Abstract:
A system for protecting a stent includes an electroactive polymer (EAP) sleeve, a stent, a balloon catheter, and a voltage source. A voltage is applied to the EAP sleeve, whereupon the EAP sleeve expands. The stent, disposed about the balloon catheter is inserted into the region defined by the inner surface of the EAP sleeve. The voltage is removed, whereupon the EAP sleeve contracts.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
       [0002]     Not Applicable  
       BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     In some embodiments this invention relates to implantable medical devices, their manufacture, and methods of use. Some embodiments are directed to delivery systems, such as catheter systems of all types, which are utilized in the delivery of such devices.  
         [0005]     2. Description of the Related Art  
         [0006]     A stent is a medical device introduced to a body lumen and is well known in the art. Typically, a stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the stent in a radially reduced configuration, optionally restrained in a radially compressed configuration by a sheath and/or catheter, is delivered by a stent delivery system or “introducer” to the site where it is required. The introducer may enter the body from an access location outside the body, such as through the patient&#39;s skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means.  
         [0007]     Stents, grafts, stent-grafts, vena cava filters, expandable frameworks, and similar implantable medical devices, collectively referred to hereinafter as stents, are radially expandable endoprostheses which are typically intravascular implants capable of being implanted transluminally and enlarged radially after being introduced percutaneously. Stents may be implanted in a variety of body lumens or vessels such as within the vascular system, urinary tracts, bile ducts, fallopian tubes, coronary vessels, secondary vessels, etc. Stents may be used to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They may be self-expanding, expanded by an internal radial force, such as when mounted on a balloon, or a combination of self-expanding and balloon expandable (hybrid expandable).  
         [0008]     Stents may be created by methods including cutting or etching a design from a tubular stock, from a flat sheet which is cut or etched and which is subsequently rolled or from one or more interwoven wires or braids.  
         [0009]     Stents are often deployed to a location within a body lumen or vessel through the use of a stent delivery system. Such systems often comprise an elongate catheter about which the stent is mounted prior to deployment of the stent. A stent delivery system is assembled prior to use by crimping the stent onto a region of the catheter.  
         [0010]     Existing crimping devices and methods are described in, for example, U.S. Pat. No. 6,387,118; U.S. Pat. No. 6,108,886; U.S. Pat. No. 6,092,273; U.S. Pat. No. 6,082,990; U.S. Pat. No. 6,074,381; U.S. Pat. No. 6,063,102; U.S. Pat. No. 5,992,000; etc.  
         [0011]     An electroactive polymer refers to a polymer that acts as an insulating dielectric between two electrodes and may deflect upon application of a voltage difference between the two electrodes. Electroactive polymers (EAP) are materials such as polypyrrole, polyalanine, polyacetylene, polythiophene and polyvinylidene difluoride (PVDF), etc. that show shape deformation when an electric field is applied. Electroactive polymer materials can be manufactured such that when there is a voltage difference between the two electrodes, the EAP material increases in volumetric size. Alternatively, the EAP material can be manufactured such that when there is a voltage difference between the two electrodes, the material decreases in volumetric size. When an electrical field is applied across the EAP, the EAP deforms as a result of stresses generated by the movement of water and mobile positive ions in the polymer.  
         [0012]     Existing electroactive polymers are described in U.S. Pat. No. 6,515,077, U.S. Pat. No. 6,545,391, and U.S. Pat. No. 6,664,718, for example.  
         [0013]     The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists.  
         [0014]     All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.  
         [0015]     Without limiting the scope of the invention a brief summary of some 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.  
         [0016]     A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.  
       BRIEF SUMMARY OF THE INVENTION  
       [0017]     In some embodiments, the present invention is concerned with the crimping and otherwise reducing in size of stents, including drug delivery or coated stents of any configuration or expansion type, including inflation expandable stents, self-expanding stents, hybrid expandable stents, etc. For the purpose of this disclosure, it is understood that the term ‘stent’ includes stents, stent-grafts, grafts and vena cava filters and other implantable medical devices for luminal support. It is also understood that the term ‘crimping’ refers to a reduction in size or profile of a stent and/or a device upon which it is to be mounted; and ‘crimper’ refers to devices for accomplishing such reduction in size or profile of same.  
         [0018]     In at least one embodiment the invention is directed towards a variety of embodiments, including a system for protecting a stent comprising a stent, a balloon catheter, and an electroactive polymer (EAP) sleeve or crimper. A voltage source, electrically connected to the EAP material and a conductive member via contacts, applies a voltage across the contacts. The EAP material is thereby activated and expands. The stent, disposed about the balloon catheter, is inserted into the expanded sleeve. Once completely inserted, the voltage source is removed, causing the EAP material to contract. A radial compression force is exerted on the stent assembly as a result of the contraction.  
         [0019]     In some embodiments the EAP sleeve may be comprised of multiple layers. For example, in a multi-layer embodiment there may be more than one layer of an EAP, more than one layer of material that is not an EAP, or more than one layer of both EAP and non-EAP material. When a voltage is applied to such an embodiment, the multiple layers could cause the combination to bend or twist, rather than expand. The multi-layered combination could take on a variety of shapes and forms, depending on the desired arrangement of the layers.  
         [0020]     In at least one embodiment, the conductive member is a sleeve upon which the EAP material is attached. In another embodiment, the conductive member can be wires distributed throughout the EAP material. In some embodiments the conductive member can be ribbons distributed throughout the EAP material. Or, in other embodiments wires or ribbons may be wrapped around the exterior of the EAP material.  
         [0021]     The EAP material can be formed in a substantially cylindrical form in one embodiment. In this embodiment, the EAP material is substantially evenly distributed such that a cross-section of the material is ring shaped. In other embodiments, the EAP material may be formed in patterns that are not ring shaped, such as trapezoidal. These trapezoidal patterns may help reduce stresses that are not directed radially inward. That is, by allowing sufficient spacing between each section of EAP material formed in a trapezoidal pattern, the EAP material may expand and apply substantially radial forces while minimizing the forces applied to nearby trapezoidal sections.  
         [0022]     Some embodiments of the present invention include a lubricious coating. After the stent and balloon catheter are inserted into the EAP sleeve and the voltage is applied, the EAP sleeve exerts a radial force on the stent as the EAP sleeve constricts. A lubricious coating can be applied to the inner surface of the EAP sleeve prior to insertion of the stent and balloon catheter, thereby reducing the risk of damaging the stent coating during EAP constriction.  
         [0023]     In some embodiments of the present invention, the stent is crimped prior to insertion into the EAP sleeve. If the stent is not crimped prior to insertion into the EAP sleeve, an embodiment of the present invention accomplishes crimping, provided that the EAP sleeve can deliver sufficient compressive forces. In some embodiments, EAP activation can take place at substantially the same time as stent crimping by a mechanical tool, thereby significantly reducing or eliminating, “bunching” fold creases that are prevalent in current methods. In other embodiments, the stent is not crimped prior to insertion into the EAP sleeve.  
         [0024]     Another embodiment envisions packaging and shipping the assembly with the EAP sleeve attached. That is, at time the stent assembly is ready to use, the medical personnel could open the packaging and then turn the voltage source to an on state, expanding the EAP sleeve. The medical personnel can remove the assembly from the EAP sleeve, thereby reducing the risk of damaging the stent coating prior to use.  
         [0025]     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 further 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 embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     A detailed description of the invention is hereafter described with specific reference being made to the drawings.  
         [0027]      FIG. 1  is a side view of an electroactive polymer sleeve in an expanded state.  
         [0028]      FIG. 2  is a side view of an electroactive polymer sleeve in an unexpanded state.  
         [0029]      FIG. 3  is a side view of a stent.  
         [0030]      FIG. 4  is a side view of a balloon catheter.  
         [0031]      FIG. 5  is a side view of the stent of  FIG. 3  disposed about the balloon catheter of  FIG. 4 .  
         [0032]      FIG. 6  is a side view of the electroactive polymer sleeve of  FIG. 1  disposed about the stent and balloon catheter combination of  FIG. 5 .  
         [0033]      FIG. 6   a  is a cross-sectional view of the embodiment of  FIG. 6 .  
         [0034]      FIG. 7  is a side view of the electroactive polymer sleeve of  FIG. 2  disposed about the stent and balloon catheter combination of  FIG. 5 .  
         [0035]      FIG. 7   a  is a cross-sectional view of the embodiment of  FIG. 7 .  
         [0036]      FIG. 8  is a cross-section of one embodiment of an electroactive polymer sleeve with insulated wires distributed therein.  
         [0037]      FIG. 9  is a cross-section of one embodiment of the electroactive polymer sleeve.  
         [0038]      FIG. 10  is a cross-section of one embodiment of an electroactive polymer sleeve with insulated ribbons distributed therein.  
         [0039]      FIG. 11  is a side view of the electroactive polymer with an insulated wire disposed about the electroactive polymer. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]     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.  
         [0041]     For the purposes of this disclosure, like reference numerals in the figures shall refer to like features unless otherwise indicated.  
         [0042]     Depicted in the figures are various aspects of the invention. Elements depicted in one figure may be combined with, and/or substituted for, elements depicted in another figure as desired  
         [0043]      FIG. 1  depicts an embodiment of an EAP sleeve, shown generally at  12 . The EAP sleeve  12  includes an EAP material  47  disposed between first conductive member  42  and second conductive member  48 . The EAP sleeve  12  of  FIG. 1  is in an expanded state and has a length  10  relative to axis  3 . The EAP material of  FIG. 1  also has a thickness  7  and may include a lubricious coating  11  on the inner surface  4 . A lubricious coating can be applied to the inner surface  4  of the EAP sleeve prior to insertion of a stent and balloon catheter, thereby reducing the risk of damaging the stent coating during EAP constriction.  
         [0044]      FIG. 2  depicts the EAP sleeve  12  shown in  FIG. 1 , but in an unexpanded state. In its unexpanded state, the EAP sleeve  12  has a length  10  relative to axis  3 , length  10  being substantially the same as in unexpanded state length  10  shown in  FIG. 1 . Furthermore, the EAP material  47  shown in  FIG. 2  has a thickness  17  which is less than expanded state thickness  7 .  
         [0045]     A stent  25  is shown in  FIG. 3 . Stent  25  has a length  28  relative to axis  29 . Also, stent  25  has an outer diameter  27 .  
         [0046]     In some embodiments the stent, the delivery system or other portion of the assembly may include one or more areas, bands, coatings, members, etc. that is (are) detectable by imaging modalities such as X-Ray, MRI, ultrasound, etc. In some embodiments at least a portion of the stent and/or adjacent assembly is at least partially radiopaque.  
         [0047]     In some embodiments at least a portion of the stent is configured to include one or more mechanisms for the delivery of a therapeutic agent. Often the agent will be in the form of a coating or other layer (or layers) of material placed on a surface region of the stent, which is adapted to be released at the site of the stent&#39;s implantation or areas adjacent thereto.  
         [0048]     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.  
         [0049]     In  FIG. 5  the stent  25  of  FIG. 3  is shown disposed about the balloon catheter  30  of  FIG. 4 .  
         [0050]      FIG. 6  depicts an embodiment of the present system for protecting a stent assembly, shown generally at  50 , in an expanded state. The expanded EAP sleeve of  FIG. 1  is shown generally at  12 . The EAP sleeve  12  may also include a lubricious coating  11  distributed on inner surface  4 . The EAP sleeve  12  is expanded by applying a voltage, supplied by a voltage source  35 , across first conductive member  42  and second conductive member  48 . This may be accomplished by attaching contact  40  to conductive member  42  and contact  45  to conductive member  48 , as shown. Alternatively, the voltage source  35  may connected directly to conductive members  42  and  48 . Conductive member  42  and conductive member  48  are separated by EAP material  47 . Closed switch  36  and contacts  40  and  45  are shown only to indicate conceptually how voltage can be applied to conductive members; a number of more practical methods of applying a voltage across the EAP material may be available. In this embodiment, conductive member  42  is a first conductive sheath shown disposed about the EAP material  47 ; EAP material  47  is disposed about a second conductive sheath, conductive member  48 . Many other embodiments of conductive members are possible, such as wires, ribbons, or both, dispersed within the EAP material. Also, conductive members such wires, ribbons, or both can be disposed about the EAP material.  
         [0051]     After voltage source  35  is applied, the thickness  17  of the EAP material  47  in its unexpanded state, shown in  FIGS. 7 and 7 a, increases to thickness  7 , shown in  FIGS. 6 and 6 a. Conductive members  42  and  48  can be ductile and change shape with EAP material  47 . Also, the inner diameter  15  of the EAP sleeve in its unexpanded state, shown in  FIG. 7 , increases to inner diameter  5 , as shown in  FIG. 6a . In the expanded state, as shown in  FIG. 6 , axial length  55  of EAP sleeve  12  is no less than axial length  28  of stent  25 , thereby providing a protective covering for the stent.  
         [0052]      FIG. 7  depicts an embodiment of the present system for protecting a stent assembly, shown generally at  50 , in an unexpanded state. The unexpanded EAP sleeve of  FIG. 1  is shown generally at  12 . As depicted by open switch  36 , voltage source  35  is not applied across contacts  40  and  45  when EAP sleeve  12  is in the unexpanded state. In its unexpanded state, the EAP material has thickness  17 . Unexpanded state thickness  17  is less than the expanded state thickness  5  that is shown in  FIGS. 6 and 6   a . Contact  40  is connected to a first conductive member  42  and contact  45  is connected to a second conductive member  48 , separated by EAP material  47 . Open switch  36  and contacts  40  and  45  are shown only to indicate conceptually how a voltage can be easily removed from an EAP material. In the unexpanded state, EAP sleeve  12  has an inner diameter  15  defined by inner surface  4 . A substantially radial compression force is exerted from EAP sleeve  12  to stent  25 , causing outer diameter  27  of stent  25  of  FIG. 6   a  to reduce to outer diameter  60 , as shown in  FIG. 7 . However, axial length  55  of EAP sleeve  12  is no less than axial length  28  of stent  25 , thereby providing a protective covering for the stent.  
         [0053]     As shown in the cross-section of  FIG. 8 , some embodiments may use wires  80  embedded in EAP material  82  in order to expand the EAP material. Other embodiments instead may use ribbons  85  embedded in the EAP material  82 , as shown in  FIG. 9 . In some embodiments, the wire/ribbon  90  may not be embedded in EAP material  82 , but is instead wrapped around the exterior of EAP material  82 , as in  FIG. 10 .  
         [0054]     Regarding the EAP material, in some embodiments it is formed such that a cross-section is substantially ring shaped, depicted by reference numeral  82  in  FIG. 8 . However, a number of other patterns are possible, such as a pattern that includes a number of trapezoids  84  when the material is cross-sectioned, as shown in  FIG. 11 . In  FIG. 11 , a EAP material  84  is disposed between first conductive member  42  and second conductive member  48 . A trapezoidal pattern could reduce the amount of stress produced that is not directed radially inward. That is, by allowing sufficient spacing between each trapezoidal section  84  of EAP material, the EAP material may expand and apply substantially radial forces while minimizing the forces applied to nearby trapezoidal sections. The trapezoidal pattern shown in  FIG. 11  is meant only to exemplify one possible pattern. Numerous other patterns are possible, such as semi-circular or rectangular.  
         [0055]     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. 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.  
         [0056]     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.