Digital Light Processing 3D Research Articles

Evolution of Self‐Assembled Lignin Nanostructure into Dendritic Fiber in Aqueous Biphasic Photocurable Resin for DLP‐Printing

AbstractThe design of lignin nanostructures where interfacial interactions enable enhanced entanglement of colloidal networks can broaden their applications in hydrogel‐based materials and light‐based 3D printing. Herein, an approach for fabricating surface‐active dendritic colloidal microparticles (DCMs) characterized by fibrous structures using nanostructured allylated lignin is proposed for the development of lignin‐based photocurable resins. With allyl‐terminated surface functionality of 0.61 mmol g−1, the entanglement between lignin‐DCM fibrils with a size of 1.4 µm successfully produces only lignin‐based hydrogels with structural integrity through photo‐crosslinking. The colloidal network of lignin dendricolloids reinforces the poly(ethylene glycol) (PEG) hydrogels during a digital light processing (DLP) 3D printing process by generating bicontinuous morphologies, resulting in six‐fold increases in toughness values with respect to the neat PEG hydrogel. The dual effectiveness of photoabsorption and free‐radical reactivity of lignin‐DCMs allow the light‐patterning of rather dilute PEG hydrogels (5–10%) with high geometric fidelity and structural complexity via DLP 3D printing. This study demonstrates a green and effective strategy for the design of 1D lignin‐DCMs that increases the versatility of the nanostructured biopolymer, opening up numerous opportunities for formulating functional hydrogels with robust structure‐property correlations.

Six smart guidelines for high-tech manufacture on low-tech 3D printers: the case of the 3Flex

While articulated surgical instruments have enabled the proliferation of minimally invasive interventions, procedures such as laparo-endoscopic single-site surgery are waning in popularity. One potential reason for this decline is a lack of sufficiently dexterous instruments. Although multi-steerable instruments exist, these are often complex and therefore expensive assemblies. Even when 3D printing was used to simplify the design of these instruments, the requirement for high-performance 3D printers limited the reduction in manufacturing costs. To tackle this issue, we propose six guidelines for converting a 3D printed compliant medical instrument from printing on a Digital Light Processing (DLP) printer to a Fused Filament Fabrication (FFF) printer. These guidelines provide a framework to manage and compensate for differences in the two processes to achieve comparable results at a reduced cost. The proposed guidelines were evaluated by assembling a FFF 3D printed prototype that shows equivalent performance to its DLP 3D printed counterpart.

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.

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 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.

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.

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.

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.

Digital light processing (DLP) 3D printing of polymer networks comprising virus-like particles.

In this work, we introduce a 3D-printable virus-like particle (VLP)-enhanced cross-linked biopolymer system. VLPs displaying surface-available acrylate groups were prepared through aza-Michael addition to serve as resins. The VLP resins were then photopolymerized into a poly(ethylene glycol) diacrylate (PEGDA) network following DLP 3D printing. This approach represents a convergence of disciplines, where the synergistic interaction between virology and additive manufacturing unlocks new frontiers in biotechnology.

Direct restoration of photocurable cross-linkers for repeated light-based 3D printing of covalent adaptable networks.

Light-based processing of thermosets has gained increasing attention because of its broad application field including its use in digital light processing (DLP) 3D printing. This technique offers efficient design and fabrication of complex structures but typically results in non-recyclable thermoset-based products. To address this issue, we describe here a photocurable, dynamic β-amino ester (BAE) based cross-linker that is not only suitable for DLP printing but can also be chemically degraded via transesterification upon the addition of 2-hydroxyethyl methacrylate (HEMA) as a decross-linker. This conceptually new protocol allows for efficient depolymerization with the direct restoration of curable monomers in a single step without the addition of external catalysts or solvents. By implementing this protocol, we have established a chemical recycling loop for multiple cycles of photo-cross-linking and restoration of cross-linkers, facilitating repeatable DLP 3D printing without generating any waste. The recycled materials exhibit full recovery of thermal properties and Young's modulus while maintaining 75% of their tensile strength for at least three cycles. Simultaneously, the presence of BAE moieties enables the (re)processability of these materials through compression molding.

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.

Simulation and Process Analysis of DLP 3D Printing with High-strength Resin

By utilizing digital light processing (DLP) printing equipment and technology, this study investigates the temperature field, stress changes, and the impact of various process parameters on the formation and strength characteristics of high-strength resin during the printing process. Abaqus birth-death element method simulation and related process tests are employed for this purpose. The simulation results demonstrate a gradual decrease in the temperature field through wavy diffusion from the center to the boundary during printing. The node temperature, displacement, and stress curves are observed to fluctuate frequently due to the subsequent printing layers, with the maximum stress point located close to the printing platform. The experimental results reveal that the test parameters possess different effects on the surface quality and tensile strength. Inappropriate parameters tend to result in surface defects. The influencing factors on the tensile strength of the sample are ranked in the following order: layer thickness, exposure time, and exposure light intensity. The molded resin sample achieves a tensile strength of 58.5MPa, which is comparable to the tensile properties of traditionally injection-molded parts.

Recent innovations in interfacial strategies for DLP 3D printing process optimization.

Three-dimensional (3D) printing, also known as additive manufacturing, is capable of transforming computer-aided designs into intricate structures directly and on demand. This technology has garnered significant attention in recent years. Among the various approaches, digital light processing (DLP) 3D printing, which utilizes polymers or prepolymers as the ink, has emerged as the leading new technology, driven by high demand across diverse fields such as customized production, healthcare, education, and art design. DLP 3D printing technology employs cured slices as molding units and is recognized for its potential to achieve both high printing speed and resolution. Recent insights into the DLP printing process highlight its inherent interface transformations between liquid and solid states. This review summarizes key aspects of the printing process, speed, precision, and material diversity optimization, from the view of interfacial interactions between solid and liquid phases which are influenced by resin formation, curing surfaces and light source properties. These interactions include those at the liquid resin-UV pattern interface, the cured structure-curing surface interface, the liquid resin-curing surface interface, and the liquid resin-cured structure interface, each contributing to the unique characteristics of the printed results. Finally, this review addresses the current challenges and limitations of DLP 3D printing, providing valuable insights for future improvements and guiding potential innovations in the field.

A photocurable polyurethane elastomer for digital light processing with comprehensive reusability based on dynamic hindered urea bonds

Digital Light Processing (DLP) 3D printing has emerged as a highly promising technique, enabling the fabrication of intricate geometric structures with ease and precision, without the need for complex mold-making processes. However, the printed objects are typically crosslinked photopolymers that cannot be reshaped, reprocessed and recycled. Herein, we successfully synthesize a dynamic soft polymer crosslinker containing hindered urea bonds (HUBs) composed of polyurethane acrylate prepolymer and tri-functional for recyclable DLP 3D printing. Contributing to the dynamic thermal response of HUBs, the printed objects can be recycled in the initial printing inks at 80 °C in 2h and the obtained recycled ink can be reprinted by DLP achieving a low viscosity and high printing resolution. In addition, the printed objects can be reprocessed by hot-press at 110 °C for 30 min upon a pressure of 5 MPa. By a reasonable proportion of monomer and crosslinker, a series of photocured elastomers were successfully prepared, in which mechanical properties could be tailored by changing the content of the crosslinker. The resulting products exhibited some fascinating attributes, such as excellent fatigue resistance, thermodynamic stability, and transparency. Significantly, the resin can regain initial 3D printing capability after undergoing solvent recycling, which maintains its printing resolution and excellent mechanical properties. This innovative design strategy not only alleviates environmental impact but also plays a pivotal role in developing the DLP 3D printing industry by tackling the long-standing issue of resin recyclability.

The influences of light scattering on digital light processing high-resolution ceramic additive manufacturing

Digital light processing (DLP) has emerged as a highly promising 3D printing technology, which is due to its ability to fabricate components and structures with low cost and high precision. The DLP is, therefore, applicable in a wide range of fields. The phenomenon of light-scattering plays a dominant role in the DLP manufacturing process, but the specific impact of ceramic particles on the distribution of incident light remains unclear. The present study has, therefore, focused on studying the effect of ceramic particles on light-scattering by performing extensive theoretical finite element simulations. The aim was then to improve the curing quality of the DLP 3D printing process. More specifically, spherically shaped particles with a uniform distribution, lower duty ratios, or materials with lower refractive indices were necessary conditions for enhancing the printing precision due to the mitigated lateral light scattering effects. The overall results of this study have provided valuable guidance for the control of the light-induced curing in the 3D printing process of ceramics, thereby facilitating advancements in ceramic-based fabrication techniques.

DLP 3D printing of TiO2-doped Al2O3 bioceramics: Manufacturing, mechanical properties, and biological evaluation

Ceramic-based biomaterials are generally produced using conventional manufacturing methods. The traditional manufacturing methods have limitations, such as material loss and a slow production process when creating personalized and complex ceramic implants. These limitations reduce the efficiency and success rate of the product. 3D printers, which are additive manufacturing methods, are a technology that enables tiny and sensitive parts to be produced quickly in the desired design. In the present study, TiO2-doped Al2O3 bioceramic parts with complicated shapes were fabricated using digital light processing (DLP) 3D printing technology. Furthermore, the mechanical, structural, and biocompatibility features of these parts were studied. The rheology studies revealed that a slurry with a solid powder loading of 50% had a suitable viscosity for 3D printing. After sintering bioceramic parts, the sintered bodies reduced significantly, with a maximum shrinkage of 41.98%. The relative density of Al2O3 ceramic decreased from 82.02 to 72.72% with 5 wt% TiO2 addition. The XRD results revealed that TiO2-doped Al2O3 bioceramic has three crystalline phases consisting of corundum (α-Al2O3), titanium dioxide (TiO2), and aluminum pentaoxotitanate (Al2TiO5). By adding 5 wt% TiO2, the compression and flexural strengths of Al2O3 increased to 3.25 to 7.07 MPa and 1.07 to 4.24 MPa, respectively. The biological test results demonstrated a high percentage of cell adhesion and proliferation confirmed by high biocompatibility. The findings show that DLP-3D printing techniques could be used to fabricate ceramics for various applications, including biomedical and dental applications, at low cost.

Swift 4D printing of thermoresponsive shape-memory polymers using vat photopolymerization

Shape-memory polymers (SMPs) are smart materials that have gained significant attention in recent years owing to their widespread application in smart structures and devices. Digital light processing (DLP), a vat-photopolymerization-based technique, is a significantly faster technology for printing a complete layer in a single step. The current study reports a facile and fast method for the 3D printing of SMP-based smart structures using a DLP 3D printer and a customized resin. A liquid crystal (LC, RM257) was combined with the resin to introduce shape-memory properties. The combination of LCs in photocurable resin provides the opportunity to directly 3D-print thermoresponsive structures, avoiding the complexity of SMP resin preparation. The structures were printed with different geometries, and the shape-memory response was measured. Lattice structures were fabricated and programmed to obtain tunable mechanical properties. Furthermore, the strain-sensing response was measured to demonstrate the utility of these lattice structures as smart patches for joint-movement sensing. The SMPs can be prepared conveniently and can potentially be used for various applications, such as smart tools, toys, and meta-material sensors.

Digital light 3D printed fast- and controlled degradation of covalent hydrogel networks

Digital light processing (DLP)-based 3D printing of hydrogels with sophisticated structures has been widely used in myriads of fields. However, the inherent covalently crosslinked network of hydrogels limits their further applications, such as working as sacrificial molds. In this work, a photocurable hydrogel system with labile covalent bonds suitable for DLP based printing to fabricate 3D complex hydrogel structures with fast- and controlled degradation ability is reported. The hydrogel precursor is composed of polyethylene glycol 400 (PEG400), a water soluble photoinitiator, and PEGDA575-Do, a degradable photocurable diacrylate monomer that can be degraded in aqueous condition via reversable aza-Michael addition reaction. The mechanical properties of formed hydrogels can be regulated by changing the PEG content and water content, and the degradation rate can be regulated by changing parameters such as PEG400 content, water content and the treating temperature. Moreover, the DLP printed degradable hydrogels networks can be used as sacrificial molds to fabricate structures from materials that cannot be directly used for DLP 3D printing (e.g. thermoplastic polycaprolactone (PCL), epoxy-based resin, and chocolate). As proofs-of-concept, a microfluidic chip is fabricated by using the biocompatible 3D printed hydrogel as a sacrificial template. Similarly, a flexible RFID tag and a flexible self-powered device are also prepared, demonstrating the potential applications in the field of flexible electronics.

DLP printing of BT/HA nanocomposite ceramic scaffolds using low refractive index BT crystals

Biological piezoelectric materials have significant potential for bone repair and energy harvesting owing to their excellent biocompatibility and piezoelectric effect. The BaTiO3/Ca10(PO4)6(OH)2 (BT/HA) composite material is an outstanding representative of biological piezoelectric materials, which has not been individually designed using digital light processing (DLP) 3D printing because of the large difference in the refractive index of its components. Therefore, in this work, double-sided-tooth plate-like BT crystals with high curvature were prepared via a hydrothermal process, and BT/HA ceramic slurries were grinded out using dispersed intermittent ball milling scheme, and BT/HA nanocomposite ceramic scaffolds were fabricated by DLP 3D printing technology. The nanostructure, dielectric properties, and piezoelectric energy harvesting performance of the BT/HA nanocomposite ceramic scaffolds were evaluated. The influences of different morphologies and contents for BT on the piezoelectric potential and stress distribution were analyzed based on a multi-physics coupling finite element simulation. The cell proliferation and adhesion abilities were investigated also. The BT/HA nanocomposite ceramic scaffolds present excellent dielectric properties, cell proliferation and adhesion abilities, and an open circuit voltage of 8 V during piezoelectric energy harvesting. The material properties and multi-physics coupling finite element analysis imply that the double-sided-tooth plate-like BT plays an important role for the fastness structure and electric field distribution in the BT/HA nanocomposite. Thus, this work provides a strategy for the application of the customized BT/HA nanocomposite ceramic scaffolds in new-generation orthopedic implants and biological energy harvesting.

Structural Design and DLP 3D Printing Preparation of High Strain Stable Flexible Pressure Sensors.

Flexible pressure sensors are crucial force-sensitive devices in wearable electronics, robotics, and other fields due to their stretchability, high sensitivity, and easy integration. However, a limitation of existing pressure sensors is their reduced sensing accuracy when subjected to stretching. This study addresses this issue by adopting finite element simulation optimization, using digital light processing (DLP) 3D printing technology to design and fabricate the force-sensitive structure of flexible pressure sensors. This is the first systematic study of how force-sensitive structures enhance tensile strain stability of flexible resistive pressure sensors. 18 types of force-sensitive structures have been investigated by finite element design, simultaneously, the modulus of the force-sensitive structure is also a critical consideration as it exerts a significant influence on the overall tensile stability of the sensor. Based on simulation results, a well-designed and highly stretch-stable flexible resistive pressure sensor has been fabricated which exhibits a resistance change rate of 0.76% and pressure sensitivity change rate of 0.22% when subjected to strains ranging from no tensile strain to 20% tensile strain, demonstrating extremely low stretching response characteristics. This study presents innovative solutions for designing and fabricating flexible resistive pressure sensors that maintain stable sensing performance even under stretch conditions.