materials that swell from hydration or osmotic pressure this swelling and expansion can be used to enhance water transport through the material the enlargement of the device can also be achieved with the use of mechanical springs that are embedded into the device alternatively the height of the device may be expanded by use of an internal spring made of one or more pieces of metal or plastic that can exert an expansion force greater than 1 newton it is anticipated that expansions greater than 10 in height will be useful for this device and are included in this invention additional adhesion to the vertebral bodies may be obtained by incorporating surface modifications on the cranial and caudal faces of the prosthesis the modifications may consist of physical scoring or indentations of the surface chemical irritants incorporated on the surface biochemical agents modified on the surface or small fibers that extend from the faces to stimulate adhesion to a vertebral body or vertebral endplate these fibers and surface modifications may induce a fibrotic or osteogenic reaction from the person to enhance attachment to the vertebral bodies fibrosis may be induced by a plurality of methods including open pore or rough surfaces porous structures with undercuts incorporation of osteoconductive or inductive agents incorporation of other polymers such as polyester fabric or fibers incorporation of other biologically active molecules such as tumor necrosis factor or collagen metal solid or mesh rough surface with features greater than 5 nanometers nm the roughness of the surface may include pores with undercuts of 2 millimeters mm in diameter similar to a sponge the surface may also be biochemically modified to provide enhanced water transport or physically modified to.