A method of manufacturing a composite interbody device is provided, comprising: assembling superior and inferior endplates: wherein the surface features increase surface area of the bone interface layer, to optimize contact with bone at an implant site； and forming a porous core interface layer on the central barrier layer opposite the bone interface layer； diffusion bonding under heat and pressure the core interface layer with the central barrier layer and the bone interface layer coating the bone interface side with hydroxyapatite； placing the inferior and superior endplates in a mold, on each side of a core cavity, with the core interface layers facing the core cavity and the bone interface sides facing away from the cavity； and injection-molding molten plastic into the core cavity, to form a plastic core between the endplates and bonded with core interface sides of the core interface layers； wherein molten plastic extrudes into pores of the core interface layers, to bond with the endplates.
