Of course, since the hydrogels only remain in the body for a controlled period of time, these hydrogels would not be useful in permanently closing off an aneurysm. [0020] Fearnot et al, in U.S. Pat. No. 5,609,629, disclose an implantable medical device that provides a controlled release of an agent, drug, or bioactive material into the vascular or other system in which a stent or other device is p