Single use medical device with retraction mechanism

A single use syringe having a permanently retractable needle for injecting fluid into a body comprising:

• (a) a hollow outer body having a longitudinal axis and being elongated axially between a tip end at the front and a back end and providing a cavity for the fluid;
• (b) a movable plunger disposed partially within the hollow outer body, having an internal space and a front portion having a piston mounted thereon in slidable sealed contact with the interior surface of the hollow outer body to form a variable chamber for the fluid below the piston;
• (c) a needle rod axially positioned partially within the internal space of the plunger, the needle rod having a front portion extending through the piston, said front portion having an embedded needle and a front end from which said needle protrudes;
• (d) a retainer member mounted on the front portion of the needle rod below the piston in contact with the interior surface of the hollow outer body, the retainer member frictionally but slidably engaging the needle rod with a frictional holding force to hold the needle rod in an unretracted position with the needle extended for use;
• (e) a biasing means within the plunger applying a retraction force to the needle rod which is less than said frictional holding force;
• (f) a stop member in the tip end of said outer body in the path of the front end of the needle rod and a stop above the retainer member to prevent the needle rod from moving axially;
• (g) a reduced size portion of the needle rod below said retainer member and above the front end of the needle rod;
• (h) whereby, the plunger may be used to draw fluid into a variable chamber above the retainer member and to expel said fluid by depression of the plunger and upon further depression of the plunger after said fluid has been expelled, the retainer member is moved forward to the reduced size portion of the needle rod whereupon the frictional holding force becomes less than the retraction force which automatically causes the needle rod and needle to permanently retract into the syringe.

A single use syringe having a permanently retractable needle for injecting fluid into a body comprising:

• a syringe body having a back and a front tip portion, the syringe body having an inner surface and an elongated plunger having a piston slidingly mounted for selective movement within the interior of the syringe body;
• an elongated needle rod coaxially mounted within said plunger for positioning in an unretracted position and a retracted position, said needle rod being biased with a retraction force in a retraction direction toward the back of said syringe;
• said needle rod having a front end from which a needle extends;
• a resilient retainer member mounted on the needle rod and spaced behind said front end, said retainer member slidingly and frictionally engaging said elongated needle rod and holding said needle rod with a friction force exceeding said retraction force;
• a variable chamber being defined within said syringe body between said retainer member and said piston and being in fluid communication with said needle;
• stop member in said syringe body to restrain the resilient release member from movement in the retraction direction and establish the needle rod in the unretracted position with the needle extended;
• means for preventing forward movement of the needle rod when the plunger is depressed;
• whereby the needle rod is released for retraction in the retraction direction by depression of the plunger causing forward movement of the retainer member on the needle rod, said forward movement of the retainer member being accompanied by reduction of said frictional holding force and release of the needle rod whereupon the retraction force drives the needle rod and needle to the retracted position in the retraction direction entirely within the syringe.

A single use syringe having a permanently retractable needle for injecting fluid into a body comprising:

• a hollow syringe body having a tip portion containing means for preventing a needle rod from moving forward;
• a hollow plunger having a front end portion equipped with a piston slidingly sealing the interior of the syringe body and defining the upper boundary of a variable fluid chamber within said syringe body;
• a needle rod having a front end equipped with a needle and being slidingly mounted in the plunger, said needle rod having an unretracted position with the needle extended from the tip portion of the syringe for use and a retracted position wherein said needle rod and needle are withdrawn within the syringe;
• a resilient release element frictionally mounted on the needle rod below the piston and cooperating with a stop in the syringe body to keep the release element from moving backward away from the tip portion of the syringe body, the release element being positioned on the needle rod at an axial location which positions the needle rod against the means for preventing the needle rod from moving forward;
• the resilient release element defining a lower boundary of said variable fluid chamber within said syringe body and being movable to a release position in response to depression of said plunger wherein said resilient release element is released from frictional engagement with said needle rod to initiate retraction of the needle rod and needle to said retracted position;
• a biasing means associated with said plunger to apply a retraction force to said needle rod so that when said resilient release element is released from said needle rod in response to depression of the plunger, said needle rod and said needle are automatically retracted into said syringe.