GB2368299A

GB2368299A - Capillary tube with internal helix formation, method and apparatus of manufacture, use of tube

Info

Publication number: GB2368299A
Application number: GB0025981A
Authority: GB
Inventors: William Thomas Dennis Bates
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-10-24
Filing date: 2000-10-24
Publication date: 2002-05-01
Anticipated expiration: 2020-10-24
Also published as: GB2368299B; GB0025981D0

Abstract

A capillary tube 1 comprises a substantially cylindrical tube 2, which may be glass, with an internal helix 3 formed from a filament, which may also be glass and may be fused to an interior surface of the tube 2. The helix 3 may provide improved take up of fluid samples, such as blood, and may aid the mixing within the tube 2, such as blood with an interior tube 2 coating of anticoagulant, by the rotation of the tube 2 about its central axis, the helix 3 providing a screw effect to better imbibe sample into, or mix the contents of, the tube 2 (fig.4). Further disclosed is a method of manufacturing the tube 1 comprising the steps of providing an elongate glass tube 5 with an elongate glass filament / rod 6, heating both of these to soften the glass, causing the filament 6 to fuse to the tube 5, and drawing out 12 the tube 5 whilst twisting it to impart a helical formation to the filament. Detail of suitable dimensions for the tube 1 are discussed in detail as is an apparatus which might perform the manufacturing method disclosed.

Description

CAPILLARY TUBE The present invention relates to capillary tubes. More particularly, but not exclusively, it relates to an improved capillary tube for use in the storage and testing of blood samples.

When blood samples are taken from humans or animals for subsequent testing, it is usually necessary to treat the blood samples to prevent them coagulating before they can be tested.

An anti-coagulant, such as heparin or the lithium salt of heparin, is conventionally added to the blood samples for this purpose. Other reagents may also be added, such as ethylene diamine tetra-acetic acid (EDTA) for measuring a platelet count and making blood films.

The amount of blood required for most modem blood testing procedures is very small, particularly when a test is based on reactions with antibodies, or other biochemical reactions. It is therefore a standard technique than when a blood sample has been taken from a subject, to take part of the blood up into a capillary tube, where it may be stored until required. The anticoagulant is conveniently and safely added to the blood by coating the interior surface of the capillary tube with anticoagulant before use. When blood is taken up into the tube, the anticoagulant dissolves into the blood and prevents premature coagulation. It is normal to roll the capillary tube about its longitudinal axis to improve the mixing of the anticoagulant with the blood.

There are, however, problems with this technique. The anticoagulant is coated on the interior surface of the capillary tube by taking up into the tube a solution of the anticoagulant, which is then allowed to dry. This can coat the interior surface unevenly, sometimes to the extent that a solid plug of anticoagulant forms, blocking the capillary tube and making it useless.

Such tubes must be checked for and discarded.

The anticoagulant does not always mix rapidly and evenly into the blood within the tube, despite the tube being rolled. This can lead to partial coagulation of the blood sample, which thereby becomes useless.

When a capillary tube is intended to be used with blood samples in hot, and particularly tropical, climates, it is normal to coat the interior of the tube with at least a double dose of anticoagulant. The above problems are thereby exacerbated.

Although the natural"capillary rise"of liquids into a capillary does assist the transfer of blood into the capillary tube, the surface tension and viscosity of blood are such that this capillary action is limited and slow. A large part of the capillary tube must be dipped into the blood sample in order to fill the tube, and a user must wait until the blood has climbed up the tube to the required level. This is inconvenient when taking large numbers of samples. A finer tube would produce a higher capillary rise, but would restrict the quantity of blood that could be stored, would not increase the speed of the capillary rise and would make the tube more fragile.

Fragility is a problem, even with stouter capillary tubes. The tubes are handled manually, so any breakages are a safety risk, both from broken glass and from any pathogens which may be present in the blood sample. Further processing, such as centrifuging, may also be carried out while the blood sample is being stored in the capillary tube. This is another point at which breakages are to be avoided, because of sample loss, because of possible contamination of other samples being processed and because of risks from blood-borne pathogens. (Blood testing for AIDS, hepatitis and other such diseases is carried out on samples stored in capillary tubes).

There is thus a need in the field of blood testing for a form of capillary tube that would obviate the above problems. It can also readily be seen that similar problems would arise in

other scientific fields, such as chromatography, in which capillary tubes are employed.

C : l It is therefore an object of the present invention to provide an improved form of capillary tube which serves to obviate the above problems and permits faster, more reliable and safer handling of samples, more particularly blood samples. It is a further object of the present invention to provide a method for the manufacture of said improved capillary tubes and apparatus to carry out said method of manufacture. It is also an object of the present invention to provide a method for the use of said improved capillary tubes for storing blood.

According to a first aspect of the present invention, there is provided a capillary tube comprising a substantially cylindrical tube and a filament, extending along a substantially helical path from an end of said tube to an opposing end thereof and in contact with an interior surface of said tube along substantially the whole length of the filament.

Preferably, said tube and said filament comprise glass.

Advantageously, the filament is fused to said interior surface of the tube.

The filament may have a diameter between one-quarter and one-fiftieth of the internal diameter of the tube.

Advantageously, said filament has a diameter between one-eighth and one-twentieth of said internal diameter.

Optionally, said filament has a diameter approximately one-tenth of said internal diameter.

The tube may have an internal diameter of between 0.5 millimetres and 2 millimetres.

Advantageously, the tube has an internal diameter of approximately 1 millimetre.

The tube may have a wall thickness between 0.1 millimetres and 0.5 millimetres. Advantageously, said wall thickness is between 0.2 millimetres and 0.3 millimetres.

9 Said helical filament may have a pitch such that one complete turn of the helix occupies a length of the tube equal to between three and one hundred times the internal diameter thereof.

Advantageously, the pitch is such that one complete turn of the helix occupies a length of the outer tube equal to between ten and twenty five times the internal diameter thereof.

Optionally, the pitch is such that one complete turn of the helix occupies a length of the outer tube equal to between fifteen and twenty times the internal diameter thereof.

In a preferred embodiment, an interior surface of said capillary tube is coated with a reagent.

Advantageously, said reagent comprises an anticoagulant substance.

Optionally, said anticoagulant substance may comprise heparin, a sodium salt or a lithium salt thereof.

Sealing means may be provided for the capillary tube to seal at least one end thereof.

Advantageously, said sealing means comprises a malleable substance such as a wax, a clay or a synthetic equivalent thereof.

According to a second aspect of the present invention, there is provided a method for the manufacture of a capillary tube, comprising the steps of providing an elongate glass tube and an elongate glass filament, locating said filament within the tube, heating the tube and filament to soften the glass thereof and to cause said filament to fuse to an interior surface of said tube, and drawing out said tube while twisting said tube to impart a helical conformation thereto.

Preferably, said step of drawing out said tube is performed by means of rollers, optionally a pair of independently driven rollers.

Advantageously, said rollers are disposed at an angle one to the other, said angle being substantially bisected by the longitudinal axis of said tube.

The angle of said rollers may be changed to vary the pitch of the tube.

The speed of the rollers may be so adjustable as to determine the diameter of the tube and also to change said pitch.

Ideally, the speed of the rollers is adapted to give a draw ratio of 11: 1.

In this case, the tube may have a starting outside diameter of 16. 5mm and the drawn tube may have an outside diameter of 1. 5mm.

Said heating step may comprise the step of passing the tube and filament through an oven, which is preferably a muffle adapted for heating glass. The temperature of the oven may be sufficient to fuse said filament to the interior surface of the tube but insufficient to cause said filament to slump or otherwise substantially change its cross-sectional form.

The method may comprise the additional step of cutting said tube into lengths suitable for use.

In a preferred embodiment, the method further comprises the step of coating an interior surface of said capillary tube with a reagent, preferably an anticoagulant, such as heparin.

Advantageously, said reagent is coated on to said interior surface by filling an interior of said capillary tube with a solution of the reagent, and allowing said solution to dry.

According to a third aspect of the present invention, there is provided an apparatus for the manufacture of said improved capillary tubes from a glass tube and a glass filament, comprising a source of heat sufficient to soften the glass of said tube and said filament, and a pair of rollers, so adapted as to draw out said tube to capillary dimensions while twisting said tube to impart a helical conformation to said filament.

Preferably, said apparatus comprises a pair of independently driven rollers, so disposed at an angle to said tube that they may draw out said tube and impart a helical conformation thereto.

Said source of heat may be an oven, preferably a muffle adapted for heating glass.

Said oven may be so configured that a glass tube may be passed continuously into, through and out of the oven.

Said apparatus may comprise a means to cool said capillary tube subsequent to it being drawn out by said rollers.

Said apparatus may comprise a means to cut said capillary tube into lengths suitable for use.

According to a fourth aspect of the present invention, there is provided a method of use of a capillary tube to store a blood sample, comprising the steps of providing a capillary tube as described above, coated on an interior surface thereof with an anticoagulant substance, dipping an end of said capillary tube into a sample of blood, previously taken from a subject, to such a depth that a required quantity of blood is taken up into the capillary tube, and rolling said capillary tube about a longitudinal axis thereof to promote dissolution and mixing into the blood of said anticoagulant substance.

Preferably, said method comprises the step of sealing an end of said capillary tube prior to rolling said capillary tube.

Said anticoagulant substance may comprise heparin. An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic elevation of part of a capillary tube embodying the present invention ; Figure 2 is a cross-section of the capillary tube of Figure 1, taken along the line 11-Il.

Figure 3 is a schematic view of an apparatus for the manufacture of capillary tubes embodying the present invention; Figure 4 is a cross-section of the capillary tube of Figure 1 in use.

Referring now to the drawings and to Figures 1 and 2 in particular, an improved capillary tube 1 comprises a cylindrical glass tube 2 and a glass filament 3, fused along a helical path to an interior surface 4 of the tube 2.

In a particularly suitable embodiment, the exterior diameter of the tube 2 is approximately 1.5 millimetres and the interior diameter thereof is approximately 1.0 millimetres. The helical filament 3 has a diameter of approximately 0.1 millimetres and has such a pitch that one complete turn of the helix 3 occupies 17 millimetres of the tube 2. Note that, for clarity, the pitch shown in Figure 1 is only 5: 1, rather than the pitch of 17: 1 described above.

The interior surface 4 of the tube 2 is coated with a dry film of heparin anticoagulant.

Figure 3 shows the preferred method of making the capillary tubing, in which relatively large bore glass tubing 5, containing a glass rod 6, held initially adjacent one end of the tubing 5 by a set of driven feed rollers 7 and a set of guide rollers 8. The feed rollers 7 gradually feed the tubing 5 and the rod 6 into a muffle 9. The tubing 5 and the rod 6 are heated in the muffle 9, reaching a temperature at which they are sufficiently soft to be drawn and at which the rod 6 fuses to the interior surface 4 of the tubing 5.

The tubing 5 and the rod 6 are then drawn out by means of a pair of independently driven draw rollers 10 to form a continuous length of capillary tube 1. The ratio of the diameter of the capillary tube 1 to the large bore glass tubing 5 is controlled by the speed of the draw rollers 10, drawing the capillary tube out of the muffle 9, relative to the speed of the feed rollers 7, feeding the tubing 5 into the muffle.

The rollers 10 are configured such that the rotational axes 11 thereof are disposed at an angle one to the other, and such that the tube 1 lies substantially along a bisector of the angle between the rotational axes 11. So configured, the draw rollers 10 impart a twist to the tubing 5 as it is drawn down to a smaller diameter to form the capillary tube 1. The angle between the rotational axes 11 determines the pitch of the twist imparted thereby, and may be adjusted to alter said pitch.

Since the rod 6 is fused to the interior surface 4 of the tubing 5, it is drawn down in proportion therewith and acquires the twist imparted thereto. The continuous length of capillary tube 1 thus comprises a helically extending glass filament 3 fused to an interior surface 4 of a cylindrical glass capillary tube 2.

The drawing down of the tubing 5 to form the capillary tube 1, the fusing of the rod 6 to the interior surface 4 of the tubing 5 and the imparting of the twist to the capillary tube 1 and the filament 3, all take place in a zone adjacent an exit 12 of the muffle 9, where the glass is still

soft enough to be worked. The capillary tube 1 passes through a cooling zone 13 before passing between the rollers 10, so that it is sufficiently rigid not to be deformed by pressure c from the rollers 10. After passing through the rollers 10, the capillary tube 1 may be cut into convenient lengths for storage and use.

In a preferred embodiment, the glass tubing 5 has an initial external diameter of 16 5 millimetres and an internal diameter of approximately 11 millimetres, and the glass rod 6 has a diameter of approximately 1 millimetre. The rollers 10 are driven at such a speed as to give a draw ratio of 11 : 1, giving a capillary tube 1 with an external diameter of approximately 1. 5 ZD millimetres, an internal diameter of approximately 1. 0 millimetres and a helically extending filament 3 of diameter approximately 0. 1 millimetre.

The lengths of capillary tube 1 are prepared for use by dipping them in a solution of heparin, which is allowed to fill the interior of the capillary tube 1, and is then dried slowly with regular movement of bundles of tubes.

It is found that a capillary tube 1 containing a helically extending filament 3 both fills more rapidly than a conventional capillary tube of the same diameter and has a greater capillary rise. This speeds the coating process, and less of the capillary tube 1 needs to be submerged in the heparin solution to fill the capillary tube 1. There is thus less heparin wasted on the outside of the capillary tube 1.

It is also found that the evenness of coverage of heparin on the interior surface 4 of the capillary tube 1 is improved to a remarkable degree. The formation of plugs of solid heparin is reduced to a negligible level and less capillary tubes 1 need to be rejected. In use, an end of the capillary tube 1 is dipped into a blood sample, previously taken from a subject, and blood 13 is taken up into the capillary tube 1 by capillary rise. As for the heparin coating step described above, the capillary rise of blood for a capillary tube 1 with a helical filament 3 is faster than for a conventional capillary tube of the same internal diameter, and the height to which the blood 13 rises is also greater. Surprisingly, a capillary rise of up to three times that for a conventional capillary tube of the same internal diameter can be achieved using capillary tubes 1 of the present invention.

Once sufficient blood 13 has been taken up into the capillary tube 1, a plug 14 of malleable material is pressed into its upper end and the capillary tube 1 is removed from the blood sample. As shown in Figure 4, the capillary tube I is then rolled about is longitudinal axis to aid dissolution and mixing of the heparin coating into the blood 13.

It is found that the presence of the helical filament 3 improves the incorporation of the heparin into the blood 13 by a remarkable degree. Even when air bubbles 15 are present within the capillary tube 1, and even under the most adverse climatic conditions, the blood 13 is rapidly dosed with sufficient heparin to protect it against coagulation.

The capillary tube 1 and contents may be stored until required for testing or for further processing.

It is also found that a capillary tube 1 comprising a helical filament 3 is significantly more robust than a conventional capillary tube, and stands up better to handling and further processing. Health and safety risks from broken glass and blood-borne pathogens are thus reduced and blood samples are better protected from loss.

It can clearly be seen that the capillary tubes of the present invention provide greatly improved protection against coagulation for blood samples, by ensuring rapid and thorough incorporation of anticoagulant into the blood. Liquids are taken up into the capillary tube more rapidly than for conventional tubes and the capillary rise is significantly higher. The capillary tubes are easier and quicker to fill with blood samples as a result. They are also easier and quicker to coat with anticoagulant before use and the anticoagulant coats the interior surface of the capillary tube more evenly, greatly reducing the number of capillary tubes rejected because of solid plugs of heparin blocking the bore of the capillary. The capillary tubes of the present invention are also significantly more reliable as a storage medium, and are significantly safer for a user to handle, as they break significantly less readily than conventional capillary tubes.

Claims

CLAIMS 1. A capillary tube comprising a substantially cylindrical tube and a filament extending along a substantially helical path from an end of said tube to an opposing end thereof and in contact with an interior surface of said tube along substantially the whole length of the filament.

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2. A capillary tube as claimed in claim 1, wherein said tube and said filament comprise glass, and the filament is fused to the interior surface of the tube.
3. A capillary tube as claimed in either claim 1 or claim 2, wherein the filament has a diameter between one-quarter and one-fiftieth of the internal diameter of the tube.
4. A capillary tube as claimed in claim 3, wherein the filament has a diameter between one eighth and one-twentieth of said internal diameter.
5. A capillary tube as claimed in either claim 3 or claim 4, wherein the filament has a diameter approximately one-tenth of said internal diameter.
6. A capillary tube as claimed in any one of the preceding claims, wherein the tube has an internal diameter of between 0.5 millimetres and 2 millimetres, preferably approximately 1 millimetre.
7. A capillary tube as claimed in any one of the preceding claims, wherein the tube has a wall thickness between 0.1 millimetres and 0.5 millimetres, preferably between 0.2 millimetres and 0. 3 millimetres.
8. A capillary tube as claimed in any one of the preceding claims, wherein the helical filament has such a pitch that one complete turn of the helical path occupies a length of the tube equal to between three and one hundred times the internal diameter thereof.
9. A capillary tube as claimed in claim 8, wherein the pitch is such that one complete turn of the helix occupies a length of the tube equal to between ten and twenty five times the internal diameter thereof.
10. A capillary tube as claimed in either claim 8 or claim 9, wherein the pitch is such that one complete turn of the helix occupies a length of the outer tube equal to between fifteen and twenty times the internal diameter thereof.
11. A capillary tube as claimed in any one of the preceding claims, wherein an interior surface of said capillary tube is coated with a reagent.
12. A capillary tube as claimed in claim 11, wherein said reagent comprises an anticoagulant substance.
13. A capillary tube as claimed in claim 12, wherein said anticoagulant substance comprises heparin, a sodium salt or a lithium salt thereof.
14. A capillary tube substantially is described herein with reference to the Figures of the accompanying drawings.
15. A method for the manufacture of a capillary tube comprising the steps of providing an elongate glass tube and an elongate glass filament, locating said filament within the tube, heating the tube and filament together to soften the glass thereof and to cause said filament to fuse to an interior surface of said tube, and drawing out said tube whilst twisting said tube to impart a helical conformation thereto.
16. A method as claimed in claim 15, wherein said step of drawing out said tube is performed by means of a pair of independently driven rollers disposed at an angle one to the other, said angle being substantially bisected by the longitudinal axis of said tube.
17. A method as claimed in claim 16, wherein the angle of said rollers may be changed to vary the pitch of the tube.
18. A method as claimed in either claim 15 or claim 16, wherein the speed of the rollers is so adjustable as to determine the diameter of the tube and also to change said pitch.
19. A method as claimed in any one of claims 16 to 18, wherein the speed of the rollers is adapted to give a draw ratio of 11: 1.
20. A method as claimed in any one of claims 15 to 19, further comprising the step of coating an interior surface of said capillary tube with a reagent, preferably an anticoagulant such as heparin or a salt thereof.
21. A method as claimed in claim 20, wherein said reagent is coated on to said interior surface by filling an interior of said capillary tube with a solution of the reagent, and allowing said solution to dry.
22. A method for the manufacture of a capillary tube substantially as described herein with reference to the Figures of the accompanying drawings.
23. An apparatus for the manufacture of capillary tubes as claimed in any one of claims I to 14, comprising a source of heat sufficient to soften the glass of said tube and said filament, and a pair of rollers adapted to draw out said tube to capillary dimensions whilst twisting said tube to impart a helical conformation to said filament.
24. An apparatus as claimed in claim 23, wherein the rollers are independently driven and disposed at an angle one to the other, said angle being substantially bisected by the longitudinal axis of said tube.
25. An apparatus for the manufacture of a capillary tube substantially as described herein with reference to the Figures of the accompanying drawings.
26. A method of use of a capillary tube to store a blood sample, comprising the steps of providing a capillary tube as claimed in any one of claims 1 to 14 and which has been coated on an interior surface thereof with an anticoagulant substance, dipping an end of said capillary tube into a sample of blood to such a depth that a required quantity of blood is taken up into the capillary tube, and rolling said capillary tube about a longitudinal axis thereof to promote dissolution and mixing into the blood of said anticoagulant substance.