue to utilize TTA-UC in ambient photochemical processes and paves the way toward fabrication of next-generation plastics with improved geometric precision and functionality.

Digital light processing technique aided 3D printing hierarchical super-wetting mesh coated with hydrophobic SiO2 for highly efficient oil-water separation

Gravity-driven filtration using super-wetting mesh surfaces holds significant promise in addressing oil pollution resulting from human activities. However, conventional techniques need help fabricating efficient separation mesh structures due to their limited stability in oily-water solutions. To overcome this, we employed a Digital Light Processing (DLP) 3D printing technique to fabricate a mesh with a micro-patterned surface using a UV light-curable polyurethane (PU). A post-UV curing step was implemented to transform the soft segments of PU into a solid state. To enhance the super-wetting properties, hydrophobic modified silica (m-SiO2)/UV curable polydimethylsiloxane (PDMS) solution was applied through dip coating, resulting in a hierarchical structure with high surface roughness and superhydrophobic characteristics. In oil–water separation tests, the hierarchical superhydrophobic mesh, featuring a pore size of 300 µm, demonstrated exceptional performance, achieving a remarkable flow flux of 37,410 L/m2 h with a separation efficiency of 97.46 %. Furthermore, the separation efficiency remained consistently above 97.0 % under varying pH conditions and oil mixtures, highlighting the excellent water-repellence capacity of the hierarchical mesh developed in this study.

AI-driven real-time failure detection in additive manufacturing

The optimisation of 3D printing parameters for manufacturing biomedical devices is an emerging interdisciplinary field that incorporates artificial intelligence techniques such as machine learning and deep learning. In this particular study, the focus is on the fabrication of biocompatible finger splints using digital light processing 3D printing technology, followed by UV curing, to evaluate their quality. By leveraging vibration data from printers, which cannot be captured through visual inspection of layer defects, this study aims to develop a predictive model for assessing the failures of printed parts. Here, a closed-loop detection system is proposed to identify failure phenomena in 3D resin printing, combining both cloud and edge computing technologies to effectively detect and address potential failures in the printing process.

High-resolution low-cost LCD 3D printing for microfluidics and organ-on-a-chip devices.

The fabrication of microfluidic devices has progressed from cleanroom manufacturing to replica molding in polymers, and more recently to direct manufacturing by subtractive (e.g., laser machining) and additive (e.g., 3D printing) techniques, notably digital light processing (DLP) photopolymerization. However, many methods require technical expertise and DLP 3D printers remain expensive at a cost ∼15-30 K USD with ∼8 M pixels that are 25-40 μm in size. Here, we introduce (i) the use of low-cost (∼150-600 USD) liquid crystal display (LCD) photopolymerization 3D printing with ∼8-58 M pixels that are 18-35 μm in size for direct microfluidic device fabrication, and (ii) a poly(ethylene glycol) diacrylate-based ink developed for LCD 3D printing (PLInk). We optimized PLInk for high resolution, fast 3D printing and biocompatibility while considering the illumination inhomogeneity and low power density of LCD 3D printers. We made lateral features as small as 75 μm, 22 μm-thick embedded membranes, and circular channels with a 110 μm radius. We 3D printed microfluidic devices previously manufactured by other methods, including an embedded 3D micromixer, a membrane microvalve, and an autonomous capillaric circuit (CC) deployed for interferon-γ detection with excellent performance (limit of detection: 12 pg mL-1, CV: 6.8%). We made PLInk-based organ-on-a-chip devices in 384-well plate format and produced 3420 individual devices within an 8 h print run. We used the devices to co-culture two spheroids separated by a vascular barrier over 5 days and observed endothelial sprouting, cellular reorganization, and migration. LCD 3D printing together with tailored inks pave the way for democratizing access to high-resolution manufacturing of ready-to-use microfluidic and organ-on-a-chip devices by anyone, anywhere.