Abstract:
The present invention provides a process for producing a lancing element in which a flat-shaped member is formed from a flat material by applying a mask and allowing an etching agent to act upon it, wherein at least a part of the flat-shaped member is shaped as a tip. The mask is provided with a shaping area for the tip to be formed and with a screening area which extends distally beyond this shaping area to prevent the tip from being etched off at the front. A sharp tip is exposed by laterally undercutting the side flanks of the shaping area and screening area.

Description:
RELATED APPLICATIONS  
       [0001]     This is a continuation application of International Application PCT/EP2005/013266, filed Dec. 10, 2005, which claims priority to EP 04029926.5, filed Dec. 17, 2004, which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND  
       [0002]     The present invention relates to a process for producing a lancing element for withdrawing bodily fluid in which a flat-shaped member is formed from a flat material by applying a mask and allowing an etching agent to act upon it. At least a part of the flat-shaped member is shaped as a tip for piercing into a body part of a test subject.  
         [0003]     Lancing elements of this type are used for the analysis of very small amounts of fluid, especially in bioanalytics, such as those which are withdrawn in situ as capillary blood for blood glucose determinations. Such microfluidic systems, in addition to the microscopic volumes (microliters and less), are also characterized by structural elements of increasingly smaller dimensions which use capillary forces and can be implemented in so-called disposables in a suitable manner for mass production. Although manufacturing processes, especially in the form of mask etching (photochemical etching), are known from the field of semiconductor technology for highly-integrated systems, the materials used cannot generally be used for mechanically stressed structures due to their brittleness. When biocompatible materials such as steel are etched, a problem arises with conventionally shaped-complementary etch masking in which the generated lancing structures are rounded off at the tip and thus do not provide a particularly optimal puncture.  
         [0004]     An etching process for producing surgical needles is known from U.S. Pat. No. 4,777,096, in which the etch mask extends beyond the tip to be formed in a distally blunted shaping area and is constructed to prevent rounding of the tip. However, this mask overhang is shorter than the undercutting width of the etching agent so that the tip is shaped by a combined lateral and frontal etching action which only slightly reduces the problem of blunting.  
       SUMMARY OF THE INVENTION  
       [0005]     Embodiments incorporating the present invention address the disadvantages of the prior art and improve upon a production process of the type described above such that sharp lancing structures for optimal lancing into a body part are created in a process suitable for mass production without requiring complicated post-processing steps.  
         [0006]     An exemplary embodiment produces a sharp tip solely by lateral and mutually converging etching agent fronts. In this embodiment, a mask is provided with a shaping area for the tip to be formed and a screening area which extends beyond this shaping area to prevent the tip from being etched off at the front. A sharp tip is exposed by laterally undercutting the side flanks or edges of the shaping and screening area. This can prevent the contour near the tip from being rounded off, whereby the etching process is terminated as soon as the bridge of material located between the side flanks of the etching mask is broken through. This allows optimized tips to be created in order to reduce the lancing pain and enable bodily fluid to be extracted with the smallest possible volume. Moreover, the required propulsion forces for lancing can be minimized and traumatization of the body tissue can be substantially reduced.  
         [0007]     The shaping area advantageously narrows toward the screening area to produce a lancing shaft that tapers toward the tip. It is additionally advantageous when the shaping area is linearly chamfered at least on one side.  
         [0008]     Another exemplary embodiment provides that at least one side flank is bent or concavely curved in the junction between the shaping area and screening area so that the substrate material in the area around the tip only has to be removed from the side.  
         [0009]     In an embodiment, the mask is constructed such that the screening area has a constant or increasing width over a given screening length where it connects with the shaping area. The screening length should be larger than the proximal undercutting width due to the action of the etching agent. This prevents the tip from being centrally etched off.  
         [0010]     The tip is formed as a result of a constriction in the mask where the width of the constriction is less than twice the lateral undercutting width so that the substrate material under the constriction is completely etched away.  
         [0011]     The screening area is advantageously widened again after the constriction. To improve the stability of the etching mask, it is advantageous when the screening area has a widening bridge section distal to the tip.  
         [0012]     While etching processes in steel mainly proceed isotropically, it is also conceivable that the lateral undercutting width is larger or smaller than the etching depth. Anisotropy, for example, occurs when the etching agent is applied at an overpressure relative to the surroundings in order to ensure a particularly effective etching action. The etching agent can be applied in a dipping bath or by being sprayed onto the flat material.  
         [0013]     For high throughput, it is advantageous when the flat material that is formed from stainless steel sheet metal is processed from roll to roll by photo-chemical mask etching. However, it is also possible to use a semiconductor wafer as a flat material.  
         [0014]     The thickness of the flat material is generally between 0.01 mm and 1 mm.  
         [0015]     According to one exemplary embodiment, the lancing element is provided with a semi-open capillary channel to transport the bodily fluid, whereby the capillary channel is formed by a channel slot in the mask where the distal ends of the channel walls form a sharp tip. In this embodiment, the screening areas for the tips of the channel walls are delimited on one side by the channel slot.  
         [0016]     In an embodiment of the shaped member, the flat material is covered on both sides with a mask, wherein a pointed lancing shaft is etched free on one side and a semi-open capillary channel with pointed channel walls that extend towards the lancing shaft is etched free on the other side.  
         [0017]     According to another embodiment, the etching mask is provided with a compensation opening at a lateral distance from an undercut edge section and an edge contour of the flat-shaped member is etched away from the edge through a compensation opening under the action of the etching agent. Therefore, undesired undercuts on the shaped member are chemically milled off without additional manufacturing effort.  
         [0018]     In order to remove the edges, it is advantageous when the compensation opening is a slot or chain of holes in the mask along the edge section. The compensation opening should have a smaller inner width than a cut-away or opening in the mask bordering the edge section.  
         [0019]     In order to achieve a combined undercutting effect on a bridge of material extending between the edge of the mask and the compensation cut-out, the width of the overlying mask bridge should be less than the undercutting width of the etching agent measured from the edge of the mask.  
         [0020]     Depending on the desired shape of the contour, an exemplary embodiment provides that the compensation opening is arranged in a shaping area and optionally in a screening area of the mask for the tip to be formed. In particular, it is advantageous when the compensation opening is laterally spaced apart from a bent or concavely curved side flank of the mask. The side flank is configured to be bent or concavely curved in a distal direction relative to the tip to be formed. The distal direction, or lancing direction, is the direction in which the lancing element moves to create a puncture.  
         [0021]     In order to protect the tip from being etched away at the front, it is advantageous when the compensation opening is introduced at the side of a central axis running towards the tip that is to be formed so that a strip of the mask is retained in front of the tip along the central axis and at least beyond the undercutting width. In principle, the same considerations apply here with regard to avoiding a frontal action of the etching agent as already set forth with regard to the edge of the mask. In any case, a V-shaped contour of the compensation opening should be avoided. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The above-mentioned embodiments of the present invention and the manner of obtaining them will become more apparent and the invention itself will be better understood by reference to the following description of the embodiments of the invention, taken in conjunction with the accompanying drawings, wherein:  
         [0023]      FIG. 1  is a top view of a lancing element with a tip and capillary channel for withdrawing blood;  
         [0024]      FIG. 2  is a top view of an etching mask for producing the tip of a lancing element;  
         [0025]      FIG. 3  is a top view of an etching mask for producing a capillary channel in the area of the tip of a lancing element;  
         [0026]      FIG. 4  is a fragmentary top view of an enlarged section of a first exemplary embodiment having an etching mask near the tip of a channel wall of a capillary channel;  
         [0027]      FIG. 5  is a cross-section taken along line  5 - 5  of  FIG. 4  illustrating the lateral etching contour of a capillary channel;  
         [0028]      FIG. 6  is a cross-section taken along line  6 - 6  of  FIG. 4  illustrating the lateral etching contour at the tip of a channel wall;  
         [0029]      FIG. 7  is a fragmentary top view of an enlarged section of a second exemplary embodiment having an etching mask near the tip of a channel wall of a capillary channel and a compensation slot;  
         [0030]      FIG. 8  is a cross-section taken along line  8 - 8  of  FIG. 7  illustrating the lateral etching contours of a capillary channel including a compensation slot;  
         [0031]      FIG. 9  is a cross-section taken along line  9 - 9  of  FIG. 7  illustrating the lateral etching contour at the tip of a channel wall; and  
         [0032]      FIG. 10  shows a top view of an etching mask for producing a tip according to the prior art. 
     
    
     DETAILED DESCRIPTION  
       [0033]     The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.  
         [0034]     The lancing and sampling element  10  shown in  FIG. 1  is used as a disposable article to withdraw and transport a small amount of blood through capillary action from a body part of a test subject to an analytical site  20 , for example, to carry out blood glucose measurements. In this exemplary embodiment, the lancing element  10  comprises a flat-shaped member  12 , a lancing member  14  extending therefrom and having a tip  16 , and a semi-open capillary channel  18  for blood transport through capillary action from the tip  16  to the analytical site  20 .  
         [0035]     The flat-shaped member  12  is made of a stainless steel metal sheet  22  having a thickness of about 100 to 300 μm. The member  12  has a proximal end section that forms a holding area for handling the lancing element  10  during the lancing process, whereas the lancing member  14 , which is shaped as one piece at the distal end of the lancet element  10 , generates a small cut in the skin of the user in order to remove microscopic volumes of blood. In this embodiment, the capillary channel  18  has a groove or is semi-open over its length so that it can be produced by photolithography. The withdrawn blood sample can be analyzed by reflection spectroscopic or electrochemical detection methods known in the art.  
         [0036]     The sheet metal or substrate material  32  is constructed by a photo-chemical machining or milling method. In this exemplary process, an etching mask  24  is applied to both sides of the substrate  22  and covers the structure of the flat-shaped member  12 , which is to be uncovered in a subsequent etching step. The mask  24  is formed by coating the substrate  22  with a photoresist and is exposed through a photomask having the desired pattern that is arranged in front of the mask, whereby the photoresist is polymerized or hardened in the covered areas while the other areas are rinsed away after development.  
         [0037]     An etching agent is subsequently applied to the substrate  22  over the (double-sided) etching mask  24  so that the masked areas are etched away according to the basic shape of the mask  24 . In an embodiment incorporating isotropic etching action, the depth of the removed material corresponds to the lateral etching rate for the undercutting of edge contours of the mask  24 . The etching process can also take place anisotropically due to external influencing parameters or material properties of the substrate  22  where, for example, the lateral undercutting rate is larger or smaller than the depth etching rate.  
         [0038]     Manufacturing the tip  16  is particularly critical for the function of the lancing element  10 . According to  FIG. 10 , an obvious approach according to the prior art would be to provide an etching mask with a pointed or triangular shaping area  26  corresponding to the desired contour of the finished part. However, the tip  28  formed in this manner is not sharp, but rather is rounded off due to the etching agent that flows in from all sides during undercutting of the triangular mask  26 .  
         [0039]     In order to address the disadvantages of the prior art, an exemplary embodiment shown in  FIG. 2  includes an etching mask  24  having a shaping area  30  for the tip  16  to be formed and an adjoining screening area  32  for preventing the front of the tip  16  from being etched off. The screening area  32  is distal with regard to the lancing direction, i.e., is positioned at or beyond tip  16  in the lancing direction. Similarly, the lancing direction of the mask  24  is the same direction in which the tip  16  to be formed points. The shaping area  30  narrows towards the screening area  32  and the side flanks or edges  34 ,  36  of the mask  24  are bevelled with a linear slope. Starting from the constriction  38 , the screening area  32  widens while forming a bridge section  40  towards the other areas of the mask so that the etching mask  24  remains more stable.  
         [0040]     Thus, a sharp tip  16  is etched free by lateral undercutting of the side flanks  34 ,  36  of the shaping area and screening area  30 ,  32 , the contour of which is shown by the dashed line in  FIG. 2 . In this embodiment, the screening area  32  has a larger screening length than the undercutting width viewed in the proximal direction, whereas the width of the constriction  38  is less than twice the lateral undercutting width. Additionally, the etched away material fronts converge at the constriction  38  until the tip  16  is finally uncovered at the completion of the etching process.  
         [0041]     The front face of the mask  24  shown in  FIG. 3  is designed to provide the desired capillary channel  18  in the area of the lancing member  14 . Accordingly, the mask  24  has a capillary slot  42  through which the channel  18  is etched to form the channel walls  44 . In order to also facilitate lancing in this case, the distal ends of the channel walls  44  are chamfered as sharp tips  16 ′. This is achieved similar to the embodiments described above by providing screening areas  32  positioned at the distal end. In contrast to  FIG. 2 , the side flanks  34 ,  36  in the area of the constriction  38  are not concavely curved on both sides, but rather are bluntly angled on one side and linearly delimited on the opposite side by the capillary slot  42  to form a wedge-shaped tip  16 ′ as shown by the dashed line.  
         [0042]     The basic geometric effects of the etching process in the area of the channel tips  16 ′ are illustrated in  FIGS. 4-6 .  FIGS. 5 and 6  only show the upper substrate area after a certain etching time where the lateral etching contours  46  only describe a circular line in the case of an isotropic etching action. Thus, lateral undercutting of the mask edges and side flanks  34 ,  36  result in undercut edges of the shaped member  48 ,  50  as shown in  FIG. 5 . Such undercuts are desirable in the area of the capillary channel  18  because they further improve the capillarity. However, as shown in  FIG. 6 , the undercut  52  results in a barb at both tips  16 ,  16 ′ which can impair lancing the skin.  
         [0043]     In order to address this impairment, a compensation slot  54  is designed in the mask  24  as shown in  FIGS. 7 and 8 . This slot extends at a lateral distance to an undercut edge  56  in the shaping area  30  of the mask  24  and ensures that the edges of the undercut  48  that would otherwise be formed are etched away. Hence, the etching agent which penetrates near the edge  48  of the compensation slot  54  results in a rounding of the edge  58  while not producing a barb. The width of the mask strip  60  between the undercut edge  56  and the compensation slot  54  is advantageously less than the lateral undercut width. This should ensure that the compensation slot  54  has a substantially smaller inner width compared to the adjacent mask cut-out  62  so that the rounded edges  58  have a correspondingly smaller etching radius.  
         [0044]     While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.