Patent Publication Number: US-2021162183-A1

Title: Adjustable guidewire

Description:
STATEMENT OF RELATED APPLICATION(S) 
     This application is a divisional of U.S. patent application Ser. No. 16/078,388 filed on Aug. 21, 2018, which is a 35 U.S.C. § 371 national phase filing of International Application No. PCT/US2017/018638 filed on Feb. 21, 2017, which claims the benefit of U.S. Provisional Patent Application No. 62/298,096 filed on Feb. 22, 2016, wherein the disclosures of the foregoing applications are hereby incorporated by reference herein in their respective entireties. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to guidewires being insertable into internal sites of mammalian bodies, and being useful for inserting, positioning, and moving catheters for diagnostic procedures, therapeutic procedures, and/or delivering therapeutic agents. 
     BACKGROUND 
     Catheters are used for performing diagnostic procedures and for delivering therapeutic agents to internal sites within a human body that can be accessed through various lumen systems, such as the vasculature. A guidewire is a device used to enter tight spaces (e.g., obstructed or tortuous passages) within the body, or to assist in inserting, positioning, and moving a catheter—such as through bends and branches of blood vessels. Guidewires vary in size, length, stiffness, composition, and tip shape. A conventional guidewire may include a slight bend at its distal end, and may be guided by selective rotation and advancement along a pathway to a desired target location. Thereafter, the guidewire may be held in place, and a catheter may be advanced along a longitudinal axis of the guidewire. 
     Insertion of a guidewire into a vessel lumen is schematically illustrated in  FIG. 1A . A guidewire  10  is advanced into a target vessel lumen  12 , which may include multiple bends or turns 14, 16. As shown in  FIG. 1B , the guidewire  10  is deflected as it is pushed forward against walls of the vessel lumen  12 . Thereafter, as shown in  FIG. 1C , a catheter  18  is advanced over the guidewire  10 , which provides a stable support during advancement. 
     A side cross-sectional schematic view of a portion of a conventional flexible guidewire  20  is shown in  FIG. 2 . A distal portion of the guidewire  20  includes a tip  22  (which may be convex along its outer perimeter) to which a longitudinal core wire or mandrel  24  and a safety ribbon wire embodied in a flexible coil  26  (e.g., distal coil) are attached. The core wire or mandrel  24  may include a constant diameter portion  24 A over much of its length, as well as first and second reduced diameter portions  24 B,  24 C between the constant diameter portion  24 A and the tip  22 . As shown in  FIG. 2 , an external coating  28  may be provided over the constant diameter portion  24 A of the longitudinal core wire or mandrel  24 , and the flexible coil  26  may be provided over the first and second reduced diameter portion(s)  24 B,  24 C between the coated constant diameter portion  24 A and the tip  22 . The flexible coil  26  may be generally helical in shape, similar to a spring. A proximal coil portion  26 A including a first (e.g., smaller) coil pitch may extend over the first reduced diameter portion  24 B of the core wire or mandrel  24 , and a distal coil portion  26 B including a second (e.g., larger) coil pitch may extend over the second reduced diameter portion  24 C of the core wire or mandrel  24 , wherein the second reduced diameter portion  24 C of the core wire or mandrel  24  has a smaller diameter than the first reduced diameter portion  24 B. Relative to the coated constant diameter portion  24 A, increased flexibility is provided by the first reduced diameter portion  24 B of the core wire or mandrel  24  covered by the proximal coil portion  26 A, and still further increased flexibility is provided by the second reduced diameter portion  24 C of the core wire or mandrel  24  covered by the distal coil portion  26 B. The guidewire  20  is therefore tapered along its length, with decreasing diameter sections toward the tip  22  to reduce stiffness to allow for better steerability. Thus, the guidewire  20  has flexibility that increases with proximity to the tip  22 , and stiffness that increases with increasing distance away from the tip  22 . As further shown in  FIG. 2 , the outside diameter of each of the external coating  28 , the proximal coil portion  26 A, and the distal coil portion  26 B may be substantially the same. The external coating  28  provides lubricity for navigation and for delivering catheters, and may include materials such as PTFE, polyurethanes, or silicone-based materials, that are preferably hydrophilic in nature. A coating may further include Heparin or other therapeutic agents to reduce thrombogenicity. 
     Maneuvering a guidewire within the body can be difficult. At least a certain degree of flexibility is necessary or desirable for most applications, but a guidewire must also maintain sufficient stiffness to provide support to permit advancement of a catheter. A static guidewire  20  such as illustrated in  FIG. 2  may have regions with differing flexibility and stiffness properties proximate to the tip  22 , but such properties are established during manufacture (therefore fixed with respect to time) and are not subject to temporal alteration (e.g., with respect to degree and/or position). Since stiffness of a static guidewire cannot be changed, a guidewire must be exchanged with another wire if a different stiffness is needed, thereby prolonging a surgical procedure with concomitant risk to the patient. Examples of conventional static guidewires (which come in various lengths, stiffnesses, and configurations) include LUNDERQUIST® Extra Stiff (Cook Inc., Bloomington, Ind., US), Amplatz™, and ASAHI INTECC® Standard (Asahi lntecc Co., Ltd., Nagoya, JP), among others. 
     Moveable core guidewires have been developed, such as the NAMIC® Angiographic Core Guidewire (North American Instrument Corp., Hudson Falls, N.Y., US) and the STARTER™ moveable core guidewire (Boston Scientific Scimed, Inc., Maple Grove, Minn., US). In certain instances, moveable core guidewires can change stiffness by moving a core wire within an outer coil. With the core removed, the remaining outer coil provides a flexible and generally atraumatic tip. A moveable core allows for changing a curvature of a J-shaped tip to aid in branch selection. However, frictional forces may render it difficult to move a core through an outer coil when the guidewire is positioned in a tightly curved path, and movement of a core relative to an outer coil also entails the risk that a core may inadvertently stab through a coil, thereby risking puncture of adjacent tissue. Safe core movement is typically limited to the most distal 10 cm (proximate to a tip) of a moveable core guidewire. Generally, moveable core guidewires have outer diameters of at least about 0.035 inch (0.89 mm) and tend to straighten when stiffness is increased. 
     Conventional guidewires may range in outer diameter from about 0.014 inch (0.36 mm) to about 0.038 inch (0.97 mm) (with smaller values corresponding to static guidewires), and may vary in length from about 45 cm to about 260 cm or more. Depending on the core material, a conventional static guidewire may have a minimum radius of curvature of from about 18 mm to about 40 mm, and a movable core guidewire may have a minimum radius of curvature (without deformation of the metal core) of from about 2 mm (e.g., in a state with the core removed) to about 18 mm (e.g., in a state with the core in place). 
     Guidewires that permit a certain degree of steerability have been developed, such as disclosed in International Patent Application Publication No. WO 2014/089273 A1 to Lenker et al. Additionally, guidewires with adjustable flexibility or stiffness are known, such as disclosed in U.S. Pat. No. 7,018,346 B2 to Griffin et al. and U.S. Pat. No. 8,551,019 B1 to Kroll. 
     Despite various developments in the guidewire art, the art continues to seek advancements in guidewires that may be actively steered and/or provide adjustable flexibility, to facilitate precise and rapid placement of a catheter in a desired location within a body. 
     SUMMARY 
     The present disclosure relates to guidewires that may be actively steered and/or provide adjustable stiffness. Active steering may include adjustment of an angle and/or curvature of a guidewire at one or more locations between a first end and a second end thereof. Adjustable stiffness may include adjustment of flexural modulus at one or more locations between a first end and a second end thereof. A guidewire with controllable stiffness may fulfill the roles of both floppy and stiff guidewires during a procedure, thereby obviating the need for guidewire exchange. 
     In one aspect, a guidewire device includes a tube having a longitudinal axis and an interior; and at least one variable stiffness segment arranged within the interior of the tube, wherein the at least one variable stiffness segment includes an electromagnet, at least one magnetically responsive element, and a compressible and/or extensible material arranged between the electromagnet and the at least one magnetically responsive element. In the at least one variable stiffness segment, the electromagnet is configured to receive at least one electrical signal to selectively generate a magnetic field sufficient to interact with the at least one magnetically responsive element, thereby exerting a compression or extension force on the compressible and/or extensible material to adjust a stiffness of the at least one variable stiffness segment. 
     In certain embodiments, the at least one variable stiffness segment comprises a plurality of variable stiffness segments that are sequentially arranged along the longitudinal axis. In certain embodiments, each variable stiffness segment of the plurality of variable stiffness segments is independently controllable. In certain embodiments, the compressible and/or extensible material includes a foam material. In certain embodiments, the at least one magnetically responsive element includes at least one metal element. 
     In certain embodiments, the guidewire device further includes a plurality of electrical conductors arranged in or on the tube and operatively coupled with the at least one variable stiffness segment to supply the at least one electrical signal. In certain embodiments, a plurality of circumferentially contractible fiber regions is arranged in or on the tube, wherein each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions is longitudinally spaced from each other circumferentially contractible fiber region. In certain embodiments, a plurality of radially contractible fiber regions is arranged in or on the tube, wherein each radially contractible fiber region of the plurality of radially contractible fiber regions is longitudinally spaced from each other radially contractible fiber region. In certain embodiments, the tube includes a polymer adhesive, and the guidewire device includes at least one electrical conductor configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
     In another aspect, a guidewire device includes a tube having a longitudinal axis, a first end, a second end, and an interior; a plurality of body elements and a plurality of pivot joints sequentially arranged in a longitudinal direction within the interior of the tube between the first end and the second end, wherein each body element of the plurality of body elements is connected to at least one other body element via at least one pivot joint of the plurality of pivot joints; and a plurality of tensile elements extending in the longitudinal direction through the tube from the first end toward the plurality of body elements. Different tensile elements of the plurality of tensile elements terminate at different body elements of the plurality of body elements, and are separately operable to cause pivotal movement between different body elements of the plurality of body elements, thereby permitting adjustment of an angle or curvature of the guidewire device at multiple positions along the longitudinal axis. 
     In certain embodiments, the plurality of tensile elements includes at least one agonist tensile element and at least one antagonist tensile element, wherein the at least one antagonist tensile element is configured to be operated to counteract the at least one agonist tensile element to control pivotal movement between different body elements of the plurality of body elements. In certain embodiments, the plurality of tensile elements are operatively connected to a plurality of tensioning elements configured to selectively apply tension to different tensile elements of the plurality of tensile elements. In certain embodiments, the plurality of tensioning elements are arranged beyond the first or second end of the tube. 
     In certain embodiments, a plurality of circumferentially contractible fiber regions is arranged in or on the tube, wherein each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions is longitudinally spaced from each other circumferentially contractible fiber region. In certain embodiments, each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions comprises an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. 
     In certain embodiments, a plurality of radially contractible fiber regions is arranged in or on the tube, wherein each radially contractible fiber region of the plurality of radially contractible fiber regions is longitudinally spaced from each other radially contractible fiber region. In certain embodiments, each radially contractible fiber region of the plurality of radially contractible fiber regions comprises an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. 
     In certain embodiments, the tube comprises a polymer adhesive, and the guidewire device includes at least one electrical conductor configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
     In another aspect, a guidewire device includes a tubular body having a longitudinal axis, a first end, a second end, and an interior; a plurality of longitudinally contractible fiber regions arranged in or on the tubular body, wherein each longitudinally contractible fiber region of the plurality of longitudinally contractible fiber regions is laterally spaced from each other longitudinally contractible fiber region; and a plurality of circumferentially contractible fiber regions arranged in or on the tubular body, wherein each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions is longitudinally spaced from each other circumferentially contractible fiber region. Different longitudinally contractible fiber regions of the plurality of longitudinally contractible fiber regions are separately operable to adjust an angle or curvature of the guidewire device between the first end and the second end; and different circumferentially contractible fiber regions of the plurality of circumferentially contractible fiber regions are separately operable to locally adjust a stiffness of the tubular body. 
     In certain embodiments, each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions includes an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. In certain embodiments, each longitudinally contractible fiber region of the plurality of longitudinally contractible fiber regions includes an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. 
     In certain embodiments, a plurality of radially contractible fiber regions are arranged in or on the tubular body, wherein each radially contractible fiber region of the plurality of radially contractible fiber regions is longitudinally spaced from each other radially contractible fiber region. In certain embodiments, each radially contractible fiber region of the plurality of radially contractible fiber regions includes an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. In certain embodiments, the tubular body includes a polymer adhesive, and the guidewire device includes at least one electrical conductor configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
     In another aspect, a guidewire device includes a tubular body having a longitudinal axis, a first end, a second end, and an interior; and a plurality of adjustable flexure elements arranged in or on the tubular body; wherein the plurality of adjustable flexure elements are electrically operable to adjust an angle or curvature of the guidewire device between the first end and the second end. In certain embodiments, the plurality of adjustable flexure elements includes at least one pair of adjustable flexure elements including first and second opposing flexure elements arranged at different lateral positions relative to the tubular body. In certain embodiments, the at least one pair of adjustable flexure elements includes a first pair of adjustable flexure elements and a second pair of adjustable flexure elements, wherein the first pair of adjustable flexure elements and the second pair of adjustable flexure elements are arranged at different longitudinal positions relative to the tubular body. 
     In certain embodiments, each adjustable flexure element of the plurality of adjustable flexure elements is electrically operable. In certain embodiments, each adjustable flexure element of the plurality of adjustable flexure elements includes an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. In certain embodiments, each adjustable flexure element of the plurality of adjustable flexure elements further includes a coating layer or backbone layer arranged in contact with the electrically responsive material. In certain embodiments, the guidewire device includes a plurality of conductors in electrical communication with the plurality of adjustable flexure elements. In certain embodiments, at least one adjustable flexure element of the plurality of adjustable flexure elements is independently controllable relative to at least one other adjustable flexure element of the plurality of adjustable flexure elements. 
     In certain embodiments, a plurality of circumferentially contractible fiber regions is arranged in or on the tubular body, wherein each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions is longitudinally spaced from each other circumferentially contractible fiber region. In certain embodiments, each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions includes an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. 
     In certain embodiments, a plurality of radially contractible fiber regions is arranged in or on the tubular body, wherein each radially contractible fiber region of the plurality of radially contractible fiber regions is longitudinally spaced from each other radially contractible fiber region. In certain embodiments, each radially contractible fiber region of the plurality of radially contractible fiber regions includes an electrically responsive material selected from the group consisting of a piezoelectric material, an electroactive polymer, and a nitinol alloy. In certain embodiments, the tubular body includes a polymer adhesive, and the guidewire device includes at least one electrical conductor configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
     In another aspect, a guidewire device includes a tube having a longitudinal axis, a first end, a second end, and an interior; a flexible guide wire or track arranged within the tube; and a plurality of translatable elements arranged to independently translate along the flexible guide wire or track parallel to the longitudinal axis; wherein each translatable element of the plurality of translatable elements is electrically operable to be translated in a longitudinal direction and thereby adjust a stiffness, angle, or curvature of the guidewire device between the first end and the second end. In certain embodiments, each translatable element of the plurality of translatable elements includes an electric motor unit. 
     In certain embodiments, the electric motor unit of each translatable element of the plurality of translatable elements is controllable by a signal of a different frequency from each other electric motor unit of the guidewire device. In certain embodiments, the flexible guide wire or track includes a plurality of grooves or teeth, and each electric motor unit includes an engagement element arranged to engage with the plurality of grooves or teeth. In certain embodiments, the tube includes a polymer adhesive, and the guidewire device includes at least one electrical conductor configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
     In another aspect, a guidewire device includes a tube having a longitudinal axis, a first end, a second end, and an interior; and a plurality of wires arranged in or on the tube. The tube includes a polymer adhesive, and at least one wire of the plurality of wires is configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
     In certain embodiments, the plurality of wires includes braided wires or multiple wires twisted about a core wire. In certain embodiments, each wire of the plurality of wires includes at least one flat side surface arranged to contact a flat side surface of another wire of the plurality of wires. In certain embodiments, each wire of the plurality of wires includes a polygonal cross-sectional shape. In certain embodiments, each wire of the plurality of wires includes a hexagonal cross-sectional shape. In certain embodiments, at least some wires of the plurality of wires comprise metal. In certain embodiments, at least some wires of the plurality of wires comprise conductive polymer material or composite material. 
     In certain embodiments, a guidewire device as disclosed herein includes a metal coil spring or flexible metal sheath extending generally parallel to the longitudinal axis and surrounding at least a portion of a tube or tubular element of the guidewire device. 
     In certain aspects, a diagnostic or therapeutic device includes a catheter as well as a guidewire device as disclosed herein, wherein the catheter is configured to be advanced over the guidewire device. 
     In certain aspects, a method for diagnosis or therapeutic intervention comprises insertion of a guidewire device as disclosed herein into a lumen system of a mammalian (e.g., human or animal) body, followed by advancement of a catheter over the guidewire device. During such insertion, one or more properties such as stiffness, angle, and/or curvature of the guidewire device may be adjusted at one or more positions between a distal end and proximal end thereof. 
     In certain aspects, any of the preceding aspects or other features disclosed here may be combined for additional advantage. 
     Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional schematic view of a flexible guidewire being advanced past a first curve or bend of a vessel lumen. 
         FIG. 1B  is a cross-sectional schematic view of the flexible guidewire and vessel lumen of  FIG. 1A  following advancement of the flexible guidewire past a second curve or bend of the vessel lumen. 
         FIG. 10  is a cross-sectional schematic view of the flexible guidewire and vessel lumen of  FIGS. 1A and 1B  following advancement of a catheter over a portion of the flexible guidewire within the vessel lumen. 
         FIG. 2  is a side cross-sectional schematic view of a portion of a conventional flexible guidewire that includes a variable diameter longitudinal core wire or mandrel and a flexible coil arranged over the core wire or mandrel proximate to a distal tip of the guidewire. 
         FIG. 3  provides perspective, partial cross-sectional views of first and second conventional bundled wire systems each including multiple wires with adhesive polymer between and around the wires. 
         FIG. 4  is a table depicting cross-sectional geometries and identifying numbers of wires and overall diameters for five different bundled wire system prototype designs A-E. 
         FIG. 5  is a perspective view of a pultruder used to make the bundled wire system prototype designs A-E described in connection with  FIG. 4 . 
         FIG. 6  is a schematic cross-sectional view of a die portion of the pultruder of  FIG. 5 . 
         FIG. 7A  is a schematic cross-sectional view of a section of an exemplary bundled wire system including a biocompatible adhesive polymer arranged between and around multiple wires. 
         FIG. 7B  is a schematic elevation view of a section of another exemplary bundled wire system similar to the bundled wire system of  FIG. 7A , following application of a polyolefin coating around a subassembly of wires and polycaprolactone (PCL) upon exit from a pultruder. 
         FIG. 7C  is a schematic elevation view of a section of another exemplary bundled wire system similar to the bundled wire system of  FIG. 7A , in which wires and PCL are pushed through a coil spring while the wires and PCL are still warm. 
         FIG. 8A  is a perspective view of a modeling diagram of the bundled wire system according to prototype design A described in connection with  FIG. 4 , to permit finite element analysis (FEA) of the bundled wire system as a cantilever beam subject to bending. 
         FIG. 8B  provides graphical FEA modeling results for the bundled wire system according to prototype design A of  FIG. 8A  in the stiff (cool) state. 
         FIG. 8C  provides graphical FEA modeling results for the bundled wire system according to prototype design A of  FIG. 8A  in the floppy (warm) state. 
         FIG. 9A  illustrates an INSTRON® materials testing machine used to apply three point bending to physical samples of bundled wire systems described herein. 
         FIG. 9B  is a magnified view of a portion of the testing machine of  FIG. 9A . 
         FIG. 10  is a plot of load or force versus displacement for “no current” (corresponding to a stiff or cool state) and “current” (corresponding to a floppy or warm state) conditions, including predicted slope obtained by FEA modeling and measured slope obtained by empirical testing for the bundled wire system according to prototype design A, including seven wires and adhesive without any coating, as described in connection with  FIG. 4 . 
         FIG. 11  is a plot of load or force versus displacement for “no current” (corresponding to a stiff or cool state) and “current” (corresponding to a floppy or warm state) conditions, including predicted slope obtained by FEA modeling and measured slope obtained by empirical testing for the bundled wire system according to prototype design B, including seven wires and adhesive sheathed in polyolefin heat shrink tubing, as described in connection with  FIG. 4 . 
         FIG. 12  is a plot of load or force versus displacement for “no current” (corresponding to a stiff or cool state) and “current” (corresponding to a floppy or warm state) conditions, including predicted slope obtained by FEA modeling and measured slope obtained by empirical testing for the bundled wire system according to prototype design C, including nineteen wires and adhesive without any coating, as described in connection with  FIG. 4 . 
         FIG. 13  is a plot of load or force versus displacement for “no current” (corresponding to a stiff or cool state) and “current” (corresponding to a floppy or warm state) conditions, including predicted slope obtained by FEA modeling and measured slope obtained by empirical testing for the bundled wire system according to prototype design D, including nineteen wires and adhesive sheathed in polyolefin heat shrink tubing, as described in connection with  FIG. 4 . 
         FIG. 14  is a plot of load or force versus displacement for “no current” (corresponding to a stiff or cool state) and “current” (corresponding to a floppy or warm state) conditions, including predicted slope obtained by FEA modeling and measured slope obtained by empirical testing for the bundled wire system according to prototype design E, including nineteen wires and adhesive sheathed in a stainless steel spring, as described in connection with  FIG. 4 . 
         FIG. 15  is a plot of retained displacement (mm) versus starting displacement (mm) for bundled wire systems according to prototype designs A and C as described in connection with  FIG. 4 . 
         FIG. 16  is a table providing numerical results obtained by the deformation-holding test described herein for bundled wire systems according to prototype designs A and C as described in connection with  FIG. 4 . 
         FIG. 17  is a table summarizing numerical results of FEA modeled E f  (stiff state), tested (physical) E f  (stiff state), FEA modeled E f  (floppy state), tested (physical) E f  (floppy state), stiff state displacement at adhesion failure, stiff state radius of curvature at adhesion failure, force at stiff state adhesion failure, and minimum radius of curvature for bundled wire systems according to prototype designs A to E as described in connection with  FIG. 4 . 
         FIG. 18  is a table summarizing numerical results of flexural modulus and minimum radius of curvature without plastic deformation, as well as observations as to whether shape is maintained during stiffness change, for bundled wire systems according to prototype designs A and C as described in connection with  FIG. 4 . 
         FIG. 19  illustrates a bundled wire system including six wires each having a hexagonal cross-sectional shape bundled around a central wire also having the same shape, with polymer adhesive arranged around and between the wires and forming a generally tubular shape. 
         FIG. 20  illustrates a bundled wire system in which multiple wires of round cross-sectional shapes are twisted about a central core wire, with polymer adhesive preferably arranged around and between the wires. 
         FIG. 21  illustrates an external sheath of a commercially available JOURNEY® guidewire. 
         FIG. 22A  schematically illustrates a portion of a guidewire device in which stiffness at one or more locations may be adjusted by selective operation or modulation of one or more electromagnetic elements, according to one embodiment of the present disclosure. 
         FIG. 22B  schematically illustrates a portion of a guidewire device in which stiffness at one or more locations may be adjusted by selective operation or modulation of one or more electromagnetic elements, including longitudinally extending conductors inset slightly relative to a tubular body, according to one embodiment of the present disclosure. 
         FIG. 23A  is a schematic cross-sectional view of a portion of a guidewire device according to one embodiment in which angle or radius of curvature at one or more locations may be adjusted by applying current to electrically operable adjustable flexure elements arranged in or on a tubular body, in which each flexure element of a pair of adjustable flexure elements is in a straightened state. 
         FIG. 23B  is a schematic cross-sectional view of a portion of the guidewire device of  FIG. 23A , in which the pair of adjustable flexure elements is curved to the left. 
         FIG. 23C  is a schematic cross-sectional view of a portion of the guidewire device of  FIG. 23A , in which the pair of adjustable flexure elements is curved to the right. 
         FIG. 24A  is a simplified schematic cross-sectional illustration of a portion of a guidewire device according to one embodiment, including multiple pairs of electrically operable adjustable flexure elements arranged at different locations in or on a tubular body around a longitudinally extended flexible core, wherein angle or radius of curvature at one or more locations may be adjusted by applying current to the pairs of electrically operable adjustable flexure elements. 
         FIG. 24B  is a first cross-sectional illustration of the guidewire device according to  FIG. 24A , including a first pair of adjustable flexure elements. 
         FIG. 24C  is a second cross-sectional illustration of the guidewire device of  FIG. 24A , including a second pair of adjustable flexure elements. 
         FIG. 25  is a cross-sectional illustration of a portion of a guidewire device according to one embodiment similar to the device of  FIGS. 24A-24C , including multiple pairs of adjustable flexure elements arranged in a tubular body with peripherally arranged electrical conductors, and with first and second pairs of adjustable flexure elements arranged at the same or a similar longitudinal position. 
         FIG. 26  is a cross-sectional illustration of a portion of a guidewire device according to one embodiment similar to the device of  FIG. 25 , including multiple pairs of adjustable flexure elements arranged in a tubular body with medially arranged electrical conductors, and with first and second pairs of adjustable flexure elements arranged at the same or a similar longitudinal position. 
         FIG. 27A  is a simplified cross-sectional schematic illustration of a portion of a guidewire device including multiple body elements and multiple pivot joints that are sequentially arranged in a longitudinal direction within a tubular body, wherein each body element is connected to at least one other body element via at least one pivot joint, according to one embodiment of the present disclosure. 
         FIG. 27B  is a cross-sectional schematic illustration of the portion of the guidewire device corresponding to  FIG. 27A , with addition of tensile elements extending in a longitudinal direction within the tubular body. 
         FIG. 27C  is a cross-sectional schematic view of a portion of the guidewire device corresponding to  FIG. 27B , while omitting one (antagonist) set of guidewires for clarity, and showing another (agonist) set of guidewires following application of tension. 
         FIG. 28A  is a grid of (horizontally arranged) longitudinally contractible fiber regions and (vertically arranged) circumferentially contractible fiber regions that may be incorporated into a guidewire device, according to one embodiment of the present disclosure. 
         FIG. 28B  is a perspective view illustration of a tubular structure of longitudinally contractible fiber regions and circumferentially contractible fiber regions obtained by rolling the grid of  FIG. 28A  into a tubular shape, according to one embodiment of the present disclosure. 
         FIG. 28C  is a cross-sectional view of a tubular body incorporating the tubular structure of  FIG. 28B . 
         FIG. 29  is a cross-sectional illustration of at least a portion of a guidewire device similar to  FIG. 28C , with addition of a longitudinally extending flexible core according to one embodiment of the present disclosure. 
         FIG. 30  is a cross-sectional illustration of at least a portion of a guidewire device similar to  FIG. 28C , with addition of a plurality of radially contractible fiber regions arranged in or on the tubular body according to one embodiment of the present disclosure. 
         FIG. 31  is a cross-sectional schematic illustration of a portion of a guidewire device according to one embodiment of the present disclosure, including a longitudinal axis, a first end, a second end, and an interior, with a centrally arranged flexible guide wire or track arranged within the interior. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to guidewires that may be actively steered and/or provide adjustable stiffness. The term “and/or” as used herein encompasses either or all of multiple stated possibilities. Active steering may include adjustment of an angle and/or curvature of a guidewire at one or more locations between a first end and a second end thereof. Adjustable stiffness may include adjustment of flexural modulus at one or more locations between a first end and a second end thereof. 
     Guidewires as disclosed herein are intended and suitable for insertion into a vessel lumen system of a mammalian (e.g., human) body, and to provide a stable platform for advancement of catheters for performance of diagnostic and/or therapeutic methods. During such insertion, one or more properties such as stiffness, angle, and/or curvature of the guidewire may be adjusted at one or more positions between a distal end and proximal end thereof. 
     To investigate a potential mechanism of action for adjusting stiffness, bundled wire systems held together with low melting point polymer adhesive were modeled and separately tested. Stiffness of each bundle may be controlled by resistive Joule heating, by applying electrical current to the wires to soften (e.g., melt) the polymer adhesive. When in a cool state, a wire bundle is stiff since the polymer firmly couples the wires to one another. However, when heated to a warm state, a wire bundle is floppy in character, since the melted polymer softens and flows, thereby decoupling the wires and permitting the wires to adopt a new geometry. 
     Representative bundled wire systems  30 ,  40  are illustrated in  FIG. 3 . At left,  FIG. 3  illustrates a bundled seven-wire system  30  with adhesive polymer 32 between and around wires  34 ,  36 , in which a group of six peripheral wires  36  form a single-layer ring around a center wire  34 . At right,  FIG. 3  illustrates a bundled nineteen-wire system  40  with adhesive polymer 42 between and around multiple wires  44 ,  46 ,  48 , in which a first group of six wires  46  forms a first ring around a center wire  44 , and a second group of twelve wires  48  forms a second ring around the first group of six wires  46 , thus forming a double layer bundle. The wires  44 ,  46 ,  48  in the double layer bundle of the nineteen-wire system  40  at right are substantially smaller in diameter than the wires  34 ,  36  in the single layer bundle of the seven-wire system  30  at left. In each instance, close-packed cylindrical bundles are formed of concentric layers of straight wire, with each bundle including wires of uniform size. The stiffness range depends on the number of wires, wherein more wires yield a greater reduction in stiffness, and the minimum radius of curvature depends on individual wire diameter. 
       FIG. 4  is a table identifying five different bundled wire system prototype designs A to E. Each prototype design used steel music wire (ASTM 228), 0.015 inch (0.38 mm) individual wire diameter, 6 inches (15.2 cm) long, with properties similar to medical grade Type 304 stainless steel as commonly used in guidewires. In each case, a biocompatible adhesive polymer (INSTAMORPH® polycaprolactone (Happy Wire Dog, LLC, Scottsdale, Ariz., US) or “PCL”) was used, with such material exhibiting a low melting point of 60° C. A bundled wire system  50  according to the design of Prototype A included seven wires (with six peripheral wires  56  forming a single-layer ring around a center wire  54 ) embedded in adhesive polymer 52 with an overall diameter of 0.045 inch (1.14 mm). The bundled wire system  60  according to the design of Prototype B included seven wires (with six peripheral wires  66  forming a single-layer ring around a center wire  64 ) embedded in adhesive polymer 62 and coated with polyolefin (PO) heat shrink tubing  65 , yielding an overall diameter of 0.067 inch (1.7 mm). The polyolefin heat shrink tubing  65  was intended to keep the wires  64 ,  66  bundled together under bending, and to resist the tendency for adhesion to fail. The bundled wire system  70  according to the design of Prototype C included nineteen wires (with a first group of six wires  76  forming a first ring around a center wire  74 , and a second group of twelve wires  78  forming a second ring around the first ring) embedded in adhesive polymer 72, with an overall diameter of 0.075 inch (1.91 mm). The bundled wire system  80  according to the design of Prototype D included nineteen wires (with a first group of six wires  86  forming a first ring around a center wire  84 , and a second group of twelve wires  88  forming a second ring around the first ring) embedded in adhesive polymer 82 and coated with polyolefin heat shrink tubing  87 , yielding an overall diameter of 0.091 inch (2.31 mm). The bundled wire system  90  according to the design of Prototype E included 19 wires (with a first group of six wires  96  forming a first ring around a center wire  94 , and a second group of twelve wires  98  forming a second ring around the first ring) embedded in adhesive polymer 92 and wrapped with a stainless steel spring  99 , yielding an overall diameter of 0.125 inch (3.18 mm). 
     The minimum radius (p) of curvature achievable by a wire bundle when bent was calculated as equal to the minimum radius of curvature achievable by the innermost wire before plastically deforming (in other words, when the maximum axial stress in the material reached its yield stress). The minimum radius (p) of curvature is calculated as the product of the flexural modulus of the wire material and the radius of the individual wire, divided by the yield stress. 
       FIG. 5  depicts a pultruder  100  used to make prototypes of bundled wire systems according to the prototype designs A to E described hereinabove. The pultruder  100  includes a support rod  102  and an adjustable height linkage  104  with a shelf  106  that supports a heated die portion  110 , with a clamp  108  affixing a die  112  to the shelf  106 . The pultruder  100  is configured to receive wires  134  from above, contain molten material therein, and eject a cylindrical wire bundle at bottom.  FIG. 6  is a schematic cross-sectional view of the heated die portion  110  of the pultruder  100  of  FIG. 5 . Referring to  FIG. 6 , the heated die portion  110  includes the die  112 , which is fabricated of aluminum and has a substantially cylindrical outer wall  114  surrounded at least in part by a peripheral heating collar  126  that is configured to supply heat to the die  112 . The die  112  further includes a cavity  122  bounded by an upper or entrance opening  116 , a tapered lower wall  118 , and a lower or exit opening  120 . In use, straight wires  134  are fed through the upper or entrance opening  116  and into the cavity  122  of the die  112  to contact molten PCL  124  contained therein. Feedback control of temperature is provided with a thermocouple  129  in conductive communication with the die  112 . When the wires  134  are fed into the die  112 , molten PCL  124  coats the wires  134  externally and therebetween, and as the wires  134  are pulled through the lower or exit opening  120 , the wires  134  and solidified PCL  132  form a cylindrical bundle  130  having the same diameter as the lower or exit opening  120 . Specifically, the close fit of the lower or exit opening  120  packs the wires  134  together into the cylindrical bundle  130 , which is held together by solidified PCL  132  (i.e., that solidifies from molten PCL  124  as it cools). 
     Three different bundled wire system configurations obtainable at least in part using the pultruder  100  and heated die portion  110  illustrated in  FIGS. 5 and 6  are schematically illustrated in  FIGS. 7A to 7C .  FIG. 7A  illustrates an exemplary bundled wire system  130  obtained by feeding multiple wires  134  through a pultruder  100  and permitting PCL  132  to cool around and between the wires  134 .  FIG. 7B  illustrates an exemplary bundled wire system  140  similar to the bundled wire system  130  of  FIG. 7A , but following application of a polyolefin coating  137  (e.g., in the form of heat shrink tubing) around an exterior of PCL  132  and wires  134  upon exit from a pultruder (not shown). More specifically, a section of tubing  137 ′ may receive heat H from a heat source (not shown) to cause the tubing  137 ′ to contract and form the polyolefin coating  137 .  FIG. 7C  illustrates an exemplary bundled wire system  141  similar to the bundled wire system  130  of  FIG. 7A , wherein the wires  134  and PCL  132  exiting a pultruder (not shown) are pushed through a coil spring  139  while the wires  134  and PCL  132  are still warm. 
     Examples of the above-described five different bundled wire systems  50 ,  60 ,  70 ,  80 ,  90  according to prototype designs A to E were subjected to finite element analysis (FEA) modeling to provide predicted performance as well as physical analysis to yield measured performance.  FIG. 8A  is a perspective view modeling diagram of the bundled wire system  50  according to prototype design A, following finite element analysis as a cantilever beam subject to bending (with one end fixed and the other end free). A beam length of 0.02 meters and an applied load of 0.05 Newtons were used, with the model being used to measure displacement D of the free end under application of an edge load F to determine flexural modulus in stiff and floppy states, to permit calculation of flexural modulus (equal to the product of the edge load F times the length of the beam L cubed, divided by three times the product of the second area moment of inertia and the displacement).  FIG. 8B  provides graphical FEA modeling results (including deformation as a function of position) for the bundled wire system  50  according to prototype design A in the stiff (cool) state, and  FIG. 8C  provides graphical FEA modeling results for the bundled wire system  50  according to prototype design A in the floppy (warm) state.  FIGS. 8B and 8C  embody diagrams converted from color to grayscale, and in each figure, letter codes have been added to the figure and corresponding legend to permit visualization of flexural modulus values as follows: R=red, O=orange, Y=yellow, G=green, LB=light blue, and B=blue. The modulus of elasticity E f  was reduced from 134 GPa in the stiff (cool) state (shown in  FIG. 8B ) to less than 17 GPa in the floppy (warm) state (shown in  FIG. 8C ). 
       FIG. 9A  illustrates an INSTRON® materials testing machine  150  (Illinois Tool Works Inc., Glenview, Ill., US), and  FIG. 9B  illustrates a magnified portion of the same machine  150 , used to apply three point bending to physical samples using an upper cylindrical roller  151  configured to translate downward and apply a force F along a centerline between two lower cylindrical rollers  152 ,  153  spaced apart by a distance L. In one set of tests, the force F required to attain a displacement D was measured in order to determine the flexural modulus E f  of a prototype bundled wire system, with determination of F and D when the prototype fails. A length L of 0.04 meter between the lower cylindrical rollers  152 ,  153  was used. The flexural modulus for a beam subjected to three-point bending is calculated as the applied force times the length cubed, divided by forty-eight times the product of the second area moment of inertia and the diameter. Each prototype bundled wire system  50 ,  60 ,  70 ,  80 ,  90  according to prototype designs A to E was tested in a stiff state (cool, with no electric current) and a floppy state (in which electric current was applied to the core wires to heat the sample). Another protocol using the same INSTRON® materials testing machine  150  was used to perform a deformation-holding test on each prototype bundled wire system  50 ,  60 ,  70 ,  80 ,  90 , with the deformation-holding test serving to measure the extent to which the bundled wire system  50 ,  60 ,  70 ,  80 ,  90  held its deformed shape (and therefore resisted straightening due to internal stresses of bent wires) after cooling. The idea is to determine the minimum bending radius that the thermoplastic adhesive can sustain without failing. In each case, a prototype bundled wire system  50 ,  60 ,  70 ,  80 ,  90  was subjected to three-point bending, whereby the bundled wire system was bent to a prescribed displacement when in the floppy (warm) state, then allowed to cool while displaced/loaded, followed by removal of the load. Thereafter, the displacement to which the bundled wire system springs back was measured, and scrutiny was applied to observe any adhesion failure. The minimum radius of curvature for any given displacement D at the midpoint is calculated as the length squared divided by twelve times the displacement D. 
       FIGS. 10-14  are plots of load or force F (in Newtons) versus displacement D (in millimeters), for “no current” (corresponding to a stiff or cool state) and “current” (corresponding to a floppy or warm state) conditions, including predicted slope obtained by FEA modeling and measured slope obtained by empirical testing (with an INSTRON® materials testing machine as outlined above), for the bundled wire systems  50 ,  60 ,  70 ,  80 ,  90  according to prototype designs A to E (illustrated and described in connection with  FIG. 4 ), respectively. The slope of each line corresponds to flexural modulus E f .  FIG. 10  provides results for the bundled wire system  50  according to Prototype design A including seven wires and adhesive without any coating. Adhesion among wires in the bundled wire system  50  failed at around 0.48 mm at a force of approximately 2.8N (indicated by the arrow at left).  FIG. 11  provides results for the bundled wire system  60  according to Prototype B, including seven wires and adhesive sheathed in polyolefin heat shrink tubing. Adhesion among wires in the bundled wire system  60  failed at around 0.37 mm at a force of approximately 2.0N (indicated by the arrow at left).  FIG. 12  provides results for the bundled wire system  70  according to Prototype C, including nineteen wires and adhesive without any coating. Adhesion among wires in the bundled wire system  70  failed at around 0.435 mm at a force of approximately 13.2N (indicated by the arrow at left).  FIG. 13  provides results for the bundled wire system  80  according to Prototype D including nineteen wires and adhesive sheathed in polyolefin heat shrink tubing. Adhesion among wires in the bundled wire system  80  failed at around 0.28 mm at a force of approximately 7.2N (indicated by the arrow at left).  FIG. 14  provides results for the bundled wire system  90  according to Prototype E including nineteen wires and adhesive sheathed in a 0.125 inch (3.18 mm) stainless steel spring. Adhesion among wires in the bundled wire system  90  failed at around 0.15 mm at a force of approximately 11.2N (indicated by the arrow at left). 
     In each of  FIGS. 10-14 , the “no current” or stiff (cool) state provides a substantially greater flexural modulus E f  value than the “current” or floppy (warm) state. Upon review of  FIGS. 10-14 , it is apparent that the “cool” wire bundles exhibit two slopes, including a high stiffness region characterized by a steep slope for up to about 0.5 mm until adhesion suddenly fails, and a low stiffness region characterized by a shallow slope in which stiffness is roughly equivalent to the “warm” or floppy state. Observation and inspection of the wires during and after this sudden change in slope showed that the wires and polymer adhesive indeed separated. Neither the polyolefin heat shrink tubing nor the stainless steel spring appeared to prevent or delay the onset of delamination; however, the stainless steel spring did keep the bundled wire system&#39;s circular cross-sectional shape from deforming, in contrast to all of the other prototypes A to D, which exhibited a flattened cross-section at the point where load was applied. All tested wires held their deformed shape when cooled from the warm state while held in position under load, and this could be reversed by reheating the wire electrically. There was a limit to how much bend a wire could hold without breaking the adhesion, and each wire exhibited a tendency to spring back. Each bundled wire system prototype would not straighten more when allowed to cool. 
       FIG. 15  is a plot of retained displacement (mm) versus starting displacement (mm) for bundled wire systems  50 ,  70  according to prototype designs A and C, and  FIG. 16  is a table providing numerical results for the same bundled wire systems  50 ,  70  according to prototype designs A and C, obtained by the deformation-holding test described hereinabove. As shown in  FIGS. 15 and 16 , the bundled wire system prototypes  50 ,  70  can maintain some of the deformation/curvature they have undergone when cooled, up to a certain displacement. The solidified polymer adhesive resists some but not all of the straightening of the steel wires. Past this displacement, the bundled wire system prototypes  50 ,  70  lose the ability to maintain deformation/curvature in the cold state due to adhesion failure. In particular, the polymer adhesive peels from the metal, and the adhesion strength is not sufficient to resist the straightening of the wires without breaking. 
       FIG. 17  is a table summarizing numerical results of FEA modeled E f  (stiff state), tested (physical) E f  (stiff state), FEA modeled E f  (floppy state), tested (physical) E f  (floppy state), stiff state displacement at adhesion failure, stiff state radius of curvature at adhesion failure, force at stiff state adhesion failure, and minimum radius of curvature for bundled wire systems  50 ,  60 ,  70 ,  80 ,  90  according to prototype designs A to E (illustrated and described in connection with  FIG. 4 ). In general, the FEA models appear to accurately predict E f  values of the prototypes A to E in the floppy state, thereby suggesting that in the floppy state, each bundled wire system prototype  50 ,  60 ,  70 ,  80 ,  90  behaves as a bundle of uncoupled wires. However, the FEA models generally overestimate E f  values for the bundled wire system prototypes  50 ,  60 ,  70 ,  80 ,  90  in the stiff state. This may suggest that the effective E f  value of the polymer adhesive is less than the literature value used in the FEA model, and/or it may suggest the possible existence of voids between the wires in which polymer adhesive is absent, thereby decreasing adhesion strength and lowering the effective stiffness of the PCL between the wires. 
       FIG. 18  is a table summarizing numerical results of flexural modulus and minimum radius of curvature without plastic deformation, as well as observations as to whether shape is maintained during stiffness change, for bundled wire systems  50 ,  70  according to prototype designs A and C. 
     The preceding disclosure including  FIGS. 3 to 18  demonstrates the viability of bundled wire systems as prototypes for guidewires having stiffness properties that can be changed by coupling at least one electrical conductor (e.g., one or more bundled wire systems) with an electric power source for resistive heating of a polymer adhesive binding the wires, by which a stiffness property of the polymer adhesive may be adjusted. Although adhesion between wires was not necessarily improved by external application of polyolefin coatings or helical coil springs, the use of coil springs did preserve the circular cross-section of a wire bundle, which would tend to permit advancement of a catheter utilizing a bundled wire system (as opposed to potential jamming of a catheter during advancement over a guidewire if a bundle of wires were flattened in shape). Wires within a bundle tend to straighten in a cool state, but, unlike moveable core wires of a conventional moveable guidewire, a bundled wire system guidewire as described in connection with the foregoing figures would not apply more straightening force against vessel walls when stiffness is increased. 
     Consistent with the foregoing disclosure, in one aspect, the present disclosure relates to a guidewire device including a tube having a longitudinal axis, a first end, a second end, and an interior; and including a plurality of wires arranged in or on the tube; wherein the tube comprises a polymer adhesive, and at least one wire of the plurality of wires is configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. In certain embodiments, at least some wires of the plurality of wires include metal. In certain embodiments, at least some wires of the plurality of wires include conductive polymer material or composite material. In certain embodiments, combinations of wires including metal and wires including conductive polymer and/or composite materials may be used. 
     To address certain issues experienced with use of bundled wire system guidewire prototypes including parallel wires of round cross-sectional shapes, other wire shapes and/or orientations may be used. For example,  FIG. 19  illustrates a bundled wire system  160  including six wires  166  each having a hexagonal cross-sectional shape bundled around a central wire  164  also having the same shape, with polymer adhesive  162  arranged around and between the wires  164 ,  166  and forming a generally tubular shape. More generally, in certain embodiments, each wire of a plurality of wires may include a polygonal cross-sectional shape, or may include at least one flat side surface (preferably multiple flat side surfaces) arranged to contact a flat side surface of another adjacent wire. As another example,  FIG. 20  illustrates a bundled wire system  170  in which multiple (e.g., six) wires  176  of round cross-sectional shapes are twisted about a central core wire  174 , with polymer adhesive  172  preferably arranged around and between the wires  174 ,  176 . Alternatively, multiple wires may be braided. The preceding conformations may assist in maintaining wires in a generally round bundle even when a polymer adhesive contacting the wires is in a softened (e.g., warm and “floppy”) state. 
     In certain embodiments, guidewire devices as disclosed herein may include a metal coil spring extending generally parallel to a longitudinal axis of a tube or tubular body, and surrounding at least a portion of the tube or tubular body. In other embodiments, guidewire devices as disclosed herein may include a flexible metal sheath extending generally parallel to a longitudinal axis of a tube or tubular body, and surrounding at least a portion of the tube or tubular body. Such a coil spring or flexible metal sheath may embody an outer surface of a guidewire. One example of a flexible metal sheath  180  is shown in  FIG. 21 , which depicts an external sheath of a JOURNEY® guidewire (Boston Scientific Scimed, Inc., Maple Grove, Minn., US). In certain embodiments, a metal coil spring or flexible metal sheath may be used in lieu of a wire bundle within a tube, with the potential of providing improved bidirectional torque transmission. 
       FIG. 22A  schematically illustrates a portion of a guidewire device  190  in which stiffness at one or more locations may be adjusted by selective operation or modulation of one or more electromagnetic elements. The guidewire device  190  includes a tubular body (e.g., a tube)  191  including multiple variable stiffness segments  192 A,  192 B that may be separated by segments  199  lacking variable stiffness capability. In each variable stiffness segment  192 A,  192 B, a compressible and/or extensible material  193 A,  193 B is arranged between an electromagnet  194 A,  194 B and at least one magnetically responsive element  197 A,  197 B. The electromagnet  194 A,  194 B is configured to receive at least one electrical signal to selectively generate a magnetic field sufficient to interact with the at least one magnetically responsive element  197 A,  197 B, thereby exerting a compression or extension force on the compressible and/or extensible material  193 A,  193 B to adjust a stiffness of the variable stiffness segment  192 A,  192 B. In certain embodiments, when an electromagnet  194 A,  194 B is energized to exert an attractive force on at least one magnetically responsive element  197 A,  197 B (e.g., a metal such as carbon steel) separated therefrom by a compressible and/or extensible material  193 A,  193 B, the resulting attraction (as indicated by the vertically arranged arrows shown in  FIG. 22A ) tends to compress the compressible and/or extensible material  193 A,  193 B, thereby increasing stiffness of the variable stiffness segment(s)  192 A,  192 B. In certain embodiments, when an electromagnet  194 A,  194 B is energized to exert a repelling force on at least one magnetically responsive element  197 A,  197 B (e.g., a magnet or another electromagnet of the same polarity), the resulting repulsion tends to elongate or extend the compressible and/or extensible material  193 A,  193 B, thereby decreasing stiffness of the variable stiffness segment(s)  192 A,  192 B. 
       FIG. 22B  schematically illustrates a portion of another guidewire device  200  in which stiffness at one or more locations may be adjusted by selectively operation or modulation of one or more electromagnetic elements  204 A,  204 B. The guidewire device  200  includes a tubular body (e.g., a tube)  201  including multiple variable stiffness segments  202 A,  202 B, with longitudinally extending conductors  208 - 1 ,  208 - 2  inset slightly relative to the tubular body  201 . In each variable stiffness segment  202 A,  202 B, a compressible and/or extensible material  203 A,  203 B is arranged between an electromagnetic element  204 A,  204 B and at least one magnetically responsive element  207 A,  207 B. Each electromagnetic element  204 A,  204 B includes contact regions  205 A,  205 B,  206 A,  206 B arranged for conductive electrical communication with the longitudinally extending conductors  208 - 1 ,  208 - 2 . In certain embodiments, one or more contact regions  205 A,  205 B,  206 A,  206 B may include switching or gating elements arranged to control flow of current through an electromagnetic element  204 A,  204 B. In certain embodiments, each variable stiffness segment  202 A,  202 B may include one or more dedicated electrical conductors and/or each variable stiffness segment  202 A,  202 B may be independently controlled. In certain embodiments, each variable stiffness segment  202 A,  202 B may be separated from one another by at least one segment  209  lacking variable stiffness capability. 
     With respect to  FIGS. 22A and 22B , in certain embodiments, the compressible and/or extensible material  193 A,  193 B,  203 A,  203 B includes a foam material, which may embody a three-dimensional matrix. In certain embodiments, multiple variable stiffness segments  192 A,  192 B,  202 A,  202 B may be sequentially arranged along the longitudinal axis of a guidewire device  190 ,  200 , and may be independently controlled. In certain embodiments, longitudinally extending conductors (e.g.,  208 - 1 ,  208 - 2 ) may be arranged in or on the tubular body structure  191 ,  201  and operatively coupled with one or more variable stiffness segments  192 A,  192 B,  202 A,  202 B (e.g., including electromagnetic elements thereof) to supply electrical signals for adjusting stiffness. In certain embodiments, a tubular body  191 ,  201  may comprise a polymer adhesive, and a guidewire  190 ,  200  may include at least one electrical conductor configured to be coupled with an electric power source (not shown) for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. In certain embodiments, a plurality of circumferentially contractible fiber regions (e.g., piezoelectric material, an electroactive polymer, or a nitinol alloy, not shown but described hereinafter in connection with  FIGS. 28A-30 ) may be arranged in or on the tubular body  191 ,  201 , wherein each circumferentially contractible fiber region is longitudinally spaced from each other circumferentially contractible fiber region. In certain embodiments, a plurality of radially contractible fiber regions (not shown, but described hereinafter in connection with  FIGS. 28A-30 ) may be arranged in or on the tubular body  191 ,  201 , wherein each radially contractible fiber region (e.g., piezoelectric material, an electroactive polymer, or a nitinol alloy) is longitudinally spaced from each other radially contractible fiber region. If provided, each circumferentially contractible fiber region or radially contractible fiber region may further permit adjustment of stiffness and/or aid in steering in one or more regions of the guidewire element. In certain embodiments, a metal coil spring or flexible metal sheath (not shown, but described previously herein) may extend generally parallel to the longitudinal axis and surround at least a portion of the tubular body. 
       FIGS. 23A-23C  provide schematic cross-sectional views of a portion of a guidewire device  210  in which angle or radius of curvature at one or more locations may be adjusted by applying current to electrically operable adjustable flexure elements  212 ,  212 ′ arranged in or on a tubular body  211 .  FIGS. 23A-23C  each illustrates a pair of adjustable flexure elements  212 ,  212 ′ that are longitudinally oriented proximate to sides of the tubular body  211 . Each adjustable flexure element  212 ,  212 ′ may include a coating layer or backbone layer  213 ,  213 ′ (e.g., a metal) arranged in contact with an electrically responsive material  214 ,  214 ′ (e.g., a piezoelectric material, an electroactive polymer, or a nitinol alloy) that contracts, bends, or straightens with application of different voltage. The metal coating layer or backbone layer  213 ,  213 ′ may be used to adjust rigidity or compliance of the adjustable flexure element  212 ,  212 ′. In certain embodiments, for each adjustable flexure element  212 ,  212 ′, the electrically responsive material  214 ,  214 ′ may be medially located, and the coating layer or backbone layer  213 ,  213 ′ may be located closer to an outer surface of the tubular body  211 . Preferably, electrical conductors (not shown in  FIGS. 23A and 23B , but shown in  FIGS. 24B, 24C, 25, and 26 ) are arranged in electrical communication with the adjustable flexure elements  212 ,  212 ′. In certain embodiments, at least one adjustable flexure element  212 ,  212 ′ of the pair of adjustable flexure elements  212 ,  212 ′ is independently controllable relative to at least one other adjustable flexure element  212 ,  212 ′ of the pair of adjustable flexure elements  212 ,  212 ′.  FIG. 23A  shows the pair of adjustable flexure elements  212 ,  212 ′ in a straightened state.  FIG. 23B  shows the pair of adjustable flexure elements  212 ,  212 ′ each curved to the left, and  FIG. 23C  shows the pair of adjustable flexure elements  212 ,  212 ′ each curved to the right. 
       FIG. 24A  is a simplified schematic cross-sectional illustration of a portion of another guidewire device  220  in which angle or radius of curvature at one or more locations may be adjusted by applying current to electrically operable adjustable flexure elements  222 A,  222 A′,  222 B arranged in or on a tubular body  221 . Each adjustable flexure element (e.g.,  222 A,  222 A′,  222 B) includes a coating layer or backbone layer  223 A,  223 A′,  223 B (e.g., a metal) arranged in contact with an electrically responsive material  224 A,  224 A′ (e.g., a piezoelectric material, an electroactive polymer, or a nitinol alloy). Multiple (e.g., first and second) pairs of adjustable flexure elements are provided, wherein each pair of adjustable flexure elements includes first and second opposing flexure elements arranged at different lateral positions relative to the tubular body  221 . The second pair of flexure elements (including flexure element  222 B and a corresponding flexure element, not shown) is arranged at a different longitudinal position along the tubular body  221  relative to the first pair of opposing flexure elements ( 222 A,  222 A′). As shown in  FIG. 24A , the tubular body  221  includes a longitudinally extending flexible core  225 , such as may include one or more wires, fibers, or similar elements. In certain embodiments, the flexible core  225  comprises an electrically conductive material (e.g., including one or more metal-containing wires) to enable resistive heating of the tubular body  221  to permit softening of the tubular body  221  to affect its stiffness properties. Although electrical conductors are not shown in  FIG. 24A , it is to be appreciated that electrical conductors extending in a generally longitudinal direction may be operatively coupled to each adjustable flexure element  222 A,  222 A′,  222 B.  FIG. 24B  is a first cross-sectional illustration of the guidewire device  220  according to  FIG. 24A , including a first pair of adjustable flexure elements  222 A,  222 A′ each including two layers of material, such as a metal coating or backbone layer  223 A,  223 A′ each arranged in contact with an electrically responsive adjustable flexure layer  224 A,  224 A′, with a first group of electrical conductors  226  being configured to conduct electrical signals to one flexure layer  224 A, and a second group of electrical conductors  226 ′ being configured to conduct electrical signals to another flexure layer  224 A′.  FIG. 24B  also shows the longitudinally extending flexible core  225  (e.g., one or more wires, fibers, or similar elements) centrally arranged within the tubular body  221 .  FIG. 24C  is a second cross-sectional illustration of the guidewire device  220  of  FIG. 24A , showing the core member  225  as well as the tubular body  221  containing a second pair of adjustable flexure elements  222 B,  222 B′ each including two layers of material, such as a metal coating or backbone layer  223 B,  223 B′ arranged in contact with an electrically responsive adjustable flexure layer  224 B,  2246 ′, with the first group of electrical conductors  226  being configured to conduct electrical signals to one flexure layer  224 B, and the second group of electrical conductors  226 ′ being configured to conduct electrical signals to the other flexure layer  2246 ′. The resulting guidewire device  220  permits each pair of adjustable flexure elements  224 A- 224 A′,  224 B- 224 B′ (and preferably each individual adjustable flexure element  224 A,  224 A′,  224 B,  2246 ′) to be independently operated to enable adjustment of angle and/or curvature of the guidewire device  220  at multiple positions along its length. Although only two pairs of adjustable flexure elements  224 A- 224 A′,  224 B- 224 B′ are shown in  FIG. 24A to 24C , it is to be appreciated that any suitable number of two, three, four, five or more pairs of adjustable flexure elements may be provided. 
     Consistent with the preceding discussion of  FIGS. 23A-24C , in certain embodiments, a guidewire device includes a tubular body having a longitudinal axis, a first end, a second end, and an interior; and a plurality of adjustable flexure elements arranged in or on the tubular body; wherein the plurality of adjustable flexure elements are electrically operable to adjust an angle or curvature of the guidewire device between the first end and the second end. In certain embodiments, a plurality of circumferentially contractible fiber regions (e.g., a piezoelectric material, an electroactive polymer, or a nitinol alloy, not shown but described hereinafter in connection with  FIGS. 28A-30 ) may be arranged in or on the tubular body, wherein each circumferentially contractible fiber region of the plurality of circumferentially contractible fiber regions is longitudinally spaced from each other circumferentially contractible fiber region. In certain embodiments, a plurality of radially contractible fiber regions (e.g., a piezoelectric material, an electroactive polymer, or a nitinol alloy, not shown but described hereinafter in connection with  FIGS. 28A-30 ) may be arranged in or on the tubular body, wherein each radially contractible fiber region of the plurality of radially contractible fiber regions is longitudinally spaced from each other radially contractible fiber region. In certain embodiments, the tubular body includes a polymer adhesive, and the guidewire device includes at least one electrical conductor configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
       FIG. 25  is a cross-sectional illustration of a portion of another guidewire device  230  (similar to the device  220  of  FIGS. 24A-24C ) including multiple pairs of adjustable flexure elements  232 A- 232 A′,  232 B- 232 B′ arranged in a tubular body  231 , wherein first and second pairs of adjustable flexure elements  232 A- 232 A′,  232 B- 232 B′ are arranged at the same or a similar longitudinal position. Each pair of adjustable flexure elements  232 A- 232 A′,  232 B- 232 B′ includes first and second opposing flexure elements  232 A- 232 A′,  232 B- 232 B′ arranged at different lateral positions relative to the tubular body  231 . Each adjustable flexure element  232 A,  232 A′,  232 B,  232 B′ may include a coating layer or backbone layer  233 A,  233 A′,  233 B,  233 B′ (e.g., a metal) arranged in contact with an electrically responsive material  234 A,  234 A′,  234 B,  234 B′ (e.g., a piezoelectric material, an electroactive polymer, or a nitinol alloy). As shown in  FIG. 25 , the tubular body  231  includes a longitudinally extending flexible core  235  (such as may include one or more wires, fibers, or similar elements) and further includes peripherally arranged groups of electrical conductors  236 ,  236 ′ extending in a generally longitudinal direction, with different electrical conductors being operatively coupled with one or more different adjustable flexure elements  232 A,  232 A′,  232 B,  2326 ′. 
       FIG. 26  is a cross-sectional illustration of a portion of another guidewire device  240  (similar to the device  240  of  FIG. 25 ) including multiple pairs of adjustable flexure elements  242 A- 242 A′,  242 B- 242 B′ arranged in a tubular body  241 , wherein first and second pairs of adjustable flexure elements  242 A- 242 A′,  242 B- 242 B′ are arranged at the same or a similar longitudinal position. Each pair of adjustable flexure elements  242 A- 242 A′,  242 B- 242 B′ includes first and second opposing flexure elements  242 A,  242 A′,  242 B,  242 B′ arranged at different lateral positions relative to the tubular body  241 . Each adjustable flexure element  242 A,  242 A′,  242 B,  242 B′ may include a coating layer or backbone layer  243 A,  243 A′,  243 B,  243 B′ (e.g., a metal) arranged in contact with an electrically responsive material  244 A,  244 A′,  244 B,  244 B′ (e.g., a piezoelectric material, an electroactive polymer, or a nitinol alloy). As shown in  FIG. 25 , the tubular body  241  includes a longitudinally extending flexible core  245  (such as may include one or more wires, fibers, or similar elements) and further includes groups of electrical conductors  246 ,  246 ′ extending in a generally longitudinal direction, with different electrical conductors  246 ,  246 ′ being operatively coupled with one or more different adjustable flexure elements  242 A,  242 A′,  242 B,  2426 ′, wherein the electrical conductors  246 ,  246 ′ are arranged generally between the flexible core  245  and the adjustable flexure elements  242 A,  242 A′,  242 B,  2426 ′. 
       FIG. 27A  is a simplified cross-sectional schematic illustration of a portion of a guidewire device  250  including multiple (e.g., four) body elements  252 A- 252 D and multiple (e.g., three) pivot joints  253 A- 253 C that are sequentially arranged in a longitudinal direction within a tubular body  251  (e.g., a tube), wherein each body element  252 A- 252 D is connected to at least one other body element  252 A- 252 D via at least one pivot joint  253 A- 253 C. In certain embodiments, each pivot joint  253 A- 253 C may include a ball and socket joint.  FIG. 27B  is a cross-sectional schematic illustration of the portion of the guidewire device  250  of  FIG. 27A , with addition of tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  extending in a longitudinal direction within the tubular body structure  251 . In certain embodiments, the tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  include wires, filaments, strands, fibers, or the like. In certain embodiments, tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  may include metal wires and/or fibrous strands of material such as small diameter fishing line. In certain embodiments, gel-spun polyethylene may be used, such as Berkley NanoFil monofilament/braid hybrid line, commercially available in a diameter as small as 0.008 inch (0.2 mm). Different tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  terminate at different body elements  252 A- 252 D, and are separately operable to cause pivotal movement of different body elements  252 A- 252 D, thereby permitting adjustment of an angle or curvature of the guidewire device  250  at multiple positions along the longitudinal axis. In certain embodiments, the tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  are operatively connected to a plurality of tensioning elements (e.g., motors, solenoids, actuators, or the like; not shown) configured to selectively apply tension to different tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2 . In certain embodiments, the plurality of tensioning elements is arranged beyond the first or second end of the tubular body structure  251 . Certain tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1  may be arranged in a first tensile element group  255 - 1 , and other tensile elements  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  may be arranged in a second tensile element group  255 - 2 . 
     In certain embodiments, the tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  include at least one agonist tensile element (or group thereof, such as the second tensile element group  255 - 2 ) and at least one antagonist tensile element (or group thereof, such as the first tensile element group  255 - 1 ), wherein the at least one antagonist tensile element is configured to be operated to counteract the at least one agonist tensile element to control pivotal movement between different body elements  252 A- 252 D.  FIG. 27B  shows the tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  without application of tensile force, with the guidewire device  250  in a straight configuration.  FIG. 27C  is a cross-sectional schematic illustration of a portion of the guidewire device  250  corresponding to  FIG. 27B , while omitting (for clarity) the first tensile element group  255 - 1  of  FIG. 27B  that may serve as an antagonist tensile element, and showing the second tensile element group  255 - 2  serving as an agonist tensile element following application of tension (according to the tension profile at bottom) to the tensile elements  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  using multiple tensioning elements (not shown). Selective application of tension to different tensile elements  255 A- 1 ,  255 B- 1 ,  255 C- 1 ,  255 D- 1 ,  255 A- 2 ,  255 B- 2 ,  255 C- 2 ,  255 D- 2  or groups thereof permits pivotal movement between different body elements  252 A- 252 D, thereby permitting angle and/or curvature of the guidewire device  250  to be adjusted, preferably at multiple positions along its length. 
     With further reference to  FIGS. 27B and 27C , in certain embodiments, a plurality of circumferentially contractible fiber regions (not shown but described hereinafter in connection with  FIGS. 28A-30 ) is arranged in or on the tubular body structure  251 , wherein each circumferentially contractible fiber region is longitudinally spaced from each other circumferentially contractible fiber region. In certain embodiments, a plurality of radially contractible fiber regions (not shown but described hereinafter in connection with  FIGS. 28A-30 ) is arranged in or on the tubular body structure  251 , wherein each radially contractible fiber region is longitudinally spaced from each other radially contractible fiber region. In certain embodiments, the tubular body structure  251  comprises a polymer adhesive, and the guidewire device  250  includes at least one electrical conductor (not shown) configured to be coupled with an electric power source for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
       FIG. 28A  illustrates a grid  264  of (horizontally arranged) longitudinally contractible fiber regions  262  and (vertically arranged) circumferentially contractible fiber regions  263  that may be incorporated into a guidewire device. Each contractible fiber region  262 ,  263  may include a piezoelectric material, an electroactive polymer, and/or a nitinol alloy, and is preferably actuated with an electrical signal.  FIG. 28B  is a perspective view illustration of a tubular structure  265  of longitudinally contractible fiber regions  262  and circumferentially contractible fiber regions  263  obtained by rolling the grid  264  of  FIG. 28A  into a tubular shape. The tubular structure  265  of  FIG. 28B  may be incorporated into a tubular body (e.g., via molding, dipping, coating, or another suitable method), such as a tubular body  261  of a guidewire device  260  shown in the cross-sectional illustration of  FIG. 28C . The guidewire device  260  includes longitudinally contractible fiber regions  262  and circumferentially contractible fiber regions  263  within the tubular body  261 . In certain embodiments, the tubular body  261  may include polymer adhesive material. Although not shown in  FIG. 28C , electrical conductors may extend in a generally longitudinal direction within the tubular body  261  to conduct electrical signals to various contractible fiber regions  262 ,  263 . Each circumferentially contractible fiber region  263  of the plurality of circumferentially contractible fiber regions  263  is longitudinally spaced from each other circumferentially contractible fiber region  263 . Actuation of different circumferentially contractible fiber regions  263  permits selective constriction of portions of the guidewire device  260 , thereby adjusting local stiffness. Actuation of different longitudinally contractible fiber regions  262  permits an angle or curvature of the guidewire device  260  to be altered. In combination, control of the circumferentially contractible fiber regions  263  and the longitudinally contractible fiber regions  262  may permit both stiffness and angle or curvature of the guidewire device  260  to be adjusted at multiple locations along its length. 
       FIG. 29  is a cross-sectional illustration of at least a portion of a guidewire device  270  similar to the guidewire device  260  of  FIG. 28C , but with addition of a longitudinally extending flexible core  277 , such as may include one or more wires, fibers, or similar elements. The guidewire device  270  further includes longitudinally contractible fiber regions  272  and circumferentially contractible fiber regions  273  within a tubular body  271 . In certain embodiments, the core  277  comprises an electrically conductive material (e.g., including one or more metal-containing wires) to enable resistive heating of the tubular body  271  to permit softening of the tubular body  271  to affect its stiffness properties. 
       FIG. 30  is a cross-sectional illustration of at least a portion of a guidewire device  280  similar to the guidewire device  260  of  FIG. 28C , but with addition of a plurality of radially contractible fiber regions  286  (e.g., a piezoelectric material, an electroactive polymer, or a nitinol alloy) arranged in or on a tubular body  281 . The radially contractible fiber regions  286  resemble spokes of a bicycle wheel. Actuation of different radially contractible fiber regions  286  permits selective constriction of portions of the guidewire device  280 , permitting stiffness of the guidewire device  280  to be locally adjusted. Multiple different radially contractible fiber regions  286  may be longitudinally spaced apart from one another and may be independently controlled. The guidewire device  280  further includes longitudinally contractible fiber regions  282  and circumferentially contractible fiber regions  283  within the tubular body  281 . In certain embodiments, the tubular body  281  includes a polymer adhesive, and the guidewire device  280  includes at least one electrical conductor (not shown) configured to be coupled with an electric power source (not shown) for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
       FIG. 31  is a cross-sectional schematic illustration of a portion of a guidewire device  290  including a longitudinal axis  299 , a first end  290 - 1 , a second end  290 - 2 , and a tubular body  291  having an interior, with a centrally arranged flexible guide wire or track  293  (optionally including teeth or grooves) arranged within the interior. Multiple (e.g., four) translatable elements  292 A- 292 D are arranged to independently translate along the flexible guide wire or track  293  parallel to the longitudinal axis  299 . Each translatable element  292 A- 292 D is electrically operable to be translated in a longitudinal direction and thereby adjust a stiffness, angle, or curvature of the guidewire device  290  between the first end  290 - 1  and the second end  290 - 2 . In certain embodiments, each translatable element  292 A- 292 D includes an electric motor unit. In certain embodiments, the electric motor unit of each translatable element  292 A- 292 D is controllable by a signal of a different frequency from each other electric motor unit of the guidewire device  290 . In this manner, a single pair of conductors  295  coupled to the motor of each translatable element  292 A- 292 D may be used to separately control each motor. In certain embodiments, the flexible guide wire or track  293  includes a plurality of grooves or teeth, and each electric motor unit of the respective translatable elements  292 A- 292 D includes an engagement element arranged to engage with the plurality of grooves or teeth. In certain embodiments, the tubular body  291  includes a polymer adhesive, and the guidewire device  290  includes at least one electrical conductor (not shown) configured to be coupled with an electric power source (not shown) for resistive heating of the polymer adhesive to adjust a stiffness property of the polymer adhesive. 
     Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.