US Patent 7066907 Injection devices

A one-shot throwaway injection device has a barrel that houses a syringe initially in a retracted state held back by a trigger against a drive spring. Actuation of the trigger causes the syringe to be thrust forwards by the spring acting on its plunger until the needle is fully projecting, and then the dose is ejected by the final expansion of the spring. Release of the trigger allows a return spring to urge the syringe back and retract the needle. The barrel is a unitary plastics moulding of two longitudinally split halves hinged together with the trigger integrally formed with one of these halves. The other components and the syringe are positioned in one half which is then closed up and fastened to the other half to complete the barrel.