Abstract:
A diagnostic test tape for liquid samples is provided comprising a flexible transport tape and a plurality of test fields applied to the transport tape that are distributed in the longitudinal direction of the tape, where said test fields comprise a detection layer and a spreading net spanning the detection layer for a planar uptake of liquid sample, wherein the spreading net is formed from a lattice-like fabric comprising fabric threads that cross at right angles. In order to prevent the fabric from arching up under tape tension it is proposed that the fabric is oriented obliquely to the transport tape such that all fabric threads run obliquely to the longitudinal direction of the tape.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/EP2010/051811 filed Feb. 12, 2010, which claims priority to EP Application No. 09152837.2 filed Feb. 13, 2009. Each of the referenced applications is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns a diagnostic test tape for liquid samples, in particular for body fluids, comprising a flexible transport tape that is wound onto or can be wound onto a spool and a plurality of test fields applied to the transport tape that are distributed in the longitudinal direction of the tape, said test fields comprising a detection layer and a spreading net spanning the detection layer for a planar uptake of liquid sample. 
       BACKGROUND 
       [0003]    Diagnostic test tape systems are designed especially for blood sugar tests in order to further improve the user friendliness compared to the test strip systems that are on the market. Thus, in order to simplify the handling, a large number of test units or test fields can be stored on a rollable transport tape in a compact manner and they can also be disposed of again after use by the tape transport. A simple assembly procedure for a test tape of this type is disclosed in EP 1 593 434. Thus, roll-to-roll processing with a high manufacturing speed is possible. In this connection the fabric used as a spreading aid to improve the distribution of the liquid sample is only held by an adhesive layer in the area of its protruding longitudinal edges for process-related reasons. However, if the fabric becomes detached from the detection layer, this can result in a non-uniform wetting with the blood sample which hinders a correct analysis. Furthermore, the spreading fabric may also not become detached from the test field until after the test field has been wetted with blood. The blood then flows into the area of fabric that is still resting on it and forms air bubbles in the separated area of fabric which have a negative effect on the measurement analysis. 
       SUMMARY 
       [0004]    On this basis the invention further improves the known products in the prior art and provides a robust tape assembly which is also optimized with regard to mass production for a reliable sample processing. 
         [0005]    A first aspect of the invention is based on the idea of harmonizing the stretching properties of the carrier tape and of the spreading fabric. Accordingly it is proposed according to the invention that the fabric is oriented obliquely to the transport tape such that all fabric threads run obliquely to the longitudinal direction of the tape. This arrangement prevents only one thread system from being subjected to a tensile load. Rather a load is placed on all fabric threads depending on their inclination when a tensile force acts on the carrier tape thus resulting in a certain ratio of transverse contraction and linear expansion also for the fabric. This can substantially reduce differences in the transverse shrinkage of the fabric and of the remaining test tape assembly so that an unwanted lifting or bulging of the spreading aid is prevented. Existing mesh materials can be adapted with little effort to the properties of the carrier tape and of the test field in order to substantially exclude the risk of an uneven wetting of the test field with test liquid and subsequent falsification of the analytical result. 
         [0006]    The orientation of the fabric is advantageously defined such that under a given tensile load the difference in the transverse contraction of the transport tape and of the fabric is minimized. 
         [0007]    Depending on the material properties it is advantageous when the fabric has an oblique orientation at a compensation angle in a range between 5° and 40°, preferably 20° to 25° where the compensation angle is defined by the smallest angle between the longitudinal direction of the tape and the fabric threads. 
         [0008]    Taking into consideration the conditions for use it is advantageous when the transport tape consists of a foil material having a Poisson number of 0.3 to 0.5, preferably of about 0.4. 
         [0009]    Also with regard to a simplified manufacture it is advantageous when the fabric in plain weave is formed from warp yarns and weft yarns and when the warp yarns run nearer to the longitudinal direction of the tape than the weft yarns. 
         [0010]    Another improvement provides that the optionally hydrophilically coated fabric threads consist of a monofilament thread material in particular of a polyester such as PET. 
         [0011]    The inclination allows a simple test field assembly to be achieved without problems where the spreading net is broader than the detection layer and is glued in the area of its protruding side edges to a carrier strip carrying the detection layer which is applied to the transport tape. 
         [0012]    Another aspect of the invention is that the spreading net is additionally secured against lifting from the detection layer by a protection against lifting in addition to or alternatively to a lateral glueing. In this connection it can also be ensured that the distance between the spreading net and detection layer under the conditions of use is no more than 40 micrometers, preferably less than 20 micrometers to substantially exclude the risk of an uneven wetting even if caused by capillary forces. 
         [0013]    An advantageous variant provides that the front ends of the rectangular spreading net each have a material bond running at right angles to the longitudinal direction of the tape and preferably a laser-welded seam as a protection against lifting. The laser-welded seam can in this case be formed in an advantageous manner for manufacturing by a laser cut while cutting the test field to length from rolls. 
         [0014]    According to a further advantageous embodiment the spreading net is wider than the detection layer and is supported in the area of its protruding side edges by strips of adhesive tape as a protection against lifting on the carrier strip. In this connection the strips of adhesive tape as spacers and the detection layer can have essentially the same thickness so that the spreading net rests flat thereon. 
         [0015]    In another advantageous embodiment the spreading net is attached circumferentially to the carrier strip by an adhesive frame as a protection against lifting which runs all around the detection layer. For this purpose the adhesive frame can advantageously be formed by laser welding and/or by spots of hot glue. 
         [0016]    Another advantageous embodiment can be that the width of the spreading net at right angles to the longitudinal direction of the tape is identical to or less than that of the detection layer and that the longitudinal edges of the said spreading net are attached by an overlapping adhesive tape as a protection against lifting while a central application window is kept free. In this case it is also advantageous when the area forming the application window is punched out of the adhesive tape. 
         [0017]    Another advantageous embodiment of the protection against ifting provides that the spreading net consists of a lattice-like fabric having a bend-resistant thread system that can be deformed in a stepped manner in the direction transverse to the tape. For this purpose it is advantageous when the fabric is provided with weft yarns made of metal. 
         [0018]    A protection against lifting can also be realized in that the carrier strip consists of a robust foil material the shear strength of which is more than 0.05 N/mm 2  and which has a peel strength of more than 1N/mm. 
         [0019]    The invention also concerns a tape cassette comprising a diagnostic test ape according to the invention, which test tape is guided over a deflection point preferably with a tape tensile force of more than 1N for sample application. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The invention is further elucidated in the following on the basis of the embodiment examples shown schematically in the drawings. 
           [0021]      FIG. 1  shows a test tape with an analytical test field in a cut-off perspective diagram. 
           [0022]      FIG. 2  shows a cross-section through the test tape according to  FIG. 1  in the area of the test field. 
           [0023]      FIG. 3  shows a top-view of the test tape according to  FIG. 1  in the area of an obliquely oriented spreading fabric covering the test field. 
           [0024]      FIG. 4  shows a diagram of the Poisson number as a function of the orientation angle of the spreading fabric according to  FIG. 3 . 
           [0025]      FIGS. 5 to 9  each shows a section of test tape with various embodiments of a protection against lifting for the spreading fabric. 
           [0026]      FIG. 10  shows a schematic of the test field manufacture using roll material; and 
           [0027]      FIG. 11  shows a diagnostic tape cassette with a test tape stored therein in a broken perspective diagram. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The diagnostic test tape  10  shown in the drawing for carrying out blood sugar tests comprises a windable flexible transport tape  12  and a plurality of test elements or test fields  14  that are stored thereon for successive single use and are spaced apart from one another in the longitudinal direction of the tape, the test fields as label-like flat structures having a rectangular contour and comprising a carrier strip  16  glued onto the transport, tape  12 , a detection layer  18  applied thereon and a spreading net  20  spanning the detection layer  18  on the upper side facing away from the carrier strip for a planar distribution of a sample liquid (blood sample) applied from above to the spreading net. The detection layer  18  reacts as a dry chemistry film, in particular on an enzyme basis, to an analyte (glucose) by a colour change so that a photometric detection can take place through the transparent foil composite  12 ,  16 . 
         [0029]    As shown in  FIGS. 1 and 2  the strip-shaped spreading net in the form of a fabric  20  is wider than the detection layer  18 . The protruding side edges  22  of the fabric  20  are glued to the upper side of the carrier strip  16  which in turn is glued onto the transport tape  12  as a double-sided piece of adhesive tape. The free outer side of the side edges  22  of the fabric  20  are provided with a hydrophobic coating  24  so that the liquid distribution or spreading can occur specifically in the non-glued central area  26  of the fabric  20  over the detection layer  18 . 
         [0030]    The test fields  14  can be successively brought into use by advancing the transport tape  12  to an application site. The flexible tape structure is subjected to a longitudinal stretching and transverse contraction due to the tensile force that is exerted in this process which could lead to a lifting or arching upwards of the central area  26  of the fabric over the detection layer  18 . This effect is due to the fact that the length but not the width of a fabric oriented in the tape longitudinal direction is changed by tape tensile forces whereas the width of the carrier ape  12  is reduced by transverse contraction. 
         [0031]    In order to avoid this lifting effect which is disadvantageous for a uniform blood distribution, the fabric  20  is oriented obliquely to the transport tape  12  as shown in  FIG. 3 . The fabric  20  has fabric threads  28 ,  30  which cross at right angles and which all run obliquely to the longitudinal tape direction or to the tape edges  32 . 
         [0032]    The fabric  20  in plain-weave is advantageously formed from warp yarns  28  and weft yarns  30  which consist of PET in the form of monofilaments. For processing rolls of material it is advantageous when the long warp yarns  28  run nearer to the longitudinal tape direction than the short weft yarns  30 . 
         [0033]    The orientation of the fabric  20  can be specified by a compensation angle α which is defined by the smallest angle between a tape edge  30  and the fabric threads (i.e. in  FIG. 3  by the warp yarns  28 ). 
         [0034]      FIG. 4  shows the dependency of the Poisson number μ on the compensation angle α of the fabric  20 . In general the Poisson number gives the change in the transverse dimension d as a ratio to the longitudinal stretching ΔL of a body of length L according to the following relationship: 
         [0000]    
       
         
           
             μ 
             = 
             
               
                 Δ 
                  
                 
                     
                 
                  
                 
                   d 
                   / 
                   d 
                 
               
               
                 Δ 
                  
                 
                     
                 
                  
                 
                   L 
                   / 
                   L 
                 
               
             
           
         
       
     
         [0000]    The oblique alignment of the fabric  20  is determined such that under a predetermined tensile load the difference in the transverse contraction of the transport tape  12  and of the fabric  20  is minimized. At a given Poisson number of the carrier tape  12  of about 0.4, the compensation angle should thus be in a range between 20° and 25°. 
         [0035]    In the embodiment examples shown in  FIGS. 5 to 9  the same or similar parts have the same reference numerals as in the above description. Here the spreading net  20  is secured against bulging or lifting from the detection layer  18  by a protection against lifting  32  instead of by an inclined orientation. In the various embodiment examples this protection against lifting  32  is provided in addition to or complementary to the lateral glueing of the side edges  22  of the spreading net  20  to the carrier strips  16 . The embodiment of the spreading net  20  in this case is not only limited to fabric but can also encompass other flat structures as liquid distributors such as a porous membrane. In any case the protection against lifting  32  is designed such that the distance between the central area  26  of the spreading net  20  and the detection layer  18  is no more than 40 μm and preferably less than 20 μm under the operating conditions of the test tape. 
         [0036]    In the embodiment shown in  FIG. 5  the rectangular spreading net  20  is secured on its front ends pointing in the longitudinal tape direction by a transverse continuous laser-welded seam  34 . This attachment can occur by melting the net material when the test fields  14  are cut by a laser as described in more detail in the following. 
         [0037]    A further improvement in the robustness of the test tape  10  is due to the fact that the bevel  36  that can be seen in  FIG. 2  is avoided in the cross-sectional profile of the spreading net  20 . This can be achieved according to  FIG. 6  in that the spreading net  20  is wider than the detection layer  18  and is laterally supported on the carrier strip  16  in the area of its protruding side edges  22  by strips of adhesive tape  36  acting as a protection against lifting  32 . In this case the strips of adhesive tape  36  should have essentially the same thickness as the detection layer  18  so that the spreading net  20  lies flat. 
         [0038]      FIG. 7  shows an embodiment example in which the front ends of the spreading net  20  also protrude beyond the detection layer  18  and the underside of the spreading net is attached all around to the carrier strip  16  by a circumferential adhesive frame  38  as a protection against lifting  32 . This can take place by laser welding or a combination of adhesive foils and laser welding. One manufacturing method is also to use an adhesive foil with spots of hot adhesive as an intermediate carrier in the tape manufacturing process in order to transfer adhesive spots to the short and long sides of the adhesive frame  38  in a precise manner. 
         [0039]    In the embodiment example shown in  FIG. 8  the spreading net  20  has at most the same width as the detection layer  18  so that the net cannot bulge in the relaxed state. All components are then attached by means of lateral adhesive tapes  40  as a protection against lifting  32 . Thus, the adhesive tape  40  overlaps the longitudinal edges of the layered structure  16 ,  18 ,  20  while keeping a central application window  42  free for the application of the liquid sample. It is also possible that the area forming the application window  42  is punched out of a transverse continuous piece of adhesive tape  40 . 
         [0040]      FIG. 9  illustrates an embodiment example in which the spreading net  20  is provided with a bend-resistant thread system  44  running at right angles to the tape direction as a protection against lifting  32 . The transverse threads are in this case designed such that they can be pressed against the edge of the detection layer  18  substantially without an air gap. This can advantageously be achieved by using a fabric  20  with weft yarns made of metal. 
         [0041]    Another possibility of improving the robustness is to select a suitable foil material for the carrier strip  16 . Such a material should have a shear strength in the range of 40N/625 mm 2  (according to DIN EN 1943) whereas the peel strength should be about 25N/25 mm 2  (according to DIN EN 1939). Such a foil material can for example be obtained under the trade name Duplocoll VP20242. 
         [0042]    In order to enable a high manufacturing rate and flexibility in the production of the test tape  10 , a roll-pull-roll process is provided.  FIG. 10  shows a preliminary stage for the multi-lane manufacture of the test fields  14 . In this process a double-sided adhesive tape is transported by a production line between two rolls  46 ,  48 . Several parallel detection films  18 ′ are applied thereto from the spools  50 . The arrangement is overlaid with spreading fabric  20 ′ which is pulled from further spools  52 . The layer assembly is subsequently fastened by means of a thermotransfer foil  54 . Then laser cuts running at right angles which separate the parallel test fields  14  from one another at their ends are introduced with a laser  56 . If the parameters are suitably selected, the laser  56  can not only cut the test fields  14  to length but also glue the edge areas to one another to form the welded seam  34  ( FIG. 5 ). The entire process is monitored by a camera system  58  so that waste is substantially avoided. Test fields  14  pre-fabricated in this manner can be transferred and glued onto a transport tape  12  in a label-like manner over a dispensing edge in the process of which the test tapes  10  manufactured in a multi-lane process are then cut lengthways. 
         [0043]    The test tape  10  is inserted as a consumable into a hand-held device in the form of a tape cassette  60  shown in  FIG. 11  in order to enable a patient to himself carry out a plurality of on-the-spot glucose tests (for example 50 tests). For this purpose the tape cassette  60  has an unwinding spool  62  to unwind unused test tape and a take-up spool  64  to wind on used test tape in the process of which the test tape  10  is pulled over an application tip  66  in order to successively provide the test fields  14  there for sample application. Further details of the measurement acquisition can be derived for example from EP-A 1 878 379 to which reference is explicitly made in this connection. 
         [0044]    During tape transport the test tape is guided over the application tip  66  under a tape tension of about 4N. In order to further reduce unwanted lifting effects of the spreading net  20  in this process, the radiuses of the deflection edges  68  must be suitably adjusted. The stress on the multi-component structure  12 ,  14  and thus the upward arching is greatly reduced by increasing the radiuses. However, radiuses which are too large increase the width of the tip  66  and thus result in a disadvantageous enlargement of the sample application area and of the required sample volume. In any case it should be ensured that it is tensioned in a planar manner between two deflection edges  68 . 
         [0045]    Although embodiments of the invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations obvious to the skilled artisan are to be considered within the scope of the claims that follow and their equivalents.