Abstract:
Medical devices may include structure or provision that permit a physician or other health care professional to adjust particular parameters such as flexibility, stiffness and compressive strength of at least a portion of the medical device. In some instances, the medical device may be adjusted prior to inserting the medical device into a patient. In some cases, the medical device may be adjusted while in use within the patient.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/280,120, filed Nov. 16, 2005. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to medical devices having or including elongate shafts and relates more particularly to medical devices having elongate shafts that provide adjustability in flexibility, stiffness or compressive strength. 
     BACKGROUND 
     Medical devices may be subject to a number of often conflicting performance requirements such as flexibility and strength. In some instances, improved flexibility may come at the expense of reduced strength. Increased strength may come at the expense of reduced flexibility. Because each patient is unique, there may be a unique balance of performance parameters such as flexibility and strength optimal for a particular patient. Moreover, the optimal balance of flexibility and strength for a particular patient may vary during a procedure, depending on vasculature encountered. 
     Therefore, a need remains for medical devices that can be adjusted in performance parameters such as flexibility, stiffness and compressive strength, particularly in situ. 
     SUMMARY 
     The invention pertains generally to medical devices that include structure or provision that permit a physician or other health care professional to adjust particular parameters such as flexibility, stiffness and compressive strength of at least a portion of the medical device. In some instances, the medical device may be adjusted while in use within the patient. 
     Accordingly, an example embodiment of the invention may be found in a medical device that includes a hypotube and structure or apparatus for changing the compressive strength of the hypotube. The hypotube includes a number of slots disposed within the hypotube. 
     Another example embodiment of the invention may be found in a medical device that includes a hypotube and an electroactive polymer sleeve that is disposed over the hypotube. The hypotube includes a number of slots disposed within the hypotube. 
     Another example embodiment of the invention may be found in a medical device that includes a hypotube having a slot. The slot has a first wall and an opposing second wall. An electroactive polymer is disposed on at least one of the first wall and the second wall. 
     Another example embodiment of the invention may be found in a medical device that includes a hypotube that has a number of slots and a lumen extending through the hypotube. A sleeve that includes a number of fingers formed within the sleeve is disposed over the hypotube. 
     Another example embodiment of the invention may be found in a medical device that includes a hypotube that has a slot formed within the hypotube, the slot including a first wall and an opposing second wall. An electroactive polymer is disposed on at least one of the first wall and the opposing second wall. An insulating layer is disposed about the hypotube, and a conductive pattern is disposed about the insulating layer. 
     Another example embodiment of the invention may be found in a medical device that includes a hypotube having a first section and a second section. The first section includes a first slot and the second section includes a second slot. An electroactive polymer is disposed within the first slot and within the second slot. An insulating layer is disposed about the hypotube. A conductive pattern is disposed about the insulating layer. The conductive pattern includes a first conductive section disposed proximate the first hypotube section and a second conductive section disposed proximate the second hypotube section. 
     Another example embodiment of the invention may be found in a medical device that includes a non-conductive hypotube having a slot disposed within the hypotube. The slot includes a first wall and an opposing second wall. An electroactive polymer is disposed on at least one of the first wall and the second wall. A first conductive apparatus or structure and a second conductive apparatus or structure are both disposed near the hypotube such that the second conductive apparatus or structure is electrically isolated from the first conductive apparatus or structure. 
     Another example embodiment of the invention may be found in a method of deploying a medical device using a deployment catheter. The deployment catheter includes an outer shaft and an inner shaft that is disposed within the outer shaft. The inner shaft includes a slotted hypotube and strength altering apparatus or structure disposed thereon. A medical device is positioned within the outer shaft adjacent a distal end of the inner shaft. The deployment catheter is advanced through a patient&#39;s vasculature to a desired site. The strength altering apparatus or structure is activated in order to increase the compressive strength of the inner shaft, and then the inner shaft is advanced relative to the outer shaft in order to deploy the medical device. 
     The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures, Detailed Description and Examples which follow more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a side elevation view of a catheter in accordance with an embodiment of the invention; 
         FIG. 2  is a perspective view of a hypotube in accordance with an embodiment of the invention; 
         FIG. 3  is a side elevation view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 4  is a view of the hypotube of  FIG. 3 ; 
         FIG. 5  is a view of the hypotube of  FIG. 3 ; 
         FIG. 6  is a side elevation view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 7  is a side elevation view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 8  is a side elevation view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 9  is a cross-section of  FIG. 8 ; 
         FIG. 10  is a view of the hypotube of  FIG. 8 ; 
         FIG. 11  is a view of the hypotube of  FIG. 8 ; 
         FIG. 12  is a side elevation view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 13  is a view of the hypotube of  FIG. 12 ; 
         FIG. 14  is a diagrammatic end view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 15  is a diagrammatic end view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 16  is a diagrammatic end view of a portion of a hypotube in accordance with an embodiment of the invention; 
         FIG. 17  is a side elevation view of a deployment catheter in accordance with an embodiment of the invention; 
         FIG. 18  is a view of the deployment catheter of  FIG. 17 ; 
         FIG. 19  is a view of the deployment catheter of  FIG. 17 ; 
         FIG. 20  is a side elevation view of a portion of a hypotube in accordance with an embodiment of the invention; and 
         FIG. 21  is a view of the hypotube of  FIG. 20 . 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
     DETAILED DESCRIPTION 
     For the following defined terms, these definitions shall be applied, unless a different definition is given in the claims or elsewhere in this specification. 
     All numeric values are herein assumed to be modified by the term “about”, whether or not explicitly indicated. The term “about” generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (i.e., having the same function or result). In many instances, the terms “about” may include numbers that are rounded to the nearest significant figure. 
     The recitation of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
     As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The drawings, which are not necessarily to scale, depict illustrative embodiments of the claimed invention. 
       FIG. 1  is a plan view of a catheter  10  in accordance with an embodiment of the present invention. The catheter  10  can be any of a variety of different catheters. In some embodiments, the catheter  10  can be an intravascular catheter. Examples of intravascular catheters include balloon catheters, atherectomy catheters, stent delivery catheters including catheters configured to deliver self-expanding stents, diagnostic catheters and guide catheters. The intravascular catheter  10  can be sized in accordance with its intended use. The catheter  10  can have a length that is in the range of about 50 to about 150 centimeters and can have any useful diameter. As illustrated,  FIG. 1  portrays a guide catheter, but the invention is not limited to such. Except as described herein, the intravascular catheter  10  can be manufactured using conventional techniques. 
     In the illustrated embodiment, the intravascular catheter  10  includes an elongate shaft  12  that has a proximal region  14  defining a proximal end  16  and a distal region  18  defining a distal end  20 . A hub and strain relief assembly  22  can be connected to the proximal end  16  of the elongate shaft  12 . The hub and strain relief assembly  22  may largely be of conventional design and can be attached using conventional techniques, apart from being adapted to accommodate electrical contacts that are in electrical communication with the electrodes that will be discussed in greater detail with respect to subsequent Figures. In some instances, it is contemplated that hubs such as those used in electrophysiology catheters may be useful. 
     The elongate shaft  12  can include one or more shaft segments having varying degrees of flexibility. For example, the elongate shaft may include a relatively stiff proximal portion, a relatively flexible distal portion and an intermediate position disposed between the proximal and distal portions having a flexibility that is intermediate to both. 
     In some cases, the elongate shaft  12  may be formed of a single polymeric layer. In some instances, the elongate shaft  12  may include an inner liner such as an inner lubricious layer and an outer layer. In some cases, the elongate shaft  12  may include a reinforcing braid layer disposed between the inner and outer layers. The elongate shaft  12  is considered herein as generically representing a catheter to which various elements can be added to provide the catheter  10  with adjustable stiffness. 
     If the elongate shaft  12  includes an inner liner, the inner liner can include or be formed from a coating of a material having a suitably low coefficient of friction. Examples of suitable materials include perfluoro polymers such as polytetrafluoroethylene (PTFE), better known as TEFLON®, high density polyethylene (HDPE), polyarylene oxides, polyvinylpyrolidones, polyvinylalcohols, hydroxy alkyl cellulosics, algins, saccharides, caprolactones, and the like, and mixtures and combinations thereof. In some instances, a polymer such as PEBAX® may be used in conjunction with a hydrophilic and/or a hydrophobic coating. 
     The elongate shaft  12  can include, as an outer layer or layers, any suitable polymer that will provide the desired strength, flexibility or other desired characteristics. Polymers with low durometer or hardness can provide increased flexibility, while polymers with high durometer or hardness can provide increased stiffness. In some embodiments, the polymer material used is a thermoplastic polymer material. Some examples of suitable materials include polyurethane, elastomeric polyamides, block polyamide/ethers (such as PEBAX®), silicones, and co-polymers. The outer polymer layer  32  can be a single polymer, multiple longitudinal sections or layers, or a blend of polymers. 
     By employing careful selection of materials and processing techniques, thermoplastic, solvent soluble, and thermosetting variants of these materials can be employed to achieve the desired results. In some instances, a thermoplastic polymer such as a co-polyester thermoplastic elastomer, for example, available commercially under the ARNITEL® name, can be used. In some instances, a thermoplastic polymer may include micro-sized or even nano-sized fillers. Examples of suitable fillers include metallic fibers, ceramic fibers, nano clays, and carbon structures such as carbon fibers and carbon tubes. 
       FIGS. 2 through 20  illustrate various hypotubes in accordance with particular embodiments of the invention. The catheter  10  may be considered as including or being formed from any of the hypotubes described hereinafter. In particular,  FIG. 2  illustrates a micromachined hypotube while  FIGS. 3 through 20  illustrate modifications and/or additions to the micromachined hypotube of  FIG. 2 . It should be noted that while the invention is discussed herein with respect to catheters, the hypotubes described herein are equally applicable to other medical devices such as guidewires. 
       FIG. 2  illustrates a micromachined hypotube  24  having a proximal region  26  defining a proximal end  28  and a distal region  30  defining a distal end  32 . The micromachined hypotube  24  can be seen as having an axial axis  34  extending the length of the hypotube  24 . A number of slots  36  are disposed along the length of the micromachined hypotube  24 . In the illustrated embodiment, the slots  36  are arranged at least substantially perpendicular to the axial axis  34 . In other instances, the slots  36  may be arranged at an angle with respect to the axial axis  34 . 
     While not illustrated, it is contemplated that at least some of the slots  36  may extend longitudinally. Moreover, it is contemplated that the dimensions of the slots  36 , either length and/or width, may vary with respect to relative position along the hypotube  24 . In some cases, the slot density, or number of slots per unit length of hypotube  24 , may vary with respect to relative position along the hypotube  24 . In some cases, one or more of the slots  36  may extend spirally about the hypotube  24 . 
     Each of the slots  36  extend only partially around the circumference of the micromachined hypotube  24 . In some instances, an individual slot  36  may extend about half way around the circumference of the micromachined hypotube  24 . In other cases, an individual slot  36  can extend more than halfway around, if for example, increased flexibility is of highest importance. Conversely, if it is desired to provide additional column strength, perhaps with a certain sacrifice in flexibility, it is contemplated that each individual slot  36  may extend less than halfway around the micromachined hypotube  24 . 
     It can be seen that individual slots  36  may be considered as being in pairs  38 , with a pair  38  including a first slot  40  and a second slot  42 . In some embodiments, as illustrated, the first slot  40  can have a first radial position on the micromachined hypotube  24  while the second slot  42  occupies a second radial position that is rotated from the first radial position. In some embodiments, as illustrated, the second slot  42  can be rotated about 90 degrees from the first slot  40 . In other instances, the radial rotation can vary, especially if, for example, first slot  40  and second slot  42  are either longer or shorter than the illustrated length. 
     The micromachined hypotube  24  may be formed of any suitable material. In some instances, the micromachined hypotube  24  may be formed of a metallic material such as stainless steel or a nickel-titanium alloy such as Nitinol. The micromachined hypotube  24  may also be formed of any suitably stiff non-metallic material, such as carbon fiber or a stiff polymer such as polyimide. 
     The micromachined hypotube  24  may be formed having any desired length, width, material thickness, and slot size as required to satisfy the requirements of any particular application. Additional details concerning micromachined hypotube  24 , including the manufacture thereof, can be found, for example, in U.S. Pat. No. 6,766,720 and published U.S. Patent Application No. 2004/0181174A2, each of which are fully incorporated, in their entirety, by reference herein. 
       FIGS. 3 and 4  show an assembly  44  that includes a sleeve  46  disposed about the hypotube  24 . The hypotube  24  includes a plurality of slots  36 , as discussed above with respect to  FIG. 2 . In  FIG. 3 , the hypotube  24  is seen in a straight configuration while in  FIG. 4 , the hypotube  24  has undergone a certain amount of bending as a result of a force being applied to the hypotube  24 . 
     As a result of being temporarily deformed into a bent configuration, the hypotube  24  can be seen as including expanded slots  48  along the outer perimeter, compressed slots  50  along the inner perimeter and unchanged slots  52  within the middle of the hypotube  24 . It should be noted in  FIG. 4  that the sleeve  46  has bent with the hypotube  24  and thus does not impact or at least does not substantially impact the flexibility of the hypotube  24 . 
     The sleeve  46  may be formed of any suitable polymeric or metallic material. In some instances, the sleeve  46  may be formed of an electroactive polymer which can, when subjected to a potential difference, accommodate ions which may cause the electroactive polymer to swell. In some cases, the sleeve  46  may be formed of a shape memory material such as a shape memory metal or a shape memory polymer. Shape memory materials are known that can change from one configuration to another configuration upon a change in temperature, application of a magnetic field, light, or other suitable stimuli. 
     In  FIG. 5 , the assembly  44  includes a sleeve  46  that has been changed into an activated configuration in which portions  54  of the sleeve  46  extend at least partially into the slots  36 . As a result, the compressive strength of the hypotube  24  has been temporarily increased, as the portions  54  will reduce the amount of compression that slots  36 , and thus the hypotube  24 , can undergo. 
     The sleeve  46  can be considered as being convertible between an un-activated configuration, such as that shown in  FIGS. 3 and 4 , and an activated configuration as shown in  FIG. 5 . If the sleeve  46  is formed of some shape memory materials, the conversion from un-activated configuration to activated configuration may be permanent. However, in some instances, the sleeve  46  may also be returned to its un-activated configuration or even held at an intermediate configuration. 
     In particular, if the sleeve  46  is formed of an electroactive polymer, halting the potential difference being applied to the electroactive polymer will permit ions already within the polymer to remain there, but additional ions will not enter. Reversing the potential difference will cause the previously entered ions to exit the polymer. It should be recognized, therefore, that if sleeve  46  is formed of an electroactive polymer, the relative amount of ions entering or exiting the electroactive polymer may be controlled by controlling the potential difference applied to the electroactive polymer. Thus, the relative stiffness of the hypotube  24 , to which sleeve  46  has been applied, may be adjusted on a continuous scale. 
     As noted, in some instances, an electroactive polymer may be employed with hypotubes in accordance with certain embodiments of the invention. In short, an electroactive polymer is a doped polymer that undergoes volume or configuration changes upon oxidation and reduction, such as may occur when the polymer is subjected to an electrical field driving the ions into or out of the polymer. Oxidation and reduction may cause ions to be either inserted into the polymer, thereby increasing the volume of the polymer, or to be removed from the polymer, thereby decreasing its volume. 
     In some instances, an electroactive polymer may be doped with a large, immobile anion A− and may be positioned in contact with an electrolyte that includes a small mobile cation M+, in which case cations are inserted and de-inserted. The electroactive polymer, in this case, expands in volume in its reduced state (a negative potential). This can be represented as the following redox (oxidation-reduction) reaction:
 
 P   + ( A   − )+ M   + (aq)+ e   −               P   0 ( A   −   M   + ).

     In some instances, the electroactive polymer can be polypyrrole that has been doped with dodecyl benzene sulfonate (DBS), and can be placed in contact with an aqueous electrolyte of 0.1 molar NaDBS (sodium dodecyl benzene sulfonate). In this case, DBS is the large, immobile anion and Nat, possibly hydrated, is the small cation that is inserted and or de-inserted into the polymer. During reduction, sodium cations move into the polypyrrole to achieve charge neutrality within the polypyrrole. On oxidation, conversely, the sodium cations are expelled from the polypyrrole. 
     Polypyrrole and NaDBS have the following chemical structures, respectively: 
     
       
                 
         
             
             
         
      
     
     As noted, sodium cations can be provided by contacting the polypyrrole with an NaDBS electrolyte solution. However, in some instances, any variety of different aqueous salt solutions are useful. In particular, bodily fluids such as blood plasma and urine are effective. 
     Thus, in some instances, the electroactive polymer may be adapted to accommodate ions from an electrolyte solution provided within the hypotube  24 . In some cases, the electroactive polymer may be adapted to accommodate ions from a patient&#39;s own blood. Ions in general, and particularly cations, may flow (as a result of an appropriate potential difference) from either an electrolyte solution such as NaDBS or from a patient&#39;s blood into the electroactive polymer, thereby swelling or otherwise activating the electroactive polymer. 
     As noted, it is useful to provide a voltage or potential difference in order to drive the redox reaction discussed above. The oxidized state, in which the sodium cations have been expelled or at least largely expelled from the polypyrrole, can be achieved at a voltage of 0 volts, i.e. no applied current. The reduced state, in which the sodium cations have moved into the polypyrrole, can be achieved, for example, at a voltage of about 1 volts, or perhaps about 1.2 volts. It should be noted that intermediate voltages, say in the range of 0.4 to 0.6 volts, can cause an intermediate level of volume increase as a result of cations migrating into the polymer. Depending on the voltage applied, the polypyrrole may achieve a volume increase of at least about 30 percent. 
     Depending on how the electroactive polymer is employed, in some cases moving from the oxidized state to the reduced state, via application of an appropriate potential difference across the electroactive polymer, simply causes a volume increase, and the electroactive polymer merely swells or grows. In some cases, the electroactive polymer may be coupled with an electrode, such as in a gold/polypyrrole bilayer, and moving between oxidized and reduced states may cause the bilayer to either bend or straighten. 
     As noted, in some instances, shape memory material may be employed with hypotubes in accordance with certain embodiments of the invention. In short, a shape memory material (either polymeric or metallic) is a material that can be moved or converted between two or more distinct configurations by application of an appropriate stimuli. In some instances, a structure or apparatus formed of a shape memory material may have an un-activated configuration and a remembered activated configuration, as will be discussed subsequently with respect to certain Figures. 
     Some shape memory materials, such as shape memory metals and shape memory polymers, can be moved between configurations via an appropriate temperature change. Suitable shape memory metals include the nickel-titanium alloys better known as nitinol. In some embodiments, nitinol alloys can include in the range of about 50 to about 60 weight percent nickel, with the remainder being essentially titanium. It should be understood, however, that in other embodiment, the range of weight percent nickel and titanium, and or other trace elements may vary from these ranges. Within the family of commercially available nitinol alloys, are categories designated as “superelastic” (i.e. pseudoelastic) and “linear elastic” which, although similar in chemistry, exhibits distinct and useful mechanical properties. In some instances, the sleeve  46  may include or be formed from nitinol. 
     In broad terms, shape memory polymers behave similarly to shape memory alloys such as the nickel-titanium alloys commonly referred to as Nitinol. The material is formed in its parent shape and is heated to a temperature that is at or above the glass transition temperature of the material. After the material has cooled, perhaps to ambient temperature, the material can be molded into any desired shape that is within the mechanical limitations of the material. This shape is temporarily retained until the material is once again subjected to its transition temperature. If desired, this process of low temperature deformation followed by thermally induced recovery of the parent shape can be repeated indefinitely. 
     One feature of shape memory polymers is that they have a large and reversible change in the modulus of elasticity of the material between the lower temperature glassy (crystalline) region and the higher temperature rubbery (elastic) region. In some embodiments, this large change in elasticity can be represented by a ratio of modulus of elasticity (below T g ) to modulus of elasticity (above T g ) of at least about 20. 
     In one aspect, shape memory polymers can be considered as having hard segments that are typically crystalline in nature, and soft segments that are typically amorphous in nature. However, some hard segments can be amorphous, and some soft segments can be crystalline. In this, segment refers to a block or sequence of the polymer that forms part of the shape memory polymer. 
     The terms hard segment and soft segment are relative in nature, and refer to differences in the transition temperatures of the segments, with a hard segment having the higher transition temperature. A shape memory polymer can have a first set of soft segments having a first transition temperature, and a second set of soft segments having a different, second transition temperature. In this case, the shape memory polymer can remember two distinct shapes that will be retrieved at different temperatures. The nature of shape memory polymers is discussed in greater detail in U.S. Pat. Nos. 6,160,084 and 6,388,043, each of which are incorporated in their entirety by reference herein. 
     In another aspect, the characteristics of shape memory polymers can be considered in terms of Brownian motion. In particular, molecular chains can undergo micro-Brownian motion above the glass transition temperature, once the modulus of elasticity has dropped. As noted above, shape memory polymers are considered as exhibiting a large drop in the modulus of elasticity when heating through the glass transition temperature. 
     In the elastic or rubbery state, the material can be easily deformed via mechanical means. As a result of the deformation, the molecular chains will orient themselves in line with the tension. Subsequently lowering the temperature below the glass transition temperature of the material freezes the micro-Brownian motion and therefore locks the material in its deformed configuration. The material will retain its deformed configuration for as long as the material remains below the glass transition temperature of the material. 
     When the material is heated above the glass transition temperature, however, micro-Brownian motion begins again, and the molecular chains will move to reduce or eliminate the tension caused by the initial deformation. As a result, the material will regain its remembered shape. 
     To function as a shape memory polymer, it is advantageous that the material either be partially crystallized or include at least some crosslinking. It has been found, however, that even when the material is partially crystallized or crosslinked, it can still be melted and processed using conventional injection or extrusion molding equipment. 
     The transition temperature of a shape memory polymer can be adjusted by varying the ratio of polymers used to create the shape memory polymer. A variety of different polymers can be made to have shape memory characteristics. Examples of suitable polymers include polynorborene (available commercially from Nippon Zeon Company), trans-polyisoprene (available from Kuraray Company), styrene-butadiene (available from Ashahi Company) and polyurethane (available from Mitsubishi Heavy Industries). 
     Additional materials that can be used include poly L-D lactic copolymer, oligo caprylactone copolymer and poly cyclo-octine. These polymers can be used separately or in conjunction with other shape memory polymers. In embodiments where more than one shape memory polymer is used, it may be useful that the polymers be compatible and that the glass transitions are similar. In some instances, if one shape memory polymer is used, for example, in a proximal section while a second shape memory polymer is used in a distal section, compatibility may not be necessary. 
     Shape memory polymers typically have three-dimensional networks as interpolymer chain interactions are important in retaining stable shapes. Examples of interpolymer chain interactions include chain entanglement, chemical cross-linking, and crystal, aggregate or glassy state formation. Entanglement and crosslinking are permanent changes and are used for constructing the original shape, while the other chain interactions are thermally reversible and thus are used to maintain the temporary (deformed) shapes. 
     For example, polynorborene relies on entanglement for memorizing an original shape, while trans-polyisoprene and polyethylene rely on crosslinking for this purpose. Polyurethane and styrene-butadiene copolymer rely on the formation of micro crystals in remembering an original shape. With respect to maintaining a deformed (temporary) shape, polynorborene and polyurethane employ the formation of a glass state. Trans-polyisoprene, styrene-butadiene copolymer and polyethylene each rely on the formation of micro-crystals. 
     As noted, in some instances, magnetic shape memory material may be employed with hypotubes in accordance with certain embodiments of the invention. In short, a magnetic shape memory material is a material that has magnetic properties and that can be moved or changed between two different configurations, or can exhibit strain, in response to applying or removing a magnetic field, or in response to a temperature change. 
     An example of a magnetic shape memory material that can exhibit shape memory strain in response to thermal cycling are single crystalline and polycrystalline FeNiCoTi. In a particular embodiment, a Fe-29Ni-18-Co-4Ti (weight percent) composition may be used. This material is unusual in that it exhibits shape memory behavior with an FCC (face centered cubic) austenitic structure. This material provides a relatively modest strain of about 2.5 percent. 
     An example of a magnetic shape memory material that can exhibit shape memory strain in response to an applied magnetic field are NiMnGa alloys. In a particular embodiment, a Ni-24 at % Mn 24.7 at % Ga composition may be used. This material provides a strain of about 5 percent in response to cyclic application of a magnetic field. The sleeve  46  may include a shape memory material such as a shape memory metal, a shape memory polymer or a magnetic shape memory material. 
     Returning now to the Figures,  FIG. 6  shows a portion of the hypotube  24 , including several slots  36 . It can be seen that each of the slots  36  includes a first wall  56  and an opposing second wall  58 . An electroactive polymer  60 , such that those discussed above, is disposed on at least one of the first wall  56  and the second wall  58 . As illustrated, the electroactive polymer  60  is evenly disposed on both the first wall  56  and the second wall  58 . 
     While not expressly illustrated in  FIG. 6 , it will be appreciated that two electrodes will be provided in order to activate the electroactive polymer  60  by providing a potential difference between the two electrodes. If the hypotube  24  is metallic, the hypotube  24  itself may serve as one of the electrodes. In some instances, a conducting wire may be provided extending within an interior of the hypotube  24  to serve as the second electrode. 
     In  FIG. 7 , a potential difference has been supplied between the two (not illustrated) electrodes, thereby causing the electroactive polymer  60  to accept ions from an appropriate source, and thereby swell to fill at least a substantial portion of the slot  36 . As a result, the compressive strength of the hypotube  24  has been increased. 
       FIGS. 8 through 11  illustrate an embodiment in which a second electrode is provided on the surface of the hypotube  24 . In  FIG. 8 , an assembly  62  includes the hypotube  24  as well as a first conductive pattern  64  and a second conductive pattern  66 . In some instances, the hypotube  24  is electrically conductive and thus may serve as an electrode, with at least one of the first conductive pattern  64  and the second conductive pattern  66  serving as a second electrode. In some instances, as shown in  FIG. 9 , it may be useful to provide an insulating layer  68  over the hypotube  24 , in order to electrically isolate the first conductive pattern  64  (and the second conductive pattern  66 ) from the hypotube  24 . 
     Returning to  FIG. 8 , it is contemplated that the upper conductive pattern and the lower conductive pattern, both labeled as first conductive pattern  64 , are electrically connected. In some instances, of course, it is contemplated that the first conductive pattern  64  may indeed be separated into electrically isolated and distinct upper and lower conductive patterns. In some instances, the second conductive pattern  66  is electrically isolated from the first conductive pattern  64 . It is contemplated, of course, that the first conductive pattern  64  and the second conductive pattern  66  may, in some instances, be electrically connected to each other. 
     Each slot  36  includes, as discussed with respect to  FIGS. 6 and 7 , a first wall  56 , an opposing second wall  58  and an electroactive polymer  60  disposed on at least one of first wall  56  and second wall  58 . As seen in  FIG. 8 , no voltage has been applied between the first electrode and the second electrode, and thus the electroactive polymer  60  remains in an un-activated configuration. 
     In  FIG. 10 , however, it can be seen that a potential difference has been applied between the second conductive pattern  66  and another electrode, such as the hypotube  24  itself. In the slots  36  bounded by the first conductive pattern  64 , the electroactive polymer  60  remains un-activated. However, in the slots  36  that are bounded by the second conductive pattern  66 , the electroactive polymer  60  has absorbed available ions and has swelled to at least substantially fill the corresponding slots  36 . 
     In contrast,  FIG. 11  shows an instance in which a potential difference has instead been applied between the first conductive pattern  64  and another electrode, such as the hypotube  24  itself. In the slots  36  bounded by the second conductive pattern  66 , the electroactive polymer  60  remains un-activated. However, in the slots  36  that are bounded by the first conductive pattern  64 , the electroactive polymer  60  has absorbed available ions and has swelled to at least substantially fill the corresponding slots  36 . 
     It will be recognized that activating the electroactive polymer  60  within certain slots  36  while not activating the electroactive polymer  60  within other slots  36  may be useful in causing the hypotube  24  to bend. For example, activating the electroactive polymer  60  only within the slots  36  along a first side of the hypotube  24  can cause the hypotube  24  to bend in a direction opposite that of the first side of the hypotube  24 . Activating the electroactive polymer  60  along two opposing sides will stiffen the hypotube  24  in a plane through the two opposing sides while permitting bending in a direction orthogonal to said plane. Adding more slots than those shown in the Figures will, of course, increase the options for controlled bending and adjustable stiffness. 
       FIGS. 12 and 13  illustrate an embodiment in which the hypotube  24  is provided with an exterior sleeve bearing fingers that may be activated into a position in which the fingers improve the compressive strength of the hypotube  24 . 
     In particular,  FIG. 12  shows a portion of the hypotube  24 , bearing a sleeve  70 . The sleeve  70  may be formed of any suitable material and includes fingers  72  that have an un-activated configuration (shown here in  FIG. 12 ) in which the fingers  72  do not extend into, or at least do not extend substantially into, the slots  36 . and an activated configuration, shown in  FIG. 13 , in which the fingers  72  extend at least partially into the slots  36  and thereby improve the compressive strength of the hypotube  24 . 
     In some instances, the sleeve  70  and hence the fingers  72  may be a multilayer assembly including an electrode layer and an electroactive polymer layer disposed on one side or the other of the electrode layer. The electrode layer, if included, may be any suitable metal such as gold. If the hypotube  24  itself is used as an electrode, the sleeve  70  may also include an insulating layer disposed between the finger electrode layer and the hypotube  24 . 
       FIGS. 14 through 16  diagrammatically illustrate particular embodiments of providing two electrodes, particularly if the hypotube  24  is non-conductive. It is contemplated that the hypotube  24  may be formed of any of a variety of non-conductive polymers. 
     In  FIG. 14 , a non-conductive hypotube  74  includes an inner conductive layer  76  formed within the interior of the hypotube  74  and an outer conductive layer  78  formed on the exterior of the hypotube  74 . Each of the inner conductive layer  76  and the outer conductive layer  78  may simply be a metallic coating formed using any suitable technique such as dipping, spraying or the like. In some instances, the outer conductive layer  78  may be a patterned conductive layer, such as the first conductive layer  64  and/or the second conductive layer  66  shown in  FIG. 8 . 
       FIG. 15  illustrates an embodiment in which the hypotube  74  includes an inner conductive layer  80  formed on the exterior of the hypotube  74 . An insulating layer  82 , which may be formed of any suitable electrically-insulating material is disposed about the inner conductive layer  80 . An outer conductive layer  84  is disposed about the insulating layer  82 . The insulating layer  82  may be, for example, a diamond-like coating, an oxide, or a polymeric shrink tube. The outer conductive layer  84  may be formed of any suitable material using any suitable technique. For example, the outer conductive layer  84  may be formed of copper, using known photolithography techniques. 
       FIG. 16  shows an embodiment in which the hypotube  74  includes a conductive layer  86  that is disposed on the exterior of the hypotube  74 . The conductive layer  86  may be formed of any suitable material using any suitable technique. A conductive wire  90  is disposed within the interior  88  of the hypotube  74 . The conductive layer  86  may be a simple conducting layer, or it may be a conductive pattern as previously discussed. Similarly, the conductive wire  90  may be a simple copper wire exposed along its length, or the conductive wire  90  may have an insulating layer (not shown) having distinct gaps therein in order to direct current to desired locations. 
       FIGS. 17 through 19  illustrate a deployment catheter  92  in accordance with a particular embodiment of the invention. While deployment catheter  92  is illustrated herein as deploying a self-expanding stent, it should not be considered as being limited to such. Rather, deployment catheter  92  may be used to deploy a variety of medical devices such as stents, distal protection filters, vena cava filters, and other intravascular filters. In some ways, the deployment catheter  92  may be considered as an application for the hypotube  24  discussed previously herein. 
     In  FIG. 17 , the deployment catheter  92  may be seen as including an outer shaft  94  defining a lumen  96  and an inner shaft  98  disposed within the lumen  96 . The outer shaft  94  may be of any suitable construction, and may be a single layer polymeric sheath. In some instances, of course, the outer shaft  94  may include multiple polymeric layers, reinforcing structures, and the like. The inner shaft  98  is a hypotube having a distal end  100 . A stent  102  is positioned within the lumen  96 , proximate the distal end  100  of the inner shaft  98 . 
     As noted, the inner shaft  98  is a hypotube and includes a number of slots  104 . Each slot  104  has a first wall  106  and an opposing second wall  108 . An electroactive polymer  110  is disposed along the first wall  106  and a second wall  108 . As seen, the electroactive polymer  110  is in an un-activated configuration, i.e. no potential difference has been applied. It is considered that this configuration may be preferable for advancing the deployment catheter  92  through a patient&#39;s vasculature. 
     Once a desired treatment site has been reached, it may be advantageous to apply a potential difference to the electroactive polymer  110 , thereby causing available ions to enter and thus swell the electroactive polymer  110 . As seen in  FIG. 18 , the electroactive polymer  110  has obtained its activated configuration in which the electroactive polymer  110  fills at least a substantial portion of the slot  104 . As seen in  FIG. 19 , the stent  102  (or other deployable structure) may be deployed as a result of relative axial movement between the outer shaft  94  and the inner shaft  98 . 
     In some instances, a hypotube  24  ( FIG. 2 ) may achieve increased compressive strength through non-electrical methods.  FIGS. 20 and 21  illustrate a mechanical solution to increasing compressive strength. 
     In  FIG. 20 , the hypotube  24  can be seen as including a number of slots  36 . An apparatus  112  bearing a number of protrusions  114  is disposed about the hypotube  24 . In  FIG. 20 , the apparatus  112  is in an un-activated configuration and is considered to be spring-loaded. Moving the apparatus  112  axially with respect to the hypotube  24  causes the protrusions  114  to move and thus enter the slots  36 . Once the protrusions  114  enter the slots  36 , the protrusions  114  limit how far the slots  36  may compress, and thereby improves the compressive strength of the hypotube  24 . 
     It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.