Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2000-06-06
2001-04-10
Kennedy, Sharon (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S187000
Reexamination Certificate
active
06213985
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a plastic tapered syringe barrel and an elastomeric tapered plunger combination for containing and dispensing a medical fluid from the syringe.
2. Reported Developments
Syringes and cartridges made of glass or polymeric material for delivery of fluids to and from a patient have been proposed and utilized by the prior art, and have achieved a highly developed state. Various requirements related to specific delivery systems have also been addressed. While specific requirements of fluid delivery to and from a patient may vary, means of delivery remain essentially the same and may be characterized by the following general description of a syringe.
A syringe comprises:
a) a cylindrical barrel having a proximal end designed for receiving a plunger with or without a plunger rod removably attached to the plunger or being integral with the plunger, and a distal end adapted to mount a needle or luer connector thereon; and
b) a plunger slidably mounted in the barrel.
The plunger is inserted into the barrel at the proximal end of the syringe and thus when fluid is contained in the barrel it may be expelled by pushing the plunger in the barrel towards its distal end; or when the syringe is used to withdraw fluid from a patient, the plunger located at the distal end of the barrel is pulled towards the proximal end of the syringe thereby drawing fluid into the barrel. Since a fluid-tight seal is necessary between the plunger and the inside wall of the barrel, a resilient rubber tip is positioned on the distal end of the plunger, or typically, the plunger is made of resilient rubber-like material. In some of the syringes of the prior art the rubber tip has been replaced with a generally flat, circular disk as part of the plunger.
In order to assure air-tight seal between the inside wall of the syringe barrel and the plunger, prior art plungers are manufactured with a larger outside diameter than the inside diameter of the syringe barrels. When the plunger is introduced into the syringe barrel, it is sufficiently compressed to provide adequate pressure between the inside wall of the syringe and the plunger to seal the interface and withstand the challenges of filling, injecting and withdrawing fluids using the syringe without leakage.
In addition to a leakage-proof seal, another requirement in the syringe/plunger combination is the chemical stability of both the syringe and the plunger. While syringes being made of glass or thermoplastic materials are sufficiently chemically inert to pharmaceutical and biological fluids contained therein, the plungers made of natural rubber or butyl rubber have some undesirable properties. The rubber contains additional chemical components such as fillers and accelerators introduced during the curing process which tend to exude to the surface of the plunger during the contact between the plunger and the fluid contained in the syringe. Such exudate is undesirable in an injection or when a biological fluid, such as blood, is withdrawn from a patient for testing purposes. The problem is further aggravated when there is a long-term storage of the content of the pharmaceutical/biological fluid in the syringe. Recognizing the problem of contamination caused by exudates from plungers made of rubber, the prior art has provided plungers made of thermoplastic materials which do not contain the additives that rubber plungers contain. However, thermoplastic materials are not as resilient as rubbers and the seals formed between thermoplastic plungers and the inside walls of syringes tend to be inadequate in some circumstances. Also, over a period of time on storage the thermoplastic plunger may achieve a compression stage wherein the outside diameter of the plunger is reduced thereby no longer capable of forming a tight seal between it and the inside wall of the syringe.
In addition to the tendency of leakage, the thermoplastic plunger does not slide smoothly in the syringe barrel and requires the exertion of excessive force on the plunger rod to move the plunger in the barrel. The exertion of excessive force on the plunger rod may result in uneven delivery of the fluid to the patient or insertion of the needle into a vein or tissue area to an undesirable depth.
In both the rubber and thermoplastic plungers a relatively large compressive force must be exerted on the plungers by the syringe barrel to provide for a tight, leakproof seal. This quality of the seal, however, makes the movement of the plunger difficult. To remedy the problem the prior art used lubricants to reduce friction and drag between the plunger and the inside surface of the syringe barrel. The use of such lubricants, however, is also undesirable with certain parenteral fluids which tend to disperse or dissolve in the parenteral fluids thereby contaminating the parenteral fluids. Attempts to avoid the use of lubricants included the use of various plunger configurations, such as plungers that were provided with one or more ribs projecting forwardly or rearwardly in the barrel to reduce the frictional drag between the plunger and the inside surface of the barrel.
While fluid tightness and sliding property have improved with these attempts, it appears that improvement in one of these properties is not quite achieved without corresponding decrease in the other property: increasing fluid tightness tends to result in decreasing sliding property, while increasing sliding property tends to result in decreasing fluid tightness.
The present invention is directed to improve the balance between fluid tightness and sliding property in a syringe and, in addition, provides a manufacturing advantage in making the syringe barrel.
SUMMARY OF THE INVENTION
The present invention provides a syringe for medical use designed for injecting a fluid into a site or withdrawing a fluid from a site comprising:
(a) a syringe barrel of polymeric material having a proximal end, a distal end, and an inner surface defining a tapered cylindrical chamber between the proximal end and the distal end for retaining a fluid therein,
the distal end terminates in a tip having a bore therethrough to which an injection needle or a connector equipped with tubing conduit can be attached; and a proximal end for receiving a plunger;
(b) a plunger comprising: a rigid plunger rod tip having a proximal end, a distal end, a tapered body extending from the proximal end to the distal end; and an elastomeric member mounted on and at least partially covering the plunger rod tip.
The tapered cylindrical chamber has a taper of at least ⅛° or more and/or a taper of at least 0.020″ variation from the proximal end to the distal end.
Preferably, the plunger profile matches the profile of the tapered cylindrical chamber of the syringe barrel, i.e., having a taper of at least ⅛° and/or a taper of at least 0.020″ variation from the proximal end to the distal end of the plunger.
The present invention is also directed to the reduction of breakaway and running forces in using the syringe when injecting a fluid from the barrel into a site. Such reduction of the forces facilitates starting and advancing the plunger from the proximal end toward the distal end of the barrel. To achieve this object of the present invention preferred elastomers having a core set of no more than 20% are used for fabricating the elastomeric member covering the plunger rod tip. Core set is defined as the reduction in size of an elastomer that is caused by compressing the elastomer 50% over a period of 24 hours at 120° C. Preferably, the core set in the present invention is no more than about 20%. Most preferred elastomers have a core set between 10% to 15%. Such elastomers include butyl rubbers, polyisoprene, EPDM and natural rubbers.
REFERENCES:
patent: 562425 (1896-06-01), Scheerer
patent: 4303070 (1981-12-01), Ichikawa et al.
patent: 4852768 (1989-08-01), Bartsch
patent: 4952209 (1990-08-01), Muhlbauer
patent: 5540660 (1996-07-01), Jenson
patent: 5735825 (1998-04-01), Stevens et al.
patent
Balogh Imre
Bracco Diagnostics Inc.
Kennedy Sharon
LandOfFree
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