A filter device for implantation in a gallbladder, comprising: a filter portion configured to filter gallstones of a certain minimum size to prevent them from exiting the gallbladder through an opening of the gallbladder； a blocking portion configured to push gallstones of a certain minimum size away from an opening of the gallbladder where the blocking portion is located distally from the filter portion with respect to the opening of the gallbladder； and, where the blocking portion and the filter portion do not attach to, or apply expansive radial force on, a wall of the gallbladder.
