Implants are not always used for structural reinforcement.  You would not consider an artificial heart a structural reinforcement, but you would consider a pin in the ankle one.  Stents, and artificial systems are considered non-structural implants.  These types of implants and bio-materials can be made of more various materials such as ceramics and polymers.

It would be best to judge these types of implants on two key areas:  effectiveness and biocompatibility.  After all, what good is a biocompatible material if it is not effective and visa versa?  There are many types of tissue biocompatibility problems that can arise with more types of materials and molecules involved that delves more into medicine and out of the scope of this project.  For more information on this subject, please feel free to check the references of this site.