Digital Light Processing 3D Printing Research Articles

Fabrication of Yb-doped silica micro-structured optical fibers from UV-curable nano-composites and their application in temperature sensing

A novel scheme for fabricating Yb-doped silica micro structured optical fibers and their application in high-temperature optical fiber sensing are reported. The Yb-doped silica micro structured optical fiber preforms consisted of Yb-doped silica core rods (0.1 wt% for Yb2O3) and holey pure silica claddings fabricated by UV-curable tube molding technology and digital light processing 3D printing technology, respectively. The silica preforms were drawn using the rod-in-tube method to Yb-doped silica micro structured optical fibers without severe distortion. The doped micro structured fibers were applied to high-temperature sensing from 296.15 to 653.15 K. The proposed technology is expected to be effective for the fabrication of various types of rare-earth-ion-doped silica micro structured optical fibers that can be used in fiber sensors, lasers, and amplifiers.

3D-printed impedance gradient Al2O3 ceramic with in-situ growing needle-like SiC nanowires for electromagnetic wave absorption

As a novel type of additive manufacturing, three-dimensional (3D) printing can efficiently realize the manufacturing of ceramic devices with more sophisticated structures. In this study, the method combining digital light processing (DLP) 3D printing technology and modified ceramic precursor polysiloxane (PSO) was not only used to fabricate Al2O3 ceramic devices with a gradient impedance bilayer structure, which consist of a cross-twist/flat structure with a torsion angle of 60°, but also to prepare needle-like SiC nanowire absorbents grown in situ to further endow the ceramic functional characteristics. The microstructure was regulated by different times of impregnation, light-curing, and thermal treatment of ferrocene-modified PSO, and Al2O3/SiCnw/SiOC composites with different electromagnetic absorption properties were prepared. We found that the Al2O3/SiCnw/SiOC composite (sample 1400–2) exhibited the optimal microwave absorption performance when it was immersed and light-cured twice, which was ascribed to its comprehensive satisfaction of the impedance matching and attenuation characteristics. When the thickness of sample 1400–2 was as thin as 2.5 mm, the minimum reflection coefficient (RCmin) reached −44.35 dB, indicating that more than 99.9990% of the electromagnetic waves could be absorbed. As the thickness increased to 2.8 mm, the effective absorption bandwidth (EAB) in the X-band was 3.6 GHz, which indicated that the effective coverage rate was as high as 85.7%. The results indicate that the generation of the stacking fault, dipole and interfacial polarization of the Al2O3/SiCnw/SiOC composites, and increasing conductivity contribute to the promotion of dielectric loss. Thus, the Al2O3/SiCnw/SiOC composite with bilayer gradient impedance structures is a good candidate for stealth radar wave absorption.

Polycrystalline alumina ceramic fabrication using digital stereolithographic light process

⍺-alumina powder with an average particle size of 180 nm was dispersed into a photosensitive resin to prepare slurry with a solid content of 40 vol% in this study. The main defects in fabricating high-performance alumina ceramics using digital light processing (DLP) 3D printing are crossing cracks resulting from the tensile stress induced by constrained shrinkage during polymerization and delamination arising from insufficient adhesion between the printed layers. The different photocurable resin systems and different amounts of plasticizer, PEG400, effects on the defect formation, sintered density, and mechanical strength were investigated. It was observed that the optimal resin composition was made up of monomer (1,6-hexanediol diacrylate) and oligomer (Bisphenol A epoxy acrylate) at the ratio of 4:1. For the slurry with binder/plasticizer of 8:2, the sintered body defects can be completely eliminated and the sintered density and average flexural strength can reach 94% and 340 MPa, respectively.

Visual presentation for monitoring layer-wise curing quality in DLP 3D printing

Purpose This paper aims to address the problem of uncertain product quality in digital light processing (DLP) three-dimensional (3D) printing, a scheme is proposed to qualitatively estimate whether a layer is printed with the qualified quality or not cured . Design/methodology/approach A thermochromic pigment whose color fades at 45°C is prepared as the indicator and it is mixed with the resin. A visual surveillance framework is proposed to monitor the visual variation in a period of the entire curing process. The exposure region is divided into 30 × 30 sub-regions; gray-level variation curves (curing curves) in all sub-regions are classified as normal or abnormal and a corresponding printing control strategy is designed to improve the percentage of qualified printed objects. Findings The temperature variation caused by the releasing reaction heat on the exposure surface is consistent in different regions under the homogenized light intensity. The temperature in depth begins to rise at different times. The temperature in the regions near the light source rises earlier, and that far from the light source rises later. Thus, the color of resin mixed with the thermochromic pigment fades gradually over a period of the entire solidification process. The color variation in the regions with defects of bubbles, insufficient material filling, etc., is much different from that in the normal curing regions. Originality/value A temperature-sensitive organic chromatic chemical pigment is prepared to present the visual variation over a period of the entire curing process. A novel 3D printing scheme with visual surveillance is proposed to monitor the layer-wise curing quality and to timely stop the possible unqualified printing resulted from bubbles, insufficient material filling, etc.

Three-Dimensional Printing Chitosan-Based Bolus Used for Radiotherapy.

A bolus is a kind of tissue equivalent material used in radiotherapy for treating superficial lesions. Despite the availability of various commercial boluses, it is hard for them to form full contact with the irregular surface of patients' skin, such as the scalp, nose, and ear, resulting in air gaps and leading to a discrepancy between the delivered dose and planned dose. To solve this problem, we provided a photocurable bioink created from chitosan (CHI) for digital light processing (DLP) three-dimensional (3D) printing the bolus in radiotherapy application. The chitosan-based bioink (CHI-MA) was obtained by a methacrylation process using methacrylic anhydride (MA). Photosensitive crosslinkers with different molecular weights were introduced into the bioink. The photocuring efficiency and mechanical properties of CHI-MA hydrogels can be well modulated by varying the crosslinkers. This CHI-MA bioink allowed us to create complex structures with reliable biocompatibility, good flexibility, and excellent structural stability. Furthermore, the nose bolus processed by 3D printing this bioink proved to be a good fit for the nose model and showed a desirable radiotherapy effect. This suggests that DLP 3D printing of the CHI-MA bioink would be a promising approach to obtain the customized bolus in the application of radiotherapy.

Rapid Fabrication by Digital Light Processing 3D Printing of a SlipChip with Movable Ports for Local Delivery to Ex Vivo Organ Cultures.

SlipChips are two-part microfluidic devices that can be reconfigured to change fluidic pathways for a wide range of functions, including tissue stimulation. Currently, fabrication of these devices at the prototype stage requires a skilled microfluidic technician, e.g., for wet etching or alignment steps. In most cases, SlipChip functionality requires an optically clear, smooth, and flat surface that is fluorophilic and hydrophobic. Here, we tested digital light processing (DLP) 3D printing, which is rapid, reproducible, and easily shared, as a solution for fabrication of SlipChips at the prototype stage. As a case study, we sought to fabricate a SlipChip intended for local delivery to live tissue slices through a movable microfluidic port. The device was comprised of two multi-layer components: an enclosed channel with a delivery port and a culture chamber for tissue slices with a permeable support. Once the design was optimized, we demonstrated its function by locally delivering a chemical probe to slices of hydrogel and to living tissue with up to 120 µm spatial resolution. By establishing the design principles for 3D printing of SlipChip devices, this work will enhance the ability to rapidly prototype such devices at mid-scale levels of production.

3D printing of sacrificial thermosetting mold for building near-infrared irradiation induced self-healable 3D smart structures

Digital light processing (DLP) 3D printing based 3D smart structures provide new solution for intelligent device production, but the material categories are limited to photoactive resins. Nanoparticles can endow materials with functionalities while high content or UV light absorbable ones are not compatible with DLP 3D printing. Herein, a bifunctional acrylate monomer TBMMA with hydrolysable acetal groups is synthesized and used as cross-linker for 4-acryloylmorpholine (ACMO) to build sacrificial thermosetting mold via DLP 3D printing. The addition of TBMMA simultaneously improves the printing precision and dimensional stability at higher temperature. The 3D printed mold can be hydrolyzed in mild acetic acid solution condition. The self-healable 3D smart structures is obtained by casting epoxy/carbon nanotubes composite (EPSS/CNTs) with dynamic disulfide bonds and sacrificing the 3D printed mold. Stepwise site-directed shape memory and self-healing processes of 3D smart composite triggered by near-infrared light is present. This study provided a unique strategy to adopt DLP 3D printing in fabrication of 3D smart composites with both precise structures and muti-fuctionalities, which will greatly expand the application fields of 3D smart structures in cutting-edge fields.

Production of Bioactive Various Lattices as an Artificial Bone Tissue by Digital Light Processing 3D Printing

Production of Bioactive Various Lattices as an Artificial Bone Tissue by Digital Light Processing 3D Printing

Effects of Cellulose Nanocrystal and Inorganic Nanofillers on the Morphological and Mechanical Properties of Digital Light Processing (DLP) 3D-Printed Photopolymer Composites

Photopolymer composites filled with cellulose nanocrystal (CNC) and/or inorganic nanofillers were fabricated by using digital light processing (DLP) 3D printing. To investigate the effects of different CNC lyophilization concentrations and behaviors of CNC particles in the photopolymer composites, morphological and mechanical properties were analyzed. CNC loading levels affected the morphological and mechanical properties of the filled composites. Better CNC dispersion was seen at a lower lyophilization concentration, and the highest mechanical strength was observed in the 0.25 wt% CNC-filled composite. Furthermore, nano-precipitated calcium carbonate (nano-PCC) and nanoclay were added to photocurable resins, and then the effect of inorganic nanofillers on the morphological and mechanical properties of the composites were evaluated. By analyzing the morphological properties, the stress transfer mechanism of nano-PCC and nanoclay in the photopolymer composites was identified and related models were presented. These supported the improved mechanical strength of the composites filled with CNC, nano-PCC, and nanoclay. This study suggested a new approach using wood-derived cellulose nanomaterials and inorganic nanofillers as effective fillers for DLP 3D printing.

Effect of Silk Fibroin Concentration on the Properties of Polyethylene Glycol Dimethacrylates for Digital Light Processing Printing

Attempts are made to use silk fibroin (SF), which is a protein produced by the silkworm, as a scaffold material in the field of regenerative medicine due to its high biocompatibility. Herein, the concentration of SF is varied and mixed with the light‐curing resin polyethylene glycol dimethacrylate (PEGDMA) to create a bioink, and the hydrogel is printed by digital light processing (DLP) 3D printing. Then, to investigate the properties of the printed hydrogel, scanning electron microscope (SEM) observation, swelling behavior measurement, and compression testing are conducted. The properties of hydrogels depend on the concentration of SF, and this result indicates that it is possible to create a scaffold with properties suitable for some tissue by controlling the amount of SF.

Digital Light Processing 4D Printing of Transparent, Strong, Highly Conductive Hydrogels.

Hydrogels have excellent biocompatibility, transparency, stretchability, and ionic conductivity, but their fabrication through photopolymerization-based 3D printing is limited due to the low solubility of hydrophobic photoinitiators and lack of efficient hydrophilic photoinitiators. Herein, a type of microemulsion is synthesized and the common hydrophobic photoinitiator can be adopted and finally, a series of transparent hydrogels with high strength (up to 22.9 MPa), elasticity (up to 583%), and ionic conductivity (up to 9.64 S m-1) are fabricated through digital light processing 3D printing technology. Objects with complex structures and a high printing resolution are printed. Hydrogels with both high strength and high ionic conductivity are obtained through chemical crosslinking and ion coordination effect. Dual-material 3D printing is applied to package the hydrogel with elastomers. Due to the high sensitivity and reliability under both stretching and compressive deformation, the hydrogel sensors are applied to monitor various human motions. In addition, the hydrogel exhibits solvent-induced dehydration and excellent water-activated shape memory properties, which are greatly beneficial for its storage and applications in the biomedical field.

Multi-element processed pyritum mixed to β-tricalcium phosphate to obtain a 3D-printed porous scaffold: An option for treatment of bone defects

Bone defects remain a challenging problem for doctors and patients in clinical practice. Processed pyritum is a traditional Chinese medicine that is often used to clinically treat bone fractures. It contains mainly Fe, Zn, Cu, Mn, and other elements. In this study, we added the extract of processed pyritum to β-tricalcium phosphate and produced a porous composite TPP (TCP/processed pyritum) scaffold using digital light processing (DLP) 3D printing technology. Scanning electron microscopy (SEM) analysis revealed that TPP scaffolds contained interconnected pore structures. When compared with TCP scaffolds (1.35 ± 0.15 MPa), TPP scaffolds (5.50 ± 0.24 MPa) have stronger mechanical strength and can effectively induce osteoblast proliferation, differentiation, and mineralization in vitro. Meanwhile, the in vivo study showed that the TPP scaffold had better osteogenic capacity than the TCP scaffold. Furthermore, the TPP scaffold had good biosafety after implantation. In summary, the TPP scaffold is a promising biomaterial for the clinical treatment of bone defects.

Digital Light Processing 3D Printing of Healable and Recyclable Polymers with Tailorable Mechanical Properties.

Three-dimensional (3D) printing is becoming a revolutionary technique across various fields. Especially, digital light processing (DLP) 3D printing shows advantages of high resolution and high efficiency. However, multifunctional monomers are commonly used to meet the rapid liquid-to-solid transformation during DLP printing, and the extensive production of unreprocessable thermosets will lead to resource waste and environmental problems. Here, we report a family of dynamic polymers with highly tailorable mechanical properties for DLP printing. The dynamic polymers cross-linked by ionic bonding and hydrogen bonding endow printed objects with excellent self-healing and recycling ability. The mechanical properties of printed objects can be easily tailored from soft elastomers to rigid plastics to satisfy practical applications. Taking advantage of the dynamic cross-linking, various assembling categories, including 2D to 3D, small to large 3D structures, and same to different materials assembly, and functional devices with a self-healing capacity can be realized. This study not only helps to address environmental issues caused by traditional DLP-printed thermosets but also realizes the on-demand fabrication of complex structures.

Design for the reduction of volume shrinkage-induced distortion in digital light processing 3D printing

Due to its high printing resolution and fast printing speed, digital light processing (DLP) has become one of the most widely used additive manufacturing technologies. In a typical DLP printing, resin is photocured from liquid into solid accompanied by a large volume shrinkage, which often leads to shape distortion of printed structures. In this study, we investigated the volume shrinkage-induced distortion of DLP-printed parts by conducting experiments, theoretical modeling, and finite element analysis (FEA) simulations. Material property evolution coupled with volume shrinkage during photocuring was first modeled constitutively. The constitutive theory was then implemented into FEA simulations of the layer-by-layer DLP printing process to study the development of shape distortion due to volume shrinkage during printing. Experiments validated the efficiency of the proposed FEA simulations. FEA was further applied to help predict the shape distortion in printed microfluidic channels and overhanging structures where printing parameters for compensating for distortion can be designed based on FEA.

Printability Study of a Conductive Polyaniline/Acrylic Formulation for 3D Printing.

There is need for developing novel conductive polymers for Digital Light Processing (DLP) 3D printing. In this work, photorheology, in combination with Jacobs working curves, efficaciously predict the printability of polyaniline (PANI)/acrylate formulations with different contents of PANI and photoinitiator. The adjustment of the layer thickness according to cure depth values (Cd) allows printing of most formulations, except those with the highest gel point times determined by photorheology. In the working conditions, the maximum amount of PANI embedded within the resin was ≃3 wt% with a conductivity of 10−5 S cm−1, three orders of magnitude higher than the pure resin. Higher PANI loadings hinder printing quality without improving electrical conductivity. The optimal photoinitiator concentration was found between 6 and 7 wt%. The mechanical properties of the acrylic matrix are maintained in the composites, confirming the viability of these simple, low-cost, conductive composites for applications in flexible electronic devices.

Temperature- and degree of cure-dependent viscoelastic properties of photopolymer resins used in digital light processing

In the present paper, the degree of cure-dependent viscoelastic properties of a commercial photopolymer resin (Loctite^{textregistered } 3D 3830) used in digital light processing (DLP) 3D printing are investigated experimentally and described by suitable model equations. To do this, tests are carried out both on the liquid resin and printed specimens under various conditions. The experimental methods include photo-DSC, UV rheometry, and dynamic mechanical analysis. A commercial digital light processing (DLP) printer (Loctite^{textregistered } EQ PR10.1) is used for the printing of the samples. Model equations are proposed to describe the behavior of the material during and after the printing process. For the representation of the degree of cure depending on temperature and light intensity, the one-dimensional differential equation proposed in a previous paper is extended to capture a temperature-dependent threshold value. The change of the viscoelastic properties during crosslinking is captured macroscopically by time-temperature and time-cure superposition principles. The parameters of the model equations are identified using nonlinear optimization algorithms. A good representation of the experimental data is achieved by the proposed model equations. The findings of this paper help users in additive manufacturing of photopolymers to predict the material properties depending on the degree of cure and temperature of printed components.

Fabrication of hollow lattice alumina ceramic with good mechanical properties by Digital Light Processing 3D printing technology

In this study, two configurations of alumina (Al2O3) ceramics (hollow lattice structure and solid lattice structure) were prepared by DLP 3D printing technology. When sintered at 1600 °C for 4 h, dense alumina ceramics with an average grain size of 4.38 ± 1.26 μm can be obtained. The Al2O3 ceramics prepared by DLP process have good forming precision and shape. The dimension error can be controlled about 0.2 mm. The compressive strength of solid block is 572 MPa. The maximum compressive strength of solid lattice (2.0 mm in diameter and 45% in porosity) is 9.70 MPa. The maximum compressive strength of hollow lattice (2.0 mm in diameter, 0.3 mm in thickness and 70% in porosity) is 4.30 MPa. The thermal simulation results show that the temperature of the hollow lattice (diameter 1.2 mm, porosity 76%) with 500 °C upper surface transferring to the lower surface is only 88.6 °C, which is lower than 133 °C of the solid lattice. Hollow lattice structure can effectively reduce heat loss and improve energy efficiency. The hollow lattice structure Al2O3 ceramics formed by DLP technology is expected to be used in industrial thermal insulation applications.

3D-printing of ceramic aerogels by spatial photopolymerization

Aerogels, the lightest solid material known, are low-density nanoporous solids that have found a wide range of applications such as thermal insulation, scaffolds for tissue engineering, catalysts supports, and micrometeorite collectors. Many types of materials have been used for their preparation, and ceramic/oxide aerogels are by far the most studied and applied family. Here we propose a new comprehensive solution to prepare these materials photochemically and fabricating them in highly complex shapes at all scales, from the macro scale down to the microns scale. The solution to these two challenges is linked, shown in the three photochemical approaches developed, allow unprecedented complexity in shape. The processes are mold irradiation, digital light processing (DLP) 3D printing, and a two-photon printing (TPP) process. The obtained 3D complex silicate objects display low density, high porosity, large surface area, and low thermal conductivity. The fabrication process also enables easy functionalization of the aerogels as inducing in them luminescence or making the printed object superhydrophobic by post printing process. The photochemical approach is ideal for the preparation of components of miniature devices, where low weight is a governing requirement.

3D printing of HAp/xSiO2 ceramic scaffolds for potential bone graft reconstruction

HAp has drawn great attention in recent years for its similarity to the inorganic component of bone and can be used as a biocompatible implant. However, the application is limited for its poor shape ability and low degradation ability. With the help of Digital Light Processing 3D printing technology, this study proposed a method for the fabrication of bone remodeling scaffolds with high complexity. In addition, this study found that the silica addition will help densify the HAp ceramic and make it transform to a more biodegradable TCP phase at low sintering temperature.

The thermal properties of a UV curable acrylate composite prepared by digital light processing 3D printing

Digital light processing (DLP) 3D printing is a potential alternative to traditional thermal curing due to its short curing time and free design customization in the absence of a mold. With this in mind, the present work is aimed at identifying the optimum composition of a printable photopolymer resin with butyl acrylate as the main-chain monomer and diurethane dimethacrylate as a crosslinker to generate a thermal interface material. In particular, the influence of the crosslinker-to-monomer ratio upon the mechanical properties of the printed material is investigated. In addition, aluminum nitride (AlN) is used as the filler due to its excellent thermal conductivity, electrical insulation, and cost effectiveness. The thermal conductivity of the printed material with 30 wt% AlN is shown to be 1.43 W/mK in the in-plane direction and 0.35 W/mK in the through-plane direction. These values are respectively 477 and 350% higher than those of pure acrylate resins, and are attributed to the creation of an efficient thermal transport pathway via dispersion of the AlN particles throughout the layered acrylate resin.