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Additive Manufacturing has significantly impacted circular design, expanding the opportunities for designing new artifacts following circular economy principles, e.g., using secondary raw materials. Small-format 3D printing has reached a broader audience of stakeholders, including end-users, when dealing with filament feedstocks from plastic and biomass waste. However, using large-format extrusion-based additive manufacturing with recycled feedstocks remains challenging, resulting in limited applications and awareness among practitioners. This work analyzes the most relevant product applications using large-format material extrusion additive manufacturing with recycled plastics and biomass waste feedstocks. It reviews the case studies from 2010 to mid-2024 dealing with new materials and applications from academic research and practical contexts. The applications were analyzed to outline the current situation and trends for large-format 3D printing with recycled plastics- and biomass-based feedstocks, focusing on secondary raw materials, manufacturability, impact on product aesthetics, application fields, and products. Despite more consolidated sectors, new technical applications using granulate feedstock systems, e.g., transportation, are emerging. Academic research studies new secondary raw materials and distributed practices through large-format 3D printing. Practitioners are exploiting different approaches to design products, optimizing building times, costs, and material usage through different manufacturing strategies, strengthening the product identity by highlighting circularity. Spreading specific expertise could enlarge the range of application sectors and products, as well as foster real-world collaborations and scaling-up. Thanks to this work, new synergies between the research and practical contexts can be encouraged for new circular economy practices, detecting and exploring new scraps, material categories, or Additive Manufacturing processes in the future. [ABSTRACT FROM AUTHOR]

There is an ongoing effort to advance methodologies for culturing functional photoreceptors in vitro for retinal regenerative strategies. To support the formation of functional photoreceptors, a scaffold should replicate the native environment. The aim of this study was to optimize a sodium alginate–gelatin (SA-G) bioink to mimic the retinal properties while ensuring the printing of constructs with high shape fidelity. The optimized bioink was thoroughly characterized in terms of its physical, mechanical, and rheological properties, printability assessment, and preliminary biocompatibility. The material showed a constant degradation rate, which is crucial for effective tissue regeneration as it provides support for cell differentiation and polarization while gradually degrading to allow cell proliferation and matrix deposition. The optimized bioink displayed stiffness comparable to the native photoreceptor layer, potentially providing appropriate mechanical cues for photoreceptor maturation. Additionally, it exhibited shear-thinning behavior, the presence of yield stress, and fast recovery kinetics, which are essential for successful extrusion. The high shape fidelity of 3D-printed constructs suggested the feasibility of printing complex patterns to drive photoreceptor polarization. The preliminary cell results demonstrated homogeneous cell distribution and sustained cell viability over time. Overall, these findings indicate that the optimized bioink can provide the mechanical and topographical cues necessary for cultivating photoreceptors in vitro for retinal regeneration. [ABSTRACT FROM AUTHOR]

The early-age material parameters of three-dimensional (3-D)-printable concrete defined under the umbrella of printability, namely, pumpability, extrudability, buildability, and the "printability window/open time," are subjective measures. The need to correlate and successively substitute these subjective measures with objective and accepted material properties, such as tensile strength, shear strength, and compressive strength, is paramount. This study validates new testing methodologies to quantify the tensile and shear strengths of printable fiber-reinforced concretes still in their fresh state. A tailored mixture with high sulfoaluminate cement and nonstructural basalt fibers has been assumed as a reference. The relation between the previously mentioned parameters and rheological parameters, such as yield strength obtained through International Center for Aggregates Research (ICAR) rheometer tests, is also explored. Furthermore, in an attempt to pave the way and contribute toward a better understanding of the mechanical properties of 3-D-printed concrete, to be further transferred into design procedures, a comparative study analyzing the work of fracture per unit crack width in three-point bending has been performed on printed and companion nominally identical monolithically cast specimens, investigating the effects of printing directions, position in the printed circuit, and specimen slenderness (length to depth) ratio. [ABSTRACT FROM AUTHOR]