Patent Publication Number: US-2011071562-A1

Title: Medical devices

Description:
CLAIM OF PRIORITY 
     This application claims priority under 35 USC §119(e) to U.S. Provisional Patent Application Ser. No. 60/488,644, filed on Jul. 18, 2003, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The invention relates to medical devices, such as, for example, catheters. 
     BACKGROUND 
     The body includes various blood vessels, for example, arteries. Sometimes, a wall portion of a blood vessel becomes stretched and thin such that the blood vessel develops a bulge, or an aneurysm. An aneurysm is potentially dangerous because it can break open, thereby causing the vessel to bleed. Bleeding can result in a stroke (e.g., in a brain aneurysm) or death. 
     One method of treating an aneurysm is to fill the aneurysm. For example, the aneurysm can be filled with helically wound coils or braids, sometimes called vaso-occlusive devices. The vaso-occlusive devices can promote formation of a clot and a mass surrounding the devices that fill and seal the aneurysm. As a result, the weakened wall of the vessel is not exposed, e.g., to pulsing blood pressure in the vessel, and the possibility of the aneurysm breaking can be reduced. 
     The vaso-occlusive devices can be delivered into an aneurysm by endovascular techniques using a guidewire and a catheter. The guidewire is first steered through the body and to the aneurysm. Next, the catheter is slid over the emplaced guidewire and tracked to the aneurysm, e.g., at the mouth of the aneurysm, and the guidewire is removed. The vaso-occlusive devices can then be delivered through a lumen of the catheter and into the aneurysm. 
     SUMMARY 
     The invention relates to medical devices. 
     In one aspect, the invention features a catheter having a portion, e.g., a distal portion, including a shape memory polymer. The catheter can be delivered to a target site, e.g., near an aneurysm, in a first configuration; and at the target site, the portion of the catheter can be changed to a second, different configuration. For example, the catheter can be delivered with the distal portion in a straight position, and subsequently, the distal portion can be changed to a bent configuration that facilitates delivery of vaso-occlusive devices into the aneurysm. 
     The shape memory polymer portion allows the catheter to be delivered, for example, without relying on a guidewire to straighten the catheter and/or without being deformed by a tortuous vasculature. After changing configuration, the shape memory polymer portion provides a stable (e.g., non-slipping) pathway for delivery of the vaso-occlusive devices. By securely staying in the predetermined changed configuration, the catheter reduces the likelihood of buckling or other forces that can exert stress on the aneurysm. 
     In another aspect, the invention features a medical catheter including a tubular member having a first portion including a shape memory polymer. 
     Embodiments can include one or more of the following features. The first portion is a distal portion of the tubular member, or a distalmost portion of the tubular member. The first portion further includes a material susceptible to heating by magnetic effects. The tubular member has a body including a polymer different than the shape memory polymer. An end of the body can be connected to an end of the first portion. The first portion surrounds a portion of the body. 
     The shape memory polymer can include, for example, polynorbonene, polycaprolactone, polyene, nylon, polycyclooctene (PCO), a blend of polcyclooctene and styrenebutadiene rubber, polyurethane, polyurethane copolymers, and/or a polyvinyl acetate/polyvinylidinefluoride. 
     The catheter can be in the form of a 5 French catheter or smaller. 
     The first portion can include a radiopaque material, a material visible by magnetic resonance imaging, and/or an ultrasound contrast agent. 
     In another aspect, the invention features a method including introducing a catheter to a target site, the catheter having a distal portion is a first configuration, and changing the distal portion from the first configuration to a second configuration. 
     Embodiments can include one or more of the following features. Changing the distal portion includes heating the distal portion, and/or applying radiofrequency energy to the distal portion. The method further includes passing a medical device, such as, for example, a vaso-occlusive device through the catheter. 
     The distal portion can be the distalmost portion of the catheter. The target site can be proximate an aneurysm. 
     In another aspect, the invention features a wire having a shape memory polymer coating over a portion of the wire, such as the tip of the wire. 
     Other aspect, features, and advantages of the invention will be apparent from the description of the preferred embodiments thereof and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is an illustration of an embodiment of a method treating an aneurysm. 
         FIG. 2A  is an illustration of an embodiment of a catheter in a generally straight position; and 
         FIG. 2B  is an illustration of the catheter of  FIG. 2A  in a bent position. 
         FIG. 3A  is an illustration of an embodiment of a catheter in a generally straight position; and 
         FIG. 3B  is an illustration of the catheter of  FIG. 3A  in a bent position. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a method  20  of treating an aneurysm  22  is shown. Method  20  includes delivering a guidewire  24  (e.g., a steerable guidewire) to aneurysm  22  using conventional endovascular techniques (arrow A). Next, a catheter  26  is passed over guidewire  24 , and advanced to near aneurysm  22  (arrow B). Catheter  26  includes a body  32  and a distal portion  28  including a shape memory polymer that is configured to remember a predetermined configuration. During advancement of catheter  26 , distal portion  28  is in a generally straight configuration (e.g., collinear with body  32 ), which allows the catheter to easily track a tortuous vascular path. Guidewire  24  is then removed (e.g., withdrawn proximally, arrow C). Next, distal portion  28  is changed from the straight configuration to the predetermined configuration (as shown, a bent configuration). Distal portion  28  is then introduced into aneurysm  22 , and vaso-occlusive coils  30  are introduced through catheter  26  and into the aneurysm, according to conventional methods. 
     Catheter  26  is generally an elongated tube having one or more lumens. Referring to  FIGS. 2A and 2B , catheter  26  generally includes body  32  and distal portion  28 . Body  32  can be a standard catheter shaft made of conventional, biocompatible polymers, as described in, e.g., U.S. Ser. No. 09/798,749, filed Mar. 2, 2001, and entitled “Multilayer Medical Balloon”. As shown, distal portion  28  is an extruded tube having a tapered portion. In some embodiments, referring to  FIGS. 3A and 3B , distal portion  28  is a sleeve that fits over a distal portion of body  32 . Body  32  can have a tapered distal end. Distal portion  28  can be attached to body  32 , for example, by laser welding, gluing with an epoxy, melt bonding, or heat shrinking In other embodiments, distal portion  28  can be a coating of a shape memory polymer applied to body  32 , e.g., by dipping the body into a solution containing a shape memory polymer. Distal portion  28  can be, for example, about six to ten inches long. 
     Distal portion  28  includes one or more shape memory polymers (SMPs). Suitable shape memory polymers include elastomers that exhibit melt or glass transitions at temperatures that are above body temperature, e.g., at about 40 to 50° C., and safe for use in the body. Examples of polymers include shape memory polyurethanes (available from Mitsubishi), polynorbornene (e.g., Norsorex (Mitsubishi)), polymethylmethacrylate (PMMA), poly(vinyl chloride), polyethylene (e.g., crystalline polyethylene), polyisoprene (e.g., trans-polyisoprene), styrene-butadiene copolymer, rubbers, or photocrosslinkable polymer including azo-dye, zwitterionic and other photochromic materials (as described in  Shape Memory Materials,  Otsuka and Wayman, Cambridge University Press, 1998). Other shape memory polymers include shape memory plastics available from MnemoScience GmbH Pauwelsstrasse 19, D-52074 Aachen, Germany. Other shape memory materials, such as thermoplastic polyurethanes and polyurethane copolymers, are described in provisional U.S. application Ser. No. ______, filed on Jul. 18, 2003, and entitled “Shape Memory Polymers Based on Semicrystalline Thermoplastic Polyurethanes Bearing Nanostructured Hard Segments”; Ge and Mather, “Synthesis of Thermoplastic Polyurethanes Bearing Nanostructured Hard Segments: New Shape Memory Polymers”; and U.S. Ser. No. 60/418,023, filed Oct. 11, 2002, and entitled “Endoprosthesis”, all hereby incorporated by reference in their entirety. The materials can be bioabsorbable or non-bioabsorbable. Mixtures of polymeric shape memory materials can be used. 
     In some embodiments, the shape memory polymer is crosslinked and/or crystalline. The degree of crosslinking and/or crystallinity is sufficient to resist excessive creep or stress relaxation, e.g., after the polymer is heated. Crosslinking can also be controlled to adjust the melt or glass transition temperature and transition temperature range. In some cases, a narrow transition range, e.g. 10° C., 5° C., or less, is desirable. Crosslinking can be achieved by application of radiation, such as e-beam, UV, gamma, x-ray radiation, or by heat-activated chemical crosslinking techniques (e.g., with peroxides). In some radiation crosslinking techniques, the polymer need not be substantially heated to achieve crosslinking 
     As noted above, the shape memory polymer is capable of exhibiting shape memory properties such that it can be configured to remember, e.g., to change to, a predetermined configuration or shape. In some embodiments, the shape memory polymer is formed or set to a primary (e.g., stress free) shape during crosslinking For example, distal portion  28  can be crosslinked in a bent configuration. Subsequently, the polymer can be formed into a temporary shape, for example, by heating the polymer to a softening point (e.g., T m  or T g ), deforming the polymer, and cooling the polymer to below a softening point. When the polymer is subsequently heated to above the softening temperature, the polymer can recover to its primary form. 
     A number of methods can be used to effect the transition of the polymer from its temporary configuration to its primary configuration. Catheter  26  can carry a heating device. For example, a resistive heater or radiofrequency (RF) heater can be provided in the interior of the catheter. Alternatively or in addition, the polymer can be compounded to include a material, such as magnetic particles, that is susceptible to heating by magnetic effects, such as hysteresis effects. A magnetic field can be imposed on the stent body by a source on a catheter or outside the body. Suitable magnetic particles are available as the Smartbond™ System from Triton Systems, Inc., Chelmsford, Mass. Heating by magnetic effects is discussed in U.S. Pat. No. 6,056,844. 
     In general, the size and configuration of catheter  26  is not limited. In some embodiments, catheter  26  is in the form of a 5 French catheter or smaller, e.g., a 4 French, 3 French, 2 French, or 1 French catheter. Catheter  26  can have a length of, for example, about 240 cm to about 3.5 meters. Examples of catheters include aneurysm catheters, guide catheters, urology catheters, and microcatheters (all available from Boston Scientific Corp., Natick, Mass.). 
     The angle at which distal portion  28  can be bent relative to body  32  can also vary. In some cases, the angle (φ) defined by distal portion  28  and body  32  ( FIG. 2B ) is between about 20° and about 180°. For example, the angle (φ) can be greater than or equal about 20°, 40°, 60°, 80°, 100°, 120°, 140°, or 160°; and/or less than or equal to about 180°, 160°, 140°, 120°, 100°, 80°, 60°, or 40°. 
     In some embodiments, distal portion  28  contains a radiopaque material, a material that is visible by magnetic resonance imaging (MRI), and/or an ultrasound contrast agent. The materials or agent allows catheter  26  to be tracked and monitored, e.g., by X-ray fluoroscopy, MRI, or ultrasound imaging. Examples of radiopaque materials include tantalum, tungsten, platinum, palladium, or gold. The radiopaque material, e.g., powder, can be mixed with the shape memory polymer. Alternatively or in addition, the radiopaque material, e.g., a band of radiopaque material, can be placed on catheter  26  at selected positions, such as, for example, adjacent to distal portion  28 . 
     Examples of MRI visible materials include non-ferrous metal-alloys containing paramagnetic elements (e.g., dysprosium or gadolinium) such as terbium-dysprosium, dysprosium, and gadolinium; non-ferrous metallic bands coated with an oxide or a carbide layer of dysprosium or gadolinium (e.g., Dy 2 O 3  or Gd 2 O 3 ); non-ferrous metals (e.g., copper, silver, platinum, or gold) coated with a layer of superparamagnetic material, such as nanocrystalline Fe 3 O 4 , CoFe 2 O 4 , MnFe 2 O 4 , or MgFe 2 O 4 ; and nanocrystalline particles of the transition metal oxides (e.g., oxides of Fe, Co, Ni). Powder of MRI visible materials can be mixed with the shape memory polymer. 
     The ultrasound contrast agent can be any material that enhances visibility during ultrasound imaging. An ultrasound contrast agent can include a suspension having trapped bubbles of sufficient size to deflect sound waves. 
     Distal portion  28  can include a drug or a therapeutic agent. For example, distal portion  28  can include an antithrombolytic agent, such as heparin, to reduce clotting on the catheter. Other examples of drugs or therapeutic agents are described in U.S. Ser. No. 10/232,265, filed Aug. 30, 2002, hereby incorporated by reference. 
     In some cases, the catheter can be formed into a desired shape by a user (such as a physician) at the time of a procedure, e.g., using heat (steam). The shape memory properties can be used to impart a predetermined shape, which the user can try. If the predetermined shape is not adequate (e.g., unsuccessful), the user can heat the shape memory material of the catheter outside the body and re-shape the catheter (e.g., using steam or hot water) to a second predetermined shape. 
     The following examples are illustrative and not intended to be limiting. 
     EXAMPLE  1 
     The following example shows a method of making a catheter having portion including a polycyclooctene/styrene butadiene rubber blend, a blend of shape memory polymers. Polycyclooctene and blends of shape memory polymers are described in U.S. Ser. No. 10/683,559, entitled “Crosslinked Polycyclooctene”, and U.S. Ser. No. 10/683,558, entitled “Blends of Amorphous and Semicrystalline Polymers Having Shape Memory Properties”, both filed on Oct. 10, 2003. 
     To form the blend, the polymers were compounded. Styrene butadiene rubber was cut in a Willy mill to 1-2 mm mesh. The rubber and the polycyclooctene were mixed in a ratio of 65% by weight polycyclooctene and 35% by weight styrene butadiene rubber, and ran in a dry blender for about 30 minutes. The mixture was then placed in a bra blender with two twin-screw head running at 20-25 RPM at 100° C. The blended mixture was then placed in a room temperature water bath and pelletized. 
     Next, the pellets were extruded. The pellets (about 500 grams) were extruded in a Davis Standard extruder (¾ to one inch) running with a feed temperature of about 50° C., a second zone at about 65° C., a third zone at about 80° C., and a die head temperature of about 80° C. The pellets were extruded through a tubular die and using pressurized air to help maintain the patency of the lumen of the extruded tube. The extruded tube was fed to a room temperature water bath and cut to length (e.g., about 6 inches). The tube can have, for example, a 0.0305 inch O.D. and a 0.027 inch I.D. 
     Next, the shape memory polymer tube (e.g., about 5 cm) was placed on a distal portion of a catheter. The catheter had a guidewire placed through the lumen of the catheter. The catheter was attached to a sleeving machine equipped with movable and heatable clamps. Next, a heat shrink tubing (available from Zeus or Target) was placed over the shape memory polymer tube. The clamps were heated to about 175° C. to about 200° C. and moved at a rate of 13.5-17 cm/min to shrink the heat shrink tubing and to secure the shape memory tubing to the catheter. Typically, only one pass of the clamps is needed. In some cases, the higher the concentration of styrene butadiene rubber in the blend, the higher the temperature is needed; for example, a blend including 35% by weight styrene butadiene was heated to about 195° C. 
     Then, the catheter was removed from the sleeving machine, and the heat shrink tubing was stripped from the catheter under a microscope. 
     The catheter was then shaped, e.g., into a curve (e.g., J shape) or a straight line. A shaping mandrel can be placed in the lumen of the catheter. 
     The catheter was then sent to a facility (such as Steris Isomedix) for crosslinking with gamma radiation. Depending on the thickness of the shape memory polymer portion, the polymer portion was irradiated with between about 1 and about 25 megarads. For microcatheters, about 1 megarad was irradiated. 
     EXAMPLE  2 
     A shape memory polymer solution was prepared by dissolving fifteen grams of polynorbonene (Nosorex, from Mitsubishi) and three grams of Kraton 1650 G (GLS Corp.) in 500 mL of xylene. The solution was heated to about 70° C. and stirred on a magnetic stirring plate at a low setting (about 50 rpm) for about 30 minutes. 
     A curved mandrel was inserted into a catheter (Imager catheter (urology) or Renegade catheter (neurology), available from Boston Scientific Corp.) to provide a curved catheter. The curved catheter (about 6-10 inches) was dipped into the shape memory solution. Depending on the rate at which the catheter was withdrawn from the solution, it is believed that the thickness of the shape memory polymer is between about 0.001-0.005 inch thick. The catheter was air dried for about twenty minutes. The mandrel was then removed. 
     The curved catheter was straightened by immersing the catheter in a 50° C. water bath. 
     The straight catheter can be returned to its curved shape by heating the catheter above body temperature, e.g., 45-50° C. 
     All publications, applications, references, and patents referred to above are incorporated by reference in their entirety. 
     Other embodiments are within the claims.