Digital Light Processing 3D Printing Research Articles

Carbon Electrodes: 3D Architected Carbon Electrodes for Energy Storage (Adv. Energy Mater. 5/2021)

In article number 2002637, Kai Narita and co-workers report a simple method using digital light processing 3D printing and pyrolysis to fabricate 3D architected carbon anodes for energy storage, with independently controlled micrometer-to-centimeter form factors and mechanical robustness. The 3D architected carbon anodes provide a potential path towards 3D Li-ion batteries when combined with the 3D architected cathodes demonstrated in Advanced Materials Technology article number 2000791, as represented by this joint cover between the journals.

Color and Translucency Stability of Three-Dimensional Printable Dental Materials for Crown and Bridge Restorations.

The purpose of this study was to examine and compare color and translucency stability of three-dimensional (3D) printable dental materials for crown and bridge restorations. Five different materials were investigated, and twelve disc-shaped specimens of two different thicknesses (1 and 2 mm) were prepared using a digital light processing 3D printer. Color measurements were made according to the CIELAB color scale (L*, a*, and b*) using a spectrophotometer 1 h, 1 day, 1 week, one month, and six months after post-curing of the materials, and the translucency parameter (TP) was calculated. The L*, a*, b*, and TP values were compared among the different materials and storage periods using repeated measures analysis of variance. Color and translucency changes of the specimens after the different storage periods were compared with 1 h measurements to determine whether they exceeded clinically perceivable thresholds. The L*, a*, b*, and TP values showed significant differences according to the storage periods, as well as among the materials. Until one month, some materials demonstrated distinct color differences, while others showed small color differences below a clinically perceivable threshold. The translucency differences were not clinically perceivable for any specimen. After six months, all specimens demonstrated large color changes, whereas the changes in translucency were relatively small. In conclusion, the color of 3D printable dental materials changed with time, and the differences varied with the materials used. On the contrary, the changes in translucency were small. Overall, the materials became darker, more yellowish, and more opaque after six months of water storage.

Analysis of FDM and DLP 3D-Printing Technologies to Prototype Electromagnetic Devices for RFID Applications.

In this work, the application in Radiofrequency Identification (RFID) of different additive manufacturing (AM) 3D-printing technologies is discussed. In particular, the well-known Fused Deposition Modeling (FDM) technology is compared with the promising Digital Light Processing (DLP), which is based on the photopolymerization of liquid resins. Based on the research activity of the authors on this topic, a brief introduction to the fundamentals of 3D-printing in electromagnetics as well as to the different applications of both FDM and DLP in realizing Radio Frequency (RF) devices, is firstly given. Then, a comparison of the two technologies is deeply faced. Finally, after evaluated the rugosity of substrates produced with both techniques to verify the potential impact on the design of electromagnetic structures, the two techniques are both exploited for the realization of the dielectric parts of a tunable RFID tag with unconventional shape. It consists of two elements interlinked one each other. The movement between them enables tuning of the resonance frequency as well as the impedance of the antenna. Despite the differences in terms of losses, rugosity, resolution, and dielectric constant, both techniques guaranteed satisfactory values of tag sensitivity, maximum reading range, and tunability. Nevertheless, the careful analysis of the results proposed at the end of the paper suggests how the selection of one technique over the other must be taken considering the specific application constraints.

Constrained stacking in DLP 3D printing

Using stacked models for 3D printing could significantly improve printing efficiency and save printing time. For standard 3D printing techniques like Fused Deposition Modeling (FDM) or Digital Light Processing (DLP), support structures are required for overhanging areas, even between the stacked models. However, there are requirements from medical applications like 3D printed dental implant guides, that support structures are not allowed to be placed on some restricted regions to maintain models’ appearance quality and accuracy. This paper introduces a constrained multi-level stacking scheme for DLP 3D printers, aiming to stack as many models as possible in the printing space; meanwhile, no support is placed on the restricted regions. We rotate each stacked model along the axis and calculate the feasible pose set that restricted regions have no overhanging surface. We further propose a level-based scaffold structure to arrange the stacked models level by level. Therefore, support structures could be generated on the scaffold, and the stacked model does not need to support each other. We employ a heuristic strategy for each level to iteratively select a candidate model and its posture to achieve a locally optimal arrangement. We then introduce perturbations in the arrangement order, using a hill-climbing method to approximate the most volume-efficient arrangement.

Fabrication of trabecular-like beta-tricalcium phosphate biomimetic scaffolds for bone tissue engineering

The introduction of 3D printing into the manufacturing of ceramic components offers new possibilities to fabricate porous bioceramic scaffold with biomimetic morphology, customized-designed shape and suitable mechanical property for bone tissue engineering. However, most of 3D printed porous ceramic scaffolds are prepared from the array of unit cells, which do not exploit the whole potential of additive manufacturing. In this paper, a novel biomimetic porous beta-tricalcium phosphate (β-TCP) scaffolds with trabecular-like morphology were obtained based on three dimension (3D) Voronoi tessellation method and generated design. This bionic pore structure is fabricated via photopolymer-based digital light processing (DLP) 3D printing technique, a suitable 30 wt% β-TCP ceramic slurry with the addition of adjuvants was prepared. After optimized debinding-sintering process according the TG-DSC analysis, the β-TCP scaffolds showed fully interconnected trabecular-like pore structure with tailorable pore size (360 μm–1200 μm) and porosity (45%–75%) and compact microstructure. Combining compressive tests and finite element analysis (FEA), the relationship between inputting parameters, pore structure and compressive strength is investigated. Thus, the mechanical strength of the trabecular-like β-TCP scaffolds could be predicted and tuned in the initial generated design stage. In addition, the shrinkage ratio and XRD pattern are also detected. The method proposed in this study may provide an efficient bionic design intended for tissue engineering applications.

High performance hydroxyapatite ceramics and a triply periodic minimum surface structure fabricated by digital light processing 3D printing

High performance hydroxyapatite (HA) ceramics with excellent densification and mechanical properties were successfully fabricated by digital light processing (DLP) three-dimensional (3D) printing technology. It was found that the sintering atmosphere of wet CO2 can dramatically improve the densification process and thus lead to better mechanical properties. HA ceramics with a relative density of 97.12% and a three-point bending strength of 92.4 MPa can be achieved at a sintering temperature of 1300 , which makes a solid foundation for application ℃ in bone engineering. Furthermore, a relatively high compressive strength of 4.09 MPa can be also achieved for a DLP-printed p-cell triply periodic minimum surface (TPMS) structure with a porosity of 74%, which meets the requirement of cancellous bone substitutes. A further cell proliferation test demonstrated that the sintering atmosphere of wet CO2 led to improve cell vitality after 7 days of cell culture Moreover, with the possible benefit from the bio-inspired structure, the 3D-printed TPMS structure significantly improved the cell vitality, which is crucial for early osteogenesis and osteointegration.

Accuracy of definitive casts manufactured by Digital Light Processing 3D printer

Accuracy of definitive casts manufactured by Digital Light Processing 3D printer

Silk fibroin microneedles fabricated by digital light processing 3D printing

In this report, one-step 3D structuring of protein-based microneedles is proposed using digital light processing (DLP) 3D printing. Such a technique is advantageous in direct 3D construction of molecules dissolved in aqueous solution at relatively low concentration. The DLP printing of silk fibroin (SF) as a safe protein-based microneedle is challenging, and use of riboflavin, an enzyme that acts as a photoinitiator, reduces the toxicity in biomedical applications. An anti-aliasing process produces SF microneedles with oblique features, while dehydration of the printed hydrogel enhances the sharpness of printed features. The flexibility of an SF microneedle array pad is investigated, and the delivery of molecules to the skin is verified using rhodamine B fluorescence dye.

Dimensional retention of photocured ceramic units during 3D printing and sintering processes

In this study, photocuring-based digital light processing (DLP) 3D-printing technology was used to prepare basic photocuring units from cordierite ceramic slurries loaded with three different average particle sizes. Exposure time was varied to realize a range of ultraviolet light-energy dosages. Basic units, including single lines, apertures, and single walls, were printed with different feature dimensions such as single-line width and thickness, aperture diameter, and single-wall thickness. The morphologies and structures of the units were studied after printing and sintering. Their dimensions were measured, and the relative and absolute differences before and after each processing step were calculated. The dimension-retention levels were finally determined and analyzed across the ranges of slurries, exposure times, and designed dimensions. Detailed insights into the printing and sintering behaviors and performances of the ceramic slurries and printed units were gained. This study contributes to the understanding and analysis of potential dimensional errors and the printed and sintered quality of ceramic components prepared based on photocuring-based DLP 3D printing.

Reprintable Polymers for Digital Light Processing 3D Printing

Abstract3D printing is becoming a disruptive technology and shows great potential for various practical applications. Specially, digital light processing (DLP) 3D printing demonstrates advantages in high resolution and high efficiency. However, extensive production of infusible and insoluble thermosets in DLP printing causes serious resource waste and environmental problems after its disposal. Herein, a reprintable linear polymer is reported for repeatable DLP printing. Taking advantage of the dissolution of linear polymer in its monomer, printed objects can be recycled into liquid resin and reprinted via the same DLP. Polymerization kinetics and printing resolution of recycled resins and mechanical properties of reprinted polymers retain identical as the original. The thermoplastic nature of linear polymer endows 3D objects with welding and reshaping property. Recyclable composites are also successfully fabricated, and sustainable usage of high‐value fillers comes true. This strategy helps to address environmental issues arising from unprocessable thermosets and may contribute to an efficient materials recycling.

Silk Polymers and Nanoparticles: A Powerful Combination for the Design of Versatile Biomaterials.

Silk fibroin (SF) is a natural protein largely used in the textile industry but also in biomedicine, catalysis, and other materials applications. SF is biocompatible, biodegradable, and possesses high tensile strength. Moreover, it is a versatile compound that can be formed into different materials at the macro, micro- and nano-scales, such as nanofibers, nanoparticles, hydrogels, microspheres, and other formats. Silk can be further integrated into emerging and promising additive manufacturing techniques like bioprinting, stereolithography or digital light processing 3D printing. As such, the development of methodologies for the functionalization of silk materials provide added value. Inorganic nanoparticles (INPs) have interesting and unexpected properties differing from bulk materials. These properties include better catalysis efficiency (better surface/volume ratio and consequently decreased quantify of catalyst), antibacterial activity, fluorescence properties, and UV-radiation protection or superparamagnetic behavior depending on the metal used. Given the promising results and performance of INPs, their use in many different procedures has been growing. Therefore, combining the useful properties of silk fibroin materials with those from INPs is increasingly relevant in many applications. Two main methodologies have been used in the literature to form silk-based bionanocomposites: in situ synthesis of INPs in silk materials, or the addition of preformed INPs to silk materials. This work presents an overview of current silk nanocomposites developed by these two main methodologies. An evaluation of overall INP characteristics and their distribution within the material is presented for each approach. Finally, an outlook is provided about the potential applications of these resultant nanocomposite materials.

Three-Dimensional Printing of Poly(glycerol sebacate) Acrylate Scaffolds via Digital Light Processing.

Digital light processing (DLP)-based three-dimensional (3D) printing offers large improvements in fabrication throughput and spatial resolution when compared to various other additive manufacturing techniques. Both properties are highly desirable when fabricating biomaterial scaffolds that require design precision. Poly(glycerol sebacate) acrylate (PGSA) is a degradable, biocompatible, and photocurable elastomer. In this work, PGSA ink was developed for DLP 3D printing of porous tubular structures. Ink formulations with varying prepolymer concentrations (10-60 wt %), diluent (dimethyl sulfoxide (DMSO), 2-butoxyethyl acetate (EGBEA), and 1:1 DMSO/EGBEA), and degree of PGSA acrylation (17-75%) were studied to optimize printing efficiency and bulk properties of the printed scaffolds. Prepolymer inks with viscosity (<5 Pa·s) and photopolymerization kinetics (exposure time <10 s) appropriate for DLP were developed. Photocrosslinked PGSA scaffolds were further exposed to postfabrication treatments including additional UV exposure or thermal curing (150 °C) to demonstrate tunability in scaffold degradation kinetics and mechanical properties. Complementary to this effort, a 3D model-generation tool was developed to enable user-friendly customization of tubular scaffold design by controlling the pore and strut size of the volumetric mesh. The resulting DLP-printed PGSA scaffolds present high mimicry to complex 3D models with a minimum feature thickness of 80 μm. The tunable properties of PGSA coupled with enhanced precision in microstructure geometry provide a fabrication platform for a variety of tissue regeneration applications.

Fabrication of superhydrophobic 3D objects by Digital Light Processing

Abstract The 3D printing process enables to print objects having various functionalities at pre-designed locations in the object. Hereby, we report on the printing of superhydrophobic objects composed of patterns of micropillars. Superhydrophobicity is an important property of surfaces that has applications in various fields such as self-cleaning, drag reduction, increased buoyancy, and air conditioning. Most existing methods for the fabrication of superhydrophobic surfaces are complicated and time-consuming. Here, we performed a simple and cost-effective process for the fabrication of superhydrophobic (SH) objects by Digital Light Processing (DLP) 3D printing. To the best of our knowledge, this is the first study that has used DLP 3D printing to fabricate SH 3D objects without further coating process. We designed a novel ink, which contained non-fluorinated acrylates and Hydrophobic Fumed Silica (HFS). We studied the effects of HFS concentration and pillar-array design for imparting the SH property, which was measured in terms of the contact and rolling angle of water droplets on the surface. As proof of the concept of increased buoyancy by superhydrophobicity, we demonstrated the floatation of the printed SH objects in comparison to their non-SH counterparts even after forcefully submerging them into water.

Accuracy evaluation of 3D printed interim prosthesis fabrication using a CBCT scanning based digital model.

ObjectivesThis study aimed to evaluate the marginal and internal gaps in 3D-printed interim crowns made from digital models of cone-beam computed tomography (CBCT) conversion data.Materials and methodsSixteen polyvinylsiloxane impressions were taken from patients for single crown restorations and were scanned using CBCT. The scanning data were converted to positive Standard Triangulation Language (STL) files using custom-developed software. The fabricated stone models were scanned with an intraoral optical scanner (IOS) to compare the surface accuracy with the STL data obtained by CBCT. The converted STL files were utilized to fabricate interim crowns with a photopolymer using a digital light-processing 3D printer. The replica method was used to analyze the accuracy. The marginal and internal gaps in the replica specimen of each interim crown were measured with a digital microscope. The Friedman test and Mann-Whitney U test (Wilcoxon-signed rank test) were conducted to compare the measurements of the marginal and internal gaps with a 95% level of confidence.ResultsThe root-mean-square values of the CBCT and IOS ranged from 41.00 to 126.60 μm, and the mean was 60.12 μm. The mean values of the marginal, internal, and total gaps were 132.96 (±139.23) μm, 137.86 (±103.09) μm, and 135.68 (±120.30) μm, respectively. There were no statistically significant differences in the marginal or internal gaps between the mesiodistal and buccolingual surfaces, but the marginal area (132.96 μm) and occlusal area (255.88 μm) had significant mean differences.ConclusionThe marginal gap of the fabricated interim crowns based on CBCT STL data was within the acceptable range of clinical success. Through ongoing developments of high-resolution CBCT and the digital model conversion technique, CBCT might be an alternative method to acquire digital models for interim crown fabrication.

Anti-biofilm multi drug-loaded 3D printed hearing aids

Over 5% of the world's population has disabling hearing loss, which affects approximately one third of individuals over 65 years. Hearing aids are commonly used in this population group, but prolonged use of these devices may cause ear infections. We describe for the first time, the use of 3D printing to fabricate hearing aids loaded with two antibiotics, ciprofloxacin and fluocinolone acetonide. Digital light processing 3D printing was employed to manufacture hearing aids from two polymer resins, ENG hard and Flexible. The inclusion of the antibiotics did not affect the mechanical properties of the hearing aids. All multi-drug-loaded devices exhibited a hydrophilic surface, excellent blood compatibility and anti-biofilm activity against P. aeruginosa and S. aureus. Hearing aids loaded with ciprofloxacin (6% w/w) and fluocinolone acetonide (0.5% w/w) sustained drug release for more than two weeks and inhibited biofilm formation on the surface of the devices and bacteria growth in the surrounding medium. In summary, this work highlights the potential of vat photopolymerization 3D printing as a versatile manufacturing approach to fabricate high-fidelity patient-specific medical devices with anti-bacterial properties.

Comparison of flexural properties and cytotoxicity of interim materials printed from mono-LCD and DLP 3D printers

Statement of problemBecause few 3D-printing resins have been specifically developed for liquid crystal display (LCD) 3D printers, mono-LCD users may use digital light processing (DLP) 3D-printing resins. However, the suitability of these resins requires evaluation. PurposeThe purpose of this in vitro study was to evaluate whether 3D-printing resins designed for DLP 3D printers can be used successfully in a mono-LCD 3D printer. Material and methods3D printers based on photopolymerization and 3D-printing resin for interim restorations were used in this study. Enlighten AA temp and NextDent C&B MFH were printed from both the MiiCraft Ultra 125 and Phrozen Sonic printers, followed by postpolymerization by using the FormCure and PhrozenCure units for different times. The flexural strength and cytotoxicity of the specimens were evaluated. ResultsAfter postpolymerization treatment, the flexural strength of Enlighten AA temp and NextDent C&B MFH from both 3D printers was over the 50-MPa minimal requirement for the flexural strength of interim resins specified in the International Standards Organization (ISO) 10477 standard. With 15 minutes of FormCure and 1 minute of PhrozenCure postpolymerization, 4 material-printer combinations reached nearly 100% in cell viability. ConclusionsInterim resins designed for DLP 3D printers can be successfully used in mono-LCD 3D printers if the printed specimens are postpolymerized in a more powerful postpolymerization unit or in a less powerful postpolymerization unit for a longer time.

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.

Assessment of Compatibility between Various Intraoral Scanners and 3D Printers through an Accuracy Analysis of 3D Printed Models.

To assess the accuracy of various intraoral scanners (IOSs) and to investigate the existence of mutual compatibility that affects the accuracy between IOS and 3-dimensional (3D) printing using a scan quadrant model. For clinical implication, crown preparations and cavity design according to prosthetic diagnosis and treatment considerations must be acquired by a digital scanner. The selected typodont model was scanned using a reference scanner, from which reference (Ref) standard tessellation language (STL) data were created. Data obtained by scanning the typodont model with IOSs based on three different technologies were divided into three groups (CS3600, i500, and Trios3). Scanned data from the groups were divided into sub-groups of digital light processing (DLP), fused deposition modeling (FDM), and stereolithography apparatus (SLA), based on which 3D printed models (3DP) were fabricated. The 3DP dental models were scanned to obtain a total of 90 3DP STL datasets. The best-fit algorithm of 3D analysis software was used for teeth and arch measurements, while trueness was analyzed by calculating the average deviation among measured values based on superimposition of Ref and IOS and 3DP data. The differences between Ref and IOS (Ref-IOS), Ref and 3DP (Ref-IOS/3DP), and IOS and 3DP data (IOS-3DP) were compared and analyzed, while accuracy within each of the three main groups was assessed. For statistical analysis, the Kruskal–Wallis, Mann–Whitney U, and repeated measures ANOVA test were used (p < 0.05). The major finding is that the mutual relationships between IOSs and 3D printers vary depending on the combination. However, i500 intraoral scanner and DLP 3D printer was the combination that showed the best trueness value.

Recyclable thermosetting polymers for digital light processing 3D printing

3D printing of various polymers has attracted great attention and developed rapidly in recent years. Digital light processing (DLP) has recently emerged as a fast growing 3D printing technique due to its high resolution and high speed. However, the lack of printable high-performance materials limits its broad applications. In addition, with the increasing adoption of DLP 3D printing, the efficient recycling of printed thermosetting materials is highly desired. Herein, we proposed a two-stage curing approach involving dynamic reactions by using the acrylate-epoxy hybrid resin for the recyclable DLP 3D printing of high-performance thermosetting polymers. Bond exchange reactions (BERs) could establish covalent bonds between the acrylate network and the epoxy network, thus partially triggering the copolymerization. The resulting new polymers exhibited excellent mechanical properties. A small-molecule assisted BER method was then used to efficiently depolymerize the thermosetting printed parts into soluble oligomers, which were formulated with fresh photopolymers for the next round of printing. The reprinted samples still showed good mechanical properties comparable to the virgin ones. In addition, the new polymers demonstrated potential applications in 4D printing of smart actuators. This work opens a novel avenue for green manufacturing technologies.

3D-Printed Ceramic Bone Scaffolds with Variable Pore Architectures.

This study evaluated the mechanical properties and bone regeneration ability of 3D-printed pure hydroxyapatite (HA)/tricalcium phosphate (TCP) pure ceramic scaffolds with variable pore architectures. A digital light processing (DLP) 3D printer was used to construct block-type scaffolds containing only HA and TCP after the polymer binder was completely removed by heat treatment. The compressive strength and porosity of the blocks with various structures were measured; scaffolds with different pore sizes were implanted in rabbit calvarial models. The animals were observed for eight weeks, and six animals were euthanized in the fourth and eighth weeks. Then, the specimens were evaluated using radiological and histological analyses. Larger scaffold pore sizes resulted in enhanced bone formation after four weeks (p < 0.05). However, in the eighth week, a correlation between pore size and bone formation was not observed (p > 0.05). The findings showed that various pore architectures of HA/TCP scaffolds can be achieved using DLP 3D printing, which can be a valuable tool for optimizing bone-scaffold properties for specific clinical treatments. As the pore size only influenced bone regeneration in the initial stage, further studies are required for pore-size optimization to balance the initial bone regeneration and mechanical strength of the scaffold.