A stent includes a first portion including first and second bands of cells that flare outwardly when the stent is expanded from a contracted to a flared condition, and a second portion connected to the first portion by flexible connectors. The hard mask and the electrically insulating layer are selectively etched in sequence using a mask to define an opening therein. As a result, the electrical system is capable of also powering a second electric motor that drives the spreader. The button may be used to move the locking mechanism between locked and unlocked positions. The stopping portion is formed with a free end abutted against an inner periphery of the open recess. The filtering device consists of a body filled with a filtering material and is provided with at least one outlet in the base of thereof, a lid having a water inlet and an air outlet, and at least one fixing means disposed between the body and the lid, wherein the fixing means is provided with at least one valve.