An implantable medical device includes at least one frame 10,60 of curved legs 12 arranged substantially in a sphere with an end opening so that the frame defines a material capture chamber. A coupling member 18 is attached to the frame and to a stabilisation member 50 which may be a second frame 60. The legs may be made of a shape memory metal such as Nitinol and in use the frame may be compressed to around 75% of its maximum unrestrained diameter. Preferably the coupling member is flexible (although it may be rigid and pivoted instead) and exerts a restoring force to bias the frames towards an inline configuration； it allows the frames to tilt in use. Three frames may be coupled together (figure 8). The device is suitable for use as a vena cava filter or as an occlusion plug.
