Described is a kit for producing a crosslinked gel for surrounding urinary calculi and/or fragments thereof, more particularly kidney stones and/or fragments thereof, comprising a composition (A) comprising one or several cationically crosslinkable polymer(s), and a composition (B) comprising one or several crosslinking agent(s) for crosslinking the cationically crosslinkable polymer(s), wherein composition (A) and/or composition (B) additionally comprise(s) magnetizable particles or the kit additionally comprises a composition (C) that contains magnetizable particles. Upon contact of composition (A) with composition (B) in a region of the urinary tract, more particularly the kidney, that contains urinary calculi and/or fragments thereof, more particularly kidney stones and/or fragments thereof, a crosslinked gel is formed that partly or fully surrounds the urinary calculi and/or fragments thereof, more particularly kidney stones and/or fragments thereof, and that contains the magnetizable particles. The gel together with the urinary calculi and/or fragments thereof, more particularly kidney stones and/or fragments thereof, can then be removed from the body by using magnetic interactions.
