Blood phase separation means

A blood collection device includes a tube for receiving a sample of whole blood for centrifugal separation into the lighter phase, plasma or serum, and the heavier cellular phase. The tube has a needle-pierceable stopper at the opposite end for maintaining a negative pressure in the tube. A blood phase partitioning device is disposed within the tube and includes upper and lower members with the upper member having a greater specific gravity greater than that of the lower member but together having a specific gravity between that of the lighter phase and that of the heavier phase. A sealant is disposed between the members and in contact with each member and has a specific gravity equal to the average of the two members. During centrifugation of the blood, the partitioning device automatically moves to the interface of the two phases, and the members move toward each other forcing the sealant radially outwardly from between the members and against the inner wall of the tube to provide a permanent partition between the two separated phases.

BACKGROUND OF THE INVENTION 
This invention relates to fluid collection devices and more particularly to 
blood collection devices having means for partitioning the lighter and 
heavier phase of blood. 
In the testing of blood samples, whole blood is usually drawn into an 
evacuated tube and the tube placed in a carriage for separating the 
lighter and heavier phases so that the lighter phase may be isolated and 
tested. Many different types of phase partitioning devices which provide a 
barrier or seal between the separated phases have been used or proposed 
for the purpose of allowing the lighter phase to be decanted or poured 
into a transfer tube free of cells, or to enable the two phases to remain 
in the collection tube without intermixing during shipment to a laboratory 
where the lighter phase is removed and subjected to analysis. 
In U.S. Pat. No. 3,852,194 and U.S. Pat. No. 3,780,935, gel-like materials, 
such as a silicone material, is disposed in a collection tube, the 
gel-like material having a specific gravity between that of the lighter 
phase and that of the heavier phase so that it flows to the interface of 
the two phases and forms a partition between them. These devices generally 
require a relatively large amount of gel-like material, and in addition to 
the relatively high cost of the material, a relatively large surface area 
of the material is in contact with the blood components during and after 
centrifugation. This relatively large surface area of contact tends to 
increase the danger of interaction between the gel-like material and 
lighter blood phase which is to be analyzed. For example, collection tubes 
are used that employ silicone gel-like materials which produce oil in the 
lighter phase which tends to clog and restrict the flow of fluid in the 
tubing of blood analyzing equipment, especially in automatic blood 
analyzers. This patent also discloses a relatively more complicated 
arrangement which includes a spool member, such as of rubber, having a 
hole through it and which has a wiper for sealing contact with the inner 
wall of the tube. The spool moves toward the closed end of the tube while 
the gel-like material moves toward the stopper and closes the hole in the 
spool member upon separation of the phases. 
In U.S. Pat. No. 3,909,419, a plasma separator is used wherein a pair of 
cylinders are disposed in the container and a plurality of micro 
encapsulated beads of gelatin are disposed between the cylinders. The 
specific gravities of the two cylinders and the gelatin beads are such 
that, by increasing the speed of the centrifuge after the phases have been 
separated, the cylinders move toward each other and rupture the 
encapsulated beads to cause the gelatin to form a seal between the 
cylinders and inner wall of the container at a location between the two 
phases. This arrangement is relatively expensive since it requires the 
manufacture of encapsulated beads and also requires centrifugation at two 
different speeds. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a novel 
partitioning means for maintaining the lighter and heavier phases of a 
fluid, such as blood, separated, and which is highly effective, relatively 
simple, and economical. In accordance with the present invention, a fluid 
collection device is provided which includes a collection container for 
receiving a liquid adapted to be centrifugally separated into relatively 
lighter and heavier phases, a pair of movable members in the container 
each having a different specific gravity, and a sealant material disposed 
in contact with and between the members. The specific gravity of the two 
members together is intermediate the specific gravity of the lighter phase 
and that of the relatively heavy phase, and the specific gravity or the 
sealant is substantially equal to that of the two members together. The 
sealant is adapted to be squeezed outwardly from between the members and 
into contact with the interior wall of the container at a location between 
the separated phases. These as well as other objects and advantages of the 
present invention will become apparent from the following detailed 
description and drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawing, and especially to FIGS. 1-4, there is shown a 
fluid collection device 10 including a container or blood collection tube 
12 which is preferably of transparent glass and which is shown closed at 
the bottom by an integral portion 14 of the tube. The tube 12 has an upper 
open end that is closed by a closure or stopper 16 which extends into the 
open end in sealing engagement with the side walls of the tube. The 
stopper 16 is pierceable by a needle and self-sealing, and may be formed 
of a suitable elastomer, such as butyl rubber. The collection tube is 
provided with a desired negative pressure or partial vacuum that is 
maintained by the stopper 16. Disposed within the tube 12 is a movable 
blood phase partitioning or separation device 18 and which is shown alone 
in FIG. 2. 
A sample of blood may be drawn into the blood collection device 10 by use 
of a double-ended needle cannula or a conventional needle holder and tube 
guide device (not shown) having a double-ended needle cannula. For 
example, after the distal pointed end of the needle cannula is inserted 
into the vein of a patient, the device 10 is moved within the holder until 
the proximal pointed end of the needle cannula has pierced the stopper 16 
and communicates with the interior of the tube 12, whereupon blood flows 
into the tube. The filled tube is removed from the holder and placed in a 
centrifuge with the lower end 14 radially outwardly of the stopper and 
axis of rotation of the centrifuge. The phase separation device 18 will 
automatically move within tube 12 during centrifugation, for example, as 
illustrated in FIGS. 3 and 4, with the device 18 forming a partition or 
barrier across the tube (FIG. 4) upon complete separation of the blood 
into the lighter phase 19, serum or plasma, and the heavier cellular phase 
20, as will be more fully discussed hereinafter. 
The phase partitioning device 18 includes, as viewed in the drawing, upper 
and lower movable members 21 and 22, and a gel-like sealant material 24 
disposed between the members 21 and 22 and which is adapted to be squeezed 
outwardly from between the members. The two members are formed so that the 
average specific gravity of the two members together is between the 
specific gravity of the separated lighter phase of blood, and that of the 
separated heavier cellular phase. Also, the sealant 24 is formed of a 
material, as will be further discussed, that has a specific gravity 
substantially equal to the average specific gravity of the two members 21 
and 22 together. Because the specific gravity of the device 18, that is, 
of the two members 21 and 22, and sealant 24 together, is intermediate 
that of separated light and heavy phases, the device 18 will move during 
centrifugation and arrive at the interface of the two phases upon complete 
separation of the phases. The upper member 21 is made to have a specific 
gravity greater than that of the lower member 22 and is located radially 
inwardly toward the axis of rotation during centrifugation. Thus, during 
separation of the phases, as the density of the fluid below the device 
increases, and particularly as the device 18 approaches its final 
position, the two members 21 and 22 move toward each other extruding or 
squeezing the sealant 24 generally radially outwardly from below the lower 
extremities of the upper member 21 and into engagement with the interior 
walls of the tube at the interface of the two phases 19 and 20 so that the 
device 18 provides an annular, permanent partition or barrier sealing the 
separated phases from each other as seen in FIG. 4. 
As indicated in FIG. 2, the upper member 21 of the partitioning device 18 
has an upper portion 26 having a generally tapered or semi-spherical, 
domed upper surface with its highest point at the vertical axis of the 
device. The upper portion 26 is integral with an annular, peripheral 
portion 28 and an annular central piston portion 30 at the bottom of the 
member 21. The annular portion 28 and piston portion 30 are concentrically 
spaced from each other. The upper domed portion 26 of member 21 allows the 
blood cells to slide off and past the member to avoid the trapping of 
cells above the device. The bottom member 22 is generally cup-shaped and 
has a bottom tapered or domed portion 32 integrally connected with an 
annular, stepped, peripheral wall 34. The sealant material 24 is disposed 
within a cup-shaped, upper recess 36 in member 22 with the bottom side of 
the piston 30 normally facing and engaging the upper surface of the 
material 24. The bottom surface of the piston portion 30 and facing bottom 
surface of recess 36 are solid, flat, circular surfaces. The diameter of 
the piston portion 30 is substantially less than the diameter of the 
annular recess 36 so that when the members 21 and 22 move toward each 
other during centrifugation, the sealant 24 flows in the space between the 
side walls of recess 36 and the outer surface of piston 30. The upper 
portion of the wall 34 enters the annular space between the portions 28 
and 30 but is spaced to permit flow of sealant from the device. More 
specifically, the sealant 24 moves generally radially outwardly across the 
bottom surfaces of the upper member 21 including the bottom surfaces of 
the piston portion 30 and bottom surfaces of annular portion 28 of member 
21, as well as flowing across the upper end surface of the portion 34 of 
member 22, as viewed in the drawing. The sealant flows into contact with 
the interior wall of the tube with the sealant completely surrounding the 
members. 
The sealant 24 is hydrophobic and inert with respect to the blood 
components, and is tacky or somewhat adherent to glass and plastics, and 
should hve a consistency or viscosity such that it is substantially 
non-flowable at rest or under normal handling conditions such as during 
tipping, mailing or shipping. Preferably, the sealant 24 includes 
principally a liquid hydrocarbon polymer, such as polybutene, liquid 
butyl, or liquid polybutadiene. A preferred sealant is a mixture of liquid 
polybutene and a filler of powder such as inert silica powder. A highly 
satisfactory mixture for use as a partitioning material 24 includes 100 
parts by weight of liquid polybutene, known as Polybutene Grade 24, 
manufactured by the Chevron Chemical Company of San Francisco, Calif., 20 
parts by weight of conventional hydrophillic silica powder (SiO.sub.2) 
filler material, known as Min-U-Sil 10, manufactured by PGS (a subsidiary 
of ITT) of Pittsburg, Pennsylvania, and 9 parts by weight of a second 
silica powder known as Aerosil R-972, from Degussa Inc., Pigments 
Division, of New York, N.Y. The above Polybutene Grade 24 has a specific 
gravity of 0.898 at 60/60.degree. F (ASTM D-287), and a viscosity of 
40,000 SSU at 100.degree. F (ASTM D-445 and D-446). The Min-U-Sil 10 
powder has a specific gravity of about 2.65 and with the majority of it 
having a particle size below 10 microns. The Aerosil R-972 silica powder 
is a hydrophobic silica powder having a specific gravity of about 2.2 and 
an average size of about 20 .times. 10.sup.-7 cm. This latter powder may 
be made hydrophobic by a process including flame hydrolysis of silica, and 
then reacting the silica with dimethyl dichlorosilane and steam in a 
fluidized bed reactor heated to about 400.degree. C by means of an inert 
gas such as nitrogen (publication Chemiker-Zeitung/Chemische Apparatur 89 
(1965), 437-440, Heidelberg/Germany). The specific gravity of the combined 
materials or mixture forming the separation material 18 was about 1.045 
and had a viscosity or consistency such that it would not flow when the 
tube was tipped or mailed, but would flow during centrifugal separation of 
the phases when there was a suitable difference in specific gravity 
between the two associated members of the device. The viscosity of the 
sealant mixture may be varied by varing the proportions of the liquid 
hydrocarbon polymer and filler. 
Since the specific gravity of whole blood is generally about 1.05, that of 
the light phase about 1.03, and that of the heavier phase about 1.08, the 
average or total specific gravity of the two members 21 and 22 together 
may be about 1.05. The specific gravity of the sealant material 24 can 
also be about 1.05, that is, approximately equal to the average specific 
gravity of the two members and which is intermediate the specific 
gravities of the light and heavy phases. The materials used in forming the 
members 21 and 22 should be inert with respect to the separated blood 
phases. Various types of materials are useful in forming the members 21 
and 22, and each may be formed, for example, of one or more plastic 
materials, such as polycarbonate, polypropylene, a copolymer of 
methylmethacrylate and styrene, or the like. One member may be formed or 
molded of a different plastic material than the other associated so that 
the specific gravity of the upper member 21 is greater than that of the 
bottom member. For example, the upper member 21 may be molded for a 
copolymer of methylmethacrylate and styrene and have a specific gravity of 
about 1.13, while the lower member 22 is formed of polypropylene and have 
a specific gravity of about 0.9. By suitable proportioning the volumes of 
the two members, the average specific gravity is readily made to be 
between those of the separated light and heavy phases of blood. 
When serum separation is required and the tube has only one end which is 
operable, such as tube 12, the outer diameter of the partitioning device 
18 should be small enough relative to the inner diameter of the tube 12 to 
permit the passage of the blood clot past the device 18 where the device 
18 is inserted prior to the introduction of blood. When plasma separation 
is required, an anti-coagulent, such as heparin, can be inserted in tube 
12, such as during manufacture of the device 10, which will, of course, 
prevent a clot from forming so that the outer diameter of the partitioning 
device 18 may be close to the inner diameter of the glass tube 12. Where 
serum is to be separated and the outer diameter of the device 18 is close 
to the inner diameter of the collection tube such that the blood clot 
cannot pass by the device 18 during centrifugation, the device 18 may be 
inserted into the tube after the blood has been introduced or a 
double-ended tube may be used. For example, in tubes having two removable 
stoppers, one on each end, the whole blood can be inserted through one 
stopper of the tube containing device 18 and the device placed in a 
centrifuge such that the heavy phase moves toward that stopper. In this 
way, the serum (or plasma) can be removed after centrifugation by removal 
of the other stopper. In the latter case, as well as in the illustrated 
embodiment, the partitioning device 18 is, of course, inserted into the 
collection tube such that the movable member having the greater specific 
gravity, member 21, is radially inwardly of the other member 22 during 
centrifugation and will be adjacent the separated ligher phase in order 
that the two members move together and force the sealant 24 to flow 
radially outwardly. 
As best seen in FIG. 2, the sealant 24 is normally substantially entirely 
enclosed by the piston portion 30 and the inner walls of recess 36. Only a 
relatively small surface area of the sealant, such as indicated at 40, is 
exposed to external fluids when the device 18 in its initial condition 
shown in FIGS. 1 and 2. Even during and after centrifugation, the surface 
area in contact with the separated phases 19 and 20 is relatively small 
since the members 21 and 22 provide a major portion of the device 18 in 
its final partitioning condition (FIG. 4). Thus, there is less chance of 
interaction between the sealant of 24 and the separated phases. 
In the modified form of the invention illustrated in FIGS. 5-8, a blood 
collection device 43 is shown including a glass tube 44 having an upper 
open end closed by a rubber stopper 46, the tube and stopper being similar 
to the tube and stopper of collection device 10. Disposed in the tube 44 
is a phase partitioning device 48 of modified construction. 
As seen also in FIG. 6, partitioning device 48 includes upper and lower 
piston members 50 and 52 and a quantity of a hydrophobic gel-like sealant 
material 54 disposed between the members 50 and 52. The upper member has 
an upper domed portion 56 integral with a circular portion 58 which has a 
flat, solid bottom surface 59 in contact with sealant 54. The lower member 
has a bottom, domed portion 60 integrally connected with a circular 
portion 62 which has a flat, solid, circular upper surface 61 in contact 
with sealant 54 and which faces the flat circular bottom surface of member 
50. The sealant material may be the same material as that of sealant 
material 24 discussed above in connection with the embodiment illustrated 
in FIGS. 1-4. The members 50 and 52 may also be formed of suitable 
plastics such as those previously mentioned herein. The specific gravity 
of the upper member 50 is greater than that of the lower member 52, while 
the specific gravity of the sealant 54 and the average specific gravity of 
the two members 50 and 52 are intermediate those of the separated lighter 
and heavier phases. For example the upper member 50 may be formed of 
polycarbonate and have a specific gravity of 1.2 while the lower member 52 
may be formed of polypropylene and have a specific gravity of 0.9. Where 
the volumes of the two members 50 and 52 are equal, the average specific 
gravity of the two is, of course, 1.05 which may also be the specific 
gravity of the sealant 54. 
As illustrated in FIGS. 7 and 8, when blood has been introduced into the 
tube 44 and the tube centrifuged, the partitioning device 48 migrates to 
the interface of the phases or to a position between the phases. Because 
the member 50 has a greater specific gravity than that of member 52 and is 
radially inwardly with respect to the axis of rotation during 
centrifugation, the members move together as the phases become separated. 
The sealant 54 is extruded or squeezed outwardly into contact with the 
inner walls of the tube 44 with the two members and sealant forming a 
permanent partition across the tube to seal the phases from each other, as 
seen in FIG. 8. 
In both partitioning devices 18 and 48, the sealant, as it is being 
squeezed out from the two associated members, flows generally radially 
outwardly past the facing sides or ends of the two members since this is 
the only flow path for the sealant in the illustrated embodiments. The 
sealant is displaced by the members and flows over the facing sides until 
the members engage each other. 
The somewhat tacky sealant is in direct contact with bottom and top 
portions or facing sides of the two associated members of the partitioning 
devices 18 and 48 in their normal or initial conditions (FIGS. 1, 2, 5 and 
6). In this way, the two members of each partitioning device are 
adhesively held together by the sealant so that the devices can be readily 
handled and inserted into collection tubes without separation of the 
members and without special means for holding the members and sealant 
together. 
With the partitioning device 48, a somewhat greater surface area of sealant 
is in contact with external fluids in the initial condition of the device 
and before centrifugation than with device 18. However, the members 50 and 
52 are of simpler configuration than members 21 and 22. 
It was found that when the sealant was a mixture of liquid polybutene and a 
filter, such as given above by way of example, substantially no oil was 
introduced into the lighter phase that would clog or restrict flow of 
fluid in tubing associated with blood analyzers. 
In partitioning device 18, the two members tend to be guided, for axial 
movement toward each other since the piston portion 30 enters the recess 
36 so that a generally even distribution of sealant around the members is 
obtained. Other guides for device 18 and 48 can be used where desired to 
ensure that the sealant is evenly squeezed out from the members. For 
example, a central guide hole may be provided in one member for guidingly 
receiving a center guide pin on the associated member to maintain the 
facing surfaces of the members parallel as the sealant is squeezed 
radially outwardly toward the tube walls. 
In each of the devices 18 and 48, an end surface at the bottom end of the 
upper member (21, 50) is axially spaced from and in facing relation with 
an end surface at the upper end of the lower member (22, 52) with the 
sealant in direct contact with these adjacent facing end surfaces. The 
sealant flows generally radially outwardly during centrifugation through 
spaces defined by adjacent or facing end surfaces of the members. The 
associated upper and lower members of each of the partitioning devices 
shown are completely axially spaced from each other with the sealant 
holding them together. The partitioning devices may be readily assembled 
by applying the sealant to one member and lightly touching the second 
member to the free surface of the sealant. 
As various changes could be made in the above construction without 
departing from the scope of the invention, it is intended that all matter 
contained in the above description or shown in the accompanying drawing 
shall be interpreted as illustrative and not in a limiting sense.