Patent ID: 8273055

Claim:
A vacuum retractable safety syringe, comprising: a syringe body having a distal end and a proximal end; a piston disposed within the syringe body and extending through the proximal end of the syringe body, the plunger being traversable between a retracted position and an engaged position; a needle assembly removeably engageable to the distal portion of the syringe body; a variable fluid chamber in fluid communication with the external environment through the needle assembly, the piston forming a proximal wall of the variable fluid chamber, the plunger configured to reduce the volume of the variable fluid chamber when the plunger is traversed toward the engaged position; a variable vacuum chamber sealed from the external environment, the variable vacuum chamber increasing in volume as the piston is traversed toward the engaged position and creating a force in a proximal direction which retracts the needle assembly into the syringe body when the needle assembly is released from engagement with the distal portion of the syringe body; wherein a diameter of the variable fluid chamber is less than a diameter of the variable vacuum chamber.