SURFACE HARDENED INJECTION NEEDLE AND METHOD OF PRODUCING SUCH

Abstract

A medical injection needle (1) having a metallic needle body (2) comprising an axially extending wall (3), a first end portion (4), a second end portion (6), and a flow path (7) providing for fluid communication between the first end portion (4) and the second end portion (6) along the axially extending wall (3), wherein at least a portion of the metallic needle body (2) comprises a hardened surface layer (10, 20) in which carbon atoms and nitrogen atoms are deposited.

Claims

1. A medical injection needle having a metallic needle body comprising: an axially extending wall, a first end portion, a second end portion, and a flow path providing for fluid communication between the first end portion and the second end portion along the axially extending wall, wherein at least a portion of the metallic needle body comprises a hardened surface layer in which carbon atoms and nitrogen atoms are deposited.

2. A medical injection needle according to claim 1, wherein the hardened surface layer has a radial extent (r.sub.o, r.sub.i) which does not exceed 25 m.

3. A medical injection needle according to claim 1, wherein the hardened surface layer has a radial extent (r.sub.o, r.sub.i) which does not exceed 10 m.

4. A medical injection needle according to claim 1, wherein the hardened surface layer comprises an inner layer in which predominantly carbon atoms are deposited and an outer layer in which predominantly nitrogen atoms are deposited.

5. A medical injection needle according to claim 1, wherein the at least a portion of the metallic needle body comprises the first end portion.

6. A medical injection needle according to claim 1, wherein the first end portion comprises a sharpened tip.

7. A medical injection needle according to claim 1, wherein the metallic needle body comprises a radially outwardly oriented surface and a radially inwardly oriented surface, and wherein the hardened surface layer is present along at least a portion of at least one of the radially outwardly oriented surface and the radially inwardly oriented surface.

8. A medical injection needle according to claim 7, wherein the axially extending wall is tubular and has a thickness (t) in the range 25 m to 50 m.

9. A medical injection needle according to claim 7, wherein a first hardened surface layer is present along at least a portion of the radially outwardly oriented surface and a second hardened surface layer is present along at least a portion of the radially inwardly oriented surface, wherein the metallic needle body further comprises a core section between the first hardened surface layer and the second hardened surface layer, and wherein the hardness of the at least a portion of the radially outwardly oriented surface is 3-5 times greater than the hardness of the core section.

10. A medical injection needle according to claim 1, forming part of an injection needle assembly further comprising a needle hub element being adapted for coupling to an injection device, wherein the metallic needle body is fixedly arranged in the needle hub element such that a portion of the axially extending wall extends distally from the needle hub element to define a front needle portion for insertion into human skin, and wherein the hardened surface layer is only present along a surface which is further away from the needle hub element than 1.5 mm.

11. A method of hardening a medical injection needle having a metallic needle body comprising a longitudinal wall extending axially between a first end portion and a second end portion, the method comprising: (i) bringing at least a portion of the medical injection needle having a first temperature, T.sub.1, in the range 200 C. to 500 C. in contact with a gaseous substance derived from a compound containing nitrogen and carbon and having a second temperature, T.sub.2, in the range 200 C. to 500 C., (ii) subsequent to (i) bringing the at least a portion of the medical injection needle in contact with a carbon gas having a third temperature, T.sub.3, in the range T.sub.1 to 500 C., and (iii) subsequent to (ii) bringing the at least a portion of the medical injection needle in contact with a nitrogen gas having a fourth temperature, T.sub.4, in the range T.sub.1 to 500 C.

12. A method according to claim 11, further comprising: (iv) prior to (i) electropolishing and/or grinding the first end portion.

13. A method according to claim 11, further comprising: (v) subsequent to (iii) electropolishing and/or grinding the first end portion.

14. A method according to any of claim 11, further comprising: (vi) prior to (i) covering a portion of the metallic needle body with a shield.

15. A method according to claim 14, wherein the first end portion comprises a sharpened tip, and wherein step (vi) comprises applying the shield at least around the metallic needle body in an area which is between 1.5 mm and 9 mm from the sharpened tip.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the following the invention will be further described with references to the drawings, wherein

[0040] FIG. 1 is a longitudinal section view of an injection needle according to an embodiment of the invention,

[0041] FIG. 2 is a cross-sectional view of the injection needle of FIG. 1,

[0042] FIG. 3 shows an injection needle having a deformed tip,

[0043] FIG. 4 is a sketch of the surface structure of an injection needle having undergone a surface hardening treatment according to an embodiment of the invention,

[0044] FIG. 5 is a cross-sectional micrograph of a wall portion of an injection needle having undergone a surface hardening treatment according to an embodiment of the invention,

[0045] FIG. 6 is a graphical representation of the hardness variation through a wall portion of an injection needle according to an embodiment of the invention,

[0046] FIGS. 7-9 show different processes for obtaining an injection needle according to different embodiments of the invention, and

[0047] FIG. 10 is a longitudinal section view of a pen needle assembly including an injection needle according to an embodiment of the invention.

[0048] In the figures like structures are mainly identified by like reference numerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0049] When in the following relative expressions, such as upper and lower, are used, these refer to the appended figures and not necessarily to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as their relative dimensions are intended to serve illustrative purposes only.

[0050] FIG. 1 is a longitudinal section view of an injection needle 1 having an elongated metallic needle body 2. The needle body 2 comprises a tubular wall 3 extending between a subject end portion 4 and a reservoir end portion 6 and defining a lumen 7 for conveying fluid. The subject end portion 4 is processed to provide a sharpened tip 5 for easy and virtually painless insertion through a human skin.

[0051] FIG. 2 shows the injection needle 1 in cross-section. It is seen that the tubular wall 3 has an external pipe diameter, D, and the lumen 7 has a diameter, d. The needle body 2 is further defined by a radially outwardly oriented exterior surface 8 and a radially inwardly oriented interior surface 9.

[0052] The injection needle 1 may be formed in accordance with any conventional method, e.g. seamless tubing in which a solid steel bar is extruded in a repeated cold drawing process to create a throughgoing bore. Work hardening as a natural consequence of the cold drawing process reduces ductility so the formed tube is normally annealed between drawing operations to increase ductility and prevent the material from becoming brittle. An alternative method, known as welded tubing, forms a flat metal strip into a tubular shape and uses a high energy source to melt the metal locally at the edges of the open seam to create a fusion juncture. The thus produced weld line is typically cold worked locally to exhibit similar properties as the base metal and annealed for stress relief, recrystallization and complete homogenizing.

[0053] A number of such formed tubes may then be assembled in a tube bundle and cut to obtain a final desired length and each tube is ground to provide either one or two sharpened tips.

[0054] Optionally, the tubes are electropolished to provide a conical exterior shape. Regardless of the specific forming method the final needle product must possess specific material and structural properties which allow it to penetrate a skin barrier without deflecting or breaking.

[0055] FIG. 3 shows a picture of an injection needle 1 with a needle body 2 and a needle tip 5. The injection needle 1 has been used multiple times and the picture shows the accumulated deformation of the needle tip 5. The exhibited phenomenon is known as hooking.

[0056] FIG. 4 is a magnified sketch of the atomic structure of a portion of the needle body 2 following a surface hardening treatment according to an embodiment of the invention. The figure shows a segment of the tubular wall 3 in cross-section and the atomic arrangement across the entire wall thickness, t=(Dd), is sketched. The original material structure is still present in a core layer 30, but an outer hardened surface layer 10 has been established at the exterior surface 8, while an inner hardened surface layer 20 has been established at the interior surface 9. Both hardened surface layers 10, 20 are characterised by an expansion of the material structure stemming from deposited nitrogen and carbon atoms.

[0057] The outer hardened surface layer 10 has a radial extent, or thickness, r.sub.o, and the inner hardened surface layer 20 has a radial extent, or thickness, r.sub.i, which are pendent on specific process parameters, including potential shielding times, where parts of the interior surface 9 and/or the exterior surface 8 are covered up by a physical shield. In FIG. 4, r.sub.o and r.sub.i are practically identical. However, it is noted that the thickness of the respective hardened surface layers 10, 20 may be designed by modification of certain process parameters so as to optimise the material and structural properties of a given injection needle type, and this optimisation needs not imply equal thicknesses. For thin-walled injection needles values of r.sub.o and r.sub.i may, for example, lie in the range [10 m; 25 m], while for very-thin-walled injection needles values of r.sub.o and r.sub.i may, for example, lie in the range [5 m; 10 m].

[0058] A surface hardening process according to an embodiment of the invention enables a particular formation of the deposited nitrogen and carbon atoms which comprises an inner layer in which predominantly carbon atoms are present and an outer layer in which predominantly nitrogen atoms are present, as also indicated in FIG. 4. The nitrogen atoms primarily increase the surface hardness while the carbon atoms bridge the gap to the softer core layer 30. Thereby, a smooth hardness profile exhibiting a steep gradient towards the core layer 30 is obtained. The steep gradient enables the realisation of very thin hardened surface layers 10, 20 prerequisite for thin-walled specimens of the order of magnitude of hypodermic injection needles.

[0059] Suitable materials for surface hardening according to the present invention are e.g. stainless steel grades 201, 301 and 304, PH steels, maraging stainless steels, and maraging stainless steels with cobalt. In particular embodiments of the invention the needle body 2 is made of austenitic stainless steel of the type X11CrNiMnN19-8-6 (ISO 15510:2014(E)).

Example

[0060] A plurality of 32G cannulas made of 304 stainless steel is heated to a temperature of 490 C. in a reducing gas, H.sub.2. The supply of H.sub.2 is cut off and the passive ferrous metal surface is activated by heating a urea compound to a temperature of 490 C. and bringing the heated urea compound in contact with the cannulas. The temperature is kept below 500 C. to avoid the formation of nitrides and carbides, which might otherwise affect the corrosion resistance of the metal. Once the surface has been activated the supply of urea is cut off and replaced with a supply of carbon gas for approximately 1 hour. Then the supply of carbon gas is interrupted and nitrogen gas is supplied to the metal surfaces for approximately 4 hours. The thereby established N/C concentrated surface layer comprises an innermost layer in which predominantly carbon atoms are deposited and an outermost layer in which predominantly nitrogen atoms are deposited. The cannulas are finally cooled to room temperature in an atmosphere of argon gas in less than 10 minutes. FIG. 5 is a microscopic scale capture of a segment of a cannula wall, in cross-section, clearly identifying the various treated and nontreated layers. The maximum total thickness of the inner hardened surface layer 20 and the outer hardened surface layer 10, respectively, was 18 m.

[0061] FIG. 6 is a graphical estimation of a hardness profile obtained by another exemplary embodiment of the invention. The graph shows the material hardness of the needle body 2, measured according to the Vickers standard, as a function of the distance from the exterior surface 8. The hardness of the core layer 30 is approximately 4.5 times lower than that of the exterior surface 8, respectively the interior surface 9, and the radial extent of each of the outer hardened surface layer 10 and the inner hardened surface layer 20 is only about 10 m. This provides for a much increased resistance of the treated surfaces to mechanical impact while a certain flexibility of the core of the needle body 2 is maintained. Because the radial extent of the respective hardened surface layers 10, 20 is so small the volume of the core layer 30 is substantial by comparison, reducing any tendency of the injection needle 1 to break.

[0062] In accordance with the present invention, the injection needle 1 may undergo various pre- and/or post-surface hardening process steps to provide desired final properties and configuration. FIG. 7(a)-(d) shows an example of a pre-surface hardening processing of the injection needle 1, according to which the raw tubing is firstly electropolished to obtain a desired conical configuration of the subject end portion 4 and subsequently ground to obtain the sharpened tip 5. The final surface hardening of both the exterior surface 8 and the interior surface 9 yields an outer hardened surface layer 10, respectively an inner hardened surface layer 20, which provides a very hooking resistant injection needle.

[0063] FIG. 8(a)-(d) shows an example of a post-surface hardening processing of the injection needle 1, according to which the raw tubing is firstly electropolished to obtain a desired conical configuration of the subject end portion 4 and subsequently ground to obtain the sharpened tip 5. During the electropolishing and the grinding portions of the hardened surface layer are removed from the subject end portion 4, resulting in a hooking resistant injection needle which is less resistant to material wear than the injection needle of FIG. 7(d), but which is instead more pliable, thus being more capable of bending without breaking.

[0064] FIG. 9(a)-(f) shows an example of a combined pre- and post-surface hardening processing of the injection needle 1. In this example the raw tubing is firstly electropolished and ground. Thereafter, a Cu paste is applied to predefined portions of the exterior surface 8 before the injection needle 1 undergoes the surface hardening process. After the surface hardening the Cu paste is removed from the portions of the exterior surface 8, providing an injection needle 1 where areas of the tubular wall 3 are surface hardened while other areas are not. Thereby, a hooking resistant injection needle 1 is provided which exhibits greater flexibility in selected areas than in other areas. This is particularly usable when the injection needle 1 is intended to form part of an injection needle assembly, such as a pen needle assembly, as described in the below.

[0065] FIG. 10 is a longitudinal section view of the injection needle 1 as part of a pen needle assembly 11. The tubular wall 3 is fixed in a needle hub 12 such that a front needle 14 comprising the sharpened tip 5 extends distally therefrom for penetration of a skin membrane. A distal portion of the front needle 14 is surface hardened according to the present invention. Notably, the portion of the tubular wall 3 in the immediate vicinity of the needle hub 12 was covered by a mask during the surface hardening process to retain flexibility in that particular area. Specifically, the mask was applied around the tubular wall 3 in the area denoted by S in FIG. 10. This area is the most critical portion of the front needle 14 in terms of likelihood of breakage during insertion through skin. The fact that no surface hardening took place there reduces the risk of the tubular wall 3 breaking instead of just bending in response to a significant lateral force being applied to the sharpened tip 5.

[0066] The particular arrangement of the masking depends on the pen needle assembly model and the length of the front needle 14. If, for example, a 4 mm front needle is employed the mask may be arranged to cover an area of the tubular wall 3 which is between 1.5 mm and 5 mm, or between 2 mm and 5 mm, from the sharpened tip 5. If, alternatively, an 8 mm front needle is employed the mask may be arranged to cover an area of the tubular wall 3 which is between 1.5 mm and 9 mm, or between 3 mm and 9 mm, from the sharpened tip 5.