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.

Fabrication of Living Entangled Network Composites Enabled by Mycelium.

Organic polymer-based composite materials with favorable mechanical performance and functionalities are keystones to various modern industries; however, the environmental pollution stemming from their processing poses a great challenge. In this study, by finding an autonomous phase separating ability of fungal mycelium, a new material fabrication approach is introduced that leverages such biological metabolism-driven, mycelial growth-induced phase separation to bypass high-energy cost and labor-intensive synthetic methods. The resulting self-regenerative composites, featuring an entangled network structure of mycelium and assembled organic polymers, exhibit remarkable self-healing properties, being capable of reversing complete separation and restoring ≈90% of the original strength. These composites further show exceptional mechanical strength, with a high specific strength of 8.15 MPa g.cm-3 , and low water absorption properties (≈33% after 15 days of immersion). This approach spearheads the development of state-of-the-art living composites, which directly utilize bioactive materials to "self-grow" into materials endowed with exceptional mechanical and functional properties.

Growth, Distribution, and Photosynthesis of Chlamydomonas Reinhardtii in 3D Hydrogels.

Engineered living materials (ELMs) are a novel class of functional materials that typically feature spatial confinement of living components within an inert polymer matrix to recreate biological functions. Understanding the growth and spatial configuration of cellular populations within a matrix is crucial to predicting and improving their responsive potential and functionality. Here, this work investigates the growth, spatial distribution, and photosynthetic productivity of eukaryotic microalga Chlamydomonas reinhardtii (C. reinhardtii) in three-dimensionally shaped hydrogels in dependence of geometry and size. The embedded C. reinhardtii cells photosynthesize and form confined cell clusters, which grow faster when located close to the ELM periphery due to favorable gas exchange and light conditions. Taking advantage of location-specific growth patterns, this work successfully designs and prints photosynthetic ELMs with increased CO2 capturing rate, featuring high surface to volume ratio. This strategy to control cell growth for higher productivity of ELMs resembles the already established adaptations found in multicellular plant leaves.

3D Printing of Flow-Inspired Anisotropic Patterns with Liquid Crystalline Polymers.

Anisotropic materials formed by living organisms possess remarkable mechanical properties due to their intricate microstructure and directional freedom. In contrast, human-made materials face challenges in achieving similar levels of directionality due to material and manufacturability constraints. To overcome these limitations, an approach using 3D printing of self-assembling thermotropic liquid crystal polymers (LCPs) is presented. Their high stiffness and strength is granted by nematic domains aligning during the extrusion process. Here, a remarkably wide range of Young's modulus from 3 to 40 GPa is obtained by utilizing directionality of the nematic flow the printing process.   By determining a relationship between stiffness, nozzle diameter, and line width, a design space where shaping and mechanical performance can be combined is identified. The ability to print LCPs with on-the-fly width changes to accommodate arbitrary spatially varying directions is demonstrated. This unlocks the possibility to manufacture exquisite patterns inspired by fluid dynamics with steep curvature variations. Utilizing the synergy between this path-planning method and LCPs, functional objects with stiffness and curvature gradients can be 3D-printed, offering potential applications in lightweight sustainable structures embedding crack-mitigation strategies. This method also opens avenues for studying and replicating intricate patterns observed in nature, such as wood or turbulent flow using 3D printing.

Three-dimensional printing of mycelium hydrogels into living complex materials.

Biological living materials, such as animal bones and plant stems, are able to self-heal, regenerate, adapt and make decisions under environmental pressures. Despite recent successful efforts to imbue synthetic materials with some of these remarkable functionalities, many emerging properties of complex adaptive systems found in biology remain unexplored in engineered living materials. Here, we describe a three-dimensional printing approach that harnesses the emerging properties of fungal mycelia to create living complex materials that self-repair, regenerate and adapt to the environment while fulfilling an engineering function. Hydrogels loaded with the fungus Ganoderma lucidum are three-dimensionally printed into lattice architectures to enable mycelial growth in a balanced exploration and exploitation pattern that simultaneously promotes colonization of the gel and bridging of air gaps. To illustrate the potential of such mycelium-based living complex materials, we three-dimensionally print a robotic skin that is mechanically robust, self-cleaning and able to autonomously regenerate after damage.

Diamagnetic Composites for High-Q Levitating Resonators.

Levitation offers extreme isolation of mechanical systems from their environment, while enabling unconstrained high-precision translation and rotation of objects. Diamagnetic levitation is one of the most attractive levitation schemes because it allows stable levitation at room temperature without the need for a continuous power supply. However, dissipation by eddy currents in conventional diamagnetic materials significantly limits the application potential of diamagnetically levitating systems. Here, a route toward high-Q macroscopic levitating resonators by substantially reducing eddy current damping using graphite particle based diamagnetic composites is presented. Resonators that feature quality factors Q above 450 000 and vibration lifetimes beyond one hour are demonstrated, while levitating above permanent magnets in high vacuum at room temperature. The composite resonators have a Q that is >400 times higher than that of diamagnetic graphite plates. By tuning the composite particle size and density, the dissipation reduction mechanism is investigated, and the Q of the levitating resonators is enhanced. Since their estimated acceleration noise is as low as some of the best superconducting levitating accelerometers at cryogenic temperatures, the high Q and large mass of the presented composite resonators positions them as one of the most promising technologies for next generation ultra-sensitive room temperature accelerometers.

Nacre-like composites with superior specific damping performance.

Biological materials such as nacre have evolved microstructural design principles that result in outstanding mechanical properties. While nacre's design concepts have led to bio-inspired materials with enhanced fracture toughness, the microstructural features underlying the remarkable damping properties of this biological material have not yet been fully explored in synthetic composites. Here, we study the damping behavior of nacre-like composites containing mineral bridges and platelet asperities as nanoscale structural features within its brick-and-mortar architecture. Dynamic mechanical analysis was performed to experimentally elucidate the role of these features on the damping response of the nacre-like composites. By enhancing stress transfer between platelets and at the brick/mortar interface, mineral bridges and nano-asperities were found to improve the damping performance of the composite to levels that surpass many biological and man-made materials. Surprisingly, the improved properties are achieved without reaching the perfect organization of the biological counterparts. Our nacre-like composites display a loss modulus 2.4-fold higher than natural nacre and 1.4-fold more than highly dissipative natural fiber composites. These findings shed light on the role of nanoscale structural features on the dynamic mechanical properties of nacre and offer design concepts for the manufacturing of bio-inspired composites for high-performance damping applications.

Light-Based Printing of Leachable Salt Molds for Facile Shaping of Complex Structures.

3D printing is a powerful manufacturing technology for shaping materials into complex structures. While the palette of printable materials continues to expand, the rheological and chemical requisites for printing are not always easy to fulfill. Here, a universal manufacturing platform is reported for shaping materials into intricate geometries without the need for their printability, but instead using light-based printed salt structures as leachable molds. The salt structures are printed using photocurable resins loaded with NaCl particles. The printing, debinding, and sintering steps involved in the process are systematically investigated to identify ink formulations enabling the preparation of crack-free salt templates. The experiments reveal that the formation of a load-bearing network of salt particles is essential to prevent cracking of the mold during the process. By infiltrating the sintered salt molds and leaching the template in water, complex-shaped architectures are created from diverse compositions such as biomedical silicone, chocolate, light metals, degradable elastomers, and fiber composites, thus demonstrating the universal, cost-effective, and sustainable nature of this new manufacturing platform.

Hierarchical porous materials made by stereolithographic printing of photo-curable emulsions.

Porous materials are relevant for a broad range of technologies from catalysis and filtration, to tissue engineering and lightweight structures. Controlling the porosity of these materials over multiple length scales often leads to enticing new functionalities and higher efficiency but has been limited by manufacturing challenges and the poor understanding of the properties of hierarchical structures. Here, we report an experimental platform for the design and manufacturing of hierarchical porous materials via the stereolithographic printing of stable photo-curable Pickering emulsions. In the printing process, the micron-sized droplets of the emulsified resins work as soft templates for the incorporation of microscale porosity within sequentially photo-polymerized layers. The light patterns used to polymerize each layer on the building stage further generate controlled pores with bespoke three-dimensional geometries at the millimetre scale. Using this combined fabrication approach, we create architectured lattices with mechanical properties tuneable over several orders of magnitude and large complex-shaped inorganic objects with unprecedented porous designs.

3D Printed Scaffolds for Monolithic Aerogel Photocatalysts with Complex Geometries.

Monolithic aerogels composed of crystalline nanoparticles enable photocatalysis in three dimensions, but they suffer from low mechanical stability and it is difficult to produce them with complex geometries. Here, an approach to control the geometry of the photocatalysts to optimize their photocatalytic performance by introducing carefully designed 3D printed polymeric scaffolds into the aerogel monoliths is reported. This allows to systematically study and improve fundamental parameters in gas phase photocatalysis, such as the gas flow through and the ultraviolet light penetration into the aerogel and to customize its geometric shape to a continuous gas flow reactor. Using photocatalytic methanol reforming as a model reaction, it is shown that the optimization of these parameters leads to an increase of the hydrogen production rate by a factor of three from 400 to 1200 µmol g-1 h-1 . The rigid scaffolds also enhance the mechanical stability of the aerogels, lowering the number of rejects during synthesis and facilitating handling during operation. The combination of nanoparticle-based aerogels with 3D printed polymeric scaffolds opens up new opportunities to tailor the geometry of the photocatalysts for the photocatalytic reaction and for the reactor to maximize overall performance without necessarily changing the material composition.

Digital light 3D printing of customized bioresorbable airway stents with elastomeric properties.

Central airway obstruction is a life-threatening disorder causing a high physical and psychological burden to patients. Standard-of-care airway stents are silicone tubes, which provide immediate relief but are prone to migration. Thus, they require additional surgeries to be removed, which may cause tissue damage. Customized bioresorbable airway stents produced by 3D printing would be highly needed in the management of this disorder. However, biocompatible and biodegradable materials for 3D printing of elastic medical implants are still lacking. Here, we report dual-polymer photoinks for digital light 3D printing of customized and bioresorbable airway stents. These stents exhibit tunable elastomeric properties with suitable biodegradability. In vivo study in healthy rabbits confirmed biocompatibility and showed that the stents stayed in place for 7 weeks after which they became radiographically invisible. This work opens promising perspectives for the rapid manufacturing of the customized medical devices for which high precision, elasticity, and degradability are sought.

A DNA-of-things storage architecture to create materials with embedded memory.

DNA storage offers substantial information density1-7 and exceptional half-life3. We devised a 'DNA-of-things' (DoT) storage architecture to produce materials with immutable memory. In a DoT framework, DNA molecules record the data, and these molecules are then encapsulated in nanometer silica beads8, which are fused into various materials that are used to print or cast objects in any shape. First, we applied DoT to three-dimensionally print a Stanford Bunny9 that contained a 45 kB digital DNA blueprint for its synthesis. We synthesized five generations of the bunny, each from the memory of the previous generation without additional DNA synthesis or degradation of information. To test the scalability of DoT, we stored a 1.4 MB video in DNA in plexiglass spectacle lenses and retrieved it by excising a tiny piece of the plexiglass and sequencing the embedded DNA. DoT could be applied to store electronic health records in medical implants, to hide data in everyday objects (steganography) and to manufacture objects containing their own blueprint. It may also facilitate the development of self-replicating machines.

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.

3D Printing of Salt as a Template for Magnesium with Structured Porosity.

Porosity is an essential feature in a wide range of applications that combine light weight with high surface area and tunable density. Porous materials can be easily prepared with a vast variety of chemistries using the salt-leaching technique. However, this templating approach has so far been limited to the fabrication of structures with random porosity and relatively simple macroscopic shapes. Here, a technique is reported that combines the ease of salt leaching with the complex shaping possibilities given by additive manufacturing (AM). By tuning the composition of surfactant and solvent, the salt-based paste is rheologically engineered and printed via direct ink writing into grid-like structures displaying structured pores that span from the sub-millimeter to the macroscopic scale. As a proof of concept, dried and sintered NaCl templates are infiltrated with magnesium (Mg), which is typically highly challenging to process by conventional AM techniques due to its highly oxidative nature and high vapor pressure. Mg scaffolds with well-controlled, ordered porosity are obtained after salt removal. The tunable mechanical properties and the potential to be predictably bioresorbed by the human body make these Mg scaffolds attractive for biomedical implants and demonstrate the great potential of this additive technique.

Tunable Wood by Reversible Interlocking and Bioinspired Mechanical Gradients.

Elegant design principles in biological materials such as stiffness gradients or sophisticated interfaces provide ingenious solutions for an efficient improvement of their mechanical properties. When materials such as wood are directly used in high-performance applications, it is not possible to entirely profit from these optimizations because stiffness alterations and fiber alignment of the natural material are not designed for the desired application. In this work, wood is turned into a versatile engineering material by incorporating mechanical gradients and by locally adapting the fiber alignment, using a shaping mechanism enabled by reversible interlocks between wood cells. Delignification of the renewable resource wood, a subsequent topographic stacking of the cellulosic scaffolds, and a final densification allow fabrication of desired 3D shapes with tunable fiber architecture. Additionally, prior functionalization of the cellulose scaffolds allows for obtaining tunable functionality combined with mechanical gradients. Locally controllable elastic moduli between 5 and 35 GPa are obtained, inspired by the ability of trees to tailor their macro- and micro-structure. The versatility of this approach has significant relevance in the emerging field of high-performance materials from renewable resources.

Quantifying the role of mineral bridges on the fracture resistance of nacre-like composites.

The nacreous layer of mollusk shells holds design concepts that can effectively enhance the fracture resistance of lightweight brittle materials. Mineral bridges are known to increase the fracture resistance of nacre-inspired materials, but their role is difficult to quantify due to the lack of experimental systems where only this parameter is controllably varied. In this study, we fabricate tunable nacre-like composites that are used as a model to experimentally quantify the influence of the density of mineral bridges alone on the fracture properties of nacre-like architectures. The composites exhibit a brick-and-mortar architecture comprising highly aligned alumina platelets that are interconnected by titania mineral bridges and infiltrated by an epoxy organic phase. By combining experimental mechanical data with image analysis of such composite microstructures, an analytical model is put forward based on a simple balance of forces acting on an individual bridged platelet. Based on this model, we predict the flexural strength of the nacre-like composite to scale linearly with the density of mineral bridges, as long as the mineral interconnectivity is low enough to keep fracture in a platelet pullout mode. Increasing the mineral interconnectivity beyond this limit leads to platelet fracture and catastrophic failure of the composite. This structure-property correlation provides powerful quantitative guidelines for the design of lightweight brittle materials with enhanced fracture resistance. We illustrate this potential by fabricating nacre-like bulk composites with unparalleled flexural strength combined with noncatastrophic failure.

Three-dimensional printing of hierarchical liquid-crystal-polymer structures.

Fibre-reinforced polymer structures are often used when stiff lightweight materials are required, such as in aircraft, vehicles and biomedical implants. Despite their very high stiffness and strength1, such lightweight materials require energy- and labour-intensive fabrication processes2, exhibit typically brittle fracture and are difficult to shape and recycle3,4. This is in stark contrast to lightweight biological materials such as bone, silk and wood, which form by directed self-assembly into complex, hierarchically structured shapes with outstanding mechanical properties5-11, and are circularly integrated into the environment. Here we demonstrate a three-dimensional (3D) printing approach to generate recyclable lightweight structures with hierarchical architectures, complex geometries and unprecedented stiffness and toughness. Their features arise from the self-assembly of liquid-crystal polymer molecules into highly oriented domains during extrusion of the molten feedstock material. By orienting the molecular domains with the print path, we are able to reinforce the polymer structure according to the expected mechanical stresses, leading to stiffness, strength and toughness that outperform state-of-the-art 3D-printed polymers by an order of magnitude and are comparable with the highest-performance lightweight composites1,12. The ability to combine the top-down shaping freedom of 3D printing with bottom-up molecular control over polymer orientation opens up the possibility to freely design and realize structures without the typical restrictions of current manufacturing processes.

Mineral Nano-Interconnectivity Stiffens and Toughens Nacre-like Composite Materials.

Bulk nacre-like composites with mineral nano-interconnectivity at the same length scale as in the biological material are produced using magnetic alignment and selective sintering techniques. These materials display stiffness and strength levels comparable to that of continuous fiber composites with the advantage of easier processability inherent of discontinuous composites. This opens new possibilities to produce parts with more complex designs.