Method of producing needle cannula with reduced end portion by electrochemical etching

Abstract

A needle cannula 100 and a method for producing a needle cannula comprising providing a needle cannula tube 10 with an end portion 30. The end portion 30 includes an outer surface, and a given type of steel comprising carbon (C) in 0.07 to 0.15% by mass, silicon (Si) in 0.50 to 1.00% by mass, manganese (Mn) in 5.0 to 7.5% by mass, phosphorus (P) in 0 to 0.030 by mass, sulfur (S) in less than or equal to 0.015% by mass, chromium (Cr) in 17.5 to 19.5% by mass, nickel (Ni) in 6.5 to 8.5% by mass, and nitrogen (N) in 0.20 to 0.30% by mass. The method further includes establishing an electrochemical reaction to remove material from the outer surface of the end portion 30, and thereby providing a needle cannula 100 with a tapered end portion.

1 . A needle cannula produced by the process comprising:
 (i.) providing a needle cannula tube, wherein the needle cannula tube comprises an end portion comprising:
 an outer surface, and 
 a steel alloy comprising:
 carbon (C) in 0.07 to 0.15% by mass, 
 silicon (Si) in 0.50 to 1.00% by mass, 
 manganese (Mn) in 5.0 to 7.5% by mass, 
 phosphorus (P) in 0 to 0.030% by mass, 
 sulfur (S) in less than or equal to 0.015% by mass, 
 chromium (Cr) in 17.5 to 19.5% by mass, 
 nickel (Ni) in 6.5 to 8.5% by mass, and 
 nitrogen (N) in 0.20 to 0.30% by mass, 
 
   (ii.) providing an electrolyte, and   (iii.) bringing the end portion into contact with the electrolyte,   (iv.) applying a potential between the needle cannula tube and a cathode, and thereby establishing an electrochemical reaction to remove material from the outer surface of the end portion, thereby providing a needle cannula with a tapered end portion,   
       wherein the end portion comprises a distal end, and wherein the tapered surface defines an angle which is constant along the longitudinal axis towards the distal end, and wherein the angle is defined as the angle between a tangent to the surface and an axis normal to the longitudinal axis (X). 
     
     
         2 . A needle cannula according to  claim 1 , wherein the needle cannula comprises:
 an end position (X 0 ), defined as the longitudinal position of the etched end of the needle cannula,   a first position (XB) with a longitudinal distance to the end position (X 0 ),   an outer surface defining a profile function (F), where the outer surface intersects with a plane containing a central longitudinal axis (x) and a radial axis (r),   wherein the profile function (F) is defined in an interval between the end position (X 0 ) and the first position (XB),   a second derivative of the profile function (F) with respect to the longitudinal coordinate (x), and wherein the second derivative of the profile function (F) is an increasing function (FXX) in the interval between the final end position (X 0 ) and the first position (XB).   
     
     
         3 . A needle cannula according to  claim 1 , wherein the needle cannula is more robust than a reference needle cannula,
 wherein the reference needle cannula is obtainable for comparison by applying steps (ii.) to (iv.) according to  claim 1  to an end portion of a reference needle cannula tube, and thereby providing a reference needle cannula,   wherein the dimensions of the reference needle cannula tube is corresponding to the needle cannula tube ( 10 ), in such a way that the needle cannula tube ( 10 ) and the reference needle cannula tube comprises the same outer diameter, and the same inner diameter within 0.2%, and   wherein the process parameters used in steps (ii.) to (iv.) are the same for the needle cannula tube ( 10 ) and the reference needle cannula tube, in such a way that the length of the end portion in contact with electrolyte, the applied potential, and the process time is the same (XXX within 0.2%),   wherein the reference needle cannula tube comprises a steel alloy comprising:
 carbon (C) in less than or equal to 0.07% by mass, 
 silicon (Si) in less than or equal to 1.00% by mass, 
 manganese (Mn) in less than or equal to 2.00% by mass, 
 phosphorus (P) in less than or equal to 0.045% by mass, 
 sulfur (S) in less than or equal to 0.030% by mass, 
 chromium (Cr) in 17.5 -19.5% by mass, 
 nickel (Ni) in 8.0 -10.5% by mass, 
 nitrogen (N) in less than or equal to 0.10% by mass, 
   wherein the end portion of the needle cannula comprises a distal end, and wherein the end portion of the reference needle cannula comprises a distal end, and   wherein the relative robustness between needle cannula and the reference needle cannula can be determined by a profile of the diameter of the end portion, and wherein the diameter at the tip end of the needle cannula is larger than the diameter at the distal end of the reference needle cannula.   
     
     
         4 . A needle cannula according to  claim 3 , wherein the reference needle cannula comprises:
 a reference end position, defined as the longitudinal position of the etched end of the reference needle cannula,   a first reference position with a longitudinal distance to the reference end position,   an outer surface defining a reference profile function, where the outer surface intersects with a plane containing a central longitudinal axis and a radial axis,   wherein the reference profile function is defined in an interval between the reference end position and the first reference position,   a second derivative of the reference profile function with respect to the longitudinal coordinate, and wherein the second derivative of the reference profile function is an increasing function in the interval between the end position and the first reference position, and   
       wherein the magnitude of the second derivative of the profile function (F) is smaller than the magnitude of the second derivative of the reference profile function. 
     
     
         5 . A needle cannula, wherein the needle cannula comprises:
 a steel alloy comprising carbon (C) in 0.07 to 0.15% by mass,   silicon (Si) in 0.50 to 1.00% by mass,   manganese (Mn) in 5.0 to 7.5% by mass,   phosphorus (P) in 0 to 0.030% by mass,   sulfur (S) in less than or equal to 0.015% by mass,   chromium (Cr) in 17.5 to 19.5% by mass,   nickel (Ni) in 6.5 to 8.5% by mass,   nitrogen (N) in 0.20 to 0.30% by mass, and   a tubular body portion ( 110 ) with a constant outer diameter, and an etched end portion ( 130 ) comprising a tapered outer surface.   
     
     
         6 . A needle cannula according to  claim 5 , wherein the end portion comprises a distal end, and wherein the tapered surface defines an angle which is constant along the longitudinal axis towards the distal end, and wherein the angle is defined as the angle between a tangent to the surface and an axis normal to the longitudinal axis (X).