Prefillable auto-retractable safety syringe

A collapsible plunger of a retractable syringe, comprising:

• a first plunger element having a proximal end and a distal end, and being formed with a protrusion near the distal end;
• and
• a second plunger element being releasably coupled with the first plunger element, and having a longitudinal slot on a sidewall of the second plunger element;
• wherein the longitudinal slot is configured to accommodate the protrusion of the first plunger element, allowing the protrusion to slide longitudinally along the longitudinal slot of the second plunger element;
• wherein the longitudinal slot has a proximal part and a distal part, and the proximal part of the longitudinal slot is formed with a pinched zone to curb the protrusion of the first plunger element, so that the first and the second plunger elements are coupled until the pinched zone of the longitudinal slot deforms to disengage the protrusion from the pinched zone of the longitudinal slot, allowing the protrusion sliding toward the distal part of the longitudinal slot, so that the first and the second plunger elements become axially slideable with respect to each other.

A retractable syringe comprising:

• a needle hub having an first end to receive and hold a needle extending distally, a nearby first guiding means on an external wall of the needle hub, and a second end being opposite to the first end;
• a hollow barrel having
• an internal surface defining a chamber allowing the needle hub releasably disposed in the chamber of the hollow barrel,
• a distal open end allowing the first end of the needle hub to protrude distally, and having a second guiding means nearby on a sidewall of the hollow barrel, and
• a proximal open end being opposite to the distal open end;
• a collapsible plunger slideably fitted into the hollow barrel, having
• a first plunger element having a proximal end and a distal end,
• a second plunger element being releasably coupled with the first plunger element, wherein
• the first plunger element is formed with a protrusion near the distal end of the first plunger element, and
• the second plunger element has a longitudinal slot on a sidewall of the second plunger element
• to accommodate the protrusion of the first plunger element allowing the protrusion to slide longitudinally along the longitudinal slot, and
• the longitudinal slot has a proximal part formed with a pinched zone to curb the protrusion and a distal part, so that the first and the second plunger elements are coupled until the pinched zone deforms to disengage the protrusion from the pinched zone, allowing the protrusion sliding toward the distal part of the longitudinal slot, so that the first and the second plunger elements become axially slideable with respect to each other;
• and
• a spring disposed between the needle hub and the internal surface of the hollow barrel such that the spring acts between the needle hub and the hollow barrel;
• wherein the needle hub is further formed with at least one fluid path extending longitudinally through the needle, to be in fluid communication with the chamber;
• and
• wherein the first guiding means releasably engages with a first portion of the second guiding means, so that the first and the second guiding means are capable of releasably holding the needle hub against an expansion force of the spring until the first guiding means disengage from the first portion of the second guiding means and moves toward a second part of the second guiding means to initiate retraction of the needle hub.