GB2081688A

GB2081688A - Anticoagulant Stopper Coating

Info

Publication number: GB2081688A
Application number: GB8025666A
Authority: GB
Original assignee: Sherwood Medical Industries Inc
Current assignee: Sherwood Medical Co
Priority date: 1980-08-06
Filing date: 1980-08-06
Publication date: 1982-02-24
Also published as: GB2081688B

Abstract

The adherence of blood cells to the closures (18) of blood collection containers (12) is prevented by coating at least that portion of the closure that may come into contact with blood in use with a binding agent such as tridodecylmethylammonium chloride and coating the binding agent with an anticoagulant such as dextran sulfate which binds to the binding agent and inhibits blood cell adhesion to the closure. A layer of a lubricant such as silicone oil can be applied to the coated closure to facilitate insertion of the closure into the container. <IMAGE>

Description

SPECIFICATION Anticoagulant Stopper Coating This invention relates to blood collection devices and more particularly, to the reduction of cell contamination of the separated lighter blood phase in a blood collection device.

It is common practice to employ a collection tube for receiving a whole blood sample from a patient whose blood is to be clinically tested, and then to centrifuge the filled tube to separate the blood into its lighter phase, serum or plasma, and its heavier cellular phase. In some cases, well known automatic or centrifugally activated phase partitioning devices or materials are placed in the tube which provide aliquid-impervious barrier between the separated phases after centrifugation. The barrier maintains the light phase isolated from the cellular phase components and facilitates subsequent removal of the light phase from the tube free of red cells.

However, red blood cells often adhere to surfaces of the stopper within the tube after the phases have been separated so that such cells remain in that portion of the tube which contains the separated lighter phase. These cells may come in contact with the light phase during handling or during removal of the stopper and light phase from the collection tube, and can contaminate the light phase such that some clinical tests performed produced inaccurate and unreliable results.

In an attempt to prevent blood cells from adhering to the stopper, the stopper has been shaped so that cells contacting it will have a tendency to slide off. However, such shaping of the stopper has not been entirely satisfactory.

U.S. Patent No. 3,958,572 illustrates a stopper shaped to reduce the chance of cells adhering to the inner side of the stopper. This method requires a special stopper construction and still does not insure against the adherence of cells to the stopper. It is also mentioned in that patent that if the stopper is made of rubber, then silicone oils or glycerine solution can be used as lubricants for easy insertion and removal of the stopper, and that such treatment also gives added protection against cell or clot adherence to the stopper.

However, coating stoppers with a lubricant has generally not been an effective solution to the prevention of cell adherence to the stopper and cell contamination of the light phase.

In U.S. Patent No. 3,882,021, a phase partitioning piston remains in its initial position and is sealed against contact with the blood by a frangible seal to prevent contamination of the piston by blood cells during phase separation.

Upon increased centrifugal force, after phase separation, the seal is broken and moves to the bottom of the tube, and the piston slides to a position adjacent the interface of the light and heavy phases. This device employs a relatively expensive tube assembly having a stopper in each end. It also requires the operator to centrifuge the tube at one speed until phase separation has taken place, and then to increase the speed in order to break the frangible seal. Thus, such a frangible seal arrangement results in a rather complicated separation procedure and a relatively expensive device.

It is therefore an object of the present invention to provide a collection device wherein the abovementioned disadvantages are substantially obviated. Another object of the present invention is to provide a stopper for a blood collection device which is effective in preventing the adherence of blood cells to it. Still another object is to provide a method of treating a blood collection tube stopper so that the tendency of blood cells to adhere to it is greatly reduced.

In accordance with one aspect of the present invention, a closure for a blood collection container is provided with a layer of a binding agent, and a layer of an anticoagulant which adheres to the binding agent to prevent cell adhesion on the stopper.

The invention will now be described, by way of example only, with reference to the accompanying drawing, in which: Figure 1 is an elevational view in cross-section of a blood collection device employing a coated stopper in accordance with a preferred embodiment of the present invention and illustrating a device containing separated relatively light and heavy blood phases; and Figure 2 is an enlarged view of the stopper of Figure 1 partly broken and in cross-section and showing the stopper coating in exaggeration.

Referring now to the drawing, and particularly to Figure 1, a blood collection device 10 is shown including a blood collection container or tube 12 closed at the bottom, such as by an integral end portion 14, and having an open upper end 1 6 closed by a stopper 1 8 made in accordance with the present invention and which will be described in detail hereafter. The stopper 18 is formed of a suitable elastomer or rubber, such as a conventional butyl rubber composition, and is pierceable by a needle cannula for the purpose of introducing a whole blood sample into the tube from a patient. Stopper 1 8 is self-sealing at the point at which it is pierced when the cannula is removed.Tube 12 is preferably of glass and provided with a partial vacuum which is maintained by stopper 1 8 until the tube is used.

Various reagents, depending upon the particular test to be conducted, may be provided in the tube. An anticoagulant, such as heparin or dextran sulfate, may be provided in the tube where plasma is to be obtained. Clot activating particles may be provided to decrease the clotting time when serum should be obtained.

In Figure 1 , the collection device 10 is shown after a whole blood sample has been taken into the tube 12 and after the device has been centrifuged. The blood is indicated as being separated into its relatively light or less dense phase indicated at 20, and its heavy or more dense cellular phase, indicated at 22. Also, shown in the tube 12 is a phase barrier or partition 23 formed of a well-known, inert, thixotropic gel-like material. For example, the barrier 23 may be formed of a suitable mixture of silicone oil and silica powder as disclosed in U.S. Patent No.

3,852,194 or a suitable mixture of polybutene and silica powder as disclosed in U.S. Patent No.

4,021,340. The gel-like material is made to have a specific gravity between the specific gravities of the separated phases, for example, it may be made so that it has a 1.05 specific gravity. In this way, it moves from its original position in the tube, such as in the bottom, to the shown location between the separated light and heavy phases 20 and 22. Other types of automatic or centrifugaliy actuated phase separators are well-known and may be used instead of the gel-like material illustrated.

Stopper 18 is shown in Figure 1 including a plug portion 24 disposed in tube 12 to sealingly close the upper end 16, and an enlarged upper portion of head 26 forming a shoulder 28 which engages the upper edge of the tube and limits the inward movement of the stopper during insertion.

The stopper 1 8 has a central outer recess 30 in its outer upper surface and a central inner recess 31 in its bottom surface within tube 1 2. The recesses 30 and 31 reduce the cross-section or axial dimension of the StOpper at its center to facilitate the penetration of the stopper by a needle.

The bottom surface of stopper 18 is, of course, subject to being contacted by whole blood during the drawing of the sample and during handling of the filled tube 12. The bottom surface of the stopper includes recess 31 having side walls 32 and a bottom wall 34, annular beveled leading surface 36, and an annular flat bottom end surface 38 that connects the beveled surface 36 with the side wall 32. The leading surface 36 is, of course, beveled to facilitate the insertion of the stopper into the tube during manufacture.

In conventional stoppers that are merely coated with a lubricant, cells often adhere to the bottom surface of the stopper and especially to the beveled surfaces and the side walls of the inner recess. During handling of such devices, the lighter phase may come in contact with such cells, with the cells contaminating the light phase so that test results may be inaccurate. Also, in conventional blood collection devices, when the stopper is removed from the tube 12, some cells that adhered to the stopper may fall into the light phase. In accordance with the present invention, stopper 18 is treated or coated such that cells substantially do not adhere to surfaces of the stopper within tube 1 2. Preferably, stopper 18, for convenience, is treated or coated over its entire surface by a coating 40, indicated in exaggeration in Figure 2.

The major constituents of the stopper coating 40 are a blood anticoagulant, shown as a layer 42, and a binding agent layer 44 which tenaciously binds the anticoagulant to the stopper. An outer layer 46 is a suitable lubricant, preferably silicone oil, may be applied over the anticoagulant layer 42 to facilitate insertion of the stopper into the tube 12. Instead of silicone oil, other known lubricants, such as glycerin, can be used.

The binding agent of layer 44 is a cationic surfactant, preferably a quatenary ammonium surfactant or salt tridodecylmethylammonium chloride (TDMAC). The TDMAC is applied as a solution in organic solvents such as toluene and petroleum ether, for example, in a 50%50% mixture of the two solvents. The nonpolar portion of the TDMAC molecule has an affinity for the nonpolar rubber surface of the stopper so that good bonding occurs. Also, the solvents swell the rubber surface and the TDMAC molecules can embed themselves in the stopper surface so that the TDMAC is tightly bound to the surface of the stopper. Other binding agents such as other cationic surfactant binding agents, for example, tridecyl or trioctalmethylammonium chloride may be used.

The anticoagulant layer 42, which is the active portion of the coating 40, is an anionic anticoagulant such as dextran sulfate which is a polymeric anticoagulant salt. The dextran sulfate is applied in an aqueous solution to the TDMACcoated stopper after the TDMAC layer 44 is dry, as will be discussed hereinafter. The cationic (nitrogen atom) portion of the TDMAC molecule, because it carries a positive charge, is attracted to the negatively charged portion of the dextran sulfate molecules which are primarily the sulfate groups. Thus, the dextran sulfate which is soluble in water or blood when free binds itself to the TDMAC layer and becomes less soluble in whole blood.

Because of the good bonding between the TDMAC and the stopper, and between the dextran sulfate and the TDMAC, the dextran sulfate layer does not dissolve away into the blood sample so that it remains on the stopper preventing or greatly reducing cell adhesion to the stopper.

Also, because the dextran sulfate layer does not dissolve away into the blood sample, it does not act as an anticoagulant in the blood sample. This is especially important where it is desired to coagulate the sample and obtain serum.

After the TDMAC and dextran sulfate layers have been applied and dried, the outer lubricant layer 46 of silicone oil is applied. The tube 1 2 is provided with the partitioning material and/or any other material desired, and then the stopper is inserted into the upper end 16 of tube 12. The stopper is inserted with the tube 12 in a vacuum where it is desired to have a negative pressure in the tube.

The dextran sulfate layer minimizes the adherence of red blood cells to the stopper surface. It is believed that the negatively charged sulfate groups present on the molecule repel red blood cells which have a small negative charge present on their surfaces. The lubricant may have some red blood cell repelling effect also.

A preferred TDMAC solution is about .325 grams of TDMAC per 100 ml of solvent, the solvent being a 50%50% mixture of a petroleum ether and toluene. The concentration of the solution may vary somewhat from .325 grams TDMAC/ml solvent; solutions of .1 gram/ml and .8/ml have been found satisfactory.

Preferably, a high molecular weight dextran sulfate is utilized. A suitable aqueous solution of dextran sulfate is one having about 82 unit of heparin activity/ml. If the solution has a heparin activity too great, for example, 1 60 units of heparin activity per ml was found excessive in one case, it will undesirably tend to dissolve in the blood and prevent or retard blood coagulation, and this is undesirable, of course, where it is desired to coagulate the blood and obtain serum.

If a dextran sulfate solution has an excessively low heparin activity, for example, below 1 5 units of heparin activity/ml has been found to be low in some cases, it will tend to be less effective in repelling red blood cells from the stopper.

The process of coating the stoppers may generally include immersing a quantity of the stoppers in a suitable cationic binding agent solution such as the above-described preferred TDMAC solution. The stoppers are removed from the solution and allowed to fully dry. The TDMACcoated stoppers are then dipped in the aqueous dextran sulfate solution and then removed and dried. The lubricant is then applied to the coated stoppers.

In one example process, clean stoppers were immersed for about 1 5 seconds in the preferred TDMAC solution, removed from the solution, and excess solution on the stoppers blown off with deionized air. The stoppers were then allowed to dry for about one hour in an atmosphere of approximately 250C.

Next, the TDMAC-coated stoppers were immersed for about 1 5 seconds in the preferred, above-described, aqueous dextran sulfate solution. The stoppers were removed and the excess dextran sulfate solution on the stoppers was blown off with deionized air. The dextran sulfate-coated stoppers were then placed in a 1000C oven for two hours to dry and age. The coated stoppers were then cooled to room temperature.

The dextran sulfate-coated stoppers were then lubricated by placing them in a drum with a relatively small amount of silicone oil disposed on the drum. For example, about five drops of oil per 50 stoppers was found satisfactory. The stoppers were tumbled in the drum until they had a thin coating of oil on them.

It was found that the above artificial aging of the dextran sulfate-coated stoppers in the 1 OO"C oven enhanced their effectiveness in repelling cells or inhibiting blood cell adhesion. The temperature and length of time of the drying and aging steps can vary.

The coated and lubricated stoppers can then be employed to seal the open ends of blood collection tubes while in a partial vacuum.

Stoppers treated in the above-described manner significantly inhibit the adherence of red cells thereto and reduce red cell contamination of the light phase.

As various changes could be made in the above-described construction and method without department from the scope of the invention it is intended that all matter contained in the above description and shown in the accompanying drawing be interpreted as illustrative and not in a limiting sense.

Claims

1. A closure for a blood collection container, which closure has a bottom surface which faces the opposed end of the container when fitted thereto, said bottom surface comprising an elastomeric member, a layer of a binding agent covering said bottom surface and a layer of an anticoagulant covering said binding agent layer and adhering thereto to inhibit blood cell adherence to the stopper.

2. A closure according to claim 1 wherein said anticoagulant layer comprises an anionic polymer anticoagulant.

3. A closure according to claim 2 wherein said anticoagulant layer comprises dextran sulfate.

4. A closure according to any one of the preceding claims wherein said binding agent is a cationic surfactant.

5. A closure according to claim 4 wherein said binding agent is a quatenary ammonium surfactant.

6. A closure according to claim 5 wherein said binding agent is tridodecylmethylammonium chloride.

7. A closure according to any one of the preceding claims further including a layer of a lubricant covering at least said layer of anticoagulant.

8. A closure according to any one of the preceding claims wherein the closure is a stopper having a plug portion having an annular sealing surface, and a layer of a lubricant covers at least said sealing surface.

9. A closure according to claim 7 or 8 wherein said lubricant is a silicone oil.

10. A closure according to any one of the preceding claims wherein said layer of binding agent covers substantially the entire outer surface of the closure and said layer of anticoagulant covers substantially the entire layer of binding agent.

11. A closure according to any one of the preceding claims which is pierceable by a needle cannula for introducing whole blood into said container.

12. A closure according to any one of the preceding claims which comprises a material including butyl rubber.

1 3. A closure for a blood collection container substantially as hereinbefore described with reference to and as illustrated by Figures 1 and 2 of the accompanying drawing.

14. A process for the preparation of a closure as claimed in any one of the preceding claims, which process comprises coating at least that portion of the closure that may come into contact with blood in use with a binding agent and coating the binding agent with an anticoagulant which binds to the binding agent and inhibits blood cell adhesion to the closure.

1 5. A process according to claim 14 wherein a binding agent solution of a quatenary ammonium salt and a solvent for said salt is applied to at least said portion of the stopper and the thus-applied coating of said solution is dried.

1 6. A process according to claim 1 5 wherein the binding agent solution comprises from 0.1 to 0.8 grams of the quatenary ammonium salt per milliliter of solvent.

1 7. A process according to claim 1 6 wherein about 0.3 grams of quatenary ammonium chloride per milliliter of solvent is used to form the binding agent solution.

18. A process according to any one of the claims 1 5 to 1 7 wherein the binding agent solution comprises tridodecylmethylammonium chloride dissolved in petroleum ether and toluene.

19. A process according to claim 18 wherein approximately equal amounts of petroleum ether and toluene are present in the binding agent solution.

20. A process according to any one of claims 1 5 to 1 9 wherein an aqueous solution of an anionic polymeric anticoagulant is applied to the dried binding agent and the thus-applied coating of said aqueous solution is dried.

21. A process according to claim 20 wherein the anticoagulant solution has from 1 5 to less than 1 60 units of heparin activity.

22. A process according to claim 21 wherein the anticoagulant solution has approximately 80 units of heparin activity.

23. A process according to any one of claims 20 to 22 wherein the dried anticoagulant solution is aged in an oven at a temperature above ambient temperature.

24. A process according to any one of claims 20 to 23 wherein the closure is immersed in the binding agent solution and in the aqueous anticoagulant solution.

25. A process according to any one of claims 14 to 24 wherein a lubricant is applied to coat the layer of anticoagulant.

26. A blood collection container fitted with a closure as claimed in any one of claims 1 to 13 or which has been prepared by a process as claimed in any one of claims 14 to 25.

27. A blood collection container according to claim 26 which has a partial vacuum therein.

28. A blood collection container according to claim 26 or 27 which contains blood which has or which has not been separated into fractions.

29. A blood collection container substantially as hereinbefore described with reference to and as illustrated by Figures 1 and 2 of the accompanying drawings.