Disclosed herein are methods and systems for the preparation of a co-injection molded multilayer plastic article. Some methods include co-extruding a combined polymeric stream having an interior core stream encased by an inner stream and an outer stream. A volumetric ratio of the inner stream to outer stream is adjusted during injection of the combined stream into the a mold cavity to alter a streamline along which the interior core stream flows thereby forming cohesion member that structurally interlocks the interior layer with the inner layer, with the outer layer or with both. Some embodiments reduce or eliminate a need for addition of an adhesive in the composite stream to prevent delamination of layers of the resulting multilayer plastic article. In some embodiments, cohesion members may be employed to produce a desired cosmetic effect in a resulting article.