Method for chemical etching of a needle cannula

Abstract

A regular metallic, cylindrical tubular needle cannula (1) is subjected to a metal etching liquid (21) in the inside lumen (4) thereby increasing the inside diameter and enhancing the flow properties while maintaining the outside appearance. The inside diameter is only increased over a controlled length (7) of the full length of the needle cannula (1) leaving sufficient length and wall thickness to also taper the outside diameter.

Claims

1. A method of manufacturing needle cannulas comprising: providing a plurality of metallic needle cannulas (1) having a back end (2) and a front end (3) and an oblong inside lumen (4) there between, providing a protection on at least a part of the outside surface (8) of at least one of the plurality of needle cannulas (1), providing a pressurized metal etching liquid (21), the needle cannula comprises a part (7) having a length less than the full axial length of the needle, and a remaining part having a length corresponding to the full axial length minus the length of the part (7), transferring the pressurized metal etching liquid (21) into a part (7) of the oblong inside lumen (4) of the metallic needle cannula (1), wherein the protected part of the outside surface (8) is commensurate with the part (7), thereby the etching increases a diameter of the part (7) of the inside lumen (4) without decreasing the outer diameter of the needle cannulas (1) in the areas where the protection of the outside surface of the at least one of the plurality of needle cannulas is provided, and thereby obtaining at least one needle cannula having a reduced wall thickness at the back end (2) at a length corresponding to the axial part (7), and an unchanged wall thickness at the front end (3) corresponding to the remaining part.

2. A method of manufacturing needle cannulas according to claim 1 further comprising: exposing the metal etching liquid (21) to a centrifugal force, thereby building up pressure in the metal etching liquid (21).

3. A method of manufacturing needle cannulas according to claim 1, where the diameter of the part (7) of the inside lumen (4) is increased by controlling how far the metal etching liquid (21) travels inside the lumen (4) of the needle cannula (1).

4. A method of manufacturing needle cannulas according to claim 1, wherein the protection on at least a part of the outside surface of at least one of the plurality of needle cannulas comprises a coating, or a sacrificial anode placed in contact with the etching liquid.

5. A method of manufacturing needle cannulas according to claim 1 further comprising: pumping the metal etching liquid (21) into the part (7) of the inside lumen (4) of the metallic needle cannulas (1) thereby building up pressure in the metal etching liquid (21).

6. A method of manufacturing needle cannulas according to claim 5 further comprising: cathodic protecting the individual needle cannulas (1) by providing a sacrificial anode (31) in contact with the metal etching liquid (21) and in electrical contact with each individual needle cannula (1).

7. A tool (40) for supporting the plurality of needle cannulas (1) when subjected to the method of claim 2, the tool (40) comprising a plurality of flexible parts (44) which each seals an area of the outside surface of each needle cannula (1) from being in contact with the metal etching liquid (21) during the execution of the method.

8. A method of manufacturing needle cannulas according to claim 7 further comprising: moving the metallic needle cannulas (1) and the metal etching liquid (21) relatively to each other such that the etching liquid flows into a part (7) of the inside lumen (4).

9. A method of manufacturing needle cannulas according to claim 8 wherein the metallic needle cannulas (1) are moved relatively to metal etching liquid (21).

10. A method of manufacturing needle cannulas according to claim 8 wherein the metal etching liquid (21) is moved relatively to the metallic needle cannulas (1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

(2) FIG. 1 show the method according to the invention

(3) FIG. 2 show the needle cannulas resulting from the method

(4) FIG. 3 show an alternative way of performing the method

(5) FIG. 4 show the tool used for the method

(6) FIG. 5 A, B, C show a schematic overview of the process

(7) The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.

DETAILED DESCRIPTION OF EMBODIMENT

(8) When in the following terms as “upper” and “lower”, “right” and “left”, “horizontal” and “vertical”, “clockwise” and “counter clockwise” or similar relative expressions are used, these only refer to the appended figures and not to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as there relative dimensions are intended to serve illustrative purposes only.

(9) In that context it may be convenient to define that the term “distal end” in the appended figures is meant to refer to the end of the needle cannula penetrating the patient whereas the term “proximal end” is meant to refer to the opposite end of the needle cannula.

(10) FIG. 1 discloses the process of manufacturing the needle cannulas 1 depictured in FIG. 2. A number of needle cannulas 1 having a back end 2 and a front end 3 and a lumen 4 there between are located inside a centrifuge 20 preferably in a not shown tool. A liquid 21 that is capable of etching a metallic surface is exposed to a centrifugal force by rotating the centrifuge 20 as indicated by the arrow A. During this rotation the liquid 21 will move towards the periphery of the centrifuge 20 leaving a centre area 23 with no liquid 21. The position of the surface 22 of the liquid will be a result of the rotation of the centrifuge 20. At the same time pressure will build up in the liquid 21. Once the centrifugal force has reached an adequate level the needle cannulas 1 are moved into the liquid 21 whereby the liquid 21 flows into the lumen 4 of the needle cannulas 1. The needle cannulas are preferably moved continuously in and out of the liquid 21 as indicated by the arrow B.

(11) Alternatively, the needle cannulas 1 can stay in the metal etching liquid 21 during the process and the liquid 21 can be moved in and out of the needle cannulas 1 by pressurizing the air contained in the centrifuge 20. If an overpressure is created in the centre area 23, the liquid 21 will be forced out of the lumen 4 of the needle cannulas 1 and when the overpressure is neutralized the liquid 21 will flow into the lumen 4 reaching the liquid surface 22 defined by the rotational force. In FIGS. 1 and 3 the needle cannulas 1 is depictured with an overpressure present in the centre area 23 such that the air contained in the centre area 23 is forced into the lumen 4 of each needle cannula 1 forcing the liquid 21 back towards the back end 2 of each needle cannula 21. The location of the surface 22 of the liquid 21 inside the lumen 4 when the overpressure is removed is illustrated with a dotted line 24 in FIG. 1.

(12) The needle cannulas 1 resulting from the process is depictured in FIG. 2. The wall thickness 6 at the back end 2 has been reduced at a length or axial part 7 equal to the part of the needle cannula 1 that has been exposed to the metal etching liquid 21. The individual needle cannulas 1 are preferably supported dislocated form each other in the axial direction such that the length 7 in which the metallic material is removed is the same for all the needle cannulas 1 in a bundle. The dislocation depends upon the diameter of the surface 22 of the liquid 21. The front end 3 of each needle cannula 1 can further be subjected to electro-chemical etching as described in WO 2002/076540 thereby decreasing the outside diameter of the front end 3 by tapering 9 the outside surface at the distal end. The tapering 9 can be done by moving the front end 3 of the needle cannulas 1 into the metal etching liquid 21 in the centrifuge 20 or it can be done in a separate process. The tip diameter of a standard needle cannula 1 having an initial cylindrical outside can in this way be reduced to an outer diameter which is smaller than the inside diameter of the predominant part of the inside lumen 4.

(13) In order to protect the outside surface 8 of the needle cannula 1 from the metal etching liquid 21, the outside surface 8 can be coated with a material 10 which are resistant to the metal etching liquid 21 used as depictured at C in FIG. 2. If wanted parts of the needle cannula 1 can remain un-coated during the process e.g. if side holes wants to be formed in the needle cannula 1.

(14) As an alternative depictured in FIG. 3, the outside surface of the needle cannulas 1 can be protected by cathodic protection. A sacrificial anode 31 is placed in contact with the liquid 21 and brought into electrical contact with the outside surface of the needle cannulas 1 though a wire 32. The individual needle cannulas are electrical connected by a connector 33 which could form part of the supporting tool holding the needle cannulas 1. The sacrificial anode is made from a metal that is more active than the material forming the needle cannulas such that the anode is corroded first. A control unit 30 can be placed in the wire connection 32 in order to control the electrochemical process.

(15) The control unit 30 can also impress a current on the cathodic protection system in which case the anode 31 can be of a material that are not easily dissolved in the etching liquid. The current impressed is then typically supplied by an external DC power unit.

(16) Each needle cannula 1 is after being subjected to the described method grinded at both ends 2, 3 and mounted in a not shown hub and glued to the hub. The needle cannula 1 is preferably glued to the hub in a position where the wall thickness 6 is greatest thereby maximising the bending resistance. The back end 2 will in use enter into the cartridge of the injection device and the front end 3 enters into the skin of the patient.

(17) An example of a tool 40 usable for the method is disclosed in FIG. 4. The tool 40 preferably has a hollow space 45 with a first side 41 and a second side 42. These two sides 41, 42 are provided with a number of openings 43 which are connected by a flexible tube 44 e.g. made from latex. Needle cannulas 1 are inserted into the openings 41, 42 thereby penetrating through the flexible tubes 44. During the process, the hollow space 45 between the sides 41, 42 are pressurized such that the needle cannulas 1 are secured in their position having the front end 3 located outside the side 41 and the opposite back end 2 located outside the second side 42.

(18) The air or liquid used for pressurising the hollow space is preferably warm such that the individual needle cannulas 1 are heated during the process in order to make the metal etching liquid 21 more aggressive and increase the effectiveness of the process. When moving the needle cannulas 1 in and out of the metal etching liquid 21 the part of the lumen 4 closest to the back end 2 is subjected to the metal etching liquid 21 for a longer time than the opposite end of the length or part 7 thereby given the inside lumen 4 a slightly conical appearance. This however can be compensated by heating the middle part of each needle cannula 1 thereby increasing the etching properties at the part on each needle cannula 1 being inside the hollow space 45 of the tool 40.

(19) FIG. 5 A, b and C discloses various steps of the process seen in a view tangential to the rotational direction of the centrifuge 20. In FIG. 5A the centrifuge has not started to rotate. The tool 40 is located between two semi open containers 25, 26 and placed inside the centrifuge 20. The first container 25 contains the metal etching liquid 21 and the second container 26 contains water 27 (or a similar liquid).

(20) The front end 3 of the needles cannulas 1 are inserted into the second container 26.

(21) In FIG. 5B the centrifuge 20 has started to rotate and the metal etching liquid 21 starts climbing up the wall 28 of the first container 25 and the water 27 starts to climb up the wall 29 of the second container 26.

(22) In FIG. 5C the centrifuge 20 has reached its process speed and the metal etching liquid 21 is pressed towards the wall 28 thereby obtaining a vertical liquid surface 22 inside the first container. In the second container the water 27 is pressed against the wall 29 also reaching a vertical stage.

(23) With the centrifuge 20 is rotating with a suitable angular velocity the tool 40 holding the needle cannulas 1 can be moved in and out (B) of the first container 25 such that the back end 2 penetrates through the liquid surface 22 thereby allowing the metal etching liquid 21 to enter a part 7 of each needle cannula 1. The second container 26 are moved simultaneously with the tool 40 such that the front end 3 of the needle cannulas 1 are constantly submerged into the water 27 inside the second container 26 thereby protecting the frontal part of the inside lumen 4 form splashes of the metal etching liquid 21.

EXAMPLE

(24) Stainless G31 steel tubes having the following characteristic were covered on their outer surfaces with melted wax: Length: 100 mm, Outer diameter: 0.26 mm, Inner diameter: 0.15 mm, Steel type: AISI 304L Wax type: Freeman Flakes, Premium Injection Wax with a melting temperature of 60° C.

(25) A coherent bundle of 100 waxed tubes were then formed by application of heat and force. The bundle was cut into shorter bundles having a length of 18 mm.

(26) A short bundle was placed in a centrifuge and subjected to 600 RPM. This resulted in a centripetal acceleration of approximately 100 times the gravitational acceleration (100G).

(27) The bundle was during centrifugation dipped repeatedly in an etching solution having a composition of: 10 wt % FeCl.sub.3, 10 wt % HCL and 5 wt % HNO.sub.3.

(28) The solution was maintained at 25° C. The bundle was moved into the etching solution such that it travelled 15 mm inside the tubes during a dipping cycle.

(29) A cycle consisted of 1 sec. for moving the bundle into position in the etching solution, followed by 5 sec. resting in the etching solution and finally 1 sec. for bringing the bundle out of the etching solution. The described cycle was repeated 400 times.

(30) The inner diameter was thus increased from 0.15 mm to 0.18 mm on the 15 mm length being subjected to the etching solution resulting in an increase in the flow rate of approximately 100% for a given pressure drop of 1 bar.

(31) Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject matter defined in the following claims.