Injection device

1. An injection device for fluid injection into a body comprising:

a housing having a proximal end and a distal end, the housing having an opening proximate the distal end, the opening configured to deliver a fluid;

a fluid chamber disposed inside the housing and configured to contain the fluid;

a propellant chamber disposed inside the housing and spaced from the distal end of the housing;

a sleeve having a proximal end and a distal end, the sleeve disposed inside the housing between the distal end of the housing and the propellant chamber, the sleeve having a first cavity in fluid communication with the propellant chamber, and having an opening between the proximal end of the sleeve and the distal end of the sleeve; and

a piston mounted on the sleeve and having a proximal end and a distal end and having an opening between the proximal end of the piston and the distal end of the piston, the piston being coupled to the sleeve and having a second cavity, the piston being movable with respect to the sleeve from a first position to a second position,

wherein, during use, a fluid is released from the propellant chamber causing the piston to slide over a surface of the sleeve from the first position to the second position, movement of the piston causing the fluid in the fluid chamber to be ejected through the housing opening, and

wherein as the piston slides over the sleeve, the opening of the piston aligns with the opening of sleeve such that at least some of the fluid from the propellant chamber travels through the aligned openings of the sleeve and piston.

2. The injection device of claim 1 , wherein the opening of the piston is configured to assist in controlling pressure of the fluid being ejected through the housing opening.

3. The injection device of claim 1 , wherein the sleeve further includes a groove, the opening of the sleeve disposed in the groove.

4. The injection device of claim 3 , wherein the groove is annular.

5. The injection device of claim 1 , wherein the opening of the piston includes a plurality of axially spaced openings that are each alignable with the opening of the sleeve.

6. The injection device of claim 1 , wherein the housing is comprised of a plurality of housing components.

7. The injection device of claim 1 , wherein the fluid from the propellant chamber is a gas that urges the piston from the first position to the second position.

8. The injection device of claim 1 , wherein the second cavity is in fluid communication with an exterior of the housing when the piston and sleeve openings are aligned.

9. The injection device of claim 1 , wherein the fluid from the propellant chamber is released from a propellant disposed within the propellant chamber.

10. The injection device of claim 9 , further comprising:

a button coupled to the housing proximate the proximal end of the housing;

a battery disposed inside the housing and adjacent to the button;

electrical leads in electrical communication with the battery; and

a wire in electrical communication with the electrical leads, the wire configured to trigger the propellant.

11. The injection device of claim 9 , wherein the propellant includes a chemical pyrotechnic material.

12. The injection device of claim 1 , wherein the device is a needleless injection device.

13. The injection device of claim 1 , further comprising:

a filter disposed between the propellant chamber and the first cavity.

14. The injection device of claim 1 , wherein the housing includes a vent, at least some of the fluid from the propellant chamber exiting through the vent after traveling through the openings of the sleeve and the piston.