An apparatus and method for seamless closed mold microreplication using a one-piece expandable mold are disclosed. The apparatus includes an expandable mold having a plurality of microstructured features on the inner surface thereof. The apparatus also includes a means for elastically expanding the mold in order to remove the finished molded article. The expandable mold may be used to make seamless articles having microstructured features, such as an illumination device comprising a fiber core having a plurality of microstructured light extraction structures on the surface thereof.