Photopolymerization 3D Printing Research Articles

Unnatural hearing—3D printing functional polymers as a path to bio-inspired microphone design

In nature, auditory organs are rarely passive transducers of their environment. Highly localized material properties and complex interdependencies mechanically filter the acoustic signal, reducing the burden of signal processing to the nervous system. Capturing these design traits in engineered systems is important for device miniaturization and energy efficiency, but manufacturing a functional electromechanical device, like a microphone, at the microscale using biologically inspired 3D designs and highly anisotropic materials remains extremely challenging. Our research uses one-pot synthesis methods for a variety of tissue-like hydrogels, polymers, and functionalized piezoelectric composites that are compatible with vat-based photopolymerization 3D printing. These materials can be used to produce reproductions of microphone designs using functional photopolymers for the conductive, piezoelectric, elastomeric, and structural elements. Used to produce mimetic structures, for example, in a device based on the directional sensitivity of the parasitoid fly Ormia ochracea, we can reproduce O. ochracea’s sound localization capability while addressing the impracticalities in frequency, sensitivity and scale of MEMS or micromachined designs. Each of the materials used has a unique set of acoustic, electrical and mechanical properties which can be tailored by altering the synthesis process leading to a truly vast design space which we are only beginning to explore.

Acute and Chronic Toxicity of Uncured Resin Feedstocks for Vat Photopolymerization 3D Printing to a Cladoceran (Ceriodaphnia Dubia).

The accessibility and popularity of additive manufacturing (AM) has increased over the past decade. Environmental hazard assessment and safety data sheets for 3D printer feedstocks has lagged technology development. Vat photopolymerization may have unique risks relative to other AM technologies due to mishandling of uncured monomers/oligomer feedstocks and its decreasing cost enabling uninformed residential use. The acute and chronic toxicity of six uncured resins to Ceriodaphnia dubia was explored. Two-day acute toxicity (LC50) ranged from 2.6 to 33mg/L and inhibition concentrations (IC25) values for reproduction ranged from 0.33 to 16mg/L. Cleaning and waste management procedures recommended in user guides could be the most hazardous handling scenario as use of isopropyl alcohol increases miscibility and thus the fate, transport and bioavailability of the uncured resins. Residential users may often be poorly informed about potential toxicity and the need for a plan for use, handling, and waste management of uncured resins.

Multi-thermo responsive double network composite hydrogel for 3D printing medical hydrogel mask

3D printing of multifunctional hydrogels offers great opportunities for developing innovative biomedical technologies as it can provide custom-designed shapes and structures conformal to arbitrary contours. There have been significant improvements of the 3D printing techniques, but the available printable hydrogel materials limit the progress. Here, we investigated the use of a poloxamer diacrylate (Pluronic P123) to augment the thermo-responsive network composed of poly(N-isopropylacrylamide) and develop a multi-thermoresponsive hydrogel for photopolymerization 3D printing. The hydrogel precursor resin was synthesised to be printable with high-fidelity of fine structures and once cured can form a robust thermo-responsive hydrogel. By utilizing N-isopropyl acrylamide monomer and a Pluronic P123 diacrylate crosslinker as 2 separate thermo-responsive components it was found that the final hydrogel displayed 2 distinct lower critical solution temperature (LCST) switches. This enables the loading of hydrophilic drugs at fridge temperature and improving the strength of the hydrogel at room temperature while still maintaining a drug release at body temperature. The thermo-responsive material properties of this multifunctional hydrogel material system were investigated, showing a significant promise as a medical hydrogel mask. Furthermore, it is demonstrated that it can be printed in sizes large enough to fit and adhere to a human face at 1:1 scale with high dimensional accuracy, as well as its ability to load with hydrophilic drugs.

Vat 3D Printing of Bioderivable Photoresins – Toward Sustainable and Robust Thermoplastic Parts

Vat photopolymerization 3D printing (3DP) of thermoplastic materials is exceedingly difficult due to the typical reliance on cross-linking to form well-defined, solid objects on timescales relevant to 3DP. Additionally, photoresin build materials overwhelmingly rely upon nonrenewable feedstocks. To address these challenges, we report the vat 3DP of bioderivable photoresins that produced thermoplastic parts with highly tunable thermal and mechanical properties. The photoresins were formulated from two monomers that are easily obtainable from lignin deconstruction: 4-propylguaiacyl acrylate (4-pGA) and syringyl methacrylate (SMA). These bioderivable materials generated printed parts that ranged from soft elastomers to rigid plastics. For example, for 4-pGA-based materials, the breaking stresses varied from 0.20 to 20 MPa and breaking strains could be tuned from 4.7% up to 1700%, whereas 3D-printed SMA-based materials resulted in higher breaking stresses (∼30 MPa) and Tgs (∼132 °C). Notably, parts printed from these bioderivable formulations exhibited thermoplastic behavior and were largely soluble in common organic solvents─expanding the application and repurposing of the 3D-printed parts. We highlight this feature by reusing a 3DP part via solvent casting. Overall, the tunable properties and thermoplastic behavior of the lignin-derivable photoresins showcase renewable lignin resources as promising biofeedstocks for sustainable 3DP.

Simple modification to allow high-efficiency and high-resolution multi-material 3D-printing fabrication of microfluidic devices.

Advances in the instrumentation and materials for photopolymerization 3D printing aided the use of this powerful technique in the fabrication of microfluidic devices. The costs of printers and supplies have been reduced to the point where this technique becomes attractive for prototyping microfluidic systems with good resolution. With all the development of multi-material 3D printers, most of the microfluidic devices prepared by photopolymerization 3D printing are based on a single substrate material. We developed a digital light processing multi-material 3D printer where two or more resins can be used to prepare complex objects and functional microfluidic devices. The printer is based on a vat inclination system and embedded peristaltic pumps that allow the injection and removal of resins and cleaning step between material changes. Although we have built the whole system, the modification can be incorporated into commercially available printers. Using a high-resolution projector, microfluidic channels as narrow as 43 μm were obtained. We demonstrate the printing of multi-material objects containing flexible, rigid, water-soluble, fluorescent, phosphorescent, and conductive (containing PEDOT or copper nanoparticles) resins. An example of a microfluidic chip containing electrodes for electrochemical detection is also presented.

Manufacturing of ceramic cores: From hot injection to 3D printing

With the improvement of aero-engine performance, the preparation of hollow blades of single-crystal superalloys with complex inner cavity cooling structures is becoming increasingly urgent. The ceramic core is the key intermediate part of the preparation and has attracted wide attention. To meet this challenge, new technologies that can make up for the defects of long periods and high costs of fabricating complex structural cores by traditional hot injection technology are needed. Vat photopolymerization 3D printing ceramic technology has been applied to the core field to realize the rapid preparation of complex structural cores. However, the industrial application of this technology still needs further research and improvement. Herein, ceramic cores were prepared using traditional hot injection and vat photopolymerization 3D printing techniques using fused silica, nano-ZrO2, and Al2O3 powders as starting materials. The 3D printed ceramic core has a typical layered structure with a small pore size and low porosity. Because of the layered structure, the pore area is larger than that of the hot injection ceramic core, the leaching performance has little effect (0.0277 g/min for 3D printing cores, 0.298 g/min for hot injection cores). In the X and Y directions, the sintering shrinkage is low (2.7%), but in the Z direction, the shrinkage is large (4.7%). The fracture occurs when the inner layer crack expands and connects with the interlayer crack, forming a stepped fracture in the 3D-printed cores. The bending strength of the 3D printed core at high temperature (1500 °C) is 17.3 MPa. These analyses show that the performance of vat photopolymerization 3D-printed ceramic cores can meet the casting requirements of single crystal superalloy blades, which is a potential technology for the preparation of complex structure ceramic cores. The research mode of 3D printing core technology based on the traditional hot injection process provides an effective new idea for promoting the industrial application of 3D printing core technology.

Vat Photopolymerization 3D-Printing of Dynamic Thiol-Acrylate Photopolymers Using Bio-Derived Building Blocks.

As an energy-efficient additive manufacturing process, vat photopolymerization 3D-printing has become a convenient technology to fabricate functional devices with high resolution and freedom in design. However, due to their permanently crosslinked network structure, photopolymers are not easily reprocessed or repaired. To improve the environmental footprint of 3D-printed objects, herein, we combine the dynamic nature of hydroxyl ester links, undergoing a catalyzed transesterification at elevated temperature, with an acrylate monomer derived from renewable resources. As a sustainable building block, we synthesized an acrylated linseed oil and mixed it with selected thiol crosslinkers. By careful selection of the transesterification catalyst, we obtained dynamic thiol-acrylate resins with a high cure rate and decent storage stability, which enabled the digital light processing (DLP) 3D-printing of objects with a structure size of 550 µm. Owing to their dynamic covalent bonds, the thiol-acrylate networks were able to relax 63% of their initial stress within 22 min at 180 °C and showed enhanced toughness after thermal annealing. We exploited the thermo-activated reflow of the dynamic networks to heal and re-shape the 3D-printed objects. The dynamic thiol-acrylate photopolymers also demonstrated promising healing, shape memory, and re-shaping properties, thus offering great potential for various industrial fields such as soft robotics and electronics.

Ceramic composites toughened by vat photopolymerization 3D printing technology

High strength and high toughness are mutually exclusive in structural materials. In ceramic materials, increasing toughness usually depends on the introduction of a ductile phase that reduces the strength and high-temperature stability of the material. In this work, vat photopolymerization 3D printing technology was used to achieve toughening of ceramic composite material. The friction sliding of the 3D-printed ceramic macrolayer structure results in effective energy dissipation and redistribution of strain in the whole structure, and macroscale toughening of the ceramic material is realized. In addition, the bridging and elongation of the crack in situ amorphous ceramic whiskers were significant microscopic toughening results, coupled with the toughening of the crack tip of nano-ZrO2. Multiscale collaborative toughening methods based on 3D-printed ceramics should find wide applications for materials in service at extreme high temperatures.

Vat photopolymerization 3D printing of thermal insulating mullite fiber-based porous ceramics

To satisfy the eagerness for mullite fiber-based porous ceramics (Mu f -based porous ceramics) with complex geometries in high-temperature thermal insulation fields, vat photopolymerization three-dimensional (3D) printing was first employed to prepare the highly complex Mu f -based porous ceramics. Herein, a photosensitive hydroxysiloxane HPMS-KH570 was employed as the resin matrix, which not only prevented the fiber agglomeration and improved the rheological properties of the slurries but also acted as a high-temperature binder to fix the fiber cross points after sintering and consequently improved the structural stability of the 3D-Mu f -based porous ceramics. The effects of mullite fiber (Mu f ) aspect ratio and content on the performance of Mu f slurries, microstructure and physical properties of the 3D-Mu f -based porous ceramics were investigated. When the fiber aspect ratio was 45 and the fiber content was 6.67 vol%, the Mu f slurry exhibited the most suitable properties for vat photopolymerization 3D printing, and the corresponding 3D-Mu f -based porous ceramics exhibited a well-defined 3D printed lattice structure with struts consisting of randomly crisscrossing Mu f . This unique 3D skeleton structure endowed the 3D-Mu f -based porous ceramics with low density (0.47 g/cm 3 ) and low room temperature thermal conductivity (0.11 W/(m·K)), enabling it a promising candidate for high-temperature (1000-1400 ℃) insulation materials. Furthermore, this printing strategy provided references for vat photopolymerization 3D printing of other fiber-based materials. • A strategy for DLP printing of 3D-Mu f -based porous ceramics was first presented. • The addition of HPMS-KH570 can prevent fiber agglomeration. • HPMS-KH570 can transform into SiO 2 binders and fix the fiber cross points. • 3D-Mu f -based porous ceramics exhibited an excellent thermal insulation property. • This work provides references for the DLP printing of other fiber-based materials.

Electrically assisted continuous vat photopolymerization 3D printing for fabricating high-performance ordered graphene/polymer composites

Ordered graphene/polymer composites have gained significant research interest due to their electrical conductivity, mechanical strength, and thermal stability. However, great challenges remain in achieving high-efficiency vat photopolymerization 3D printing of high-performance ordered graphene/polymer composites due to the low printing speed and the decreased ductility caused by the polymerization difficulty from the light-absorbing and shadowing of graphene nanoplatelets. Here, an electrically assisted continuous vat photopolymerization 3D printing technology using a dual-cure polymer (photo/thermal) is proposed for fabricating the high-performance ordered graphene/polymer composites. Firstly, process parameters (graphene content, printing speed, and light intensity) in the 3D printing were optimized and investigated on the composites with various graphene contents. Then, the relationship of the graphene nanoplatelets arrangement and the intensity of the electric field was established. Subsequently, multiple mechanical properties of ordered composites resulted from various graphene amounts were systematically investigated. Our results demonstrated that compared to the pure polymer, the ordered 2 wt% graphene/polymer composite has a 101% higher tensile strength (89 MPa), 200% higher total elongation (27.69%), 126% higher flexural strength (139.9 MPa and 20.6%), and 98% higher fracture strain. Besides, the electrical conductivity of the polymer composite with ordered graphene structure was 15 times higher than that of the random polymer composite. Thus, the proposed electrically assisted continuous vat photopolymerization 3D printing with photo/thermal dual-curing polymer matrix not only successfully realizes the continuous fabrication of ordered graphene/polymer composites, but also improves mechanical properties (both strength and ductility) and electrical conductivity.

3D-printed electrically conductive silicon carbide

The development of electrically conductive ceramics could achieve robust mechanical strength as well as practically high conductivity, offering applications in structural electrodes, conductors, catalyst supports, etc. However, its operating temperature is limited due to the intrinsic dense structures inevitably hindering the thermal management capability, thus resulting in a temperature-dependent electrical behavior in high-temperature environments. We report an additive manufacturing protocol through vat photopolymerization 3D printing to fabricate the architectured conductive silicon carbide (SiC) ceramics that simultaneously possess high electrical conductivity as well as low thermal conductivity, and demonstrate electric reliability under high-temperature environments above 600°C. The percolation of graphene into the ceramic scaffold establishes a uniform conductive network, exhibiting its electrical conductivity up to 1000 S m−1. The bulk density of the 3D-printed ceramic is measured from 0.366 g cm−3 to 0.897 g cm−3, with thermal conductivity ranging from 62 mW m−1 K−1 to 88 mW m−1 K−1. Furthermore, the mechanical performance of conductive ceramic can be effectively reinforced by densifying the microstructures via spark plasma sintering treatment. The proposed additive manufacturing strategy widens the potential of ceramics as a structural and functional material, offering a promising pathway toward high-temperature electronics applications.

A review on Vat Photopolymerization 3D-printing processes for dental application.

To give a critical and realistic state-of-the-art overview of research conducted in the field of Vat Photopolymerization for use in the dental field, with recommendations for further research. The search of articles published for the period 2005-2022 was performed using Scopus and PubMed databases using keywords. Apart from that, a search for patents in the Patentscope database for the period 2000-2021 was also conducted. Based on the found articles, insight on the publication's activity and discussion of some possible areas of future examination, on the mechanical properties of 3D-printed resin-based dental parts, their biocompatibility, antimicrobial properties, accuracy, and surface properties are presented. After reviewing all relevant articles, it was found that there is a need for more research in order to elevate this field to the next level. Vat Photopolymerization technologies are evidently more or less incorporated into everyday dental practice. In the future, a complete transition to digital workflow is expected. To enable this, it is necessary to examine in detail the materials used in this field, in order not only to ensure patient safety, but also to reduce the cost of dental services. However, not many studies have been published in the searched databases, and more research is needed, the results of which can be compared with previously conducted studies.

3D printing and in situ transformation of SiCnw/SiC structures

Successful preparation of photopolymerizable ceramic slurries using non-oxide ceramics and their 3D printing is highly challenging as the ceramic powders often possess high UV-light absorbance. Even though pre-oxidation of the powders could improve the slurry printability, the residual oxygen element in the material would eventually deteriorate the material purity and performance. In this study, a separated redox route (pre-oxidation, 3D printing and carbothermal reduction) was proposed to overcome these challenges. SiC ceramic powder was pre-oxidized into SiC@SiO 2 core-shell form to lower the UV-light absorbance. It was found that the ultraviolet (UV) light absorbance value of SiC powder at 405 nm decreased 20% from 0.357 to 0.284 after pre-oxidation process. The UV-light penetration depth of SiC@SiO 2 ceramic slurries at 40 ~ 55 vol% solid loading ranging from 14.81 to 12.82 µm, which surpassed two times that for 40 vol% raw SiC ceramic slurry. Different-shaped structures of SiC@SiO 2 /resin green ceramic bodies were successfully fabricated by vat photopolymerization 3D printing. The oxygen element resided was then eliminated by carbothermal reduction to avoid detriment of SiO 2 to the mechanical performance of the SiC ceramics. Phenolic epoxy acrylate resin with 14 wt% pyrolytic carbon (PyC) yield was chosen as the carbon source and thus the SiC@SiO 2 /resin green body pyrolyzed into SiC@SiO 2 /PyC ceramics after 1200 °C. It was found that after the heating temperature was further raised to 1600 °C, most of the pre-introduced SiO 2 shells on the surface of SiC particles were in situ transformed into SiC nanowires through carbothermal reduction reaction between SiO 2 and PyC, and the content of oxygen element in the ceramic matrix sharply dropped from 20.21% to 2.08%. The results demonstrated that through the proposed redox route, the photopolymerization-related issues including high UV-light absorbance and pre-oxidation-induced impurity for 3D printing of SiC ceramic slurries can be tackled. Finally, high purity porous SiC nw /SiC ceramic components with different structures were produced. This study provides a promising route for the preparation and 3D printing of photopolymerization ceramic slurries using non-oxide ceramics possessing high UV-light absorbance. • UV-light absorbance of SiC powder at 405 nm decreased 20% after pre-oxidation. • UV-light penetration depth of SiC@SiO 2 slurries (40 ~ 55 vol%) surpassed two times that for 40 vol% raw SiC slurry. • Pre-introduced SiO 2 shells on SiC particles in situ transformed into SiC nanowires through carbothermal reduction. • SiC nw /SiC components with complex structures successfully fabricated by photopolymerization 3D printing.

Effect of different sintering additives type on Vat photopolymerization 3D printing of Al2O3 ceramics

The mechanical properties of 3D printed alumina ceramics are degraded due to the micro anisotropy, interlayer interface defects and microporous characteristics. In order to improve its mechanical properties, solid phase sintered, liquid phase sintered and solid-liquid phase sintered alumina (Al2O3) ceramics were prepared by Vat photopolymerization 3D printing technology, respectively. In the experiment, Al2O3 was used as the main material to study the effects of TiO2 solid phase additive, MgO-SiO2 liquid phase additives and TiO2-MgO-SiO2 solid-liquid phase additives on Al2O3 ceramics sintering behavior and mechanical properties, so as to improve the sintering density and mechanical properties of alumina ceramics. The best composition ratio and sintering temperature were determined by shrinkage, relative density, Raman, XRD and SEM characterization. Under optimal sintering conditions, The comprehensive properties of Al2O3 ceramics prepared by liquid phase sintering are more balanced. And has excellent mechanical properties. The flexural strength reached 317 ± 34 MPa and the Vickers hardness up to 1250 ± 102 HV30. Thus, nine types of truss structures are prepared to study their mechanical properties. By changing the structure types, the order of compressive strength is FCC > BCC > DLS. By changing the number of units, the order of compressive strength is 3 × 3 × 3 units >2 × 2 × 2 units >1 × 1 × 1 units. The Al2O3 ceramics prepared by the liquid phase sintering exhibit excellent mechanical compression properties and energy absorption capacity. The FCC structure of 3 × 3 × 3 units can reach 23.2 ± 1.7 MPa compressive strength.

Spatially controlling the mechanical properties of 3D printed objects by dual-wavelength vat photopolymerization

To date, the 3D printing of polymers with heterogeneous and locally controlled material properties is still a challenging area in additive manufacturing. In terms of vat photopolymerization 3D printing, the fabrication of multi-material objects typically relies on an automatic material exchange of different resin vats. However, along with the high complexity of the printing equipment, this technique suffers from a low build speed and often yields 3D printed objects with week interlayer adhesion across the various material interfaces. Herein, we use chemo-selective wavelengths to fabricate objects with multi-material properties by dual-wavelength vat photopolymerization 3D printing employing a single vat. The photopolymers’ stiffness and flexibility are conveniently controlled by two photoreactions working at two different wavelengths. In particular, a dual photocurable resin is applied containing multi-functional acrylates, which are cured by a radical induced chain growth reaction at 405 nm, and bi-functional epoxy monomers, which additionally undergo cationic curing upon UV exposure (365 nm). FT-IR experiments confirm the wavelength selective network formation whilst dynamic mechanical analysis and tensile tests give evidence of the distinctive difference of the related mechanical properties. By being able to produce soft (ε = 24%, σ = 1.0 MPa) and stiff (ε = 4%, σ = 39.1 MPa) networks with a single resin vat, we demonstrate the efficient fabrication of 3D structures with locally controlled mechanical properties using a dual-wavelength 3D printer operating at 405 and 365 nm. In contrast to previous work in this field, we were able to significantly expand the range of mechanical properties by appropriate selection of the acrylic components and to drastically accelerate the build speed by changing the cationic photoinitiator and using a customized printer with high intensity LED sources.

3D printing of gadolinium oxide structure neutron absorber

The exceptional proprieties of gadolinium oxide (Gd2O3) enable wide applications as sensitized fluorescent material, optical additive, and especially neutron absorber material for nuclear industry or nuclear medicine. Herein, to address the challenge of manufacturing custom-designed Gd2O3 structures, we propose a new approach to fabricating the Gd2O3 structure by vat photopolymerization 3D printing. The preparation of printing feedstock, photo-curing parameters and post-processing were investigated thoughtfully. It was found that the printing feedstock was a typical non-Newtonian fluid. The optimal machine light intensity and exposure time were 6 (∼977 μW/cm2) and 3 s, respectively. After being sintered at 1600 °C for 2 h, the resulting sample reached a density of 58%, a bending stress of 40 MPa, and a flexural elastic modulus of and 20.219 GPa. The successful manufacturing of pure Gd2O3 was further evidenced by the SEM results and XRD pattern. The phase transition of Gd2O3 from cubic to monoclinic occurred around 1400 °C, leading to significant densification. Finally, a green mesh structure with a length of 10 cm was prepared, demonstrating the practical application potential in the neutron absorption and shielding.

3D Printing of Soft Magnetoactive Devices with Thiol‐Click Photopolymer Composites

Magnetoresponsive polymers have gained increased attention in the design of soft actuators as they can be spatially as well as temporally activated and enable an external noninvasive control of movement. By introducing the magnetoresponsive properties in photocurable resins, one can fabricate personalized and complex structures (via vat photopolymerization 3D printing), whose movement can be conveniently controlled by an external magnetic field. Advancing from acrylate‐based photopolymers, which often suffer from shrinkage stress, low monomer conversion, and oxygen inhibition, the fabrication of magnetoresponsive thiol‐click photopolymers containing Fe3O4 nanoparticles as magnetic fillers is highlighted. The addition of the thiol crosslinker yields soft and flexible polymer composites, whose cure kinetics, viscosity, thermal, and mechanical properties are studied as a function of the thiol and filler content. Although cure rate and final monomer conversion decrease with rising filler concentration, the cure kinetics is reasonably fast at 6 wt%. The short pot life, a result of thiol‐Michael reactions induced by Fe3O4 nanoparticles, and a high thiol content, are overcome by the addition of an appropriate stabilizer. As proof of concept, 3D structures are fabricated by digital light processing (DLP) 3D printing and their magnetically driven movement is demonstrated.

Microstructure and mechanical properties of 3D-printed nano-silica reinforced alumina cores

Ceramic cores are an important component in the preparation of hollow turbine blades for aero-engines. Compared with traditional hot injection technology, 3D printing technology overcomes the disadvantages of a long production cycle and the difficulty in producing highly complex ceramic cores. The ceramic cores of hollow turbine blades require a high bending strength at high temperatures, and nano-mineralizers greatly improve their strength. In this study, nano-silica-reinforced alumina-based ceramic cores were prepared, and the effects of nanopowder content on the microstructure and properties of the ceramic cores were investigated. Alumina-based ceramic cores contained with nano-silica were prepared using the vat photopolymerization 3D printing technique and sintered at 1500 °C. The results showed that the linear shrinkage of ceramic cores first increased and then decreased as the nano-silica powder content increased, and the bending strength showed the same trend. The fracture mode changed from intergranular to transgranular. The open porosity and bulk density fluctuated slightly. The weight loss rate was approximately 20%. When the nano-silica content was 3%, the bending strength reached a maximum of 46.2 MPa and 26.1 MPa at 25 °C and 1500 °C, respectively. The precipitation of the glass phase, change in the fracture mode of the material, pinning crack of nanoparticles, and reduction of fracture energy due to the interlocking of cracks, were the main reasons for material strengthening. The successful preparation of 3D printed nano-silica reinforced alumina-based ceramic cores is expected to promote the preparation of high-performance ceramic cores with complex structures of hollow turbine blades.

Enhanced 3D printed Al2O3 core via in-situ mullite

The ceramic core plays an important role in the preparation of aero-engine hollow blades, as it can directly determine the precision and pass rate of the cooling passage in the blade cavity. Sufficient high-temperature bending strength, high open porosity, and low sintering shrinkage are the main requirements for qualified ceramic cores. In order to prepare qualified ceramic cores with complex structures, in-situ mullite-reinforced Al 2 O 3 -based ceramic cores were successfully prepared using vat photopolymerization 3D printing technology. The in-situ synthesis of mullite was designed through thermodynamic analysis. The influence mechanisms of the sintering temperature and doping amount of fused silica on the open porosity, sintering shrinkage, and bending strength of the core were systematically investigated. With an increase in the sintering temperature and doping amount of fused silica, the porosity of the in situ mullite-reinforced ceramic core decreased. Sintering shrinkage increased with an increase in the sintering temperature and doping amount of fused silica. The cores containing 20 wt% fused silica showed the smallest sintering shrinkage. The bending strength increased with an increase in the sintering temperature and the doping amount of fused silica. A core doped with 20 wt% fused silica had the highest bending strength at 1773.15 K. Furthermore, 20 wt% fused silica doping, sintered at 1673.15 K, can be used to prepare in-situ mullite enhanced Al 2 O 3 -based cores with the best comprehensive properties. This core has a higher open porosity (40%), suitable bending strength of 25 MPa (at 1773.15 K), and lower sintering shrinkage in the Z direction. The significance of this study lies in the regulation of in-situ mullite generation and viscous flow in solid-liquid sintering by adjusting the doping amount of fused silica and the sintering process, and this opens up new pathways by the coordinated regulation of strength, open porosity, and sintering shrinkage of 3D printed ceramic cores. • An in situ mullite-enhanced ceramic core was successfully prepared using 3D printing technology. • In-situ mullite was synthesized through thermodynamic analysis in 3D printing ceramic cores. • Strength, porosity and sintering shrinkage of 3D printing ceramic cores were controlled. • A novel method for the coordinated regulation of strength, porosity and sintering shrinkage of 3D printing ceramic cores.

3D‐Printed Holographic Fresnel Lenses

Additive manufacturing processes are capable of fabricating optical devices, including the production of contact lenses, waveguides, and Fresnel lenses used in a variety of applications. This study presents a novel fabrication method for high‐quality Fresnel lenses through a vat photopolymerization 3D printing method. Here, the 3D printing process is integrated with the micro/nanostructure fabrication to produce 3D optical components with imprinted micro/nanostructures in a single step. This straightforward approach allows imprinting a micro‐pattern (5 μm features size) onto the flat surface of a 3D‐printed Fresnel lens, achieve light focusing properties along with holographic rainbow effects. The printed lenses achieve focal lengths within ≤8 mm deviation from the predicted values. Such holographic Fresnel lenses are highly desirable in imaging‐based miniature spectrometers for mechanoluminescence sensoring. Thus, the masked stereolithography (MSLA) based 3D printing process can produce normal and holographic Fresnel lenses, vital in optical sensing and communication.