Abstract:
The invention relates to a tube ( 2 ) and a steerable introduction element like a catheter, an endoscope or a sheath comprising the tube. The tube comprises a composite material including a shape memory alloy material ( 12 ) and a non-shape-memory polymer material ( 22 ). The tube is used for making the introduction element steerable in a relatively easy way by modifying the temperature of the tube as required for achieving a preferred bending of the introduction element. By using this steering mechanism the introduction element can be positioned relatively accurately, because the composite material includes a non-shape-memory polymer material, which is more stable than, for instance, a shape-memory polymer material and which may be optimized for other properties like hardness, stiffness, et cetera. Furthermore, using the tube for steering an introduction element can lead to cost reductions and can enable miniaturization.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a tube and a steerable introduction element like a catheter, an endoscope or a sheath comprising the tube. The invention relates further to a production method and a production apparatus for producing the tube. 
       BACKGROUND OF THE INVENTION 
       [0002]    U.S. Pat. No. 6,872,433 B2 discloses an apparatus for minimally invasive applications. The apparatus has a longitudinal axis with the apparatus extending in a radial direction from the longitudinal axis and wherein the apparatus is activated by a change in temperature. The apparatus comprises a first unit with a first structure for at least positioning the apparatus, wherein the first structure includes a quantity of shape memory alloy. The apparatus further comprises a second unit with a second structure for at least positioning the apparatus, wherein the second structure includes a quantity of shape memory polymer. The first unit has a longitudinally extending coiled configuration with more than one wrap and the second unit comprises a cylinder, wherein the first unit is positioned in the second unit such that changes in temperature of the shape memory alloy cause the first unit to change position by a radial contraction and a longitudinal extension and to stretch the second unit comprising the second structure including the shape memory polymer along the longitudinal axis. 
       SUMMARY OF THE INVENTION 
       [0003]    The combination of a shape memory alloy and a shape memory polymer is not very stable. Moreover, the shape memory polymer changes its properties, when being heated. This leads to a reduced accuracy of positioning the apparatus. 
         [0004]    It is an object of the present invention to provide a tube and a steerable introduction element comprising the tube, which allow for an increased accuracy of positioning the steerable introduction element. It is a further object of the present invention to provide a production apparatus and a production method for producing the tube. 
         [0005]    In a first aspect of the present invention a tube comprising a composite material including a shape memory alloy material and a non-shape-memory polymer material is presented. 
         [0006]    The tube material can be used to make an introduction element like a catheter, endoscope or sheath, which comprises the tube, steerable in a relatively easy way by modifying the temperature of the tube as required for achieving a preferred bending of the introduction element. Moreover, by using this steering mechanism the introduction element can be positioned relatively accurately, because the composite material includes a non-shape-memory polymer material, which is more stable than a shape-memory polymer material and which may be optimized for other properties like hardness, stiffness, et cetera. Furthermore, since the composite material includes the non-shape-memory polymer material a wide range of potential materials, which have been proven for a wide range of applications and characteristics, is available, which can be used, for instance, for adapting the tube to requirements of a desired application. Moreover, using the tube for steering an introduction element can lead to cost reductions and can enable miniaturization. 
         [0007]    The shape memory alloy material comprises preferentially elongated shape memory alloy elements like shape memory alloy fibers which may be shape memory alloy wire pieces. The elongated shape memory alloy elements can increase the stiffness of the tube. 
         [0008]    The shape memory alloy material comprises preferentially nitinol. For instance, nitinol fibers may be used as the shape memory alloy material. Nitinol is biocompatible such that it allows using the tube in medical applications. 
         [0009]    The adhesion between the elongated shape memory alloy elements and the non-shape-memory polymer is preferentially good enough for allowing the non-shape-memory polymer to follow a change in length of the elongated shape memory alloy elements. For instance, if the elongated shape memory alloy elements shrink or become longer again, the good adhesion ensures that the non-shape-memory polymer material can follow these length changes. Moreover, the good adhesion can ensure that stress applied by the non-shape-memory polymer on the elongated shape memory alloy elements will reset them to the original size after stopping a thermal activation. For providing this good adhesion the surface of the elongated shape memory alloy elements can be surface treated. For instance, the elongated shape memory alloy elements can have a roughened surface. The surface of the shape memory alloy elements can be roughened by, for instance, grinding, rolling, forging, in particular, making indents, etching, blasting or any other roughening technique. Also other surface treatments can be used for improving the adhesion between the elongated shape memory alloy elements and the non-shape-memory polymer material like surface coatings. 
         [0010]    The non-shape-memory polymer material is preferentially a conventional polymer like thermoplastic, silicone or thermoset. It may also comprise a combination of two or all of these exemplarily mentioned conventional polymers. The non-shape-memory polymer material is not a shape memory polymer material like the shape memory polymer material disclosed in, for instance, the article “Shape-memory polymers and their composites: Stimulus methods and applications” by J. Leng et al., Progress in Materials Science 56, pages 1077 to 1135 (2011). 
         [0011]    The tube is preferentially producible by using a polymer shaping technique. The polymer shaping technique is preferentially a conventional one like extrusion or injection molding, i.e. the tube may be producible by extrusion and/or injection molding. In the extrusion process the shape memory alloy material, in particular, the elongated shape memory alloy elements, which may be chopped fibers or wire pieces, will align in the length direction of the tube automatically. If the shape memory alloy elements, especially the shape memory alloy fibers, align in the length direction of the tube, they are more effective in creating a bending response. For instance, less shape memory alloy material may be required for the same bending response. 
         [0012]    It is preferred that the composite material comprises a further material for modifying at least one of the thermal conductivity, the electrical resistance and the stiffness of the tube. For instance, the further material may include conductive particles, in particular, thermally and/or electrically conductive particles. It may comprise a metal material and/or a carbon material like carbon nanotubes and/or a ceramic material. By mixing a further material into the composite material it is possible, for example, to make the composite material itself a heating element, wherein in this case the tube just needs to be electrically connected to be heated by resistive heating. The further material can also be used to optimize the response of the tube to a thermal stimulus by modifying the thermal conductivity of the composite material as desired. 
         [0013]    In further aspect of the present invention a steerable introduction element for being introduced into an object is presented, wherein the steerable introduction element comprises: 
         [0014]    a tube as defined in claim  1 , and 
         [0015]    a temperature modifying element for modifying the temperature of at least a part of the tube for bending the tube. 
         [0016]    By modifying the temperature of at least a part of the tube the temperature of the tube can be modified, i.e. heated or cooled, especially locally, causing the tube to bend. The steerable introduction element can therefore also be regarded as being a steerable tube. 
         [0017]    The steerable introduction element is preferentially a steerable sheath, a steerable catheter or a steerable endoscope. The steerable sheath can be pulled over another instrument like a conventional catheter, in order to make the other instrument steerable. The tube can be combined with a further tube. For instance, the tube with the composite material including shape memory alloy material and non-shape-memory polymer material can be an intermediate tube arranged in between an outer tube and an inner tube. 
         [0018]    The temperature modifying element preferentially comprises at least one of a heating element and a cooling element. The heating element is preferentially adapted to heat a wall of the tube at one side, in order to cause the tube to bend. The cooling element can be used to reset the steerable introduction element faster into its original position, after a thermal activation by heating has been stopped. 
         [0019]    The heating element is preferentially adapted to heat the part of the tube by at least one of resistive heating, fluidic heating and optical heating. In particular, the heating element can be adapted to apply an electrical current to the tube such that the tube material itself can be resistively heated. Or, the heating element can comprise a separate element being adapted to heat the part of the tube by fluidic, especially liquid, or optical heating. For instance, the heating element can comprise an optical fiber or another optical means for providing light to be absorbed by the part of the tube to be heated. 
         [0020]    The cooling element can be adapted to provide a fluidic cooling. In particular, the cooling element can be adapted to provide a liquid cooling for cooling a part of the tube for bending the same. Instead of providing an active cooling, the temperature modifying element may only comprise a heating element for heating the tube, wherein in this case natural cooling by, for instance, conduction of heat through elements of the introduction element may be used, for example, through metal parts of the introduction element such as a braiding or a coil. 
         [0021]    In an embodiment the temperature modifying element comprises several temperature modifying sub elements located at different locations for modifying the temperature of different parts of the tube, wherein at least two of the temperature modifying sub elements are separately from each other controllable. By addressing different temperature modifying sub elements different bendings of the tube can be obtained for steering the introduction element as desired. For instance, the temperature modifying sub elements can be heating sub elements, wherein the multiple heating sub elements can be used for bending in different directions, in particular, in all directions, preferentially at any location of the tube length. 
         [0022]    In another aspect of the present invention a production apparatus for producing a tube as defined in claim  1  is presented, wherein the production apparatus comprises: 
         [0023]    a composite material providing unit for providing a composite material comprising shape memory alloy material and non-shape-memory polymer material, 
         [0024]    a polymer shaping unit for producing the tube by applying a polymer shaping technique to the composite material. 
         [0025]    In a further aspect of the present invention a production method for producing a tube as defined in claim  1  is presented, wherein the production method comprises: 
         [0026]    providing a composite material comprising shape memory alloy material and non-shape-memory polymer material, 
         [0027]    producing the tube by applying a polymer shaping technique to the composite material. 
         [0028]    It shall be understood that the tube of claim  1 , the steerable introduction element of claim  9 , the production apparatus of claim  14  and the production method of claim  15  have similar and/or identical preferred embodiments, in particular, as defined in the dependent claims. 
         [0029]    It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim. 
         [0030]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    In the following drawings: 
           [0032]      FIG. 1  shows schematically and exemplarily an embodiment of an interventional apparatus for performing an interventional procedure, 
           [0033]      FIG. 2  shows schematically and exemplarily a tube of the interventional apparatus, 
           [0034]      FIG. 3  shows schematically and exemplarily a tube with several temperature modifying sub elements, 
           [0035]      FIG. 4  shows schematically and exemplarily a resistive heating element arranged on a tube, 
           [0036]      FIG. 5  shows schematically and exemplarily electrical connections arranged on a tube for applying electrical current to the tube, 
           [0037]      FIG. 6  shows schematically and exemplarily a tip of an introduction element comprising an optical heating element, 
           [0038]      FIG. 7  shows schematically and exemplarily a tip of an introduction element comprising a fluidic heating and cooling element, 
           [0039]      FIG. 8  shows schematically and exemplarily a production apparatus for producing the tube of the interventional apparatus, and 
           [0040]      FIG. 9  shows a flowchart exemplarily illustrating an embodiment of a production method for producing the tube of the interventional apparatus. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0041]      FIG. 1  shows schematically and exemplarily an embodiment of an interventional apparatus for performing an interventional procedure. In this embodiment the interventional apparatus is an ablation apparatus for performing an ablation procedure. However, in other embodiments the interventional apparatus can also another apparatus being adapted to perform another interventional procedure. 
         [0042]    The interventional apparatus  20  comprises a steerable introduction element  1  for being introduced into an object. In this embodiment the steerable introduction element  1  is an ablation catheter for being introduced into the heart  21  of a person  3  lying on a support element  4  like a patient table. The ablation catheter  1  preferentially comprises ablation electrodes at the tip of the ablation catheter  1  for ablating cardiac tissue at desired locations within the heart  21 . The provision of the ablation energy can be controlled via an ablation energy control unit  11  of a control system  9 . The ablation energy control unit  11  comprises an ablation power source for providing ablation power like radiofrequency power which can be supplied to the tip of the ablation catheter  1  by using electrical wires within the ablation catheter  1 . 
         [0043]    The ablation catheter  1  comprises a tube  2  made of a composite material including a shape memory alloy material and a non-memory polymer material. Generally, the non-shape-memory polymer material can be any polymer material, which is not a shape memory polymer material as described, for instance, in the above mentioned article. The tube  2  is schematically and exemplarily shown in more detail in  FIG. 2 . 
         [0044]    As can be seen in  FIG. 2 , the tube  2  comprises the non-shape-memory polymer material  22  and the shape memory alloy material  12 , wherein in this embodiment the shape memory alloy material  12  is provided as fibers. The fibers can be, for instance, chopped fibers or wire pieces. The fibers  12  can increase the stiffness of the tube  2 . The fibers  12  are made of nitinol. The surface of the fibers is preferentially roughened, for instance, forged, grinded, etched, blasted, et cetera, in order to increase the adhesion between the non-shape-memory polymer material and the shape memory alloy fibers. 
         [0045]    The non-shape-memory polymer material  22  is preferentially at thermoplastic, silicone or thermoset. The non-shape-memory polymer material  22  can also be a combination of two of these materials or of all of these materials. 
         [0046]    The tube  2  is producible by using a polymer shaping technique being preferentially a conventional one like extrusion or injection molding. In particular, if the tube is produced by using extrusion, the shape memory alloy fibers  12  will automatically be aligned in the length direction of the tube  2  within the non-shape-memory polymer material  22 . 
         [0047]    The composite material formed by the non-shape-memory polymer material  22  and the shape memory alloy fibers  12  can further comprise additives like additional conductive particles, which may be metal particles or carbon particles, in particular, carbon nanotubes, or ceramic particles. These additional particles can be used for modifying the thermal conductivity of the composite material. Moreover, these particles can be used for modifying the electrical resistance of the tube such that, for instance, a part of the tube  2  can be heated by resistive heating. These particles or other additional particles can also be used for increasing the stiffness of the tube  2 . 
         [0048]    The steerable introduction element  1  further comprises a temperature modifying element for modifying the temperature of a part of the tube  2  relative to another part of the tube  2  for bending the tube  2 . By modifying the temperature of a part of the tube  2  the temperature of the tube  2  can be locally modified, i.e. heated or cooled, causing the tube  2  to bend. In this embodiment, the temperature modifying element is a heating element adapted to heat a wall of the tube  2  at one side, in order to cause the tube  2  to bend. For instance, the heating element can be adapted to heat the elliptical region  23  shown in  FIG. 2 , which may lead to shrinkage as indicated by the arrows  13 ,  14 , wherein this shrinkage can lead to a bending of the tube  2  as indicated by the arrow  15 . 
         [0049]    The heating element can be controlled by a temperature modifying element control unit  10  of the control system  9 , which can be adapted to allow a user to heat the tube  2  at a desired location with a desired intensity, in order to bend and, thus, steer the tube  2  in a desired direction. 
         [0050]    The heating element can be adapted to heat the respective part of the tube  2  by at least one of resistive heating, fluidic heating and optical heating. For instance, the heating element can be adapted to apply an electrical current to the tube  2  such that the tube material itself can be resistively heated at the desired location. Or, the heating element can comprise a separate element being adapted to heat the respective part of the tube  2  by fluidic, especially liquid, or optical heating. For instance, the heating element can comprise an optical fiber or another optical means for providing light to be absorbed by the part of the tube  2  to be heated. 
         [0051]    The heating element can comprise several sub heating elements located at different locations for modifying the temperature of different parts of the tube  2 , wherein at least two of the heating sub elements are controllable separately from each other. By addressing different heating sub elements different bendings of the tube  2  can be obtained for steering the introduction element  1  as desired. The heating sub elements can be adapted and controlled such that the tube  2  can be bent in different directions, in particular, in all directions, preferentially at any location along the tube length. 
         [0052]    The temperature modifying element can also comprise a cooling element being adapted to provide a fluidic cooling for cooling a part of the tube  2  for bending the same. The cooling element can be used to reset the steerable introduction element faster into its original position, after a thermal activation by heating has been stopped. Alternatively or in addition, after a certain part of the tube has been thermally activitated by heating the same and after this heating has been stopped, an opposite part of the tube can be heated for resetting the tube and, thus, the steerable introduction element faster into its original position. 
         [0053]    In the following several arrangements of heating elements and cooling elements for heating and cooling, respectively, the tube will exemplarily be described with reference to  FIGS. 3 to 7 . 
         [0054]      FIG. 3  shows schematically and exemplarily four heating elements  30  . . .  33  equidistantly arranged along the circumference of the tube  2 . Each heating element  30  . . .  33  can be separately electrically connected to the temperature modifying element control unit  10 , which in this example may be an electrical current source, in order to apply electrical current to the several heating elements  30  . . .  33  independently from each other. Preferentially, at several longitudinal positions along the length direction of the tube  2  different sets of heating elements  30  . . .  33  are arranged, in order to allow the tube  2  to be bent at different longitudinal positions along the length direction. The heating elements can also be arranged only at the inner circumference of the tube  2  or the heating elements can be arranged on the outer circumference and on the inner circumference of the tube  2 . 
         [0055]      FIG. 4  shows schematically and exemplarily a resistive heating element  37  arranged on the tube  2 . The resistive heating element  37  is electrically connected to the temperature modifying element control unit  10  via electrical conductors  36  like electrical wires. Also in this embodiment the temperature modifying element control unit  10  is a current source for applying electrical current to the resistive heating element  37 . Although in  FIG. 4  only a single resistive heating element  37  is shown for illustrative purposes, also more resistive heating elements can be arranged on the tube  2  for heating the tube  2  at the respective locations. 
         [0056]      FIG. 5  shows schematically and exemplarily a further possible heating element. In this example the heating element comprises electrical connections  38 ,  39 ,  40  for introducing electrical current into the tube  2 , wherein in this embodiment the tube  2  itself can generate heat by resistive heating. Thus, the electrical connections  38 ,  39 ,  40  are substantially only used for applying electrical current to the tube  2 , wherein the heat is substantially generated in the composite material of the tube  2 . Also in this embodiment the temperature modifying element control unit  10  is preferentially a current source for providing the electrical current to be applied to the tube  2 . The electrical connections  38  are preferentially insulated. 
         [0057]    The heating elements, for instance, the heating elements  30  . . .  33  and the resistive heating element  37 , can be separate components. For instance, they can be formed by a resistive pattern on a foil, wires or a dispensed pattern on the tube. The electrical connections like the electrical connections  36 ,  38 ,  39 ,  40  can be wires, dispensed lines, conducting lines on a flex foil, et cetera. 
         [0058]      FIG. 6  shows schematically and exemplarily a further possible arrangement for heating the tube  2 . In this embodiment the steerable introduction element is an ablation catheter having an ablation electrode  41 , an inner tube  35  and an outer tube  34 . In between the inner tube  35  and the outer tube  34  the tube  2  being an intermediate tube and having the composite material including the shape memory alloy material and the non-shape-memory polymer material is arranged. Optical fibers  42  are located adjacent to the intermediate tube  2 , in order to optically heat the intermediate tube  2 . The intermediate tube  2  is optically heated at the ends  50  of the optical fibers  42 . In this embodiment the temperature modifying element control unit  10  comprises a light source for providing light to be coupled into the optical fibers  42  for optically heating the intermediate tube  2 . In  FIG. 6 , the optical fibers  42  are arranged between the inner tube  35  and the intermediate tube  2 . However, alternatively or in addition, optical fibers  42  can also be arranged between the intermediate tube  2  and the outer tube  34 . Electrical connections for connecting the ablation electrode  41  to the ablation energy control unit  11  are not shown in  FIG. 6  for clarity reasons. 
         [0059]    The introduction element, in particular, the ablation catheter, can comprise an active cooling as it is known from known ablation catheters. This known active cooling can also be used to actively cool the tube  2 , in particular, the composite material including the shape memory alloy material and the non-shape-memory polymer material. Using active cooling can make the steering faster. However, the introduction element may also not comprise a separate cooling element and just provide a natural cooling using, for instance, metal components like a braiding, a coil, et cetera, which may be used for providing desired mechanical properties. 
         [0060]      FIG. 7  shows schematically and exemplarily an embodiment of the introduction element providing an active fluidic cooling and an active fluidic heating. Also in this embodiment the introduction element comprises an outer tube  34 , an inner tube  35  and an intermediate tube  2  arranged in between the outer tube  34  and the inner tube  35 . The intermediate tube  2  comprises the composite material including the shape memory alloy material and the non-shape-memory polymer material. Within the inner tube  35  a channel  44  is provided for allowing fluid to flow from a fluid source to a conductive element  43  and from the conductive element  43  back to the fluid source. The conductive element is a part of the inner tube  35  and forms a kind of bridge for allowing the temperature of the provided fluid to be transferred to the intermediate tube  2 . The conductive element  43  is preferentially a metal segment introduced into the inner tube  35  for heat exchange. The channel  44  can be provided by using extra tubing or a lumen as generally present in ablation catheters. By providing a relatively cold fluid the intermediate tube  2  can be cooled down and by providing a relatively hot fluid the intermediate tube  2  can be heated. In this embodiment the fluid source is preferentially part of the temperature modifying element control unit  10  for allowing the temperature modifying element control unit  10  to control the temperature of the intermediate tube  2  by providing the fluid with a desired temperature. Also in this embodiment the ablation electrode  41  is electrically connected to the ablation energy control unit  11  via electrical connections like electrical wires not shown in  FIG. 7  for clarity reasons. 
         [0061]    A position detection apparatus  30  is used for detecting the position of the tip of the catheter  1  within the person  3 . In this embodiment the position detection apparatus  30  comprises an x-ray source  5  for providing x-rays  8  traversing the person  3  and being detected by an x-ray detector  6 , after having traversed the person  3 . The x-ray source  5  and the x-ray detector  6  are controlled by a position detection control unit  7 . 
         [0062]    The position detection apparatus  30  is adapted to generate x-ray projection images of the inside of the person  3  including the catheter  1 , in particular, including the tip of the catheter  1 . The projection images can be shown on a display  31  to a user such that the user can steer the catheter  1  within the person  3  depending on the projection images shown on the display  31 . 
         [0063]      FIG. 8  shows schematically and exemplarily a production apparatus  16  for producing the tube  2  and  FIG. 9  shows a flowchart exemplarily illustrating an embodiment of a production method for producing the tube  2  by using the production apparatus  16  shown in  FIG. 8 . 
         [0064]    The production apparatus  16  comprises a composite material providing unit  17  for providing a composite material comprising shape memory alloy material and non-shape-memory polymer material. This provision of the composite material is performed in step  101 . In this embodiment a composite material is provided comprising shape memory alloy fibers like nitinol fibers and a non-shape-memory polymer material like thermoplastic, silicone and/or thermoset. The shape memory alloy fibers can be made from a wire that is chopped into wire parts forming the fibers. These wire parts can be mixed with the non-shape-memory polymer material using polymer mixing equipment like a mixer, a kneader, a twin screw extruder, et cetera. 
         [0065]    The production apparatus  16  further comprises a polymer shaping unit  18  for producing the tube  2  by applying a polymer shaping technique to the provided composite material. This application of the polymer shaping technique is performed in step  102 . In this embodiment the polymer shaping unit  18  uses extrusion for producing the tube  2 . 
         [0066]    Although in the above described embodiment the introduction element is an ablation catheter, in other embodiments the introduction element can also be another one. For instance, it can be another kind of catheter, an endoscope or a sheath. The tube, in particular, the introduction element comprising the tube, is preferentially adapted for minimal invasive surgery. 
         [0067]    Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. 
         [0068]    In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. 
         [0069]    A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. 
         [0070]    Operations like the control of the ablation energy provision or of the heating and/or cooling for bending the tube as desired performed by one or several units or devices can be performed by any other number of units or devices. 
         [0071]    Any reference signs in the claims should not be construed as limiting the scope.