Wearable injection device

A wearable injection device adapted to be placed on the body of a user and to perform a subcutaneous injection at an injection site on the skin of the user over some time after activation of the device, comprising:

• a base plate for interfacing the skin of the user,
• an osmotic actuator,
• at least one plunger, which is movable by osmotic pressure in the osmotic actuator,
• a trigger button to initiate the injection,
• a cartridge containing a therapeutic agent,
• a needle with a sharpened end, and
• wherein the osmotic actuator comprises:
• a low-pressure chamber containing a solution,
• a high-pressure chamber containing a solution,
• an activation chamber containing a solvent, and
• a forward osmosis membrane,
• wherein the activation chamber and the low-pressure chamber are separated by a barrier and the high-pressure chamber and the low-pressure chamber are separated by the forward osmosis membrane
• wherein the volumes of both low-pressure chamber and high-pressure chamber are expandable,
• wherein a pressure large enough to move the solvent through the barrier and into the low-pressure chamber is induced in the activation chamber during activation of the actuator, and
• wherein force exerted on the trigger button activates the wearable injection device, including:
• mechanically advances the sharpened end of the needle so as to be inserted into the skin of the user at the injection site through an opening in the base plate,
• establishes fluid communication between the injection site and the cartridge simultaneous with or after the insertion of the sharpened end of the needle into the skin of the user at the injection site, and
• activates the osmotic actuator to inject the therapeutic agent from the cartridge into the user through the needle.