When the ethanolic solution of Fe(BF4)2 was introduced through the side inlets and the aqueous alginate/Htrz solution through the central inlet, we obtained robust, solid fibers with a pink hue (Class I fibers). Conversely, injecting the Fe(BF4)2 solution through the central inlet and the alginate/Htrz solution through the side inlets produced darker composite fibers (Class II fibers).