Patent ID: 8517986

Claim:
A retractable safety syringe for preventing accidental needle pricking and needle reuse after completion of an injection stroke, the syringe comprising: a syringe body defining a proximal portion and a distal portion; a seal located in the proximal portion of the syringe body; a needle coupled to a needle holder, the needle holder removeably engageable to the body distal portion; a piston disposed within the body and biasable to the body proximal portion via a vacuum force when the piston is traversed toward the body distal portion, the piston being traverseable between a retracted position and an engaged position; a vacuum chamber disposed within the syringe body, the vacuum chamber located intermediate the piston and the seal, the vacuum chamber configured to provide a vacuum force on the piston in a direction from the syringe body distal portion toward the syringe body proximal portion upon movement of the piston toward the syringe body distal portion responsive to the distal translation of the piston; a fluid chamber disposed within the syringe body, the fluid chamber located distally from the piston, the fluid chamber having a distal and proximal end, the proximal end of the fluid chamber being sealed, the fluid chamber in fluid communication with the needle through the distal end of the fluid chamber and configured to be reduced in volume as the piston is traversed towards the engaged position; and a shaft attached to the piston and disposed within the body, the shaft comprising an engaging portion and a non-engaging portion, the shaft extending through the proximal portion of the body and proximate the seal, traversal of the shaft though the body operative to traverse the piston within the syringe body between a storage position and working positions, the engaging portion proximate the seal and in sealing engagement with the seal in the working positions and the non-engaging portion proximate the seal and in a substantially non-sealing engagement with the seal in the storage position.