Conventionally used metal biomedical devices in the medical field are often used for the part of the body that need strength, such as bone and tooth. 
The reason is that the metal biomaterials used for such devices have superior mechanical properties to polymeric materials and ceramic materials. 
Conventional metallic biomedical devices, such as dental implants, total hip prosthesis, fracture fixation systems, stents, etc.  will remain inside of the body until removal thereof by operation etc.  after being implanted in the living body, and it is desirable that some of the devices are promptly removed after the restoration of peripheral tissues. 
For example, in the case of coronary stents, they become unnecessary after the restoration of damaged vascular tissues by opening of the narrowed area. 
However, since the removal needs an open chest surgery and gives large physical, mental, temporal, and financial burden to the patient the coronary stents are left behind inside of the body in most cases. 
In such a case, the difference in the mechanical properties between the metallic materials that form the device and the living tissue causes mechanical stimulation at every pulsation of the heart to surrounding vascular tissues of the device, resulting in possible induction of the restinosis by the intimal thickening. 
Moreover, removal of the device by reoperation is not often performed in fracture fixation systems.  Therefore, metal fixtures having a strength superior to that of the bones will support most of the load and sufficient loads are not applied for the bones, leading to insufficient restoration of the bones. 
Under these conditions, biodegradable polymeric or ceramic materials have been proposed. 
In some cases, however, the biodegradable polymeric and ceramic materials cannot serve as substitute for metallic biomedical devices in respect of their mechanical properties. 
Meanwhile, implant devices composed by biodegradable metallic materials in the living body have been proposed (for example, refer to Patent Documents 1 and 2).     Patent Document 1: PCT National Publication No.  2001-511049    Patent Document 2: Japanese Patent Application Laid-Open No.  2004-160236