Stereolithography 3D Printing Research Articles

Additive Manufactured Waveguide for E-Band Using Ceramic Materials

Ceramic materials are chemical- and temperature-resistant and, therefore, enable novel application fields ranging from automotive to aerospace. With this in mind, this contribution focuses on developing an additive manufacturing approach for 3D-printed waveguides made of ceramic materials. In particular, a special design approach for ceramic waveguides, which introduces non-radiating slots into the waveguides sidewalls, and a customized metallization process, are presented. The developed process allows for using conventional stereolithographic desktop-grade 3D-printers. The proposed approach has, therefore, benefits such as low-cost fabrication, moderate handling effort and independence of the concrete waveguide geometry. The performance of a manufactured ceramic WR12 waveguide is compared to a commercial waveguide and a conventionally printed counterpart. For that reason, relevant properties, such as surface roughness and waveguide geometry, are characterized. Parsing the electrical measurements, the ceramic waveguide specimen features an attenuation coefficient of 30–60 dB/m within the E-Band. The measured attenuation coefficient is 200% and 300% higher compared to the epoxy resin and the commercial waveguide and is attributed to the increased surface roughness of the ceramic substrate.

Development of Dental Poly(methyl methacrylate)-Based Resin for Stereolithography Additive Manufacturing.

Poly(methyl methacrylate) (PMMA) is widely used in dental applications. However, PMMA specialized for stereolithography (SLA) additive manufacturing (3D-printing) has not been developed yet. This study aims to develop a novel PMMA-based resin for SLA 3D-printing by mixing methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDMA), and PMMA powder in various mixing ratios. The printability and the viscosity of the PMMA-based resins were examined to determine their suitability for 3D-printing. The mechanical properties (flexural strength and Vickers hardness), shear bond strength, degree of conversion, physicochemical properties (water sorption and solubility), and cytotoxicity for L929 cells of the resulting resins were compared with those of three commercial resins: one self-cured resin and two 3D-print resins. EGDMA and PMMA were found to be essential components for SLA 3D-printing. The viscosity increased with PMMA content, while the mechanical properties improved as EGDMA content increased. The shear bond strength tended to decrease as EGDMA increased. Based on these characteristics, the optimal composition was determined to be 30% PMMA, 56% EGDMA, 14% MMA with flexural strength (84.6 ± 7.1 MPa), Vickers hardness (21.6 ± 1.9), and shear bond strength (10.5 ± 1.8 MPa) which were comparable to or higher than those of commercial resins. The resin’s degree of conversion (71.5 ± 0.7%), water sorption (19.7 ± 0.6 μg/mm3), solubility (below detection limit), and cell viability (80.7 ± 6.2% at day 10) were all acceptable for use in an oral environment. The printable PMMA-based resin is a potential candidate material for dental applications.

Dual-Material 3D-Printed Intestinal Model Devices with Integrated Villi-like Scaffolds.

In vitro small intestinal models aim to mimic the in vivo intestinal function and structure, including the villi architecture of the native tissue. Accurate models in a scalable format are in great demand to advance, for example, the development of orally administered pharmaceutical products. Widely used planar intestinal cell monolayers for compound screening applications fail to recapitulate the three-dimensional (3D) microstructural characteristics of the intestinal villi arrays. This study employs stereolithographic 3D printing to manufacture biocompatible hydrogel-based scaffolds with villi-like micropillar arrays of tunable dimensions in poly(ethylene glycol) diacrylates (PEGDAs). The resulting 3D-printed microstructures are demonstrated to support a month-long culture and induce apicobasal polarization of Caco-2 epithelial cell layers along the villus axis, similar to the native intestinal microenvironment. Transport analysis requires confinement of compound transport to the epithelial cell layer within a compound diffusion-closed reservoir compartment. We meet this challenge by sequential printing of PEGDAs of different molecular weights into a monolithic device, where a diffusion-open villus-structured hydrogel bottom supports the cell culture and mass transport within the confines of a diffusion-closed solid wall. As a functional demonstrator of this scalable dual-material 3D micromanufacturing technology, we show that Caco-2 cells seeded in villi-wells form a tight epithelial barrier covering the villi-like micropillars and that compound-induced challenges to the barrier integrity can be monitored by standard high-throughput analysis tools (fluorescent tracer diffusion and transepithelial electrical resistance).

Projection-suspended stereolithography 3D printing for low-loss optical hydrogel fiber fabrication

Hydrogel fibers (HFs) have shown great potential for delivering light and sensing in vivo. However, HFs commonly suffer from high optical attenuation, which significantly affects their light-guiding efficiency and sensing performance. Here, we demonstrate a projection-suspended stereolithography (PSS) 3D printing method for fabricating low-loss HFs. Axially continuous and uniform HFs are produced via a light-curing area that floats on the precursor solution. Additionally, PSS improves the guiding efficiency of the HF by simultaneously regulating the fiber diameter, core–cladding structure, and refractive index. We obtained a loss of ≤0.15 dB/cm, which is better than that reported by previous studies. We also demonstrate that the fabricated HF provides light delivery and sensing capability in deep tissues, which will benefit the development of biomedicine and optogenetics. The PSS method heralds a novel fabrication for advanced waveguides.

3D quantum dot-lens fabricated by stereolithographic printing with in-situ UV curing for lighting and displays

3D polymer/quantum dots (QDs) nanocomposite QD-lens is fabricated by stereolithography (SLA) 3D printer with in-situ UV curing system. Various UV-curable polymer precursors are mixed with QDs to investigate their printability and optical performance. 2D QD-thin film and 3D QD-lens are printed and attached to a blue InGaN chip to form a light-emitting diode (LED) device. An air gap between the 3D QD-lens and the chip provides more uniform light emission at different angles and better heat dissipation. Compared with conventional QD-on-chip LED, the 3D QD-lens LED operated at 20 mA has ∼100% enhancement of half-lifetime (T 50 ) in a standard reliability test. The LED T 50 can be further improved 75% by coating the QD-lens with hydrophobic parylene as a gas barrier layer against water and oxygen. By mixing both green- (G-) and red- (R-) QDs in the 3D QD-lens, a white light-emitting 3D QD-lens LED is demonstrated to possess a color gamut of ∼130% NTSC standard.

Design, manufacture and characterization of compact filter assemblies for radiofrequency applications

This paper presents the use of additive manufacturing in the design and fabrication of a non-planar fully 3D-printed low-pass filter. The process implements stereolithographic 3D printing and copper electroplating to produce the necessary parts and their casing. The filter we produce acts as a demonstrator: we present the possibility of constructing building blocks and combining different elements into a full assembly for system integration. We introduce the “drop-and-screw” concept, which is implemented to mount the parts into a single connectorized assembly without the need for welding. The method we propose may be suitable for building other components by simply changing the building blocks. We pay special attention to the design of the constituent parts of the filter (a 3D conical inductor and a 3D capacitor), exploring new geometries to reduce the size of the final filter prototypes. The results demonstrate the potential of additive manufacturing in the construction of high-performance RF components and assemblies, and we present a modular prototype with a high degree of reconfigurability and multifunctionality.

Stereolithography-assisted fabrication of 3D printed polymeric film for topical berberine delivery: in-vitro, ex-vivo and in-vivo investigations.

3D printed polymeric film intended for topical delivery of berberine (BBR) was developed using stereolithography (SLA) to enhance its local concentrations. PEGDMA was utilized as photopolymerizing resin, with PEG 400 as an inert component to facilitate BBR solubilization and permeation. Three batches of topical films were printed by varying resin and PEG 400 compositions. In-vitro physicochemical characterizations of the 3D printed films were performed using several analytical techniques including ex-vivo drug permeation studies. In-vivo skin irritation studies were also conducted to assess the skin irritation potential. Films were 3D printed according to design specifications with minimal variations. Microscopic analysis confirmed 3D architecture, while thermal and X-ray diffraction studies revealed amorphous BBR entrapment. Drug permeation study showed effective ex-vivo diffusion up to 344.32 ± 61.20 µg/cm2 after 24.0 h possessing a higher ratio of PEG 400. In-vivo skin irritation studies have suggested the non-irritant nature of printed films. Results indicated the suitability of SLA 3D printing for topical application in the treatment of skin diseases. The presence of PEG 400 in the printed 3D films facilitated BBR diffusion, resulting in an improved flux in ex-vivo model and non-irritant properties in vivo.

Complex optical elements for scanning helium microscopy through 3D printing

Developing the next generation of scanning helium microscopes requires the fabrication of optical elements with complex internal geometries. We show that resin stereolithography (SLA) 3D printing produces low-cost components with the requisite convoluted structures whilst achieving the required vacuum properties, even without in situ baking. As a case study, a redesigned pinhole plate optical element of an existing scanning helium microscope was fabricated using SLA 3D printing. In comparison to the original machined component, the new optical element minimised the key sources of background signal, in particular multiple scattering and the secondary effusive beam.

Preparation of Mn–Zn ferrite ceramic using stereolithography 3D printing technology

In this work, tailored Mn–Zn ferrite ceramics are prepared by stereolithography (SLA) 3D printing technology, and its performances are measured utilizing the printing accuracy, magnetic properties, density, and microstructures. The major obstacle forming difficultly by single curing of self-made ferrite pastes with increasing solid content in the printing process is removed by using six scanning numbers. In addition, the prediction formulas of the linewidth and curing depth are established. The printing process parameters, namely scanning space, scanning speed, and laser power, are optimized at 2 μm, 2500 mm/s, and 240 mW, respectively. The size of convex platform bigger than 1 mm × 1.2 mm possessing circular and square holes with a diameter and a side length of 0.2 mm can be printed using the printing process parameters above. Specifically, the sintering temperature and holding time below 1200 °C and 90 min, respectively, are optimized conducive limits. The sintered parts show a density of 4.04 g/cm3 and a saturation magnetization of 58.6 emu/g, along with a small value of coercivity and remanence. The SLA-3D printing, debinding, and sintering technologies can print the complex shapes Mn–Zn ferrite ceramics using the proposed process.

Effects of Curing on Photosensitive Resins in SLA Additive Manufacturing

Different mechanical properties characterise the materials of 3D printed components, depending on the specific additive manufacturing (AM) process, its parameters, and the post-treatment adopted. Specifically, stereolithography (SLA) uses a photopolymerisation technique that creates solid components through selective solidification. In this study, 72 specimens were 3D printed using 12 commercial-grade methacrylate resins and tested under uniaxial tensile loads. The resin specimens were evaluated before and after curing. The recommended cure temperature and time were followed for all materials. The stress-strain curves measured during the testing campaign were evaluated in terms of maximum tensile strength, Young’s modulus, ductility, resilience, and toughness. The results reveal that the curing process increases the material stiffness and resistance to tensile loads. However, it was found that the curing process generally reduces the plasticity of the resins, causing a more or less marked brittle behaviour. This represents a potential limitation to the use of SLA 3D printing for structural elements which require some plasticity to avoid dangerous sudden failures.

A customizable 3D printed device for enzymatic removal of drugs in water

The infiltration of drugs into water is a key global issue, with pharmaceuticals being detected in all nearly aqueous systems at often alarming concentrations. Pharmaceutical contamination of environmental water supplies has been shown to negatively impact ecological equilibrium and pose a risk to human health. In this study, we design and develop a novel system for the removal of drugs from water, termed as Printzyme. The device, fabricated with stereolithography (SLA) 3D printing, immobilises laccase sourced from Trametes Versicolor within a poly(ethylene glycol) diacrylate hydrogel. We show that SLA printing is a sustainable method for enzyme entrapment under mild conditions, and measure the stability of the system when exposed to extremes of pH and temperature in comparison to free laccase. When tested for its drug removal capacity, the 3D printed device substantially degraded two dissolved drugs on the European water pollution watch list. When configured in the shape of a torus, the device effectively removed 95% of diclofenac and ethinylestradiol from aqueous solution within 24 and 2 h, respectively, more efficiently than free enzyme. Being customizable and reusable, these 3D printed devices could help to efficiently tackle the world's water pollution crisis, in a flexible, easily scalable, and cost-efficient manner.

Synthesis and Characterization of Fiber-Reinforced Resorcinol Epoxy Acrylate Applied to Stereolithography 3D Printing

As perceived, fiber-reinforced photocuring resins possess various distinctive advantages over traditional reinforced resin systems. This includes a rapid curing rate, energy efficiency, no volatile organic compounds, high strength, good thermal stability, and chemical resistance. Printing 3D composite objects using vat polymerization techniques has been a center of interest where photocuring resins are applied. In our present study, we have synthesized resorcinol-based diglycidyl ether, that is, a resorcinol-based epoxy resin, and further acrylated to the resorcinol epoxy acrylate oligomer. This oligomer was further formulated to photocuring resins using a suitable quantity of reactive diluents and photoinitiators. Now, three types of synthetic fibers, that is, glass fibers, nylon fibers, and polyester fibers, were incorporated in this formulated resin at different loading percentages. The oligomer synthesized was analyzed for structural conformation using Fourier transform infrared spectroscopy and 13C nuclear magnetic resonance. Further, we comparatively examined the rheological behavior of prepared formulations, and compatible formulations were applied to stereolithography 3D printers. Finally, physical, mechanical, thermal, transmittance, and morphological characteristics were comparatively analyzed for prepared UV-cured composites. The outcomes obtained during characterizations of UV-cured composites will be inevitably reflected in 3D-printed objects.

Ti3C2Tx MXene as a novel functional photo blocker for stereolithographic 3D printing of multifunctional gels via Continuous Liquid Interface Production

Stereolithographic 3D printing has been increasingly applied in the rapid fabrication of gels with specially-designed 3D structures. Herein, MXene (Ti 3 C 2 T x ) is reported for the first time as a versatile photo blocker for a photo-curable aqueous ink for a newly developed stereolithography technology (Continuous Liquid Interface Production, CLIP) to fabricate hydrogels with delicate geometries. As an effective photo blocker, the MXene nanosheets can significantly suppress the light scatting in the hydrogel precursor ink during CLIP printing, giving rise to printing quality. Subsequent solvent exchange with glycerin produces an organogel, which shows excellent adhesive properties towards various surfaces, making it a promising adhesive sensor to detect different body movements. Meanwhile, the CLIP-printed organogel demonstrates promise in atmospheric water harvesting taking advantage of the natural hygroscopicity of organogel and excellent light-to-heat conversion performance with MXene nanosheets. Furthermore, the CLIP-printed hollow organogel shows higher efficiency benefiting from larger surface area of hollow organogel. The results of this work strongly suggest that MXene can serve as an effective multifunctional additive for CLIP inks, which may open up new opportunities for the 3D printing of various advanced devices.

Mechanical response of shape-recovering metamaterial structures fabricated by additive manufacturing

Three different metamaterial structures were fabricated using stereolithography 3D printing and a shape recovering material. Mechanical properties and recovery efficiency were assessed after compression testing. All three structures exhibited similar initial specific compressive moduli, while the highest specific toughness was observed for the stretch-dominated structure. The three metamaterial structures were re-tested after shape recovery. Significant strengthening was observed for all structures, with the bend-stretch-dominated structure strengthening to the highest degree. This strengthening phenomenon was characterized as strain hardening. It was found that the strengthening is highly geometry dependent. The geometry with stretch-dominated behavior exhibited the highest mechanical properties after a second test was performed. Improvements in specific toughness of up to 67% were observed after the second compressive test.

Thermal and flow characteristics of liquid flow in a 3D-printed micro-reactor: A numerical and experimental study

• Stereo lithography was utilised to construct pin–fin photo-thermal micro-reactors. • 3D printing was successfully utilised to print micro-pin fins inside microchannels. • Thermal and fluid characteristics of constructed micro-reaactors were assessed. • Validated CFD model was used to evaluate velocity and pressure profiles. • Size of pin-fins in micro-reactor was optimised with response surface modelling. In this article, we report on a unique design and build technique based on stereolithographic 3D printing technology (SLA) for constructing ultraviolet cured resin-made micro-reactors. The main objective of this study is gaining insight into the thermal performance of micro-reactors for optofluidic applications. Several micro-reactors equipped with pin fins were manufactured. A high-fidelity test-rig was developed and used to collect data from water flowing in the micro-reactors as they are exposed to various heat flux loading. The measured data was also used for validating the numerical (CFD) models. The CFD models provided in-depth spatial data on the pressure and temperature profiles in the microchannel, which could not be easily measured. The results showed that conventional empirical correlations failed to accurately predict the pressure drop of the system in the microfluidics regime (Re < 190), although are reasonably accurate in the conventional fluid regime (Re > 190). For both regimes, however, CFD results were sufficiently accurate in predicting the temperature and pressure differences across the micro-reactor. It was also identified that pin fins arrangements offer a great design benefit in enhancing heat transfer coefficient in micro-reactors, achieving values up to ∼2300 W/m 2 .K compared to a plain micro-reactor at ∼1875 W/m 2 .K (or 300 W/m 2 .K for conventional combustion systems). A multi-objective optimisation on the geometrical specifications of various pin fins showed that the micro-reactor with pin fins of 250 µm in diameter and 100 µm in height, yielded the best thermo-hydraulic performance of highest thermal transfer coefficient (2100 W/m 2 .K) and the lowest pressure- drop (∼0.1 kPa) across a wide range of heat flux loadings. The outcome of this study has created a significant knowledge and understanding of the flow behaviour in polymer-based micro-channels. It also established a methodology for designing and optimising the thermal–hydraulic performance of optofluidic micro-reactors, with potential loading of nano-photocatalyst mediated in pin fins sites. New correlations for predicting the pressure drop and temperature difference across polymer-based micro-reactors are also developed.

Tailoring of functionally graded hyperelastic materials via grayscale mask stereolithography 3D printing

Photopolymerization-based additive manufacturing methods like stereolithography and digital light processing only allow typically the monolithic fabrication of structures made from a single material. To overcome this limitation, grayscale digital light processing has been proposed for 3D printing of functionally graded materials. Here, this concept is extended to grayscale masked stereolithography (MSLA) printing using a LED light source and a LCD photomask to control the degree of photopolymerization of a UV-curable resin by varying grayscale pixels and thus light intensities. In this scale, tailorable hyperelastic material properties and functionally graded structures for finite deformations are realized. In this paper, the dependency of the resulting material properties on the parameters of the grayscale MSLA process is investigated and a grayscale-dependent hyperelastic material model is formulated. This parametric hyperelastic material model is fitted to the experiments and validated against experimental results for uniaxial tension and uniaxial compression tests. Then, functionally graded structures with tailored mechanical properties at finite deformations are designed and fabricated using grayscale MSLA printing. The hyperelastic material model is validated with experimental results for different geometries, showing good agreement between experimental tests and numerical calculations.

Effect of print orientation on the dimensional accuracy of orthodontic aligners printed 3-dimensionally

Fabrication of orthodontic aligners directly via 3-dimensional (3D) printing presents the potential to increase the efficiency of aligner production relative to traditional workflows; however tunable aspects of the 3D-printing process might affect the dimensional fidelity of the fabricated appliances. This study aimed to investigate the effect of print orientation on the dimensional accuracy of orthodontic aligners printed directly with a 3D printer. A digitally designed aligner of 500μm thickness was printed in 3D in Grey V4 (Formlabs, Somerville, Mass) resin at 8 angulations at 45° intervals (n=10 per angulation) using a stereolithography 3D printer. Each aligner was scanned with an optical scanner, and all but the intaglio surface of each scan was digitally removed. Each resultant scan file was superimposed onto the isolated intaglio of the designed master aligner file. The dimensional deviation was quantified with Geomagic Control software (3D Systems, Rock Hill, SC), and data were analyzed using R statistical software (version 2018; R Core Team, Vienna, Austria) (P<0.05). Print angle showed a statistically significant effect on standard deviation, average positive deviation, absolute average negative deviation, and percentage of points out of bounds (tolerance bounds defined as ±250μm)(P<0.05). Qualitative analysis of the 3D surface deviation maps indicated that the 0° and 90° groups showed less deviation and appeared to be the most accurate in the anterior regions. Overall, the majority of the print angle groups studied were not printed within clinically acceptable tolerance ranges, with the major exception being the 90° group, which printed nominally within clinically acceptable tolerance ranges. With the workflow applied, print orientation significantly affects the dimensional accuracy of directly 3D-printed orthodontic aligners. Within the limitations of this study, printing at the 90° angulation would be advised as it is the group with the most accurate prints relative to the 7 other orientations investigated, although not all differences were statistically significant.

Fused silica ceramic core based on network-structured zircon design via 3D printing

A ceramic core of network-structured ZrSiO4 surrounding large particles of fused quartz was designed. Experimental results show that the ceramic core prepared by digital light processing (DLP)-3D printing technology, nano-sized ZrO2 reacting with large SiO2 particles to generate network-structure ZrSiO4 in the process of re-sintering. The network structure significantly improves the bending strength of the core while maintaining a high porosity. The stable Al2O3 in the core improved the high-temperature strength of the ceramic core. This is the first study on designing the microstructure of ceramic cores using stereolithography 3D printing technology. The study provides a new idea on the additive manufacturing of ceramic cores.

Rapid digital light 3D printing enabled by a soft and deformable hydrogel separation interface

The low productivity of typical 3D printing is a major hurdle for its utilization in large-scale manufacturing. Innovative techniques have been developed to break the limitation of printing speed, however, sophisticated facilities or costly consumables are required, which still substantially restricts the economic efficiency. Here we report that a common stereolithographic 3D printing facility can achieve a very high printing speed (400 mm/h) using a green and inexpensive hydrogel as a separation interface against the cured part. In sharp contrast to other techniques, the unique separation mechanism relies on the large recoverable deformation along the thickness direction of the hydrogel interface during the layer-wise printing. The hydrogel needs to be extraordinarily soft and unusually thick to remarkably reduce the adhesion force which is a key factor for achieving rapid 3D printing. This technique shows excellent printing stability even for fabricating large continuous solid structures, which is extremely challenging for other rapid 3D printing techniques. The printing process is highly robust for fabricating diversified materials with various functions. With the advantages mentioned above, the presented technique is believed to make a large impact on large-scale manufacturing.

3D Printed Integrated Multi-Layer Microfluidic Chips for Ultra-High Volumetric Throughput Nanoliposome Preparation.

Although microfluidic approaches for liposomes preparation have been developed, fabricating microfluidic devices remains expensive and time-consuming. Also, owing to the traditional layout of microchannels, the volumetric throughput of microfluidics has been greatly limited. Herein an ultra-high volumetric throughput nanoliposome preparation method using 3D printed microfluidic chips is presented. A high-resolution projection micro stereolithography (PμSL) 3D printer is applied to produce microfluidic chips with critical dimensions of 400 µm. The microchannels of the microfluidic chip adopt a three-layer layout, achieving the total flow rate (TFR) up to 474 ml min−1, which is remarkably higher than those in the reported literature. The liposome size can be as small as 80 nm. The state of flows in microchannels and the effect of turbulence on liposome formation are explored. The experimental results demonstrate that the 3D printed integrated microfluidic chip enables ultra-high volumetric throughput nanoliposome preparation and can control size efficiently, which has great potential in targeting drug delivery systems.