Coaxial additive manufacturing (AM) is an emerging technology involving the simultaneous deposition of two or more materials with a common longitudinal axis. It has the potential to overcome the disadvantages associated with conventional single‐material AM for the production of core‐shell or multi‐core‐shell multimaterial structures. The coaxial AM techniques can be classified into extrusion and material jetting technologies. The extrusion‐based technologies rely on the co‐extrusion of multiple materials through a coaxial nozzle whereas the material jetting technologies are based on the introduction of a high voltage electric field between a coaxial nozzle and a grounded collector plate. This review is aimed to provide a comprehensive overview of multimaterial coaxial AM, including the technologies, nozzle designs, materials, and applications. The advances in coaxial AM and the benefits of this novel technology in various fields are highlighted. For instance, in biomedicine coaxial AM offers an exciting alternative to single‐material bioprinting for the fabrication of bio‐scaffolds and vascular networks as well as for tissue engineering and cell encapsulations. Coaxial AM is also a subject of growing interest in the fields of flexible sensors, e‐textiles, and printed electronics. Perspectives on the limitations, existing challenges, opportunities, and future directions for further development are also provided.
Nonplanar multi‐material additive manufacturing (AM) of piezoelectric devices is an important step for innovation in digital manufacturing. Herein this work, the development of a manufacturing platform based on multi‐material multi‐process AM that enables fabrication of piezoelectric and conductive electrode materials with complex planar and nonplanar (conformal) structures is reported. Also, the development of conductive and piezoelectric paste‐like printing materials, herein called inks, for extrusion‐based direct‐writing AM processes is presented. The developed inks are highly stretchable (e.g., up to 100% before breaking), easy to process, and less toxic compared to existing solvent evaporation‐based inks in the literature. Several piezoelectric energy‐harvesting (PEH) devices are fabricated. The innovative inks within a multi‐material multi‐process 3D printing platform can substantially broaden the design space of multi‐material AM and open up new opportunities for the production of application‐oriented parts that are more integrable, conformable, scalable, and versatile.
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