WO2005051183A1

WO2005051183A1 - A needle sensor and a mechanism for inserting the needle sensor through the skin

Info

Publication number: WO2005051183A1
Application number: PCT/DK2004/000770
Authority: WO
Inventors: Kristian GLEJBØL
Original assignee: Novo Nordisk A/S
Priority date: 2003-11-25
Filing date: 2004-11-05
Publication date: 2005-06-09

Abstract

A needle sensor for subcutaneous measurement of the concentration of a substance in a body fluid has one electrode (1) also serving as a cutting device (2) and at least one further electrode (3) which is displaceable (4) from one position in which the end of the further electrode is essentially flush with or behind the end of the cutting device to an advanced position. The invention also comprises a mechanism for inserting the electrodes of the needle sensor to mutually different positions in the tissue by one single activation.

Description

A needle sensor and a mechanism for inserting the needle sensor through the skin

The invention relates to a needle sensor for subcutaneous measurement of the concentration of a substance in a body fluid, eg the blood glucose concentration, comprising multiple electrodes, wherein the one is constituted of a cutting device, whose end is sharp, thereby enabling the needle to penetrate the skin.

A typical use of needle sensors of the type is for the measurement of the blood glucose concentration in humans suffering from diabetes. In such cases, it is a fact that, in order to keep sequelar diseases at bay, it is a prerequisite that the blood glucose level is measured - and corrected - frequently. However, many people are reluctant to perform such frequent measurements since they involve cutting the skin with a lancet (for extracting a blood sample) or a needle sensor of the kind concerned by the invention. It is therefore important that the needle sensor is as slim as possible in order to reduce the pain inflicted by the insertion, but, on the other hand, the needle sensor must also be so large as to provide an adequate electrode area, which is one of the prerequisites for obtaining a reliable measurement result.

US 5,680,858 teaches a needle sensor, wherein the needle is used as the one electrode, while the other electrode is configured at the elliptical end of the obliquely cut, stainless-steel needle. In order to obtain adequate signal quality of the measurement, the electrode at the elliptical end of the needle must have a certain size, which constraints the possibilities for reducing the needle diameter.

US patent No. 5,165,407 teaches a needle sensor comprising, in a first embodiment, a flexible measurement and reference electrode that is to be inserted by means of a relatively thick catheter; which can, however, be made relatively slim in an alternative embodiment, a portion adjacent one side of a rigid needle being removed, thereby enabling glucose to diffuse from the environment in which the needle is implanted to an internal coaxial electrode, whereby measurement of the glucose level is enabled.

However, it applies to all of the described prior art needle sensors that they are associated with the drawback that the measurement electrode is located in immediate contact with tissue that has been damaged by the sharp tip of the needle. The body will quickly start to regenerate the damaged tissue, whereby changes will occur that may substantially reduce the reliability of the measurements.

It is the object of the invention to provide a needle sensor for painless insertion into the body inflicting minimal trauma to the tissue such that long- term stable measurement reliability is accomplished.

This object is accomplished in that the second electrode of the needle sensor is arranged to be movable within and electrically insulated from the cutting device, ^"whereby the second electrode is displaceable from one position in which the end of the second electrode is essentially flush with or behind the end of the cutting device to an advanced position. By the second electrode being inserted into loose tissue, the electrode may itself serve as sensor wire and it may be eg a platinum wire.

The second electrode may be displaced eg a few millimetres ahead of the end of the cutting device, whereby the surface of the electrode area can be made relatively large, albeit the wire is relatively thin. It follows that the cutting device can be made very thin, which means that largely no pain is experienced during insertion of the needle. As mentioned, by the needle sensor according to the invention the condition that the tissue immediately below the skin does not yield significant resistance to insertion of e.g. a wire and that thus it does not damage the tissue it penetrates is used to advantage. Thus the invention enables that the needle sensor can be made very thin and painless in use, and that an excellent area for the measurement electrode can be obtained, which electrode will furthermore be located in tissue that is not damaged by the cutting action required for insertion of the needle sensor. Therefore the measurements are also stable over the long term.

The cutting device can be in the form of a needle and can be manufactured from various materials, but preferably at least the needle surface comprises silver. It may be made of pure silver, a silver alloy or it may be a silver-plated steel needle. Conversion of the silver surface to silver chloride enables an Ag/AgCI reference electrode that becomes electrically connected to the second electrode via the chloride ions that occur inherently in the body fluid. In case of some embodiments it is preferred to also provide the cutting device with a membrane.

According to a preferred embodiment the second electrode is a relatively thin platinum wire that has to be insulated relative to the needle. Preferably this is accomplished in that the platinum wire is coated with an electrically insulating layer. At the end or proximate to the end, the insulation will be interrupted to the effect that some of the platinum wire is exposed. At this point the electrode is coated with eg glucose oxidase or other enzyme, and around this a membrane is typically added.

It is also known to use a reference electrode and two measurement electrodes of which the one is provided with glucose oxidase, while the second measurement electrode is not provided with glucose oxidase. Thereby it is possible, in a known manner, to compensate for error signals deriving from other substances in the body fluid; employing the prior art, however, involved even more pain since insertion of such needle sensor through the skin involved insertion of a correspondingly thicker needle sensor. The technique taught by the invention can also be used for considerably reducing the pain and trauma caused by such type of needle sensor, while simultaneously adequate signal quality is accomplished.

The second electrode may also comprise a preformed flexible substrate of the kind shown e.g. in US 6,484,045. This patent also discloses a cutting device in the form of a needle having a longitudinal slot for receiving the substrate on which one or more electrodes are formed.

The invention also relates to a mechanism for inserting a cutting device or a needle in tissue, eg a needle sensor according to the invention.

Various mechanisms for inserting needles in tissue are known, eg the one taught in US patent No. 5,282,793. This prior art mechanism comprises a spring and a device for releasing the spring.

It is the object of the invention to provide a mechanism that allows a needle consisting of a first part and a second part to be inserted into the tissue, such that the first and the second part of the needle are, following insertion, located in mutually different positions in the tissue. As will appear from the following, a number of embodiments within this concept are perceivable that were previously not used to advantage. The invention is particularly advantageous in connection with two needle parts that both serve as electrodes for measuring the concentration of a substance in a body fluid, because the mechanism ensures a well-defined distance between the electrodes.

By one embodiment the first part of the needle may be a cutting device for receiving the second part of the needle, but it is not necessary for the needle to completely enclose the second part of the needle; it being sufficient that the tube only partially encloses the second part of the needle. This embodiment may be relevant in connection with the first part of the needle being used for cutting through the resistant epidermis, and to this end it is not necessary that the first part of the needle completely encloses the second part of the needle. According to a preferred embodiment the first part of the needle is inserted in a depth, where the tissue yields relatively little resistance to penetration, which makes it very easy to further insert the second part of the needle by means of the mechanism. When the tissue yields little resistance to penetration, it is possible to round the tip of the second needle part, which can thus be used as measurement electrode in the area of a tissue which is not damaged by the cutting. Alternatively, the second needle part may comprise a flexible substrate which can be inserted beyond the end of the cutting device by means of the mechanism.

According to a preferred embodiment, the mechanism is configured such that by a simple grip it is possible to manually insert both needles to the desired position. This may be accomplished eg by means of a friction bushing that transmits the forces from an operating handle to the first part of the needle until it hits an end stop. Then the second part of the needle cay be caused to travel a distance further, as the friction bushing slides on the operating handle.

Preferably the entire mechanism is sterile, which may conveniently be accomplished by the mechanism and operating handle being enclosed in a bellows housing.

The movement of the needle parts relative to each other can be ensured by means of end plates that are guided in relation to each other, and it will be understood that other means may also be used for generating the insertion force, eg a spring mechanism that can be tensioned and released. The invention will be explained in further detail in the following description of exemplary embodiments, reference being made to the drawing, wherein:

Figure 1 is a sectional view through an embodiment of the measurement electrode according to the invention;

Figure 2 is an enlarged sectional view through the second electrode (the internal one shown in Figure 1); Figure 3 is a perspective view of a second embodiment of a needle and associated second electrode;

Figure 4 shows an embodiment of a mechanism for inserting a needle, comprising a first and a second needle part;

Figure 5 shows the same as Figure 4, wherein, however, the interior parts of the mechanism are shown; whereas

Figures 6-8 show further details of the interior parts that ^"will appear from Figure 5.

Figure 1 is a sectional view through an embodiment of the needle sensor according to the invention. The sensor comprises an external needle 1 the end of which 2 is sharp and hollow for receiving a second electrode 3 which is movable in the longitudinal direction relative to the needle 1 , as shown by the arrow 4. The second electrode is movable between the position shown in Figure 1 by fully drawn line and the position shown by dotted line.

The gist of the invention is that the second electrode 3 is pushed forwards to the position shown by dotted line only when the needle 1 has been conveyed through the skin that yields relatively much resistance. Therefore the skin is cut by the sharp end 2, but the tissue is damaged in this process and it will, following such damage, relatively quickly seek to repair itself, ia by the formation of a membrane around the needle, which will relatively quickly impair the electrical measurements compared to the requisite implantation time for the electrode in the tissue, By the second electrode 3 being finally advanced through the soft subjacent tissue it is accomplished both that the free end of the second electrode can be rounded so as not to damage the tissue, and also that the second electrode may be in the form of a quite thin wire. Thereby the needle 1 can also be made very thin and thus the pain experienced by the user when the needle is inserted can be reduced considerably, see the introductory part of this specification.

In accordance with the invention the needle 1 can be used as reference electrode and for this purpose the needle is made of silver or a silver alloy or silver plated steel. By converting the silver surface to silver chloride a well- known reference electrode is accomplished that may optionally comprise a membrane that is also known.

Figure 2 shows an enlarged section through the second electrode 3. Interiorly, the electrode consists of a thin platinum wire 5 having a thin layer of insulation 6 to the effect that the second electrode is electrically insulated from the needle 1. At the exterior end the insulation 6 is removed in an area that is partly or fully covered with glucose oxidase 7 which is a well-known substance used for measuring the glucose present in the blood when employing electrochemical detection. Around this active part of the second electrode 3, a membrane 8 is arranged. It is noted that the active area comprising the glucose oxidases may be arranged in other ways on the wire 5.

Figure 3 shows an alternative embodiment, wherein the needle 1 shown in Figure 1 is replaced by a dish 9 having a cutting front edge 10. In the dish the second electrode 11 rests which may, in a manner similar to the above disclosures, be caused to travel a distance further when the dish 9 has cut its way through the resistant tissue and has arrived in loose tissue. Thus, there exist a number of different embodiments how a measurement electrode according to the invention can be accomplished, by which embodiments the measurement electrode can be made quite thin and be arranged in a well- known position in relation to the reference electrode in tissue that is not damaged, whereby errors in the electrical measurements are avoided. Figure 4 shows an embodiment of a mechanism according to the invention for inserting the needle sensor. The mechanism comprises a bottom plate 12 intended for being attached to the skin, eg by means of an adhesive. Figure 4 also shows a bellows housing 13 that contains a mechanism for advancing the needle sensor, which will be subject to further explanation in the description that follows in respect of Figures 4-8. The mechanism acts such that, when the outer bellows housing is compressed to approximately half the axial length of what appears in in Figure 4, the needle sensor that consists of two needle parts is inserted into the skin in specific positions as will appear from the following.

Figure 5 shows a number of internal parts that are each shown more clearly in Figures 6-8.

An ejector pin 14 is, at its upper end, connected to the inner top face of the bellows 13 and the opposite end of the ejector pin 14 acts directly on an end plate 15 that carries the first electrode part, such as eg the part 3 shown in

Figure 1. Around the ejector pin 14 a friction jacket 16 is also provided that is configured for pressing against a second end plate 17 that carries the second electrode part, eg the needle 1 shown in Figure 1. The two end plates are guided for mutual displacement by means of control pins 18. The friction jacket 16 fits around the ejector pin 14 such that, when a pressure is exerted on the ejector pin, the needle part on the end plate 17 will be pushed first into the tissue. This movement is stopped in a well-defined manner by the friction jacket 16 abutting on a stop 18, which means that the cutting needle is stopped, while the internal second electrode part is advanced further due to the ejector pin 14 being able to slide on within the friction jacket 16.

It is to be understood that the electrodes can be inserted by fully or semiautomatic means. For example the end plates mentioned above could be driven by one or more springs. Also a cannulla may be used to nest a flexible electrode said cannulla may be driven manually or automatiacally.

Claims

C l a i m s

1. A needle sensor for subcutaneous measurement of the concentration of a substance in a body fluid, eg the blood glucose concentration, comprising multiple electrodes, of which the one is constituted by a cutting device, whose end is sharp, whereby the cutting device may be inserted through the skin, characterised in that a second electrode is movable in the direction of the cutting device immediately proximate to and electrically insulated from the cutting device, such that the second electrode is displaceable from one position in which the end of the second electrode is essentially flush with or behind the end of the cutting device to an advanced position.

2. A needle sensor according to claim 1 , characterised in that the cutting device encloses the second electrode at least in part.

3. A needle sensor according to claim 1 , characterised in that the cutting device a needle made of silver.

4. A needle sensor according to claim 1 , characterised in that the cutting device is a needle made of a silver alloy.

5. A needle sensor according to claim 1 , characterised in that the cutting device is a needle made of silver plated steel.

6. A needle sensor according to any one of claims 3-5, characterised in that the silver surface is converted to silver chloride.

7. A needle sensor according to claim 1 , characterised in that the cutting device comprises a membrane.

8. A needle sensor according to claim 1 , characterised in that the electrochemically active surface of the second electrode contains platinum or a platinum metal.

9. A needle sensor according to claim 8, characterised in that the wire is insulated.

10. A needle sensor according to claim 9, characterised in that a part of the insulation of the platinum wire is removed in proximity of its end.

11. A needle sensor according to claim 10, characterised in that glucose oxidase is arranged on the exposed part of the wire.

12. A needle sensor according to claim 8, characterised in that two insulating platinum wires are arranged within the needle, wherein the one wire is coated with glucose oxidase, while the other wire is not coated with glucose oxidase.

13. A^' needle sensor according to claims 8-12, characterised in that a membrane is provided around the wire.

14. A needle sensor according to claims 1-7, characterised in that the second electrode comprises a flexible substrate.

15. A needle sensor according to claim 14, characterised in that the second electrode has one or more electrode areas comprising metal layers on the flexible substrate.

16. A mechanism for inserting a needle in tissue, eg an electrode for measuring the concentration of a substance in a body fluid, characterised in that the needle comprises a first and a second part that are movable in relation to each other; and that the mechanism is configured for inserting the needle parts to mutually different positions in the tissue by one single activation.

17. A mechanism according to claim 16, characterised in that the first part of the needle encloses the second part of the needle at least in part; and that, upon activation, the mechanism is configured for advancing first both needle parts, following which the second needle part is advanced a further distance into the tissue.

18. A mechanism according to claims 16-17, characterised in that the first part of the needle is cutting; and that it is inserted by means of the mechanism to a depth, in which the tissue yields relatively little resistance to penetration.

19. A mechanism according to claims 17-18, characterised in that the first part is a reference electrode; and that the second part is a measurement electrode with a rounded tip which is advanced a further distance by means of the mechanism.

20. A mechanism according to claims 16-18, characterised in that the mechanism comprises an operating handle configured for converting a manual impact into an insertion force for both of the needle parts.

21. A mechanism according to claim 20, characterised in that the operating handle is directly connected to the second needle part; and that the first needle part is operated by the operating handle via a friction jacket configured for cooperating with an end stop, thereby enabling the operating handle to press the second needle part a distance further into the tissue.

22. A mechanism according to claim 20 or 21 , characterised in that the operating handle is enclosed by a bellows housing.

23. A mechanism according to claims 16-22, characterised in that the two needle parts are arranged on each their end plate; and that the end plates have cooperating guide means that allow mutual movement in the direction of the needle.

24. A mechanism according to claims 16-23, characterised in that it comprises a spring and a device for releasing the spring, such that at least the one of the needle parts is inserted by means of spring force.