Device for compressing a hydrogel, comprising - a separate graft frame comprising a circumferential frame member and a membrane bottom connected to said frame member, wherein the graft frame is designed to receive said hydrogel so that a hydrogel layer is formed covering said membrane bottom, - a guiding frame having a plurality of guiding rods extending along a compression direction, - a filter plate, - a first component comprising a base having a plurality of openings, wherein each opening is associated to one of the guiding rods, wherein the first component is designed to be arranged on the guiding frame in an operating mode of the device such that each guiding rod extends through its associated opening, wherein the first component further comprises a circumferential wall protruding from said base of the first component, so that the first component forms a container that is designed to receive the filter plate and the graft frame in said operating mode so that the filter plate is arranged between a bottom of said container and the membrane bottom of the graft frame, - a second component comprising a base having a plurality of openings, wherein each opening is associated to one of the guiding rods, wherein the second component is designed to be arranged on said first component in said operating mode, such that each guiding rod that extends through its associated opening of the first component is also inserted into its associated opening of the second component so that the second component is guided by said rods along the compression direction, - a separate piston that is designed to be connected to said second component in a releasable manner in said operating mode of the device, wherein in said operating mode the second component is designed to press the piston along the compression direction against said hydrogel layer residing on the membrane bottom of the graft frame so as to compress the hydrogel layer between the piston and the membrane bottom. - a separate graft frame comprising a circumferential frame member and a membrane bottom connected to said frame member, wherein the graft frame is designed to receive said hydrogel so that a hydrogel layer is formed covering said membrane bottom, - a guiding frame having a plurality of guiding rods extending along a compression direction, - a filter plate, - a first component comprising a base having a plurality of openings, wherein each opening is associated to one of the guiding rods, wherein the first component is designed to be arranged on the guiding frame in an operating mode of the device such that each guiding rod extends through its associated opening, wherein the first component further comprises a circumferential wall protruding from said base of the first component, so that the first component forms a container that is designed to receive the filter plate and the graft frame in said operating mode so that the filter plate is arranged between a bottom of said container and the membrane bottom of the graft frame, - a second component comprising a base having a plurality of openings, wherein each opening is associated to one of the guiding rods, wherein the second component is designed to be arranged on said first component in said operating mode, such that each guiding rod that extends through its associated opening of the first component is also inserted into its associated opening of the second component so that the second component is guided by said rods along the compression direction, - a separate piston that is designed to be connected to said second component in a releasable manner in said operating mode of the device, wherein in said operating mode the second component is designed to press the piston along the compression direction against said hydrogel layer residing on the membrane bottom of the graft frame so as to compress the hydrogel layer between the piston and the membrane bottom.