Abstract:
A tubular, expandable prosthesis comprises a framework with a plurality of openings therethrough and a carbon nanotube sheet. The carbon nanotube sheet extends across at least one of the openings.

Description:
BACKGROUND  
       [0001]     The body includes various passageways such as arteries, other blood vessels, and other body lumens. These passageways sometimes become occluded or weakened. For example, the passageways can be occluded by a tumor, restricted by plaque, or weakened by an aneurysm. When this occurs, the passageway can be reopened or reinforced, or even replaced, with a medical endoprosthesis. An endoprosthesis is typically a tubular member that is placed in a lumen in the body. Examples of endoprostheses include but are not limited to stents and covered stents, sometimes called ‘stent-grafts’ and other expandable, tubular frameworks.  
         [0002]     Endoprostheses can be delivered inside the body in a compacted or reduced-size form by a catheter. Upon reaching the site, the endoprosthesis is expanded, for example, so that it can contact the walls of the lumen.  
         [0003]     In one delivery technique, the endoprosthesis is formed of a material that can be reversibly compacted and expanded, e.g., elastically or through a material phase transition. During introduction into the body, the endoprosthesis is restrained in a compacted condition. Upon reaching the desired implantation site, the restraint is removed, for example, by retracting a restraining device such as an outer sheath, enabling the endoprosthesis to self expand by its own internal restoring force.  
         [0004]     In another technique, a force may be applied to the endoprosthesis to expand it radially. For example, the catheter may carry a balloon, which carries a balloon-expandable endoprosthesis. The balloon can be inflated to deform and to fix the endoprosthesis at a predetermined position in contact with the lumen wall. The balloon can then be deflated, and the catheter withdrawn.  
         [0005]     In some cases, the stent is to be positioned at a location in which vulnerable plaque (i.e. a lipid pool) is residing in the artery wall. If the vulnerable plaque is not treated, problems may arise when the wall allows the plaque to be released into the blood stream. This release may result in instant clotting of the vascular system at the location of the vulnerable plaque as well as instant clotting downstream from the location the plaque was released thereby reducing or completely stopping the flow of blood. In treating such a portion of the artery wall, care must be taken in order to avoid any rupture due to the pressure exerted by the stent or delivery system on the vulnerable plaque. Especially during placement of the stent rotational movement of the unfolding stent due to the unfolding balloon might result in high circumferential oriented shear forces. Stents typically provide a uniform radial pressure in all directions; this pressure may cause a rupture in the area of the plaque, as might the combination of radial pressure and shear forces.  
         [0006]     For these reasons, it would be desirable to both provide an improved endoluminal device which would exert less pressure on the vulnerable plaque while exerting radial pressure sufficient to maintain the fixation of the endoluminal device within the lumen and to reduce the or eliminate the shear forces that the stent is exerting on the membrane of the vulnerable plaque.  
         [0007]     All US patents and applications and all other published documents mentioned anywhere in this disclosure are incorporated herein by reference in their entirety.  
         [0008]     Without limiting the scope of the invention a brief summary of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.  
         [0009]     A brief abstract of the technical disclosure in the specification is provided as well for the purposes of complying with 37 C.F.R. 1.72.  
       SUMMARY  
       [0010]     In at least one embodiment of the invention, a stent comprises a framework with a plurality of openings therethrough and carbon nanotube sheet or “bucky paper”. The carbon nanotube sheet may extend across at least one of the openings or across a plurality of openings in the framework. The carbon nanotube sheet may be disposed within the interior of the framework and/or about the exterior of the framework and/or between exterior and interior of the framework.  
         [0011]     In at least one embodiment of the invention, the framework of the stent may include a plurality of interconnected struts, where the struts form a more rigid portion of the framework and a less rigid portion of the framework. The carbon nanotube sheet may extend across at least a portion of the more rigid portion.  
         [0012]     In at least one embodiment of the invention, the framework of the stent may include a plurality of interconnected cells including expandable cells and non-expandable cells, wherein the carbon nanotube sheet may extend across one or more non-expandable cells. Though maintaining the substantially same shape throughout delivery, the non-expandable cells may be capable of flexing when the expandable portions of the framework of the stent expand from an unexpanded state to an expanded state.  
         [0013]     The carbon nanotube sheet may be applied to the framework along the periphery of the carbon nanotube sheet and/or along other regions along the carbon nanotube sheet.  
         [0014]     In at least one embodiment of the invention, the carbon nanotube sheet may be between portions of the framework.  
         [0015]     In at least one embodiment of the invention, the framework may have a distal end and a proximal end wherein the distal end and the proximal end may be uniformly expandable about the circumference of the framework. Desirably, the ends will be capable of exerting a substantially uniform radial pressure. In the case of non-uniform vessels, for example vessels of non-uniform diameter, the stent will desirably exert different radial outward forces at the two ends of the stent.  
         [0016]     In at least one embodiment of the invention, a therapeutic agent may be applied to the stent or the carbon canotube sheet. The agent may be on the surface of the stent and/or within the stent framework. In at least one embodiment, the carbon nanotube has strips of polymer which have a therapeutic agent within them.  
         [0017]     In at least one embodiment of the invention, a SIBS sheet (e.g. polystyrene-polyisobutylene-polystyrene) may be used in affixing at least one carbon nanotube sheet to the framework. The SIBS sheet may be on the interior of the stent between the stent framework and a carbon nanotube sheet. In at least one embodiment the SIBS sheet may be on the stent framework and between two carbon nanotube sheets.  
         [0018]     In at least one embodiment of the invention, at least one carbon nanotube sheet may be affixed to the framework by annealing. In at least one embodiment, a carbon nanotube sheet may be affixed to the framework by toluene treatment. In at least one embodiment, a carbon nanotube sheet may be affixed to a polymer framework by toluene treatment.  
         [0019]     In at least one embodiment of the invention, at least one carbon nanotube sheet may be sprayed onto the exterior of the framework. In at least one embodiment, carbon nanotubes in solution are sprayed. In at least one embodiment, carbon nanotubes in a solution comprising tetrahydrofuran THF are sprayed onto the exterior of the framework. In at least one embodiment, a carbon nanotube sheet may be affixed to the interior of the framework in order to provide an additional backing for at least one carbon nanotube sheet being sprayed on the exterior of the stent framework.  
         [0020]     In at least one embodiment, a sheet of carbon nanotube is affixed to the framework by brushing on a solution comprising carbon nanotubes which then dries onto the framework. In at least one embodiment, a sheet of carbon nanotube is affixed to the framework by dipping the framework into a solution comprising carbon nanotubes which then dries onto the framework. In at least one embodiment, a sheet of carbon nanotube is affixed to the framework by microdropping a solution comprising carbon nanotubes which then dries onto the framework.  
         [0021]     In at least one embodiment of the invention, the stent may be selected from the group consisting of self-expanding stents, balloon expandable stents, hybrid stents, polymer stents, and degradable stents. In at least one embodiment, the stent may have a single backbone running along the length of the stent, thereby forming the basic scaffold of the stent design (henceforth referred to as a backbone stent); the backbone may have affixed to it a strip of carbon nanotube.  
         [0022]     In at least one embodiment of the invention, at least one carbon nanotube sheet may cover at least one opening. In at least one embodiment of the invention, expansion of the at least one opening may be restricted by at least one carbon nanotube sheet which covers the at least one opening.  
         [0023]     In at least one embodiment of the invention, at least one of the non-expandable cells may be constructed of ceramic or ploymer.  
         [0024]     In at least one embodiment of the invention, the stent may comprise a rolled framework, the carbon nanotube sheet covering openings which are non-expanding.  
         [0025]     The invention is also directed to an expandable tubular insert for a bodily passage comprising a plurality of interconnected cells having openings therethrough. The insert includes expandable cells and cells which are non-expandable. Two or more of the non-expandable cells have one or more sidewalls in common. Desirably, one or more of the non-expandable cells have a maximum longitudinal length which is at least 50% of the maximum longitudinal length of at least one of the expandable cells. More desirably, one or more of the non-expandable cells have a maximum longitudinal length which is at least 75% of the maximum longitudinal length of at least one of the expandable cells. Most desirably, one or more of the non-expandable cells have a maximum longitudinal length which is substantially equal to the maximum longitudinal length of at least one of the expandable cells. The term “substantially equal to” is intended to include variations of up to 5%.  
         [0026]     Desirably, the non-expandable cells are not located at either the proximal or distal end of the stent.  
         [0027]     In at least one embodiment of the invention, the tubular insert may further comprise carbon nanotube sheet extending across at least one of the openings in the non-expandable cells.  
         [0028]     The invention is also directed to any of the inventive devices disclosed herein disposed about a delivery device such as a catheter. The device may optionally be configured to release a therapeutic agent. In use, the therapeutic agent will desirably be delivered in the region of the carbon nanotube sheet.  
         [0029]     These and other embodiments which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages and objectives obtained by its use, reference should be made to the drawings which form a further part hereof and the accompanying descriptive matter, in which there is illustrated and described a embodiments of the invention. 
     
    
     DESCRIPTION of DRAWINGS  
       [0030]      FIGS. 1-2  are flat views of a stent with one portion having a carbon nanotube sheet.  
         [0031]      FIG. 3  is a flat view of a stent having more rigid portions which may be covered with a carbon nanotube sheet.  
         [0032]      FIG. 4  is a flat view of a stent with the expandable portion having a carbon nanotube sheet.  
         [0033]      FIG. 5  is a perspective view of a stent with a carbon nanotube sheet portion.  
         [0034]      FIG. 6   a  is a cross-sectional view of a stent in an unexpanded state with a carbon nanotube sheet applied.  
         [0035]      FIG. 6   b  is a cross-sectional view of a stent in an expanded state with a carbon nanotube sheet applied.  
         [0036]      FIG. 7   a  is a cross-sectional view of a rolled stent in an unexpanded state with a carbon nanotube sheet applied.  
         [0037]      FIG. 7   b  is a cross-sectional view of a rolled stent in an expanded state with a carbon nanotube sheet applied.  
         [0038]      FIG. 8   a  is a cross-sectional view of a stent with polymer strips applied to the carbon nanotube sheet.  
         [0039]      FIG. 8   b  is a cross-sectional view of a stent with polymer strips within the carbon nanotube sheet.  
         [0040]      FIG. 9  is a cross-sectional view of a stent with a SIBS sheet used in applying carbon nanotube sheets.  
         [0041]      FIG. 10  is a cross-sectional view of a stent with two carbon nanotube sheets applied.  
         [0042]      FIG. 11  is a cross-sectional view of a stent with a carbon nanotube sheet applied and another carbon nanotube sheet which is sprayed on.  
         [0043]      FIG. 12  is a cross-sectional view of a stent and delivery device within a lumen showing the stent being delivered and therapeutic agent applied.  
         [0044]      FIG. 13  is a cross-sectional view of a stent and delivery device within a lumen showing the delivered stent and the delivered therapeutic agent.  
     
    
     DETAILED DESCRIPTION  
       [0045]     While this invention may be embodied in many different forms, there are described in detail herein specific embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.  
         [0046]     For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated.  
         [0047]     Also for the purposes of this disclosure, the term ‘endoprosthesis’ refers to an expandable prosthesis for implantation into a body lumen or vessel and includes devices such as stents, grafts, stent-grafts, vena cava filters, tubular expandable frameworks (regardless of whether they can support a vessel), etc.  
         [0048]     Referring to  FIG. 1 , a stent  10  is shown generally having an expandable portion  20  and a non-expandable portion  30 . The non-expandable portion  30  may be flexible longitudinally. The expandable portion  20  may have portions that smoothly transition into the non-expandable portion  30 . In some embodiments this transition is gradual. This can occur when, for example, there is a gradual change in flexibility over a desired region. The change in flexibility can be accomplished by, for example, a change in framework geometry and/or a change in some other framework parameter(s) such as thickness of the struts, width of the struts or combinations thereof. In some embodiments the transition is abrupt, for instance as when an expandable portion  20  and a non-expandable portion  30  are welded together. The non-expandable portion  30  may have less structure than the expandable portion  20 .  
         [0049]     The non-expandable portion may have one or more carbon nanotube sheets  40  applied to it. The carbon nanotube sheet  40  may disposed on the interior of the framework and/or on the exterior of the framework. The carbon nanotube sheet desirably will allow red blood cells through to feed the tissue but will be impervious to lipids. Typically, the carbon nanotube sheet will be provided only in the less flexible or non-flexible portion of the framework. Desirably, the carbon nanotube sheet will be operatively associated with a portion of a framework which will be used to cover a lipid pool such that lipids are not released from beneath the carbon nanotube sheet. In some embodiments, the carbon nanotube sheet  40  may only be attached on its periphery to the framework  50  of the stent  10 .  
         [0050]     Carbon nanotube is described in greater detail in copending U.S. application Ser. No. 10/270815 published as US 20040073251, incorporated herein by reference.  
         [0051]     In  FIG. 2 , the non-expandable portion  30  has less structure than in  FIG. 1 . Thus, the amount of stent material (e.g. metal or polymeric material) per unit area is less in the non-expandable portion than in the expandable portion. In some embodiments, the carbon nanotube sheet  40  may be supported only on its periphery by framework  50  of the stent  10 .  
         [0052]     As shown in  FIG. 3  there may be more than one non-expandable portion  30 . At least one connector  45  may be disposed longitudinally between the non-expandable portions  30 . The connector may have one or more curves or may be straight. The connector may be parallel to the longitudinal axis or may extend at a non-zero angle relative to the longitudinal axis. The ends of the connector may lie along a line parallel to the longitudinal axis of the stent. It is also within the scope of the invention for the ends of the connector to lie along two separate lines parallel to the longitudinal axis of the stent. In such a case, the ends of the connectors are not considered to be aligned circumferentially. It is also with the scope of the invention for there to be a plurality of non-expandable portions which are separated from one another by expandable portions. Some or all of the non-expanding portions  30  may be rigid and/or may have a greater concentration of structure than the expandable portions  20 .  
         [0053]     A carbon nanotube sheet may be applied to one or more of the non-expandable portions  30 . In some embodiments a single sheet of carbon nanotube covers more than one non-expandable portion  30  and the at least one connector  45  between the two non-expandable portions.  
         [0054]     In some embodiments, as illustrated in  FIG. 4 , the carbon nanotube sheet may be applied to at least a portion of the expandable portion  40  of the stent  10 . In some embodiments, the carbon nanotube sheet  40  may be applied to both the non-expandable portion(s)  30  and the expandable portion(s)  20 . Desirably, particularly in the case where the carbon nanotube sheet is provided in the expandable portion(s), the carbon nanotube sheet may expand or unfold from a folded condition.  
         [0055]     The region with carbon nanotube sheet may be at one or both ends of the stent or may be disposed between the ends of the stent, as illustrated in  FIG. 5 . Stent  10 , shown in  FIG. 5 , includes a patch of carbon nanotube sheet  40  between the ends of the stent and extending over a portion of the circumference of the framework of the stent but not over the entirety of the circumference of the framework.  
         [0056]     Any of the embodiments disclosed herein may be provided in self-expanding, balloon expandable, or hybrid designs. In the case of self-expanding stents, the portion of the stent having the carbon nanotube sheet patch  40  may not exert as much radial pressure as the other portions of the stent  10 .  
         [0057]     In  FIG. 6   a , a stent is shown in the unexpanded state having a carbon nanotube sheet  40 . The sheet  40  may be attached to the stent framework  50  at a single connection point  55 . The stent framework may be in the form of a backbone stent wherein the connection point  55  is located on the “backbone” of the framework  50 . The unattached portions of sheet  40  may freely glide along the framework  50  such that when the stent framework  50  is expanded, as shown in  FIG. 6   b , the sheet  40  moves with the expansion without restricting the expansion.  
         [0058]      FIG. 7   a  illustrates a rolled stent framework  50  in the unexpanded state having a carbon nanotube sheet  40  applied. In the expanded state shown in  FIG. 7   b , the rolled stent framework  50  unrolls while the sheet  40  continues to cover the same portion of the framework  50  covered in the unexpanded state.  
         [0059]     A therapeutic agent may be applied to the carbon nanotube sheet  40  as shown in  FIGS. 8   a  and  8   b . Polymer strips  60  containing the therapeutic agent may be applied to the surface of the carbon nanotube sheet  40  or within the sheet  40 .  
         [0060]     As shown in  FIG. 9 a  SIBS sheet  65  may be used in applying one or more carbon nanotube sheets  40  to the stent framework  50 .  FIG. 10  illustrates two carbon nanotube sheets  40  applied to the stent framework  50 . The sheets  40  may be affixed to the framework  50  through annealing, or through toluene treatment in the case of a polymer framework  50 .  
         [0061]     A carbon nanotube sheet may also be applied to the stent framework  50  by spraying on the sheet  40 ′ by a sprayer  68  as shown in  FIG. 11 . An additional carbon nanotube sheet  40  may be applied to the framework  50  before the sprayed on sheet  50  is applied. In some embodiments the additional sheet  40  is not applied.  
         [0062]     In some embodiments the stent framework may degrade within the body lumen such that only the carbon nanotube sheet remains at the treated site.  
         [0063]     The invention is also directed to methods of stenting vessels using stents comprising carbon nanotube sheet.  
         [0064]     In  FIG. 12 , an embodiment is shown in which a stent is delivered to a portion of a body lumen  80  having a lipid pool  70  or “vulnerable plaque”. The delivery device  90  may release one end of the stent  10  distal to the lipid pool  70 . The distal most end of the stent  10  may comprise an expandable portion which may expand and exert radial pressure on the lumen  80 . The carbon nanotube sheet portion  40  may then be partially released and positioned such that, upon complete delivery of the stent  10 , the carbon nanotube sheet portion  40  may be disposed upon the lipid pool  70 . The carbon nanotube sheet portion  40  may exert less radial pressure than the expandable portions  20  of the stent  10  such that the stent may maintain the patency of the lumen  80  while at the same time covering the lipid pool portion  70  without rupturing it due to excessive radial pressure. In at least one embodiment, as the stent  10  is being delivered, a therapeutic agent  100  may be released upon the lipid pool  70  such that upon full delivery the carbon nanotube sheet portion  40  may be disposed upon both the lipid pool  70  and the therapeutic agent  100 .  
         [0065]      FIG. 13  shows a stent  10  which has been deployed in a vessel with vulnerable plaque. The stent is held in position in lumen  80  because of the expandable portions  20  which have circumferential stiffness both proximally and distally of the lipid pool  70 . The stent is aligned such that the carbon nanotube sheet covers the vulnerable plaque to prevent or hinder the release of lipids into the lumen  80 . In addition, a seal may be created about a therapeutic agent  100  such that the therapeutic agent is spread onto the vulnerable plaque. In at least one embodiment, the stent framework  50  or other element of the device  10  may comprise one or more therapeutic agents. In some embodiments, the agent is placed on the stent in the form of a coating. In at least one embodiment, the coating includes at least one therapeutic agent and at least one polymer agent.  
         [0066]     A therapeutic agent may be a drug or other pharmaceutical product such as non-genetic agents, genetic agents, cellular material, etc. Some examples of suitable non-genetic therapeutic agents include but are not limited to: anti-thrombogenic agents such as heparin, heparin derivatives, vascular cell growth promoters, growth factor inhibitors, Paclitaxel, etc. Where an agent includes a genetic therapeutic agent, such a genetic agent may include but is not limited to: DNA, RNA and their respective derivatives and/or components; hedgehog proteins, etc. Where a therapeutic agent includes cellular material, the cellular material may include but is not limited to: cells of human origin and/or non-human origin as well as their respective components and/or derivatives thereof. Where the therapeutic agent includes a polymer agent, the polymer agent may be a polystyrene-polyisobutylene-polystyrene triblock copolymer (SIBS), polyethylene oxide, silicone rubber and/or any other suitable substrate.  
         [0067]     The use of carbon nanotube sheet has been discussed above with respect to stents. More generally, it is within the scope of the invention to use carbon nanotube sheet with endoprostheses. The carbon nanotube sheet may be associated with the entirety of the endoprosthesis or with less than the entirety of the endoprosthesis. Desirably, the endoprosthesis will include non-expandable cells and expandable cells and expandable cells and the carbon nanotube sheet will be disposed on or in one or more of the non-expandable cells, as is discussed specifically for stents.  
         [0068]     Desirably, the portion of the inventive stents in particular and inventive endoprostheses in general that includes the carbon nanotube sheet will exert a lesser outward force as compared to those regions that do not include carbon nanotube sheet. This may be of particular importance where the portion of the device with the carbon nanotube sheet is disposed against a weaker region of a vessel or a region with vulnerable plaque.  
         [0069]     The inventive stents and, more generally, endoprostheses may find use in coronary arteries, renal arteries, peripheral arteries including illiac arteries, arteries of the neck and cerebral arteries. The stents and, more generally, endoprostheses of the present invention, however, are not limited to use in the vascular system and may also be advantageously employed in other body structures, including but not limited to arteries, veins, biliary ducts, urethras, fallopian tubes, bronchial tubes, the trachea, the esophagus and the prostate.  
         [0070]     The inventive stents and endoprostheses disclosed herein may be at least partially constructed of any of a variety of materials such as stainless steel, nickel, titanium, nitinol, platinum, gold, chrome, cobalt, as well as any other metals and their combinations or alloys. In some embodiments, the endoprosthesis may be at least partially constructed of a polymer material. In some embodiments, the endoprosthesis may be at least partially constructed of a shape-memory polymer or material. In some embodiments, the endoprosthesis may be balloon expandable, self-expandable, hybrid expandable or a combination thereof. In some embodiments, the endoprosthesis may include one or more radiopaque members. In some embodiments, the endoprosthesis may include one or more therapeutic and/or lubricious coatings applied thereto. In another embodiment the invention is also directed to the expandable framework geometries shown herein.  
         [0071]     The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. The various elements shown in the individual figures and described above may be combined or modified for combination as desired. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.  
         [0072]     Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.  
         [0073]     The description above describes several embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.