Abstract:
A guidewire device and methods for containing and removing embolic materials from within a vascular system. The guidewire provides a very low profile expandable structure that can be carried at the distal end of any guidewire used in an endovascular intervention. The structure can be expanded at a location distal to a targeted treatment site, and due to its very low profile when non-expanded, can be passed through any narrow and tortuous occluded vessels that can accommodate a guidewire. The expandable structure comprises a thin film filter portion coupled to at least one support portion for supporting the filter portion in an expanded state. The support portion in its first non-extended state comprises at least one tensioned nitinol member constrained by an electrolytic sacrificial weld. The guidewire is coupled to a remote electrical source and controller for causing electrolysis of the sacrificial component of the invention.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority from Provisional U.S. Patent Application Ser. No. 60/295,939 filed Jun. 4, 2001 (Docket No. S-AES-001) having the same title as this disclosure, which is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to guidewire devices and methods for containing and removing embolic materials from within an endovascular treatment site. More in particular, the invention provides a system for maintaining a very low profile working end of a guidewire that can expand in cross-section to open a filter sac to capture embolic particles. The working end thus can be passed through any narrow or tortuous occluded vessels that can accommodate a guidewire of a standard dimension. Thereafter, the guidewire&#39;s working end can be expanded by means of a sacrificial coupling to deploy a filter sac distal to a targeted treatment site. The device is particularly suited for neurothrombectomy and embolectomy procedures, and a paired guidewire system with two identical low profile expandable working ends can be sued to provide distal protection in two branch arteries for thrombectomy at a branch location.  
           [0004]    2. Description of the Related Art  
           [0005]    Interventional cardiology procedures for treating occlusive vascular disease, such as angioplasty, thrombectomy, atherectomy or stent placement, can result in embolic material migrating downstream from the treatment site. Such embolic particles often are large and can occlude small vessels, for example, resulting in embolic stroke. Such ischemia can threaten the patient&#39;s life. Emboli also can lodge in the heart or lungs.  
           [0006]    Various devices have been proposed for reducing the risk of emboli by blocking or capturing emboli with the downstream deployment of a balloon, filter, basket or similar structure. A particular disadvantage of all prior art systems is the large cross-section of the devices in the collapsed state. Many are too large in diameter, or too rigid, for navigating through small diameter arteries and through partially occluded vessels. As a consequence, most devices realistically cannot be used for carotid artery treatments or in the cerebral vasculature. Nor can the basic components of the prior art devices be scaled down in size for use in smaller arteries, due to the required cross-section of the components necessary to expand and collapse a filter-type structure.  
           [0007]    FIGS.  1 A- 1 B show a prior art distal protection device that may be the smallest diameter system that is commercially available and of the type disclosed in U.S. Pat. No. 6,179,861 (believed to be available in Europe; awaiting FDA approval). The system comprises a catheter housing, a nitinol expandable hoop and a basket of perforated material. In terms of the necessary functionality, (i) the perforated basket material is adapted for capturing embolic particles while allowing blood perfusion; (ii) the shape memory nitinol hoop performs the function of moving the proximal end of the basket to an expanded shape after being slidably deployed outwardly from the catheter housing; and (iii) the catheter housing is adapted for retaining the springable basket in the contracted position for navigating through and occlusion and then for returning the basket to the contracted position by retraction of the basket into the catheter bore. The entire device also may be adapted for deployment over a guidewire, which would further expand its cross section.  
           [0008]    [0008]FIG. 1A depicts the prior art catheter being advanced through an occluded portion of an artery. FIG. 1B shows a realistic cross-section of the prior art catheter of FIG. 1B, in which the overall diameter is about 3.9 French (about 0.052″). For example, the guidewire portion  2  is about 0.14″ with each leg portion  3   a  and  3   b  of the hoop having a similar diameter. The thickness of wall  4  of the catheter housing is from about 0.005″ to 0.010″ with the thin film of the basket being foldable to fit with the catheter bore. Thus, it can be seen that the minimum cross-section C is an aggregation of the component dimensions—with no component scalable to a smaller dimension to provide a smaller cross-section C. The guidewire portion  2  is somewhat standardized in diameter for flexibility and pushability; the legs  3   a  and  3   b  of the hoop need sufficient springing strength to press against the vessel wall.  
           [0009]    With reference to FIG. 1A, it can easily be understood that a 3.9 French catheter can be too large to navigate through many occluded vessels that are targeted for treatment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1A is a longitudinal sectional view of a blood vessel that illustrates a prior art distal protection catheter system in its contracted state being navigated through an occlusion in the blood vessel.  
         [0011]    [0011]FIG. 1B is (i) a transverse sectional view of the prior art distal protection catheter of FIG. 1A in its contracted state showing the minimal cross-sectional dimensions of this type of system, together with (ii) a transverse sectional profile of system of the present invention in the same scale illustrating reduction in scale offered by the system of the invention.  
         [0012]    [0012]FIG. 2 is a perspective view of a Type “A” guidewire and distal protection system corresponding to the invention in its contracted (tensioned) state.  
         [0013]    [0013]FIG. 3 is another perspective view of the guidewire of FIG. 2 with the shape memory distal protection structure in its deployed or expanded (untensioned) state.  
         [0014]    [0014]FIG. 4 is an enlarged view of a portion of the shape memory elements of FIG. 3 without the sac in a contracted position to show the sacrificial coupling and the insulative coating of the working end.  
         [0015]    [0015]FIG. 5 depicts the guidewire and expanded emboli-capturing sac of FIG. 3 being collapsed and retracted into a catheter sheath for removal from the deployment site.  
         [0016]    [0016]FIG. 6 is an alternative embodiment of a guidewire and distal protection system corresponding to the invention in its contracted state with the emboli collection sac in a cut-away view.  
         [0017]    [0017]FIG. 7 is another view of the guidewire of FIG. 6 with the distal protection structure in its deployed or expanded state.  
         [0018]    [0018]FIG. 8 is an alternative embodiment of a guidewire with and shape memory expandable emboli-capturing sac in its deployed state after sacrifice of a weld that maintained the sac in a collapsed position.  
         [0019]    [0019]FIG. 9 is an another embodiment of a guidewire with a shape memory expandable emboli-capturing sac in its deployed state after sacrifice of a weld that maintained the sac in a collapsed position.  
         [0020]    [0020]FIG. 10 is an alternative embodiment of a guidewire and distal protection system corresponding to the invention in its contracted state that utilizes a constraining sheath with an electrolytic sacrificial joint to constrain and release a shape memory structure that open a sac.  
         [0021]    [0021]FIG. 11 is another view of the guidewire of FIG. 10 with the distal protection structure in its deployed or expanded state.  
         [0022]    [0022]FIG. 12 is a perspective view of a Type “B” guidewire and distal protection system in its contracted state.  
         [0023]    [0023]FIG. 13 is a perspective view of the guidewire and distal protection sac of FIG. 13 in its expanded or deployed state.  
         [0024]    FIGS.  14 A- 14 B are views of the support portions of the distal protection sac of FIGS. 12 &amp; 13 in the non-extended an extended states.  
         [0025]    [0025]FIG. 15 depicts the guidewire and expanded emboli-capturing sac of FIG. 13 being collapsed and retracted into a catheter sheath for removal from the deployment site.  
         [0026]    [0026]FIG. 16 is a perspective view of an alternative guidewire and filter structure with support members having two free ends that expand the filter by stiffening wall portions of the filter.  
         [0027]    FIGS.  17 A- 17 C are enlarged views of a thin film wall of an unfolded emboli-capturing sac with an electrically responsive hydrogel layer that allow intra-operative change of the pore size of the filter wall.  
         [0028]    [0028]FIG. 18 is a view of the strut portion of a working end of a guidewire filter structure with the strut and guidewire of a nitinol or piezoelectric element that can change its cross-section in response to electrical energy delivery thereto. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    1. Type “A” Embodiment of Guidewire with Emboli Capturing Sac.  
         [0030]    The objective of the present invention is to greatly reduce the scale of a distal protection system, in its contracted position, for navigating through tortuous arteries, severely occluded arteries and middle cerebral vasculature. As shown in FIG. 1A, it is an objective of the invention to reduce the scale of the inventive system  10  (profile in phantom view) to provide a contracted cross-section indicated at C′ that is about 40% to 50% of the diameter of the prior art system—i.e., the inventive system being about 1.5 Fr. to 2.0 Fr (about 0.020″-0.025″).  
         [0031]    Referring again to FIG. 1B, it can be understood that a distal protection system in its contracted position can only be reduced in profile by altering the nature of the components. The present invention, in some embodiments, (i) entirely eliminates the use of a straight guidewire shaft for carrying the functional components of the filter sac and it support structure; and (ii) in all embodiments eliminates the use of a catheter sheath for constraining the springable structure in its contracted position for navigation through an occluded region of a vessel.  
         [0032]    In other words, the present invention in some cases can be reduced in dimension to the approximate effective diameter of the guidewire and the thin film material that makes up the microporous structure for capturing emboli. Still the inventive system provides expansion means for expanding the emboli capturing structure from a contracted position to an expanded position and for springably pressing an engagement support portion of the structure into contact with the vessel wall—in manner that is improved over the prior art. Further, the structure of the emboli-capturing sac and its attachment to the guidewire allows the guidewire to have the flexibility and pushability of an unencumbered guidewire. Thus, the guidewire with embolic removal system of the present in invention can be standardized for use in practically any interventional procedure.  
         [0033]    Now referring to FIG. 2, an exemplary Type “A” system  10  of the present invention is shown with of guidewire  11  having a working end  12  that carries an emboli collection structure or sac  15  in cut-away view in a first contracted state about the guidewire. FIG. 3 is a similar view of the working end  12 , this time with collection sac  15  in a second extended state with the proximal sac end substantially open to allow blood flow and emboli to enter therein. As shown in FIG. 2, the guidewire  12  has proximal and medial portions  16  and  17  made of a solid metal wire core  18  without a lumen as is known in the art, and is typically about 0.014″ in diameter although any smaller or larger dimension falls within the scope of the invention. Any tapered or coiled distal tip  19  is possible (not shown) as is known in the art. FIG. 3 shows that the distal portion  20  of the guidewire comprises a plurality of shape memory extension elements  22   a - 22   b  (numbering from about two to six, with two such elements in FIG. 3) that extend generally along or about the axis  25  of the guidewire when in the first contracted state (FIG. 2).  
         [0034]    The extension elements  22   a - 22   b  are of a type of nitinol, or nickel titanium alloy, that is known in the art as well suited for shape memory applications. Thus, FIG. 2 shows elements  22   a - 22   b  in a contracted (tensioned) state and FIG. 3 shows elements  22   a - 22   b  in an expanded (untensioned) state. In FIGS. 3 &amp; 4, it can be seen that the core  18  of the guidewire transitions into the cores  28   a  and  28   b  of proximal ends  30   a  and  30   b  of elements  22   a - 22   b . The extension elements  22   a - 22   b  further define medial portions  32   a - 32   b  that extend to distal ends  33   a - 33   b  that transition back into a single guidewire member portion indicated at  36 . In this embodiment, the elements  22   a - 22   b  wrap around each other in a helical manner in from about one to six revolutions. FIGS. 3 &amp; 4 further show that a thin insulative coating layer  30  covers the core  18  of the guidewire and cores  28   a  and  28   b  of elements  22   a - 22   b . The metallic cores  18  and  28   a - 28   b  are electrically conductive and are coupled to a remote electrical source  40  and controller  45  for delivering electric current to the working end as will be described further below.  
         [0035]    Of particular interest, FIGS. 2 and 4 further show that the two elements  22   a - 22   b  provide a constraining structure to maintained the working end and sac  15  in the first contracted and tensioned position by at least one sacrificial coupling indicated at  50 . The sacrificial coupling  50  acts as a weld to bond the medial portions  32   a  and  32   b  of the elements  22   a - 22   b  together to provide the contracted profile. FIG. 2 shows a single sacrificial coupling  50  but it should be appreciated that a plurality of such discrete couplings at spaced apart locations are possible. Alternatively, one or more elongated or continuous couplings are possible and fall within the scope of the invention. FIG. 4 shows an enlarged view of a portion of one elongate element  22   a  with the insulative coating layer  30  removed to expose the metallic core  28   a  at location  52   a . The other elongate element  22   a  is similarly provided with an exposed core portion and it is at these locations that the weld-type sacrificial coupling  50 , for example of stainless steel, is provided.  
         [0036]    As can be seen in FIGS. 2 and 3, the emboli collection sac  15  has a wall  56  of a microporous thin film polymer material known in the art with pores or perforations  60  preferably ranging between about 5 microns and 200 microns. More preferably, the pores  60  range between about 40 microns and 120 microns in dimension across a principal axis. Such microporous polymer materials are known in the art of endovascular filters, but it should be appreciated that the sac wall  56  can be any type of mesh, net, web or the like with similar dimension pores or opening therethrough. Referring to FIG. 3, the emboli collection structure  15  has a proximal portion indicated at  62   a , a medial portion  62   b  and a distal end  62   c  with a proximal-facing opening portion  65  for receiving blood flow that may contain emboli. The thin film material of the sac  15  can be folded and pleated to be maintained between the elements  22   a  and  22   b  to provide the contracted position of FIG. 2.  
         [0037]    As can be seen in FIG. 3, the emboli sac wall  56  is maintained in an expanded form by support from the elements  22   a  and  22   b  when allowed to expand to their untensioned shape. The outer portions of elements  22   a  and  22   b  are thus adapted to press against the interior of the walls of a blood vessel to insure that substantially all blood flow passes through the filter sac  15 .  
         [0038]    In use, the guidewire  10  is introduced endovascularly as is known in interventional cardiology. After the distal end  12  of the guidewire is passed beyond a stenosis or other targeted treatment site, the guidewire is maintained in a stationary position and low level direct electric current is delivered from electrical source  40  through wire core  18  to the sacrificial coupling or couplings  50 . A return electrode is coupled to the patient&#39;s body by a pad or needle at a remote location to allow current flow through conductive blood to thereby cause electrolysis at the coupling  50 . This system can cause electrolysis of coupling  50  until the joint fails and allows the elements  22   a  and  22   b  to spring apart to the untensioned position as depicted in FIG. 3. The delivery of an electric current to a joint is known in the detachment of an embolic coil from the distal end of a catheter in treating an intracranial aneurysm, in which the objective is the detachment of two static members. The author believes this invention is the first use of a sacrificial joint to release pent-up forces stored in a tensioned nitinol assembly or structure. The prior use of the electrolytic detachment system for embolic coils is disclosed in U.S. Pat. No. 5,855,578 and 5,122,136, incorporated herein by reference, among others authored by Guglielmi.  
         [0039]    After use as an endovascular filter while performing a procedure at an upstream site (e.g., angioplastly, stent deployment, atherectomy, etc.), the guidewire  10  and sac  15  are removed from the site by advancing a catheter sleeve  63  toward the filter sac  15  and retracting the filter sac and collected emboli into a receiving bore  64  of the catheter sleeve as depicted in FIG. 5. The receiving bore  64  bore is dimensioned to collapse and receive the nitinol extension elements  22   a - 22   b  and the filter sac  15 .  
         [0040]    While FIGS.  2 - 4  depict two extension elements  22   a  and  22   b  that extend helically relative to one another to provide a generally round cross-section to better engage the vessel wall, it should be appreciated a working end with from 3 to 6 linear extension members of nickel titanium alloy (not shown) also can be used to extend and open a sac  15  with the medial portions of the linear elements secured in the contracted position by a electrolytically sacrificial weld.  
         [0041]    [0041]FIGS. 6 and 7 show an alternative working end  12  that is based on the principle of a sacrificial weld that can be removed by electrolysis to move a sac or basket  15  to an open position (FIG. 7) from a closed position (FIG. 6). In this embodiment, a single shape memory extension element  66  has its proximal end  68  fixedly coupled to straight guidewire  10 . The medial portion  69  of the extension element  66  is helically wrapped about a straight wire portion  70  of the guidewire that is of non-shape memory material. The distal portion  72  of extension element  66  terminates in a substantially tight coil (or an optional sleeve member) that forms a sleeve portion  74  that can slide over the wire portion  70  when not welded. Thus, it can be understood that the extension member  66  can have a repose (untensioned) shape as in FIG. 7 wherein the sleeve portion  74  is slid proximally over wire portion  70 . To provide a contracted position, the sleeve portion  74  can be slid distally over wire portion  70  to a tensioned state and thereafter a sacrificial weld  75  can be provided to maintain the extension member and guidewire in the low profile state. The system would be used as described previously and collapsibly retracted into a catheter sleeve following its deployment and use.  
         [0042]    [0042]FIG. 8 shows an alternative embodiment of working end  12  based on the principle of utilizing a sacrificial weld that can be eliminated by electrolysis to open a sac  15  to the open position of FIG. 8 from a closed position (not shown). In this embodiment, the constraining structure comprises a plurality of shape memory (nitinol) extension elements  77  (collectively) have proximal ends  78  (collectively) that are fixedly coupled to the straight guidewire  10 . The medial portion  79  of each extension element  77  is either linear or helically positioned against the straight portion  80  of the more rigid guidewire. To function as a constraining structure, the distal end portion  82  of each extension element  77  terminates in a free end that has a releasable weld connection (not shown) between each end  82  and the straight portion  80  of guidewire  10 . After an electrolytic release, the extension elements  77  function as supports for the wall of the filter sac  15  and return to an untensioned shape that comprises a segment of an arc or hoop to open the sac. The outer surfaces  87  of the extension elements  77  are bonded to the walls of the sac to maintain the sac in a selected open configuration. It should be appreciated that the number of extension elements  77  can number from about two to eight and be coupled to the guidewire  10  at spaced apart locations or one or more proximal ends  78  of the elements  77  can be attached at single location. It is believed that this type of support members can suitably press against the vessel walls in a wider range of lumen diameters. The working end would be collapsibly retracted into a catheter sleeve following its deployment and collection of emboli.  
         [0043]    [0043]FIG. 9 shows a variation of the previous type of working end  12  based on the same principles that utilized a sacrificial weld to provide to a contracted sac position (cf. FIGS. 2 and 6) and an expanded sac position (FIG. 9). In this embodiment, at least one of shape memory (nitinol) hoop-type support member  88  is provided to provide an open mouth  89  to sac  15 . The hoop member defines first and second ends  90   a  and  90   b  that are fixedly coupled to the straight guidewire  10  by a permanent weld or other bond. The medial portion  91  of the hoop element  88  is folded in the contracted position (not shown) and one or more locations  92  of the medial portion  91  of the hoop are coupled to the straight portion  93  of the guidewire (of non-shape memory material) with the sacrificial weld connection, for example at location  95  when the hoop is collapsed against the guidewire phantom view). After release delivery of electric current to cause electrolysis of the weld, the hoop-type extension element  88  will open the sac  15  as the hoop returns to the untensioned shape of FIG. 9. Again, the edges of the sac  15  are bonded to the hoop element  88  and the guidewire to maintain the sac in the open shape as the hoop is pressed against the vessel walls. The first and second ends  90   a  and  90   b  of the hoop element  88  can be coupled to the guidewire at slightly spaced apart locations as depicted in FIG. 9, or at a single location. The working end would be collapsibly retracted into a catheter sleeve following its deployment and collection of emboli as generally illustrated in FIG. 5.  
         [0044]    The sac of FIG. 9 has its edges bonded to the hoop element  88  and to the guidewire and thus can be preformed to a desired sac shape that will deploy on one side of the guidewire. It should be appreciated that the sac of any of the above embodiments can (i) deploy on the side of the guidewire, or (ii) deploy about the guidewire with the guide wire extending through the distal end of the sac where the sac is bonded to the guidewire.  
         [0045]    [0045]FIGS. 10 &amp; 11 show another variation of a working end  12  that utilizes and electrical source  40  and an electrolytic sacrificial joint to release a shape memory nitinol frame or support structure that opens a emboli-collection sac  15 . In this embodiment, the nitinol structure preferably is of the type shown in FIGS.  8 - 9 , but alternatively can be any of the types described above. FIG. 10 shows the working end in a collapsed position with this embodiment providing a constraining sheath structure  96  (cut-away view) of a thin film material bonded to sac  15  along line  97  (FIG. 11). The constraining sheath structure  96  encases and retains the combination of the sac  15  and the tensioned nitinol extension elements  99  that support the sac in a contracted, tensioned position (FIG. 10). It should be appreciated that the retaining sheath structure can simply comprise a folded over portion of the sac itself. The sheath  96  in the closed position has an elongate metallic sacrificial joint  98  that comprises a thin metallic coating either or both sides of, or impregnated into, the polymer of the thin film sheath material. Upon delivery of electric current to the sacrificial joint or coupling  98  in the manner described previously, the sheath will decouple or split along the joint  98  thereby releasing the tensioned nitinol extension element(s)  99  to pop open to the untensioned position to open the emboli-capturing sac (FIG. 11). The sacrificial coupling region may have a plurality of perforations along the joint  98  to pre-weaken the targeted line of separation in the thin film polymer. The sacrificial coupling  98  is coupled to the core of the insulated guidewire as described previously to connect to the remote electrical source and controller.  
         [0046]    2. Type “B” Embodiment of Guidewire with Emboli-Capturing Sac.  
         [0047]    Now referring to FIG. 12, an exemplary Type “B” system  100  of the present invention is shown with the working end of guidewire  102  carrying emboli collection structure or sac  105  in a first contracted state about the guidewire shaft FIG. 13 is a similar view of the system working end, this time in a second expanded or extended state. As shown in FIG. 12, the guidewire  102  is a solid metal wire without a lumen, and can typically be about 0.014″ in diameter although any other size falls within the scope of the invention. Any tapered or coiled distal tip is possible (not shown) as is known in the art.  
         [0048]    As can be seen in FIG. 13, the emboli collection sac  105  has a wall  106  of a microporous thin film material known in the art with pores or perforations  110  preferably ranging between about 5 microns and 200 microns. More preferably, the pores  110  range between about 40 microns and 120 microns in dimension across a principal axis. Such microporous material is known in the art of endovascular filters, but it should be appreciated that the sac wall  106  can be any type of mesh, net, web or the like with similar dimension pores or opening therethrough.  
         [0049]    Still referring to FIG. 13, the emboli collection structure  105  has a proximal portion indicated at  112   a  medial portion  112   b  and distal end  112   c  with a proximal-facing open portion  115  from receiving blood flow that may contain emboli.  
         [0050]    The emboli sac wall  106  is maintained in an expanded form by a support portion indicated at  120  which may also be referred to as a support member, support strut, or support rib or frame herein. Comparing FIG. 12 with FIG. 13, it can be seen that support member  120  in FIG. 12 has substantially no cross-sectional dimension wherein in FIG. 13, the support member  120  has a cross-section similar in dimension to guidewire  102 . Of particular interest, to provide a support member for expanding and maintaining the emboli sac wall  106  in an expanded state, the system of the invention uses fluid from the endovascular environment—together with thin film material—to create a support member  120 . More in particular, referring to FIGS.  14 A- 14 B, the support member  120  comprises first and second film layers or sides  122   a  and  122   b  of a thin film material, e.g., two film layers with thermoseals  124   a - 124   b , or a flattened tubular material with or without a reinforcing braid that defines sides  122   a - 122   b . At the interior of first and second layers  122   a  and  122   b  is a volume of a desiccated porous hydrogel as in known in the art, or more preferably a desiccated microporous hydrogel indicated at  125 . A microporous or superporous hydrogel is an open cell foam that can be desiccated and collapsed into a thin film or particles and disposed within the thin films layers  122   a - 122   b . When exposed to a fluid such as blood which is substantially water, the hydrogel will expand a controlled amount to expand, stiffen and flex the support portion of or strut outwardly as in FIG. 13. The hydrogel preferably is carried within the film layers in the form of particles or strings as when the hydrogel is bonded to discrete elements of a biocompatible polymer having an suitable shape and dimension. Alternatively, the hydrogel can be coated to the film layers that contain the gel, or to other thin film elements that are tethered to the interior of the film layers  122   a  and  122   b . The film layers  122   a  and  122   b  thus define an interior chamber indicated at  128  that contains the hydrogel and directs the swelled volume of the hydrogel to extend the containing film layer(s) in the desired direction. It is this directional extension of the film layers or tube that provides the support structure of the invention.  
         [0051]    A suitable hydrogel can be any fast-response gel, for example of PVME, HPC or the like (see, e.g., S. H. Gehrke,  Synthesis, Swelling Permeability and Applications of Responsive Gels  in Responsive Gels, K. Du{haeck over (s)}ek (Ed.) Springer-Verlag (1993) pp. 86-143).  
         [0052]    The invention further comprises a novel means or exposure mechanism for controllably exposing the hydrogel to endovascular fluids. As can be seen in FIGS.  12 - 13 , the film layer  122   a  carrying the hydrogel also carries at least one sacrificial conductive film layer  140  covering a portion of chamber  128  carrying the hydrogel. Each sacrificial conductive layer portion  140  is coupled to an electrical lead  142  which in turn is coupled to conductive guidewire  102  and thereafter coupled to a remote electrical source  150 . A controller  155  also is provided to control delivery energy to sacrificial layer  140  to cause electrolysis thereof to remove the layer and to thereby expose the hydrogel to blood. The system also provides a return (ground pad or needle) for coupling to the patient cause electrical potential at, or across sacrificial conductive layer  140  to cause electrolysis thereof. The sacrificial conductive film layer(s)  140  preferably are carried over porosities  156  (FIGS.  14 A- 14 B) that have an adequate dimension to rapidly introduce fluids into chamber  128  but sufficiently small to prevent the swelled gel from escaping through the film layer.  
         [0053]    [0053]FIG. 15 depicts the Type “B” guidewire and expanded distal protection structure of FIG. 13 being collapsed and retracted into a catheter sheath  180  (phantom view) for removal from the deployment site. The method of using the system thus allows a sheath  180  of adequate size to easily receive the emboli sac which may carry a substantial amount of embolic material.  
         [0054]    As shown in FIG. 13, the expanded support portion or strut  120  has a first end  160   a , medial portion  106   b  and second end  160   c . The first end  160   a  and second end  160   c  are can be coupled to guidewire at the same axial location, but preferable are spaced apart angularly and axially. The edge  162  of the filter film not bonded to the support member is bonded to the guidewire. Thus, a preferred embodiment has the support portion or strut  120  extending in a helical or partly helical path about the guidewire.  
         [0055]    Also, a plurality of support members can be formed in a linear arrangement, instead of a helical arrangement, to open an emboli-capturing sac  105  (not shown). The emboli-containing sac  105  also can be of a thin film material wherein the proximal open end portion carries a plurality of large openings in the film wall for receiving blood flow an emboli and wherein the distal end portion of the sac has smaller filtering pores (not shown). In another embodiment, as shown in FIG. 16, the guidewire of the invention also can have an emboli-containing sac  105  that is expanded by one or more support members  120  (collectively) with one end  170   a  attached to the guidewire and the other free end  170   b  (collectively) terminating away from the guidewire but attached to the filter element  105 .  
         [0056]    It can be understood that the principles of the invention comprise (i) a support member or members  120  comprising a thin film layer around an interior chamber  128  that contains a hydrogel  125  for expanding a filter structure together with means for on-demand fluid introduction of fluids to the hydrogel from the endovascular site, and (ii) a porous filtering structure  105  coupled to the support member(s)  120  capable of a contracted or folded configuration and an expanded configuration wherein the support member(s) engage the walls of the vessel. The scope of the invention included any manner of fabricating and folding or collapsing the thin walls of support member(s) when the hydrogel is desiccated to optimize the extension of the support member(s).  
         [0057]    3. Type “C” Embodiment of Guidewire with Emboli-Capturing Sac.  
         [0058]    Now referring to FIG. 17A- 17 C, an exemplary Type “C” system  300  can be any of the above described embodiments with the improvement consisting of a new form of thin film material for the porous filter membrane of the emboli-capturing sac.  
         [0059]    As can be seen in FIG. 24A, the emboli collection sac  305  has a wall  306  of a microporous thin film polymer material with a pores  310  therein similar to that described previously, this time for example having pores ranging between about 50 microns and 250 microns in diameter. Such porous materials are known in the art of endovascular filters, and the sac wall  306  alternatively can be any type of mesh, net, web or the like with similarly dimensioned pores or openings therein.  
         [0060]    The improvement is depicted in the enlarged views of FIG. 17A- 17 C wherein the sac wall  306  carries an additional layer of a responsive hydrogel indicated at  312  which can be activated by electrical stimulation to absorb or repel water (a solute). The hydrogel extends into and about the pores  310 . It can be understood that by expanding or swelling the gel, the actual pore size of the filter can be altered. By this means, it is believed that the improved emboli-capturing sac can have any variable pore dimension ranging between about 25 microns and 250 microns. This characteristic of the filter would be advantageous when deployment of the filter and imaging suggests that perfusion is higher or lower than desired—and an adjustment can be made. The hydrogel is of the type that responds to an external stimulus and preferably is an electric field responsive gel. Such gels are described in: S. H. Gehrke,  Synthesis, Swelling, Permeability and Applications of Responsive Gels  in Responsive Gels K. Du{haeck over (s)}ek (Ed.) Springer-Verlag (1993) pp. 86-143). Thus, the actual pore dimensions of the filter structure can be altered intra-operatively by electrical energy delivery to the hydrogel along a conductive guidewire from a remote electrical source.  
         [0061]    In another embodiment (not shown), the interior surface of the filter sac can carry an electrolytically sacrificial layer coupled to the electrical source described above. During use, the layer could be intermittently or continuously reduces to remove platelets and other coagulative material that is smaller that embolic particles. It is believed that such a filter surface would be useful in extending the treatment time, wherein a typical filter may begin to clog due to the fibrogenic cascade that occurs about the foreign object in the vasculature.  
         [0062]    4. Type “D” Guidewire with Emboli-Capturing Sac.  
         [0063]    [0063]FIG. 25 depicts a Type “D” embodiment of guidewire  400  that carries expandable emboli-capturing structure  415  at it distal end. This embodiment is similar to that of FIG. 6- 7  which have a sleeve portion that is detachably coupled to the guidewire in a tensioned position. The Type “D” embodiment utilizes an electrically activated release mechanism that comprises a nickel titanium sleeve or a piezoelectric sleeve that is moveable between first and second dimensions to release the distal end  412  of a tensioned support member  420  from a guidewire portion indicated at  410 . The distal end  412  of a support member  420  carries the sleeve that can change the dimension of its bore  422  to compress and grip the fixed diameter guidewire. It is well known in the art that electrical energy can be delivered to a nitinol sleeve to cause resistive heating thereof to cause a change in its dimension to a remembered condition. In use, the physician extends and tensions the support member  420  to provide the contracted position and then actuates the electrical source to alter the dimension of the sleeve  420  to maintain the structure in the contracted position. After introducing the working end to the targeted location, electrical energy is delivered to the sleeve to altered its cross-section to release the coupling from the guidewire to thereby open and expand the emboli-capturing structure  415  to the second expanded position.  
         [0064]    Those skilled in the art will appreciate that the exemplary embodiments and descriptions thereof are merely illustrative of the invention as a whole. While the principles of the invention have been made clear in the exemplary embodiments, it will be obvious to those skilled in the art that modifications of the structure, arrangement, proportions, elements, and materials may be utilized in the practice of the invention, and otherwise, which are particularly adapted to specific environments and operative requirements without departing from the principles of the invention.