Digital Light Processing 3D Printing Research Articles

Influence of Printing Angulation on the Flexural Strength of 3D Printed Resins: An In Vitro Study

This study compared the flexural strength of various 3D printed resins fabricated at different building angles (0°, 45°, and 90°). Four groups of resins were tested: Varseo Smile Teeth (Bego GmbH & Co., Bremen, Germany), V-print C&B Temp (Voco GmbH, Cuxhaven, Germany), Bego Triniq (Bego GmbH & Co. KG, Bremen, Germany), and Sprintray Crown (SprintRay, Los Angeles, CA, USA). A digital light processing 3D printer (Asiga MAX UV, NSW, Sydney, Australia) was used to fabricate the samples at the specified build angles (0°, 45°, and 90°) in accordance with the ISO 4049:2019 standard. Flexural strength was measured using a universal testing machine (Instron 5567; Instron Ltd., Norwood, MA, USA), and fracture analysis was performed using a scanning electron microscope (Jeol JSM-6060LV, Tokyo, Japan). Statistical analysis was carried out using the Statistical Package for the Social Sciences (SPSS, version 26; IBM Corp., Chicago, IL, USA). Means and standard deviations were calculated for each group, and statistical differences were assessed using one-way ANOVA followed by the Bonferroni post hoc test (p < 0.05). All tested resins exhibited high flexural strength values. The maximum flexural strength was observed in the 0° printed samples (137.18 ± 18.92 MPa), while the lowest values were recorded for the 90° printed samples (116.75 ± 24.74 MPa). For V-print C&B Temp, the flexural strength at 90° (116.97 ± 34.87 MPa) was significantly lower compared to the 0° (156.56 ± 25.58 MPa) and 45° (130.46 ± 12.33 MPa) orientations. In contrast, Bego Triniq samples printed at 45° (148.91 ± 21.23 MPa) demonstrated significantly higher flexural strength than those printed at 0° (113.37 ± 31.93 MPa) or 90° (100.96 ± 16.66 MPa). Overall, the results indicate that the printing angle has a significant impact on the flexural strength of the materials, with some resins showing lower strength values at the 90° build angle.

Impact of Graphene Nanoparticles on DLP-Printed Parts' Mechanical Behavior

Digital Light Processing (DLP) is one of the most promising techniques among the additive manufacturing (AM) technologies for polymer resin. The polymer parts produced through this technique demonstrate a diverse range of characteristics that can be specifically designed for various fields of application. Specific attributes can be attained by utilizing polymer composites composed of multiple materials in numerous ratios. This research delves into evaluating and comparing different properties, including microstructure, surface texture, and mechanical behavior, of resin-based polymer composites fabricated using the DLP 3D printing technology. To achieve this, specimens have been printed using photopolymer resin as the base material, with varying percentages of graphene nanoparticles added to the resin. Tensile tests and particle analysis based on optical microscope images validate that optimizing parameters, especially the energy setting of the printer, significantly impact the printed samples' strength, surface texture, layering, and microstructure. The findings indicate that at a specific percentage of graphene, such as 0.5%, there is an increase in tensile strength by 38.1%, Young’s modulus by 54.7%, and Yield strength by 11.2%, accompanied by an improved surface roughness. A graphene concentration of 0.75% results in diminished tensile strength, yield strength, and Young’s modulus. The significance of fine-tuning printing parameters to achieve desired properties in resin-based polymer composites manufactured via 3D printing is highlighted.

Digital light processing 3D printing of yttria stabilized zirconia ceramics: microstructures, characterizations, and cytocompatibility

Digital light processing 3D printing of yttria stabilized zirconia ceramics: microstructures, characterizations, and cytocompatibility

Biocompatible PVAc-g-PLLA Acrylate Polymers for DLP 3D Printing with Tunable Mechanical Properties.

The technological advancement of Additive Manufacturing has enabled the fabrication of various customized artifacts and devices, which has prompted a huge demand for multimaterials that can cater to stringent mechanical, chemical, and other functional property requirements. Photocurable formulations that are widely used for Digital Light Processing (DLP)/Stereolithography (SLA) 3D printing applications are now expected to meet these new challenges of hard and soft or stretchable structural requirements in addition to good resolution in multiple scales. Here we present a biocompatible photocurable resin formulation with tunable mechanical properties that can produce hard or stretchable elastomeric 3D printed materials in a graded manner. Acrylate poly(lactic acid) (PLA) grafted polyvinyl acetate (PVAc) polymer was mixed with hydroxyl ethyl methacrylate (HEMA) and hydroxyl ethyl acrylate (HEA) as reactive diluents (50-70 wt %) in various compositions to form a series of photocurable resin formulations. Depending on the nature of the reactive diluent (HEMA or HEA) and their weight percentage, the mechanical properties of the 3D printed parts could be fine-tuned from hard (Tensile strength 20.6 ± 2 MPa, elongation 2 ± 1%) to soft (Tensile strength 1.1 ± 0.2 MPa, elongation 62 ± 8%) materials. The printed materials displayed remarkable dye absorption (95%), showing stimuli-responsive behavior for dye release (with respect to both pH and enzyme), while also demonstrating high cell viability (>90%) for mouse embryonic (WT-MEF) cells and degradability in PBS solution. These biobased 3D printing resins have the potential for a variety of applications, including tissue engineering, soft robotics, dye absorption, and elastomeric actuators.

Strain Sensing Enhancement of 3D-printed Polyurethane through Surface Deposition of Carbon Black

Strain sensors for wearable electronics function by identifying mechanical deformations and translating into electrical signals. For optimal performance, electrical conductivity, electrical sensitivity, and flexibility are major properties of strain sensors. Polyurethane (PU) shows promise for custom strain sensors due to its high flexibility. Additionally, using digital light processing (DLP) 3D printing to shape PU is suitable for detecting body movements. Therefore, the aim of this study is developing 3D-printed PU to strain sensing devices, utilizing the surface coating method on 3D-printed PU with carbon black (CB) and polydimethylsiloxane (PDMS) to fabricate the (PDMS+CB)/CB/PU strain sensor. The conductive network of CB enhances sensitivity, while PDMS is incorporated to act as an adhesive for the durability of CB on the PU surface. The results of the experiment reveal a gauge factor of 6.04 with range from 1 to 10% elongation. The strain sensor of this study has high potential to use for strain sensing technology and is capable of detecting small body movements.

A hydrogel sensor based on conic baston structure

AbstractResistive flexible pressure sensors are extensively employed in wearable devices owing to their wide operational range and straightforward construction. This study presents a conic bastion‐structured sensor microunit to improve the sensor sensitivity. The base hydrogel is synthesized using acrylamide (AM), with Mg2+ and Na+ acting as conductive ions. The sensor is fabricated using digital light processing (DLP) 3D printing technology and is subjected to experimental evaluation. The findings indicate that the hydrogel sensor with a 50 wt% AM composition demonstrates enhanced mechanical strength and conductive properties, achieving a peak sensitivity of 0.534 kPa−1 within a pressure range of 0–0.8 kPa. Furthermore, the sensor exhibits favorable response characteristics (30 ms) and recovery characteristics (40 ms), along with stability. The proposed sensor is suitable for wearable devices and live joint angle detection. Additionally, the “handwriting fingerprint” pattern recognition and document verification proposed in this article make it applicable in scenarios, such as banking, notarization, and other handwriting and seal verification contexts.

A Scalable Digital Light Processing 3D Printing Method

The 3D printing method based on digital light processing (DLP) technology can transform liquid resin materials into complex 3D models. However, due to the limitations of digital micromirror device (DMD) specifications, the normal DLP 3D printing method (NDPM) cannot simultaneously process large-size and small-feature parts. Therefore, a scalable DLP 3D printing method (SDPM) was proposed. Different printing resolutions for a part were designed by changing the distance between the projector and the molding liquid level. A scalable DLP printer was built to realize the printing resolution requirements at different sizes. A series of experiments were performed. Firstly, the orthogonal experimental method was used, and the minimum and maximum projection distances were obtained as 20.5 cm and 30.5 cm, respectively. Accordingly, the layer thickness, exposure time, and waiting leveling time were 0.08 mm, 3 s, and 6 s and 0.08 mm, 7 s, and 10 s. Secondly, single-layer column feature printing was finished, which was shown to have two minimum printing resolutions of 101 μm and 157 μm at a projection distance of 20.5 cm and 30.5 cm. Thirdly, a shape accuracy test was conducted by using the SDPM. Compared with the NDPM, the shape accuracy of the small-feature round, diamond, and square parts was improved by 49%, 42%, and 2%, respectively. This study verified that the SDPM can build models with features demonstrating high local shape accuracy.

Influence of Material, Sterilization, and Disinfection on the Accuracy of Three-Dimensional Printed Surgical Templates: An InVitro Study.

To evaluate the influence of the three-dimensional (3D) printing technology, material, sterilization, and disinfection on the accuracy of guided surgical templates. Fifty printed resin surgical templates were designed and fabricated using a digital light processing 3D printer with a photopolymerizing resin, and 50 printed metal surgical templates were designed and fabricated using a selective laser melting 3D printer with a titanium alloy. Templates from both groups were randomly divided into five subgroups involving different sterilization and disinfection procedures. The group without any sterilization or disinfection procedure served as the control group, whereas the other groups were used as the study groups (hydrogen peroxide gas plasma sterilization, 5% povidone-iodine disinfection, 75% ethyl alcohol disinfection, and steam autoclave sterilization). Implant simulations were performed on the 3D-printed resin models, and postoperative impressions were acquired with scan bodies attached to the implants. All surgical templates were digitally scanned. The root mean square was used to determine and quantify fabrication accuracy and reproducibility, and the definitive and planned implant positions were compared. The printed resin templates exhibited lower fabrication accuracy and reproducibility, as well as higher 3D deviations, after steam autoclave sterilization (p < 0.001); however, the printed metal templates were not affected by the different sterilization or disinfection procedures (p > 0.05). Printed metal surgical templates are viable alternatives for guided implant surgery. Preoperative steam or gas plasma sterilization is recommended, especially for metal templates, as resin templates show deformation and decreased accuracy after steam sterilization. chictr.org.cn number: ChiCTR2400081334.

Shape-programmable hard-magnetic soft actuators with high magnetic particle content via digital light processing method

In this work, we developed a novel hard-magnetic photosensitive suspension with high solid loadings of 50 wt% for digital light processing 3D printing. The suspension combining photosensitive resin and reactive diluent can retain stability for 6 h. The printed materials from the suspension achieve a low modulus of below 900 kPa and high remanence of 83.7 kA/m. The suspension’s cure behavior was studied in detail to obtain the optimal printing parameters. The printing error of the small structures with feature size of about 1000 μm is kept below 20 %. Moreover, we proposed an efficient magnetization programming strategy for hard-magnetic soft actuators with desirable shapes based on the rod model considering the non-magnetic load. The accuracy and reliability of the strategy are verified by the experiment results. Finally, we designed and fabricated a “flower” using our method, achieving its closing action in accordance with the prescribed shape.

Simultaneous Color- and Dose-Controlled Thiol-Ene Resins for Multimodulus 3D Printing with Programmable Interfacial Gradients.

Drawing inspiration from nature's own intricate designs, synthetic multimaterial structures have the potential to offer properties and functionality that exceed those of the individual components. However, several contemporary hurdles, from a lack of efficient chemistries to processing constraints, preclude the rapid and precise manufacturing of such materials. Herein, the development of a photocurable resin comprising color-selective initiators is reported, triggering disparate polymerization mechanisms between acrylate and thiol functionality. Exposure of the resin to UV light (365nm) leads to the formation of a rigid, highly crosslinked network via a radical chain-growth mechanism, while violet light (405nm) forms a soft, lightly crosslinked network via an anionic step-growth mechanism. The efficient photocurable resin is employed in multicolor digital light processing 3D printing to provide structures with moduli spanning over two orders of magnitude. Furthermore, local intensity (i.e., grayscale) control enables the formation of programmable stiffness gradients with ≈150× change in modulus occurring across sharp (≈200µm) and shallow (≈9mm) interfaces, mimetic of the human knee entheses and squid beaks, respectively. This study provides composition-processing-property relationships to inform advanced manufacturing of next-generation multimaterial objects having a myriad of applications from healthcare to education.

Effect of wound dressing porosity and exudate viscosity on the exudate absorption: In vitro and in silico tests with 3D printed hydrogels

Exudate absorption is a key parameter for proper wound dressing performance. Unlike standardized tests that consider exudate viscosity close to that of water, patients' exudates vary greatly in composition and, therefore, viscosity. This work aimed to investigate the effects of exudate viscosity and pore size of hydrogel-like dressings on the exudate absorption rate to establish rational criteria for the design of dressings that can meet the personalized needs of wound treatment. Computer-aided design (CAD) was used for Digital Light Processing (DLP) 3D printing of hydrogels with 0%, 30% and 60% porosity. The hydrogels were characterized in detail, and the absorption of two simulated exudate fluids (SEFs) was video-recorded. The same CAD files were used to develop in silico models to simulate exudate uptake rate. Both in vitro data and in silico modeling revealed that low-viscosity SEF penetrates faster through relatively small hydrogel pores (approx. 400 μm) compared to larger pores (approx. 1100 μm) due to capillary forces. However, in vitro vertical uptake took longer than when simulated using CAD design due to lateral fluid absorption through the pore walls in the hydrogel bulk. Distortions of hydrogel channels (micro-CT images) and lateral fluid absorption should be both considered for in silico simulation of SEF penetration. Overall, the results evidenced that porous hydrogel dressings allow rapid penetration (within a few seconds) and hosting of exudates, especially for pore size <1 mm. This information may be useful for design criteria of wound dressings with adequate fluid handling and drug release rate.

Sawtooth-shaped microsaws for enhanced transdermal drug delivery: Improved drug loading and piercing efficiency

This study presents a novel approach to transdermal drug delivery with the introduction of sawtooth-shaped MicroSaws (MSs), a bioinspired microneedle design that significantly enhances drug loading and piercing efficiency. Unlike traditional microneedles (MNs), MSs, with dimensions of 0.2 mm width, 0.4 mm length, and 0.65 mm height, are engineered using epoxy acrylate (EA) via digital light processing (DLP) 3D printing and coated with polyethylene glycol diacrylate (PEGDA) to ensure biocompatibility. Experimental results demonstrate that MSs outperform conventional MNs in both mechanical piercing tests and drug release studies, showcasing a 30 % increase in drug loading capacity and a 25 % improvement in pierceability. The unique sawtooth design not only facilitates deeper penetration but also creates microchannels that enhance drug diffusion across the stratum corneum. This innovation in microneedle technology holds significant promise for improving patient compliance and therapeutic outcomes in transdermal drug delivery systems.

Fast and Efficient Fabrication of Functional Electronic Devices through Grayscale Digital Light Processing 3D Printing.

Fabricating polymeric composites with desirable characteristics for electronic applications is a complex and costly process. Digital light processing (DLP) 3D printing emerges as a promising technique for manufacturing intricate structures. In this study, polymeric samples are fabricated with a conductivity difference exceeding three orders of magnitude in various portions of a part by employing grayscale DLP (g-DLP) single-vat single-cure 3D printing deliberate resin design. This is realized through the manipulation of light intensity during the curing process. Specifically, the rational resin design with added lithium ions results in the polymer cured under the maximum UV-light intensity exhibiting higher electrical resistance. Conversely, sections that are only partially cured retains uncured monomers, serving as a medium that facilitates ion mobility, consequently leading to higher conductivity. The versatility of g-DLP allows precise control of light intensity in different regions during the printing process. This characteristic opens up possibilities for applications, notably the low-cost, facile, and rapid production of complex electrical circuits and sensors. The utilization of this technique makes it feasible to fabricate materials with tailored conductivity and functionality, providing an innovative pathway to advance the accelerated and facile creation of sophisticated electronic devices.

High mechanical performance and multifunctional degraded fucoidan-derived bioink for 3D bioprinting

While 3D bioprinting serves as a powerful tool in the field of tissue engineering, there is still a lack of natural biomaterial inks that simultaneously combine high mechanical performance with multiple biofunctionalities. Here, a single-component natural bioink with high strength and multi-biofunctionality was developed through the simple degradation and methacrylation of natural fucoidan. Hydrothermal degradation significantly decreased the natural fucoidan solution's viscosity by 99.9 %, meeting the necessary viscosity for Digital Light Processing (DLP) 3D printing. Meanwhile, various biofunctionalities of low molecular weight fucoidan obtained through degradation, such as antimicrobial and antioxidant properties, were developed. The resulting bioink exhibited good mechanical performance (compression modulus of 311 kPa), antimicrobial properties (antibacterial rates of 95.5 % and 97.9 % against E. coli and S. aureus, respectively), and antioxidant properties (intracellular ROS inhibition rates of 94.7 %). Using DLP 3D bioprinting, all printed products showed high shape fidelity with exceptional viability and activity of the encapsulated cells. Due to the unique sulfate structure resembling the natural components of chondroitin sulfate, the in vivo tests revealed its efficacy in promoting cartilage defect repair. In conclusion, the novel bioink blending high mechanical performance with multiple biofunctionalities, shows great potential in the 3D printing of tissue and organ regeneration.

Reinforcement of 3D-printed resins for denture base by adding aramid fibers: Effect on mechanical, surface, and optical properties.

The present study evaluated the mechanical, surface, and optical properties of 3D-printed resins for removable prostheses reinforced by the addition of aramid fibers. According to ISO 20795-1:2013 standards, specimens were printed using a digital light processing 3D printer and divided into two groups (n=06/group): 3D-printed resin for denture base as the control group, and a group with the same 3D-printed resin in addition of 5% aramid fibers as the experimental group. Red aramid fibers were chosen for aesthetic characterization. The specimens were evaluated for their mechanical properties, such as elastic modulus (GPa), flexural strength (MPa), and superficial properties by their surface microhardness (KHN), surface roughness (μm), and surface free energy (mJ/m2). Optical properties were evaluated by the color difference (∆E00) between groups. The statistical test chosen after the exploratory analysis of the data was One-way ANOVA followed by Tukey's HSD (α=0.05). The results showed statistical differences in elastic modulus (p<0.0001), flexural strength (p<0.0001), surface free energy polar variable (p=0.0322), total surface free energy (p=0.0344), with higher values for the experimental. Surface hardness and surface roughness showed no statistical difference (p≥0.05). The color difference (∆E00) obtained through the CIEDE2000 calculus was below the perceptibility threshold (≤1.1). Adding aramid fibers to 3D-printed resin for denture bases resulted in better mechanical properties, without major alterations in surface properties. In addition, it is an easy-to-apply choice for mechanical reinforcement and aesthetic characterization, with the expression of small blood vessels in the 3D-printed resin for removable denture bases.

3D Printed Metal Organic Framework Hydrogel for Dye Adsorption and Gas Sensing

AbstractMetal organic frameworks (MOFs) have tunable chemical structures, orderly pore structures, and modifiable surface functional groups making them a promising material for environmental remediation. However, their rigid powder morphology poses significant challenges for customizing MOF structures with adjustable mechanical properties. Here, we synthesis the stretchable UV‐curable MOF hydrogels through high‐resolution digital light processing 3D printing, and evaluated its adsorption effect on seven common dyesand.The results showed that it had selective adsorption effect on methylene blue (MB), and the adsorption effect increased with the increase of the initial concentration of MB: its adsorption capacity on 6 mgL−1, 12 mgL−1 and 24 mgL−1 MB solution reached 13.55 mgg−1, 26.31 mgg−1 and 50.70 mgg−1 respectively. Compared to powdered MOFs, the 3D‐printed MOF (Cu‐BTC) exhibited superior adsorption for dye and radioactive pollution, with methylene blue adsorption increasing from 8.93 mgg−1 to 25.05 mgg−1 and I2 adsorption from 141.56 mgg−1 to 792.65 mgg−1. Furthermore, the 3D‐printed MOF structure proved easily cleanable with dilute HCl and reusable over five times without degradation. In addition, our study highlighted the suitability of the 3D‐printed MOF for CO2‐sensing devices, demonstrating its broad applicability in environmental remediation and sensing technology.

Digital Light Processing (DLP) 3D Printing of Caprolactone Copolymers with Tailored Properties through Crystallinity.

Digital light processing (DLP) 3D printing has shown great advantages such as high resolution in the fabrication of 3D objects toward a range of applications. Despite the rapid development of photocurable materials for DLP printing, tailoring properties to meet the specific demands for various applications remains challenging. Herein, we introduce copolymers of caprolactone and allyl caprolactone offering built-in functionality for thiol-ene photochemistry, thereby omitting the need for postfunctionalization. A crystalline block copolymer and an amorphous statistical copolymer were synthesized with the same comonomer composition and molecular weight. Thio-ene photocuring with a tetrafunctional thiol cross-linker was studied at different thiol to double-bond ratios for the copolymers and their blends. All formulations undergo rapid photocuring within several seconds of irradiation with slightly higher gel fractions observed for the statistical copolymer over the block copolymer under the same conditions, suggesting a somewhat higher cross-link density. Thermal properties of the networks were dependent on the presence of the semicrystalline block copolymer, where higher melting enthalpies were reached at higher block copolymer content. Similarly, crystallinity was found to be the main contributor to the mechanical properties. For a comparable composition, the modulus of a block copolymer network was found to be 31 times higher than that of the statistical copolymer network (27.7 vs 0.89 MPa). Intermediate moduli could be obtained by blending the two copolymers. DLP-printed scaffolds from these copolymers retained their thermal properties, therefore offering an efficient approach to tailoring mechanical properties, through crystallinity. Moreover, the printed scaffold displayed shape memory properties as the first example of poly(carprolactone) (PCL) copolymers in DLP printing. These materials are readily synthesized, offer fast and high-resolution 3D printing, and are degradable and cell compatible. They offer a straightforward approach to tailoring properties of PCL-based biomaterials and devices.

The application of synthetic wollastonite in digital light processing 3D printing

In this study, 3D printable organic-inorganic resins were developed using glycerol dimethacrylate, which can be synthesised from glycerol obtained as a by-product of the biodiesel production process, and wollastonite synthesised from reagent-grade materials, the by-product of the aluminium fluoride manufacturing process, silica gel waste or natural rock. The developed recyclable waste-based material was proven to be compatible with the widely available desktop DLP 3D PICO2 39 printer. It allowed straightforward additive manufacturing of true 3D structures with sub-millimetre spatial definition using standard printing parameters. This opens the way for the production of inorganic objects from reusable industrial waste.

Digital Light Processing of Thermoresponsive Hydrogels from Polyproline-Based Star Polypeptides.

The first report of star poly(L-proline) crosslinkers is disclosed for digital light processing 3D printing of thermoresponsive hydrogels. Through chain end functionalization of star poly(L-proline)s with methacryloyl groups, access to high-resolution defined 3D hydrogel structures via digital light processing is achieved through photoinitiated free radical polymerization. Changing the poly(L-proline) molecular weight has a direct influence on both thermoresponsiveness and printability, while shape-morphing behavior can be induced thermally.

Low-temperature DLP 3D printing of low-concentration collagen methacryloyl for the fabrication of durable and bioactive personalized scaffolds

Digital Light Processing (DLP) bioprinting has revolutionized tissue engineering and regenerative medicine with its speed and precision. Although commonly used in DLP printing, Gelatin Methacrylate (GelMA) lacks the mechanical strength and complex biological signaling of collagen, owing to the absence of collagen’s unique triple helix structure. However, collagen faces challenges such as denaturation at high temperatures and aggregation at neutral pH, limiting its use as a bioink. Herein, we present for the first time the development of a low-temperature DLP 3D printing technique using low-concentration Collagen Methacryloyl (ColMA) for fabricating durable and bioactive personalized scaffolds. Our study shows that pH significantly influences ColMA printing, with pH 3 producing low-concentration scaffolds that exhibit enhanced mechanical properties, minimal swelling, and prolonged resistance to enzymatic hydrolysis compared to high-concentration GelMA scaffolds, while low-concentration GelMA cannot be printed independently. ColMA scaffolds notably boost the proliferation, adhesion, migration, and differentiation of human foreskin fibroblasts. In vivo rat model tests demonstrate that ColMA scaffolds reduce inflammation, enhance collagen deposition, and accelerate epidermal regeneration. This method offers a robust solution for low-temperature DLP 3D printing of collagen ink, facilitating the creation of personalized scaffolds with superior bioactivity and representing a significant advancement in tissue engineering applications.