GB2194904A - Improvements relating to centrifuges - Google Patents

Abstract

A centrifuge chamber, e.g. for separating components of whole blood, has a hollow body (18) rotatable about its axis and with a lid (22) on its axis. A barrier (24) at an intermediate radius acts as a non-return valve that opens by centrifugal force when the body is rotating and closes when it is stationary to isolate the separated components. This barrier may take the form of resilient annular skirts (24) secured to the top and base of the chamber with their free edges just in contact or of a resilient member unattached but captive within the body. A separating gel (25) may also be used, of a density intermediate that of the components to be separated, and this may suffice as the barrier in itself. The chamber can be small, cheap and "throwaway", and be designed for fitting into a hand-held power unit (1). In a variation, the chamber is a spiral transparent tube with markings by which the proportions of the sample components can be determined. <IMAGE>

Description

SPECIFICATION Improvements relating to centrifuges This invention relates to centrifuges, and in particular to small scale apparatus primarily for medical use.

When considered in its simplest form, blood in the body is a suspension of cells (mostly red) in a fluid, known as plasma. A large proportion of blood tests, particularly biochemical, are performed on this cell-free fluid. The concentration of many chemicals inside the cells is substantially different to that of the surrounding plasma, but the enclosing membrane or wall of the cell can over a period of time allow the passage or diffusion of chemicals through it. Furthermore, the membrane is quite fragile and can rupture or lyse, thus allowing the ceil contents freely to enter the plasma.

Analysis of plasma containing lysed cells can give erroneous laboratory results.

When a blood sample is required the blood is usually taken from a vein with a needle and syringe (2, 5 or 10ml capacity). The sample is dispensed into a blood collection tube. The latter is generally made of transparent (or translucent) plastics or glass and may, or may not, contain chemicals to prevent the sample clotting. If such an anti-coagulant chemical is present the cells will remain suspended in plasma as they were in the blood vessel before sampling, whereas if no anti-coagulant is added the blood will soon clot. Some time later the clot will contract is size and exude a fluid almost identical to plasma but called serum. The cells are largely (but not entirely) enmeshed in the clot.

It is, as a general rule, considered good practice to separate the fluid from the cellular material as soon as possible, and in certain cases it is mandatory that this is done almost immediately. The process of separation is achieved in two stages. First, the blood is subjected to centrifugal forces in which the cellular material (and clot if present) is deposited at the bottom of the tube. Then the cellfree fluid forming the upper layer is removed using a pasteur pipette and bulb (similar to an 'eye dropper'), and ejected into another tube.

The first stage involves the use of a centrifuge. The smallest laboratory centrifuge is about the size of a portable television set and is similar to a "fairground roundabout", the "buckets" of which are designed to take the size of tube in use. It revolves at between 3000 and 5000 r.p.m. There are, of course, safety features associated with such instruments since they operate at mains voltage and considerable forces are engendered when they are working. The cost of a small bench centrifuge is currently approximately 500 and larger ones, accommodating more or larger samples, cost several thousand pounds.

It is therefore not practical for each ward, operating theatre, out-patients' department, health centre and general practitioner to possess or even have immediate access to such apparatus. As a result of this a heavy demand is made upon rapid transport systems both within and between health care establishments. Outside normal working hours it is often necessary to "call out" a duty technician to centrifuge a sample, thus involving more cost. Even so, many samples arrive at the laboratory unsuitable for use and this involves time and expense in obtaining a replacement.

An alternative method for the collection of blood involves the use of evacuated containers. These are glass tubes fitted with rubber stoppers to "contain" a vacuum. When fitted with a specially designed adaptor blood is drawn into the tube to fill the vacuum. That is, the evacuted tube becomes the blood collection tube, which is then sent to the laboratory. It still requires centrifugation.

It is the aim of this invention to provide a small-scale centrifuge which can be easily carried around by a doctor as part of his visiting equipment and which can be operated "on the spot". Furthermore, once the sample has been separated it should be kept so while its container is taken back for analysis of the contents.

According to one aspect of the present invention there is provided a centrifuge chamber comprising a hollow body of rotation adapted to be rotated about its axis, means for obtaining access to the central zone thereof and a barrier at an intermediate radius adapted to operate as a non-return valve that opens by centrifugal force and closes when the body is stationary.

To assist this, a charge of separating gel may be included to a density intermediate that of the components to be centrifuged.

According to another aspect of the present invention there is provided a centrifuge chamber comprising a hollow body of rotation adapted to be rotated about its axis, means for obtaining access to the central zone thereof, and a charge of separating gel of a density intermediate that of the components of the substance to be centrifuged.

With the barrier version, the barrier may comprise resilient means of annular form fixed within the chamber but with a free edge which flexes to the open position under centrifugal force. Conveniently, these resilient means are two skirts fixed to opposed end walls with their free edges contiguous when relaxed.

In one preferred form, the hollow body has shallow generally frusto-conic or domed end walls, said access means being a closable opening central of one such wall. This body may have peripheral support to enable it to be stood stably on a level surface, said one wall uppermost. The end walls may be separable for cleaning, sterilisation and subsequent reuse.

The closable opening may have a cap adapted to co-operate with a freely rotatable support or bearing, while the rotational drive is applied to the centre of the other said wall.

In an alternative embodiment, the barrier comprises resilient means inserted in the chamber, and in its relaxed state, having inner wall contact therewith to divide the chamber into two zones, but being deformable by cen- trifugal force to relieve that contact. This inner wall may be generally conic, and convenient forms of the resilient means are a pliant sphere or cylinder.

The hollow body, especially in this form, is conveniently a generally conic flask, said access means being a closable opening at the apex.

The rotational drive may not be applied directly to the hollow body; instead that may be received and wholly supported in some form of a carrier to which the rotational drive is applied.

According to further aspect of the present invention, there is provided a centrifuge chamber comprising a body of rotation including a spiral tube generally in the plane of rotation and whose centre is co-incident with the axis of rotation, the tube having a closable access for charging with and extracting fluid, being at least partially transparent, and having scale markings associated therewith, whereby when visible separation of components of a fluid has occurred along the length of the tube after centrifuging, the proportions of said components can be gauged by reference to said markings.

According to yet another aspect of the present invention there is provided a centrifuge comprising a hand-holdable body containing a battery means and an electric motor drivable thereby, and adapted to receive and enclose a removable centrifuge chamber as defined above, the chamber, when so received and enclosed, being in driver connection with said motor.

Mains power or power from a vehicle battery through a cigar lighter socket could be used on other versions.

It is envisaged that the chambers will be made in one piece (apart from the cap) and be of a size and produced in such numbers as to be economically disposable.

For a better understanding of the invention, some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a casing containing a centrifuge, Figure 2 is an axial section of the body of the casing, Figure 3 is a perspective view of a centrifuge chamber fittable within the casing, Figure 4 is an axial section of the upper portion of the casing, with its lid, and showing the centrifuge chamber mounted, Figure 5 shows steps in a process using one form of centrifuge chamber, Figure 6 shows steps in a modified process using that chamber, Figure 7 shows perspective views of alternative centrifuge chambers, and Figure 8 is a plan view of another centrifuge chamber.

The casing is generally cylindrical with a main body 1 and a screw-on lid 2. Here the lid is shown as hexagonal, to stop rolling if it is laid on its side and incidentally to afford a good grip, and the body 1 has a similarly shaped base 3. Also shown in Figure 1 is a switch 4 for operating the centrifuge motor 5 within, and warning lights 6, for example LEDs, to indicate power on, lid secure, leak detected and other functions or events. As well as warning, the safety provisions may automatically shut down the motor 5. There will also be provision for ventilating the casing.

Referring to Figure 2, the motor 5 is operated by a battery (not shown) which will be housed in compartment 7. It drives a capstan 8 at the upper end, this being a disc with a transverse slot 9, and a co-axial shaft 10 which extends down through a liquid-proof sealing ring 11 and a needle bearing 12. The lower end of this shaft is recessed to contain a spring 13 and to be engaged by the drive shaft 14 of the motor 5.

The lid 2 is a screw fit onto the upper end of the body 1. As shown in Figure 4, internally at the centre of its top there is a squat spindle 15 in a needle bearing 16, this spindle having a transverse rib 17 projecting downwardly. It can be arranged that the apparatus is only operable if the lid is secure and also that the lid cannot be removed until the centrifuge has stopped.

The lid 2, when fitted, encases a centrifuge chamber 18, preferably made of durable plastics material. In this embodiment, it is generally discus-shaped with a top and base each of shallow frusto-conical form, but also with a depending skirt 19 about the periphery. At the centre of the base there is a projection 20 adapted to engage the slot 9 in the capstan 8. The top has a central neck 21 on which a screw cap 22 fits, this giving access to the inside of the chamber. The screw cap 22 has a transverse recess 23 for engagement by the rib 17.

When the chamber 18 is removed for charging or removal of a sample it can stand stably on a level surface by means of the skirt 19. Also with several such chambers, they can be vertically stacked. For operation, the chamber 18 is placed with the projection 20 engaging the capstan 8, and the lid 2 is offered up so that the rib 17 engages the recess 23. The lid is screwed down and as this happens the spring 13 is compressed.

It will be noted that the compartment for the centrifuge chamber 18 is sealed from the motor and is easy to clean and disinfect.

Referring now to Figure 5, in one version the chamber 18 is internally equipped with an annular barrier 24 consisting of two resilient flexible skirts at an intermediate radius. One is secured to the base and the other to the top of the chamber and their free edges are just in contact. The sample of whole blood to be centrifuged is dropped into the inner zone defined by this barrier, the cap 22 having been temporarily removed as shown in stage (a).

The chamber is then closed, fitted into the casing as described and rotated at high speed, say 17,000 r.p.m. The casing does not have to be upright as shown in Figure 1.

The sample then separates as illustrated by state (b) and (c), the centrifugal force causing the skirts of the barrier to flex outwardly and ailow the denser material (the red cells) to escape to the outer annular zone. At stage (d), the chamber has been removed from the casing, the cap taken off and the material in the central zone (the plasma) is being drawn off. This need not be done immediately for the separation can remain intact while the chamber is transported to a laboratory.

Figure 6 shows a similar sequence, but initially the central zone is partially charged with a separation gel 25. As rotation continues, this builds up around the barrier 24, and provides more secure separation.

It may be possible to dispense with the barrier 24 and just rely on a charge of separation gel.

In an alternative arrangement, the chamber 18 may be adapted to fit within a rotative body and to turn with it. After centrifuging, the lid of the body is removed and the chamber is lifted out. This obviates the need for the capstan 8 and the spindle 15. It may also be of a different shape.

Such an alternative is illustrated in Figure 7.

Here the centrifuge chamber is provided by a conical flask 26 with a screw cap 27 at its upper, narrow end. Various measures may be taken to maintain separation.

In Figure 7(a) just a separating gel is used, introduced with the sample before centrifuging. When rotating at high speed, the denser material will concentrate in the outer region near the base, where the flask is widest, and the gel will interpose itself between the plasma and the cells in an approximately cylindrical formation. However, as the centrifuge slows and stops, this will revert to a disc-like separation barrier 28, with the plasma 29 above and the cells 30 below.

In Figure 7(b), there is a barrier in the form of a pliable sphere 31 which can be deformed sufficiently to be pushed through the neck of the flask and then expand. When centrifuging, liquid can force itself between the sphere and the coned wall and so separation takes place.

But when rotation ceases, the sphere reverts to near normal shape with circular line contact with the flask wall.

In Figure 7(c), another form of barrier is a pliable cylinder 32 which performs in a similar manner to the sphere 31.

With both the sphere and cylinder, the eventual division of the flask by the circular line of contact is unlikely to be the division between plasma and cells; there will generally be a certain amount of plasma in the lower portion of the flask, the boundary between phases being indicated by 33 in both Figures.

However, there will be plasma above the contact line which cannot then re-mix with the cells, and this can be taken for tests and analysis.

In a variation on the above, shown in Figure 8 the apparatus may be adapted to provide an analysis of relative quantities, such as the ratio of cells to plasma. This may be achieved by centrifuging the mixture on a disc-like body 34 with a flat spiral transparent tube 35 on it, with graduations 36. The components separate into inner and outer portions of the spiral, and the ratio is ascertained by reference to the graduations 36 and the division point between components.

The length of time the centrifuge operates on each occasion may be pre-set, so that it automatically closes down when separation should have been achieved. This may be announced by a light and/or an audible signal.

Each chamber will have water resistant label for patient and sampling details, and they will also be clearly labelled or colour coded for different uses.

A range of sizes may be provided, each being acceptable by the motor casing.

It will be appreciated that the above need not be limited to blood sampling or indeed to medical use in general. Another use, for example, would be testing river water.

Claims (20)

1. A centrifuge chamber comprising a hollow body of rotation adapted to be rotated about its axis, means for obtaining access to the central zone thereof and a barrier at an intermediate radius adapted to operate as a non-return valve that opens by centrifugal force and closes when the body is stationary.

2. A centrifuge chamber as claimed in Claim 1, and further including a charge of separating gel of a density intermediate that of the components of the substance to be centrifuged.

3. A centrifuge chamber comprising a hollow body of rotation adapted to be rotated about its axis, means for obtaining access to the central zone thereof, and a charge of separating gel of a density intermediate that of the components of the substance to be centrifuged.

4. A centrifuge chamber as claimed in Claim 1 or 2, wherein the barrier comprises resilient means of annular form fixed within the cham ber but with a free edge that flexes to the open position under centrifugal force.

5. A centrifuge chamber as claimed in Claim 4, wherein the resilient means are two skirts fixed to opposed end walls and with their free edges contiguous when relaxed.

6. A centrifuge chamber as claimed in any preceding claim, wherein the hollow body has shallow generally frusto-conic or domed end walls, said access means being a closable opening central of one such wall.

7. A centrifuge chamber as claimed in Claim 6, wherein the body has peripheral support to enable it to be stood stably on a level surface, said one wall uppermost.

8. A centrifuge chamber as claimed in Claim 6 or 7, wherein the end walls are separable for cleaning, sterilisation and subsequent reuse.

9. A centrifuge chamber as claimed in Claim 6, 7 or 8 wherein the closable opening has a cap adapted to co-operate with a freely rotatable support or bearing.

10. A centrifuge as claimed in any one of Claims 6 to 9, wherein the rotational drive is applied to the centre of the other said wall.

11. A centrifuge chamber as claimed in Claim 1 or 2, wherein the barrier comprises resilient means inserted in the chamber and, in its relaxed state, having inner wall contact therewith to divide the chamber into two zones, but being deformable by centrifugal force to relieve that contact.

12. A centrifuge chamber as claimed in Claim 11, wherein the inner wall is generally conic.

13. A centrifuge chamber as claimed in Claim 11 or 12, wherein the resilient means is a pliant sphere.

14. A centrifuge chamber as claimed in Claim 11 or 12, wherein the resilient means is a pliant cylinder.

15. A centrifuge chamber as claimed in any one of Claims 1 to 3 or 11 to 14, wherein the hollow body is a generally conic flask, said access means being a closable opening at the apex.

16. A centrifuge chamber as claimed in any one of Claims 1 to 9 or 11 to 15, wherein the rotational drive is applied by means for receiving and wholly supporting the hollow body.

17. A centrifuge chamber comprising a body of rotation including a spiral tube generally in the plane of rotation and whose centre is co-incident with the axis of rotation, the tube having a closable access for charging with and extracting fluid, being at least partially transparent, and having scale markings associated therewith, whereby when visible separation of components of a fluid has occurred along the length of the tube after centrifuging, the proportions of said components can be gauged by reference to said markings.

18. A centrifuge chamber substantially as hereinbefore described with reference to Figures 3 and 4 with Figure 5 or 6, Figure 7 or 8 of the accompanying drawings.

19. A centrifuge comprising a hand-holdable body containing battery means and an electric motor drivable thereby, and adapted to receive and enclose a removable centrifuge chamber as claimed in any preceding claim, the chamber, when so received and enclosed, being in driver connection with said motor.

20. A centrifuge substantially as hereinbefore described with reference to Figures 1, 2 and 4.