Abstract:
The disclosure pertains to a medical device deployment system comprising a restraint member which holds the embolic protection filter in a restrained, or partially collapsed, state for insertion into a lumen and transit to a desired deployment site. The restraint member comprises two or more portions which differ in their mechanical ability to resist the radial forces exerted by various portions of the medical device when it is in a restrained, or partially collapsed, state. The restraint member is maintained in a restraint configuration by an actuation member which engages portions of the restraint member lying on opposite sides of a generally axial gap until deployment of the medical device is desired. Withdrawal of the actuation member allows the restraint member to release the medical device which may then return to a deployed state. The invention also provides a method for assembling a medical device deployment system.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/122,575 filed Dec. 15, 2008. 
     
    
     FIELD 
       [0002]    This disclosure pertains generally to a delivery system for embolic filters to be deployed in a lumen such as a blood vessel or other duct within the body. 
       BACKGROUND 
       [0003]    Human blood vessels often become occluded or blocked by plaque, thrombi, other deposits, or material that reduce the blood carrying capacity of the vessel. Should the blockage occur at a critical place in the circulatory system, serious and permanent injury, and even death, can occur. To prevent this, some form of medical intervention is usually performed when significant occlusion is detected. 
         [0004]    Several procedures are now used to open these stenosed or occluded blood vessels in a patient caused by the deposit of plaque or other material on the walls of the blood vessels. Angioplasty, for example, is a widely known procedure wherein an inflatable balloon is introduced into the occluded region. The balloon is inflated, dilating the occlusion, thereby increasing the intraluminal diameter. 
         [0005]    Another procedure is atherectomy. During atherectomy, a catheter is inserted into a narrowed artery to remove the matter occluding or narrowing the artery, i.e., fatty material. The catheter includes a rotating blade or cutter disposed in the tip thereof. Also located at the tip are an aperture and a balloon disposed on the opposite side of the catheter tip from the aperture. As the tip is placed in close proximity to the fatty material, the balloon is inflated to force the aperture into contact with the fatty material. When the blade is rotated, portions of the fatty material are shaved off and retained within the interior lumen of the catheter. This process is repeated until a sufficient amount of fatty material is removed and substantially normal blood flow is resumed. 
         [0006]    In another procedure, stenosis within arteries and other blood vessels is treated by permanently or temporarily introducing a stent into the stenosed region to open the lumen of the vessel. The stent typically comprises a substantially cylindrical tube or mesh sleeve made from such materials as stainless steel or nitinol. The design of the material permits the diameter of the stent to be radially expanded, while still providing sufficient rigidity such that the stent maintains its shape once it has been enlarged to a desired size. 
         [0007]    Such percutaneous interventional procedures, i.e., angioplasty, atherectomy, and stenting, often dislodge material from the vessel walls. This dislodged material can enter the bloodstream, and may be large enough to occlude smaller downstream vessels, potentially blocking blood flow to tissue. 
       SUMMARY 
       [0008]    The present disclosure pertains to medical embolic protection systems and methods of preparing such medical embolic protection systems for use within a body lumen. The systems of the invention are well suited for delivering medical devices which are self-expanding and which require a low delivery profile such as embolic filters and/or stents. Such devices are often positioned near the distal end of a guide wire, hypotube, or catheter and advanced to, or slightly beyond, an obstruction in the lumen being treated. In some treatment options, the device, or part thereof, may be advanced beyond an obstruction while in other options, the device, or part thereof, may remain proximal of the obstruction. In yet other options, the medical device may be centered with respect to the axial dimension of the obstruction. In each option, it is generally desirable that the medical device be deployed without significant axial movement during deployment which might tend to scrape the lumen wall with an attendant risk of debris generation. 
         [0009]    The disclosure also pertains to an embolic filter assembly delivery system having an elongated member and a medical device having a first portion and a second portion disposed axially with respect to the elongated member and near the distal end of the said member. A first portion of the embolic filter assembly device can be mechanically biased toward a radially expanded position and a second portion of the device is less strongly biased toward a radially expanded position. A restraint member, can have one axial gap, a first portion, a second portion, a restraint configuration, and a deployed configuration, is disposed about the medical device wherein the first and second portion of the restraint member are disposed about the first and second portions of the embolic filter assembly, respectively. The first portion of the restraint member can exert a greater restraint force on the embolic filter assembly in the restraint configuration than the restraint force exerted on the embolic filter assembly by the second portion of the restraint member in the restraint configuration. An actuation member interacts with the restraint member in the restraint configuration and is substantially free of interaction with the restraint member in the deployed configuration. 
         [0010]    The disclosure also pertains to a method of assembling an embolic filter assembly delivery system having an elongated member with a medical device having a first portion and a second portion disposed axially with respect to the elongated member and near the distal end of the member. The embolic filter assembly has a first portion which is mechanically biased toward a radially expanded position and a second portion which is less strongly biased toward a radially expanded position. A temporary containment sleeve having an interior dimension commensurate with a radially retracted state of the first portion of the embolic filter assembly is placed about the first portion of the medical device while the first portion of the embolic filter assembly is in the radially retracted state. A mandrel having an exterior dimension commensurate with a radially retracted state of the first portion of the embolic filter assembly and a restraint member is disposed about the mandrel such that an axial gap is substantially closed whereupon an activation member bridging the axial gap is provided to engage the restraint member at points on alternating opposite sides of the axial gap. The preformed restraint member is then transferred from the mandrel to the medical device thereby displacing the temporary containment sleeve while replacing it with at least a portion of the restraint member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an exemplary embolic filter assembly, an embolic filter. 
           [0012]      FIG. 2  is an embolic filter assembly in a restraint configuration. 
           [0013]      FIG. 3  is a detail of an alternate of a restraint member. 
           [0014]      FIG. 4  is an alternate restraint configuration of an embolic filter. 
           [0015]      FIG. 5A-D  illustrates steps in assembling a embolic filter assembly delivery system. 
           [0016]      FIG. 6  illustrates a deployed embolic filter assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The drawings, which are not necessarily to scale, are not intended to limit the scope of the claimed invention. The detailed description and drawings illustrate example embodiments of the claimed invention. 
         [0018]    All numbers are herein assumed to be modified by the term “about.” The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). 
         [0019]    As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include the plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
         [0020]    One specific example of a medical device which may be delivered by the medical device delivery system disclosed herein, is embolic filter  30 , as shown in  FIG. 1 . The embolic filter  30  includes radially self-expanding struts  32 , joined at a hub  12 , which support a generally conical filter material  34 . The filter material, or basket, is often a membrane or mesh having openings sized to allow blood cells to pass while retaining larger debris such as emboli or dislodged plaque. Materials and methods for assembling embolic filters are known in the art. The embolic filter  30  of  FIG. 1  in mounted on guidewire  18 . More generally, the embolic filter may be fixed to the guidewire  18  near its distal end or may be advanced along a guidewire, for example by a catheter attached to hub  12 . In some embodiments, the embolic filter  30  is attached near the distal end of a catheter or hypotube  28  as shown in the medical device delivery system  10  of  FIG. 2 . The catheter or hypotube  28  may also serve to contain the proximal and intermediate portions of actuation member  20  which may be activated by withdrawing proximal end  22  of actuation member  20  relative to catheter or hypotube  28 . 
         [0021]    In  FIG. 2 , embolic filter  30 , shown in cutaway, is constrained by restraint member  40  which includes a first portion  42  and a second portion  44  joined along shared axial gap  26  by the laced actuation member  20 . Catheter or hypotube  28  extends distally of the constrained filter and terminates in a distal coil  14  or other atraumatic tip. The first portion  42  of restraint member  40  surrounds the radially self-expanding struts  32  (not shown) while the second portion  44  of restraint member  40  surrounds the filter element or basket. First portion  42  of restraint member  40  is formed of materials selected to resist the outward forces exerted by collapsed struts  32 . Additional strength in portion  42  may be supplied by material selection, by additional thickness, by reinforcing elements, and the like. Second portion  44  of restraint member  40  is formed of materials which are capable of withstanding the lesser radial forces of the constrained filter element or basket. Accordingly, it may be convenient to fabricate second portion  44  from materials having a lower strength or a lesser thickness. 
         [0022]    Although the restraint member  40  has been illustrated as a substantially solid sheet, it will be appreciated that other forms of restraint member  40  may be employed.  FIG. 3  is a detail of an embodiment of a second portion of restraint member  40  in which the restraint material is formed as a series of loops  46 , 47  which surround the medical device  30 . In this embodiment, the axial gap is formed by “edges” created by the collective loops  46  on one side of the axial gap and collective loops  47  on the other side of the axial gap. Actuation member  20  alternately engages loops  46  and loops  47  to maintain the restraint configuration until actuation member  20  is withdrawn allowing the embolic filter to deploy. 
         [0023]      FIG. 4  illustrates an alternate embodiment of a medical device delivery system in which the delivery system has been configured for a staged deployment of the medical device and in which the first portion  42  of restraint member  40  is located distally, rather than proximally, with respect to second portion  44  of restraint member  40 . In the case of an embolic filter, this configuration may be used to position the filter within the blood vessel by approaching the protection site within the blood vessel from downstream. In some embodiments, releasing the medical device in a staged sequence may result in a smoother deployment. As illustrated, struts  32  of embolic filter  30  have been partially released from restraint member  40  by withdrawing a second actuation member (not shown) from a second axial gap in first portion  42  of restraint member  40 . Alternatively, first portion  42  could have been positioned such that partial withdrawal of actuation member  20  would have released first portion  42  along an axial gap generally corresponding to an extension of axial gap  26 . Continued withdrawal of actuation member  20  could then release complete release of second portion  44  of restraint member  40  leading to full deployment of the filter. 
         [0024]    As mentioned above, it will be understood that the medical device delivery system may be used to deliver a variety of medical devices and even a plurality of medical devices. In addition to an embolic filter which has already been discussed to an extent, the delivery system may deliver a stent or even a stent and a filter. In such embodiments, one device, for example the stent, may thought of as the portion of the overall medical device which is biased toward a radially expanded position while the filter is the portion of the device which is less strongly biased toward an expanded position. The roles of the stent and the filter may, of course, be reversed in a particular embodiment. Embodiments are envisioned in which the more strongly radially biased portion of the medical device is located distally of the less strongly radially biased portion. Additionally, embodiments are envisioned in which the more strongly radially biased portion of the medical device is located proximally of the less strongly radially biased portion. In yet other embodiments, strongly radially biased portions may alternate with less strongly biased portions. In those embodiments in which multiple medical devices are present, it may be advantageous to provide each medical device with a separate restraint member. It will be appreciated that in those embodiments in which a single restraint member encloses two or more medical devices, the actuation member may partially withdrawn to deploy one medical device component and fully withdrawn to deploy both medical device components. 
         [0025]    In some embodiments, the tighter constraint permitted by a restraint member or members of the invention may exacerbate a problem occasionally seen when a constrained medical device includes thermoplastic components. Such components, when subjected to prolonged storage, especially at elevated temperatures occasionally encountered in distribution, may tend to auto-adhere or to cling to other thermoplastic elements within the device. While common fabrication techniques and materials may lead to a preference for the use of thermoplastic elements during assembly of the medical device, it has been found that auto-adhesion within the medical device delivery systems of the invention may be avoided by partially crosslinking the thermoplastic material prior to use. In some embodiments, partial crosslinking may be induced by exposure to ionizing radiation provided by a source producing at least one of electron beam irradiation, gamma irradiation, and ultraviolet irradiation. It has been found that exposure to ionizing radiation may be effective in reducing auto-adhesion when exposure occurs before a medical device containing thermoplastic components is in the restraint configuration and even when exposure to ionizing radiation occurs after the medical device is in the restraint configuration. In some embodiments, it has been found that exposure of the surface of a medical device, or thermoplastic portions thereof, to radiation curable species prior to exposure to ionizing radiation is effective in further reducing auto-adhesion. 
         [0026]    The assembly of the medical device delivery system may be facilitated by separately providing the medical device to be delivered in an at least partially collapsed configuration and separately engaging the actuation member with the restraint member to form a structure into which the medical device may be introduced. Returning to the non-limiting example of an embolic filter to be delivered at the distal end of a guidewire, the embolic filter may be affixed to or about the guidewire and optionally exposed to one or more radiation curable species followed by exposure to ionizing radiation. The self-expanding, radially biased struts which support the filter material may then be compressed to lie generally along the guidewire and a temporary containment sleeve or clamp may used to secure the filter in a radially retracted state. It may be desirable at this point to arrange, pleat, or otherwise deploy the filter element in a configuration which efficiently utilizes the space which will be available within the restraint member and which ensures a smooth transition from the compact state to the deployed state as the struts expand. 
         [0027]    The restraint member may then be formed around a mandrel having dimensions which approximate the collapsed medical device and the actuation member may be engaged with the restraint member in a state which it is not stressed by the outward bias of the filter struts or any compression of the filter member which may occur when the embolic filter is fully constrained. Once the restraint member assembly is positioned and the actuation member is inserted, the mandrel may be removed. In some embodiments, the mandrel may be used to facilitate transfer of the preformed restraint member assembly to the embolic filter by sliding the restraint member assembly directly from the mandrel onto the constrained embolic filter. The preformed restraint member assembly may be transferred, directly or indirectly, to the embolic filter with simultaneous removal of the temporary containment sleeve. An optional ionizing radiation treatment may also be performed at this point to reduce auto-adhesion during storage and to sterilize the medical device and the device delivery system. 
         [0028]      FIGS. 5A-D  illustrate a method for the assembly of a medical device delivery system. In  FIG. 5A , struts  32  of embolic filter  30  have been collapsed and enclosed in a temporary containment sleeve  50  and filter material  34  has been smoothed into a configuration suitable for being restrained. In  FIG. 5B , restraint member  40  has been disposed about mandrel  60  which approximates the desired restraint configuration of embolic filter  30 . Actuation member  20  has been engaged with first portion  42  and second portion  44  of restraint member  40  in one of the manners described above or the like. In  FIG. 5C , the restraint member, in its restraint configuration is advanced along the embolic filter  30  displacing temporary containment sleeve  50 . As illustrated, restraint member  40  was removed from mandrel  60  before it replaces temporary containment sleeve  50  by sliding proximally. It will be appreciated that the transfer may be accomplished by sliding the restraint member  40  directly from the mandrel  60  an over embolic filter  30 . In other embodiments of the method, displacement of temporary containment sleeve  50  may be accomplished by sliding the restraint member  40  distally along filter  30 , providing that the second portion  44  of restraint member  40  is sufficiently strong to withstand the transitory outward pressure as struts  32  pass through. The constrained embolic filter  30  is illustrated in  FIG. 511   
         [0029]    Following insertion of the medical device delivery system into a lumen and navigation to a desired deployment site, actuation member  20 , not shown, may be withdrawn allowing the embolic filter to move from a constrained state to a deployed state as shown in  FIG. 6 . Although first portion  42  and second portion  44  of restraint member  40  have been shown as fully released and folded back for clarity in illustrating the deployment process, it will be appreciated that when an embolic filter  30  is deployed in a vessel, significant portions of restraint member  40  may lie generally along the filter and/or along the vessel wall where they will not create a significant bypass. 
         [0030]    It can be useful to provide a restraint member having two or more portions which differ in the degree of restraint which they provide. In this way, the overall bulk of the restrained medical device delivery system may be reduced while still reliably providing the necessary restraint. In some embodiments, a first portion of the restraint member has a different axial dimension than the second portion reflecting, for example, a relatively short group of collapsed struts may lie adjacent to a relatively longer collapsed filter member. In such configurations, it may be common for the collapsed struts to require a higher total restraining force than the relatively longer collapsed filter member. Accordingly, the material of that portion of the restraining member, and the corresponding actuation member, surrounding the higher force portion of the filter may be formed from higher strength materials and/or from thicker materials. For example, the collapsed struts may advantageously be constrained by a sheet of PEEK (polyetheretherketone) or PET (polyethylene terephthalate), while a thin sheet or even a mesh of polyurethane may suffice to restrain the filter element. Similar considerations may apply to the selection of material for the actuation member which may use, for example wire in the higher force section and thread or polymer in the lower force section. In addition, it may be desirable to arrange for the actuation member to span the gap between the edges of the restraint member more frequently, in an axial sense, in the higher force region and less frequently in the lower force region. This difference in frequency of spanning of the edges of the restraint member by the actuation member may, in some embodiments, suffice to define the two regions of the restraint member. Such changes may be made continuously or in a step-wise fashion. It is believed that the expedient of frequent spannings may lessen the stress at the points of contact between the restraint member and the actuation member and thus reduce the possibility of a premature release. 
         [0031]    In some embodiments, the restraint member substantially surrounds at least part of each of the first and second portions of the medical device in the restrained configuration. The restraint member does not necessarily completely enclose the medical device along its entire length or completely envelop its circumference at all points. In certain embodiments, the restraint member substantially surrounds at least part of each of the first and second portions of the medical device in the restraint configuration. In some embodiments, the first portion of the restraint member and the second portion of the restraint member have different circumferential dimensions. Typically, this will reflect the relative dimensions of the portions of the medical device in the restrained configuration; however it may also reflect a design decision related creating a smooth profile to facilitate advancing the restrained device through the lumen, particularly in the vicinity of an obstruction. 
         [0032]    In some embodiments, the actuation member, which bridges the axial gap in the restraint configuration, will be completely disengaged from the restraint member in the deployed configuration. In other embodiments, the actuation member may be partially disengaged or merely allowed to loosen to expand the gap. In yet other embodiments, the actuation member may disengage from the restraint member in stages to control deployment of the medical device. It should be understood that the term “axial gap”, as used in this document, is to be broadly interpreted to include a variety of configurations of the join between edges of a restraint element. In some embodiments, the gap may not be readily discernable due to overlap of the restraint member edges as in a stitched seam. The term may denote a continuous gap or a sequence of gaps which lie along a line generally parallel to the axis of the elongated member as described below. In the case of cylindrical restraint member, in the restraint configuration, the gap typically would be substantially parallel to the axis of the cylinder and the associated elongated member. In those embodiments where a portion of the restraint member forms a tapered section such as a frustum, an axial gap will be understood to follow generally along a generatrix of the associated cone. In other embodiments, the axial gap may form a helix forming at least a partial turn about a generally cylindrical restraint member. Similarly, the axial gap may assume a generally spiral form around a conical or frustoconical restraint member, or a portion thereof, such that the helix may be thought of as having a decreasing radius in at least one axial direction. In some embodiments, the restraint member may be created by multiple circumferential panels forming multiple axial gaps. Such multiple gaps may share a common actuation member or may employ a multiple actuation members. In some embodiments, portions of the restraint member may alternately cross the axial gap. In such embodiments, the actuation member will typically assume a more nearly linear configuration resembling the pin of a common hinge passing successively through aligned cylinders formed from the restraint member along the edge of the axial gap as in a piano hinge. In other embodiments, the activation member bridges the axial gap by alternately passing through the restraint member at points adjacent to and on opposite sides of the axial gap. 
         [0033]    Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and principles of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth hereinabove. All publications and patents are herein incorporated by reference to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference.