WO1996018897A1 - Separator float for blood collection tubes - Google Patents

Abstract

A separator float (40) has a generally cylindrical body (44) and a water swellable material (45) fitted around at least a portion of the generally cylindrical body. Upon being exposed to water the water swellable material (45) swells to form a seal within the tube (30) or other vessel containing the seperator float (40). The separator float (40) is preferably used in a blood collection tube (30) and has a specific gravity between specific gravities of a light phase and a heavy phase of the blood. After the blood has been collected and centrifuged the separator float (40) moves to a position between the light phase and the heavy phase and the water swellable material (45) is exposed to water in the blood causing the material to swell and create a seal. Thereafter, the serum or plasma as well as white blood cells, lymphocytes, monocytes and platelets can be removed from the blood collection tube (30).

Description

96/18897 PC17US95/16133

SEPARATORFLOATFORBLOOD COLLECTIONTUBES

BACKGROUNDOFTHEINVENTION

Field of the Invention

The invention is related to methods and apparatus to separate, and

isolate for testing, serum or plasma, red cells, and white cells in evacuated blood

collection tubes; obtaining oil free plasma or serum; and harvesting of white cells.

Brief Description of the Prior Art

Human blood is routinely collected in sealed, evacuated test tubes and

centrifuged to separate the lighter serum or plasma portion from the heavier red blood

cells. Typically a portion of the serum or plasma is then removed and tested. While the

separated blood is stored awaiting testing certain chemicals can migrate between the

separated layers giving incorrect test results. Consequently, the art has developed a

variety of separators having a specific gravity between the serum or plasma and the red

blood cells. These separators are either solid devices or gels.

The first solid separator was disclosed in United States Patent No.

3,508,653 to Coleman. That device was a rubber or other elastomeric cylinder. A

major problem with that device was the inability to maintain a seal because it is costly

to maintain the precise inner diameter of the test tube when mass produced. The

separator of Lawhead's United States Patent No. 3,814,248 was the next solid separator

development following Coleman's invention. Lawhead's separator is a centrifugally

motivated spool originating from and placed adjacent to a vacuum maintaining stopper.

There is also a polystyrene sphere free and unconstricted within the hollow inside of the tube. In use, blood is collected in the tube and is centrifuged. That action induces the

free sphere to move under centrifugal force to join the socket-like underside of the

floating rubber spool at the interface of the heavy and light phases. This product was

unable to be used for the harvesting of serum because the floating ball frequently

became enmeshed in the clot, preventing enclosure of the valve-like separator. Further,

the separator did not seal firmly enough to withstand more than mild shock to the tube

of separated blood, resulting in remixing of plasma and cells during transport, and other

handling.

Ayres' United States Patent No. 3,779,383 describes a complicated,

costly device in which the blood introduction end of the tube is opposite to the movable separator end of the tube, .and abutting an impenetrable rubber closure. Ayres'

embodiment was unable to provide interface separation of the light .and heavy phases of

the blood because the separation element did not possess a specific gravity intermediate

the two phases, but relied on an arbitrary stop element molded into the collection tube, combined with a centrifugally operated element having a specific gravity considerably

higher than the blood cells. Blaivas was issued United States Patent No. 3,786,985 for

a device very similar to the Ayres' collection tube, excepting that the centrifugally

motivated separator element abutted the needle penetrable stopper.

North in United States Patent No. 3,931,018 discloses a solid separator

for use in separation of blood serum and blood plasma using centrifugal force that must

be inserted into the blood collection tube after blood collection. This device has a disc

filter element above the solid separator having a specific gravity intermediate the light

and heavy phases. The product has not attained significant acceptance because it is less

convenient and less efficient to use and compromises sterility. Others have made centrifugally motivated solid separator devices of various configurations including a

hollow, piston like, coaxial tube disclosed in United States Patent No.4,159,896 to

Levine et al., or ring disclosed in United States Patent No. 5,236,604 to Fiehler, a

closed end coaxial tube disclosed in United States Patent No., 4,946,601 to Fiehler, an

umbrella shaped solid separator device designated to ascend to the interface during

centrifugation disclosed in United States Patent No. 4,152,270 to Cornell, and a dual

component assembly having a rigid conical core surrounded by a cup-shaped

elastomeric component disclosed in United States Patent No.4,877,520 to Burns.

Tubes containing these separators are limited in their function, and cannot be used for

transport, or with many of the newer large high through-put analyzers.

J.A. McEwen, et al, in United States Patent No. 5,030,341, disclose a

solid separator system in which blood collection tubes are rotated on their axis to

centrifuge the contents, rather than in the conventional way in which a blood filled tube

is rotated with the tube's axis and contents rotate perpendicular to the centrifuge's axis

of rotation. Such a system does not appear to be economical, since a complete change

in equipment requirements, particularly the centrifuge device must be made. The system also requires relatively expensive disposable collection tubes.

As a result of the difficulty in designing what has been considered a

commercially viable solid separator, manufacturers have resorted to the use of semi-

solid, or thixotropic gel materials. A thixotropic gel is used in this context to mean a

material formulated to remain rigid enough to remain in place, i.e., "firm", or "solid",

until an external stress, such as a centrifugal force is applied. In a vacuum collection tube containing blood and gel, centrifugation of the tube at the proper level of

acceleration (g force) would cause the gel to deform, flow to the interface between the packing cells and the lighter liquid phase, and finally come to a stable settled state

reformed into a disc or cylindrical segmented barrier between the heavy phase, and the

light phase.

Lukacs and Jacoby (United States Patent Nos. 3,780,935 and 3,963,119)

introduced the use of a very viscous silicone separator material prepared by intimate

mixing of silicone oil and amorphous silica in proper proportions to yield a highly

viscous sealant material having a specific gravity in the range between the specific

gravity of the light phase and the specific gravity of the heavy phase of blood. They

claim the silicone material in these patents, used with a funnel-like device inserted into

the tube of collected blood, flows into the centrifugally separating blood, forming a

barrier layer of viscous silicone oil and silica material with a specific gravity about 1.03

to 1.05. This product, sold under the trademark "SURE-SEP", provides a poor seal

because the composition is not a firm gel and flows under gravitational force alone. It

has the great disadvantage of needing to be inserted after the blood has been collected

and not being an element assembled and integrated into the blood collection tube.

A further approach is the addition of granulated or powdered materials

having a specific gravity intermediate the light and heavy blood phases to tubes of

collected whole blood, followed by centrifugation, for separation of the heavy and light

phases of the blood. Use of insoluble small particles of the desired specific gravity first

described by Nishi in 1965, CJin. Chem. Acta. ϋ (1 65) pp. 290-292. Another

modification of this technique was patented by Adler in United States Patent No.

3,647,070. Adler added water-swellable, non-ionic hydrophilic

polyhydroxyethylmethacrylates or polyacrylamide hydrogels in granulated or disc form, with a specific gravity between the two centrifuged, separated phases. These materials were added to blood collection tubes only afrer centrifugation to provide for a

barrier between the heavy and light phases. Neither case provides for an integrated

blood collection tube that permits a separation of whole blood collected, without the

transference of plasma through the interstices. The blood corpuscles squeeze through

the gaps between the solid particles, even when swollen and compacted after

centrifugation. Further, the granulated separator mass is readily broken by impact, or

unusual movement, and the container must be protected from shock during transport.

Zine, received United States Patent No. 3,852,194 for the apparatus and

method of using a silicone oil containing a silica thixotropic composition in a vacuum

blood collection tube. The tube assembly with the silica/silicone oil gel composition in

a vacuum collection tube uses an energizer plunger to move the gel toward it's sealing

position between the separated phases. Subsequent to that patent there has been much

development of an incremental nature intended to formulate many subspecies of

silicone gels having desirable properties such as radiation stability. These efforts have

generally been directed to mixing silicone oil with amorphous silica, and often a

surfactant for gel network formation and maintenance. Usually, hydrophobic

amorphous silica particles were used to provide optimal conditions of stability of the

thixotropic material, along with the desired specific gravity, and stabile viscosity.

Other manufacturers later replaced the original dimethylsiloxane (silicone) oils with

other organic oils to compound thixotropic gels from amorphous silica.

Difficulties in providing silicone gel commercial products, have caused

abandonment of this material for use in blood separator assemblies by Sherwood,

Becton Dickinson, and the original group that introduced the Lukacs and Jacoby

products, General Diagnostics. United States Patents Nos. 4,021,340 and 4,180,465 96/18897 PC17US95/16133

have been issued for thixotropic blood separator gels using polybutene in lieu of

dimethylsiloxane oil for use in mixing with amorphous silica. Becton Dickinson

replaced silicone oil based gels around 1980 using gels based on polyester oil in the

"SST" product following the teaching of Lamont and Braun in United States Patent

Nos. 4,101,422 and 4,148,764. This polyester gel, and virtually all commercial

thixotropic gels, require mixing an oil with amorphous, usually hydrophobic silica to

adjust specific gravity and to ensure thixotropy. Following the same trend of mixing a

base oil with silica, the Terumo Corporation obtained United States Patent

No.4,172,803 for a gel containing four additional butene related polymers.

Okuda, Abo, and Shinohara were issued United States Patent No.

4,140,631 for a sealant comprising alkyl acrylates or methacrylates as sealants, claiming a significant advantage of clarity, and ability to dispense with the need for

amorphous silica. In this case a high viscosity Newtonian sealant is the result. If

amorphous silica is added the resultant sealant becomes a thixotropic gel which will be

practically transparent.

Mendershausen has demonstrated the existence of serious problems

associated with the use of gel compositions of oil and silica when used as separators in

blood collection tubes. In the case of certain Eastman Kodak Products, oil globules

have been seen in the light phase of the blood and oil films at the top of the light phase

often seriously affect results of blood glucose ("blood sugar") tests. The oil can form a

film on the test slides, causing blocked diffusion of the substance being analyzed into

the slide.

In one Boehringer-Mannheim product, the BMC Hitachi 747 Chemistry

Analyzer, it was found that ion specific electrodes can cause reporting of spurious sodium levels in patients, because polyester oil droplets originating from gels float

freely in the light phase of separated blood, or form oil films over the light phase of the

blood. The oil is thereupon transferred onto electrode probes that are immersed into the

light phases of the blood for testing. Mendershausen believes that the oil coating on the

surface of the sodium electrode probe insulates the electrode, changing the electrical

potential, and consequently the reported values of the sodium. Such changes on the

sodium electrode can affect other electrodes (potassium, calcium, chloride, etc.) and can

lead to grave problems resulting from the inaccuracies reported.

Separation of oil from the gel in blood separator tubes of oil has been

noted by engineers in Sherwood assigned patents, earlier by Murty, and subsequently

by Fiehler (United States Patent Nos. 4,180,465, 4,946,601, 5,236,604, and 5,269,927)

Solutions offered ranged from use of polybutene oil in place of silicone oil, isolation of

the gel prior to blood collection, and the use of plastic oil capturing devices. In all the

disclosures, the importance of the problem was restated and reoutlined, but no

satisfactory solutions were provided because the root cause was not eliminated.

Inevitably, blood separation tubes containing gel released oil during centrifugation,

because all the gels comprise an inherently unstable mixture of two phases of materials,

one is heavier than the heaviest phase of the blood, while the other (the oil) is lighter

than the lightest phase of the blood and rises to the top.

Burns in United States Patent No.4,877,520 provides additional support for the need to replace gel separators with solid separators. At Column 1, lines 60-66,

he states, "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."

The use of silicone separator gel in evacuated blood collection tubes

preceded a number of patents dealing with separation of lymphocytes and monocytes

blood containing anticoagulants for testing purposes. A. A. Luderer et al, in United

States Patents. Nos. 5,053,134 and 4,190,535, and W. C. Smith et al, in United States

Patent Nos. 4,957,638, 4,954,264, 4,867,887, and 4,844,818 all basically use gel separators of defined specific gravity to separate and isolate the mononuclear white

cellular elements from the red cells of the blood. Many add other components to the

gel base. These methods are feasible, but they are not necessarily simple, rapid, or

particularly well suited to automation.

Wardlaw, et al, in United States Patent Nos. 4,027,660 and 4,077,396 et

seq., describe a blood testing device which expands the axial presentation of white

blood cells in a small bore tube of blood upon centrifugation. This was used to provide

a simple, rapid means to determine both total, and differential white blood counts.

Such an invention has become the basis of widely used blood counting systems, often

in a physician's office laboratory. Such a device is designed for diagnostic purposes

only, since no means are provided to collect the various white blood cells separated in the system. Further, the devices contain stain to differentiate the type of white cells

present in the tubes.

In our United States Patent No. 5,065,768 we disclose tubes with self-

sealing plugs having an air vent channel which automatically seals a few seconds after

the blood sample contacts the plug. The blood sample may then be dispensed with aid

of a special pipette, or centrifuged in a microhematocrit or functionally similar centrifuge at about 11 ,000 g after collection of the fluid. This provides a packed cell

volume reading, which may be followed by plasma dispensation from that tube. This

invention is directed primarily toward the collection of blood from fingersticks, and

discloses self-sealing plugs that seal off the air vent as a direct result of contact with the

specimen at the time the sample is filled with blood from skin punctures. This

invention does not relate to sealing devices that are intended to begin to seal during and

after centrifugation has begun. Furthermore, the patent teaches that solid separators or

gels are used to separate the phases of centrifuged blood.

Water swellable materials have been used for toys. United States Patent

Nos. 2,760,302 and 2,952,462 disclose sheets of foam or sponge rubber or synthetic

plastics which are cut into desired shapes. These shapes are then compressed into a

cyllinder or cube. When placed in water the compressed material expands to the

desired shape. There is no teaching or suggestion in these patents that water swellable

materials can be used for sealing blood collection tubes.

Walder et al, in United States Patent No. 5,322,659 disclose a two-layer

tubing having a hydrophilic polymer outer layer. The tubing is dipped into a solution that carries anti-infective reagents or other agents which are absorbed by the polymer

layer. There is no concern with a change in dimension after absorption of the solution.

The tubing is then inserted into the body and there releases the reagent. These tubes are

not intended or suitable for use as sealing devices.

There is a need for a simple, effective, and economical solid device for

separation of serum and plasma. There is also a need for a solid separator to facilitate

the harvesting of lymphocytes and monocytes in contemporary clinical laboratory

testing for a multitude of immunological, genetic, microbiological, and other testing purposes as well as to aid collection of platelets and small white cells used in

coagulation studies.

SUMMARY OF THE INVENTION

The present invention provides a solid separator which seals the

separated blood phases in a blood collection tube. It requires minimal retraining for its

use by phlebotomists and other healthcare workers collecting and separating blood.

Being a solid separator device, and not a thixotropic gel mixture requiring both a light

phase and a heavy phase as essential components, it will not release oil into the serum

or plasma. Our device will not lead to obstruction or clogging of sample aspirator

tubes. It will not lead to interference on dry chemistry slides from the oil released from

thixotropic gels.

The method of the present invention provides for a centrifugally

motivated separation of the light and heavy phases of blood previously collected within

a tubular container and placement of a freely movable separator float of defined specific

gravity between the two phases; followed by expansion of a peripheral sealing element

of the float radially toward and against the inner wall of the tubular container or against

the inner wall of a channel through the separator float over a time period to provide a stable, impact-resistant, non-contaminating, isolation of the separated phases within the

tubular container.

The light phase can then be decanted or drawn from the tube. To collect

monocytes, lymphocytes, platelets or small white cells a needle is inserted through the

seal to draw these cells from below the sealing band. Alternatively, a second

passageway could be provided through the sealing band so that a fluid injected through the needle would push the cells through the second passageway to a position above the

seal. From there they could be drawn or decanted.

Our device utilizes a separator float that has a specific gravity between

the light and heavy phases of the blood, preferably between 1.03 to 1.06. The separator

float has a peripheral water swellable band generally flush and recessed within a

molded float body. The specific gravity of the separator float is determined primarily

by the specific gravity of the float body, and to a lesser amount by the water swellable

band. The float body may be a single element, or a combination of subelements that

taken together provide the desired specific gravity and other desired properties. For

example, a magnetic separator float can be constructed from a combination of a molded

polypropylene component and iron or steel elements to provide a separator float with

combined specific gravity between 1.03 and 1.06.

The water swellable band of this invention may be fabricated from the

category of materials described in our United States Patent No. 5,065,768 as super

absorbent materials dispersed within an organic or silicone elastomer support matrix.

Cross-linked hydrogels fabricated from hydrophilic acrylic and acrylamide monomeric

components and certain polyether-amide or certain polyether urethane block

copolymers are also suitable. Thermoplastic polyurethane elastomers containing

superabsorbents may also be used, but they tend to be more expensive and ion- exchanging. The block copolymers of ethylene oxide with polymides or polyurethanes

are preferred because they can absorb water in amount from half to three times their

weight, yet are non-ionic and thus will not affect the electrolyte values.

The assembly of the invention permits initial positioning of the separator float having a swellable band in the evacuated blood collection tube. Yet, the separator float does not become enmeshed in the coagulum during centrifugation, preventing its

movement and emplacement between the two separated phases. In addition, the

assembly of the invention provides for inhibition of premature actuation of the water

swellable band, a frequent requirement for isolation of both plasma and serum light

phases.

We prefer to provide two categories of separator isolation assemblies.

The first is that in which plasma only is obtained, while the second is that in which both

serum and plasma are obtained. In the case of plasma, the separator float may be

located in the bottom of the tube, immersed in a bath of a relatively high specific

gravity liquid so that the water swellable band is covered sufficiently to prevent blood collected by phlebotomy from coming into contact with it. The amount and specific

gravity of the isolation liquid should permit both adequate immersion of the separator

float, and sufficient coverage of the water swellable seal. If the specific gravity of the liquid is too high, buoyancy of the float will cause the band to be positioned above the

liquid levels and the seal will not be sufficiently covered. Satisfactory liquids for this

purpose are polymethyl-3,3,3-tri-fluorpropylene siloxane with a specific gravity range

of 1.26 to 1.30 and viscosities from 1000 to 10,000 centipoises and polyadipate esters with specific gravities between 1.10 to 1.16 and viscosities between 2,000 and

30,000 centipoises.

If wicking of the blood is found to provide excessive premature swelling

of the available seal, the separator float and the upper zone of the blood collection tube

may both be coated with a viscous hydrophobic oil, with a specific gravity sufficiently

greater than the specific gravity of the blood cells to drain off the separator float and

sink below the blood cells at the time of centrifugation and so removed from interfering with the function of the tube and contamination of testing materials. Another method to

isolate the water swellable band from contact with the blood, with its water causing

premature swelling, is to jacket the band with a sleeve located in the upper end of the

collection tube. Channels can be molded, or profiled in the sleeve if the part be

extruded, so that blood might flow in the channels and fill the main body of the tube.

The preferred means to prevent wicking is to utilize localized elevations

on the plastic or glass collection tube to isolate the body of the separator float from the

wall by about 0.5 to 1.0 mm using ridges, conical points, or topological equivalents, in

combination with a single attachment point, above the water swellable seal. Isolation

of the float body from the inner tube wall can be made by several means, including

deposition of a patch by hot melt adhesives, room temperature vulcanization materials,

such as silicone cement, or by attachment of small pressure sensitive patches.

However, it is preferred to incorporate the projections as integral components of the

collection tube itself during tube manufacture either as part of the original molding

process or during secondary localized thermoforming after the test tube is molded. The

water swellable seal may also be coated with a hydrophobic oil, as noted above, which will serve to shed blood as it flows past the band into the tube cavity under vacuum.

Attachment of the float to the tube wall at its forward end can be made by hot melt

attachment, or any other suitable means known to those skilled in the art of fastening.

In the case where collection of whole blood is required, i.e., where

serum is used for testing, the separator float must be positioned so that it will not

become enmeshed in the clot after the blood has coagulated. In addition, the swellable

band must not have sufficient blood contact to expand the band prematurely which

would prevent correct emplacement of the separator float. Generally, most clinical /18897 PC17US95/1

laboratory centrifuges at this time cannot produce adequate g force to force the

separator float through the clot, and become positioned between the serum and the clot

to result in a clean insolation. Nevertheless, higher g force centrifuges are capable of

thrusting the float through the clot and isolating the phases.

Our simplest assembly positions the separator float with its upper

extremity far enough from the upper edge of the evacuated collection tube to avoid

contact with the tip of the blood collecting cannula, which is about 10 to 15 mm from the

bottom of a standard plug vacuum closure. The separator float may be suspended by

pressure from ridges arising from the tube wall, elastomer hot melt, or silicone rubber

tips or balls located on the inside wall of the tube against the float at the upper end of

the evacuated tube. The blood can then clot without sufficient contact with the swellable band to cause malfunctions from excessive swelling.

Tubes may be made with closures at both ends, permitting direct

sampling of the contents of both of the isolated compartments.

Other objects and advantages of the invention will become apparent

from a description of the present preferred embodiments shown in the drawings.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a perspective view of a first present preferred embodiment of the separator float of the present invention.

Figure 2 is a cross-sectional view taken along line II-II of Figure 1.

Figure 3 is a cross-sectional view taken along line III-III of Figure 1.

Figure 4 is an elevational view of the separator float of Figure 1 in a

blood collection tube. 18897 PCI7US95/16133

Figure 5 is an elevational view of a second present preferred separator

float in a blood collection tube.

Figure 6 is a cross-sectional view taken along line VI- VI of Figure 5.

Figure 7 is an elevational view of a third present preferred separator float

in a blood collection tube.

Figure 8 is an elevational view of a fourth present preferred separator

float in a blood collection tube.

Figure 9 is a cross-sectional view taken along line IX-IX of Figure 8.

Figure 10 is a perspective view of a fifth present embodiment of our

separator float.

Figure 11 is an elevational view of the separator float shown in Figure 1

in a blood collection tube after the tube has been centrifuged, the plasma or serum has

been removed and a needle has been inserted into a selected layer of cells.

Figure 12 is a view similar to Figure 11 after fluid has been injected through the needle.

Figure 13 is a cross-sectional view taken along the line XIII-XIII in

Figure 11.

Figure 14 is a perspective view of a sixth present preferred embodiment of our separator float.

Figure 15 is a cross-sectional view taken along the line XV-XV of

Figure 1 .

Figure 16 is a elevational view of the sixth present preferred separator float in a blood collection tube. Figure 17 is a perspective view partially cut away of a seventh present

preferred embodiment of our separator float.

Figure 18 is a cross-sectional view taken along the line XVIII-XVIII of

Figure 17.

Figure 19 is a cross sectional view similar to Figure 18 showing a eighth

present preferred embodiment of our separator float.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first present preferred embodiment of the invention is shown in

Figures 1 thru 3 in which the separator float 10 is shown to consist of a water swellable

band 12 encircling the neck 16 of the float body 14. The separator has a specific gravity intermediate the light and heavy phases of blood preferably between 1.03 and 1.06.

The float body 14 preferably has a conical nose cone 18 that will be directed toward the

tube closure, usually a butyl rubber stopper when the float 10 is placed in a blood

collection tube.

The water swellable band 12 fits into a groove 24, which surrounds

neck 16. This groove may be V-shaped, concave or otherwise shaped, but we prefer the

rectangular groove shown in the Figures. The band 12 is preferably a simple die cut

having an outer diameter slightly less than the outer diameter of the float body 14. This

washer like part is stretched over the nose cone 18 and positioned to encircle the neck

16. This water swellable washer-like band 12 will fit with slight clearance from the

wall of groove 24 until it becomes exposed to the blood during centrifugation. When exposed to blood the band 12 starts to swell. The preferred material from which to form the water swellable band 12 is a the hydrophilic polyether-block-amide copolymer

containing about equal weight percents nylon 6 and polyethylene glycol. One such

composition is sold by Atochem under the designation "PEBAX MX 1657".

Although we prefer to place the water swellable band 12 in a groove

located as shown in Figure 1, that band could be placed in a groove 15 in the conical

head 18 shown in chain line in Figure 3. The water swellable band could also be placed

around the generally cylindrical body 14 which has no groove as indicated by band 17

also shown in chain line in Figure 3.

The separator float main body segment is generally cylindrical, but it

may have a slight to moderate taper. The base end 0, of the float body 14 may be flat,

slightly conical, or rounded. A hemispherical dome structure such as is shown in the

drawings is appropriate for use with a molded round bottom plastic evacuated

collection tube. The separator float is sized to fit within a blood collection tube. A

float body having a diameter of 8.9 mm and overall length of about 28 mm works well

in a 13 x 100 mm plastic evacuated blood collection tube. The neck 16 is then about

4.5 mm in diameter. For this body the water swellable band 12 preferably has a

4.7 mm inside diameter and 8.7 mm outside diameter, and is 1.2 mm thick. The

band 12 may be cut tangentially along line 13 from the inside to the outside to facilitate seating within the groove. When in place the band has about 0.02 mm clearance

between band 12 and groove walls 23 and 25. Specification of the dimensions of the

float and the band affect the sealing rate of the float.

We have constructed floats from ABS polymer and silicon rubber.

Other plastics which may be used are liigh impact polystyrene, "crystal" (clear)

polystyrene, polyethylene, thermoplastic polymers and reaction molded polymers. /18897 P

These materials are particularly suitable for use because the readily available

commercial grades of molded resins fall within the required specific gravity range

critical for operation of the invention. There are higher purity FDA grades of these

plastics readily available from several manufacturers.

It is also feasible to construct compound float bodies of materials other

than those having specific gravities in the required ranges. For example, a float may be

constructed from a polypropylene with a specific gravity of about 0.90. This material

has surface properties that under certain conditions are preferable to ABS, HIPS, or

clear polystyrene. The low specific gravity of polypropylene may be counterbalanced

with a material of higher specific gravity. Iron wire pieces are useful as the higher

density material which can be molded into the polypropylene. The quantity of this

material can readily be precisely adjusted to achieve the required specific quantity value. Such a float will move with a magnet passing along the exterior of a tube

containing the float. Thus, the separator float can be moved at will in the filled blood

collection tube for purposes of mixing anticoagulants, in the case of plasma separation

tubes. A magnet can also be used for the unique purpose of maintaining the separator float above, and out of reach of the clotting blood in the serum separator tubes.

Figure 4 shows the separator float of Figure 1 at the bottom of a

plastic 13 x 100 mm evacuated plasma separator tube 30 having a conventional rubber

stopper 31. The tube preferably contains lithium heparin anticoagulant, and is

evacuated at the level of vacuum required to collect about 4.7 ml of blood. At the

bottom of the tube there is a water-immiscible oil 32 with a specific gravity greater than

that of the red blood cells. The oil's function is to isolate the water swellable band from the collected blood, and prevent activation of the water swellable band before centrifugation begins. There should be sufficient oil to maintain complete coverage of

the top of the water -swellable band 12 before centrifugation begins. Preferably the oil

will extend a distance of 1.0 to 3.2 mm above the band 12. Polymethyl-3,3,3-

trifluoropropylsiloxane fluid, 1000 centistokes viscosity and specific gravity 1.28, has

been found to work excellently, although other suitable water-immersible oils such as

polyesters of adipic acid and propylene glycol may be used. After blood is collected

into an evacuated blood collection tube, and the blood has been sufficiently mixed with

a selected anticoagulant contained therein centrifugation begins. The oil remains in a

small pool at the bottom of the collection tube, and the float separator becomes

centripetally displaced to the interface formed between the blood cells and the plasma.

Centrifugation at 1200 g for 10 minutes gave good separation, float emplacement, and

isolation of the light and heavy phases of the blood. However, centrifugation of 1750 g

was preferable, with faster, and more clearly defined blood separation and separator

float emplacement.

A second preferred embodiment that can be used to obtain either serum

or plasma is depicted in Figures 5 and 6. The separator 40 is suspended near the

collection end of the evacuated blood collection tube 30 having stopper 31 by

compression against three elastomeric pads 42. If desired a fewer or greater number of

pads could be used. This separator float 40 is otherwise constructed like the first

embodiment having a float body 44, water swellable band 45 which fits over neck 46,

conical top 48 and hemispherical bottom 49. Silicone RTV single component sealant, or hot melt sealant were found to be satisfactory for the elastomeric pads 42. These

pads hold the separator 40 in place during blood collection and transport. As blood is

collected it may flow around the separator through channels 47 between the separator pads 42. During centrifugation the pads elongate to release the separator 40 allowing it

to move to a position between the light phase and the heavy phase.

At, or slightly more distal from the water swellable seal 45, elevations

may be placed at each of the locations noted for the three pads 42. These elevations can

also compress against the float body 44, and support float 40. Thus, the elevations

could be molded indentations of the tube 30 itself. There is also an optional hot melt

attachment 43 made near the base of the conical top 48. This attachment will yield

under moderate tension produced when the tube is centrifuged. The three isolating, or

wall offsetting elevations, preferably are 0.5 to 0.7 mm in altitude from the wall base,

depending upon the location, the taper and diameter of tube 30, and the outside

diameter of float body 44.

If desired, the elastomeric pads 42 of the second embodiment could be one or more elastomer balls held against the inside tube wall by compression. The balls

hold the separator float under compression, until the separator is released by rolling

radially off the compressed balls into the blood during centrifugation. In this configuration, when a single ball is used, it is inserted with the separator float into the

tube and squeezed tangentially against the separator band, causing the separator float to

be pressed and held firmly against the opposite wall. If two or more equally spaced

elastomeric balls are used, the float may be held suspended off the wall until the

separator float rolls off the compressed balls. Two or three compression loci reduce

wicking for uncoated floats and tube walls. The embodiment has the advantage of

simplicity in manufacture, and facility of operation. There is wide selection of sizes,

diameter, and elastomeric materials that can be used for the suspending roller balls. 18897 PC17US95/16133

Figure 7 shows a third preferred embodiment having an external support

for a separator float usable for serum, as well as plasma, in the widely used 16 mm x

100 mm glass evacuated tube. It is one of several alternatives to the

compression friction support mechanism shown in Figures 5 and 6. The third

embodiment is similar in shape to the first two embodiments. The separator float 50

has a float body 54 with a conical top 58 and a hemispherical bottom 59. A water

swellable band 56 fits around a neck not visible in the drawing. A metal rod 55

indicated by dotted lines is molded into the body 54. Thus, when the float is placed

within a test tube 30, a magnetic support ring 52 will hold the separator float in place

within the center of the ring 52. The separator 50 can be made using an economical,

low density, widely used disposable laboratory plastic such as polypropylene for the

body of the separator float and at least one length of iron wire 2.3 mm in diameter

molded within the body of the separator float. A neodymium iron boron ring magnet

(30 mm O.D., 16 mm I.D., by 10 mm thick) can be used as the ring support

mechanism 52. The polypropylene/iron composite separator float is sized to move

freely within the blood collection tube. A present preferred float of the type depicted in

Figure 7 has a float weight of 2.406 grams, and a volume of 2.313 milliliters, with a

specific gravity of 1.04 when the polypropylene has a specific gravity of 0.90, a

10.8 mm length of wire (specific gravity 7.8) is used. A water swellable band die cut

from PEB AX MX 1657 polymer (specific gravity 1.19) having a 11.9 mm outside

diameter and a 7.1 mm inside diameter, and being 1.6 mm thick is seated around a

7.0 mm diameter neck and within a rectangular groove 1.7 mm wide and 2.3 mm deep.

The outside diameter of the polypropylene float body is 12.7 mm. The usual inside

diameter of the glass tube, for which this embodiment is depicted is generally about 13.5 mm. If this were to be a 16 mm x 100 mm plastic tube, design of the separator

float would be partially determined by the taper of the tube.

The magnetizable compound separator float is moved into support

position immediately after blood is drawn into the collection tube by vacuum. The ring

magnet is moved by hand, or positioned on a rack so the plastic/magnetic separator

within the blood filled tube must pass through the ring drawing and magnetically

holding the magnetic separator float within the tube immediately above the clotting

blood, practically adjacent to the closure 31, preventing entrapment of the separator

float in the clot. When the blood has clotted, the tube may be removed from its magnet

collar and centrifuged. The blood phases will be separated and the separator float will

move unhindered by the clot and become emplaced. The water swellable band will

operate, and the two phases become sealed and isolated form each other.

The magnetic ring 52 may be attached to or within a test tube rack

shown in chain line 53. One method of use for such an arrangement is to place the

separator float 55 in an evacuated test tube 30. Blood is collected into the evacuated

blood collection tube 30 with magnetic core separator float 50 in the bottom of the tube.

The tube is slowly inserted through the magnetic ring attached to test tube rack 53.

During insertion the separator float 50 is drawn from the bottom through the collected

blood 51 to the position shown in Figure 7. There should be minimal contact between the band and the collected blood during this time resulting in minor expansion of the

water swellable band 56. The tube may contain additives that need to be mixed for

optimal functioning. Clot accelerators, or anticoagulants can readily and efficiently be

mixed manually by several movements through the collar, if recommended, before storing the tube within the ring 52 and rack 53. The tube is maintained in the vertical position for the usual 1/2 hour clotting period. Then the tube is centrifuged, preferably

at 1750 g for 10 minutes to obtain serum or plasma, depending on the tube additives.

During centrifugation the separator will move to the interface of the light phase and the

heavy phase and the washer like seal will swell.

Figure 8 depicts a fourth present preferred embodiment 60 in which an

elastomeric tubular covering or sleeve 63 is provided around the upper section 62 of the

separator float body 64 for the dual purpose of supporting the separator float 60 above

the clotting blood 61, and to cover the water swellable band 65 from contact with the

blood. The sleeve is shown here in a 13 mm x 100 mm collection tube typically having

a 10.4 mm inner diameter. This sleeve has channels 66 parallel with the axis of the

blood collection tube on the exterior surface of the sleeve to permit blood flow into the

evacuated tube during blood collection. Four channels between the external surface of

the sleeve, and the inside wall of the blood collection tube are shown in Figure 9. More

or fewer channels may be provided.

Alternatively, a segment of heat shrinkable tubing may be used to cover

the water swellable band. The float may be held in place according to any of the

methods described with respect to Figures 5 and 6. On centrifugation, the separator

float 60 will be released gradually due to the friction between the elastomeric cover and

the inside wall of the tube 30. This provides a controlled, delayed release of the float

into the clot, permitting the clot to pack to some extent before movement of the

separator float into the packed cells. The elastomeric tubular sleeve may be an

extruded or molded thermoplastic material such as the silicone/polystyrene block

copolymer such as sold by Concept Polymer Technologies, Inc. under the trademark

"C-FLEX" or it may be silicone rubber. Dimensions of the sleeve, before it is stretched and placed over the separator float, may be 8.7 mm outside diameter, 7.1 mm inside

diameter with the groove depth of 0.4 mm providing the groove diameter of 7.9 mm.

This provides the tubular covering a slight amount of circumferential compressional

stress on the separator float. The tubular cover 63 with the separator float contained

therein should have its outside surface bonded to the inside of the collection tube 30

into which it is inserted. Although there are several ways to do this we prefer to use an

adhesive. Silicon RTV sealant, or alkyl cyanoacrylate are two materials that have been

found to be effective among a variety of possible choices of cements for use with

thermoplastic ester evacuated blood collection tubes.

A fifth embodiment which can be used to separate either serum or

plasma, is shown in Figure 10. It is buoyant in freshly collected whole blood and has a

self-contained metal protective sleeve 76 covering the water swellable band 72 recessed

in a polypropylene float 70. This float assembly is designed to have a resultant specific gravity, preferably between 1.035 and 1.045, making it buoyant in uncentrifuged blood,

but merely thrusting through the surface of collected whole blood if floating

unimpeded. When a tube of blood containing this free floating embodiment is

centrifuged, the metal slip ring 76 moves to the position shown in chain line to expose water swellable band 72, and is prevented from slipping off the float 70 by base flange

78. Centrifugal force operates to: 1) emplace the float at its proper position relative to

the phase boundaries of the separating blood; 2) cause radially directed slip/sliding of

the metal ring protective sleeve covering the water swellable band; 3) separate the

cellular and liquid phases of the blood; and 4) pack of the centrifuged cells with

subsequent isolation of the phases by the water swellable band 72. 18897 PCI7US95/16133

When the float 70 is used in an evacuated tube such as is shown in

Figure 4 to obtain plasma, blood is collected into a tube containing an anticoagulant of

choice, the tube is gently rocked a few times per standard procedure, and then placed

vertically and undisturbed, into a rack. The float is next lifted and held magnetically

within a rack, according to the method prescribed in the description of the third

embodiment shown in Figure 7. The float is best suspended by a ring magnet of

adequate strength, e.g., the neodymium iron boron type mentioned above with the wire

core float of Figure 7. The float often resists buoyant movement to the surface when

unaided by external magnet force because of the relatively high viscosity of the

collected blood, or some other impediment to free buoyancy within the tube of

collected blood. High volume, precision stamped nickel plated metal sleeves are

available at reasonable cost and have been found satisfactory for this use in the

collection of whole blood for coagulation, and subsequent isolation of serum. When

the float embodiments shown in Figures 7 and 10 are used for serum separation with

generally available centrifuges in clinical laboratories, the floats are suspended in

positions where they will not require the relatively high level of centripetal force

needed to bypass the impacted clot, as would be if the float were to be located at the

bottom of the tube, as in Figure 4.

Figure 10 shows polypropylene float 70, of specific gravity 0.90 and

weighing 1.422 g, metal slip ring 76, with specific gravity 7.8 and weighing 0.245 g,

and a water swellable band 72, of 1.19 specific gravity and weighing 0.080 g. The

specific gravity of the compound float of Figure 10 is 1.040. The float should be used with water insoluble oils of the type recommended (e.g., fluorosilicone, polyester, or

similarly functioning oils of like specific gravity) so as to exclude blood from the gap /18897 PCI7US95/1613

between the metal ring 76 and water swellable band 72, and to reduce fiictional binding

between ring 76, band 72 and float 70. The gap between float 70 and slip ring 76 is

0.02 to 0.08 mm.

This invention facilitates harvesting of white cellular elements of the

blood within a lighter fraction of the heavy phase of the blood. Isolation and

separation, also known as harvesting of white blood cells, especially lymphocytes, from

human blood is clinically necessary for histocompatibility determinations, particularly

in those patients requiring organ transplants, in prognosis for treatment of AIDS, and

rapidly expanding use in many other areas of DNA/genetic analysis.

To harvest lymphocytes/monocytes, blood is collected into a 13 x 100

mm evacuated plastic tube of the type in Figure 4, containing sufficient EDTA, or

preferred anticoagulant, and centrifuged, preferably for 10 minutes at 1750 g, and the

plasma is removed from the collection tube by decanation, transfer pipetting, or other

appropriate means, after a firm seal has been made against the wall of the tube. At that

point the collection tube 30 will appear as shown in Figure 11. The lymphocytes and

monocytes will form a band 80 along the wall of the separator float 10 above the packed erythrocytes and granulocytes 82, and below the water swellable band 12. The

lymphocytes and monocytes may be withdrawn through a syringe 86 having a needle

87 passing through the swollen band 12. Alternatively, they may be harvested by

injection of an iso tonic Ca++ and Mg-t-+ free salt buffer solution 96 using a syringe 86

with a small gauge 28 needle 87 injected through the water swellable band compressed

against the wall of the collection tube. A widely available disposable insulin syringe

with a 1/2", 28 or 29 gauge needle is well adapted to inject the isotonic harvesting

buffer. A transfer channel must also be used to pass the cells carried in the irrigation stream of isotonic harvesting buffer. For this purpose a small cannula 90, as for

example a 3/4" 26 gauge hypodermic needle inserted with forceps through the band,

diametrically opposite to the buffer injection side, or a small notch at the edge of the

water swellable band prior to assembly into the evacuated plasma separator tube (e.g., a

semi-circle of a radius 0.4 to 0.8 mm) serves well as an irrigation exit channel. Careful

injection of the buffer solution 96, which has a specific gravity less than the mass of

packed red cells/granulocytes 81 below the lymphocyte/monocyte band 80, will cause

the cells to be washed up and out of the space between the float and the inner wall of

the collection tube, exiting through the passageway in the water swellable band into the

empty space 92 previously holding the removed plasma as shown in Figure 12. From

there these cells can be drawn through pipette 88 for testing.

The sharpness of definition of the boundary between

erythrocytes/granulocytes and lymphocytes/monocytes may be improved by the

inclusion of a barrier material 94, which may be either a sufficiently high viscosity

Newtonian liquid separator material having a specific gravity between 1.065 to 1.077,

or a thixotropic gel in the same specific gravity range, either of which can be

substituted for the water-immiscible oil with a specific gravity less than the red cells

which was covering the float shown in Figure 4. Such a commercially available

Newtonian liquid is (79-82%)-dimethyl-(18-21%)-diphenylsiloxane copolymer,

methoxy terminated, with a specific gravity 1.07, and viscosity of 650 to 700

centistokes. Examples of suitable gels for this purpose are described in Luderer et al.

U.S. Patent No.4,190,535, which describes the formulations of gel-like oils to prepare

the polymers with specific gravity ranging from 1.065 to 1.077 suitable for forming a

viscous band between the packed erythrocytes/granulocytes and lymphocytes/monocytes. This band 94 separating the cellular fractions diminishes the

contamination by red cells/granulocytes of lymphocytes/monocytes pushed by the

injected harvesting buffer solution into the emptied plasma compartment.

A sixth present preferred embodiment of our separator float is generally

spherical and shown in Figures 14, 15 and 16. The separator float 100 is comprised of

a spherical core 101 preferably of crystal polystyrene. The core 101 is covered with a

shell 102 of a hydrophilic polymer such as PEBAX MX 1657 polymer. A series of

conical projections 103 and 104 are formed on the outer surface of the shell 102.

Preferably the shell has a thickness of 1.40 mm. The cones preferably have a height of

about 1.25 mm and are 45° apart. A separator having a shell of this size on a spherical

polystyrene-butadine core 10.44 mm in diameter has a specific gravity of about 1.08.

Such a float is suitable for blood collection tubes.

As shown in Figure 16, the separator 100 is placed in a blood collection

tube 30. The float is sized so that cones 104 around the equator of the float press

against the inner wall of the collection tube 30. This frictional engagement holds the separator float 100 in place above the collected fluid such as blood 61 until

centrifugation.

During centrifuging of blood the float moves to the interface between

the serum and plasma. Contact with the blood causes the hydrophilic polymer shell to

expand outwardly against the collection tube forming a seal.

A seventh embodiment of our separator float 110 is shown in Figures 17

and 18. The float 110 has a generally cylindrical body 111 having annular rings 115 at

one or both ends giving the body a spool-like appearance. The annular rings 115 are sized to fit snugly against the interior wall of a separator tube (not shown) in which the float is placed. A central channel 112 through the separator body 111 permits fluid to

pass through the separator float during centrifugation. The central channel is shaped to

have projections 114 which define a cavity 116. A hydrophilic polymer ball 118,

which preferably is PEBAX MX 1657 polymer, is placed within the cavity. When fluid

flows through the channel 112 the fluid causes the ball 118 to expand and seal the

channel. Expansion of the ball 118 within the channel also pushes the separator body

111 outward, thereby strengthening the seal between the exterior of the separator body

111 and the interior wall of the tube in which the separator is placed. A channel having

a diameter of 7.5 mm with restrictions to confine a 6.4 mm PEBAX ball is suitable for

separator floats used in blood collection tubes. The body 111 can be made of an

elastomer having a specific gravity of 1.05.

Instead of using a water swellable ball in a channel through the separator

float the water swellable material may be attached to the wall of the channel. This

separator will be similar in appearance to the separator float shown in Figure 17 but

have an internal structure like that shown in Figure 19. Referring to Figure 19, the

separator float 120 has a generally cylindrical body 121 which is preferably spool shaped like the body 111 of separator float 110 in Figure 17. A longitudinal channel

122 extends through the float body 121. An insert 124 of a water swellable material; is

fitted within the longitudinal channel. The insert 124 is sized to fit tightly against the

interior wall of the longitudinal channel and has a fluid passageway through its center.

When water containing fluid passes through the insert 124, the insert will swell to close

the longitudinal channel and expand the separator body 121 outward against the interior

wall of the tube in the same manner as the PEBAX ball in the previous embodiment shown in Figure 17. The separator floats can be variously sized and shaped for particular

applications. A separator float about 12 mm in diameter and 20 mm long is usable in

most of the larger diameter 16 x 100 mm, or 16 x 125 mm evacuated blood collection

tubes.

To obtain plasma all of the various configurations of the separator can be

used in tubes containing a variety of anticoagulants, including ammonium, lithium, or

sodium heparin salts, or even EDTA, or citrate may be used. To accelerate clotting to

obtain serum, glass powder, silica, or other satisfactory siliceous particulate material

may be used. Biologically derived clot inducers such as thrombin, prothrombin and

certain snake venom derivatives may be added instead of siliceous particles to induce

faster coagulation.

The separator tubes of this invention may be made from glass or molded

plastic. Plastics are becoming the materials of choice because neither mechanical or thermal shock causes tubes to break and transmit blood borne infections. Also, plastic

tubes can be fabricated economically with excellent dimensional precision. Plastics

tubes are less fragile than glass tubes permitting centrifugation of a much higher g force

with concomitantly improved separations, and reduced centrifugation time required. When plastic is used rather than glass to construct the separator tubes of this invention

the separated phases may be frozen for archival storage without need for preliminary

removal and transfer of the contents to separate storage vessels. The water swellable

band can be modified readily to operate more rapidly, or more slowly, or to be used

wherein the clearance between float and tube wall is greater, or less than depicted here.

These modifications to the composition and dimensions of the band can be readily

made by those skilled in the art. The choice of materials and sizing will depend upon 18897 PCIYUS95/16133

the requirements of the user, the operations of the blood handler, the collection tubes

available, and marketing and manufacturing considerations. Examples of such

considerations are the volume of blood to be collected; the form of the light phase

(serum or plasma); g force available by the centrifuge to be used (the higher the g force

the shorter the period needed to separate the blood phases and position the separator);

type of centrifugation (horizontal or angle head); vacuum or non-vacuum collection

tube; use of plastic (tapered wall) or glass (parallel wall) collection tube and the

presence of other materials such as anticoagulants in the tube.

Although we have shown and described certain present preferred

embodiments of our separator float and methods of using the device, it should be

distinctly understood that the invention is not limited thereto, but may be variously

embodied within the scope of the following claims.

Claims

We claim:

1. A separator float for use in a fluid collection tube and the like

which has at least one inner wall which defines a cavity, the separator float comprised

of

a. a body sized and shaped to fit within the cavity and

comprised of a material which will not swell when in contact with water;

b. a water swellable material covering at least a portion of

the body, the water swellable material being sized and positioned so that when the float

is placed within the cavity and exposed to water containing fluid the water swellable

material will swell forming a seal within the cavity.

2. The separator float of claim 1 wherein the body has a circumferential groove and the water swellable material is within the circumferential

groove and swells to a greater diameter which is larger than a diameter of the float

body.

3. The separator float of claim 1 wherein the body also comprises a

conical top.

4. The separator float of claim 3 wherein the water swellable

material is fitted circumferentially around a portion of the conical top.

5. The separator float of claim 1 also comprising a hemispherical

bottom attached to the body. 6 18897 PCIYUS9S/16133

6. The separator float of claim 1 also comprising an oil covering at

least a portion of the water swellable material.

7. The separator float of claim 6 wherein the oil has a specific

gravity such that after centrifugation of a fluid collection tube containing the separator

float and the oil, the oil will be below the water swellable material.

8. The separator float of claim 1 also comprising a metal slip ring

fitted over the water swellable material.

9. The separator float of claim 1 also comprising a tubular sleeve

fitted over the water swellable material.

10. The separator float of claim 9 wherein the tubular sleeve has at

least one longitudinal channel.

11. The separator float of claim 1 also comprising at least one piece

of a ferrous metal within the body.

12. The separator float of claim 11 also comprising a magnetic ring

having a central bore sized to receive a blood collection tube having the separator float

therein.

13. The separator float of claim 1 wherein the body is comprised of a

material selected from the group consisting of polypropylene, acrylonitrile-butadiene- styrene, polystyrene, thermoplastic polymers and reaction molded polymers, silicone

rubber and polyethylene. 6 18897 PCIYUS95/16133

14. The separator float of claim 1 wherein the water swellable

material is comprised of a material selected from the group consisting of

superabsorbent materials being dispersed in a support matrix comprised of at least one

of a silicone elastomer, an organic elastomer, vulcanized rubber containing a

superabsorbent, thermoplastic polyurethane containing a superabsorbent, and

cross-linked hydrogels.

15. The separator float of claim 1 wherein the water swellable

material is comprised of a material selected from the group consisting of polyether

block copolymers of polyamides and polyether block copolymers of polyurethanes

which block copolymers will absorb water in an amount of from one half to three times their weight.

16. The separator float of claim 15 wherein the polyether block

copolymer is a polyether block amide copolymer containing about equal parts nylon 6

and polyethyleneoxide ether.

17. The separator float of claim 1 wherein the separator float has a

specific gravity from 1.025 to 1.085.

18. The separator float of claim 1 also comprising at least one elastomeric pad in contact with a portion of the generally cylindrical body.

19. The separator float of claim 1 wherein the at least one

elastomeric pad is a ball.

20. The separator float of claim 1 wherein the water swellable

material forms a shell around the body.

21. The separator float of claim 1 wherein the body has a channel

passing therethrough and at least a portion of the water swellable material is within the

channel, such that a water containing fluid passing through the channel will cause the

water swellable material to swell sealing the channel.

22. The separator float of claim 21 wherein the water swellable

material is substantially spherical in shape.

23. The separator float of claim 21 wherein one surface of the water

swellable material abuts a portion of the channel and an opposite side of the water

swellable material is shaped to allow fluid entering the channel to pass over that

opposite side.

24. The separator float of claim 21 wherein the float body is

comprised of a material which will radially expand outwardly when the water swellable

material swells sufficiently to close the channel and exert a force on the float body.

25. A fluid collection tube comprising:

a. a tubular body closed at both ends and having an inner

wall; and b. a separator float positioned within the tubular body, the

separator float comprised of:

i. a generally cylindrical body comprised of a material that

will not swell when exposed to water, and

ii. a water swellable material covering at least a portion of

the generally cylindrical body, the water swellable material being sized and positioned

so that upon being exposed to water the water swellable material will swell forming a seal within the tube.

26. The fluid collection tube of claim 25 also comprising a

removable stopper at one closed end.

27. The fluid collection tube of claim 25 also comprising two

removable stoppers, one of which is at each closed end.

28. The fluid collection tube of claim 25 also comprising an oil within the tubular body and covering at least a portion of the separator float.

29. The fluid collection tube of claim 25 also comprising a tubular

sleeve attached to the inner wall of the tubular body and sized to releasably hold the

separator float within the tubular body.

30. The fluid collection tube of claim 25 also comprising at least one

elastomeric pad in contact with a portion of the generally cylindrical body and with the

inner wall of the tubular body.

31. The fluid collection tube of claim 30 wherein the at least one

elastomeric pad is a ball.

32. The fluid collection tube of claim 25 wherein the inner wall of

the tube has at least one projection against which the generally cylindrical float body

rests.

33. The fluid collection tube of claim 25 wherein the water

swellable material forms a shell around the body.

34. The fluid collection tube of claim 25 wherein the body has a

channel passing therethrough and at least a portion of the water swellable material is

within the channel, such that a water containing fluid passing through the channel will

cause the water swellable material to swell sealing the channel.

35. The fluid collection tube of claim 34 wherein the water swellable

material is substantially spherical in shape.

36. The fluid collection tube of claim 34 wherein one surface of the

water swellable material abuts a portion of the channel and an opposite side of the water swellable material is shaped to allow fluid entering the channel to pass over that

opposite side.

37. The fluid collection tube of claim 34 wherein the float body is comprised of a material which will radially expand outwardly when the water swellable

material swells sufficiently to close the channel and exert a force on the body.

38. A method of collecting blood comprising the steps of: a. providing a blood collection tube comprised of a tubular

body closed at both ends having an inner wall and a separator float positioned within

the tubular body, the separator float having a specific gravity between specific gravities

of a light phase and a heavy phase of the blood and comprised of:

i. a generally cylindrical body, and

ii. a water swellable material covering at least a portion of

the generally cylindrical body, the water swellable material being sized and positioned

so that upon being exposed to water the water swellable material will swell forming a

seal within the collection tube;

b. drawing blood into the collection tube; and

c. centrifuging the blood collection tube thereby separating

the blood into a light phase and a heavy phase during which centrifugation the separator

float moves to a position between the light phase and the heavy phase and the water swellable marerial is exposed to water in the blood causing the water swellable marerial

to swell and create a seal within the collection tube adjacent the separator float.

39. The method of claim 38 also comprising the step of coating at

least a portion of the tubule float with one of an oil and a grease before drawing blood

into the blood collection tube.

40. The method of claim 38 wherein the body of the separator float

contains a metal and also comprising the step of placing a magnet near the blood

collection tube to hold the separator float adjacent the magnet. 6/18897 PC17US95/16133

41. The method of claim 40 also comprising the step of moving one

of the magnet and the blood collection tube relative to one another thereby causing the

separator float to move within the tubular body.

42. The method of claim 38 also comprising the steps of:

a. inserting a tube through the swelled water swellable

material so that a distal end is positioned within a selected layer of blood cells below

the water swellable material; and

b. harvesting the blood cells within the selected layer.

43. The method of claim 42 wherein the selected layer of blood cells

contains at least one of white blood cells, lymphocytes, monocytes and platelets.

44. The method of claim 42 also comprising the step of drawing the blood cells within the selected layer through the inserted tube.

45. The method of claim 42 also comprising the steps of:

a. providing a passageway through the swelled band;

b. injecting a fluid through the inserted tube into a selected

layer of blood cells below the water swellable material thereby causing blood cells

from the selected layer to pass through the passageway to a position above the swelled water swellable material; and

c. removing those blood cells from the blood collection

tube.