Retractable safety syringe with non-loaded seal

1. 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 needle removeably engageable to the body distal portion;

a piston disposed within the syringe body and biasable to the body proximal portion via a vacuum force when the piston is traversed toward the syringe body distal portion, the piston being traverseable between a retracted position and an engaged position;

a shaft attached to the piston and disposed within the body, at least one of the shaft and the syringe body including a seal, the shaft extending through the proximal portion of the body;

a vacuum chamber disposed within the syringe body, the vacuum chamber located intermediate the piston and the seal, the vacuum chamber configured to provide the 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; and

a fluid chamber disposed within the syringe body, the fluid chamber located distally from the piston, the fluid chamber having a distal end and a 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

wherein at least one of the shaft and the syringe body includes an engaging portion and a non-engaging portion, traversal of the shaft through the syringe 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.

2. The retractable safety syringe of claim 1 , wherein the needle is coupled to a needle holder, the needle holder removeably engageable to the body distal portion.

3. The retractable safety syringe of claim 1 , wherein the seal is located in the proximal portion of the syringe body.

4. The retractable safety syringe of claim 1 , wherein the seal is located on a proximal side of the vacuum chamber.

5. The retractable safety syringe of claim 1 , wherein the shaft includes the engaging portion and the non-engaging portion, and wherein the engaging portion has a first outer diameter and the non-engaging portion has a second outer diameter, the first outer diameter greater than the second outer diameter.

6. The retractable safety syringe of claim 1 , further including a brake member disposed in a first cavity of the syringe body, the brake member proximate the non-engaging portion and in a substantially non-frictional engagement with the non-engaging portion when the shaft is in the storage position, the brake member biased toward and frictionally engaged to the engaging portion for providing a braking force to maintain a position of the piston within the syringe body before completion of the injection stroke when the shaft is in the working positions, the brake member completely disengaged from the shaft after completion of the injection stroke by axially traversing the brake member into a second cavity so the vacuum force withdraws the needle into the syringe body to prevent accidental needle pricking and needle reuse.

7. The retractable safety syringe of claim 1 , wherein the non-engaging portion is positioned intermediate the piston and the engaging portion.

8. The retractable safety syringe of claim 1 , wherein the non-engaging portion is proximally offset from the piston in the storage position.

9. The retractable safety syringe of claim 1 , wherein the fluid chamber has a storage position volume that is a function of a distance between the piston and the non-engaging portion in the storage position.

10. The retractable safety syringe of claim 1 , wherein the piston is offset from the syringe body distal portion in the storage position.

11. 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 needle removeably engageable to the body distal portion;

a piston disposed within the syringe body and biasable to the body proximal portion via a vacuum force when the piston is traversed toward the syringe body distal portion, the piston being traverseable between a retracted position and an engaged position;

a shaft attached to the piston and disposed within the body, at least one of the shaft and the syringe body including a seal, the shaft extending through the proximal portion of the body;

a vacuum chamber disposed within the syringe body, the vacuum chamber located intermediate the piston and the seal, the vacuum chamber configured to provide the 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; and

a fluid chamber disposed within the syringe body, the fluid chamber located distally from the piston, the fluid chamber having a distal end and a 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

wherein at least one of the shaft and the syringe body includes an engaging portion, traversal of the shaft through the syringe body operative to traverse the piston within the syringe body between a storage position and working positions, the engaging portion offset from the seal in the storage position and in sealing engagement with the seal in the working positions, the engaging portion and seal sealing the vacuum chamber when the piston is in the working position, the vacuum chamber being substantially unsealed when the piston is in the storage position.

12. The retractable safety syringe of claim 11 , wherein at least one of the shaft and the syringe body includes a non-engaging portion, the non-engaging portion proximate the seal and in a substantially non-sealing engagement with the seal in the storage position.

13. The retractable safety syringe of claim 12 , wherein the non-engaging portion is positioned intermediate the piston and the engaging portion.

14. The retractable safety syringe of claim 12 , wherein the non-engaging portion is proximally offset from the piston in the storage position.

15. The retractable safety syringe of claim 11 , wherein engagement of the engaging portion with the seal causes the vacuum force in the vacuum chamber.

16. A method of operating an automatically retracting syringe, the method comprising:

receiving a syringe comprising:

a syringe body defining a proximal portion and a distal portion;

a fluid chamber within the syringe body;

a needle removeably engageable to the body distal portion;

a shaft coupled to a piston, at least one of the shaft and the syringe body including a seal, the other of the shaft and the syringe body including at least one engaging portion and at least one non-engaging portion, the piston disposed in a storage position within the syringe body and substantially maintained in the storage position by the at least one engaging portion, the non-engaging portion positioned proximate the seal and in substantial non-sealing engagement;

a vacuum chamber within the syringe body configured to urge the piston toward a retracted position;

depressing a thumb platform to traverse the piston toward the distal portion of the syringe during an injection stroke;

inducing a biasing force on the piston via the vacuum chamber to urge the piston assembly back toward the retracted position;

engaging the piston to the needle upon completion of the injection stroke;

disengaging the needle from the syringe body;

removing thumb pressure on the thumb platform; and

traversing the needle into the syringe body under a biasing force.

17. The method of operating an automatically retracting syringe of claim 16 , further including distally translating the non-engaging portion away from the seal when the thumb platform is depressed.

18. The method of operating an automatically retracting syringe of claim 16 , wherein the fluid chamber is at least partially filled with fluidic medication when the syringe is received.

19. The method of operating an automatically retracting syringe of claim 16 , wherein disengaging the needle from the syringe body includes disengaging a needle holder from the syringe body, the needle holder coupled to the needle.