Apparatus and methods for lyophilizing and sealing a medicament within a medical delivery device having an opening. The apparatus includes a stopper for sealing the opening. The stopper has one or more elongated members extending from a base, in a direction that is parallel to a central axis of the base. The one or more members are set radially away from the axis and define a coaxial central well. The central well tapers continuously towards the base. The elongated member or members define a void that partitioned from the central well. The elongated member or members engage a device inner wall and support the base away from the opening. The void allows gas exchange between a device interior and a device exterior when the stopper is in a first position. The gas may be a lyophilization byproduct that escapes from the device interior between the inner wall, the base and the member or members. The stopper can be advanced into the device to seal the opening. The stopper reduces the exposure to humidity of medicament desiccated within a device.
