The invention relates to a device and a method for compressing a hydrogel layer (H), wherein a separate piston (600) that is designed to be connected to a second component (400) of the device in a releasable manner in an operating mode of the device, particularly by means of a latching connection, presses along a compression direction (C) against said hydrogel layer (H) residing on a membrane bottom (501) of a graft frame (500) so as to compress the hydrogel layer (H) between the piston (600) and the membrane bottom (501).
