WO2007059277A1

WO2007059277A1 - Cannula

Info

Publication number: WO2007059277A1
Application number: PCT/US2006/044486
Authority: WO
Inventors: Palle M. Hansen
Original assignee: William Cook Europe Aps; Cook Incorporated
Priority date: 2005-11-16
Filing date: 2006-11-16
Publication date: 2007-05-24
Also published as: WO2007059277A8

Abstract

The invention relates to a cannula (1) for use in body tissue and body lumens and a method for producing the cannula. The cannula is substantially rod-shaped and has varying stiffness along its length. The cannula s divided into at least a first part (2) adapted to be located within body tissue or body lumens and a second part (3) adapted to extend from the body, and the cannula comprises a super elastic material that has been treated so the bending stiffness of the first part is different from the bending stiffness of the second part .

Description

CANNULA

Description Technical Field

The present invention relates to a cannula for use in body tissue and body lumen.

Background of the Invention The present invention relates to a cannula for use in body tissue and body lumen, said cannula being substantially rod-shaped and having varying stiffness along its length, said length being divided into at least a first part adapted to be located within body tissue or body lumen and a second part adapted to extend from the body. EP 0 916 359 A1 discloses a cannula where the stiffness along the length of the cannula is differentiated. This differentiated stiffness is obtained by use of at least two materials of different stiffness, which are combined with varying thickness in the wall of the cannula.

However, the construction of the cannula is rather intricate, as the materials of different stiffness have to be combined in a very complex structure to obtain the cannula with differentiated stiffness.

An object of the present invention is to provide a cannula with varying bending stiffness along its length that can be obtained in a simple manner. Summary of the Invention The present invention provides a cannula with excellent properties in respect of flexibility. Unexpectedly, it has appeared that it is possible, in a relatively simple manner and by use of super elastic materials, to produce a cannula in which the bending stiffness varies in sections of the longitudinal extension of the cannula. Thereby, it is possible to design a cannula, which is highly flexible in respect of bending stiffness and manufactured from one single material.

Accordingly, the present invention provides a cannula for use in body tissue and body lumens, which is substantially rod-shaped with varying stiffness along its length and divided lengthwise into at least a first part adapted to be located within body tissue or body lumens and a second part adapted to extend from the body; the cannula comprises a super elastic material, in which the bending stiffness of the first part is different from the bending stiffness of the second part.

Depending on the intended use the cannula may be hollow or solid, and as such the cannula according to the invention may be adapted for various uses. For use in connection with syringes or for biopsy the cannula is preferably hollow. The rod shaped member is, thus, a tube when the cannula is hollow. For use as sound or probe, the cannula may be solid.

The invention provides the possibility of the part of the cannula extending from the body being relatively soft, thereby reducing the risk of damage to the tissue due to unintentional touching or pushing. The invention also provides the possibility of the cannula being flexible or soft if it is inserted via body lumens, e.g. nostril or urethra. Such flexibility may also be preferred when the cannula is to be inserted in a vein.

Normally, the part of the cannula that is to be inserted in tissue or lumen (the first part) has a higher stiffness than the second part; a preferred embodiment of the cannula is a cannula where the bending stiffness of the first part is at least four times, preferably at least eight times higher than the bending stiffness of the second part.

As it will be understood, the bending stiffness expresses the tendency of the cannula to bend when exposed to forces perpendicular to the longitudinal direction of the cannula. The less the tendency to bend the more stiff or rigid the cannula will be.

In a further preferred cannula according to the invention, the bending stiffness of the first part is at least 20 times higher than the bending stiffness of the second part.

The cross-section of the cannula may remain substantially constant along its length.

The cannula may be formed from a single piece of material. According to the invention suitable super elastic materials are selected from the group consisting of super elastic alloys, such as Ni-Ti, Cu-Al, Ni-Al, Cu-Al-Ni, Cu- Zn, and Cu-Zn-Al.

In a preferred embodiment of the cannula according to the invention, the super elastic material is selected from the group consisting of super elastic alloys based on nickel and titanium. The super elastic alloy may be a pure NiTi alloy, or it may comprise minor amounts or traces of Cu, Al, Ag, Au, Zn, O, C, and N. The amount of the latter constituents does preferably not exceed 2 weight-%, more preferably the constituents do not exceed 1 weight-% of the alloy. Preferably, the super elastic material is the Ni-Ti alloy nitinol. Nitinol alloys comprising 50-60 weight-% Ti, are highly suitable for use for medical purposes due to their tissue friendly properties.

The transition temperature of the super elastic material is usually not critical as long as the material is able to provide its super elastic properties around normal body temperatures (i.e. 36-39 ⁰C). The transition temperature is the temperature where super elastic material undergoes a phase transformation from one phase to another; these phases have different properties in relation to hardness, stiffness, elasticity etc. In case of nitinol, the phase transformation will be a change in phase from a martensitic phase at low temperatures to an austenitic phase at high temperature. Nitinol in the martensitic phase is less stiff or softer than nitinol in the austenitic phase. Thus, when applying nitinol with a transition temperature below approx. 35⁰C, the first part of the cannula will be in a austenitic phase when located in body tissue having a temperature of approximately 37⁰C, while the second part extending from the body will be at room-temperature, e.g. 23⁰C, in the martensitic phase in which the alloy is softer.

In an alternatively preferred embodiment of the cannula according to the invention the super elastic material of the first part has a transition temperature below 35⁰C, and the super elastic material of the second part has a transition temperature below 50⁰C and above 40⁰C. Thus, in case of nitinol, the second part will not transform from the martensitic phase to the austenitic phase at temperatures below 40⁰C but will remain in the softer martensitic phase. Therefore, the cannula is useable at temperatures exceeding normal room temperatures, e.g. 25-35 ⁰C (in operating rooms the temperature may be quite high due to heating caused by lamps and other equipment), while still maintaining the second part in a softer phase. Hereby, another advantage of the NiTi alloy can be utilized as the same piece of the alloy material can be designed with different properties in different parts of the alloy material.

Similar embodiments, wherein the super elastic material of one part of the cannula has a transition temperature in the range of 28-35⁰C, and the super elastic material in another part of the cannula has a transition temperature in the range of 50-60⁰C, may be desirable. Thus, phase transformation may appear in one section, but not in another section of the cannula when it is located in body tissue or body lumens.

Although the cannula according to the invention may have any length that is suitable for its intended use, normally the cannula has a length in the range of 10 to 450 mm, preferably 20 to 300 mm. Cannulas with lengths in the range of 10 to

100 mm are e.g. suitable for use with syringes. Longer cannulas may be suitable for e.g. biopsy or sounds.

The diameter of the cannula may also vary within a wide range, but for most purposes a circular cross-section with a diameter in the range of 0.25 to 6.5 mm is suitable. However, for some purposes a square, triangular, oval or other shape of cross-section may be suitable.

Preferably, the second part of the cannula is adapted to communicate with a syringe or an infusion set. The second part may, therefore, be equipped with an adaptor allowing it to connect to a syringe or an infusion set. The cannula may also be adapted for use in biopsy or as a probe.

In another aspect, the invention relates to a method for producing a cannula for use in body tissue and body lumens, having varying stiffness along its length. The method comprises the steps of: providing a rod shaped member of super elastic material; dividing the rod shaped member in at least a first part and a second part; processing the rod shaped member along its length; wherein the processing involves the first part of the rod shaped member being subjected to a treatment different from the treatment of the second part of the rod shaped member.

By use of different treatments along the length of the rod shaped member of super elastic material, it is possible to build in different properties in respect of bending stiffness, thereby obtaining desired properties.

According to the method, the super elastic material is selected from the group consisting of super elastic alloys, like Ni-Ti, Cu-Al, Ni-Al, Cu-Al-Ni, Cu-Zn, and

Cu-Zn-Al. Conveniently, the shape memory material is a Ni-Ti alloy with 50-60 weight-% Ti. Preferably, the super elastic material is nitinol. Super elastic materials based on titanium are particularly useful due to their tissue friendly properties.

The processing of the super elastic material is conveniently a heat-treatment with different temperatures along the length of the rod shaped member, and preferably the heat-treatment is performed with laser, an inert gas brazing torch, electric wires, and/or a salt bath. Heat treatment with laser, with electric wire and to some extend with an inert gas brazing torch can be performed very local, and the distance between different treated sections on the cannula can be reduced.

In an alternative embodiment of the method according to the invention, the processing is a cold working treatment. Moreover, the super elastic material may be subjected to a combination of both cold working treatment and heat treatment in order to obtain the desired properties. However, suitable treatment for a specific super elastic material can be determined by a skilled person from the specific data of the material.

Brief Description of the Drawing Fig. 1 shows a cannula according to the invention adapted for connection to a syringe.

Fig. 2 shows a cannula according to the invention adapted for connection with an infusion set.

Fig. 3 shows the cannula of figure 1 when exposed to a lateral force. Detailed Description

Figure 1 illustrates a cannula 1 for use in connection with a syringe. The first part 2 of the cannula 1 is adapted to penetrate skin and tissue for placement in e.g. a vein. The second part 3 of the cannula 1 is equipped with an adaptor 4 to connect it to a syringe (not shown).

Figure 2 illustrates a somewhat larger cannula 10 adapted to connect to an infusion set by adaptor 1 1 . The first part 12 of the cannula 10 is adapted to penetrate skin and tissue and e.g. to be located in a vein.

In figure 3, the cannula 1 of figure 1 is shown when exposed to lateral forces as indicated with arrows 5. The first part 2 of the cannula remains unbended (stiff) while the second part 3 is bending because of the effect of the lateral forces. This behaviour is due to the different treatment of the first part 2 and the second part 3.

The behaviour may be advantageous when the cannula is located in a vein or tissue thus reducing the risk of damaging the walls of the vein or tissue due to accidental touching of the second part of the cannula.

The different values of bending stiffness of the cannulas according to the invention may be determined by using a Tinius Olsen stiffness tester in accordance with e.g. the ASTM E855 method A. However, for the purpose of having a quick an uncomplicated method for estimating the bending stiffness of the first part of the cannula in relation to the second part of the cannula, the following test method was established.

Example

A number of cannulas corresponding to the cannulas depicted in figure 1 and 2 were manufactured for test purposes (without adaption for syringe or infusion set). The cannulas were manufactured from nitinol tubes (nitinol alloy SE508

Tubing, obtained from NDC, Germany) with an outer diameter of 1 .00 mm and an inner diameter of approx 0.60 mm. The tubes delivered from NDC had an overall transition temperature below 18⁰C. The tubes were cut to have a length of 8.00 cm and divided in a first part (4.0 cm) and a second part (4.0 cm). The second part was subjected to the following thermal treatment (performed by ADMEDES Schuessler, Germany): The second part was placed in a salt bath and heated to 540-550 ⁰C for approx 22 hours, while the first part was kept as close to room temperature as possible.

After the thermal treatment, the second part of the nitinol tubes had a transition temperature in the range of about 26-30⁰C. Thus above 30⁰C, the second part of the tubes was in an austenitic phase with a relatively high bending stiffness. Below 26⁰C, the second part of the tubes was in a martensitic phase with a significantly lower bending stiffness. The first part of the tubes maintained a transition temperature below 18⁰C and appeared rather stiff. The bending stiffness of the cannulas (first part in relation to the second part) was examined. Measurements of bending stiffness on the manufactured cannulas were carried out as follows:

The cannulas to be examined for bending stiffness were placed on a horizontal table with a substantially friction-free surface. Initially, the first part of the cannula was fixed in a tubular holder attached to the table in such a manner that the second part could move freely on the table in horizontal directions.

A probe (stainless steel rod, diameter 2 mm) connected to a dynamometer (MARK 10) was placed horizontally on the table and perpendicular to the second part of the cannula in such a way that the end of the probe contacted the second part of the cannula 2.0 cm from the fixing point of the cannula. The probe was then moved 0,5 cm in the direction perpendicular to the extension of the cannula while forcing the second part of the cannula to bend 0.5 cm at the contact point. The force applied on the second part was then measured with the dynamometer. The procedure was then repeated on the first part of the cannula, while the second part was fixed to the table. The temperature during the measurements was 21 -23⁰C.

The results of the measurement are given in table 1 .

Table 1 . Results of measurements of bending stiffness of cannulas according to the invention

The results of the measurements clearly demonstrate that the bending stiffness of the cannulas in the first part was significantly higher than for the second part.

Claims

1. A cannula for use in body tissue and body lumens, said cannula being substantially rod-shaped and having varying stiffness along its length, said length being divided into at least a first part adapted to be located within body tissue or body lumens and a second part adapted to extend from the body, wherein said cannula comprises a super elastic material, and that the bending stiffness of said first part is different from the bending stiffness of said second part.

2. The cannula of claim 1 , wherein the cross-section of the cannula remains substantially constant along its length.

3. The cannula of claimi or claim 2, being formed from a single piece of material.

4. The cannula of any one of the preceding claims, wherein the bending stiffness of said first part is greater than the bending stiffness of said second part.

5. The cannula of any one of the preceding claims, wherein the bending stiffness of the first part is at least four times higher than the bending stiffness of the second part

6. The cannula of claim 5, wherein the bending stiffness of the first part is at least eight times higher than the bending stiffness of the second part.

7. The cannula of claim 6, wherein the bending stiffness of the first part is at least 20 times higher than the bending stiffness of the second part.

8. The cannula of any one of the preceding claims, wherein the super elastic material is selected from the group consisting of super elastic alloys, such as Ni- Ti, Cu-Al, Ni-Al, Cu-Al-Ni, Cu-Zn, and Cu-Zn-Al alloys.

9. The cannula of claim 8, wherein the super elastic material is a Ni-Ti alloy, preferably a nitinol alloy with 50-60 weight-% Ti.

10. The cannula of any one of the preceding claims, wherein the super elastic material has a transition temperature below 35⁰C.

1 1 . The cannula of any one of the preceding claims, wherein the super elastic material of one part of the cannula has a transition temperature which is different from a transition temperature of super elastic material in another part of the cannula.

12. The cannula of claim 1 1 , wherein the super elastic material of one part of the cannula has a transition temperature below 35⁰C, and the super elastic material in another part of the cannula has a transition temperature in the range 40-60⁰C.

13. The cannula of any one of the preceding claims, wherein the cannula has a length in the range of 10 to 450 mm.

14. The cannula of claim 14, wherein the cannula has a length in the range of 20 to 300 mm.

15. The cannula of any one of the preceding claims, wherein the cannula has a circular cross-section with a diameter in the range of 0.25 to 6.5 mm.

16. The cannula of any one of the preceding claims, wherein the second part of the cannula is equipped to communicate with a syringe.

17. The cannula of any one of the preceding claims, wherein the second part of the cannula is equipped to communicate with an infusion set.

18. A method for producing a cannula for use in body tissue and body lumens, having varying stiffness along its length, said method comprising the steps of: providing a rod shaped member of super elastic material; dividing the rod shaped member in at least a first part and a second part; processing the rod shaped member along its length; wherein the processing involves the first part of the rod shaped member being subjected to a treatment different from the treatment of the second part of the rod shaped member.

19. The method of claim 18, wherein the super elastic material is selected from the group consisting of super elastic alloys, such as Ni-Ti, Cu-Al, Ni-Al, Cu-

Al-Ni, Cu-Zn, and Cu-Zn-Al.

20. The method of claim 18, wherein the super elastic material is a super elastic Ni-Ti alloy, preferably with.

50-60 weight- % Ti.

21. The method of claim 18, wherein the processing is heat-treatment with different temperatures for the first part and the second part of the rod shaped member.

22. The method of claim 21 , wherein the heat-treatment is performed with a laser; an inert gas brazing torch; an electric wire or a salt bath,

23. The method of claim 18, wherein the processing Is a cold working treatment.