Single use syringe
A syringe including a plunger rod assembly including a proximal portion a distal portion with a stopper for expelling fluids from the syringe and a breakable connection between the proximal portion and the distal portion is disclosed. An impulse reduction system, which may be an elastic element or braking surfaces, reduces the contact impulse imparted by the proximal portion upon the distal portion when the connection between the distal portion and proximal portion breaks is also disclosed.
1. A syringe comprising:
a barrel including an interior surface, a proximal end, a distal end, a fluid chamber and a tip at the distal end including an opening to allow fluid to pass therethrough;
a plunger rod including a proximal portion having a proximal end with a flange adapted to accept a force applied from a user along a longitudinal centerline of the plunger rod and a distal end; a distal portion having a distal end with a stopper adapted to provide a slidable seal with the interior surface of the barrel; a breakable connection between the proximal portion and the distal portion adapted to break when the force applied by the user exceeds a breaking force, wherein the breaking force is greater than a force needed to expel fluid through the syringe tip during normal use; and
means for reducing a contact impulse between the proximal and distal portions of the plunger rod when the breakable connection is broken, the means comprising a first surface on the plunger rod which contacts a second surface after breaking of the breakable connection, thereby reducing impact of the distal end of the proximal portion on the distal portion.
2. The syringe of claim 1 wherein the means for reducing the contact impulse comprises:
a first braking surface disposed on the proximal portion; and
a second braking surface disposed on the distal portion, the second braking surface adapted to slidingly engage with the first braking surface to create a motion-resistive force between the proximal portion and the distal portion.
3. The syringe of claim 2 wherein the first braking surface is sloped with respect to the longitudinal centerline of the plunger rod.
4. The plunger rod of claim 2 wherein the second braking surface is sloped with respect to the longitudinal centerline of the plunger rod.
5. The syringe of claim 3 wherein a first distance along the longitudinal centerline of the plunger rod separating a distal end of the proximal portion from the distal portion exceeds a second distance separating a most distal portion of the first braking surface from a most proximal portion of the second braking surface.
6. The syringe of claim 2 wherein the first braking surface is disposed along a distal region of the proximal portion, and the second braking surface is disposed along a proximal region of the distal portion.
7. The syringe of claim 5 wherein the first braking surface or the second braking surface is disposed adjacent to the breakable connection.
8. The syringe of claim 1 wherein the means for reducing the contact impulse comprises an elastic element disposed within a gap along the longitudinal centerline that separates the proximal portion from the distal portion.
9. The syringe of claim 8 wherein the elastic element is disposed adjacent to the breakable connection.
10. The syringe of claim 9 wherein the elastic element is disposed distally adjacent to the breakable connection.
11. The syringe of claim 10 wherein the elastic element includes a first arm adapted to compress into a second arm in response to the breakable connection breaking.
12. The syringe of claim 9 wherein the elastic element is disposed proximally adjacent to the breakable connection.
13. The syringe of claim 8 wherein the elastic element includes one or more springs.