After demonstrating the precise control over the RD zone that the coaxial 3D flow-focusing microfluidic device provides, we explored its versatility in continuously printing Class I and II fibers. As shown in Figure , Class I and II fibers can be printed to construct different architectures, including 3D structures and intricate patterns (Figure , respectively), or even to produce freestanding isolated fibers (Figure ). Regardless of the printing configuration, the fibers clearly exhibit a color change from pink to white upon heating to 100 °C, indicating the LS to HS transition in [Fe(Htrz)₂(trz)]BF₄ (Figure ). This effect is reversible, with the pink color returning when the fiber is cooled back to room temperature. This continuous printing of thermochromic fibers overcomes many of the challenges previously encountered in the processing of SCO materials. However, note that in Class I and Class II fibers, the SCO material can only be distributed radially within the alginate fiber. In contrast, nature provides remarkable examples of compositional control in freestanding structures. For example, spiders can modulate the chemical composition of proteins within their silk fibers sequentially and non-radially across the fiber's diameter, tailoring the silk precisely to its intended function. Inspired by this natural phenomenon, we redesigned the microfluidic device to achieve temporal control over the spatial distribution of [Fe(Htrz)₂(trz)]BF₄ within the fibers to generate SCO-encoded fibers.