Patent Publication Number: US-2012042517-A1

Title: Method for making smooth transitions between differing lead segments

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 12/707,116, filed Feb. 17, 2010, now allowed, which claims the benefit of priority to U.S. Provisional Patent Application No. 61/154,461, filed on Feb. 23, 2009, which applications are hereby incorporated herein by reference in their entirety to the extent that they do not conflict with the disclosure presented herein. 
    
    
     FIELD 
     This application relates to medical devices, more particularly implantable medical leads and to methods for manufacturing leads. 
     BACKGROUND 
     Electrical stimulation technology is expanding in scope, resulting in therapies that place leads in more and more areas of the body and in leads that have increasing levels of complexity. The stiffness of a lead body can be important for its function in many ways. For example, a very flexible lead body may be desirable for implantation in tissues that experience a lot of movement. A stiffer lead body may be important for guiding through tissue or for insertion into a device, such as an electrical signal generator. For example, if the portion of a lead to be inserted into a device is not sufficiently stiff, pushing the lead into a receptacle of the device may be difficult. 
     In transitioning from a stiff to a more flexible segment along the length of a lead, it is desirable for the transition to be smooth to spread any stresses out evenly over the length of the transition. Many ways of transitioning between segments of differing lead flexibilities have been devised. However, some are impractical from a manufacturing perspective or result in undesired characteristics. For example, lap bonding of two sections of differing stiffnesses can result in a reliable bond that spreads stresses out over the length of the lap bonded section; however, such lap bonding also results in increased thickness of the lead body. Such leads have a bulge in their outer diameter, which may be undesirable. 
     BRIEF SUMMARY 
     Leads having smooth transitions between differing segments and having uniform outer diameters along and in proximity to the transition section are described herein. Practical methods for manufacturing such leads are also described herein. 
     In various embodiments, a method for forming a lead body having a transition from a section having a first lead body characteristic to a section having a second lead body characteristic, as described herein, includes contacting a proximal section of the lead body having the first lead body characteristic to a distal section of the lead body having the second lead body characteristic. The proximal and distal sections of the lead body define lumens. The proximal and distal sections are contacted such that the lumen of the proximal section is axially aligned with the lumen of the distal section. The method further comprises disposing a lap band about a portion of the proximal section and a portion of the distal section, and thermally forming the lead body by bonding the lap band to the proximal and distal sections. Axially compressive pressure is applied to the lap band as the lead body is being thermally formed. The pressure applied is sufficient to result in the lead body having an outer diameter in regions proximally and distally adjacent to the lap band that are substantially the same as an outer diameter in a region formed by the lap band. 
     In various embodiments, a method for forming a lead body having a transition from a section having a first lead body characteristic to a section having a second lead body characteristic, as described herein, includes contacting a proximal section of the lead body to a distal section of the lead body. The distal section of the lead body defines a lumen extending through the distal section, has a substantially uniform inner diameter, has a first outer diameter along a first length from a proximal end of the first precursor to a first location distal the proximal end, and has a second outer diameter distal the first location. The first outer diameter is smaller than the second outer diameter. The proximal section of the lead body defines a lumen extending through the proximal section, has a substantially uniform inner diameter, has a first outer diameter along a first length from a distal end of the second precursor to a first location proximal the distal end to form the proximal section of the lead body, and has a second outer diameter proximal the location proximal the distal end. The first outer diameter is smaller than the second outer diameter. The proximal and distal sections are contacted such that the lumen of the proximal section is axially aligned with the lumen of the distal section. A lap band is disposed about a portion of the proximal section and a portion of the distal section and is thermally bonded to the proximal and distal sections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-2  are schematic drawings of side views of representative leads. 
         FIG. 3  is a schematic drawing of a side view of a representative system including an electrical signal generator and a lead. 
         FIGS. 4A-B  are schematic drawings of side views ( 4 A, exploded) of a representative lead and introducer. 
         FIG. 4C  is a schematic drawing of a cross section through the lead and introducer shown in  FIG. 4B  taken through line  4 C- 4 C. 
         FIG. 5  is a schematic drawing of a representative lead illustrating a method for making the lead. 
         FIGS. 6A-B  are schematic drawings of a representative lead illustrating a method for making the lead. 
         FIGS. 7A-B  are schematic drawings of a representative lead illustrating a method for making the lead. 
         FIGS. 8A-C  are schematic drawings of a representative lead illustrating a method for making the lead. 
         FIGS. 9A-C  are schematic drawings illustrating a method for making a distal section of a lead as shown in  FIG. 8A . 
         FIGS. 10A-B  are schematic drawings illustrating a method for making a proximal section of a lead as shown in  FIG. 8A . 
     
    
    
     The drawings are not necessarily to scale. Like numbers used in the figures refer to like components, steps and the like. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. In addition, the use of different numbers to refer to components is not intended to indicate that the different numbered components cannot be the same or similar. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration several specific embodiments of devices, systems and methods. It is to be understood that other embodiments are contemplated and may be made without departing from the scope of spirit of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. 
     All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure. 
     As used herein “substantially” means to a great extent or degree. Thus, two items or characteristics that are substantially the same are the same to a great extent or degree. For example, the two items or characteristics may be the same to the extent that processes for producing the things or characteristics are reproducible. Alternatively, or in addition, two things or characteristics that are substantially the same may be generally indistinguishable when considered for their intended purpose or purposes. For example, if two sections of a lead are to have substantially the same outer diameter so that the lead may be slidably disposed in an introducer with tight tolerances, then if the both sections slide through the introducer without difficulty the two outer diameters can be considered substantially the same. 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” encompass embodiments having plural referents, unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The present disclosure relates to medical leads, such as leads and lead extensions, having smooth transitions between segments having differing characteristics. The leads have uniform diameters along and in proximity to the transition section. 
     Leads as described herein may be used in conjunction with any suitable electrical medical device, such as an electrical signal generator system or a monitoring system. Examples of electrical signal generator systems that such leads may be used with include spinal cord stimulators, gastric stimulators, sacral nerve stimulators, deep brain stimulators, cochlear implants, defibrillators, pacemakers, and the like. In many embodiments, such electrical medical devices are implantable. 
     Any suitable type of lead may be adapted according to the teaching presented herein. By way of example and with reference to  FIG. 1  and  FIG. 2 , examples of representative leads  20  are shown. Leads  20 , as shown in  FIGS. 1 and 2 , contain four exposed electrical contacts  80  and four electrodes  90 . However, leads  20  may contain any suitable number of electrodes  90  or contacts  80 . The contacts  80  are disposed in proximity to the proximal end  40  of the lead  20 . The electrodes  90  are disposed in proximity to the distal end  50  of the lead  20 . Conductive wires (not shown) electrically couple discrete contacts  80  with discrete electrodes  90 . The conductors run within the lead body  30 . The contacts  80  are configured to couple electrical contacts of an electrical signal generator, such that signals generated by the active device may be applied to a tissue of a patient in which the distal end  50  of the lead  20  is implanted. A signal generated by the device is transmitted via a contact  80  along a conductor to an electrode  90  and to tissue in which the electrode  90  is implanted. The lead  20  shown in  FIG. 1  is of a type generally referred to as a percutaneous lead. The lead  20  shown in  FIG. 2  is a paddle-type, or surgical, lead. However, it will be understood that any lead configuration may be employed in accordance with the teachings provided herein. 
     Still with reference to  FIGS. 1-2 , at some point along the length of the lead body  30  there is a transition region  60  where the lead body  30  transitions from a section  70  having a first characteristic to a section having a second characteristic  75 . The transition may be between any two characteristics. For example the transition may be between a region having more rigidity to a region having more flexibility, between a region having one color and a region having another color, or the like. The transition region  60  may be located at any suitable position along the length of the lead body  30 . 
     In various embodiments, the lead body transitions at a transition region  60  from a first rigid section  70  to a second more flexible section  75 . The rigid section  75  includes the proximal end  40  of the lead body  30  and is sufficiently stiff to allow easy and reliable insertion into a receptacle of an active electrical medical device. For example, in some embodiments, the rigid section  75  has a flexural modulus of about 0.003 lbf-in 2  or greater. 
     For example and with reference to  FIG. 3 , the rigid proximal section  70  of the depicted lead body  30  is configured to be inserted into a receptacle  110  of a header  120  of an implantable electrical signal generator  10 . The receptacle  110  includes internal electrical contacts (not shown) configured to contact an electrically couple with contacts  80  of the lead. Hermetically sealed feedthroughs not shown) electrically couple the internal contacts to electronics in the primary hermetically sealed housing of the signal generator  10 . The proximal portion  70  of the lead body  30  is sufficiently rigid to allow for reproducible and ready insertion into, or withdrawal from, the receptacle  110  to provide reliable electrical coupling between contacts  80  of the lead and the receptacle  110  of the active electrical device  10 . While not shown, it will be understood that leads configured to be coupled to lead extensions or other devices having receptacles configured to receive the lead may also benefit from having a rigid proximal section. 
     In the embodiments depicted in  FIGS. 1-3 , the transition section  60  through which the lead body  30  transitions from a section  70  having a first characteristic, e.g. rigidity, to a section  75  having a second characteristic, e.g. flexibility, has a substantially uniform outer diameter in the transition section  60  and proximal and distal to the transition section  60 . In addition to aesthetic purposes, the substantially uniform outer diameter may serve a variety of functional purposes. For example and with reference to  FIGS. 4A-C , a lead  20  having a substantially uniform outer diameter may be beneficial when the lead  30  is introduced into a patient through an introducer  200 , such as a Touhy needle. The depicted introducer  200  has a proximal end  210 , a distal end  220  and a lumen  230  extending through the introducer  200  from the proximal end  210  to the distal end  220 . The lumen  230  is configured to slidably receive the lead  20 . The clearance between the outer diameter of the lead body  30  and the inner diameter of the introducer  200  is desirably kept small so that use of excessively small gauge introducer needles, which may cause trauma to the patient, is avoided. Due to the typically small clearance between the lead body  30  and the inner surface of the introducer  200  defining the lumen  230 , it is desirable to minimize differences in the outer diameter in the transition region  60  and those regions proximal and distal to the transition region  60  so that lead  20  may be readily inserted into, or withdrawn from, the introducer  200 . 
     Leads that have a smooth transition between a section having a first characteristic and a section having a second characteristic and which have a substantially uniform diameter throughout the transition section and proximal and distal to the transition section are described below. Methods for making such leads are also described in more detail below. Referring now to  FIGS. 5-9 , various representative longitudinal sections of lead bodies and methods are shown. For the purposes of clarity only polymeric tubes or portions thereof that are used to form the lead body are shown. It will be understood that leads may include other components such as a shield, conductive wires, contacts, electrodes, reinforcement members such as a mesh, and the like. In the embodiments depicted, a proximal section  310  of the lead body is shown as being the section having the first characteristic  70  and a distal section of the lead body  320  is shown as being the section having the second characteristic  75 . Of course, it will be understood that the distal section may have the first characteristic and the proximal section may have the second characteristic. 
     In the embodiment depicted in  FIG. 5 , the proximal section  310  of the lead body is contacted with the distal section  320  of the lead body and the lumen  330  of the proximal section  310  is axially aligned with the lumen  340  of the distal section  320 . The distal end of the proximal section  310  is in contact with the proximal end of the distal section  320 . The inner diameters of the distal and proximal sections of the lead body are substantially the same. The proximal lead body section  310  has a first outer diameter from the distal end to a location  350  proximal the distal end and has a second outer diameter proximal to the location  350 . The second outer diameter is greater than the first outer diameter. The distal lead body section  320  has a first outer diameter from the proximal end to a location  360  distal the proximal end and has a second outer diameter distal to the location  360 . The second outer diameter is greater than the first outer diameter. The first outer diameter of the proximal section  310  is substantially the same as the first outer diameter of the distal section  320 . A lap band  300  has a thickness that is about half the difference between the second outer diameter and the first outer diameter of either the proximal  310  or distal  320  sections. The lap band  300  has a length that is substantially the same as the cumulative length of: the distance from the distal end of the proximal section  310  to the location  350  proximal the distal end; and the distance from the proximal end of the distal section  320  to the location  360  distal the proximal end. Thus, the lap band  300  is configured to abut the shoulder formed at the location  350  where the proximal section  310  transitions from the first outer diameter to the second outer diameter and is configured to abut the shoulder at the location  360  where the distal section  320  transitions from the first outer diameter to the second outer diameter, when the distal end of the proximal section  310  and the proximal end of the distal section  320  are in contact. The area of the lead body formed by the lap band  300  is the transition section  60  of the lead body, and the outer diameter of the lead body is substantially uniform along the transition region  60  and proximal and distal to the transition section  60 . 
     The lead body may be formed by thermally bonding the lap band  300  to the proximal section  310  and the distal section  320 . In various embodiments, such lap bonding occurs when the lap band material is heated to 100° C. or higher depending on the material. The lap band  300 , proximal section  310  and distal section  320  may be made of any suitable thermoplastic polymer. Examples of suitable thermoplastic polymers include polyurethane, polysulfone, polyethylene, and polypropylene. In various embodiments, the lap band  300 , the proximal section  310 , and the distal section  320  are made of the same type of polymeric material. In the case of polyurethane, lap bonding may occur at about 250° C. to about 300° C. 
     When each of the lap band  300 , the proximal section  310 , and the distal section  320  are made of the same type of polymeric material and the proximal section is more rigid than the distal section, similar materials of different durometers may be used. 
     Referring now to  FIGS. 6A-B , a proximal section  310  of a precursor to a lead body is contacted with a distal section  320  of a lead body such that the lumen  330  of the proximal section  310  is axially aligned with the lumen  330  of the distal section  320 . The distal end of the proximal section  310  is in contact with the proximal end of the distal section  320 . A lap band  300  is disposed about the proximal  310  and distal  320  sections. The lead body (see  FIG. 6B ) is thermally formed by bonding the lap band  300  to the proximal  310  and distal  320  sections. An axially compressive force is applied to the lap band  300  as the lead body is being thermally formed. Sufficient axial pressure is applied to result in the lead body having an outer diameter in regions proximal and distal the transition section  60  formed by the lap band that are substantially the same as the outer diameter in the region  60  formed by the lap band  300 . 
     To prevent collapse of the lumen  370  as the lead body is being formed and to provide sufficient normal force to the axially compressive force applied to the lap band  300  to form the uniform transition section  60 , the proximal  310  and distal  320  sections may be placed about a mandrel (not shown) having an outer diameter substantially the same as the inner diameter of the sections  310 ,  320 . To achieve sufficient axially compressive force to result in a substantially uniform outer diameter of the lead body in the transition section  60 , a die (not shown) may be used to provide the axial pressure. It will be understood that the amount of axial pressure applied necessary to achieve a substantially uniform outer diameter will vary from material to material and process conditions to process conditions. For purposes of example, when employing distal  320  and proximal  310  polyurethane sections having an 0.050 inch OD×0.030 inch ID and durometers of 55D and 75D and a polyurethane lap band  300  having a 55D durometer and an 0.057 inch OD×0.051 inch ID, axial pressure pneumatically applied by a die for a time of 5 seconds, when the transition region  60  was heated at 250° C., was sufficient to result in a substantially uniform outer diameter when formed about a mandrel. 
     Referring now to  FIGS. 7A-B , an alternative lead and method are shown. In the depicted embodiment, the proximal section  310  having the first characteristic has substantially uniform outer and inner diameters. The distal section  320  having the second characteristic has a substantially inner diameter forming a lumen  340  and has first and second outer diameters. The first outer diameter being smaller than the second outer diameter. The region of the distal portion  320  having the first outer diameter extends from the proximal end to a location  360  distal the proximal end. The second outer diameter extends distally from the location  360 . The inner diameter of the proximal section  310  is substantially the same as the first outer diameter of the distal section  320 . The outer diameter of the proximal section  310  is substantially the same as the outer diameter of the distal section  320 . The proximal section  310  is disposed about the section of the distal section  320  that has the first outer diameter. The distal end of the proximal section  310  is in contact with the proximal face of the shoulder formed at the location  360  as the distal section  320  transitions from the first outer diameter to the second outer diameter. In the depicted embodiments, the proximal section  310  and the distal section  320  are co-axial or axially aligned. A lap bad  300  is disposed about the proximal  310  and distal  320  sections at the region where the sections  310 ,  320  intersect. As discussed above with regard to  FIG. 6 , the lead body is thermally formed while axially compressive force is applied to the lap band to result in a lead body having a substantially uniform outer diameter in the transition section  60  defined by the length of the lap band  300  and proximal and distal to the transition section  60  (see  FIG. 7B ). 
     In the embodiment depicted in  FIG. 7 , the portion of the distal section  320  having the first outer diameter is co-extensive with proximal section  310 . Such an arrangement may be advantageous relative to the arrangement depicted in  FIG. 6  because the surface area of the bond between the two sections  310 ,  320  is increased. However, the processing steps or manufacturing costs associated with a distal section  320  having two outer diameters as shown in  FIG. 7A  may be increased relative to a distal section  320  as shown in  FIG. 6 . 
     Referring now to  FIG. 8 , an alternative embodiment of a lead body and a process are shown. In the depicted embodiment, a proximal section  310  having a first characteristic and a distal section  320  having a second characteristic are shown. The proximal section  310  has a substantially uniform inner diameter forming a lumen  330 , and has first and second outer diameters. The first outer diameter is smaller than the second outer diameter. A region of the proximal section  310  extending from the distal end to a location  350  proximal the distal end has the first outer diameter. A region of the proximal section  310  extending proximally from the location  350  has the second outer diameter. 
     The distal section  320  depicted in  FIG. 8  has a substantially uniform inner diameter forming a lumen  340 , and has first, second and third outer diameters. The first outer diameter is smaller than the second outer diameter. The second outer diameter is smaller than the third outer diameter. A region of the distal section  320  extending from the proximal end to a first location  360  distal the proximal end has the first outer diameter. A region of the distal section  320  extending distally from the first location  360  to a second location  400  distal the first location  360  has the second outer diameter. A region of the distal section  320  extending distally from the second location  400  has the third outer diameter. 
     The inner diameter of the proximal section  310  is substantially the same as the first outer diameter of the distal section  320 . The first outer diameter of the proximal section  310  is substantially the same as the second outer diameter of the distal section  320 . The second outer diameter of the proximal section  310  is substantially the same as the third outer diameter of the distal section  320 . 
     In the embodiment depicted in  FIGS. 8A-C , the proximal section  310  is placed about the portion of the distal section  320  having the first outer diameter such that the distal end of the proximal section  310  contacts the shoulder formed at the transition from the first outer diameter to the second outer diameter of the distal section  320  (see  FIG. 8B ). A lap band  300  is placed about the portion of the proximal section  310  having the first outer diameter and the portion of the distal section  320  having the second outer diameter such that the lap band  300  contacts the shoulder of the proximal section  320  formed at the transition from the first outer diameter to the second outer diameter and contacts the shoulder of the distal section  320  formed at the transition from the second outer diameter to the third outer diameter (see  FIG. 8C ). The lead body may then be thermally formed to produce a lead body having a substantially uniform outer diameter along the transition section formed by the lap band  300  and proximal and distal to the transition region (see  FIG. 8C ). 
     Proximal and distal sections as described above that have differing outer diameters along their length may be made by any suitable process such as machining, molding or etching. With reference to  FIGS. 9-10 , process schemes for forming the proximal section  310  ( FIG. 10 ) or distal section  320  ( FIG. 9 ) depicted in  FIG. 8  are shown for purposes of example. In  FIG. 9 , illustrated is a precursor polymeric tube  500  having a substantially uniform outer diameter, which corresponds to the third outer diameter of the distal section  320  (depicted in  FIG. 8 ), and a substantially uniform inner diameter (see  FIG. 9A ). As depicted, a portion of the polymeric precursor  500  may be removed; e.g., by etching or machining, or a series of steps made via a stretching and thermal forming. In the embodiment depicted in  FIG. 99 , the portion of the thickness from the proximal end to the first location  360  or the second location  400  may be removed to form intermediates. In the case of removal to the first location  360 , a sufficient amount of the precursor is removed to leave a section having an outer diameter equivalent to the first outer diameter of the proximal section  320 . In the case of removal to the second location  400 , a sufficient amount of the precursor is removed to leave a section having an outer diameter equivalent to the second outer diameter of the proximal section  320 . The intermediates may be further processed; e.g. via etching or machining, to arrive at the completed distal section  320  (see  FIG. 9C ). 
     With reference to  FIGS. 10A-B , a precursor  510  is processed such that a portion of the thickness of the precursor  510  is removed from the distal end to a first location  350  proximal the distal end to result in the proximal section  310 . 
     Of course any other suitable method for making proximal and distal sections as described herein may be employed. 
     Thus, embodiments of the METHOD FOR MAKING SMOOTH TRANSITIONS BETWEEN DIFFERING LEAD SEGMENTS are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.