Abstract
<title>Abstract</title> <p>Core-shell structures, widely observed in nature and engineering systems, offer functional advantages by spatially separating materials within a single architecture. While these structures have been increasingly adopted in advanced manufacturing, including 3D printing, even more complex devices are enabled by printing fibers whose composition changes along the length. Achieving sharp transitions between these regions can be beneficial in many applications. Here, we characterize the dynamic switching of core-shell 3D printing nozzles, which allows on-demand transitions between core-only, core-shell, and shell-only print modes. We investigate the effects of the nozzle retraction degree and nozzle diameters and achieve programmable fiber architectures with transition lengths as small as 0.81 times the nozzle diameter. The technology is leveraged to fabricate soft 3D grid structures capable of implementing logic circuits such as switches, AND gates, and OR gates. It was also used to print flexible soft circuits for two-stage operational amplifiers, which include intersecting conductive lines, demonstrating the advantage of the selective insulation. This versatile printing approach opens new possibilities for fabricating complex, multimaterial geometries in applications ranging from soft electronic devices to biomedical sensors.</p>