Design for composite material additive manufacturing is governed by multiple process variables that can be computationally expensive to optimize. This is especially true when considering discrete variables, such as the material type to be used, which lead to a lot of possible solutions that have to be evaluated. Here, we propose a workflow for optimizing topology and fiber placement of 3D volumetric structures based on mechanical performance under multiple load cases and environmental impact. An eco-informed material selection from a set fibers and polymers is followed by a methodology to optimize the manufacturing setting. By performing these two steps sequentially, the number of input parameter sets to be tested is reduced in a combinatorial scale, along with the computational cost. The framework can be easily extended by adapting the analyses and holds significant promise for the design of additive manufactured sustainable structures.

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In the collaborative effort towards standardisation of out-of-plane permeability measurement, an international benchmarking exercise was carried out whereby 19 participants worldwide were instructed to measure the out-of-plane permeability following a number of strict guidelines, informed by the outcomes of the first international benchmarking exercise completed in 2021. This paper presents the results of the exercise and an assessment of the reproducibility of the data and the suitability of the proposed test method. The data returned were subjected to a number of statistical analysis methods, which showed that adherence to the test guidelines resulted in a high likelihood of a participant not being an outlier and therefore providing evidence that the test method proposed in this paper is a suitable way forward for a standardised test method.@en

Spider silk is known for its excellent strength and fracture resistance properties due to its molecular design structure, characterized by sacrificial bonds and hidden lengths. These structures have inspired reinforcements of synthetic polymer materials to enhance toughness. In this study, we mimic these natural toughening mechanisms by designing and manufacturing 3D-printed polymeric structures incorporating overlapping curls consisting of coiling fiber with sacrificial bonds and hidden lengths. Utilizing the liquid rope coiling effect, we manufactured overlapping curls using three polymers: polylactic acid (PLA), liquid crystal polymer (LCP), and polyamide 6 (PA6). Uniaxial tensile tests were performed to characterize the mechanical properties of overlapping curl as a function of geometries, post-treatments, and material constitutive parameters. Our results show that single-sided overlapping curls can fully unfold while double-sided curls are prone to premature failure. Heat-pressure post-treatment was found to significantly increase the load-capacity of the sacrificial bonds by up to [Formula presented] due to increased contact area. However, the defects introduced in the fibre after the break of the sacrificial bonds, make the structure more susceptible to premature failure, limit the complete unfolding of the hidden length, and lead to a decrease up to [Formula presented] of the toughness. To guarantee the complete unfolding of the hidden lengths and improve the toughness, we demonstrate that selecting a polymer material with either high fracture strength (e.g., LCP, [Formula presented]) or high fracture strain (e.g., PA6, >2) is crucial, and increase toughness up to [Formula presented] and [Formula presented], respectively.

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In addition to the well-documented resource efficiency and geometrical freedom, Digital Fabrication (DFAB) revolutionizes architecture by integrating functionalities into building elements, unlocking untapped potential from the micro- to the macroscales. This study uses binder-jet printed sand for a DFAB prototype—Fireplace2—tailored for indoor heating. Named after its traditional counterpart, Fireplace2 showcases DFAB’s prowess in crafting precise microclimates for heightened thermal comfort. Our research, tuning mechanical and thermal properties across micro and meso scales, illustrates DFAB's utility in architects' hands for crafting tailored microclimates. This approach manipulates the effective thermal conductivity and macroscale topology for stability against toppling (0.8 kN). A vertical infill porosity gradient establishes a surface temperature gradient, countering ventilation-induced thermal gradients. With a minimal operational temperature vertical gradient (+0.2°C), complying with international comfort standards (Predicted Mean Vote −0.23, People Dissatisfied 6%), Fireplace2 stands testament to DFAB’s microclimate-shaping capabilities despite challenges like foot-level ventilation. The study propels DFAB into a sustainable paradigm, aligning occupant comfort with environmental consciousness, thereby fostering more efficient and enjoyable indoor spaces.

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Carbon-based products are essential to society, yet producing them from fossil fuels is unsustainable. Microorganisms have the ability to take up electrons from solid electrodes and convert carbon dioxide (CO₂) to valuable carbon-based chemicals. However, higher productivities and energy efficiencies are needed to reach a viability that can make the technology transformative. Here, we show how a biofilm-based microbial porous cathode in a directed flow-through electrochemical system can continuously reduce CO₂ to even-chain C2–C6 carboxylic acids over 248 days. We demonstrate a threefold higher biofilm concentration, volumetric current density, and productivity compared with the state of the art. Most notably, the volumetric productivity (VP) resembles those achieved in laboratory-scale and industrial syngas (CO-H₂-CO₂) fermentation and chain elongation fermentation. This work highlights key design parameters for efficient electricity-driven microbial CO₂ reduction. There is need and room to improve the rates of electrode colonization and microbe-specific kinetics to scale up the technology.

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Since the inception of fibre-reinforced composite materials, they have been widely acknowledged for their unparalleled weight-to-performance ratio. Nonetheless, concerns are escalating regarding the environmental impact of these materials amidst global warming and pollution. This perspective explores a ground-breaking shift towards harnessing living organisms to produce composite materials. Living composites not only offer sustainable, carbon-capturing alternatives but also afford an unprecedented level of control over shape and anisotropy. Recent advancements in biology, particularly genetic engineering and sequencing, have provided extraordinary control over living organisms. Coupled with ever-evolving additive manufacturing techniques, these breakthroughs enable the construction of engineered living materials from the ground up. Here, we explore the key factors propelling the emergence of engineered living materials for structural applications and delves into the capabilities of living organisms that can be harnessed for creating functional materials, including harvesting energy, forming structures, sensing/adapting, growing and remodelling. Incorporating living organisms can revolutionise manufacturing for renewable and sustainable composite materials, unlocking previously unattainable functionalities.

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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.

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Signaling pathways in fungi offer a profound avenue for harnessing cellular communication and have garnered considerable interest in biomaterial engineering. Fungi respond to environmental stimuli through intricate signaling networks involving biochemical and electrical pathways, yet deciphering these mechanisms remains a challenge. In this review, an overview of fungal biology and their signaling pathways is provided, which can be activated in response to external stimuli and direct fungal growth and orientation. By examining the hyphal structure and the pathways involved in fungal signaling, the current state of recording fungal electrophysiological signals as well as the landscape of fungal biomaterials is explored. Innovative applications are highlighted, from sustainable materials to biomonitoring systems, and an outlook on the future of harnessing fungi signaling in living composites is provided.

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Recent numerical studies have suggested the potential of substrates with streamwise-preferential permeability to reduce drag in turbulent boundary layers. Such a substrate is theorized to facilitate relaxation of the no-slip condition and thereby reduce the skin friction. So far, these beneficial effects have not been demonstrated experimentally yet and therefore the scope of this work is to present this concept in air flow where the substrate geometry satisfies the theoretical permeability requirements for an expected reduction in drag. For this, a three-dimensional-printed structure with anisotropic permeability (φxz=2.7, φxy=3.9) and small pores (s≈250μm), akin to an acoustic liner, was developed. The substrate was investigated using direct force measurements and 2D-2C PIV in the range of U∞≈5-35 ms-1, corresponding to frictional Reynolds numbers of Reτ≈430-1960. Results show an increase in drag of 0%<ΔCD<8% and, while contrasting the model predictions, this agrees with DNS data on structures with similar geometric properties when using the inverse wall-normal Forchheimer coefficient, or inertial permeability, as the equivalent roughness parameter. Hence the present results constitute the first experimental evidence that this is the governing property for the drag behavior of acoustic liners. The absence of the predicted beneficial flow modulation effects is attributed to the investigated substrate not strictly satisfying the theoretical framework assumptions on characteristic length scales. However, to expand beyond this structural limitation, we analytically derive that, for realistic, geometrically resolved cases, this length scale mismatch is unavoidable and thereby render it unfeasible to model the substrate as a continuum for the virtual-origin approach. We expect that translating the abstraction of substrates with streamwise-preferential permeability into physical realisations relevant for practical applications would result in structures very similar to riblets.

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Multi-material direct ink writing (DIW) of smart materials opens new possibilities for manufacturing complex-shaped structures with embedded sensing and actuation capabilities. In this study, DIW of UV-curable piezoelectric actuators is developed, which do not require high-temperature sintering, allowing direct integration with structural materials. Through particle size and ink rheology optimization, the highest d₃₃^*g₃₃ piezoelectric constant compared to other DIW fabricated piezo composites is achieved, enabling tunable actuation performance. This is used to fabricate ultrasound transducers by printing piezoelectric vibrating membranes along with their support structures made from a structural ink. The impact of transducer design and scaling up transducer dimensions on the resonance behavior to design millimeter-scale ultrasound transducers with desired out-of-plane displacement is explored. A significant increase in output pressure with increasing membrane dimensions is observed. Finally, a practical application is demonstrated by using the printed transducer for accurate proximity sensing using time of flight measurements. The scalability and flexibility of the reported DIW of piezo composites can open up new advancements in biomedical, human-computer interaction, and aerospace fields.

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Fused Filament Fabrication is a promising manufacturing technology for the circularity of space missions. Potential scenarios include in-orbit applications to maximize mission life and to support long-term exploration missions with in situ manufacturing and recycling. However, its adoption is restricted by the availability of engineering polymers displaying mechanical performance combined with resistance to space conditions. Here, a thermotropic Liquid Crystal Polymer (LCP) is reported as a candidate material with extrusion 3D printing. To expand its scope of applicability to structural parts for space applications, four different exposure conditions are studied: thermal cycling under vacuum, atomic oxygen, UV, and electron irradiations. While 1 MeV-electron irradiation leads to a green coloration due to annealable color centers, the mechanical performance is only slightly decreased in dynamic mode. It is also found that increased printing temperature improves transverse strength and resistance to thermal cycling with the trade-off of tensile stiffness and strength. Samples exposed to thermal cycling and the highest irradiation dose at lower printing temperatures still display a Young's modulus of 30 GPa and 503 MPa of tensile strength which is exceptionally high for a 3D-printed polymer. For the types of exposure studied, overall, the results indicate that LCP 3D-printed parts are well suited for space applications.@en

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.

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This work explores a spatial printing method to fabricate continuous fiber-reinforced thermoplastic composites (CFRTPCs), which can achieve exceptional mechanical performance. For models giving complex 3D stress distribution under loads, typical planar-layer based fiber placement usually fails to provide sufficient reinforcement due to their orientations being constrained to planes. The effectiveness of fiber reinforcement could be maximized by using multi-axis additive manufacturing (MAAM) to better control the orientation of continuous fibers in 3D-printed composites. Here, we propose a computational approach to generate 3D toolpaths that satisfy two major reinforcement objectives: (1) following the maximal stress directions in critical regions and (2) connecting multiple load-bearing regions by continuous fibers. Principal stress lines are first extracted in an input solid model to identify critical regions. Curved layers aligned with maximal stresses in these critical regions are generated by computing an optimized scalar field and extracting its iso-surfaces. Then, topological analysis and operations are applied to each curved layer to generate a computational domain that preserves fiber continuity between load-bearing regions. Lastly, continuous fiber toolpaths aligned with maximal stresses are generated on each surface layer by computing an optimized scalar field and extracting its iso-curves. A hardware system with dual robotic arms is employed to conduct the physical MAAM tasks depositing polymer or fiber reinforced polymer composite materials by applying a force normal to the extrusion plane to aid consolidation. When comparing to planar-layer based printing results in tension, up to 644% failure load and 240% stiffness are observed on shapes fabricated by our spatial printing method. We demonstrate the versatility of our approach through various complex load cases which demonstrate their successful implementation of continuous fiber printing in 3D.

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A novel approach is presented to 3D print vacuum–tight polymer components using liquid crystal polymers (LCPs). Vacuum–tight components are essential for gas storage and passive heat transfer, but traditional polymer 3D printing methods often suffer from poor interfaces between layers and high free volume, compromising vacuum integrity. By harnessing the unique properties of LCPs, including low free volume and low melt viscosity, highly ordered domains are achieved through nematic alignment of polymer chains. Critical gas–barrier properties are demonstrated, even in thin, single–print line–walled samples ranging from 0.8 to 1.6 mm. A 200 mm evacuated thermosiphon is successfully printed, which exhibits a thermal resistance of up to 2.18 K/W and an effective thermal conductivity of up to 28 W/mK at 60 °C. These values represent a significant increase compared to the base LCP material. Furthermore, the geometric freedom, enabled by 3D printing through the fabrication of complex–shaped thermosiphons, is showcased. The authors study highlights the potential of LCPs as high–performance materials for 3D printing vacuum–tight components with intricate geometries, opening new avenues for functional design. An application of integrating 3D printed thermosiphons as selective heat transfer components in building envelopes is presented, contributing to greenhouse gas emissions mitigation in the construction sector.

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Chopped Tape Thermoplastic Composites (CTTCs) offer high formability and performance for complex-shaped components in the aerospace and automotive industries. However, the mesoscopic discontinuity leads to spatial variabilities and correspondingly high scatter in the elastic properties of CTTCs due to the random orientations of chopped tapes and chopped tape-cavity edge interactions. Here we propose a new approach to investigate the effect of mould cavity edges on chopped tape orientation and hence the mechanical properties of CTTCs. Based on this approach, a Set Voronoi tessellation was implemented to represent the variability of local Young's Modulus and chopped tape-cavity edge interactions occurring during the manufacturing process. It was confirmed that the chopped tapes align along the edges, and progressively transition to a random orientation towards the middle of the specimen. The results were validated on moulded specimens and demonstrated the ability to deconvolute the edge interaction.

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Dynamic building facades offer untapped potential for reducing building energy consumption and emissions. However, there is currently a lack of suitable technologies for bespoke components for new and retrofit applications. In previous work, we developed a 3D printed polymer facade component that selectively acts as a thermal conductor or insulator depending on outdoor and indoor conditions. Our experiments demonstrate that the element can achieve effective thermal conductivities as low as 0.03 W/mK and as high as 28 W/mK in insulating and conducting modes. In this work, we assess the potential impact of this technology on reducing heating and cooling energy demand. We conducted a parametric analysis of ten physical characteristics of the facade component. Then, we simulated the façade component employed in 270 building typologies and climate combinations. Our results indicate annual energy reduction of up to 80 kWh/m2 (heating) and 15 kWh/m2 (cooling) for building typology-climate combinations that can benefit the most from this technology.

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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.

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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 during by utilizing directionality of the nematic flow during 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.

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Ultra-high angular resolution in astronomy has always been an important vehicle for making fundamental discoveries. Recent results in direct imaging of the vicinity of the supermassive black hole in the nucleus of the radio galaxy M87 by the millimeter VLBI system Event Horizon Telescope and various pioneering results of the Space VLBI mission RadioAstron provided new momentum in high angular resolution astrophysics. In both mentioned cases, the angular resolution reached the values of about 10–20 microarcseconds (0.05–0.1 nanoradian). Further developments towards at least an order of magnitude “sharper” values, at the level of 1 microarcsecond are dictated by the needs of advanced astrophysical studies. The paper emphasis that these higher values can only be achieved by placing millimeter and submillimeter wavelength interferometric systems in space. A concept of such the system, called Terahertz Exploration and Zooming-in for Astrophysics, has been proposed in the framework of the ESA Call for White Papers for the Voyage 2050 long term plan in 2019. In the current paper we present new science objectives for such the concept based on recent results in studies of active galactic nuclei and supermassive black holes. We also discuss several approaches for addressing technological challenges of creating a millimeter/sub-millimeter wavelength interferometric system in space. In particular, we consider a novel configuration of a space-borne millimeter/sub-millimeter antenna which might resolve several bottlenecks in creating large precise mechanical structures. The paper also presents an overview of prospective space-qualified technologies of low-noise analogue front-end instrumentation for millimeter/sub-millimeter telescopes. Data handling and processing instrumentation is another key technological component of a sub-millimeter Space VLBI system. Requirements and possible implementation options for this instrumentation are described as an extrapolation of the current state-of-the-art Earth-based VLBI data transport and processing instrumentation. The paper also briefly discusses approaches to the interferometric baseline state vector determination and synchronisation and heterodyning system. The technology-oriented sections of the paper do not aim at presenting a complete set of technological solutions for sub-millimeter (terahertz) space-borne interferometers. Rather, in combination with the original ESA Voyage 2050 White Paper, it sharpens the case for the next generation microarcsecond-level imaging instruments and provides starting points for further in-depth technology trade-off studies.

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Lightweight biological materials such as bone, silk and wood demonstrate complex hierarchically structured shapes with outstanding mechanical properties by utilising directed self-assembly to grow structures. Here1, we demonstrate a bioinspired 3D printing approach to create lightweight structures with hierarchical architectures, complex geometries and unprecedented stiffness and toughness. Using the self-assembly of liquid crystal polymer molecules combined withorienting the molecular domains with the print path, we can reinforce the polymer according to the expected mechanical stresses. The resulting material is recyclable and leads to stiffness, strength and toughness that outperform state-ofthe- art 3D printed polymers by an order of magnitude and rival even high-performance composites. Thermotropic LCPs form nematic liquid crystalline domains when molten. These domains can be aligned in the FDM nozzle along the extrusion direction. After exiting the nozzle, solidification stops the thermal reorientation of the molecules due to the cessation of flow resulting in a skin-core morphology. The maximal Young’s modulus and strength were achieved when printing parallel (0°) to the loading direction (17 GPa stiffness and 400 MPa strength). The dependence of the modulus on the print direction can successfully be predicted using a classical laminate theory approach. It is possible to adapt the local material architecture to the specific loading conditions that are applied to the part by designing the filament deposition direction during 3D printing. We show 3D printed objects with stressadapted print line architecture with mechanical properties that are much stronger than state-of-the-art 3D printed polymers and rival the highest performance lightweight materials using a readily available polymer and a commercial desktop printer. In addition, we present a new approach to combine conventional 3D printing with in-situ spinning of fibres. By controlling the volume of molten polymer at the nozzle tip and rapidly translating the printhead, we are able to spin fibres with diameters down to 20 um, reaching tensile strength and Young’s modulus as high as 2.6 GPa and 208 GPa, respectively. These values are comparable to those of carbon fibres, which require energy-intensive fabrication processes. By spin-printing complex-shaped structures with unusual fibre-reinforcing architectures, we show that this new manufacturing platform opens new opportunities for the design and fabrication of lightweight parts combining recyclability and high mechanical performance. @en