a spinal implant for replacing the natural nucleus of the disc made from a polymer such as hydrogel having a radiopaque material located within the polymer . the material may be in the form of a powder dispersed throughout the polymer or may be in he form of a powder dispersed in layers or in other specific locations within the polymer . the radiopaque material is metal such as gold , tungsten , titanium , tantalum or platinum . the metal may also be in the form of a foil or wire located within the hydrogel such as polyurethane , thereby making the implant visible on x - rays . other polymers besides hydrogel may be used with the radiopaque material being dispersed therein .