A locking syringe with an integrated bias member, for delivering medical fluids at high pressure, can include a housing, a shaft, a piston, a cap assembly, a bias member, and a locking member. A distal end of the housing can interface with a patient delivery apparatus. A piston can be connected to the distal end of the shaft and can include a peripheral sealing surface that can slidably engage the inside surface of the housing to form a movable seal. The cap assembly at the proximal end of the housing can engage the shaft. A base cap can secure the piston within the housing. The bias member can have a distal end coupled to the piston and a proximal end restrained, such as to help pressurize the internal cavity. The user-actuatable locking member can user-selectively engage and inhibit unwanted movement of the shaft.