This article investigates the mechanical behavior of polyamide and carbon fiber‐reinforced (CFR) polyamide structures produced by Fused Filament Fabrication. CFR improves solid polyamide's tensile strength and modulus by more than 200% and 800%, respectively. The enhancement is highest in the parallel raster due to the alignment of the fibers in the printing direction. The compression tests of gyroid, honeycomb, and Voronoi cellular structures revealed the effect of geometry and fiber reinforcement on energy absorption performance. CFR gyroid infill offers the best performance with a specific energy absorption capacity reaching 10 kJ/kg and an efficiency close to 50%. Fiber reinforcement improves energy absorption by a factor of four or higher while increasing the weight by only 10%. The energy absorption capacity of the reinforced polyamide offers enormous potential for developing new lightweight load‐bearing and impact‐absorbing structures.

Material extrusion additive manufacturing (MEAM) has revolutionized the production of complex designs while minimizing the amount of effort required due to its simple production pipeline. However, MEAM naturally comes with a well-known trade-off; higher build resolution often tends to enhance the product quality at the cost of a slower build rate. Nozzles, the standard tool for thermoplastic extrusion in MEAM, have evolved into a crucial component of the process for controlling the product’s build resolution. The purpose of this study is to investigate the details of a novel extrusion system that makes use of a rotating nozzle with an unconventional aperture, in contrast to its typical (i.e., circular-orifice) counterparts. The unique nozzle configuration that lacks axial symmetry allows for precise control over the effective dimension of the extrusion via rotational guiding. By positioning the oblong orifice at intermediate orientations, the presented approach seeks to provide continuously variable intralayer and interlayer resolutions for MEAM processes. This paper explores the distinctive characteristics of this new nozzle design as well as the potential uses of the novel extrusion system. The outcomes of the conducted tests demonstrate the proof-of-concept for creating variable bead width within the layers, in addition to adaptable layer heights throughout the 3D objects. Possible limitations of the new approach and future perspectives are discussed in detail.

Geopolymers (GPs) are inorganic binders synthesised from reactive aluminosilicate materials such as metakaolin, fly ash, and blast furnace slag, using strongly alkaline solutions at room temperature. They are more environmentally friendly than Portland cement and exhibit high hardness, weathering resistance, thermal stability, and precise mouldability. These properties make them suitable for additive manufacturing (AM) and specialised underwater applications, such as encapsulating hazardous substances or stabilising corroding shipwrecks. This study investigates the compressive strength of metakaolin-based GP reinforced with recycled carbon fibres, comparing performance in different water environments over time. Samples were produced by mould casting in air, manual underwater extrusion, and AM via material extrusion with chemical reaction bonding (MEX-CRB) in air. The 3D-printed and mould-cast samples produced in air were stored for up to 3 months in different water environments with varying salt and mineral contents to assess durability, mechanical performance, and environmental impact at defined intervals. For manually printed underwater specimens, the storage period was extended to almost 6 months, with only conducted in tap water conditions. Mould-cast specimens in air reached ∼50 MPa, while MEX-CRB samples achieved ∼20 MPa; after 3 months in salt water, mould-cast samples retained ∼30 MPa, whereas printed ones remained below 20 MPa. Manually printed underwater samples increased from ∼8 MPa at casting to ∼14–15 MPa by week 4 before stabilizing. Microstructural observations showed crack-bridging by fibres, with random orientation in cast samples improving isotropic strength, while fibre alignment and higher porosity in printed samples limited performance. The water analysis results underscore the environmentally friendly potential of GPs in reducing environmental risks and developing sustainable methods for underwater construction and hazard prevention.

Glass offers unique advantages such as high optical transparency, thermal stability, and chemical resistance, making it indispensable in optics, microelectronics, sensing, and biomedical applications. However, its high melting point, brittle nature, and incompatibility with traditional manufacturing methods present significant fabrication challenges. Additive manufacturing (AM) introduces new possibilities for the glass industry by enabling the fabrication of customised, complex 3D structures and the integration of glass with other compatible materials. In particular, multi-material glass additive manufacturing (MMGAM) has emerged as a promising frontier, enabling both the spatial tuning of glass composition, dopants, and functionalities, as well as the co-fabrication of glass with dissimilar materials, such as polymers, metals, or ceramics, within a single component using integrated AM platforms. This paper provides a comprehensive overview of the current state of MMGAM, structured around four key themes: (i) key material properties and interfacial compatibility considerations, (ii) AM techniques adapted for multi-material glass systems, (iii) material combinations and strategies for functional integration, and (iv) future challenges and research directions. Particular emphasis is placed on the challenges of interfacial bonding, material compatibility, and the formulation of printable glass systems suitable for co-processing with other materials. The review explores recent strategies for enabling multifunctional, integrated architectures that combine optical, structural, or chemical functionalities within a single component. By synthesising current advances and outlining key research gaps, this work aims to accelerate the development and broader adoption of MMGAM technologies.

Geopolymers are inorganic aluminosilicate binders formed by alkali activation of reactive powders, offering a sustainable, low-carbon alternative to Portland cement. Their rapid setting and chemical durability make them well-suited for additive manufacturing (AM) in demanding environments, including underwater construction, where chemical stability is essential for both structural integrity and environmental safety. This study evaluates two metakaolin-based formulations designed for underwater extrusion, differing in activator chemistry and rheology control. Standardized leaching tests revealed alkaline but stable leachates with strong immobilization of most ions; major anions and total dissolved solids remained within regulatory thresholds. Limited exceedances were observed—soluble organic carbon in the NaOH-activated mix and arsenic/selenium in the waterglass–sand system—highlighting specific areas for mix improvement rather than fundamental limitations of the material. Complementary radioactivity screening confirmed activity concentration indices well below the regulatory limit, with measured radionuclide activities falling comfortably within exemption ranges. Together, the leaching and radioactivity results demonstrate that both formulations provide robust matrix integrity and environmental compatibility, while highlighting clear opportunities for mix design improvements to further minimize ecological risks.