CA1327557C - Plasma separator - Google Patents

Abstract

Title: PLASMA SEPARATOR
Inventor: JOHN D. MULL
ABSTRACT OF THE DISCLOSURE

A plasma separator for receiving a blood sample includes a central chamber of inverted conical shape and an outer annular chamber connected to the central chamber by a downwardly inclined passageway. The separator is designed to be rotated at high speed about a vertical axis so that red blood cells in the sample migrate down the passageway and into the outer chamber, leaving clear plasma in the central chamber than can then be removed by pipette.

Description

FI~LD ~F T~ INVENTION
This invention relates generally to a device for separating plasma from red cells (erythrocytes) in blood samples.
BAC~GROUND OF T~E INVE~TIO~

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Various blood analysis techniques require clear plasma samples free of red cells. Separation of plasma from red cells can be accomplished by various methods based on the fact that the red cells are of a higher specific gravity than the plasma. For example, if a blood sample can be allowed to stand for two or more days, the red blood cells will settle to the bottom by gravity. A faster technique is centri~ugation using an ordinary laboratory centrifuge. In routine laboratory analysis, a centrifugation step does not delay the work flow. However, centrifugation does take some time (20 minutes or so) and may be unacceptable in an emergency situation, for example in an operating room. Even in non-emergency situations such as in a doctor's office, it may be desirable for the doctor himself or an assistant to be able to quickly obtain a clear plasma sample without having to send the blood sample to a laboratory.
~ ~ESCRIPTI~N O~ T~ PRIO~ ~RT
; Centrifuge devices comprising a rotor that rotates at high speed about a vertical axis have been proposed for clearing blood samples of chylomicrons (fat particles 80 -500 nm diameter) prior to clinical analysis. Devices of this type are available from Beckman Instruments, Inc. of California and are described in United States Patents NosO

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4,142,670 issued Narch 6, 1979 (Ishimaru et ~l.) and 4,177,921issued December 11, 1979 (Nielsen~. Both of these patents have been assigned to Beckman Instruments, Inc.
The Beckman chylomicron rotor recei~es a disposable liner in which chylomicron~ are isolated by flotation. The liner has a cylindrical centre chamber and a doughnut-shaped outer chamber. The liner is made of a thin and flexible polyethylene material and flexes subs~antially under centrifugal force during centrifugation while being constrained by the rotor. At this time, the chylomicrons float to the centre of the liner where they are isolated. The serum can :, then be removed from the liner b'y pipette.
- BRIEF D~SCRIPTIO~ OF_THE INV~T ~W
The invention provides a plasma separator comprising a container which is symmetrical about a normally vertical xis and is adapted for rotation at high speed about that axis. The container is self supporting during such rotation and defines internally a central chamber for receiving a blood sample, an annular outer chamber, and an annular passageway connec~ing the chambers and having respective inner and outer ~nds. The central chamber has a top wall and a lower wall of inverted conical shape extending about the said axis, the lower wall ~` having an upper end and a circular edge at said upper end, the circular edge being dispo~ed at the inner end of the passageway. The passageway extends downwardly and outwardly from the edge to the outer chamber and the outer chamber is located at the outer end of the pas~ageway and below the circular edge. The inverted conical shape of the lower wall . . .
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of the central chamber provides an internal surface of the cen~ral chambPr which extends up~ardly away from ~he said axi~
to the circular edge at an inclination selected to permit red blood cells in a blood sample to migrate up the surface, 5 through the annular passageway and into the outer chamber upon rotation of the chamber at an appropriate high speed, while plasma is retained in the inner chamber. The container has a single opening located in its top wall for permitting insertion , of a blood sample into and removal of plasma from the central chamber.
The invention also provides a method of separating plasma from red cells in a blood sarnple. The method involYes ; providing a transparent container having an axis and being symmetrical about said axis and self-supporting. The container defines internally a central chamber, an annular outer chambex and an annular passageway connecting the chambers and having respective inn~r and outer ends. ~he central chamber has a top wall and a lower wall of inverted conical shape extending ~bout the ~iaid axis. ~he lower wall has an upper end and a circular edge at said upper end, the said circular edge being dispos~d at the inner end of the passageway and the passa~eway extending downwardly and outwardly from the edge to the outer chamber.
The outer chamber i9 located at the outer end of the passageway and below the circular edge. The container has a single opening located in the top wall for providing access to the chamber. A blood sample is inserted into the central chamber through the opening in the top wall, for example by using a pipette or syringe. By means of a rotating device, the ~` B, , .. . .... .
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- 4a -container is then rotated about its axis with the axis vertical, at a speed selected to cause red cells in the blood ~;; sample to migrate up the lower wall, through the annular - passageway and into the outer chamber, while plasma is retained 5 in the inner chambex. The container is visually monitored and the rotation is terminated when the plasma in the inner chamber is seen to be substantially clear. Plasma is removed from the ,,, ~- central chamber through the opening in the top wall of the ,, ~ ~hamber. In experiments, it has been found that a clear plasma - 10 sample can be obtained in the order of 30 seconds.
BRIl~F D33SCRIPTIOll!l OF ~D3 DRAWINGS
In order that the invention may be more clearly understood, reference will now bP made to the accompanying drawings which illustrate particular preferred embodiments y . /
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~ 5 --of the invention by way of example, and in which:
Fig. 1 is a perspective view from above of a plasma - separator in accordance with the invention;
Fig. 2 is a vertical sectional view through the `~ 5 central axis of the separator shown in Fig. 1, with the separator shown mounted on a device for rotating the separator;
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'Fig. 3 is a view similar to Fig. 2 illustrating ' removal of a separated plasma sample from the central chamber of the separator; and, Fig. 4 is a view similar to Fig. 2 (but without the rotary device) illustrating an alternative embodiment of the invention.
DESCRIPTION OF THE P~EFERRED EMB~DIME~TS
i 15 Referring now to the drawings, Fig. 1 shows the ., external appearance of the plasma separator provided by the invention, as seen from above. In this embodiment, the separator is made in one piece in a semi-rigid plastic material, for example by blow-moulding. In an alternative embodiment, however, the separator could be made in two or more parts.
The separator itself is generally denoted by reference numeral 20 and essentially comprises a container which is symmetrical about a normally vertical axis 22. The container is designed so that it can be coupled to a device ,,, that is capable of rotating the container at high speed about axis 22. In ~ig. 2, part of such a device is shown , .~

~ supporting the separator. The device comprises a platform 24 :; ~
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having a recess 26 into which the separator is frictionally engaged. The plat~orm 24 ls carried by a vertical shaft 28 that is connected to a drive motor (not shown) for rotating the shaft and with it the separator at high speed. The S structure surrounding the platform 24 is indicated at 30.
I The container is designed to be self-supporting ; during rotation and, to this end, is made of a semi-rigid plastic material as noted previously. The container defines internally a central chamber 32 for receiving a blood sample, and an annular outer chamber 34 for receiving red blood cells separated out of the blood sample by rotation of the container about axis 22. An annular passageway 36 connects the two chambers 32 and 34.
lSThe central chamber 32 has a lower wall 38 of inverted conical shape extending to a circular edge 40 at an upper end of wall 38 and at the inner end of passageway 36.
The passageway extends downwardly and outwardly from edge 40 to the outer chamber 34, which chamher is located at the ~1 20 outer end of the passageway and below the circular edge 40.
, The container has a single opening 42 located in a top wall -' 44 above the central chamber for permitting insertion of a blood sample into and removable of plasma from the chamber.
In practice, a blood sample will typically be introduced into the central chamber 32 through opening 42 by ~means of a pipette. Preferably, the central chamber will be ifilled to the level of edge 40 as indicated by the level line "1" in Fig. 2. The container will be frictionally retained in the recess 26 in platform 24 sufficiently ' .

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-tightly that the container will stay in place when the platform is rotated at high speed. At this time, red cells in the blood sample will tend to migrate up the inclined inner surface of wall 38 as shown generally at 46b in Fig.
- 5 2, over edge 40 as indicated at 46a and down the passageway - 36 into chamber 34.
Preferably, the plasma separator will be made of a transparent or transluscent plastic material so that the sample can be visually observed during rotation of the separator. The person operating the device on which the separator is rotated can then stop rotation when substan-tially all of the red cells appear to have migrated into the outer chamber 34.
Fi~. 3 shows the plasma separator after it has been removed from platform 24 when separation has been completed.
; Clear plasma indicated by reference numeral 48 remains in the central chamber 32 while thle outer chamber 34 contains red blood cells indicated at 50. The stem of a pipette is shown at 52 as having been inserted through opening 42 for ; 20 withdrawing the plasma sample from chamber 32. Normally, the ":
red blood cells 50 would not be required for analysis and ~ would be simply discarded. It is anticipated that the ; separator will be disposable so that it can be simply thrown away aftex the plasma has been removed from chamber 32. On the other hand, if it is desired to either retrieve the red i cells or reuse the separator, then the red cells can be - transferred into the central chamber by appropriately ., ~ tipping the separator and the red cells can then be removed ,.. ~
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'~, by pipette.
From a comparison of Figs. 2 and 3 it will be noted that the walls of the container that define the passageway 36 are shown spaced apart somewhat in Fig. 2 but in contact in Fig. 3. Thus, the container is designed so that the walls that define passageway 36 will tend to move apart under centrifugal force to allow liquid flow through passageway 36 during rotation of the separator, but will close to in effect isolate the red cells from the plasma sample when the separator is stationary. Referring specifically to Fig. 2, the container has a wall 54 at the inner side of passageway 36 that remains relatively stationary under the effects of centrifugal force due to the bracing effect of the inverted conical wall 38. The wall 56 at the outer side of passageway 36 on the other hand is designed to be more flexible and to move away from wall 54 under the effect of centrifugal force.
Fig. 4 shows an alternative embodiment of the invention in which primed reference numerals have been used to denote parts corresponding to parts shown in the previous views. In this case, the container forming the separator is ; essentially the same as the container shown in the previoùs ; views except in that an outlet for plasma is provided at the centre of the bottom wall 38 of chamb~r 32. In Fig. 4, the .25 outlet is denoted by reference numeral 58 and is surrounded i, by a short neck 60 over which is frictionally fitted an -inverted cap 62 that acts as a collection chamber for the plasma. In thls embodiment, when the separation of plasma :; .

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g from red blood cells has been completed, all that need be done is to remove the cap 62, containing the plasma. The step of inserting a pipette to remove the plasma is ; unnecessary. Opening 42' is still provided in the top wall 44 of the container for the purpose of introducing a blood sample into the container. The sample would be introduced at a location off axis 22' while the separator is rotating.
Alternatively, cap 62 may be provided with a plug for outlet 58 as indicated in ghost outline at 64 in Fig. 4.
; 10 The device used to rotate the plasma separator need ;~ not be a high quality laboratory-standard centrifuge as is required in the prior art, although such a device could undoubtedly be used for this purpose. All that is required is a drive means that is capable of engaging and rotating the separator at relatively high speed. It should also be noted that the separator is self-supporting during rotation and that it is unnecessary to confine the separator within some sort of rotor structure as in the prior art.
In summary, the device provided by the invention provides an extremely simple and inexpensive means for ;
~` separating plasma from a blood sample, quickly and e~ficiently. Numerous other advantages are also provided by - the device. For example, in terms of safety, no handling of , the blood sample is required. The separator can be made of a ~ 3 plastic material so that there is no glass that might break.
' '1 t the same time, the separator can be made transparent so that the blood separation action is visible and the separa-tor can be made relatively inexpensively so that it can be : 3 ~'' f , . . .
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" - 10 -; disposable. ~nlike blood separation techniques performed using a centrifuge, balancing of the rotary device is not a :
concern. Also, aerosoling of the sample is minimized because the sample is substantially closed by the separator.
Other advantages are that the separator can be used to "harvest" plasma by adding one blood sample after another to a large size separator.
The separators can also be made stackable so that multiple units can be stacked on the same spinner.
It will of course be understood that the preceding description relates to particula~ preferred embodiments of the invention only and that the invention is not limited to these embodiments.
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Claims (6)

1. A plasma separator comprising a container having an axis, the container being symmetrical about said axis and being adapted for rotation at high speed about said axis with the container oriented so that said axis is vertical, the container being self supporting during such rotation and defining internally a central chamber for receiving a blood sample, an annular outer chamber, and an annular passageway connecting said chambers and having respective inner and outer ends, the central chamber having a top wall and a lower wall of inverted conical shape extending about said axis, the lower wall having an upper end and a circular edge at said upper end, said circular edge being disposed at said inner end of said passageway, the passageway extending downwardly and outwardly from said edge to said outer chamber, said outer chamber being located at said outer end of said passageway and below said circular edge, the inverted conical shape of the lower wall of the central chamber providing an internal surface of said central chamber which extends upwardly away from said axis to said circular edge at an inclination selected to permit red blood cells in a said blood sample to migrate up said surface, through said annular passageway, and into said outer chamber upon said rotation of the container at an appropriate said high speed, while plasma is retained in said inner chamber, the container having a single opening located in said top wall for permitting insertion of a blood sample into and removal of plasma from said central chamber.

2. A plasma separator as claimed in claim 1, wherein said container is a one-piece moulding in a plastic material.

3. A plasma separator as claimed in claim 1, wherein said container is shaped to define an annular structure extending below said lower wall of inverted conical shape and defining part of said outer chamber, said annular structure being shaped to be frictionally received in a complimentary recess in a device capable of rotating the container at high speed.

4. A plasma separator as claimed in claim 1, wherein said passageway is defined by inner and outer walls of the container which are normally in contact, and wherein the container is designed to flex under the effect of centrifugal force to permit said walls to move apart and open the passageway for liquid flow therealong.

5. A plasma separator as claimed in claim 1, wherein said lower wall of inverted conical shape has an opening at its centre surrounded by a neck to which is frictionally coupled a cap forming a collecting chamber for plasma that has drained from said central chamber.

6. A method of separating plasma from red cells in a blood sample, the method comprising the steps of:
providing a transparent container having an axis, the container being symmetrical about said axis and being self supporting, the container defining internally a central chamber, an annular outer chamber and an annular passageway connecting said chambers and having respective inner and outer ends, the central chamber having a top wall and a lower wall of inverted conical shape extending about said axis, the lower wall having an upper end and a circular edge at said upper end, said circular edge being disposed at said inner end of said passageway, the passageway extending downwardly and outwardly from said edge to said outer chamber, said outer chamber being located at said outer end of said passageway and below said circular edge, the container having a single opening located in said top wall for providing access to said central chamber;
inserting a said blood sample into said central chamber through said opening in the top wall;
rotating the container about said axis with the axis vertical at a speed selected to cause red cells in said blood sample to migrate up said lower wall, through said annular passageway, and into said outer chamber, while plasma is retained in said inner chamber;
visually monitoring the container and terminating said rotation when the plasma in said inner chamber is seen to be substantially clear;
removing plasma from said central chamber through said opening in said top wall of said chamber.