Retractable syringe assembly designed for one use

A syringe comprising a hollow body with first and second open ends and an inside wall of varying inside diameter extending between the first and second open ends, a needle retraction mechanism, a plunger having a forwardly extending plunger head insertable into the body through the second open end, and a needle extending forwardly of the first open end, wherein:

• the body further comprises a nose adjacent to the first open end, a substantially cylindrical barrel adjacent to the second open end, and a transition zone connecting the barrel and nose;
• the needle retraction mechanism comprises an elongated needle holder, a compressed retraction spring, and a retainer member holding the retraction spring in compression prior to retraction;
• the elongated needle holder further comprises a needle holding portion secured in fixed relation to the needle and a head opposite the needle holding portion, the needle holding portion extending forwardly through the first open end;
• a fluid path extending longitudinally through the needle holder in fluid communication with the needle and with a variable fluid chamber inside the body between the needle holder and the plunger;
• wherein the needle retraction mechanism is grounded inside the nose by a barrier limiting forward motion of the elongated needle holder inside a front portion of the nose prior to or during retraction;
• the compressed retraction spring is positioned prior to retraction in an annulus disposed between the needle holder and the inside wall of the hollow body;
• the plunger head comprises a seal mounted in fixed axial relation to the plunger, the seal slidably engaging the inside wall of the body;
• the plunger head advances beyond a portion of the needle holder following injection to release the compressed retraction spring during retraction;
• the plunger comprises a retraction cavity into which part of the retraction mechanism is received during retraction so that the needle no longer extends forwardly of the first open end;
• and
• the plunger comprises an end cap having an outer periphery, the outer periphery being disposed in close proximity to the second open end of the body during retraction to prevent reuse of the syringe.

A syringe assembly having a hollow body with an inside wall, a retractable needle, a needle retraction assembly seated inside the body and a plunger slidably engaging a portion of the inside wall,

• the retraction assembly comprising a compressible retraction spring, a needle holder and a retainer member continuously surrounding the needle holder to hold the retraction spring in compression prior to retraction, the inside wall and needle holder cooperating as a spring guide during compression of the retraction spring,
• the plunger comprising a handle with a longitudinally extending retraction cavity having a first inside diameter and a forwardly extending tip having a second inside diameter less than the first inside diameter, the tip defining an opening through which the needle holder is receivable into the retraction cavity during retraction;
• a seal disposed in fixed longitudinal relation to the plunger handle and in sliding engagement with the inside wall of the body, and having a forwardly facing surface,
• the body further comprising a rigid stop surface that is contacted directly by the forward facing surface of the plunger seal and stops forward movement of the plunger inside the body following release of the retractable needle.

A syringe assembly having a retractable needle that is rendered unusable after a single injection of fluid into a patient, the assembly comprising:

• a hollow syringe body comprising a barrel and having a front end portion and a back end portion, the back end portion further comprising at least one radially extending member providing finger grips for the syringe body;
• a retraction mechanism disposed in the front end portion, the retraction mechanism further comprising a needle holder having a head portion, an elongated needle holding portion, and a longitudinally extending fluid passageway through the head portion and the elongated needle holding portion, the head portion further comprising an inner head, a continuous retainer member surrounding the inner head, and a bridging portion disposed between the continuous retainer member and the inner head, wherein said bridging portion couples the continuous retainer member and the inner head to form a fluid seal between the fluid passageway and the barrel prior to retraction, and a compressed retraction spring surrounding at least part of the elongated needle holding portion and biasing the inner head toward the back end portion prior to retraction;
• a retractable needle extending into the front end portion of the body through an opening in the front end portion of the body, the retractable needle being held in fixed relation to the elongated needle holding portion of the needle holder and in fluid communication with the longitudinally extending fluid passageway through the head portion and the needle holding portion;
• a plunger reciprocally disposed inside the barrel and forming a variable chamber between the plunger and the needle holder prior to and during injection, the plunger being receivable into the barrel through the back end portion of the body and comprising an outer wall, a retraction cavity disposed inwardly of the outer wall, a plunger seal element providing sliding, sealed engagement between the plunger and the barrel and preventing fluid leakage between the plunger and the barrel, the plunger seal element being restrained from sliding longitudinally along the outer wall of the plunger, and a back end with an end cap having an outer periphery;
• and
• a barrier disposed in the front end portion of the body that limits forward motion of the needle holding portion and the retractable needle relative to the body as the plunger is depressed inside the barrel during injection and retraction;
• wherein the continuous retainer member is releasable from the inner head of the needle holder when the plunger is further depressed inside the barrel following injection.