Patent Publication Number: US-2003233141-A1

Title: Stent coated with stent graft and method therefor

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates generally to stents and stent grafts, and particularly to a stent coated with a stent graft.  
       BACKGROUND OF THE INVENTION  
       [0002] Stents, such as vascular stents, may be deployed at a narrowed site in a vessel of a patient for widening the vessel lumen and circumferentially supporting the vessel wall. The stent may typically have a small cross-sectional diameter and/or profile for introducing the stent into the affected vessel lumen, and the stent may be expandable after placement in the vessel lumen.  
       [0003] There are many kinds of constructions of stents, such as but not limited to, bent-wire stents, wire mesh stents, flat metal sheets formed into a stent shape, metal cannula stents with flexible regions or articulations, or expandable stents (e.g., made of a shape memory alloy, such as nickel-titanium alloy).  
       [0004] Portions of stents have been coated with different materials. For example, the metal wires of some stents have been coated with polytetrafluoroethylene (PTFE) to reduce friction during insertion of the stent in a lumen or to enhance or modify flows characteristics of a fluid (e.g., blood) flowing through the stent. As another example, the metal wires of some stents have been coated with radiopaque material to enhance the visibility of the stent in fluoroscopic or X-ray imaging. Coatings may protect against scratches, flaking and galvanic corrosion, for example.  
       [0005] Stent grafts are materials used to cover the stent. Grafts may be used for various purposes, such as but not limited to, enhancement of flow properties of fluids such as blood flowing through the stent, or protection of tissues against injury upon introduction of the stent in a body lumen. Stent grafts may be made in a variety of manners. For example, stent grafts are known that comprise a plastic flexible sleeve slipped over the stent and bonded or sewn thereto.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention seeks to provide an improved stent coated with a stent graft. In one example, the stent may be manufactured by coating the stent in an elastomeric (for example, an elastomeric polymer, such as silicone rubber) dispersion, wherein the elastomeric material cures and forms interior and exterior coatings on the stent. Apertures in the stent graft may be formed during or after the coating process.  
       [0007] There is thus provided in accordance with a an embodiment of the invention a method for manufacturing a stent comprising coating a stent body in an elastomeric material to form an elastomeric film coating over exterior and interior surfaces of the stent body over a longitudinal length thereof, the stent body comprising a plurality of structural members connected to one another with openings formed between at least a portion of the structural members, and the elastomeric film coating extending over the openings and the structural members. The coating may be cured afterwards.  
       [0008] In accordance with an embodiment of the invention the elastomeric material comprises an elastomer dispersed in a solvent, such as but not limited to, a silicone elastomer dispersed in xylene.  
       [0009] Further in accordance with a an embodiment of the invention a mandrel is placed in an interior portion of the stent body prior to coating the stent body in the elastomeric material.  
       [0010] Still further in accordance with an embodiment of the invention the elastomeric material covers the interior surface of the stent body between the stent body and the mandrel.  
       [0011] In accordance with a an embodiment of the invention a smoother elastomeric film coating is formed over the interior surface of the stent body than over the exterior surface thereof.  
       [0012] Further in accordance with an embodiment of the invention one or more apertures are formed through a thickness of the elastomeric film coating.  
       [0013] There is also provided in accordance with a an embodiment of the invention a stent comprising a stent body comprising a plurality of structural members connected to one another with openings formed between at least a portion of the structural members, and a stent graft comprising an elastomeric film coating coated over exterior and interior surfaces of the stent body over a longitudinal length thereof, the elastomeric film coating extending over the openings and the structural members. The elastomeric material may include a radiopaque substance or a medicinal substance. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:  
     [0015]FIG. 1 is a simplified pictorial illustration of a stent prior to coating with an elastomeric material, in accordance with an embodiment of the invention;  
     [0016]FIG. 2 is a simplified pictorial illustration of the stent of FIG. 1 during coating with the elastomeric material, in accordance with an embodiment of the invention; and  
     [0017]FIGS. 3 and 4 are simplified pictorial and sectional illustrations, respectively, of the stent of FIG. 1 coated with the elastomeric material, in accordance with an embodiment of the invention, FIG. 4 being taken along lines IV-IV in FIG. 3. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT  
     [0018] Reference is now made to FIG. 1, which illustrates a stent  10 , comprising a stent body  12  made of any suitable biocompatible, and preferably flexible material, such as but not limited to, a shape memory alloy (e.g., a nickel-titanium alloy) or a stainless steel alloy. Stent body  12  may be constructed of a plurality of structural members  14  connected to one another with openings  16  formed between at least some of structural members  14 . Structural member  14  may comprise, without limitation, a strut, radial element, or longitudinal element, and may be made from wire, cut stock, or other materials. The invention is not limited to any particular stent construction. A mandrel  18  may be placed in an interior portion  20  of stent body  12 , as indicated by arrow  21  in FIG. 1.  
     [0019] Reference is now made to FIG. 2. After mandrel  18  has been inserted in stent body  12 , stent body  12  may be coated with an elastomeric material  22 . Stent body  12  may be dipped in elastomeric material  22 , or elastomeric material  22  may be otherwise applied on stent body  12 . Elastomeric material  22  may cover the interior surface of stent body  12  between stent body  12  and mandrel  18 . Elastomeric material  22  may comprise an elastomer dispersed in a solvent. For example, elastomeric material  22  may comprise a two-component silicone elastomer dispersed in xylene, such as the MED-66xx silicone dispersion elastomers (e.g., those approved for unrestricted use for over 29 days) commercially available from NuSil Technology, Carpinteria, Calif., USA. Other dispersion silicone rubbers or polymers may also be used. After coating, elastomeric material  22  may be cured, such as in accordance with manufacturer&#39;s instructions.  
     [0020] Coating stent body  12  with elastomeric material  22  may form a stent graft comprising an elastomeric film coating  30  over exterior and interior surfaces of stent body  12  over a longitudinal length thereof, as seen in FIG. 3. The elastomeric film coating  30  may extend over openings  16  and structural members  14 . The engineering properties of elastomeric material  22  may be selected to control viscosity, coating ability, surface tension and other factors that may affect how elastomeric material  22  covers the openings  16  (e.g., what size opening may be covered) and structural members  14  (e.g., what thickness of coating is obtained). The stent graft so obtained may be flexible, contractible, expandable and stretchable. For example, the stent with the stent graft of the invention may be compressed for introduction into a body lumen with a very small diameter catheter introducer and expanded after placement in the lumen to a much larger diameter.  
     [0021] As seen in FIG. 4, the elastomeric film coating  30  formed over the interior surface of stent body  12  may be smooth, if mandrel  18  is smooth. The elastomeric film coating  30  formed over the exterior surface of stent body  12  may be as smooth, smoother or less smooth. In the illustrated embodiment, the elastomeric film coating  30  formed over the exterior surface of stent body  12  is wavy, conforming to the contour of the outer surface of the stent  10 , and not as smooth as the interior coating.  
     [0022] In accordance with an embodiment of the invention, elastomeric film coating  30  may be porous or non-porous.  
     [0023] In accordance with an embodiment of the invention, one or more apertures  32  may be formed through a thickness of elastomeric film coating  30 , as seen in FIG. 4. Apertures  32  may be formed by pricking the coating  30  after curing thereof. Alternatively, apertures  32  may be formed during the casting or coating process, by providing mandrel  18  with small spike-like protrusions that protrude through stent body  12 . The elastomeric material  22  may be wiped over the exterior surface of the stent body  12 , with the result that no elastomeric material remains at the extremities of the protrusions. Such a technique may form apertures  32  in the cured elastomeric film coating  30  at the sites of the protrusions. It is appreciated that other techniques may be used to form apertures  32 .  
     [0024] Elastomeric material  22  may comprise different additives for enhancing physical, mechanical, medicinal or other properties thereof. For example, elastomeric material  22  may be mixed with a radiopaque substance  24  (FIG. 2) for enhancing the visibility of stent  10  in fluoroscopic or X-ray imaging. As another example, elastomeric material  22  may be mixed with a medicinal substance  26 , for introduction into a patient, such as by means of dissolving, absorption, osmosis or iontophoresis, for example. Alternatively, these substances may be applied over the elastomeric material  22  after curing thereof.  
     [0025] Stent body  12  does not have to be straight, and may be bent or otherwise formed to a variety of shapes and cross-sections. For example, as seen in FIG. 4, stent body  12  may be formed with a non-uniform cross-section  34 , such as but not limited to, a generally cylindrical shape with a nozzle, venturi or constriction, which may serve to control flow of a substance in the lumen where stent  10  is positioned, such as reducing turbulent flow. The elastomeric film coating  30  may conform to the shape of the non-uniform cross-section  34 . Alternatively, the elastomeric film coating  30  may be used to form the non-uniform cross-section  34  to control flow of the substance in the lumen.  
     [0026] The elastomeric film coating  30  may be uniform and homogeneous. Alternatively, the elastomeric film coating  30  may comprise a non-homogeneous coating comprising different elastomeric materials with different properties, such as but not limited to, different stretching properties, flexibility, thermal conductivity, tensile strength and viscosity, to name a few. Different portions of the stent may be coated with different kinds of elastomeric materials.  
     [0027] It will be appreciated by person skilled in the art, that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the present invention is defined only by the claims that follow: