Hypodermic syringe cartridge with non-retractable drive piston

Claim 1

An insert, part of which is permanently embedded within the drive piston that is pushed by an actuating rod within the tubular member of a hypodermic syringe to expel fluid from the hypodermic syringe, characterized in that said insert simultaneously serves the dual purposes of preventing retraction of the drive piston from any position along the tubular member to which the drive piston has been advanced and of preventing penetration of the drive piston by a hypodermic needle, thereby rendering the hypodermic syringe pilfer-proof, said insert comprising: a resilient element spanning the bore of the tubular member when inside the tubular member, impenetrable by a hypodermic needle, and extending radially when removed from the tubular member to a diameter greater than the bore of the tubular member so that peripheral portions of said resilient element are forced to bow rearward when the drive piston is inserted into the tubular member from the rear; said peripheral portions frictionally contacting the inside wall of the tubular member, the friction between said peripheral portions and the inside wall resisting rearward motion of the drive piston at all positions of the drive piston within the tubular member so that any attempt to pull the drive piston toward the rear of the tubular member will force said peripheral portions to jam even more tightly against the inside wall of the tubular member, thereby preventing retraction of the drive piston at all positions of the drive piston within the tubular member.