Patent Publication Number: US-2022233826-A1

Title: Split sheath introducer and method of manufacturing a split sheath introducer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/233,601, filed on Dec. 27, 2018, which claims the benefit of U.S. Provisional Application Ser. No. 62/610,616, filed on Dec. 27, 2017, both of which are hereby incorporated by reference herein in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to medical devices and, more particularly, to a splittable or peelable sheath used for the introduction of catheters and other medical devices into a patient, and a method of manufacturing such a sheath. 
     BACKGROUND OF THE INVENTION 
     A variety of medical procedures involve or require the introduction of devices through the skin and underlying tissue layers into blood vessels or other locations inside the body of a patient. These purposes include, for example, the introduction of catheters, pacemaker leads and other such devices into a patient&#39;s body. These devices are transcutaneous devices which pass through the skin and into the blood vessel during use. 
     A number of systems and device have been developed to aid in the placement of such devices into the body of a patient. Once such device, known as an introducer set, includes a peel away introducer sheath and a dilator. The peel away introducer sheath is a thin-walled, usually cylindrical, device that is placed in position so that it provides a communicating passageway through the tissue. This is accomplished by fitting the introducer sheath tightly over the dilator and advancing both devices through the tissue together as a unit. The long, tapered tip of the dilator acts to stretch the opening in the skin and blood vessel to allow for the insertion of the larger sheath. The dilator is then removed, leaving the introducer sheath alone in the desired position, acting to hold the penetrated site open. At that point, the catheter tube or other invasive device is advanced through the introducer sheath into the desired position. The peel away introducer sheath is then removed from the tissue and pulled apart lengthwise into two pieces, separating it from the inserted device. 
     Existing peelable introducer sheaths are typically formed from polypropylene or polyethylene tubing and have a score line imparted along the length of the sheath. After application/insertion, the sheath can be pulled apart along the score line so that the sheath can be removed. With such polypropylene or polyethylene tubing, however, tearing or peeling of the sheath along the score line can be difficult or cumbersome to initiate, and often produces a jagged tear along the score line, which is undesirable. Other known sheaths are manufactured from Teflon, which has a propensity to tear linearly on its own (i.e., without the need for a score line). Teflon, however, is an expensive material that inhibits its widespread use in such devices. 
     Other efforts to produce peelable or splittable introducer sheaths have involved using co-extrusion and/or injection molding processes to form a tubular sheath with longitudinal stripes of a different material than the main body of the sheath, which are intended to allow for easy peeling along the length of the sheath at the stripe/main body interface. Existing manufacturing processes, tooling and materials utilized in the manufacture of such sheaths have not, however, succeeded in producing a reliable product. In particular, despite such introducer sheaths (with opposing stripes along which the sheath is intended to be peeled) having been invented almost 30 years ago, such sheaths are not in use today due to a number of problems and unique constraints that have heretofore not been overcome or met. 
     For example, the sheath of an introducer must be internally lubricous to allow for dilators, catheters and other devices to easily slide therethrough and into the body of a patient. In addition, the stripes must be weaker than the material of the main body, and must be able to peel easily while at the same time form a reliable attachment to the main body prior peeling to prevent inadvertent detachment during insertion of the sheath and dilator. To date, stripe materials that are able to provide this functionality have been inherently tacky, which can create a problem with ovality (i.e., the sheath not being round) in the tube while processing. 
     In view of the above, there is a long-felt need in the art for an effective means of manufacturing a peelable or splittable sheath that has a lubricous interior, is able to be easily split when desired, but which resists inadvertent splitting during insertion, is substantially round, has minimal tackiness, and has peel stripes of minimal width. Despite the desire of others to provide a splittable sheath with the characteristics indicated above for quite some time, to date, efforts directed to this end have failed to produce a saleable and useable product. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a splittable or peelable introducer sheath. 
     It is an object of the present invention to provide a splittable or peelable introducer sheath that has a lubricous interior. 
     It is an object of the present invention to provide a splittable or peelable introducer sheath that is able to be easily split when desired, but which resists inadvertent splitting during insertion. 
     It is an object of the present invention to provide a splittable or peelable introducer sheath that is substantially round. 
     It is an object of the present invention to provide a splittable or peelable introducer sheath that has a peel stripe of minimal width. 
     It is another object of the invention to provide a method of manufacturing a splittable or peelable sheath having the specific combination of characteristics described above. 
     These and other objects are achieved by the present invention. 
     In an embodiment, a splittable introducer sheath includes a tubular body portion formed from a first material and at least one stripe extending an entire length of the main body portion, the at least one stripe being formed form a second material. The first material is one of a medium-density polyethylene modified with a friction-reducing additive or high-density polyethylene (HDPE) modified with a friction-reducing additive. The second material is a thermoplastic elastomer modified with a siloxane additive. The sheath is dividable longitudinally along the at least one stripe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below: 
         FIG. 1  is a perspective view of a peelable or splittable sheath according to an embodiment of the present invention, showing the sheath prior to peeling or splitting. 
         FIG. 2  is a perspective view of the peelable or splittable sheath of  FIG. 1 , illustrating peeling or splitting of the sheath along opposed peel stripes. 
         FIG. 3  is a perspective view illustrating an extrusion head of an extrusion assembly, utilized in the manufacture of the peelable or splittable sheath of  FIG. 1 , according to an embodiment of the invention. 
         FIG. 4  is an enlarged, rear perspective view of a die of the extrusion head of  FIG. 3 . 
         FIG. 5  is an enlarged, front perspective view of the die of  FIG. 4 . 
         FIG. 6  is an end view of the die of  FIG. 4 . 
         FIG. 7  is an enlarged, front perspective view of the extrusion head of  FIG. 3 , showing the die and mandrel. 
         FIG. 8  is another perspective view illustrating the manufacture of the peelable or splittable sheath of  FIG. 1 , using the extrusion head of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIG. 1 , a peelable or splittable sheath  10  of an introducer set or assembly is illustrated. The sheath  10  includes a substantially cylindrical or tubular main body portion  12  formed from two opposed, semi-circular walls  18 ,  20 , and a pair of longitudinal stripes  16  or strips joined to the main body portion  12  and extending substantially the entire length of the sheath  10 . The main body portion  12  and the stripes  16  define an interior passageway  14  of the sheath  10 . The longitudinal stripes  16  have a wall thickness that is substantially equal to a wall thickness of the main body portion  12  and are formed on opposite sides of the sheath  10  (e.g., 180 degrees apart). While  FIG. 1  illustrates two opposed stripes  16 , it is contemplated that the sheath  10  may have a single stripe, or more than two stripes, without departing from the broader aspects of the invention. Where more than two stripes are utilized, they may be equally or unequally spaced along the circumference of the sheath  10 . 
     In an embodiment, the main body portion  12  is formed from a first material, and the stripes  16  are formed from a second material that is different from the first material. The first material may be, for example, medium-density polyethylene (MDPE), high-density polyethylene (HDPE) or polypropylene (PP). More preferably, the first material is MDPE modified with a friction-reducing additive, or HDPE modified with a friction-reducing additive. In an embodiment, the friction-reducing additive may be a non-leaching siloxane additive, although other additives that impart lubricity and remove tackiness from the stripes, as discussed below, can be utilized. 
     The second material is preferably a thermoplastic elastomer (TPE) having a Shore A durometer of between about 37 and about 53, modified with a siloxane additive that functions to decrease the tackiness of the second material. The functionality of the stripes  16  and the peel strength required to split the sheath  10  lengthwise along the stripes  16  is dependent on the durometer of the stripes. Stripe materials with a lower durometer decreases the peel strength, while materials with a higher durometer increase the peel strength. It has been discovered that a TPE having a Shore A durometer in the range noted above, with a siloxane additive, provides for an optimal peel strength while minimizing tackiness of the material. 
     In the preferred embodiment, the stripes  16  are quite narrow in relation to the circumference of the sheath  10 , and may be, for example, less than 1/16 inches in width. More preferably, the stripes  16  have a width in the circumferential direction about a few thousandths of an inch (e.g., 0.002-0.005 inches) to substantially hide them from view. 
     In one embodiment, a 5 French sheath has a main body portion  12  formed from A Dow MDPE modified with a siloxane additive to be approximately 5% active, and stripes  16  that are formed from Teknor Apex Medalists TPE likewise modified with a siloxane additive to be approximately 5% active. 
       FIG. 2  illustrates the sheath  10  of the present invention in a partially peeled or split state. As shown therein, the sheath  10  is split in half at the stripe/main body portion interface. In an embodiment, handles (not shown) may be integrated with the sheath  10  to aid in splitting. 
     The sheath  10  of the present invention is manufactured using a coextrusion process, where a primary melt stream that eventually forms the main body portion  12  and a secondary melt stream that eventually forms the stripes  16  are fed to a head comprising a die (which forms the outside diameter of the sheath  10 ) and a mandrel or tip (which forms the inside diameter of the sheath  10 ).  FIG. 3  is a rear (upstream to downstream), perspective illustration of an extrusion head  100  that may be utilized to manufacture the sheath  10  of the present invention. As shown therein, the head  100  includes a die  110  having a central opening  112  within which is concentrically mounted a mandrel or tip  114 . The back side of the die  110  is formed with feed channels  116  located 180 degrees apart that allow the secondary melt stream to run from a feed to the tip  114 .  FIG. 4  is an enlarged view of the die  110  showing the opposed channels  116  through which the secondary melt stream flows, according to one embodiment of the invention. 
     Referring now to  FIG. 5 , a front view of the die  110  is shown. As shown therein, the central opening  112  includes a pair of opposed baffles  118  that project radially inward. Importantly, the outlets of the feed channels  116  are precisely aligned (angularly) with the baffles  118 .  FIG. 6  is an end view of the die  110  showing the location of the outlets  120  of the feed channels  116  in relation to the baffles  118  in the central opening  112 . In an embodiment, the width of the baffles  118  are selected to generally correspond to the desired width of the peel stripes  16 . In particular, in an embodiment, the baffles may be between about 0.003 inches and about 1/16 inches. 
     With reference to  FIG. 7 , an enlarged, perspective view of a downstream end of the head  100  (including the die  110  and tip  114 ) is shown. Importantly, the baffles  118  block or inhibit the flow of the first material of the primary melt stream against the tip  114 , creating a void where the second material from the secondary melt stream can enter the flow stream undisturbed to form the stripes  16 . This tooling configuration, namely, the use of the baffles  118 , ensures that the secondary melt stream is permitted to reach the tip  114 . This, in turn, ensures that the stripes  16  extend all the way through the thickness of the sheath  10 , which facilitates easy splitting of the sheath  10 . 
     In operation, the first material that forms the main body portion  12  of the sheath  10  will flow into the head  100  from a primary extruder (not shown). A secondary extruder (not shown) will feed the second material that forms the stripes  16  through a port into the head  100 . The second material that will form the stripes  16  will be diverted into two paths/channels  116  that are about 180 degrees apart and flow into the path of the primary melt stream. Importantly, in an embodiment, a cylindrical core is positioned downstream from the tip  114 , so that coextrusion of the main body portion  12  and stripes  16  take place over the cylindrical core. This extrusion process is illustrated in  FIG. 8 . Once the material cures to form the cylindrical sheath  10 , the core can be removed (or the sheath removed from the core). 
     Importantly, coextruding the sheath  10  over a cylindrical core ensures that the sheath  10  is formed in a cylindrical shape and that the cylindrical shape is maintained during the duration of cure. In particular, extruding over a cylindrical core prevents the sheath from deforming into an oval (i.e., ovality) during the coextrusion and curing process, which is typically due to the use of differing materials for the main body portion and stripe. As discussed above, this has long been a problem with sheaths having a main body portion and stripes formed from dissimilar materials. 
     Alternatively, or in addition to extruding the sheath  10  over a cylindrical core, vacuum sizing may be utilized to ensure that the sheath  10  is formed in with a substantially circular cross-section, with no or minimal ovality. In particular, vacuum sizing may be used downstream from the extruder assembly to assist in forming the circular cross-section. In an embodiment, after exiting the extruder, the still molten extrudate is fed through a sealed chamber in which a vacuum is being drawn. The extrudate passes through a series of vacuum sizing bushes or plates and is formed into its final shape before cooling. Cooling in the vacuum bath may be using water or air. 
     In an embodiment, the materials chosen for the stripes and main body portion may varied to some degree depending on dimeter of the sheath and the wall thickness. 
     Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of this disclosure.