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Background of the Invention This invention relates to separator tubes and separator assemblies used for the separation of form~ed elements, i.e,, white cells, red cells and platelets of blood, from the serum or plasma of the blood and to a valve a~Faratus used thexein and to the method of making that valve apparatus.
7 Serum separation is typically performed by centrifuging a blood sample in a collection tube such that the heavier formed g elements of the blood are forced to the bottom or closecl end of the collection tube and the lighter plasma or serum of the sample 11 remains on top or toward the open end of the collection tube.
12 After such separation by centrifugation, it is desirable 13 to physically separate the formed elements of the blood from the 14 serum or plasma in order to prevent the contamination o~ the serum or plasma. Such contamination can occur as the red blood cells 16 begin to liberate potassium and other contaminants which might 17 interfere with tests performed on the serum or plasma. It is ~;
18 also possible that any fibrin which remains in the sample may 19 produce some contamination.
In order to achieve this isolation or fluid separation of 21 the formed elements of the blood from the serum or plasma, separa-22 tor tubes have been utilized. ~he separator tubes which are adapted 23 to be inserted into a collection tube typically comprise a tubular 24 member having one end closed by a plug or valve apparatus which is formed from an elastomeric material. The plug includes a 26 centrally located one-way valve which is forced open as the separa-27 tor tube is forced downwardly through a blood sample in a collection 28 tube so as to allow the serum or plasma to flow into the separator 29 tube. When the separator tube becomes stationary relative to the collection tube i.e., just before contact with the foxmed elements 31 of the blood, the one-way valve closes so as to isolate the plasma
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~87573 1 within the separator tube. The separator tube may then be withdrawn. --2 However, it would be desirable to close the end of a separator tube
3 with a plug or valve apparatus which maintains a more substantial
4 seating form when closed than valve apparatus presently available.
It has been found to be particularly desirable to utilize 6 the separator tube in and of itself as a transport device for 7 transporting the serum or plasma to the laboratory from the point 8 at which the blood sample is taken. This requires that the one-9 way valve at the closed end of the separator tuba be essentially leak-proof. My U.S. patents 3,661,265 and 3,799,342 disclose a 11 substantially leak-proof valve which does permit the use of the 12 separator tube as a transport device. The one-way valve disclosed 13 therein essentially relies upon the elastomeric properties o the 14 plug to return the valve to the closed condition, i.e., there is no force or bias acting on the valve when the separ~tor tube is in 16 the stationary position and the valve is closed. Rather, the valve 17 elements, when properly structured, merely contact one another when 18 returning to a natural or unbiased state in which they were originally 19 molded. Proper closure of these valves may be assisted by the tubular member if the inside diameter of the tubular member lS
21 slightly smaller than the outside diameter of the plug but the 22 tolerances on the inside diameter of the tubular member are diffi-23 cult to control particularly where the tubes are extruded.
24 U.S. patent 3,954,614 also discloses a valve in a separator tube which is characterized by little or no seating forces when the 26 vaive is in the closed position. The same is true with respect to 27 U.S. patent 3,962,085 wherein the periphery of a disc acts as a 28 valve which is closed when the disc is in the closed position.
29 However, there are no substantial seating forces beyond weight of the blood sample itself. Valves such as those shown in U.S.
31 patents 1,777,408 and 2,191,636 are biased so as to provide a 32 substantial sealing force when in the closed position, but such 33 valves are too complex for use in serum separators.
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~ 7S~73 1 In addition to the use o~ separator tubes, separator 2 assemblies of the Vacutainer type have also been suggested.
3 Examples of such Vacutainer assemblies are shown in U.S. patents 4 3,891,553, 3,894,951 and 3,894,952.
Such blood separation assemblies typically comprise 6 a ~ollection container having elastomeric plugs sealing opposite 7 ends of the container with a piston-likle plug located withi~
8 the container and forming a seal with the walls of the container.
9 A partial vacuum is created on the interior of the container so as to assist in drawing the blood sample into the container . .
11 through a cannula which penetrates one of the end plugs. The 12 piston-like plug which is characterized by an average specific 13 gravity greater than the light phase o~ the blood comprises a 14 pressure-responsive val~e which, under the ~orce of centrifuging and ~he pressure of serum or plasma against the valve, will open 16 the valve to allow the plasma or serum to pass therethrough.
17 The plug typically also comprises a filter member associated 18 with the valve to prevent fibrin or formed elements of the 19 blood frcm clogging or passing through the valve. As centri-fugation continues, the plug will stop at the interface between 21 the light phase and the heavy phase as the filter becomes clogged 22 with the elements of the heavy phase. Once centrifugation is 23 completed, the light phase should be on one side of the plug 24 and the heavy phase should be on the other side~of the plug.
Reliance on the clogged filter to stop the plug at the 26 - interface of the light phase and the heavy phase can result in 27 lysing of the blood cells due to the pressure placed on the 28 cells by the clogged filter. Once lysing occurs, any contact 29 between the lysed cells and the serum or plasma will produce contamination of the serum or plasma.
31 It has also been found to be desirable to utilize the 2 Vacutainer type separator assembly in and of its~31f as a trans-te s r~-aQ~e ,~ 3~
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port apparatus or transportlng the blood sample to the laboratory from the point at which the blood sample is taken. Thls also requires the valve of the assembly to close tightly after centrifugation and remain closed so as to prevent any contamination between the two phaser, of the blood.
Heretofore, valves of self-contained separator assemblies have also in general relied upon the elastomeric properties of the plug or valve to return the valve to the closed condition, i.e., there is no force or bias ~ ;
acting on the valve after centrifugation to hold the valve closed. Again, the valve elements, when properly structured, merely contact one another when returning to a natural or unbiased state. Closure of these valves may be assisted by the tubular member of the container if the inside diameter of the tubular member is slightly smaller than the outside diameter of the plug but the tolerances on the inslde d:lameter of the tubular member are difficult to control particularly where the tubes are extruded.
A further difficulty assoc:Lated with such sepAratOr apparatus i9 a result of the necessity for the valve to open with the force generated during centrifugation and still close after centrifugation. -~
Summary of the Invention The lnvention provides a separator tube adapted to be pushed into a collection tube containing blood for separating serum or plasma from the ~ ;
formed elements of the blood, said separator tube comprising~
a tubular member, means adapted to form a seal with the collection tube as the separator tube is pushed into the collection tube, and a valve apparatus, said apparatus having~
a valve seating portion having a valve opening therein, said valve opening permitting serum or plasma to flow into said tubular member when the `
separator tube is plunged into the collection tube, a movable valve member adapted to seat on said seat-ing portion so as to close said valve opening, and connective means comprising at least one elastomeric strand main-tained under tension and extending between said valve member and said valve ~5~
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seating portion for maintaining a substantial seating force an said valve ~`
member when said valve opening is closed.
The separator tube with the improved valve apparatus is rela~ively easy to manufacture, and the valve will maintain itself in the closed or ~ ;
seated position.
The valve apparatus is preferably integrally molded from an elastomeric material with the valve member on one side of the valve opening and the connective or bias means in an unstretched or untensioned state.
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Subsequent to molding, at least a portion of the valve member is passed through the valve opening and set on the other side thereof so as to create `
a bias on the valve member due to tension in the bias means which thus tends to seat the valve member on the other side of the opening. ;~
The improved valve permits ease in operating the separator tube slnce the valve member is free to float above the valve opening so as to be Ereely movable and separable from the valve opening around the entire periphery of the valve opening. ; ;;
To prevent the squirting of serum or plasma from the open end of ~i~
! the separator tube means are preferably provided adjacent the valve opening for deflecting serum or plasma passing therethrough. In addition, the connective or bias means control deEormation of the valve member so as to prevent undesirable, excessive opening of the valve. As the separator tube is Eorced into a collection tube anl plasma or serum pushes agalnst the valve member, the elastomeric strand stretches and the valve member becomes ~ :
unseated so as to allow the plasma or serum to flow upward into the separator tube. When the separator tube becomes stationary, the tension on the ;
elastomeric strand returns the head to the seated position on the valve open~
ing while the strand remains under tension so as to assure the desired ,~ closure of the valve.
In the preferred embodiment of the invention, the valve seatlng - -portion may comprise a cylindrical section and a seating section at one end -~
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~ of the cylindrical section where the seating section includes the valve open-i ~ ing. The flexible strand extends from the valve member down through the : ~ ::
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central chamber formed by the cylindrlcal section and the flexible strand is anchored on the cylindrical section. Preferably, a plurality of flexible strands are utilized which are connected to a wafer-like valve member after extending across the valve opening to ~he opposite side of t~e valve opening so as to maximize the control of the valve member, i.e., prevent undesirable deflection of the valve member which could cause faulty closure or squirting of the plasma or serum from the separator tube. In the alternative, the valve member could comprise an elongated body section positloned beneath a head which ~seats on the valve seating portion with the strands attached thereto.
The preferred embodiment of the invention also comprises a hood located above the valve member for deflecting plasma or serum passing through the valve opening.
The closed end of the separator tube may comprise a valve apparatus or plug whlch ls lntegrally molded so as to include the valve seatlng por-tion, the valve member and the bias means. Various elastomerlc materials may be utilized in the molded plug so long as the material is capable of achieving the necessary tension on the strands which anchor the valve member to the valve seating portion. ~;
Brief Description of the Drawings Figure 1 is a sectional view of a preferred embodiment of the invention comprlslng a separator tube and a collection tube;
Figure 2 i8 a sectional view of the plug or valve apparatus incorporated ln the separator tube of Figure l;
Figure 3 is a sectional view taken along line 3-3 of Figure 2;
` Figure 4 is an enlarged sectional view of the separator tube and collection tube of Figure 1 as the separator tube is inserted into the collection tube;
Figure 5 is an enlarged sectional view of the separator tube of Figure 1 wherein the separator tube is being withdrawn from the collection tube;
Figure 6 is a sectional view of an alternative plug which may be !~,.. ., , -1~8 75 73 utilized in the apparatus of Figure l;
Figure 7 is a sectional view of yet another plug which ls utilized in the apparatus of Figure l; :
Figure 8 is a view of the plug of Figure 7 taken along line 8~8 .
of Figure 7.
Figure 9 is a sectional view of a mold in which the valve apparatus ::
of Figure 6 is molded;
Figure 10 is a sectional view of the mold of Figure 9 as the mold ; :;:
begins to open;
Figure 11 is a sectional view of the mold of Figure 9 as the : ~:
mold continues to open and the setting of the valve begins;
Figure 12 is a sectional view of the mold of Figure 9 in a further :
state of opening with the valve opening deformed 80 as to permit setting of .
the valve; ~ ;
Flgure 13 ls a sectlonal v:Lew of the mold of Flgure 9 ln a stlll .
further state of opening with the mold beginnlng to release the valve during setting;
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1 Fig. 14 is a sectional view of the mold of Fig. 9 with 2 the valve apparatus substantially released from the mold and the ~ ;
3 valve member fully set in the valve opening;
4 Fig. 15 is a sectional view of a separator assembly in accordance with this invention which has been filled with a blood 6 sample but has not yet been centrifuged;
7 Fig. 16 is a sectional view of the apparatus of Fig.
8 15 after centrifugation; and , ~
9 Fig. 17 is a modification of the separator assembly of Fig. 15 in accordance with another embodiment of the present in-11 vention.
12 Detailed Description of Preferred Embodiments 13 Fig. 1 discloses separation apparatus comprising a collection 14 tube 10 having a closed end 12 and an open end 14. As shown, the separator tube 16 has been inserted into the collection tube 10 16 through the open end 14. The separator tube 16 comprises a tubular 17 member 18 which is closed at one end by a plug 20.
18 ~he collection tube 10 is partially filled with a sample 22 19 which has been subjected to separ~ting, e.g., centrifugation, so as to move the formed elements o the blood 24 to the closed end 12 21 o the collection tube 10 while the serum or plasma 26 is located 22 above the formed elements 24. As shown in Fig. 1, the separator 23 tube 16 has been inserted into the collection tube lQ down through 24 the serum or plasma 26 to a point where the serum or plasma has entered the separator tube 18 through a novel valve mechanlsm in ~;
26 the valve apparatus or plug 20 which will now be described in detail with reference to Figs. 2-5.
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1 As shown in Fig. 2, the valve apparatus or plug 20 comprises 2 a substantially cylindrical body portion 28 ~hich is terminated at 3 one end by a flange 30 which is adapted to form a seal along the ~?~
4 wall of the collection tube 10 a~ a seali,ng surface 32. The other end of the body member 28 comprises a radially inwardly directed 6 annu~ar flange 34 which is adapted to for~m a valve seat along the 7 surface 36 for a movable valve member 38. As shown in Fig. 2, the 8 valve member 38 comprises a body portion 40 terminated by a sealing 9 head portion 42 which is adapted to seat on the surfac~e 36 along a surface 44 when the sealing portion or head 42 is pushed through 11 an opening 46 in the flange 34 as shown in Figs. 4 and 5.
12 In order to provide a closing bias on the valve member 13 38 wh~ch is independent of the diameter of the tubular member 14 18, resilient strand or strut members 48 are atta~hed to the interior walls 50 of the cylindrical body 28 of the plug 20.
16 As shown in Fig. 3, three such struts or strands 48 may be uti-17 lized which are evenly spaced around the wall 5~ and the valve 18 member 38 at points of attachment 52 so as to assure that the 19 appropriate seal will be formed between the sealing surface 44 and the seating surface 36 shown in Fig. 2.
21 Figs. 2 and 3 show an integrally molded plug 20 which 22 comprises an elastomeric material such as Kraton*or rubber. As ';
23 shown in Fig. 2, the valve member 38 is in the unbiased position 24 since there is no tension on the strands 48. However, once the head or sealing portion 42 is forced through the opening 46 26 as shown in Figs. 4 and 5, the strands 48 are under tension and 27 store energy so as to force the sealing surface 44 into contact 28 with the seating surface 36 when the separator tube is in the 29 stationary position as shown in Fig. 1.
As also shown in Figs. 2 and 3, the flange 30 comprises 31 annular relieved areas 54 located on opposite sides of the flange ' ~ ~e,~ a~es r~aletn ~ r,~
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~L~187573 1 30. The relieved areas 54 allow the sealing surface 32 to be 2 extended radially outwardly or retracted radially inwardly so as 3 to accommodate different internal diameters in the collection tube 4 10 as shown in Fig. 1. Fig. 2 also shows an annular bead 55 which is adapted to form a seal with the separator tube 16 as 6 shown in Figs. 4 and 5. By relying on thle bead 55 to form the 7 necessary seal, the tolerances on the diameter of the tubular 8 member 18 as shown in Figs. 4 and 5 becomes less critical.
9 Similarly, an annular recess 57 is provided adjacent the flange 34 so as to preclude contact between the tubular member 18 and 11 the flange 34 which could impair proper operation of the valve.
12 Referring now to Figs. 4 and 5, the valve apparatus or 13 plug 20 is shown in the operable position, i.e., the head 42 is 14 located above the seating surface 36. As also shown in Figs. 4 and 5, a filter 56 is inserted into the central cavity formed by 16 the wall 50 of the body member 28 so as to filter out fibrin and 17 any formed elements of blood which remain suspended in the plasma 18 or serum as the separator tube 16 is inserted into the collection 19 tube 10 in the direction indicated ~y arrow I as shown in Fig. 4.
~s the separator tube 16 is pushed in the direction indicated by 21 the arrow I, the head 42 is forced upwardly off the seating 22 surface 36 so as to permit the filtered serum or plasma to flow 23 around the valve body 40 and the head 42 and through the opening 24 46 in the flange 34 as depicted by arrows II.
In Fig. 5, the separator tube 16 is being withdrawn from 26 the collection tube 10 in the direction indicated by the arrows 27 III. Under these circumstances, the seating surface 44 of the 28 head 42 is in sealing engagement with sealing surface 36 so as 29 to prevent the flow of the serum or plasma 33 through the valve opening 46. As the separator tube 16 is withdrawn from the . .,~
~l M-727 1~87~ 73 1 collection tube 10, air passes between the sealing surface 32 and 2 the collection tube 10 as depicted by the arrows IV.
3 Reference will now be made to Fig. 6 wherein a modification 4 of the valve apparatus or plug of Figs. ].-5 is shown. More particularly, the valve apparatus or plug 20a includes a hood 58 6 adjacent the valve opening 46 and the head 42. The hood 58 7 includes a radially inwardly directed flange 60 and a central 8 opening 62. The flange 60 serves to deflect the serum or plasma 9 which flows through the opening 46 so as to avoid any squirting of the plasma out the end of the separator tube (not shown in 11 Fig. 6). The arrows V depict the deflection of the serum or 12 plasma. The remainder of the plug 20a shown in Fig. 6 is substan-13 tially identical to the plug 20 shown in detail in Figs. 2-5.
14 Referring now to the valve apparat~s or plug shown in Fig. 7, a plug 20b comprises a modified valve member 38b having substan-16 tially no body but merely the head 42. The struts or strands 17 48b are attached to a wafer-like projection 40b. Due to the 18 forces exerted by the strands 48b at the periphery of the head 19 42, the head 42 of the valve member 38b is particularly resistent to any deformation which cou:Ld result in squirting of the plasma 21 or serum through the opening 62. In other words, these forces 22 exerted by strands tend to maintain the valve head 42 in the 23 shape shown in Fig. 7 and th:is is also particularly important 24 in preventing the head 42 from becoming jammed open in the opening 46. As shown in Fig. 8, the strands 48b extend across the valve 26 opening 46 from the wall 50. This assures that the strands 48b 27 do not rub or become hung up on the flange 34 at the edge of the 28 opening 46 which might occur if the strands 48b did not cross to 29 the opposite side of the opening 46. It will be appreciated that even the projection 40b may be eliminated and the~strands attached 31 directly to the head 42. In order to avoid interEerence at point 63, , ~ ., .,. ,, ~; :
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M-727 1~87573 1 the strands 48b are attached at different elevations on the 2 wall 50.
3 The plug 20b of Fig. 7 also comprises an annular projection ~ ~
4 or bead 64 located on the wall 50 just above the filter 56. The ~;
bead 64 assures that the filter is not orced upwardly toward the ;~
6 valve member 38b thereby preventing interference therewith. An 7 additional annular bead 55 on the body 28 is also provided to form 8 the seal with the tubular member 18. In addition, a plurality 9 of check valves 66 extend through the flange 30 beneath the tubular member 18. These valves are closed when the separator tube 16 11 is inserted into the collection tube 10 as shown in Fig. 7, but 12 opened as the separator tube 18 is removed from the collection tube 13 10 as shown in Fig. 7a so as to allow air to enter the collection 14 tube. Such check valves 66 are disclosed in U.S. patent 3,954,614.
The valve apparatus or plugs 20, 20a and 20b are all made 16 by a similar method and therefore only the manufacture of plug 20a 17 will be specifically described by reference to Figs. 9-14.
18 As shown in Fig. 9, a valve apparatus or plug 20a has been 19 molded between a first mold section 100 and a second mold section 102. The first mold section 100 includes an outer portion 104 21 which partially forms the flange 30 and a central portion 106 22 whioh partially forms the walls 50 and a portion of the valve member 23 38 as well as the strands 48 within the chamber formed by the 24 walls 50.
The second section 102 of the mold comprises an outer 26 portion 108, an inner or central portion 110 and a sleeve 112 27 therebetween. The outer portion 108 forms the wall of the plug 28 20 including the beads 55. The inner or central portion 110 29 forms the flanges 34 and 60 as well as the valve opening 46. The central portion 110 also forms a substantial portion of the valve .
, ,, ~-727 ` ~)87S73 1 member 40 including the head 42 as well as cooperating with the ~-2 first section 100 of the mold to form the strands 48. After the 3 molding has been completed as depicted by Fig. 9, the mold sections 4 100 and 102 begin to separate as shown in Fig. 10. As the second section 102 separa~es from the first section 100, the flange 30 6 is released from the outer portion 104 of the first section 100 7 and the inner portion 106 is withdrawn from the interior chamber 8 of the plug 20a. The plug 20a remains in place with respect to 9 the outer portion 108, the inner portion 110 and the sleeve 112 of the second mold section 102 which, at this initial stage of 11 release, move as a unit.
12 In Fig. 11, the sleeve 112 has become stationary as the 13 outer mold portion 108 and the inner mold portion l:L0 of the 14 ~econd sectlon 102 continue to move so as to hola the flange 60 and the flange 34 and begin the release of the plug 20a with 16 respect to the second mold section 102. Simultaneously and in 17 accordance with this invention, the setting of the valve member 40 18 is initiated as the flange 34 which forms the valve opening 46 19 begins to deform so as to permit passage of the head 46 thexethrough.
Referring now to Fig. 12, the opening 46 in the flange 34 21 is now fully deformed as the head 42 of the valve member 38 passes 22 therethrough. This is accomplished by permitting the outer portion 23 108 and the inner portion 110 of the mold section 102 to continue 24 opening or moving with respect to the valve section 100 while the stationary sleeve 112 holds the flanges 60 and 34. It will be ;~
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26 noted that the valve member 38 including the head 42 is fully 27 retained within the mold members 108 and 110 as long as the flange 28 34 continues to be deformed so as to enlarge the opening 46. It 29 will be further noted that the strands 48 of the connective means are extensively stretched at this stage in the mold opening 31 procedure.
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1 In Fig. 13, as the mold section 102 exclusive of the 2 sleeve li2 continues to move, the strands 48 are stretched to a 3 point so as to provide sufficient force to pull the ~alve member 4 38 fxom the inner portion 110 of the mold section 102. Since the flange 34 has now returned to the original molded state, 6 i.e., underformed, the head 42 o the valve member 38 will not 7 pass through valve opening 46 when the valve member 38 is fully 8 released from the inner mold portion 110 as shown in Fig. 14.
9 It will therefore be appreciated that valve member 38 is molded within the chamber ormed by the walls 50 of the plug 11 20a. However, prior to removal of the valve from the mold, the 12 valve member 38 with the head 42 is moved from one side of the 13 valve opening to the other side to se~ the valve. Simultaneously 1~ with the setting of the valve, the connective means, i.e., the strands 48, are subjected to stretching so as to ul~imately 16 bias the valve member 38 to the closed position.
17 In the foregoing, a description is provided as to how 18 tension is developed on the strands 48. It will also be understood 19 that the tension on the strands 48 may be relieved by forcing the head 42 back through the opening 46. It will also be understood 21 that the head 42 may be molded in place on the opposite side of 22 the valve opening and then pushed ~hrough the opening thereby 23 placing tension on the strands which are appropriately positioned 24 on the wall 50 for this purpose.
In accordance with another aspect of the present in-26 vention, the valve apparatus described above may be employed with 27 a separator assembly of the Vacutainer type as shown in Fig. 15.
28 Fig. 15 discloses a sel-contained separation apparatus embodying 29 the invention which comprises a tubular container member 210 having two open ends which are closed respectively by a first closure 212 31 and a second closure 214 which are seated in the open ends. Each _ ~ _ 1~37573 :
1 of the closures 212 and 214 comprise a self~sealing elastomeric 2 material such as rubber or Kraton. As shown, closure 214 is 3 penetrated by a cannula 216 through which blood 218 is received 4 into the container 210. By creating a vacuum within the container 210,the blood is readily drawn into the container. Because of the 6 elastomeric nature of the closure 214, the cannula 216 may be re-7 moved from the closure 214 with the hole automatically closing.
8 In accordance with this invention, container 210 en-9 closes a novel piston means comprising a plug 220. The plug 220 comprises a sealing portion 228 including a substantially 11 cylindrical body which comprises a plurality of annular, peri-12 pheral sealing beads 230 which form a seal with the walls of the 13 container 210. The end of the sealing portion 228 remote from 14 the blood sample 218 comprises a radially inwardly directed ~n-nular flange 234 which i5 adapted to form a valve seat along the 16 surface 236 for movable valve member 238. The valve member 238 17 comprises a body poxtion 240 terminated by a sealing head por-18 tion 242 which is adapted to seat on the surface 236 along a 19 surface 244 at a valve opening 246.
In order to provide a closing bias on the valve member 21 238 which is independent of the diameter of the container 210, 22 resilient strands or strut members 248 are attached to the in-23 terior walls of the valve seating portion 228 o~ the plug 220.
24 As shown in Fig. 15, a filter 256 is inserted into the~
central cavity formed by the wall 250 of the valve seating por-26 tion 228. The purpose of the filter is to prevent ~fibrin and 27 any formed elements o the blood from passing through the valve 28 opening 44 during centrifugation. To prevent the filter 256 29 from riding up in the cavity formed by the wall 250, an annular projection or bead 264 is located on the wall 250 just abo~e 31 the filter 256. The bead 264 assures that the ~lter is not -1~, x Ib M-727 ~
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1 forced upwardly so as to interfere with the valve member 238.
2 The filter may comprise a variety of materials having pores 3 sufficiently smaller than the blood cellular material so as 4 to prevent the cellular material from piassing through the valve
5 opening 246.
6 During centrifugation, the plasma or serum of the blood
7 sample forces the head 242 upwardly and off the seating surface
8 236 so as to allow the serum or plasma to pass therethrough to
9 achieve a light phase at the end of the container 210 adjacent the closure 212 and a heavy phase at the end of the container 11 210 adjacent closure 214 as shown in Fig. 16. It will be under-12 stood that the strands 248 must provide the appropriate amount 13 of bias on the head 242 so as to permit the head 242 to lift 14 off the seating surface 236 during centriugation. At the same time, the strands 248 must provide sufficient b~as on the head 16 242 to assure closure on the surface 23~ after centrifugation is 17 completed.
18 In order to assure that the plug 220 w~ll appropriately 19 seek the interface between the light phase and the heavy phase as shown in Fig. 16, the plug 220 must have the appropriate 21 specific gravity. In this connection, it has been found that 22 an average specific gravity of 1.030 to 1.040 is particularly 23 suitable. One elastomeric material which has been found to be 24 well suited for providing the necessary bias on the valve member ~j f 25 38 as well as the appropriate specific gravity for the entire 26 plug including the filter is Kraton with appropriate fillers.
27 It must be appreciated that othèr elastomeric materials with 28 suitable specific gravities might be substituted.
29 In the embodiment of Fig. 17, a mechanical stop in the form of a projection 270is used to stop the plug 220 rather 31 than the specific gravity relied upon in Figs. 1-5. Accordingly, ' , ., ,; ,,~ .
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1 the average specific gravity of the plug 220 need only be greater 2 than the light phase, i.e., 1.030 or grleater so as to be sure 3 that the plug may be centrifuged through the plasma or serum.
4 In the plug of Fig. 17, an annular sealing flange 272 has been substituted for the beads 230. The flange 270 includes 6 annular relieved areas 276 which are provided so that the flange 7 may radially retract and extend to achieve the appropriate seal 8 at a sealing surface 274 which contacts the wall of the con-9 tainer 10. The remainder of the plug 220 is identical to that shown in Figs. 1-5.
11 Although specific embodiments of the invention have 12 been shown and described, it will be understood that other 13 embodiments and modifications may be utilized without departing 14 ~rom the true spirit and scope of the invention as set forth in the appended claims.
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