Wearable injection device

A wearable injection device, comprising:

• a cartridge with a septum and a movable plunger, the plunger movable along a longitudinal axis of the cartridge and the cartridge containing a therapeutic agent to be injected, and
• a needle assembly, the needle assembly comprising:
• a first part and a needle, the needle held by the first part and the needle configured to penetrate an injection site on the skin of a user, and the first part and the needle movable in a first direction that is mainly perpendicular to the longitudinal axis of the cartridge,
• a second part and a penetrating portion, the penetrating portion held by the second part and the penetrating portion configured to penetrate the septum of the cartridge, and the second part and the penetrating portion movable in a second direction that is along the longitudinal axis of the cartridge, and
• a spring that biases the first part toward an initial position in which the needle is hidden within the wearable injection device,
• wherein, during activation of the device:
• the first part with the needle is moved in the first direction against the biasing of the spring to an inserted position in which the needle penetrates the injection site;
• and
• the second part is moved in the second direction so that the penetrating portion penetrates the septum of the cartridge, and a locking portion of the second part engages a portion of the first part to preclude movement of the first part in a direction opposite to the first direction so that the second part locks the first part in the inserted position with the needle penetrated into the injection site,
• wherein a fluid communication between the first part and the second part is established simultaneous with or after the locking of the first part in the inserted position, and
• wherein movement of the moveable plunger injects the therapeutic agent out through the needle into the user, and wherein the second part is moved in a direction opposite to the second direction by the movable plunger near an end of an injection of the therapeutic agent so that the locking portion disengages the first part and the first part is released from the inserted position and moved back toward the initial position by the spring.