Device for separating the components of a liquid sample having higher and lower specific gravities

A device is provided for separating the components of a liquid sample by centrifugation by dividing that portion of the sample having a higher specific gravity from that portion having a lower specific gravity, by utilizing a dual component assembly arranged to move in an evacuated container into the area adjacent the two portions of the sample under centrifugal force. The assembly includes a substantially rigid core component which nests within a cup-shaped elastomeric component, and which components interact with each other to provide alternating dual seals and open flow paths in response to different pressure differentials on each side thereof.

BACKGROUND AND STATEMENT OF THE INVENTION 
This invention relates generally to a device which separates what is 
usually called the heavier and lighter fractions of a liquid sample. More 
particularly, this invention relates to devices or assemblies utilizing an 
evacuated tube placed under centrifugation wherein a liquid sample is 
placed in the tube, and subsequently the tube is subjected to centrifugal 
force in order to cause the heavier fraction (or the fraction having the 
higher specific gravity) to the closed end of the tube while the lighter 
fraction (or that fraction having a lower specific gravity) moves toward 
the open end of the tube. 
Such arrangements utilize some sort of barrier for moving into the area 
adjacent the two phases of the sample being separated in order to maintain 
the components separated for subsequent examination of the individual 
components. The thrust of all of the devices developed for use in the 
environment discussed above is to provide a barrier which divides cleanly 
the heavier and lighter fractions of the sample being separated. 
When taking blood samples for test purposes, for example, whole blood 
generally is drawn into an evacuated collection tube, and the tube is 
centrifuged to separate the blood into the relatively lighter phase or 
component, as discussed above which is serum or plasma, and a heavier 
cellular phase. A variety of mechanical devices have been utilized in the 
past including piston-type arrangements for moving freely in the liquid 
sample in the evacuated tube so that the piston arrangements subsequently 
come to rest in the divided area between the heavier and lighter phases. 
While these mechanical arrangements have proved useful in a limited sense, 
they have not been entirely successful because they do not provide the 
clean separation discussed above. 
The material utilized generally at this time for providing the barrier or 
separation between the heavier and lighter phases or the components having 
the lower and higher specific gravities include various thixotropic gel 
materials or sealants such as those described in U.S. Pat. No. 3,852,194, 
which is a mixture of silicone and hydrophobic silicon dioxide powders. 
Another form of thixotropic gel is a polyester gel which is presently 
utilized for a great many serum and/or plasma separation tube devices on 
the market. That material is taught and claimed in U.S. Pat. No. 4,101,422 
issued July 18, 1978. 
However, the present polyester gel serum separation tube requires, for 
example, special manufacturing equipment to prepare the gel and to fill 
the tubes. Both processes require rigid controls. Moreover, the shelf-life 
of the product is limited in that globules are sometimes released from the 
gel mass or network. These globules have a specific gravity that is less 
than the separated serum and will float in the serum and can clog the 
measuring instruments, subsequently, during the clinical examination of 
the sample collected in the tube. 
Moreover, while the gel is chemically inert to blood samples, if certain 
drugs are present in the blood sample when it is taken, there can be an 
adverse chemical reaction with the gel interface. 
With this invention, by contrast, a mechanical separator is utilized which 
is non-temperature dependent during storage and shipping, is more stable 
to radiation sterilization, and eliminates the need for a special 
transport tube which is required for gel separation devices as discussed 
above for improved barrier integrity during transportation. The 
arrangement herein utilizes a dual component mechanical assembly arranged 
to move in an evacuated tube under the action of centrifugal force in 
order to separate the two portions of the sample. 
The assembly includes a substantially rigid core component which nests 
within a cup-shaped elastomer component. The solid component, under 
certain operating conditions, is movable within the cup-shaped component. 
The two components operate together, and complement each other under the 
differing pressure differentials which are inherent in serum separation 
tubes, to provide alternating dual seals and open flow paths in response 
to those pressure differentials. As such, the arrangement herein provides 
a much more precise division between the two portions being separated from 
the original sample introduced into the tube. 
Before describing this invention in more detail, it should be well to note 
that the dual component device of the invention herein has a conventional 
specific gravity range within between about 1.03 and 1.09, and more 
specifically within the range of between about 1.05 and 1.06 so that the 
device will come to rest under centrifugal force substantially at the 
border between the heavier and lighter phases of the sample under 
consideration. 
In addition, the central core portion of the dual component device may be 
comprised of a substantially rigid moldable thermoplastic material such as 
polyvinyl chloride, polystyrene, polyethylene, polypropylene, polyesters, 
and mixtures thereof, with a limitation being that the material is inert 
to the sample introduced in the assembly of the invention so as not to 
interfere with any desired subsequent testing. The cup-shaped portion, in 
turn, may be comprised of any natural or synthetic elastomer or mixtures 
thereof, with, again, the limitation concerning being inert to the sample 
of interest. The stopper may be comprised of similar elastomer 
combinations. 
While the invention is directed to evacuated tubes in order to facilitate 
introduction of blood samples from the vein of a patient, it will be 
understood that the container in accordance with this invention does not 
necessarily need to be evacuated. 
Other objects and advantages of this invention will be apparent from the 
following description, the accompanying drawings, and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings in which like reference characters refer to like 
parts throughout the several views thereof, FIG. 1 illustrates the 
invention in the form of a serum separation tube having a closed end and 
an open end with the latter being arranged to be sealed by a cooperating 
stopper so as to maintain a vacuum in the tube once the stopper is in 
place. 
In FIG. 1, the assembly of the invention generally designated 10 includes 
tube 12 having an open end 14 and a closed end 16. Tube 12 is transparent 
so that the user may readily observe what is going on with the contents 
thereof. Tube 12 may be plastic but it is preferably glass. 
Elastomeric stopper 20 is provided for insertion into the open end 14 of 
tube 12. Stopper 20 includes an upper annular portion 22 and a lower 
annular portion 26 of lesser diameter, with the lower portion 26 being 
arranged to be inserted into tube 12 so that the internal surface 32 of 
tube 12 adheres to and seals against the external surface 30 of annular 
portion 26. Because of the differing diameters of lower portion 26 and 
upper portion 22 of stopper 20, an annular ledge or abutment 24 is 
arranged to seat on the top surface of open end 14 of tube 12 to further 
enhance the sealing between tube 12 and stopper 20. Stopper 20 further 
includes a vent 28 positioned at one point in the circumferential extent 
of the lower portion 26 of stopper 20. The purpose of vent 28 will be 
described below. Tube 12 may be open at both ends (not shown) with a 
stopper 20 inserted in each end. 
Further shown in FIG. 1 is a dual separator assembly 34, including a molded 
solid core 36 and an elastomeric cup-shaped flexible component 38. Solid 
core 36 nests in the cup-shaped elastomeric component 38. These two parts 
form dual seals 60 and 70. This is achieved by the annular ring portion 46 
of solid core 36 cooperating with the upper annular ring portion 44 of the 
elastomeric cup-shaped lower portion 38. 
Thus, surface 40 of portion 44 of the cup-shaped elastomeric portion 38 
bears against the internal surface 32 of tube 12 under certain conditions 
of operation of the device herein, while internal surface 42 of portion 44 
bears against the annular ring 46, as discussed above. These dual sealing 
positions come about when the pressure 56 above the dual component 
arrangement 34 is the same as the pressure 58 below the dual component 34. 
Further as can be seen in FIG. 1, central core component 36 includes a snap 
connector 50, integral with central core component 36, which extends 
through a bore 52 in the bottom wall 64 of the elastomeric cup-shaped 
component 38. Groove 54 serves to provide liquid access adjacent the 
bottom of component 36. As can be seen in FIG. 1, the snap connector 50 
extends through the bore and spreads to hold the two parts together. 
Further in bottom wall 64 of component 38 is a plurality of apertures 48 
providing flow communication between area 78 below the dual separator 
assembly 34, and area 84 between the two components forming the dual 
assembly 34 in conjunction with groove 54. 
In FIG. 1, because stopper 20 has not been seated within and sealed against 
the internal surface 32 of tube 12, the pressure differential between 
pressures 56 and 58 above and below dual assembly 34 are equal and at 
atmospheric pressure so that the dual assembly 34 provides the dual 
sealing action at annular contact points 60 and 70. 
Referring now to FIG. 2, the positioning of the parts is shown for the 
assembly 10 when evacuation is initiated. In this connection, it should be 
borne in mind that it is within the purview of the practitioner-in-the-art 
to simultaneously seat the elastomeric stopper 20 in the tube 12 with the 
evacuation of the tube through vent 28. That is, the application of a 
vacuum causes a withdrawal of air from the internal space of tube 12 
simultaneously with the stopper gradually sliding into the tube into a 
sealing closure of the open end 14 of tube 12. Thus, in the position shown 
in FIG. 2, a pressure differential has developed between the pressure 56 
above the assembly 34 (&lt;P) and the pressure 58 below the assembly 34. As a 
result, the assembly 34 is unseated due to that pressure differential. 
Referring to FIGS. 1 and 2, cylindrical core 36 is forced upward, and its 
outermost diameter is disengaged from the innermost diameter the 
cup-shaped portion 38. This causes a reduction in pressure, in addition, 
in a radial direction on the annular portion 44 of cup-shaped portion 38, 
along with the flexing upward of the bottom wall 64 which is in the form 
of a stretchable diaphragm. The outermost surface 40 of the upper annular 
sealing portion 44 of portion 38 moves radially inwardly from the inner 
surface 32 of tube 12. This causes a passage 62 and communication between 
the area above the assembly 34 and the area below assembly 34 as well as 
flow through passage 63 (former seal 70) between surfaces 42 and 46. 
When the evacuation has been completed, as shown in FIG. 3, stopper 20 is 
completely inserted into the open end 14 of tube 12. In addition, because 
pressures 56 and 58 have again equalized (P.sub.1), diaphragm wall 64 of 
the cup-shaped lower portion 38 of the assembly 34 moves downwardly into 
its normal position, and solid core 36 is pulled in a downward direction 
to return to the position causing the reestablishment of inner and outer 
dual seals 70 and 60. 
Referring now to FIG. 4, a blood draw needle 72 has been inserted through a 
stopper 20 for introducing a blood sample into container 12 from the vein 
of a patient. At the initial start of a blood draw, the assembly 34 is in 
the normal position shown in FIG. 4 with equalized vacuum 56, 58 above and 
below the assembly 34, respectively. 
Referring now to FIG. 5, in this position, the blood draw continues and a 
pressure differential is set up again between the pressure 56 (&gt;P.sub.1) 
and the pressure 58 (P.sub.1), with the pressure 56 being greater than the 
evacuated pressure established prior to blood draw. Because of the 
pressure differential, again, the separator assembly 34 moves into an 
unsealed position as shown in FIG. 5 with the solid core moving downwardly 
into the cup-shaped portion 38. Also, because of the pressure 
differential, the diaphragm bottom wall 64 of portion 38 moves downwardly. 
As blood draw continues, blood passes through the various areas indicated 
at 76 in FIG. 5 from upper portion 74 above assembly 34 and into the 
bottom portion 78 below assembly 34. For this passage, of course, both 
dual seals 60 and 70 are opened for allowing the passage of blood. Once 
the quantity of blood required is introduced into container 12, the needle 
72 is withdrawn and equalized pressure 80 (P.sub.2) and 82 (P.sub.2) is 
established above and below assembly 34 (FIG. 6). At this point, 64 has 
moved upwardly to its normal position resealing dual passages 60, 70. 
Then, the tube 12 is subjected to centrifugation. During centrifugation, 
the assembly 34 is forced into the unsealed position shown in FIG. 7. In 
this position, there is open passage between the area 78 below assembly 34 
and the area 74 above assembly 34 establishing momentary equilibrium areas 
90, 94 for the introduced sample just prior to separation. Moreover, 
because the assembly 34 has a specific gravity which is heavier than the 
serum and/or plasma or light phase of the sample being centrifuged in 
container 12, that portion of the sample having a specific gravity heavier 
than the assembly 34 moves below the assembly, while that portion of the 
sample which is lighter than the specific gravity of assembly 34 moves 
above the assembly. (FIG. 8) During centrifugation, the assembly 34 itself 
moves to the interface between the heavier phase 93 and the lighter phase 
92 of the initial sample taken. At this point, when centrifugation ends, 
diaphragm 64 moves to the position shown in FIG. 8, and the dual seals 60, 
70 move into place simultaneously with this movement of the assembly into 
its position at the interface, as discussed above. Because of this, a 
barrier is formed between the two phases. 
Referring now to FIGS. 9-13, inclusive, FIG. 9 shows a cross-sectional view 
of the cup-shaped component 100 of this embodiment. As can be seen, 
component 100 is configured somewhat differently than 38 in that side 
walls 104 are clearly thinner than bottom wall 106. Also, bottom wall 106 
has a beveled configuration ending in a central plateau 110 which imparts 
more rigidity to wall 106. A plurality of liquid flow communication bores 
108 are disposed around the circumference of wall 106, as clearly shown in 
FIG. 10. FIG. 10, in this regard is a top-plan view of component 100. 
Also, shown in FIGS. 9 and 11 is the upper annular sealing portion 102 of 
cup-shaped component 100 with inner 120 and outer 128 sealing surfaces. 
FIG. 11 shows the solid central core component 114 with sealing ring 118 
and sealing surface 122 cooperating in the sealing position with the 
resilient cup-shaped component 100. As can be seen in FIG. 11, an integral 
snap connector 116 depends from the bottom surface of core 114 with an 
enlarged portion 119 which snaps through bore 112 into locking engagement 
with the bottom surface of wall 106. 
Thus, as can be seen in FIG. 11, the device is in the sealed position or 
mode as it is assembled and inserted into tube 12 and engaging surface 32 
thereof. Side wall 104, as can be seen, has less curvature due to the 
compression of the outer seal 124 with surface 32. While the device is 
fairly tight at this period it can be moved or positioned in the tube. 
Bottom point i03 may touch surface 32 depending upon tolerances. 
FIG. 12 shows the device in the unsealed upper position or mode which takes 
place during evacuation of tube 12. Due to the pressure differential above 
and below the dual component system, a force is applied upward on the 
system. The seal 124 resists most of the force imparted and the device 
remains generally stationary. The strength of the bottom wall 106 also 
resists this force. As can be seen, however, the thinner and weaker side 
wall 104 collapses until pressure equilibrium is reached, at which time 
the side wall will return to its natural state and pull core 114 back to 
its sealed position shown in FIG. 11 with dual seals 124 and 126. 
In FIG. 13, the device 100 is shown in the unsealed downward position or 
mode. This occurs during blood draw or centrifugation. During blood draw, 
the pressure differential creates a downward force. Thus, the beveled 
bottom wall 106 moves or collapses downward pulling core 114 into the 
unsealed position through snap connection 116, and then returns to normal 
when pressure equalizes. During centrifugation, the device moves up or 
down the tube in the unsealed position as described previously with the 
embodiment 34. 
Thus, as can be seen from the above, the invention provides a dual assembly 
arrangement for separating a liquid sample into the components thereof 
having a higher specific gravity and the components thereof having a lower 
specific gravity, or more specifically the serum/plasma phase and the 
cellular phase of a blood sample. The arrangement herein utilizes a unique 
dual arrangement of a solid core with a flexible cup-shaped diaphragm 
portion holding the solid core, and with the two parts interacting with 
each other in response to variations in pressure differential on each side 
thereof to form dual seals at appropriate times during use, and to provide 
flow passage around this dual assembly, at appropriate times to cause the 
appropriate separation of the two phases. 
Also, because the arrangement herein is a mechanical arrangement as opposed 
to a gel, less rigid control is required in order to prepare and 
manufacture the device of the invention. Moreover, less procedures are 
required in order to produce a product, in accordance herewith, having an 
extended shelf-life, with the product being chemically inert to any 
chemicals in a sample introduced into the device. In addition, the device 
of the invention is substantially more stable in the environment of 
radiation sterilization, and is not temperature dependent during storage. 
While the form of apparatus herein described constitutes a preferred 
embodiment of the invention, it is to be understood that the invention is 
not limited to this precise form of apparatus, and that changes may be 
made therein without departing from the scope of the invention which is 
defined in the appended claims.