Patent Publication Number: US-2010130963-A1

Title: Medical devices with dual modality visible segments

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 61/117,200, filed Nov. 23, 2008, which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to medical devices and, more particularly, to medical devices that include selected segments that are visible using both fluoroscopy and ultrasonic imaging. 
     BACKGROUND 
     It may be desirable to monitor the position of medical devices such as, e.g., catheters, while they are within a patient&#39;s body. For example, it may be useful to monitor the position of guide catheters which are used to place catheters, electrode leads and the like in desired locations within the body of a patient. A guide catheter typically includes an elongated sheath that is inserted into a blood vessel or another portion of the body. A catheter or lead is introduced through an inner channel defined by the sheath. 
     To enable precise positioning of a medical device, one or more selected segments may include visibility materials that are visible under fluoroscopy and/or ultrasonic imaging. Using fluoroscopic or ultrasonic imaging techniques, the physician can visualize the guide catheter, and place the catheter or electrode lead in a desired position. Guide catheters, for example, may incorporate radiopaque and/or echogenic materials to promote visibility. 
    
    
     
       BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWING 
       The present disclosure will be further described with reference to the figures of the drawing, wherein: 
         FIG. 1  is a perspective view of one exemplary medical device in the form of a catheter. 
         FIG. 2  is an enlarged cross-sectional view of a portion of one embodiment of a catheter according to the present disclosure. 
         FIG. 3  is an enlarged cross-sectional view of a portion of another embodiment of a catheter according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The present disclosure is directed to medical devices (such as, e.g., catheters, guide catheters, etc.) that include one or more selected segments that are constructed using visibility materials compounded with one or more polymeric materials that make the selected segments visible using both fluoroscopy and ultrasonic imaging. The visibility material may take the form of tungsten and/or tungsten carbide particles dispersed within a polymeric material. 
     The use of visibility material as described herein can potentially promote enhanced visibility of a medical device (such as a guide catheter) using both fluoroscopic and ultrasonic imaging techniques. This feature provides a physician with flexible imaging options. The medical device can be used by physicians who prefer fluoroscopic imaging, for example, as well as those who prefer ultrasound. In each case, the physician may select the same guide catheter without regard to the desired imaging modality. 
     In some embodiments, the use of a visibility material that is both echogenic and radiopaque as an additive to enable both fluoroscopic and ultrasonic imaging can potentially allow the overall additive level to be lower, which may tend to preserve the mechanical properties of a composite blend incorporating the visibility material. 
     In some instances, a reduced amount of visibility material in a composite blend may also enhance the slittability of a guide catheter. In this manner, the visible material can potentially be loaded into polymeric material in amounts that promote visibility while maintaining slittability. 
     Although it is known that polyether block amides can be loaded with tungsten and/or tungsten carbide to provide visibility using both fluoroscopy and ultrasonic imaging, these compositions can, in some instances, suffer from degradation during aging. The degradation can adversely impact the flexibility and other mechanical properties of the segments in which the visibility materials are provided. The approaches to providing the visible medical device segments as described herein may address these aging issues while still retaining an suitable level or enhanced level of visibility using both fluoroscopic and ultrasonic imaging. 
     In one embodiment, the present disclosure provides a medical device. The medical device includes: an inner layer including a radiopaque and echogenic material, wherein the radiopaque and echogenic material includes tungsten and/or tungsten carbide particles distributed within a base polymeric material (i.e., a first polymeric material) including a polyether block amide; and an outer layer including an additional polymeric material (i.e., a second polymeric material). In certain embodiments, the additional polymeric material is a thermoplastic elastomer. Optionally, the additional polymeric material is more resistant to hydrolysis and/or oxidation than the base polymeric material. In certain embodiments, the medical device is a guide catheter including an elongated sheath including a proximal end and a distal tip, and at least a portion of the distal tip and/or elongated sheath includes the radiopaque and echogenic material. Methods of preparing such medical devices are also provided. 
     In another embodiment, the present disclosure provides a method of increasing the shelf life of at least a portion of a medical device. In certain embodiments, the method includes: providing a radiopaque and echogenic material including tungsten and/or tungsten carbide particles distributed within a base polymeric material (i.e., a first polymeric material); and forming a layer including an additional polymeric material (i.e., a second polymeric material) over the radiopaque and echogenic material, wherein the additional polymeric material is more resistant to hydrolysis and/or oxidation than the base polymeric material. 
     The above brief description is not intended to describe each embodiment or every implementation of the present disclosure. Rather, a more complete understanding of the disclosure will become apparent and appreciated by reference to the following description and claims in view of the accompanying figures of the drawing. 
     In the following detailed description of illustrative embodiments of the disclosure, reference is made to the accompanying figures of the drawing which form a part hereof, and in which are shown, by way of illustration, specific embodiments that may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present disclosure. 
       FIG. 1  is a perspective view of one medical device that may be used in connection with the present disclosure which is in the form of a catheter  10 . As shown in  FIG. 1 , catheter  10  includes a proximal end  12 , distal tip  14 , and an elongated sheath  20  extending between the proximal and distal ends. Catheter  10  may be sized for insertion into a lumen, such as a blood vessel, within the human body. Catheter  10  preferably defines at least one inner channel (not shown in  FIG. 1 ) through which other elements such as other catheters, electrode leads, etc. may be inserted. A handle  30  may be coupled to proximal end  12  of catheter  10 . A slitter (not shown) may be positioned near proximal end  12 , e.g., adjacent handle  20  if the catheter  10  is to be slit during removal of the catheter  10 . 
     The sheath  20  of the catheter  10  may include any number of segments, with the sheath  10  including three segments  22 ,  24 , and  26  disposed along the length of catheter  10 . Sheath  20  may be formed to provide either a straight or pre-bent shape to catheter  10 , depending on the desired end application. 
     Sheath  20  may be manufactured using materials that promote maneuverability and that may also permit slitting along the length of catheter  10 . In particular, each segment  22 ,  24 , and  26  of the sheath  20  may be constructed of one or more polymeric materials, such as polyether block amide, nylon block polymer, silicone, or polyurethane, as well as composites or mono-polymers. An example of one potentially suitable group of polymeric materials that can be used are polyether block amides marketed under the trademark PEBAX and commercially available from Arkema, Inc. (Philadelphia, Pa.). 
     In some embodiments, the sheath may also include other components such as, e.g., reinforcing braids, etc. If a reinforcing braid is provided, it may terminate short of the distal segment  22  such that the flexibility of the sheath  16  is higher within at least the distal segment  22  as compared to the portions of the sheath  16  that do include a reinforcing braid. Examples of some sheath constructions including reinforcing braids or strands are described in, e.g., U.S. Pat. No. 7,065,394 (Robot et al.). 
     Medical devices of the present disclosure, such as catheter  10 , are constructed to exhibit properties that enhance visibility of selected portions of the medical device when using fluoroscopic or ultrasonic imaging techniques. With reference to  FIG. 1 , distal segment  22  is found at the distal tip of catheter  10  and incorporates visibility material that makes the segment  22  visible using both fluoroscopy and ultrasonic imaging modalities. The visibility material also may be provided in other segments and/or along the entire length of the catheter. 
     Each sheath segment  22 ,  24 , and  26  may, in some embodiments, be constructed from a similar material with a similar concentration of tungsten and/or tungsten carbide particles. However, the different sheath segments may be manufactured with polymeric materials that have different hardness characteristics. It may be preferred that the distal segment  22  be flexible such that the distal end of the catheter  10  is more flexible than the segments  24  and  26  such that that tip  14  of the catheter  10  is relatively atraumatic. As a particular illustration, sheath segments  22 ,  24 , and  26  may be constructed from PEBAX material with 25, 35, and 55 Shore D hardnesses, respectively. In another illustration, each sheath segment  22 ,  24 , and  26  may be independently constructed from PEBAX material having a desired hardness (e.g., 25, 35, 40, 55, 63, 70, or 72 Shore D hardness). The tungsten and/or tungsten carbide particles can be added to selected sheath segments  22 ,  24 , and  26  in concentrations that do not significantly degrade the overall mechanical properties of sheath  20 , e.g., on the order of about 60 to about 90 percent by weight. As previously described, other ranges can be used. In another embodiment, the tungsten and/or tungsten carbide particles can be added to selected sheath segments  22 ,  24 , and  26  in concentrations on the order of about 60 to about 85 percent by weight. In still yet another embodiment, the tungsten and/or tungsten carbide particles can be added to selected sheath segments  22 ,  24 , and  26  in concentrations on the order of about 60 to about 80 percent by weight. In another embodiment, the tungsten and/or tungsten carbide particles can be added to selected sheath segments  22 ,  24 , and  26  in concentrations on the order of about 65 to about 80 percent by weight. In another embodiment, the tungsten and/or tungsten carbide particles can be added to selected sheath segments  22 ,  24 , and  26  in concentrations on the order of about 65 to about 75 percent by weight. 
     As one particular example, the tungsten and/or tungsten carbide particles may be added to the base polymeric material (also referred to as the first polymeric material) in sheath segment  22  in the amount of about 70 to about 75 percent by weight and, more preferably, about 73 to about 74 percent by weight. In an exemplary embodiment, the jet milled tungsten carbide material is added to the polymeric material in a weight of about 73.2 percent by weight. A concentration of 73.2 percent by weight tungsten carbide particles to PEBAX material corresponds to a concentration of about 15 percent by volume. Barium sulfate particles may be added to sheath segments  24  and  26  in the amount of about 20 to about 40 percent by weight and, more preferably, about 30 percent by weight. 
     If the catheter  10  is a guide catheter that is to be slit along its length during use, the addition of tungsten and/or tungsten carbide particles may offer exceptional echogenicity and, when added to the polymeric material, permit ready slitting along the length of catheter  10 . As a result, it may be desirable to balance the degree of echogenicity against the slittability of sheath  20 . As more tungsten and/or tungsten carbide particles are added to segments  22 ,  24 , and  26 , the material forming the sheath  20  becomes difficult to process and, in some cases, difficult to maneuver for insertion into and removal from the body of a patient. 
     Although polyether block amides can be loaded with tungsten and/or tungsten carbide particles to provide visibility using both fluoroscopy and ultrasonic imaging, it has been discovered that, in some instances, these compositions can potentially suffer from degradation due to temperature (e.g., oxidation) and/or humidity (e.g., hydrolysis). The degradation can adversely impact the flexibility and other properties of the segments in which the visibility materials are provided. 
     It has been found that by using an outer layer of an additional polymeric material (also referred to as the second polymeric material) that is more resistant to hydrolysis and/or oxidation than the base polymeric material, over a visibility material-loaded inner layer (e.g., a tungsten and/or tungsten carbide loaded polyether block amide core), the desired visibility can be attained, and in preferred embodiments, the degradation due to temperature and/or humidity can potentially be reduced. 
     A wide variety of polymers can be used as the base polymeric material. In certain embodiments, the base polymeric material is a thermoplastic material. Examples of polymers that can be used as the base polymeric material include, but are not limited to, polyolefins (e.g., polyethylene and/or polypropylene), fluoropolymers, polycarbonates, polyurethanes, polyesters, polyester ethers, polyether block amides, and combinations thereof. 
     A wide variety of polymers can be used as the additional polymeric material. In certain embodiments, the additional polymeric material is a thermoplastic material. Examples of polymers that can be used as the additional polymeric material include, but are not limited to, polyolefins (e.g., polyethylene and/or polypropylene), fluoropolymers, polycarbonates, polyurethanes, polyesters, polyester ethers, and combinations thereof. In certain embodiments, the softening temperature (e.g., melt temperature or glass transition temperature) of the additional polymeric material can be lower than the softening temperature of the base polymeric material. In certain embodiments, the softening temperature (e.g., melt temperature or glass transition temperature) of the additional polymeric material can be the same as or higher than the softening temperature of the base polymeric material. 
       FIG. 2  is an enlarged cross-sectional view of a sheath  120  to illustrate one such construction in which an inner visibility layer  140  that includes particles  142  in a base polymeric material (e.g., polyether block amide) is jacketed by an outer layer  150  that is constructed of an additional polymeric material. In some embodiments, the outer layer  150  may extend only over limited portions of the length of the sheath, for example, over only those portions of the sheath  120  that include the particulate loaded inner visibility layer  140  for which protection is desired. 
     In some medical devices (e.g., catheters), it can be desirable to use a high visibility band in the form of a visibility material loaded into a polymeric ring that is located between a distal segment and the proximal segment of the device. The high visibility band may preferably include a highly loaded tungsten and/or tungsten carbide particles in a polymeric carrier. The band (i.e., that forms the inner layer) can then be overlaid with an additional polymeric material (i.e., that forms the outer layer) loaded, for example, with BaSO 4 , with the additional polymeric material extending over the high visibility band and extending over the distal segment to the distal tip of the device. 
     Referring to  FIG. 3 , the polymeric carrier forming the band  240  may preferably be selected for its ability to be highly loaded with tungsten and/or tungsten carbide particles while retaining some level of flexibility. An example of one potentially suitable group of polymeric materials that can be used for the ring  240  are polyether block amides marketed under the trademark PEBAX. It may further be preferred that the polymeric materials of the ring  240  also remain slittable if the medical device is a guide catheter that is to be slit during use. 
     One embodiment of such a construction is depicted in  FIG. 3  which is an enlarged cross-sectional view of a portion of one sheath having an inner sleeve  270  over which an optional braided layer  260  is positioned. The sheath  220  also includes a band  240  that is highly loaded with tungsten and/or tungsten carbide particles  242 . The band  240  may preferably be positioned over the end of the braided layer  260  to, e.g., assist in containing the filaments or wires making up the braided layer in addition to providing visibility. All of the features, such as the band  240 , braided layer  260 , and inner sleeve  270  are then jacketed with an outer layer  250  in a manner similar to that described in connection with  FIG. 2 . 
     Medical devices that include a more hydrolytically stable outer layer over a visibility material-loaded inner layer or ring can be prepared by a wide variety of methods including, for example, coextrusion. For example, an inner layer including tungsten and/or tungsten carbide particles in polyether block amide and an outer layer including a polyurethane can be coextruded. Alternatively, the inner layer can be extruded, and the outer layer can subsequently be extruded on the inner layer. 
     For another example, the band that includes tungsten and/or tungsten carbide particles in the base polymer (e.g., polyether block amide, either in a ring construction or throughout the layer) can be constructed by a wide variety of convenient methods. An outer layer can then be formed over the inner components by a wide variety of convenient methods. Methods for constructing or forming the inner and outer layers include, but are not limited to, forming one or both layers on a mandrel; extruding one or both layers; injection molding one or both layers; compression molding one or both layers, dip coating, fusing, or combinations thereof. 
     Accordingly, methods of increasing the shelf life of at least a portion of a medical device are also provided herein. For example, an outer layer that is more resistant to hydrolysis and/or oxidation can be provided over a visibility material-loaded inner layer (e.g., a tungsten and/or tungsten carbide loaded polyether block amide core) to form at least a portion of a medical device. In preferred embodiments, a medical device that includes an outer layer that is more resistant to hydrolysis and/or oxidation can have increased shelf life in comparison to comparable medical devices without the outer layer. In certain embodiments, the outer layer includes a thermoplastic elastomer such as, e.g., a polyurethane. 
     ALTERNATIVE/ADDITIONAL APPROACHES: In addition, one or more of the following approaches may be used as an alternative to the approaches described above or in conjunction with the approaches described above to further increase the shelf life of the medical device. 
     Tungsten particles (as opposed to tungsten carbide particles) can be selected as a visibility material. Generally, tungsten particles may have less of a tendency to effect degradation (e.g., less catalytic filler) than tungsten carbide particles. 
     Polyurethane (as opposed to polyether block amide) can be selected as the base polymeric material into which the visibility particles are loaded. In some instances, the polyurethane may be limited to the portion of the medical device (e.g., catheter) that incorporates the visibility material. Polyurethanes can be more hydrolytically stable than, for example, polyether block amides. Tungsten and/or tungsten carbide particles may be used with this approach. 
     Tungsten carbide and/or tungsten particles can be used as the visibility material in a higher durometer polyether block amide (e.g., such as those available under the trade designation PEBAX MX 1205 polyether block amides from Arkema), with the loading level of the visibility material reduced to offset the higher durometer of the polymeric material such that the resulting composite material retains selected mechanical properties, e.g., still provides an atraumatic tip. 
     One or more additives can be used to enhance stability by reducing hydrolysis and/or oxidation. The additives may include one or more of: antioxidants (e.g., a peroxide decomposer such as IRGAFOS 168; a non-polar anti-oxidant such as IRGANOX 1098; metal deactivators such as IRGANOX MD-1024; etc.); anti-hydrolysis agents (e.g., carbodiimides such as, e.g., CARBAXOL, etc.); etc. 
     The medical device can be sterilized using ethylene oxide or other sterilization methodologies, and the sterile pouch can be placed into a bag that is impervious to moisture and/or oxygen. Optionally, this bag can be back filled with a dry (inert) gas, such as nitrogen, argon, and the like, and then the bag can be sealed. In another embodiment, the medical device pouch can be placed into a bag that is impervious to moisture and/or oxygen, a dessicant can be added to adsorb any moisture present in the bag, and then the bag can be sealed. For example, the medical device can be sterilized and placed in a moisture proof package that includes added dessicant, the package can be purged with a dry (inert) gas, and the package sealed. For embodiments in which at least a portion of the medical device includes a hydrophilic polymer, the bag can be purged with a humidified gas such that the relative humidity is less than or equal to about 30 percent to prevent unnecessary drying of the hydrophilic polymer. 
     The complete disclosure of the patents, patent documents, and publications cited in the Background, the Detailed Description of Exemplary Embodiments, and elsewhere herein are incorporated by reference in their entirety as if each were individually incorporated. 
     Illustrative embodiments of this disclosure are discussed and reference has been made to possible variations within the scope of this disclosure. These and other variations and modifications in the disclosure will be apparent without departing from the scope of the disclosure, and it should be understood that this disclosure is not limited to the illustrative embodiments set forth herein. Accordingly, the disclosure is to be limited only by the claims provided below and equivalents thereof.