Abstract: A stopper for a syringe including a body having a tail adapted for attachment to a plunger of the syringe, and a head, the head having a outer surface that is convex, such that the outer surface is curved with an apex of the curvature extending away from a plane orthogonal to the longitudinal axis of the stopper and comprising an outer perimeter of the outer surface and the apex of the outer surface of the head is higher than the outer perimeter of the outer surface when the stopper is viewed from a side in a direction perpendicular to the longitudinal axis of the stopper. The stopper may optionally include a plurality of protrusions extending from an outer surface of the head. Also, a syringe including such a stopper.

Abstract: The invention relates to a valve stopper configured to be positioned inside a barrel of an injection device for injecting a composition through a distal, including: a membrane having a proximal and distal face, the membrane being configured to separate a, distal chamber of the barrel from a proximal chamber; a lateral wall extending from the membrane to define a distal cavity, the lateral wall having a circumferential sealing surface configured to sealingly engage the inner surface of the barrel; where the proximal face presents a concave shape and the membrane includes a notch extending through the membrane between the proximal and distal face, being configured to selectively create a fluid path through the membrane from the proximal face to the distal face depending on the pressure exerted by a composition onto the proximal face of the membrane for transferring fluid only from the second chamber to the first.