Additive Manufacturing of Transparent Silica Glass from Solutions

Printing of In Situ Functionalized Mesoporous Silica with Digital Light Processing for Combinatorial Sensing

Combinatorial sensing is especially important in the context of modern drug development to enable fast screening of large data sets. Mesoporous silica materials offer high surface area and a wide range of functionalization possibilities. By adding structural control, the combination of structural and functional control along all length scales opens a new pathway that permits larger amounts of analytes being tested simultaneously for complex sensing tasks. This study presents a fast and simple way to produce mesoporous silica in various shapes and sizes between 0.27-6 mm by using light-induced sol-gel chemistry and digital light processing (DLP). Shape-selective functionalization of mesoporous silica is successfully carried out either after printing using organosilanes or in situ while printing through the use of functional mesopore template for the in situ functionalization approach. Shape-selective adsorption of dyes is shown as a demonstrator toward shape selective screening of potential analytes.

Phase-separating resins for light-based three-dimensional printing of oxide glasses

Silica-based glasses can be shaped into complex geometries using a variety of additive manufacturing technologies. While the three-dimensional printing of glasses opens unprecedented design opportunities, the development of up-scaled, reliable manufacturing processes is crucial for the broader dissemination of this technology. Here, we design and study phase-separating resins that enable light-based 3D printing of oxide glasses with high-aspect-ratio features and enhanced manufacturing yields. The effect of the resin composition on the microstructure, mechanical properties and delamination resistance of parts printed by digital light processing is investigated with the help of printing experiments, compression tests and electron microscopy analysis. The chemical composition and microstructure of the cured resins were found to strongly affect the stiffness, delamination resistance, and calcination behavior of printed parts. These findings provide useful guidelines to enhance the reliability and yield of the DLP printing process of multicomponent silica-based glasses.

Efficient Fabrication of Quartz Glass Using Laser Coaxial Powder-Fed Additive Manufacturing Approach

This article investigates a laser-directed energy deposition additive manufacturing (AM) method, based on coaxial powder feeding, for preparing quartz glass. Through synergistic optimization of line deposition and plane deposition experiments, key parameters of laser coaxial powder feeding AM were identified. The corresponding mechanical properties, thermal properties, and microstructure of the bulk parts were analyzed. The maximum mechanical strength of the obtained quartz glass element reached 72.36 ± 5.98 MPa, which is ca. 95% that of quartz glass prepared by traditional methods. The thermal properties of the obtained quartz glass element were also close to those prepared by traditional methods. The present research indicates that one can use laser AM technology that is based on coaxial powder feeding to form quartz glass with high density and good thermodynamic properties. Such quartz glass has substantial potential in, for example, optics and biomedicine.

High-Quality Acousto-Optic Modulators with High Diffraction Efficiency, Polarization Extinction Ratio, and Small Insertion Loss Based on a Novel BaO-TeO2 -WO3 Glass

The Q-switched material and device have attracted extensive attention due to their irreplaceable role in pulsed lasers. In this paper, BaO-TeO2 -WO3 glass (BTW glass) with sound velocity and sound attenuation coefficient of 3422 m-1 s and 0.653 dB cm-1 is successfully selected and fabricated as acousto-optic material. Both free-spaced and fiber-coupled acousto-optic modulation devices based on BTW glass are designed and fabricated. The primary parameters such as diffraction efficiency, polarization extinction ratio, and insertion loss are comparable to or even surpassed that of commercial devices. A 1064 nm pulsed laser is successfully realized with a BTW glass free-spaced acousto-optic modulator. The maximum optical conversion efficiency, the narrowest pulse width, and the maximum single pulse energy of the 1064 nm pulsed laser are 32%, 54 ns, and 242.6 µJ, respectively. Both the device and laser performance indicate that the BTW glass is a remarkable acousto-optic material.

Additive Manufacturing of Transparent Multi-Component Nanoporous Glasses

Fabrication of glass with complex geocd the low resolution of particle-based or fused glass technologies. Herein, a high-resolution 3D printing of transparent nanoporous glass is presented, by the combination of transparent photo-curable sol-gel printing compositions and digital light processing (DLP) technology. Multi-component glass, including binary (Al2 O3 -SiO2 ), ternary (ZnO-Al2 O3 -SiO2 , TiO2 -Al2 O3 -SiO2 ), and quaternary oxide (CaO-P2 O5 -Al2 O3 -SiO2 ) nanoporous glass objects with complex shapes, high spatial resolutions, and multi-oxide chemical compositions are fabricated, by DLP printing and subsequent sintering process. The uniform nanopores of Al2 O3 -SiO2 -based nanoporous glasses with the diameter (≈6.04 nm), which is much smaller than the visible light wavelength, result in high transmittance (>95%) at the visible range. The high surface area of printed glass objectives allows post-functionalization via the adsorption of functional guest molecules. The photoluminescence and hydrophobic modification of 3D printed glass objectives are successfully demonstrated. This work extends the scope of 3D printing to transparent nanoporous glasses with complex geometry and facile functionalization, making them available for a wide range of applications.

Room-Temperature Molding of Complex-Shaped Transparent Fused Silica Lenses

The high hardness, brittleness, and thermal resistance impose significant challenges in the scalable manufacturing of fused silica lenses, which are widely used in numerous applications. Taking advantage of the nanocomposites by stirring silica nanopowders with photocurable resins, the newly emerged low-temperature pre-shaping technique provides a paradigm shift in fabricating transparent fused silica components. However, preparing the silica slurry and carefully evaporating the organics may significantly increase the process complexity and decrease the manufacturing efficiency for the nanocomposite-based technique. By directly pressing pure silica nanopowders against the complex-shaped metal molds in minutes, this work reports an entirely different room-temperature molding method capable of mass replication of complex-shaped silica lenses without organic additives. After sintering the replicated lenses, fully transparent fused silica lenses with spherical, arrayed, and freeform patterns are generated with nanometric surface roughness and well-reserved mold shapes, demonstrating a scalable and cost-effective route surpassing the current techniques for the manufacturing of high-quality fused silica lenses.

Two-photon polymerization of silica glass diffractive micro-optics with minimal lateral shrinkage

Three-dimensional printing enables the fabrication of silica glass optics with complex structures. However, shrinkage remains a significant obstacle to high-precision 3D printing of glass optics. Here we 3D-printed Dammann gratings (DGs) with low lateral shrinkage (<4%) using a two-photon polymerization (2PP) technique. The process consists of two steps: patterning two-photon polymerizable glass slurry with a 515 nm femtosecond laser to form desired structures and debinding/sintering the structures into transparent and dense silica glass. The sintered structures exhibited distinct shrinkage rates in the lateral against longitudinal directions. As the aspect ratio of the structures increased, the lateral shrinkage decreased, while the longitudinal shrinkage increased. Specifically, the structure with an aspect ratio of approximately 60 achieved a minimal lateral shrinkage of 1.1%, the corresponding longitudinal shrinkage was 61.7%. The printed DGs with a surface roughness below 20 nm demonstrated good beam-shaping performance. The presented technique opens up possibilities for rapid prototyping of silica diffractive optical elements.

Low-temperature 3D printing of transparent silica glass microstructures

Transparent silica glass is one of the most essential materials used in society and industry, owing to its exceptional optical, thermal, and chemical properties. However, glass is extremely difficult to shape, especially into complex and miniaturized structures. Recent advances in three-dimensional (3D) printing have allowed for the creation of glass structures, but these methods involve time-consuming and high-temperature processes. Here, we report a photochemistry-based strategy for making glass structures of micrometer size under mild conditions. Our technique uses a photocurable polydimethylsiloxane resin that is 3D printed into complex structures and converted to silica glass via deep ultraviolet (DUV) irradiation in an ozone environment. The unique DUV-ozone conversion process for silica microstructures is low temperature (~220°C) and fast (<5 hours). The printed silica glass is highly transparent with smooth surface, comparable to commercial fused silica glass. This work enables the creation of arbitrary structures in silica glass through photochemistry and opens opportunities in unexplored territories for glass processing techniques.

A review of materials used in tomographic volumetric additive manufacturing

Volumetric additive manufacturing is a novel fabrication method allowing rapid, freeform, layer-less 3D printing. Analogous to computer tomography (CT), the method projects dynamic light patterns into a rotating vat of photosensitive resin. These light patterns build up a three-dimensional energy dose within the photosensitive resin, solidifying the volume of the desired object within seconds. Departing from established sequential fabrication methods like stereolithography or digital light printing, volumetric additive manufacturing offers new opportunities for the materials that can be used for printing. These include viscous acrylates and elastomers, epoxies (and orthogonal epoxy-acrylate formulations with spatially controlled stiffness) formulations, tunable stiffness thiol-enes and shape memory foams, polymer derived ceramics, silica-nanocomposite based glass, and gelatin-based hydrogels for cell-laden biofabrication. Here we review these materials, highlight the challenges to adapt them to volumetric additive manufacturing, and discuss the perspectives they present.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at10.1557/s43579-023-00447-x.

Ratio-Tuning of Silica Aerogel Co-Hydrolyzed Precursors Enables Broadband, Angle-Independent, Deformation-Tolerant, Achieving 99.7% Reflectivity

The super-white body might be defined as its reflectivity exceeding 98% at any angle in the visible light spectrum, which can be used in a variety of emerging fields including optics, energy, environment, aerospace, etc. However, elaborate synthesis of a light-weight, highly reflective super-white aerogel body remains a great challenge. In this work, fine-tuning of silica aerogel co-hydrolyzed precursor ratios, 99.7% reflectivity with angle-independence in the visible light spectrum has been successfully achieved when the areal density is only 0.129 g cm-2 , which breaks through the theoretical bandwidth limit of photonic crystals as well as the measured reflectivity limit of conventional porous materials. Furthermore, the reflectivity of super-white silica aerogel remains unchanged after various harsh deformations including compression and bending 1000 times, solar (≈800 W m-2 ), ultraviolet (≈0.68 W m-2 ), and humidity (100%) aging for 100 days, liquid nitrogen (-196 °C) and high-temperature (300 °C) thermal shock 100 times. As proofs of performance, the resulting super-white silica aerogels have been used as the novel standard white plate  for better spectrum calibration, as the flexible projector curtains for optical display, as well as the transmitted light reflective layer in the photovoltaic cell for improving the relative power conversion efficiency of 5.6%.

Additive Manufacturing of Advanced Ceramics Using Preceramic Polymers

Ceramic materials are used in various industrial applications, as they possess exceptional physical, chemical, thermal, mechanical, electrical, magnetic, and optical properties. Ceramic structural components, especially those with highly complex structures and shapes, are difficult to fabricate with conventional methods, such as sintering and hot isostatic pressing (HIP). The use of preceramic polymers has many advantages, such as excellent processibility, easy shape change, and tailorable composition for fabricating high-performance ceramic components. Additive manufacturing (AM) is an evolving manufacturing technique that can be used to construct complex and intricate structural components. Integrating polymer-derived ceramics and AM techniques has drawn significant attention, as it overcomes the limitations and challenges of conventional fabrication approaches. This review discusses the current research that used AM technologies to fabricate ceramic articles from preceramic feedstock materials, and it demonstrates that AM processes are effective and versatile approaches for fabricating ceramic components. The future of producing ceramics using preceramic feedstock materials for AM processes is also discussed at the end.

A sinterless, low-temperature route to 3D print nanoscale optical-grade glass

Three-dimensional (3D) printing of silica glass is dominated by techniques that rely on traditional particle sintering. At the nanoscale, this limits their adoption within microsystem technology, which prevents technological breakthroughs. We introduce the sinterless, two-photon polymerization 3D printing of free-form fused silica nanostructures from a polyhedral oligomeric silsesquioxane (POSS) resin. Contrary to particle-loaded sacrificial binders, our POSS resin itself constitutes a continuous silicon-oxygen molecular network that forms transparent fused silica at only 650°C. This temperature is 500°C lower than the sintering temperatures for fusing discrete silica particles to a continuum, which brings silica 3D printing below the melting points of essential microsystem materials. Simultaneously, we achieve a fourfold resolution enhancement, which enables visible light nanophotonics. By demonstrating excellent optical quality, mechanical resilience, ease of processing, and coverable size scale, our material sets a benchmark for micro- and nano-3D printing of inorganic solids.

Angle-independent solar radiation capture by 3D printed lattice structures for efficient photoelectrochemical water splitting

Photoelectrochemical water splitting is one of the sustainable routes to renewable hydrogen production. One of the challenges to deploying photoelectrochemical (PEC) based electrolyzers is the difficulty in the effective capture of solar radiation as the illumination angle changes throughout the day. Herein, we demonstrate a method for the angle-independent capture of solar irradiation by using transparent 3 dimensional (3D) lattice structures as the photoanode in PEC water splitting. The transparent 3D lattice structures were fabricated by 3D printing a silica sol-gel followed by aging and sintering. These transparent 3D lattice structures were coated with a conductive indium tin oxide (ITO) thin film and a Mo-doped BiVO₄ photoanode thin film by dip coating. The sheet resistance of the conductive lattice structures can reach as low as 340 Ohms per sq for ∼82% optical transmission. The 3D lattice structures furnished large volumetric current densities of 1.39 mA cm^-3 which is about 2.4 times higher than a flat glass substrate (0.58 mA cm^-3) at 1.23 V and 1.5 G illumination. Further, the 3D lattice structures showed no significant loss in performance due to a change in the angle of illumination, whereas the performance of the flat glass substrate was significantly affected. This work opens a new paradigm for more effective capture of solar radiation that will increase the solar to energy conversion efficiency.

Chromaticity-Tunable All-Inorganic Color Converters Fabricated by 3D Printing for Modular Plant Growth Lighting Devices

In photopolymerization-induced 3D printing of glass and ceramics, the demand for a slurry that has high photosensitivity, low viscosity, and high solid content leads to a limited selection of suspended particles. To this end, ultraviolet-assisted direct ink writing (UV-DIW) is proposed as a new 3D printing compatible approach. A curable UV ink is synthesized, which overcomes the material limitation. Benefiting from the advantage of the UV-DIW process, CaAlSiN₃:Eu²⁺/BaMgAl₁₀O₁₇:Eu²⁺ phosphors in glass (CASN/BAM-PiG) as chromaticity-tunable specially shaped all-inorganic color converters are prepared for plant growth lighting using an optimized heat treatment procedure. Size compatible dome-type and flat-type CaAlSiN₃:Eu²⁺ phosphors in glass (CASN-PiG) are constructed in batches. The manufactured dome-type PiG-based light-emitting diodes (LEDs) exhibit better heat dissipation capacity and a larger divergence angle. The advantage of CASN/BAM-PiG in plant growth lighting is confirmed by the high degree of resemblance between the emission spectra of CASN/BAM-PiG and the absorption spectra of carotenoid and chlorophyll. A series of dome-type CASN/BAM-PiG based LEDs with selective region doping are constructed, which can weaken reabsorption effects and scientifically match the requirements of different plants. The excellent color-tunable ability and high degree of spectral resemblance indicate the superiority of the proposed UV-DIW process in all-inorganic CASN/BAM-PiG color converters for intelligent agricultural lighting.

Random Silica-Glass Microlens Arrays Based on the Molding Technology of Photocurable Nanocomposites

Random microlens arrays (rMLAs) have been widely applied as a beam-shaping component within an optical system. Silica glass is undoubtedly the best choice for rMLAs because of its wide range of spectra with high transmission and high damage threshold. Yet, machining silica glass with user-defined shapes is still challenging. In this work, novel design and fabrication methods of random silica-glass microlens arrays (rSMLAs) are proposed and a detailed investigation of this technology is presented. Based on the molding technology, the fabricated rSMLAs with tunable divergent angles demonstrate superior physical properties with 1.81 nm roughness, 1074.33 HV hardness, and excellent thermal stability at 1250 °C for 3 h. Meanwhile, their characterized optical performance shows a high transmission of over 90% in the ultraviolet spectrum. The fabricated two types of rSMLAs exhibit excellent effects of beam homogenization with surprising energy utilization (more than 90%) and light spot uniformity (more than 80%). This innovative process paves a new route for fabricating rMLAs on solid silica glass and breaking down the barrier of rMLAs to broader applications.

In Vivo Application of Silica-Derived Inks for Bone Tissue Engineering: A 10-Year Systematic Review

As the need for efficient, sustainable, customizable, handy and affordable substitute materials for bone repair is critical, this systematic review aimed to assess the use and outcomes of silica-derived inks to promote in vivo bone regeneration. An algorithmic selection of articles was performed following the PRISMA guidelines and PICO method. After the initial selection, 51 articles were included. Silicon in ink formulations was mostly found to be in either the native material, but associated with a secondary role, or to be a crucial additive element used to dope an existing material. The inks and materials presented here were essentially extrusion-based 3D-printed (80%), and, overall, the most investigated animal model was the rabbit (65%) with a femoral defect (51%). Quality (ARRIVE 2.0) and risk of bias (SYRCLE) assessments outlined that although a large majority of ARRIVE items were “reported”, most risks of bias were left “unclear” due to a lack of precise information. Almost all studies, despite a broad range of strategies and formulations, reported their silica-derived material to improve bone regeneration. The rising number of publications over the past few years highlights Si as a leverage element for bone tissue engineering to closely consider in the future.

High-Precision Printing of Complex Glass Imaging Optics with Precondensed Liquid Silica Resin

3D printing of optics has gained significant attention in optical industry, but most of the research has been focused on organic polymers. In spite of recent progress in 3D printing glass, 3D printing of precision glass optics for imaging applications still faces challenges from shrinkage during printing and thermal processing, and from inadequate surface shape and quality to meet the requirements for imaging applications. This paper reports a new liquid silica resin (LSR) with higher curing speed, better mechanical properties, lower sintering temperature, and reduced shrinkage, as well as the printing process for high-precision glass optics for imaging applications. It is demonstrated that the proposed material and printing process can print almost all types of optical surfaces, including flat, spherical, aspherical, freeform, and discontinuous surfaces, with accurate surface shape and high surface quality for imaging applications. It is also demonstrated that the proposed method can print complex optical systems with multiple optical elements, completely removing the time-consuming and error-prone alignment process. Most importantly, the proposed printing method is able to print optical systems with active moving elements, significantly improving system flexibility and functionality. The printing method will enable the much-needed transformational manufacturing of complex freeform glass optics that are currently inaccessible with conventional processes.

Silica-Encapsulated Germania Colloids as 3D-Printable Glass Precursors

Core-shell colloids make attractive feedstocks for three-dimensional (3D) printing mixed oxide glass materials because they enable synthetic control of precursor dimensions and compositions, improving glass fabrication precision. Toward that end, we report the design and use of core-shell germania-silica (GeO₂-SiO₂) colloids and their use as precursors to fabricate GeO₂-SiO₂ glass monoliths by direct ink write (DIW) 3D printing. By this method, GeO₂ colloids were prepared in solution using sol-gel chemistry and formed oblong, raspberry-like agglomerates with ∼15 nm diameter primary particles that were predominantly amorphous but contained polycrystalline domains. An ∼15 nm encapsulating SiO₂ shell layer was formed directly on the GeO₂ core agglomerates to form core-shell GeO₂-SiO₂ colloids. For glass 3D printing, GeO₂-SiO₂ colloidal sols were formulated into a viscous ink by solvent exchange, printed into monoliths by DIW additive manufacturing, and sintered to transparent glasses. Characterization of the glass components demonstrates that the core-shell GeO₂-SiO₂ presents a feasible route to prepare quality, optically transparent low wt % GeO₂-SiO₂ glasses by DIW printing. Additionally, the results offer a novel, hybrid colloid approach to fabricating 3D-printed Ge-doped silica glass.

Volumetric additive manufacturing of silica glass with microscale computed axial lithography

Glass is increasingly desired as a material for manufacturing complex microscopic geometries, from the micro-optics in compact consumer products to microfluidic systems for chemical synthesis and biological analyses. As the size, geometric, surface roughness, and mechanical strength requirements of glass evolve, conventional processing methods are challenged. We introduce microscale computed axial lithography (micro-CAL) of fused silica components, by tomographically illuminating a photopolymer-silica nanocomposite that is then sintered. We fabricated three-dimensional microfluidics with internal diameters of 150 micrometers, free-form micro-optical elements with a surface roughness of 6 nanometers, and complex high-strength trusses and lattice structures with minimum feature sizes of 50 micrometers. As a high-speed, layer-free digital light manufacturing process, micro-CAL can process nanocomposites with high solids content and high geometric freedom, enabling new device structures and applications.

Rapid Manufacturing of Complex-Structured Transparent Silica Glass Materials through a Hybridized Approach of Photo-Curing and Machining from Interparticle Photo-Cross-Linkable Suspensions

The rapid manufacturing of transparent SiO₂ glass components via a hybridized 3D structuring approach for photo-curing and green machining, followed by a fast debinding/sintering process (at a heating rate of 20 °C min^-1), is reported to be based on the design of a new series of interparticle photo-cross-linkable suspensions. In these suspensions, small amounts of multifunctional acrylates and silane alkoxides with acryloyl groups (A-Si) are co-photo-polymerized and further reacted with SiO₂ particles modified using functionalized polyethyleneimine to form hybridized interparticle networks. The addition of A-Si increases the interparticle cross-linking densities, leading to an improvement in the mechanical properties and green machinability of the photo-cured bodies. Furthermore, the A-Si component in the cross-links forms siloxane-based networks among SiO₂ particles in situ during the debinding/sintering process, which increases the mechanical strength of the debinded bodies and successfully prevents structural collapses under rapid heating conditions. The study demonstrates that the photo-cured body from the newly designed suspensions can be green-machined into pillars, microfluids, and assembling blocks and can be sintered into highly transparent SiO₂ glass components. Overall, this work provides new options for the time- and energy-effective processing of SiO₂ glass materials with tailor-made 3D structures.

Overview of 3D-Printed Silica Glass

Not satisfied with the current stage of the extensive research on 3D printing technology for polymers and metals, researchers are searching for more innovative 3D printing technologies for glass fabrication in what has become the latest trend of interest. The traditional glass manufacturing process requires complex high-temperature melting and casting processes, which presents a great challenge to the fabrication of arbitrarily complex glass devices. The emergence of 3D printing technology provides a good solution. This paper reviews the recent advances in glass 3D printing, describes the history and development of related technologies, and lists popular applications of 3D printing for glass preparation. This review compares the advantages and disadvantages of various processing methods, summarizes the problems encountered in the process of technology application, and proposes the corresponding solutions to select the most appropriate preparation method in practical applications. The application of additive manufacturing in glass fabrication is in its infancy but has great potential. Based on this view, the methods for glass preparation with 3D printing technology are expected to achieve both high-speed and high-precision fabrication.

Present state of 3D printing from glass

This paper deals with the issue of additive technologies using glass. At the beginning, our research dealt with a review of the current state and specification of potentially interesting methods and solutions. At present, this technology is being actively developed and studied in glass research. However, as the project started at the Department of Glass Producing Machines and Robotics, the following text will be more focused on the existing 3D printing machinery and basic technological approaches. Although “additive manufacturing” in the sense of adding materials has been used in glass manufacturing since the beginning of the production of glass by humans, the term additive manufacturing nowadays refers to 3D printing. Currently, there are several approaches to 3D printing of glass that have various outstanding advantages, but also several serious limitations. The resulting products very often have a high degree of shrinkage and rounding (after sintering), and specific shape structures (after the application in layers), but they generally have a large number of defects (especially bubbles or crystallization issues). Some technologies do not lead to the production of transparent glass and, therefore, its optical properties are significantly restricted. So far, the additive manufacturing of glass do not produce goods that are price competitive to goods produced by conventional glass-making technologies. If 3D glass printing is to be successful as an industrial and/or highly aesthetically valuable method, then it must bring new and otherwise unachievable features and properties, as with 3D printing of plastic, metal, or ceramics. Nowadays, these technologies promise to be such a tool and are beginning to attract more and more interest.

Melt-Extrusion-Based Additive Manufacturing of Transparent Fused Silica Glass

In recent years, additive manufacturing (AM) of glass has attracted great interest in academia and industry, yet it is still mostly limited to liquid nanocomposite-based approaches for stereolithography, two-photon polymerization, or direct ink writing. Melt-extrusion-based processes, such as fused deposition modeling (FDM), which will allow facile manufacturing of large thin-walled components or simple multimaterial printing processes, are so far inaccessible for AM of transparent fused silica glass. Here, melt-extrusion-based AM of transparent fused silica is introduced by FDM and fused feedstock deposition (FFD) using thermoplastic silica nanocomposites that are converted to transparent glass using debinding and sintering. This will enable printing of previously inaccessible glass structures like high-aspect-ratio (>480) vessels with wall thicknesses down to 250 µm, delicate parts including overhanging features using polymer support structures, as well as dual extrusion for multicolored glasses.

3D Printing and Pyrolysis of Optical ZrO2 Nanostructures by Two-Photon Lithography: Reduced Shrinkage and Crystallization Mediated by Nanoparticles Seeds

Two-photon lithography is a potential route to produce high-resolution 3D ceramics. However, the large shrinkage due to the elimination of an important organic counterpart of the printed material during debinding/sintering remains a lock to further development of this technology. To limit this phenomenon, an original approach based on a composite resin incorporating 45 wt% ultrasmall (5 nm) zirconia stabilized nanoparticles into the zirconium acrylate precursor is proposed to process 3D zirconia microlattices and nanostructured optical surfaces. Interestingly, the nanoparticles are used both as seeds allowing control of the crystallographic phase formed during the calcination process and as structural stabilizing agent preventing important shrinkage of the printed ceramic. After 3D photolithography and pyrolysis, the weight and volume loss of the microstructures are drastically reduced as compared to similar systems processed with the reference resin without nanoparticles, and stable 3D microstructures of cubic zirconia are obtained with high spatial resolution. In the case of a patterned surface, the refractive index of 2.1 leads to a diffraction efficiency large enough to obtain microfocusing with linewidths of 0.1 µm, and the demonstration of a microlens array with a period as small as 0.8 µm.

3D printing of glass by additive manufacturing techniques: a review

Additive manufacturing (AM), which is also known as three-dimensional (3D) printing, uses computer-aided design to build objects layer by layer. Here, we focus on the recent progress in the development of techniques for 3D printing of glass, an important optoelectronic material, including fused deposition modeling, selective laser sintering/melting, stereolithography (SLA) and direct ink writing. We compare these 3D printing methods and analyze their benefits and problems for the manufacturing of functional glass objects. In addition, we discuss the technological principles of 3D glass printing and applications of 3D printed glass objects. This review is finalized by a summary of the current achievements and perspectives for the future development of the 3D glass printing technique.

Facile Surface Functionalization Strategy for Two-Photon Lithography Microstructures

Two-photon lithography (TPL) is a powerful tool to construct small-scale objects with complex and precise 3D architectures. While the limited selection of chemical functionalities on the printed structures has restricted the application of this method in fabricating functional objects and devices, this study presents a facile, efficient, and extensively applicable method to functionalize the surfaces of the objects printed by TPL. TPL-printed objects, regardless of their compositions, can be efficiently functionalized by combining trichlorovinylsilane treatment and thiol-ene chemistry. Various functionalities can be introduced on the printed objects, without affecting their micro-nano topographies. Hence, microstructures with diverse functions can be generated using non-functional photoresists. Compared to existed strategies, this method is fast, highly efficient, and non photoresist-dependent. In addition, this method can be applied to various materials, such as metals, metal oxides, and plastics that can be potentially utilized in TPL or other 3D printing technologies. The applications of this method on the biofunctionalization of microrobots and cell scaffolds are also demonstrated.

Transparent origami glass

The art of origami has emerged as an engineering tool with ever increasing potential, but the technique is typically limited to soft and deformable materials. Glass is indispensable in many applications, but its processing options are limited by its brittle nature and the requirement to achieve optical transparency. We report a strategy that allows making three dimensional transparent glass with origami techniques. Our process starts from a dynamic covalent polymer matrix with homogeneously dispersed silica nanoparticles. Particle cavitation and dynamic bond exchange offer two complementary plasticity mechanisms that allow the nanocomposite to be permanently folded into designable geometries. Further pyrolysis and sintering convert it into transparent three dimensional glass. Our method expands the scope of glass shaping and potentially opens up its utilities in unexplored territories.

Glass is indispensable but its processing options are limited. Here the authors extend origami techniques to shaping three-dimensional transparent glass by introducing physical cavitation and chemical dynamic bond exchange in the pre-glass polymer-silica nanocomposites.

Introduction of Chalcogenide Glasses to Additive Manufacturing: Nanoparticle Ink Formulation, Inkjet Printing, and Phase Change Devices Fabrication

Chalcogenide glasses are one of the most versatile materials that have been widely researched because of their flexible optical, chemical, electronic, and phase change properties. Their application is usually in the form of thin films, which work as active layers in sensors and memory devices. In this work, we investigate the formulation of nanoparticle ink of Ge-Se chalcogenide glasses and its potential applications. The process steps reported in this work describe nanoparticle ink formulation from chalcogenide glasses, its application via inkjet printing and dip-coating methods and sintering to manufacture phase change devices. We report data regarding nanoparticle production by ball milling and ultrasonication along with the essential characteristics of the formed inks, like contact angle and viscosity. The printed chalcogenide glass films were characterized by Raman spectroscopy, X-ray diffraction, energy dispersive spectroscopy and atomic force microscopy. The printed films exhibited similar compositional, structural, electronic and optical properties as the thermally evaporated thin films. The crystallization processes of the printed films are discussed compared to those obtained by vacuum thermal deposition. We demonstrate the formation of printed thin films using nanoparticle inks, low-temperature sintering and proof for the first time, their application in electronic and photonic temperature sensors utilizing their phase change property. This work adds chalcogenide glasses to the list of inkjet printable materials, thus offering an easy way to form arbitrary device structures for optical and electronic applications.

What Is Driving the Growth of Inorganic Glass in Smart Materials and Opto-Electronic Devices?

Inorganic glass is a transparent functional material and one of the few materials that keeps leading innovation. In the last decades, inorganic glass was integrated into opto-electronic devices such as optical fibers, semiconductors, solar cells, transparent photovoltaic devices, or photonic crystals and in smart materials applications such as environmental, pharmaceutical, and medical sensors, reinforcing its influence as an essential material and providing potential growth opportunities for the market. Moreover, inorganic glass is the only material that is 100% recyclable and can incorporate other industrial offscourings and/or residues to be used as raw materials. Over time, inorganic glass experienced an extensive range of fabrication techniques, from traditional melting-quenching (with an immense diversity of protocols) to chemical vapor deposition (CVD), physical vapor deposition (PVD), and wet chemistry routes as sol-gel and solvothermal processes. Additive manufacturing (AM) was recently added to the list. Bulks (3D), thin/thick films (2D), flexible glass (2D), powders (2D), fibers (1D), and nanoparticles (NPs) (0D) are examples of possible inorganic glass architectures able to integrate smart materials and opto-electronic devices, leading to added-value products in a wide range of markets. In this review, selected examples of inorganic glasses in areas such as: (i) magnetic glass materials, (ii) solar cells and transparent photovoltaic devices, (iii) photonic crystal, and (iv) smart materials are presented and discussed.

3D Printing Materials for Soft Robotics

Soft robotics is a growing field of research, focusing on constructing motor-less robots from highly compliant materials, some are similar to those found in living organisms. Soft robotics has a high potential for applications in various fields such as soft grippers, actuators, and biomedical devices. 3D printing of soft robotics presents a novel and promising approach to form objects with complex structures, directly from a digital design. Here, recent developments in the field of materials for 3D printing of soft robotics are summarized, including high-performance flexible and stretchable materials, hydrogels, self-healing materials, and shape memory polymers, as well as fabrication of all-printed robots (multi-material printing, embedded electronics, untethered and autonomous robotics). The current challenges in the fabrication of 3D printed soft robotics, including the materials available and printing abilities, are presented and the recent activities addressing these challenges are also surveyed.

3D Printing of Transparent Spinel Ceramics with Transmittance Approaching the Theoretical Limit

3D printing of transparent ceramics has attracted great attention recently but faces the challenges of low transparency and low printing resolution. Herein, magnesium aluminate spinel transparent ceramics with transmittance reaching 97% of the theoretical limit are successfully fabricated using a stereolithography-based 3D printing method assisted by hot isostatic pressing and the critical factors governing the transparency are revealed. Various transparent spinel lenses and microlattices are printed at a high resolution of ≈100-200 µm. The 3D printed spinel lens demonstrates fairly good optical imaging ability, and the printed spinel diamond microlattices as a transparent photocatalyst support for TiO₂ significantly enhance its photocatalytic efficiency compared with its opaque counterparts. Compared with other 3D printed transparent materials such as silica glass or organic polymers, the printed spinel ceramics have the advantages of broad optical window, high hardness, excellent high-temperature stability, and chemical resistance and therefore, have great potential to be used in various optical lenses/windows and photocatalyst supports for application in harsh environments.

Two-Photon Polymerization of Nanocomposites for the Fabrication of Transparent Fused Silica Glass Microstructures

Fused silica glass is the material of choice for many high-performance components in optics due to its high optical transparency combined with its high thermal, chemical, and mechanical stability. Especially, the generation of fused silica microstructures is of high interest for microoptical and biomedical applications. Direct laser writing (DLW) is a suitable technique for generating such devices, as it enables nearly arbitrary structuring down to the sub-micrometer level. In this work, true 3D structuring of transparent fused silica glass using DLW with tens of micrometer resolution and a surface roughness of R_a  ≈ 6 nm is demonstrated. The process uses a two-photon curable silica nanocomposite resin that can be structured by DLW, with the printout being convertible to transparent fused silica glass via thermal debinding and sintering. This technology will enable a plethora of applications from next-generation optics and photonics to microfluidic and biomedical applications with resolutions on the scale of tens of micrometers.

Printed aerogels: chemistry, processing, and applications

As an extraordinarily lightweight and porous functional nanomaterial family, aerogels have attracted considerable interest in academia and industry in recent decades. Despite the application scopes, the modest mechanical durability of aerogels makes their processing and operation challenging, in particular, for situations demanding intricate physical structures. "Bottom-up" additive manufacturing technology has the potential to address this drawback. Indeed, since the first report of 3D printed aerogels in 2015, a new interdisciplinary research area combining aerogel and printing technology has emerged to push the boundaries of structure and performance, further broadening their application scope. This review summarizes the state-of-the-art of printed aerogels and presents a comprehensive view of their developments in the past 5 years, and highlights the key near- and mid-term challenges.

3D printing of silica glass through a multiphoton polymerization process

We introduce a laser-based process relying on multiphoton-induced polymerization to produce complex three-dimensional (3D) glass parts. A focused, intense laser beam is used to polymerize a transparent resin, loaded with additives and silica nanoparticles, at the wavelength of the laser beam through nonlinear absorption processes. The object is created directly in the volume, overcoming the limitation of the layer-by-layer process. The process enables the production of silica parts with consecutive debinding and sintering processes. With bulk silica density and a resolution that depends on the laser spot size, 3D objects of centimetric dimensions are obtained.

3D printed gradient index glass optics

We demonstrate an additive manufacturing approach to produce gradient refractive index glass optics. Using direct ink writing with an active inline micromixer, we three-dimensionally print multimaterial green bodies with compositional gradients, consisting primarily of silica nanoparticles and varying concentrations of titania as the index-modifying dopant. The green bodies are then consolidated into glass and polished, resulting in optics with tailored spatial profiles of the refractive index. We show that this approach can be used to achieve a variety of conventional and unconventional optical functions in a flat glass component with no surface curvature.

3D Printing of Ordered Mesoporous Silica Complex Structures

Ordered mesoporous silica materials gain high interest because of their potential applications in catalysis, selective adsorption, separation, and controlled drug release. Due to their morphological characteristics, mainly the tunable, ordered nanometric pores, they can be utilized as supporting hosts for confined chemical reactions. Applications of these materials, however, are limited by structural design. Here, we present a new approach for the 3D printing of complex geometry silica objects with an ordered mesoporous structure by stereolithography. The process uses photocurable liquid compositions that contain a structure-directing agent, silica precursors, and elastomer-forming monomers that, after printing and calcination, form porous silica monoliths. The objects have extremely high surface area, 1900 m²/g, and very low density and are thermally and chemically stable. This work enables the formation of ordered porous objects having complex geometries that can be utilized in applications in both the industry and academia, overcoming the structural limitations associated with traditional processing methods.

High-Complexity WO3-Based Catalyst with Multi-Catalytic Species via 3D Printing

Three-dimensional (3D) printing has recently been introduced into the field of chemistry as an enabling tool employed to perform reactions, but so far, its use has been limited due to material and structural constraints. We have developed a new approach for fabricating 3D catalysts with high-complexity features for chemical reactions via digital light processing printing (DLP). PtO2-WO3 heterogeneous catalysts with complex shapes were directly fabricated from a clear solution, composed of photo-curable organic monomers, photoinitiators, and metallic salts. The 3D-printed catalysts were tested for the hydrogenation of alkynes and nitrobenzene, and displayed excellent reactivity in these catalytic transformations. Furthermore, to demonstrate the versatility of this approach and prove the concept of multifunctional reactors, a tungsten oxide-based tube consisting of three orderly sections containing platinum, rhodium, and palladium was 3D printed.

3D Printing of Micrometer-Sized Transparent Ceramics with On-Demand Optical-Gain Properties

Transparent ceramics are usually polycrystalline materials, which are wildly used in many optical applications, such as lasers. As of today, the fabrication of transparent ceramic structures is still limited to conventional fabrication methods, which do not enable the formation of complex structures. A new approach for 3D printing of micrometer-size, transparent ceramic structures is presented. By using a solution of metal salts that can undergo a sol-gel process and photopolymerization by two-photon printing, micrometer-sized yttrium aluminum garnet (YAG) structures doped with neodymium (Nd) are fabricated. The resulting structures are not only transparent in the visible spectrum but can also emit light at 1064 nm due to the doping with Nd. By using solution-based precursors, without any particles, the sintering can be performed under air at ambient pressure and at a relatively low temperature, compared to conventional processes for YAG. The crystalline structure is imaged at atomic resolution by ultrahigh-resolution scanning transmission electron microscopy (STEM), indicating that the doped Nd atoms are located at the yttrium positions. Such miniaturized structures can be used for diverse applications, e.g., optical components in high-intensity laser systems, which require heat resistance, or as light sources in optical circuits.

Additive Manufacturing of Optical Quality Germania-Silica Glasses

Direct ink writing (DIW) three-dimensional (3D) printing provides a revolutionary approach to fabricating components with gradients in material properties. Herein, we report a method for generating colloidal germania feedstock and germania-silica inks for the production of optical quality germania-silica (GeO₂-SiO₂) glasses by DIW, making available a new material composition for the development of multimaterial and functionally graded optical quality glasses and ceramics by additive manufacturing. Colloidal germania and silica particles are prepared by a base-catalyzed sol-gel method and converted to printable shear-thinning suspensions with desired viscoelastic properties for DIW. The volatile solvents are then evaporated, and the green bodies are calcined and sintered to produce transparent, crack-free glasses. Chemical and structural evolution of GeO₂-SiO₂ glasses is confirmed by nuclear magnetic resonance, X-ray diffraction, and Raman spectroscopy. UV-vis transmission and optical homogeneity measurements reveal comparable performance of the 3D printed GeO₂-SiO₂ glasses to glasses produced using conventional approaches and improved performance over 3D printed TiO₂-SiO₂ inks. Moreover, because GeO₂-SiO₂ inks are compatible with DIW technology, they offer exciting options for forming new materials with patterned compositions such as gradients in the refractive index that cannot be achieved with conventional manufacturing approaches.

Three-dimensional printing of multicomponent glasses using phase-separating resins

The digital fabrication of oxide glasses by three-dimensional (3D) printing represents a major paradigm shift in the way glasses are designed and manufactured, opening opportunities to explore functionalities inaccessible by current technologies. The few enticing examples of 3D printed glasses are limited in their chemical compositions and suffer from the low resolution achievable with particle-based or molten glass technologies. Here, we report a digital light-processing 3D printing platform that exploits the photopolymerization-induced phase separation of hybrid resins to create glass parts with complex shapes, high spatial resolutions and multi-oxide chemical compositions. Analogously to conventional porous glass fabrication methods, we exploit phase separation phenomena to fabricate complex glass parts displaying light-controlled multiscale porosity and dense multicomponent transparent glasses with arbitrary geometry using a desktop printer. Because most functional properties of glasses emerge from their transparency and multicomponent nature, this 3D printing platform may be useful for distinct technologies, sciences and arts.

Hierarchical ordering in light-triggered additive manufacturing

Herein, recent developments in the 3D printing of materials with structural hierarchy and their future prospects are reviewed. It is shown that increasing the extent of ordering, is essential to access novel properties and functionalities.

Continuous synthesis of 2,5-hexanedione through direct C–C coupling of acetone in a Hilbert fractal photo microreactor

A Hilbert fractal photo microreactor (PMR) was developed and used in the continuous photochemical synthesis of 2,5-hexanedione (2,5-HDN) via direct C–C coupling of acetone.

Additive Manufacturing of 3D-Architected Multifunctional Metal Oxides

Additive manufacturing (AM) of complex three-dimensional (3D) metal oxides at the micro- and nanoscales has attracted considerable attention in recent years. State-of-the-art techniques that use slurry-based or organic-inorganic photoresins are often hampered by challenges in resin preparation and synthesis, and/or by the limited resolution of patterned features. A facile process for fabricating 3D-architected metal oxides via the use of an aqueous metal-ion-containing photoresin is presented. The efficacy of this process, which is termed photopolymer complex synthesis, is demonstrated by creating nanoarchitected zinc oxide (ZnO) architectures with feature sizes of 250 nm, by first patterning a zinc-ion-containing aqueous photoresin using two-photon lithography and subsequently calcining them at 500 ºC. Transmission electron microscopy (TEM) analysis reveals their microstructure to be nanocrystalline ZnO with grain sizes of 5.1 ± 1.6 nm. In situ compression experiments conducted in a scanning electron microscope show an emergent electromechanical response: a 200 nm mechanical compression of an architected ZnO structure results in a voltage drop of 0.52 mV. This photopolymer complex synthesis provides a pathway to easily create arbitrarily shaped 3D metal oxides that could enable previously impossible devices and smart materials.

High-Performance Materials for 3D Printing in Chemical Synthesis Applications

3D printing has emerged as an enabling technology for miniaturization. High-precision printing techniques such as stereolithography are capable of printing microreactors and lab-on-a-chip devices for efficient parallelization of biological and biochemical reactions under reduced uptake of reactants. In the world of chemistry, however, up until now, miniaturization has played a minor role. The chemical and thermal stability of regular 3D printing resins is insufficient for sustaining the harsh conditions of chemical reactions. Novel material formulations that produce highly stable 3D-printed chips are highly sought for bringing chemistry up-to-date on the development of miniaturization. In this work, a brief review of recent developments in highly stable materials for 3D printing is given. This work focuses on three highly stable 3D-printable material systems: transparent silicate glasses, ceramics, and fluorinated polymers. It is further demonstrated that 3D printing is also a versatile technique for surface structuring of polymers to enhance their wetting performance. Such micro/nanostructuring is key to selectively wetting surface patterns that are versatile for chemical arrays and droplet synthesis.

Advances in Optical Sensing and Bioanalysis Enabled by 3D Printing

The recent explosion of 3D printing applications in scientific literature has expanded the speed and effectiveness of analytical technological development. 3D printing allows for manufacture that is simply designed in software and printed in-house with nearly no constraints on geometry, and analytical methodologies can thus be prototyped and optimized with little difficulty. The versatility of methods and materials available allows the analytical chemist or biologist to fine-tune both the structural and functional portions of their apparatus. This flexibility has more recently been extended to optical-based bioanalysis, with higher resolution techniques and new printing materials opening the door for a wider variety of optical components, plasmonic surfaces, optical interfaces, and biomimetic systems that can be made in the laboratory. There have been discussions and reviews of various aspects of 3D printing technologies in analytical chemistry; this Review highlights recent literature and trends in their applications to optical sensing and bioanalysis.

3D printing of multicolor luminescent glass

The development of the stereolithography technique for the additive manufacturing of silica glass has brought revolutionary change in glass manufacturing. Here, we demonstrate the fabrication of 3D luminescent transparent glass parts manufactured by the stereolithographic technique together with solution impregnation and high temperature sintering. Prefabricated glass parts with nanopores were prepared by the stereolithography technique and debinded and pre-sintered at first. To functionalize the additive manufactured glass with photoluminescence, Eu³⁺, Tb³⁺ and Ce³⁺ ions were doped with a solution impregnation method and further sintered at high temperature. The photoluminescence from these rare earth ions in the blue, cyan and red spectral region can be facilely generated by illumination with a 254 nm UV lamp. Furthermore, we developed a space-selective doping method that enables the doping of different ions in different parts of a silica glass in a space-selective fashion, resulting in a multicolor luminescent glass object giving distinguishable luminescence from each part.

A novel technique enables the design of both the shape and the function of single glass devices.