A device comprising - a housing , - a first chamber within the housing, wherein the first chamber contains a first material, - a second chamber comprising a first piston and a second piston , wherein the first piston and the second piston are axially moveable within the second chamber , and - a second fluid material initially contained within the second chamber between the first piston and the second piston , wherein the device is adapted such that activation of the device causes movement of one of the first piston and the second piston in an axial direction of the device thereby - moving the other one of the first piston and the second piston into the same axial direction of the device , - opening a fluid communication path between the second chamber and the first chamber and - expelling the second material from the second chamber into the first chamber via the fluid communication path, wherein the device further comprises a plunger which closes a proximal end of the first chamber within the housing , wherein the plunger contains the second chamber , wherein the plunger is axially moveable within the housing of the device , wherein axial movement of the plunger into a proximal direction within the housing activates the device and causes a pressure drop in the first chamber , such that the second fluid material is pulled into the first chamber to promote mixing and/ or reconstitution of the first material and the second material, characterized in that a non-return mechanism between the plunger and the housing prevents the plunger from moving back in a distal direction opposite to the proximal direction until the plunger has moved through its full proximal stroke. - a housing , - a first chamber within the housing, wherein the first chamber contains a first material, - a second chamber comprising a first piston and a second piston , wherein the first piston and the second piston are axially moveable within the second chamber , and - a second fluid material initially contained within the second chamber between the first piston and the second piston , wherein the device is adapted such that activation of the device causes movement of one of the first piston and the second piston in an axial direction of the device thereby - moving the other one of the first piston and the second piston into the same axial direction of the device , - opening a fluid communication path between the second chamber and the first chamber and - expelling the second material from the second chamber into the first chamber via the fluid communication path, wherein the device further comprises a plunger which closes a proximal end of the first chamber within the housing , wherein the plunger contains the second chamber , wherein the plunger is axially moveable within the housing of the device , wherein axial movement of the plunger into a proximal direction within the housing activates the device and causes a pressure drop in the first chamber , such that the second fluid material is pulled into the first chamber to promote mixing and/ or reconstitution of the first material and the second material, characterized in that a non-return mechanism between the plunger and the housing prevents the plunger from moving back in a distal direction opposite to the proximal direction until the plunger has moved through its full proximal stroke. <EOS>