Digital Light Processing Method Research Articles

Photopolymer-Based Composite with Substance Release Capability Manufactured Additively with DLP Method.

In this study, caffeine-loaded photoresin composites with homogeneous structures, suitable for additive manufacturing of transdermal microneedle systems, were obtained. The properties of the composites with varying caffeine concentrations (0.1-0.4% w/w) were investigated for carbon-carbon double bond conversion using Fourier Transform Infrared Spectroscopy, surface wettability and mechanical properties using a static tensile test and nanoindentation, and caffeine release in ethanol using UV-Vis. The caffeine concentration did not affect the final degree of double bond conversion, which was confirmed in tensile tests, where the strength and Young's modulus of caffeine-loaded samples had comparable values to control ones. Samples with 0.1 and 0.2% caffeine content showed an increase in nanohardness and reduced elastic modulus of 50 MPa and 1.5 MPa, respectively. The good wettability of the samples with water and the increase in surface energy is a favorable aspect for the dedicated application of the obtained composite materials. The amount of caffeine released into the ethanol solution at 1, 3 and 7 days reached a maximum value of 81%, was higher for the lower concentration of caffeine in the sample and increased over time. The conducted research may enhance the potential application of composite materials obtained through the digital light processing method in additive manufacturing.

Comparison of three-dimensional printed composite fabrics with different surface textures made with digital light processing and fused deposition modeling

There is increasing interest in the development of functional composite materials in the field of textiles/clothing, and 3D printing technology has been researched widely to allow practical applications. Previous studies have proposed solutions to improve the adhesion of composite fabrics produced by fused deposition modeling (FDM) technology, but analysis of the adhesion characteristics of fabric composites manufactured by digital light processing (DLP) is insufficient. In this study, the DLP method was used to print rectangular patterns on four textured fabrics (woven polyester (PET), Velour, Fleece, Pleated), peeling experiments and mechanical property tests were conducted on 3D-printed composite fabrics, and these results were compared with those of the FDM method to analyze adhesion based on the surface properties of the fabrics. For composite fabrics printed using the DLP method, a liquid photosensitive resin penetrates the fibers, resulting in greater adhesion of composite fabrics and accuracy of printed patterns than those prepared using FDM. The DLP-PET showed the best mechanical properties in all groups. This research verified that adhesion can be improved by the 3D printing method and the surface characteristics of the fabric and presents a new method to prepare composite fabrics with improved properties.

High-performance 0.9Al2O3-0.1TiO2 microwave dielectric ceramics prepared by digital light processing

In this work, the 0.9Al 2 O 3 -0.1TiO 2 ceramic sample with good microwave dielectric properties and complex structures can be well fabricated by digital light processing (DLP). A relationship between dispersant content and rheological behavior of 0.9Al 2 O 3 -0.1TiO 2 slurry was explored. When dispersant content was 3.0 wt%, 0.9Al 2 O 3 -0.1TiO 2 slurry with high solid loading (50 vol%) and low viscosity (2.9 Pa s) could be obtained. 0.9Al 2 O 3 -0.1TiO 2 ceramic parts with high accuracy were fabricated successfully by adding 3.0 wt% photoinitiator under 600 mJ/cm 2 exposure energy. With the increase of sintering temperature from 1400 °C to 1600 °C, relative density, dielectric constant ( ε r ), and quality factor ( Q × f ) of 0.9Al 2 O 3 -0.1TiO 2 ceramic sample increased first and then decreased, and all reached the maximum value at 1550 °C due to the uniformity and densification of microstructures. The temperature coefficient of resonant frequency ( τ f ) value showed an almost monotonous increase, changing from negative to positive, and near-zero τ f value at 1550 °C. In addition, 0.9Al 2 O 3 -0.1TiO 2 ceramic samples sintered at 1550 °C fabricated by DLP method presented much better microwave dielectric properties: ε r = 11.30 ± 0.02, Q × f = 35,345 ± 143 GHz (@∼12 GHz), τ f = 2.16 ± 0.21 ppm/°C than that of by dry pressing method: ε r = 11.16 ± 0.11, Q × f = 30,195 ± 257 GHz (@∼12 GHz), τ f = 4.45 ± 0.13 ppm/°C, especially the Q × f value achieved a 17% increase. Accordingly, DLP technique, which has advantages of producing relatively high properties and complex geometry of microwave dielectric ceramics as well as without extra high-cost mold, greatly satisfies application requirements.

Fit Accuracy of Complete Denture Base Fabricated by CAD/CAM Milling and 3D-Printing Methods.

Digital complete denture fabrication can be accomplished by either milling or three-dimensional (3D)-printing approach in which minimal distortion during processing contributes to effective denture base adaption, which leads to good denture retention. The purpose of this study was to compare the fit accuracy of milled and 3D-printed complete denture bases. The reference edentulous maxillary arch model was scanned to generate virtual denture bases using computer-aided manufacturing software that exports as standard tessellation language files. Denture bases were constructed using a milling and 3D-printing technique using digital light processing method (n = 10). Intaglio surfaces of denture bases were scanned and superimposed on the reference model. The fit accuracy was quantified as root mean square error and evaluated statistically using independent t-test comparisons with a significance level of 0.05. Milled denture bases were significantly more accurate in adaptation than 3D-printed dentures in the overall intaglio area and primary bearing area of denture bases. 3D-printed denture bases demonstrated significantly greater accuracy in adaptation than milled denture bases in the peripheral/posterior palatal seal area. Milled denture bases fit better in the overall and primary stress-bearing areas than 3D-printed dentures, while 3D-printed dentures appeared more accurate in the peripheral seal area, which had a minor undercut that is not suitable for using milling technology.

Microwave sintering of dense and lattice 3Y-TZP samples shaped by digital light processing

Nowadays it is possible to produce ceramic parts with solid and complex shapes with rapid and efficient shaping and sintering techniques. In this paper, 3mol% yttria stabilized zirconia (3Y-TZP) dense and lattice parts were shaped by Digital light processing method (DLP) and densified by conventional (CV) and microwave (MW) sintering. 3Y-TZP samples were MW sintered up to 1550 °C with different heating rates (10, 30, and 50 °C/min) for the dense samples and 30 °C/min for the lattice samples. Controlled thermal cycles with a homogenous heating and no thermal runaway was reached. CV sintering was carried out at 10 °C/min up to 1550 °C. No inter-layer delamination was detected after sintering by the two methods. Both dense and lattice MW-sintered samples reached high final densities (equivalent to obtained values with CV-sintered samples, i.e., ≥98% T.D.), but exhibited a lower average grain size than CV-sintered materials. The different architectures between dense and lattice samples resulted in a different specific absorbed power: the power absorbed by the dense sample is lower than that absorbed by the lattice one meaning that this sample architecture heats up easily.

4D Printing of Freestanding Liquid Crystal Elastomers via Hybrid Additive Manufacturing.

Liquid crystal elastomers (LCE) are appealing candidates among active materials for 4D printing, due to their reversible, programmable and rapid actuation capabilities. Recent progress has been made on direct ink writing (DIW) or Digital Light Processing (DLP) to print LCEs with certain actuation. However, it remains a challenge to achieve complicated structures, such as spatial lattices with large actuation, due to the limitation of printing LCEs on the build platform or the previous layer. Herein, a novel method to 4D print freestanding LCEs on-the-fly by using laser-assisted DIW with an actuation strain up to -40% is proposed. This process is further hybridized with the DLP method for optional structural or removable supports to create active 3D architectures in a one-step additive process. Various objects, including hybrid active lattices, active tensegrity, an actuator with tunable stability, and 3D spatial LCE lattices, can be additively fabricated. The combination of DIW-printed functionally freestanding LCEs with the DLP-printed supporting structures thus provides new design freedom and fabrication capability for applications including soft robotics, smart structures, active metamaterials, and smart wearable devices.

The Influence of Microstructure on the Flexural Properties of 3D Printed Zirconia Part via Digital Light Processing Technology.

In recent years, additive manufacturing of ceramics is becoming of increasing interest due to the possibility of the fabrication of complex shaped parts. However, the fabrication of a fully dense bulk ceramic part without cracks and defects is still challenging. In the presented work, the digital light processing method was introduced for fabricating zirconia parts. The flexural properties of the printed zirconia were systematically investigated via a three-point bending test with the digital image correlation method, scanning electron microscopy observation and fractography analysis. Due to the anisotropy of the sample, the bending deformation behaviors of the zirconia samples in the parallel and vertical printing directions were significantly different. The flexural strength and the related elastic modulus of the samples under vertical loading were higher than that of the parallel loading, as the in-plane strength is higher than that of the interlayer strength. The maximum horizontal strain always appeared at the bottom center before the failure for the parallel loading case; while the maximum horizontal strain for the vertical loading moved upward from the bottom center to the top center. There was a clear dividing line between the minimum perpendicular strain and the maximum perpendicular strain of the samples under parallel loading; however, under vertical loading, the perpendicular strain declined from the bottom to the top along the crack path. The surrounding dense part of the sintered sample (a few hundred microns) was mainly composed of large and straight cracks between printing layers, whereas the interior contained numerous small winding cracks. The intense cracks inside the sample led to a low flexural property compared to other well-prepared zirconia samples, which the inadequate additive formulations would be the main reason for the generation of cracks. A better understanding of the additive formulation (particularly the dispersant) and the debinding-sintering process are necessary for future improvement.

Polydopamine surface functionalization of 3D printed resin material for enhanced polystyrene adhesion towards insulation layers for 3D microelectrode arrays (3D MEAs).

3D printing involves the use of photopolymerizable resins, which are toxic and typically have incompatible properties with materials such as polystyrene (PS), which present limitations for biomedical applications. We present a method to dramatically improve the poor adhesion between the PS insulative layer on 3D printed Microelectrode Array (MEA) substrates by functionalizing the resin surface with polydopamine (PDA), a mussel-inspired surface chemistry derivative. A commercial 3D printing prepolymer resin, FormLabs Clear (FLC), was printed using a digital light processing (DLP) printer and then surface functionalized with PDA by alkali-induced aqueous immersion deposition and self-polymerization. It was observed that the adhesion of the PS to FLC was improved due to the precision emanating from the DLP method and further improved after the functionalization of DLP printed substrates with PDA at 1, 12, and 24 h time intervals. The adhesion of PS was evaluated through scotch tape peel testing and instron measurements of planar substrates and incubation testing with qualitative analysis of printed culture wells. The composition and topology of the samples were studied to understand how the properties of the surface change after PDA functionalization and how this contributes to the overall improvement in PS adhesion. Furthermore, the surface energies at each PDA deposition time were calculated from contact angle studies as it related to adhesion. Finally, biocompatibility assays of the newly modified surfaces were performed using mouse cardiac cells (HL-1) to demonstrate the biocompatibility of the PDA functionalization process. PDA surface functionalization of 3D DLP printed FLC resin resulted in a dramatic improvement of thin film PS adhesion and proved to be a biocompatible solution for improving additive manufacturing processes to realize biosensors such as in vitro MEAs.

Utilization of Antibacterial Nanoparticles in Photocurable Additive Manufacturing of Advanced Composites for Improved Public Health.

This paper presents the additive manufacturing and characterization of nanoparticle-reinforced photocurable resin-based nanocomposites with a potential antimicrobial function for improved public health applications. Two types of photocurable resins are reinforced by titanium dioxide (TiO2) or zinc oxide (ZnO) nanoparticles with average diameters in the 10–30 nm range to provide antimicrobial properties. The developed nanocomposites can be additively manufactured using the digital light processing method with an outstanding surface quality and precise geometrical accuracy. Experimental characterizations are conducted to investigate key mechanical properties of the 3D printed nanocomposites, including Young’s Modulus, tensile strength, and abrasion resistance. Specimens produced were observed to demonstrate the following characteristics during testing. Tensile strength increased by 42.2% at a maximum value of 29.53 MPa. The modulus of elasticity increased by 14.3%, and abrasion resistance increased by 15.8%. The proper dispersion of the nanoparticles within the cured resin is validated by scanning electron images. The wettability and water absorption testing results indicate that the developed nanocomposites have an outstanding water resistance capability. The pairing of digital light processing with these novel nanocomposites allows for the creation of complex composite geometries that are not capable through other manufacturing processes. Therefore, they have the potential for long-term usage to improve general public health with antimicrobial functionality. The pairing of an unmodified photocurable resin with a 1% ZnO concentration demonstrated the most promise for commercial applications.

Three-dimensional printing of blue-colored zirconia accessories using digital light processing-based stereolithography

ABSTRACT Digital light processing (DLP) based stereolithography opens new possibilities for fabricating ceramic accessories with complex structures. The cure depth is a critical criterion for analyzing the production efficiency of ceramic accessories. As predicted using the absorption model, the absorbance from the photoinitiator and dye has a direct effect on the cure depth. In this study, blue-colored powder composed of 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) and CoAl2O4 powder was prepared through ball-milling. The cure depth of a single layer exposed to varying energy levels was measured, and the values of the depth sensitivity Sd and critical energy Ec were also calculated. The results showed that the absorbance of blue-colored 3Y-TZP powder increased with CoAl2O4 content, which increased the critical energy Ec and depth sensitivity reciprocal 1/Sd . Compared with the pure 3Y-TZP, the cure depth decreased, which was attributable to the absorbance of CoAl2O4. In addition, blue-colored accessories were fabricated using the DLP method, and the microstructures of the accessories were characterized through scanning electron microscopy.

3D-Printed Objects for Multipurpose Applications.

3D printing is a popular nonconventional manufacturing technique used to print 3D objects by using conventional and nonconventional materials. The application and uses of 3D printing are rapidly increasing in each dimension of the engineering and medical sectors. This article overviews the multipurpose applications of 3D printing based on current research. In the beginning, various popular methods including fused deposition method, stereolithography 3D printing method, powder bed fusion method, digital light processing method, and metal transfer dynamic method used in 3D printing are discussed. Popular materials utilized randomly in printing techniques such as hydrogel, ABS, steel, silver, and epoxy are overviewed. Engineering applications under the current development of the printing technique which include electrode, 4D printing technique, twisting object, photosensitive polymer, and engines are focused. Printing of medical equipment including artificial tissues, scaffolds, bioprinted model, prostheses, surgical instruments, COVID-19, skull, and heart is of major focus. Characterization techniques of the printed 3D products are mentioned. In addition, potential challenges and future prospects are evaluated based on the current scenario. This review article will work as a masterpiece for the researchers interested to work in this field.

High-resolution linearity measurements of photovoltaic devices using digital light processing projection

Although photovoltaic (PV) devices are rated at standard testing conditions (STCs), these STCs are rarely met, either outdoors, or when PV devices are used for indoor applications. Thus, it is beneficial to fully characterise the linearity of PV devices with respect to irradiance. Moreover, high accuracy linearity measurements are essential for reference cells (RCs), as they ensure the precision of the measured irradiance. This work presents a new technique for linearity measurements of PV devices based on digital light processing (DLP). The proposed system uses a digital micromirror device coupled with projection optics and a high-power LED array. By creating a series of patterns projected on the device under test with a specific number of bright and dark pixels, linearity measurements can be implemented through a spatial dithering process. Since the dithering process is mechanical, it is expected that any spectral variability effects for the different dithering levels or electrical non-linearities of the light source are avoided. The developed system can provide thousands of measurement points on the linearity curve of a device in seconds, which is impossible with any other currently established methods. Measurements of RCs with known linearity curves are acquired and are validated by conventional methods. Results demonstrate that the DLP method provides equal measurement accuracy compared to conventional systems, but at significantly higher resolution (points on the linearity curve) and order of magnitude higher measurement speed.

An in vitro study on the key features of Poly L-lactic acid/biphasic calcium phosphate scaffolds fabricated via DLP 3D printing for bone grafting

The main aim of this study was to assess the influence of adding BCP particles on enhancing essential properties of PLLA matrix scaffolds for bone grafting purpose. Poly L-lactic acid (PLLA)/biphasic calcium phosphate (BCP) scaffolds were fabricated via a digital light processing (DLP) 3D printer, with 70% porosity and 600 µm pore size. DLP method was utilized to generate scaffolds with sophisticated geometry, and the bio-composite material was introduced to benefit from positive aspects of polymeric/inorganic substances for bone regeneration. The selected BCP contents were 22.5, and 45 wt% compared with the control specimens with no content. Morphology, exact amount of BCP concentration as well as their distribution were assessed using computerized tomography (µ-CT), thermogravimetry analysis (TGA) and scanning electron microscopy (SEM). Moreover, in vitro biodegradability, cell viability and attachment of the specimens were also investigated. The results showed that in spite of decreasing effect of BCP particles on the mechanical properties of the printed scaffolds, cell adherence and hydrophilicity of the samples were considerably improved. Moreover, a 22.5 wt% of BCP content was found to be an optimum amount to preserve the mechanical properties during biodegradation. The paper showed the effectiveness of adding BCP particles as a biocompatible ceramic to enhance properties of the scaffolds for dental bone regeneration.

The Fabrication of Micro Beam from Photopolymer by Digital Light Processing 3D Printing Technology.

3D printing has lately received considerable critical attention for the fast fabrication of 3D structures to be utilized in various industrial applications. This study aimed to fabricate a micro beam with digital light processing (DLP) based 3D printing technology. Compound technology and essential coefficients of the 3D printing operation were applied. To observe the success of the DLP method, it was compared with another fabrication method, called projection micro-stereolithography (PμSL). Evaluation experiments showed that the 3D printer could print materials with smaller than 86.7 µm dimension properties. The micro beam that moves in one direction (y-axis) was designed using the determined criteria. Though the same design was used for the DLP and PμSL methods, the supporting structures were not manufactured with PμSL. The micro beam was fabricated by removing the supports from the original design in PμSL. Though 3 μm diameter supports could be produced with the DLP, it was not possible to fabricate them with PμSL. Besides, DLP was found to be better than PμSL for the fabrication of complex, non-symmetric support structures. The presented results in this study demonstrate the efficiency of 3D printing technology and the simplicity of manufacturing a micro beam using the DLP method with speed and high sensitivity.

Automated storage and active cleaning for multi-material digital-light-processing printer

PurposeThe purpose of this paper is to introduce a novel technique for printing with multiple materials using the DLP method. Digital-light-processing (DLP) printing uses a digital projector to selectively cure a full layer of resin using a mask image. One of the challenges with DLP printing is the difficulty of incorporating multiple materials within the same part. As the part is cured within a liquid basin, resin switching introduces issues of cross-contamination and significantly increased print time.Design/methodology/approachThe material handling challenges are investigated and addressed by taking inspiration from automated storage and retrieval systems and using an active cleaning solution. The material tower is a compact design to facilitate the storage and retrieval of different materials during the printing process. A spray mechanism is used for actively cleaning excess resin from the part between material changes.FindingsChallenges encountered within the multi-material DLP technology are addressed and the experimental prototype validates the proposed solution. The system has a cleaning effectiveness of over 90 per cent in 15 s with the build area of 72 inches, in contrast to the previous work of 50 per cent cleaning effectiveness in 2 min with only 6 inches build area. The method can also hold more materials than the previous work.Originality/valueThe techniques from automated storage and retrieval system is applied to develop a storage system so that the time complexity of swapping is reduced from linear to constant. The whole system is sustainable and scalable by using a spraying mechanism. The design of the printer is modular and highly customizable, and the material waste for build materials and cleaning solution is minimized.

Fabrication of Graphene-Reinforced Nanocomposites with Improved Fracture Toughness in Net Shape for Complex 3D Structures via Digital Light Processing

A solvent-free method to fabricate graphene-reinforced nanocomposites in net shape via digital light processing (DLP) 3D printing has been developed in this work. The effect of graphene nanofillers on resin viscosity and wettability for various printing parameters has been examined, with a systematic characterization of the mechanical and thermomechanical properties. With the addition of 0.5 wt.% graphene nanoplatelets in the resin, the flexural modulus and fracture toughness have been improved by 14% and 28% from neat resin, respectively. Thermomechanical properties of graphene-reinforced nanocomposites were also enhanced compared with the neat resin, without scarification in their printability. The feasibility of utilizing the DLP method to fabricate a fracture toughness specimen (KIC test) without complex skill-dependent notch preparation steps was explored, with different notch tip angles printed for net-shaped specimens. This provided a simple and versatile way to perform a quick examination of reinforcing efficiency from nanofillers at very low cost with high resolution and reproducibility. To demonstrate the suitability of current resins for complexly shaped structures, a gyroid scaffold for tissue engineering applications based on current graphene nanocomposite resins has been successfully fabricated via DLP, showing the great potential of current photocurable resins for applications in various fields such as tissue engineering or personalized medical devices without the cost barriers of traditional methods.

Additive manufacturing of hydroxyapatite bone scaffolds via digital light processing and in vitro compatibility

The bioceramic material hydroxyapatite (HA) is widely used in the field of bone repair. Based on additive manufacturing (AM) techniques, HA is fabricated with complex geometry to satisfy biomedical application requirements. Digital light processing (DLP) is a promising AM technique that is capable of producing HA parts with high accuracy and efficiency. The fabrication of HA parts using DLP is investigated in this study. Properties of the HA ceramic slurry and the process parameters of curing, debinding, and sintering are initially examined. The mechanical properties, porosity, and shrinkage of the sintered samples is then investigated. The experimental results show that ceramic samples with density above 90%, microhardness up to 270 HV, and flexural strength of 41.3 MPa can be manufactured using the DLP method. Hydroxyapatite bone scaffolds are then prepared with pore sizes of 300–600 μm, porosity of about 49.8%, and compressive strength of 15.25 MPa, and the scaffolds are cultured with osteoblast precursor cells to detect biocompatibility. Results illustrate that the produced scaffolds possess strong biocompatibility and can promote osteoblast proliferation, adhesion, and differentiation. The HA bone scaffolds fabricated by DLP AM show strong potential to fulfill a constructive role in the medical field of human bone repair.

Fabrication of complex shaped ceramic parts with surface-oxidized Si3N4 powder via digital light processing based stereolithography method

Si3N4 ceramic is difficultly fabricated by digital light processing (DLP) based stereolithography method, due to a large refractive index difference between Si3N4 powder and resin. In this paper, a surface oxidation approach of Si3N4 powder for improving cure depth is proposed. The results showed that, the amorphous SiO2 layer was uniformly attached onto the surface of Si3N4 powder by surface oxidation, and the absorbance of Si3N4 powder decreased as increasing oxidation degree. Moreover, the cure depth of the suspension significantly increased because of a smaller absorbance and a refractive index difference at the interface between oxidized Si3N4 powder and resin. At the exposure energy of 500 mJ/cm2, the cure depth of the raw Si3N4 powder was 34 µm. After oxidizing at 1150 °C and 1200 °C for 1 h, the cure depth effectively increased to 42 µm and 51 µm, respectively. Finally, the complex-shaped Si3N4 parts were successfully fabricated using surface-oxidized Si3N4 powder via DLP method.