As shown in Figure , the redesigned microfluidic device features a central channel that is fed by two inlets, while one of the original side channels has been removed, leaving a single side inlet (Figure and). Using this configuration, customized fibers (Figure ) were fabricated by injecting a 0.75% (w/v) sodium alginate solution with 2M Htrz through central inlet 1, a pure 0.75% (w/v) sodium alginate solution through central inlet 2, and a 0.4 M ethanolic solution of Fe(BF₄)₂ through sheath flow inlet 3 (see the SI for further details). By selectively activating the central inlets while keeping the reagent-laden flow of inlet 3 consistently active throughout fiber fabrication, we successfully produced continuous SCOencoded fibers on-the-fly. When only central inlet 1 is activated alongside the reagent-laden flow of inlet 3, we obtain alginate fragments fully loaded with SCO particles, closely resembling Class I fibers, as confirmed by SEM and EDX analysis (Figure ). Activating only central inlet 2 together with the reagent-laden flow of inlet 3 produces pure alginate fragments, confirmed by the absence of nitrogen throughout the fiber (Figure ). Finally, simultaneously activating all the inlets yields alginate fiber fragments with SCO particles distributed non-radially across the fiber's diameter, i.e. only on one side (Figure ), as evidenced by the distinct "two-faced" structure observed in SEM images and the EDX analysis, which shows differing Fe intensity across the central symmetry line. To our knowledge, this represents the first demonstration of spatiotemporal control over the chemical composition of an SCO composite material achieved in a single step, through a continuous process, and with remarkably short preparation times (within seconds; see SI). This chemical encoding of molecular switches unlocks exciting new possibilities for their application in real-world devices. For instance, by enabling the precise printing of these SCO composites and SCO-encoded fibers into defined shapes and architectures, we pave the way for their integration into devices, expanding the possibilities for application-specific customization and facilitating their real-world implementation.