A kind of implantable medical device includes the main body with the flexible outer layer of encapsulation compositions. The composition includes one or more first microballoons, one or more second microballoons and carrier. Each first microballoon includes the first therapeutic agent and the wall containing the first biodegradable polymer, which encapsulates first therapeutic agent. Each second microballoon includes second therapeutic agent and the wall containing biodegradable polymer, which encapsulates the second therapeutic agent.
