Bioactive metallic glass is a subset of bioactive glass, wherein the bulk material is composed of a metal-glass substrate and is coated with bioactive glass in order to make the material bioactive. The reasoning behind the introduction of the metallic base is to create a less brittle, stronger material that will be permanently implanted within the body. Metallic glasses tout lower Youngs Moduli and higher elastic limits than bioactive glass, and as such, will allow for more deformation of the material before fracture occurs. This is highly desirable, as a permanent implant would need to avoid shattering within the patients body. Common materials which compose the metallic bulk include Zr and Ti, whereas some examples of the few key metals that shouldn't be used as bulk materials are Al, Be, and Ni.