Hip prosthesis is a very good example of biomaterials restoring function and livelihood to the patients.  Although most hip implant surgeries are performed on older patients, young patients are not ruled out.  The two categories however are separated due to the fact that a child's bones will grow and be more active. 

An adult patient will more than likely have a hip implant that will involve a cement to adhere the bone to the metal.  This is needed because there is little or no bone-tissue growth around the material.  A child's bone will tend to have more bone-tissue growth around the material and thus form a naturally occurring adhesive.  A naturally occurring adhesive is ideal as the foreign material in essence becomes a part of the body.  This does not however solve all the problems with the bone-metal interface.

A new technique called gene therapy is also helping the situation where as it helps older patients get this needed growth around the material.  Gene therapy is still being tested for bone growth, but looks very promising and is currently in stage three testing and could definitely revolutionize the artificial hip industry. 

Historically, hip implants were comprised of a stainless steel shaft and ball with a polyethylene socket.  Due to problems with osteolysis, aluminum was then used for its better biocompatibility mechanical and weight characteristics.  Aluminum was later found to increase your chances of getting Alzheimer's Disease.  Titanium has thus been used since and has not created any biocompatibility problems, but has produced problems in the mechanical properties.  A movement in research has thus pushed material scientists to create a biocompatible material with mechanical properties closer to that of bone.  The main atomic ingredient of these alloys are usually comprised of titanium.  Some of the other metals that are known as biocompatible are:  Palladium, Platinum, Vanadium, Niobium, Manganese.