Plunger with reduced leakage during storage
A plunger seal for a drug delivery device may have a mobile and an enhanced sealing parked state. Optionally, the cartridge is stored with the plunger seal in the parked state. Optionally, drug discharge occurs with the plunger seal in the mobile state. For example in the parked state there may be increased normal force between the plunger seal and an inner wall of the cartridge. Optionally there is limited deformation of the plunger seal between the parked and mobile states. Optionally the plunger seal is biased to the parked state. Optionally, a distal force switches the plunger seal to the mobile state. For example, the plunger seal may have an inner cavity that is expanded radially by core. A biasing element optionally biases the core wedging it proximally to the parked state. A distal force on the core may push it distally to the mobile state.
1. A cartridge for a drug delivery device comprising:
a reservoir including a longitudinally oriented cylindrical bore having a proximal opening;
a plunger seal having a sealing region on an exterior surface thereof, said sealing region sized to fit closely into said cylindrical bore; said plunger seal including a cavity; and
a core fitting into said cavity and being movable relative to the cavity between a parked state of the plunger seal and a mobile state of the plunger seal, wherein:
the core is shaped to apply a radially outward force against an inner wall of said cavity, in the parked state, increasing a normal force between said sealing region and an interior wall of said cylindrical bore, and wherein a distal force applied to the core advances the core forward within the cavity into the mobile state, reducing the radially outward force against the interior wall of said cavity; and
an inner distal wall of the plunger seal abuts a distal head of the core to stabilize the core in the parked state, and at least one of an inner distal-most wall of the plunger seal and a distal-most head of the core is compressed to move the core into the mobile state.
2. The cartridge of claim 1 , wherein said core includes an interference element with a distally increasing radius and wherein said cavity includes a region with distally increasing radius.
3. The cartridge of claim 1 , wherein said core has a length less than 2 cm.
4. The cartridge of claim 1 , wherein an unstressed outer diameter of said sealing region ranges between 99 to 103% an inner diameter of said cylindrical bore.
5. The cartridge of claim 1 , wherein a maximum deformation of a diameter across said sealing region remains less than 0.5 mm.