Abstract:
A medical device constraint includes an elastic element having proximal and distal ends, a continuous lumen extending between the proximal and distal ends of the tubular elastic element; and a medical device disposed at least partially within the continuous lumen, wherein the generally tubular element has a first state in which the tubular element is longitudinally held in tension to conceal a gap between the medical device and a distal tip and a second state in which the tubular element is longitudinally relaxed and spaced apart from the gap.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional of, and claims priority to, U.S. Provisional Patent Application No. 61/412,621, entitled “Deployment Sleeve Shortening Mechanism” filed Nov. 11, 2010, the content of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates to catheter based systems used to deliver medical devices. 
     2. Discussion of the Related Art 
     Various medical devices require catheter based delivery systems. Such medical devices include implantable, diagnostic and therapeutic devices. Common implantable, endovascular devices can include stents, stent grafts, filters, occluders, sensors and other devices. Endovascular devices are commonly advanced through the native vasculature to a treatment site by the use of a flexible catheter. When properly positioned at the treatment site the device (in the case of a stent) can be expanded to appose the vasculature. The device can then be released from the catheter allowing the catheter to be withdrawn from the vasculature. It is desirable to pre-compact endovascular devices into small delivery profiles in order to minimize vascular trauma and enhance maneuverability through torturous anatomies. A highly compacted device is often relatively stiff and is therefore difficult to bend into a small radius. A soft, flexible “olive” or tip is commonly positioned distal to the compacted device at the leading end of the delivery catheter, again to minimize vascular trauma and to enhance the positioning accuracy. As the device is advanced through a curved vessel, the junction between the relatively stiff compacted device and the soft flexible tip can “open up” presenting a gap. 
     To minimize this gap between a semi-rigid compacted device and a soft flexible leading tip various gap fillers and covers have been suggested. For example, a rigid catheter can be used to constrain a device into a small profile. The rigid catheter can extend distally beyond the device and over a portion of a leading tip, therefore covering a potential gap. The device can be allowed to expand by retracting the rigid catheter. 
     It remains desirable to have a device delivery system incorporating a releasable sleeve constraint along with an effective means to cover any potential undesirable gap between the compacted device and a leading catheter tip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following drawings: 
         FIG. 1  is a partial side view of a delivery system showing a medical device in a compacted and constrained delivery state and illustrating a gap between the compacted device and a catheter leading tip or olive. 
         FIG. 2  is a partial side view of a delivery system showing a medical device in a compacted and constrained delivery state, incorporating a restraining member having a retractable section. 
         FIG. 2 a    is a partial side view of a delivery system showing a medical device in a compacted and constrained delivery state, incorporating a restraining member having a retractable section. 
         FIGS. 3 a  and 3 b    are partial side views of a delivery system showing a medical device in a compacted and constrained delivery state, wherein the device is constrained by a restraining member having a retractable section. 
         FIGS. 3 c  and 3 d    are partial side views of a delivery system showing the release of a constrained medical device 
     
    
    
     DETAILED DESCRIPTION 
     Persons skilled in the art will readily appreciate that various aspects of the present disclosure can be realized by any number of methods and apparatuses configured to perform the intended functions. Stated differently, other methods and apparatuses can be incorporated herein to perform the intended functions. It should also be noted that the accompanying drawing figures referred to herein are not all drawn to scale, but can be exaggerated to illustrate various aspects of the present disclosure, and in that regard, the drawing figures should not be construed as limiting. Finally, although the present disclosure can be described in connection with various principles and beliefs, the present disclosure should not be bound by theory. 
     As used herein, the term “elastomer” generally defines a polymer that has the ability to be stretched to at least twice its original length and to retract rapidly to approximately its original length when released. The term “elastomeric” is intended to describe a condition whereby a polymer displays stretch and recovery properties similar to an elastomer, although not necessarily to the same degree of stretch and/or recovery. 
     In accordance with various embodiments, a partial side view of a catheter system used to implant a medical device is shown and generally indicated at  100  in  FIG. 1 . The catheter system  100  includes a catheter shaft  102  and an expandable device  104  constrained to a delivery profile or constrained state suitable for endoluminal delivery of the device to a treatment site. The device  104  is held in the constrained state by a flexible, generally tubular constraining sleeve or restraining member  106 . The flexible restraining member  106  is held or maintained in a tubular shape by a removable stitch line  108 . When the stitch line  108  is actuated by pulling or tensioning in the direction indicated at  114 , the restraining member  106  will split open and allow the device  104  to expand. Examples of restraining members and coupling members for releasably maintaining expandable devices in a constrained or collapsed state for endoluminal delivery to a treatment site can be found in U.S. Pat. No. 6,352,561 to Leopold et al, the content of which is incorporated herein by reference in its entirety. 
     Still referring to  FIG. 1 , as the catheter system  100  is advanced through a curved vessel, a gap  112  can form between the constrained device  104  and a compliant distal catheter tip  110 . Described in greater detail below, the restraining member, in accordance with various embodiments, comprises a retractable section that extends over at least a portion of the compacted or constrained device and at least a portion of the catheter tip so as to cover or bridge a gap therebetween. The retractable section can retract away from the catheter tip sequentially or concurrently with at least a partial actuation or opening of the restraining member. 
     Referring to  FIG. 2 , a partial side view of a catheter system, in accordance with various embodiments, used to implant a medical device is shown and generally indicated at  100 . The catheter system  100  includes a catheter shaft  102  having opposite proximal and distal ends, and an expandable device  104  (shown in dashed lines) disposed near or at the distal end of the catheter shaft  102 . The device  104  is held in a constrained state suitable for endoluminal delivery of the device to a treatment site by a flexible, generally tubular constraining sleeve or restraining member  106 . The flexible restraining member  106  is held in the tubular shape by a removable stitch line  108 . When the stitch line  108  is actuated by pulling or tensioning in the direction indicated at  114 , the restraining member  106  will split open and allow the device  104  to expand. The restraining member  106  at its distal end incorporates a retractable section  200  that extends over at least a portion of both the device  104  and the catheter tip  110 . In various embodiments, the retractable section can be a generally tubular element. As the catheter system is advanced through a curved vessel, a gap  112  can form between the constrained device  104  and a compliant distal catheter tip  110 . As shown, the retractable section  200  extends over at least a portion of both the device  104  and the catheter tip  110  to bridge the gap  112  therebetween. The retractable section  200  can retract away from the catheter tip  110  sequentially or concurrently with actuation or opening of the restraining member. 
     In various embodiments, a retracting element can be operatively coupled to the retractable section to facilitate retraction of the retractable section away from the catheter tip. The retracting element can be an elongated member, such as a tether, wire, string and the like coupled to the retracting section and extending through the catheter for access and selective actuation of the retracting element by the clinician at a proximal end of the catheter. 
     In various embodiments, the retracting element, for example as illustrated at  201  in  FIG. 2 a   , can be formed from an elastomeric material and operatively coupled to the retractable section  200 , such that the retracting element  201  is in a tensioned state while the retractable section  200  is releasably held or maintained over the device  104  and the catheter tip  110  to bridge the gap  112  therebetween. Release or opening of the retractable section  200  allows the retracting element  201  to shorten as it moves toward a relaxed, untensioned state. The retractable section  200  is pulled or displaced away from the catheter tip  110  in response to the shortening of the retracting element  201 . 
     In various embodiments, the retractable section can be formed from an elastomeric material and tensioned or stretched such that the retractable section can be releasably maintained in a tensioned state while extending over the device and the catheter tip to bridge the gap therebetween, and released to allow movement of the retractable section toward a shortened, relaxed state sequentially or concurrently with opening of the restraining member. 
     Upon delivery, the restraining member is released allowing the restraining member to release or “split-open” and permit the compacted device to expand. The device can be expanded by a balloon or can expand due to an outward force applied by a compressed stent wire frame. The restraining member may remain with the device at the treatment site in the vasculature, captured between the device and vascular wall. As the restraining member is released, the retractable section of the restraining member retracts proximally away from the catheter tip. In some cases, the medical device has anchors or barbs that aid in securing the device to the vascular wall along with a blood sealing cuff. Thus, retraction of the retractable section can further expose such anchors or barbs and/or sealing cuffs for engaging the vascular wall. 
     Referring to  FIG. 3 a   , a catheter system  100 , in accordance with various embodiments, is shown having an expandable device  104  partially covered by a constraining sleeve or restraining member  106 . The restraining member  106  has a retractable section  200   a  extending from a relatively non-elastic portion  300 . The retractable section  200   a  is shown in a non-tensioned state having a relaxed, original longitudinal length. As shown in  FIG. 3 b   , the retractable section  200   b  of the restraining member  106  can be longitudinally tensioned (stretched or elongated) in the direction depicted by arrows  302 . The retractable section  200   b  of the restraining member  106  can be stretched longitudinally to extend over the proximal end of the catheter olive or tip  110  to conceal or bridge a gap between the device  104  and the catheter tip  110 . Once longitudinally tensioned to the desired stretched length, the retractable section of the restraining member can be longitudinally restrained in tension. The retractable section  200   b  can, for example, be longitudinally tensioned or stretched to at least about 10% longitudinal elongation or at least about 110% of an initial or original (relaxed) length and held (restrained) in this stretched condition to bridge the gap between the device and the catheter tip. As illustrated in  FIG. 3 b   , a releasable stitch line  108  maintains the retractable section  200   b  in the elongated, tensioned state. 
     As shown in  FIG. 3 c   , the releasable stitch line  108  can be actuated or tensioned to allow the restraining member  106  to split open and release the expandable device  104 . As the restraining member  106  opens, the retractable section  200   c  is free to retract in the direction depicted by arrows  304  toward a relaxed, non-tensioned state. The restraining member therefore shortens longitudinally in length and retracts proximally along the compacted device. In some cases, the medical device has anchors or barbs that aid in securing the device to the vascular wall along with a blood sealing cuff. By shortening in length, the restraining member can retract proximally to expose any optional anchors and/or sealing cuffs for engaging the vascular wall. 
     As shown in  FIG. 3 d   , the releasable stitch line can be actuated, allowing the device  104  to fully expand. The retractable section  200   a  of the restraining member  106  is now longitudinally shortened as it moves toward the relaxed, non-tensioned state, as shown. Since the retractable section  200   a  is relaxed and non-tensioned, the retractable section retracts to a length shorter than a longitudinally tensioned or stretched length (as illustrated in  FIG. 3 b , 200 b   ). The restraining member  106  therefore does not cover or interfere with device sealing cuffs  306  or anchor barbs  308 , as shown in  FIG. 3   d.    
     In various embodiment, a restraining member and retracting element or retractable section of the restraining member can be retained in an elongated and tensioned state by friction between the constrained device and the inner surface of the restraining member. Opening of the restraining member by actuation of the stitch line as described above relieves the friction and allows the restraining member to longitudinally retract as the elastic element returns to a shorter, untensioned state. 
     In various embodiments, a restraining member can include an elastic element that is held in an elongated tensioned state to conceal a gap along the catheter assembly, such as between the expandable device and an adjacent component of the catheter assembly, and that retracts toward a shortened relaxed state upon release or opening of the restraining member to reveal the gap and/or portions of the expandable device and/or adjacent component. 
     In various embodiments, the restraining member can include proximal and distal elastic elements which can be held in elongated tensioned states to conceal proximal and distal gaps on opposite ends of the expandable device, and which retract toward shortened relaxed states upon release or opening of the restraining member to reveal the respective proximal and distal gaps and/or portions of the expandable device and/or adjacent components at opposite proximal and distal ends of the expandable device. 
     Elastic restraining members can comprise a variety of polymeric material, such as silicone. Other exemplary biocompatible elastomers can include, but are not limited to, elastomeric copolymers of 6-caprolactone and glycolide (including polyglycolic acid) with a mole ratio of 6-caprolactone to glycolide of from about 35:65 to about 65:35, more preferably from 35:65 to 45:55; elastomeric copolymers of 6-caprolactone and lactide (including L-lactide, D-lactide, blends thereof, and lactic acid polymers and copolymers) where the mole ratio of 6-caprolactone to lactide is from about 35:65 to about 65:35 and more preferably from about 30:70 to 45:55; other preferable blends include a mole ratio of 6-caprolactone to lactide from about 85:15 to 95:5; elastomeric copolymers of p-dioxanone (1,4-dioxan-2-one) and lactide (including L-lactide, D-lactide, blends thereof, and lactic acid polymers and copolymers) where the mole ratio of p-dioxanone to lactide is from about 40:60 to about 60:40; elastomeric copolymers of 6-caprolactone and p-dioxanone where the mole ratio of 6-caprolactone to p-dioxanone is from about from 30:70 to about 70:30; elastomeric copolymers of p-dioxanone and trimethylene carbonate where the mole ratio of p-dioxanone to trimethylene carbonate is from about 30:70 to about 70:30; elastomeric copolymers of trimethylene carbonate and glycolide (including polyglycolic acid) where the mole ratio of trimethylene carbonate to glycolide is from about 30:70 to about 70;30; elastomeric copolymers of trimethylene carbonate and lactide (including L-lactide, D-lactide, blends thereof, and lactic acid polymers and copolymers) where the mole ratio of trimethylene carbonate to lactide is from about 30:70 to about 70;30; and blends thereof. 
     Examples of suitable biocompatible elastomers are described in U.S. Pat. Nos. 4,045,418; 4,057,537 and 5,468,253. 
     An optional external sleeve, or external sock may be incorporated to cover the retractable section of the restraining member. 
     Typical catheters used to deliver medical devices can comprise commonly known materials such as Amorphous Commodity Thermoplastics that include Polymethyl Methacrylate (PMMA or Acrylic), Polystyrene (PS), Acrylonitrile Butadiene Styrene (ABS), Polyvinyl Chloride (PVC), Modified Polyethylene Terephthalate Glycol (PETG), Cellulose Acetate Butyrate (CAB); Semi-Crystalline Commodity Plastics that include Polyethylene (PE), High Density Polyethylene (HDPE), Low Density Polyethylene (LDPE or LLDPE), Polypropylene (PP), Polymethylpentene (PMP); Amorphous Engineering Thermoplastics that include Polycarbonate (PC), Polyphenylene Oxide (PPO), Modified Polyphenylene Oxide (Mod PPO), Polyphenelyne Ether (PPE), Modified Polyphenelyne Ether (Mod PPE), Thermoplastic Polyurethane (TPU); Semi-Crystalline Engineering Thermoplastics that include Polyamide (PA or Nylon), Polyoxymethylene (POM or Acetal), Polyethylene Terephthalate (PET, Thermoplastic Polyester), Polybutylene Terephthalate (PBT, Thermoplastic Polyester), Ultra High Molecular Weight Polyethylene (UHMW-PE); High Performance Thermoplastics that include Polyimide (PI, Imidized Plastic), Polyamide Imide (PAI, Imidized Plastic), Polybenzimidazole (PBI, Imidized Plastic); Amorphous High Performance Thermoplastics that include Polysulfone (PSU), Polyetherimide (PEI), Polyether Sulfone (PES), Polyaryl Sulfone (PAS); Semi-Crystalline High Performance Thermoplastics that include Polyphenylene Sulfide (PPS), Polyetheretherketone (PEEK); and Semi-Crystalline High Performance Thermoplastics, Fluoropolymers that include Fluorinated Ethylene Propylene (FEP), Ethylene Chlorotrifluroethylene (ECTFE), Ethylene, Ethylene Tetrafluoroethylene (ETFE), Polychlortrifluoroethylene (PCTFE), Polytetrafluoroethylene (PTFE), Polyvinylidene Fluoride (PVDF), Perfluoroalkoxy (PFA). Other commonly known medical grade materials include elastomeric organosilicon polymers, polyether block amide or thermoplastic copolyether (PEBAX) and metals such as stainless steel and nickel/titanium alloys. Semi-rigid restraining members can comprise appropriate materials listed above. 
     Medical devices incorporating stents can have various configurations as known in the art and can be fabricated, for example, from cut tubes, wound wires (or ribbons) or flat patterned sheets rolled into a tubular form. Stents can be formed from metallic, polymeric or natural materials and can comprise conventional medical grade materials such as nylon, polyacrylamide, polycarbonate, polyethylene, polyformaldehyde, polymethylmethacrylate, polypropylene, polytetrafluoroethylene, polytrifluorochlorethylene, polyvinylchloride, polyurethane, elastomeric organosilicon polymers; metals such as stainless steels, cobalt-chromium alloys and nitinol and biologically derived materials such as bovine arteries/veins, pericardium and collagen. Stents can also comprise bioresorbable materials such as poly(amino acids), poly(anhydrides), poly(caprolactones), poly(lactic/glycolic acid) polymers, poly(hydroxybutyrates) and poly(orthoesters). 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.