Syringe with Multifunctional Needle Holder and Retainer Ring Assembly

In a syringe comprising a barrel, a selectively retractable needle, a plunger assembly slidably engaging the barrel, and a needle retraction assembly, the improvement comprising:

• a multifunctional needle holder and retainer ring assembly, the multifunctional needle holder and retainer ring assembly further comprising:
• a needle holder having a head section with an outwardly facing surface,
• a retainer ring disposed between the barrel and the needle holder, and having a radially expanded, inwardly facing surface portion contacting the outwardly facing surface of the needle holder;
• wherein at least one of the inwardly facing surface portion of the retainer ring and the outwardly facing surface of a head section of the needle holder comprises an annular projection that is desirably configured to enhance frictional interference between the head section of the needle holder and the retainer ring while still permitting relative sliding movement between them during needle retraction.

A method for increasing the push-out force without increasing the activation force before and during an injection administered using with a syringe having a barrel;

• a rearwardly biased, forwardly projecting needle;
• a needle retraction assembly slidably seated inside a forward portion of the barrel;
• and a plunger assembly slidably engaging an inside wall of the barrel, comprising:
• providing as part of the needle retraction assembly a multifunctional needle holder and retainer ring assembly further comprising:
• a needle holder with an elongate front section, a larger diameter head section, and a fluid pathway extending through the needle holder in coaxial alignment with the needle;
• and
• an elastomeric retainer ring disposed between the needle holder and the barrel;
• wherein the head section further comprises a rear opening into an inwardly tapering frustoconical section of the fluid pathway, and a rearwardly facing annular surface surrounding the rear opening, and wherein a substantially unexpanded, circumferentially extending portion of the retainer ring extends rearwardly behind a portion of the rearwardly facing annular surface;
• and
• administering an injection with the syringe.

A syringe comprising a retractable needle and a cooperatively configured needle holder and retainer ring assembly wherein:

• the retainer ring is elastomeric and comprises an axially extending, inwardly facing wall having an inside diameter;
• the needle holder has a head section having an outside diameter greater than the inside diameter of the retainer ring that is inserted into a forwardly facing, radially expanded portion of the retainer ring;
• and
• a substantially unexpanded portion of the retainer ring extends rearwardly behind the head section of the needle holder.

A syringe comprising a retractable needle and a cooperatively configured needle holder and retainer ring assembly wherein:

• the needle holder further comprises a head section having a first axial length and an outside diameter;
• the retainer ring is elastomeric and further comprises an inwardly facing wall having a second axial length and an inside diameter that is less than the outside diameter of the needle holder;
• the first axial length is less than the second axial length;
• and
• wherein the head section of the needle holder is inserted into a forwardly facing, radially expanded first portion of the elastomeric retainer ring and an unexpanded second portion of the elastomeric retainer ring extends rearwardly behind the inserted head section of the needle holder.

A syringe having a retractable needle and a needle holder and retainer ring assembly comprising a needle holder and an elastomeric retainer ring wherein:

• needle holder further comprises a head section with an outside diameter;
• the elastomeric retainer ring has an unexpanded inside diameter less than the outside diameter;
• the head section is inserted into a front portion of the elastomeric retainer ring that is expanded to accommodate the head section;
• and
• an unexpanded rear portion of the elastomeric retainer ring extends rearwardly behind the head section by a distance that is less than half the diameter of the head section.

A syringe having a barrel, a plunger assembly, a retractable needle and a cooperatively configured needle holder and retainer ring assembly comprising:

• a head section of the needle holder further comprising a rear opening into a coaxially aligned fluid flow path communicating with the retractable needle and a frustoconical, inwardly facing wall surface located proximally to the rear opening;
• and
• an elastomeric retainer ring having a first longitudinally extending portion that is expanded radially and surrounds the head section of the needle holder and a second longitudinally extending collar portion that is substantially unexpanded radially and extends rearwardly behind the head section of the needle holder;
• wherein
• the rearwardly extending collar portion of the elastomeric retainer ring cooperates with the frustoconical, inwardly facing wall surface to reduce a thumb force required to advance the plunger assembly inside the barrel and to reduce turbulence in a fluid entering the rear opening into the fluid flow path during an injection, and to reduce the retention of any air bubble in fluid disposed around the opening during use of the syringe.