Abstract:
The disclosure pertains to percutaneously deliverable bioabsorbable closure devices for an ostium of a left atrial appendage which devices promote endothelialization across the ostium and then are bioabsorbed to leave little or no foreign residue, methods of manufacturing such bioabsorbable closure devices, and the use thereof.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/254,969, filed Nov. 13, 2015. 
     
    
     BACKGROUND 
       [0002]    There are a number of heart diseases (e.g. coronary artery disease, mitral valve disease) that have various adverse effects on the heart. An adverse effect of certain cardiac diseases, such as mitral valve disease, is atrial (or auricular) fibrillation. Atrial fibrillation may result in pooling of blood in the left atrial appendage. Blood pooling may also be spontaneous. When blood pools in the atrial appendage, blood clots can form and accumulate therein, build upon themselves, and propagate out from the atrial appendage into the atrium. These blood clots can then enter the systemic or pulmonary circulations and cause serious problems if they migrate from the atrial appendage and become free in the blood stream and embolize distally into the arterial system. Similar problems also occur when a blood clot extending from an atrial appendage into an atrium breaks off and enters the blood supply. Since blood from the left atrium and ventricle supply the heart and brain, blood clots from the atrial appendages can obstruct blood flow therein causing heart attacks, strokes or other organ ischemia. It is therefore necessary to find a means of preventing blood clots from forming in the atrial appendages and to prevent these blood clots, once formed, from leaving the atrial appendages to the heart lungs, brain or other circulations of the patient which can cause heart attacks or strokes or other organ ischemia. 
         [0003]    U.S. Pat. No. 5,865,791 relates to the reduction of regions of blood stasis and ultimately thrombus formation in such regions, particularly in the atrial appendages of patients with atrial fibrillation. More specifically, the invention relates to procedures and devices for affixing the atrial appendages in an orientation that prevents subsequent formation of thrombus. The invention removes the appendage from the atrium by pulling on it and putting a loop around it to form a sack of the atrial appendage and then cut off from the rest of the heart. 
         [0004]    U.S. Pat. No. 5,306,234 relates to a method for surgically closing the passage between the atrium and the atrial appendage or severing the atrial appendage. 
         [0005]    U.S. Pat. Nos. 6,551,303 and 6,689150 disclose barrier devices and filter devices respectively which may be deployed at the ostium of a left atrial appendage to block thrombus generated within the left atrial appendage from entering the left atrium and general circulation. 
         [0006]    While current treatment methods are effective for minimizing migration of thrombus from the left atrial appendage into the general circulation, a need still exists for a percutaneous treatment option which does not result in the long term introduction of foreign matter which may provoke an inflammatory response. 
       SUMMARY 
       [0007]    In some aspects, the invention relates to a left atrial appendage closure device comprising a plurality of centrally joined bioabsorbable struts forming an umbrella-like support structure which is concave when viewed from a distal end of the plurality of centrally joined bioabsorbable struts, wherein the umbrella-like support structure has a first radially compact configuration and a second expanded configuration in which second expanded configuration the umbrella-like support structure has a proximal circumferential dimension sized and adapted to span the ostium of a left atrial appendage and a distal extent sized and adapted to be contained within the left atrial appendage; a bioabsobable porous membrane which forms a porous cap coextensive with centrally joined portions of the bioabsorbable struts and which extends distally along at least a portion of the umbrella-like support structure sized and adapted to be contained within the left atrial appendage, wherein the porous membrane is bioabsorbable, the pores of the porous membrane are sized and adapted to retain thrombi within the left atrial appendage when the left atrial appendage closure device is deployed within the left atrial appendage, and the porous membrane includes a tissue growth promoting component. In some aspects, at least some of the bioabsorbable struts of the umbrella-like support structure may be joined near their distal ends to form a closed support structure cage. 
         [0008]    In addition or alternatively, the invention relates to a left atrial appendage closure device wherein the bioabsorbable porous membrane is selected from the group consisting of a textile, a nonwoven, a braid, a laser cut sheet, an etched sheet, and a 3D printed article. 
         [0009]    In some aspects, the bioabsorbable polymer of the plurality of centrally joined bioabsorbable struts and the polymer of the bioabsorbable porous membrane of the left atrial appendage closure device are selected from the group consisting of polyglycolic acid, polylactic acid, polycaprolactone, polyvalerolactone, poly(1,4-dioxane-2,3-dione), poly(1,3-dioxane-2-one), poly(p-dioxanone), poly(1,5-dioxepan-2-one), poly(β-R,S-malic acid), poly(α-malic acid), polyhydroxyalkanoates, and mixtures or copolymers thereof. 
         [0010]    In some aspects of the invention, the polymer of the plurality of bioabsorbable struts is the same as the polymer of the bioabsorbable porous membrane. 
         [0011]    In some aspects of the invention, the polymer of the plurality of centrally joined bioabsorbable struts is different from the polymer of the bioabsorbable porous membrane. 
         [0012]    In certain aspects of the invention, the porous membrane includes a tissue growth promoting component selected from the group consisting of fibronectin, vascular endothelial growth factor, and fibroblast growth factor. 
         [0013]    In some aspects of the invention the tissue growth promoting component of the left atrial appendage closure device is a layer on the porous membrane. 
         [0014]    In certain aspects of the invention the tissue growth promoting component of the left atrial appendage closure device is dispersed within the bioabsorbable porous membrane. 
         [0015]    In addition, the thicknesses of the struts of the plurality of centrally joined bioabsorbable struts and of the bioabsorbable porous membrane of the left atrial appendage device of the invention are selected to provide a controlled bioabsorption profile which minimizes release of particulate material. 
         [0016]    In some aspects of the invention, the left atrial appendage closure device further comprises a hub which is attached to the centrally joined plurality of bioabsorbable struts and adapted to be releaseably attached to a distal end of a delivery shaft. 
         [0017]    In addition or alternatively, the invention includes a method of manufacturing a left atrial appendage closure device comprising the steps of creating a plurality of centrally joined bioabsorbable struts forming an umbrella-like support structure and creating a porous bioabsorbable membrane which forms a porous cap coextensive with centrally joined portions of the bioabsorbable struts and extending distally along at least a portion of the umbrella-like support structure, wherein the porous membrane is fixedly attached to the plurality of centrally joined bioabsorbable struts forming an umbrella-like support structure and wherein the porous membrane includes a tissue growth promoting component. In some aspects of the method of manufacturing a left atrial appendage closure device, at least some of the distal ends of the bioabsorbable struts forming an umbrella-like support structure may be joined to form a closed support structure cage. 
         [0018]    In certain aspects of the method of manufacturing a left atrial appendage closure device of the invention, the step of creating the plurality of centrally joined bioabsorbable struts forming an umbrella-like support structure includes one or more of welding, molding, vacuum forming, removing material from a solid workpiece, and 3D printing. 
         [0019]    In some aspects of the method of manufacturing a left atrial appendage closure device, the step of creating the porous bioabsorbable membrane which forms a porous cap coextensive with centrally joined portions of the bioabsorbable struts and which extends distally along at least a portion of the umbrella-like support structure includes one or more of weaving, braiding, electrospraying, electrospinning, molding, vacuum forming, laser cutting, etching, and 3D printing. 
         [0020]    In addition or alternatively, in the method of manufacturing a left atrial appendage closure device of the invention, the step of creating a plurality of centrally joined bioabsorbable struts forming an umbrella-like support structure and the step of creating a porous bioabsorbable membrane which forms a porous cap coextensive with centrally joined portions of the bioabsorbable struts and which extends distally along at least a portion of the umbrella-like support structure are carried out simultaneously to create a unitary left atrial appendage closure device. In some aspects, at least some of the bioabsorbable struts of the umbrella-like support structure may be joined near their distal ends to form a closed support structure cage. 
         [0021]    In addition or alternatively the method of manufacturing a left atrial appendage closure device further comprises attaching a hub to the centrally joined bioabsorbable struts, said hub being adapted to be releaseably attached to a distal end of a delivery shaft. 
         [0022]    In some aspects of the invention, left atrial appendage closure device comprises a plurality of bioabsorbable struts having a proximal end and a distal end which are joined at their proximal portions to form an umbrella-like support structure which is concave when viewed from a distal end of the plurality of proximally joined bioabsorbable struts, wherein the umbrella-like support structure has a first compact delivery configuration and a second expanded deployed configuration in which the umbrella-like support structure has a proximal circumferential dimension sized and adapted to span and engage the ostium of a left atrial appendage and a longitudinal extent sized and adapted to be contained within the left atrial appendage; a bioabsorbable porous cap coextensive with the joined proximal portions of the bioabsorbable struts and which extends distally therefrom along at least a portion of the umbrella-like support structure sized and adapted to be contained within the left atrial appendage, wherein the porous cap is bioabsorbable, the pores of the porous cap are sized and adapted to retain thrombi within the left atrial appendage when the left atrial appendage closure device is deployed within the left atrial appendage, and the porous cap includes a tissue growth promoting component. In some aspects, at least some of the bioabsorbable struts of the umbrella-like support structure may be joined near their distal ends to form a closed support structure cage. 
         [0023]    In some aspects, the bioabsorbable porous cap of the left atrial appendage closure device of the invention is selected from the group consisting of a textile, a nonwoven, a braid, a laser cut sheet, an etched sheet, and a 3D printed article. 
         [0024]    In addition, the bioabsorbable polymer of the plurality of proximally joined bioabsorbable struts and the polymer of the bioabsorbable porous cap of the left atrial appendage closure device of the invention are selected from the group consisting of polyglycolic acid, polylactic acid, polycaprolactone, polyvalerolactone, poly(1,4-dioxane-2,3-dione), poly(1,3-dioxane-2-one), poly(p-dioxanone), poly(1,5-dioxepan-2-one), poly(β-R,S-malic acid), poly(α-malic acid), polyhydroxyalkanoates, and mixtures or copolymers thereof. 
         [0025]    In some aspects of the invention, the polymer of the plurality of bioabsorbable struts is the same as the polymer of the bioabsorbable porous cap. 
         [0026]    In certain aspects of the invention, the plurality of proximally joined bioabsorbable struts and the bioabsorbable porous cap of the left atrial appendage closure device are integrally formed. 
         [0027]    In some aspects of the invention, the polymer of the plurality of proximally joined bioabsorbable struts of left atrial appendage closure device of the invention is different from the polymer of the bioabsorbable porous cap. 
         [0028]    In certain aspects of the invention, the tissue growth promoting component of the left atrial appendage closure device is selected from the group consisting of fibronectin, vascular endothelial growth factor, and fibroblast growth factor. 
         [0029]    In some aspects of the invention, tissue growth promoting component of the left atrial appendage device of the invention is a layer on the bioabsorbable porous cap. 
         [0030]    In addition or in the alternative, the tissue growth promoting component of the left atrial appendage device of the invention is dispersed within the bioabsorbable porous cap. 
         [0031]    In addition or in the alternative, the tissue growth promoting component of the left atrial appendage device of the invention is absorbed within a surface layer of the bioabsorbable porous cap. 
         [0032]    In some aspects of the invention, the thicknesses of the plurality of proximally joined bioabsorbable struts and the bioabsorbable porous cap of the left atrial appendage closure device are selected to provide a controlled bioabsorption profile which minimizes release of particulate material. 
         [0033]    In addition or in the alternative, the left atrial appendage closure device further comprises a hub attached to the plurality of proximally joined bioabsorbable struts and adapted to be releaseably attached to a distal end of a delivery shaft. 
         [0034]    In addition or in the alternative, the invention includes a method of manufacturing a left atrial appendage closure device comprising the steps of creating a plurality of bioabsorbable struts joined at their proximal portions to form a distally opening umbrella-like support structure and creating a porous bioabsorbable cap coextensive with proximally joined portions of the bioabsorbable struts and extending distally along at least a portion of the umbrella-like support structure, wherein the bioabsorbable porous cap is fixedly attached to the plurality of proximally joined bioabsorbable struts forming an umbrella-like support structure and wherein the bioabsorbable porous cap includes a tissue growth promoting component. In some aspects, at least some of the bioabsorbable struts of the umbrella-like support structure may be joined near their distal ends to form a closed support structure cage. 
         [0035]    In certain aspects of the method of manufacturing a left atrial appendage closure device, the step of creating the plurality of bioabsorbable struts joined at their proximal portions to form a distally opening umbrella-like support structure includes one or more of welding, molding, vacuum forming, removing material from a solid workpiece, and 3D printing. In some aspects, at least some of the bioabsorbable struts of the umbrella-like support structure may be joined near their distal ends to form a closed support structure cage. 
         [0036]    In some aspects of the method of manufacturing a left atrial appendage closure device of the invention, the step of creating the bioabsorbable porous cap which forms a porous cap coextensive with proximally joined portions of the bioabsorbable struts and which extends distally along at least a portion of the umbrella-like support structure includes one or more of weaving, braiding, electrospraying, electrospinning, molding, vacuum forming, laser cutting, etching, and 3D printing. 
         [0037]    In the alternative or in addition, the method of manufacturing a left atrial appendage closure device of claim  28 , wherein the steps of creating a plurality of bioabsorbable struts joined at their proximal portions to form a distally opening umbrella-like support structure and creating a porous bioabsorbable membrane which forms a porous cap coextensive with the plurality of bioabsorbable struts joined at their proximal portions to form a distally opening umbrella-like support structure which extends distally along at least a portion of the umbrella-like support structure are carried out simultaneously to create a unitary left atrial appendage closure device. In some aspects, at least some of the bioabsorbable struts of the umbrella-like support structure may be joined near their distal ends to form a closed support structure cage. 
         [0038]    In some aspects of the method of manufacturing a left atrial appendage closure device of the invention, the bioabsorbable polymer of the plurality of bioabsorbable struts and of the bioabsorbable porous cap is selected from the group consisting of polyglycolic acid, polylactic acid, polycaprolactone, polyvalerolactone, poly(1,4-dioxane-2,3-dione), poly(1,3-dioxane-2-one), poly(p-dioxanone), poly(1,5-dioxepan-2-one), poly(β-R,S-malic acid), poly(α-malic acid), polyhydroxyalkanoates, and mixtures or copolymers thereof. 
         [0039]    In certain aspects of the method of manufacturing a left atrial appendage closure device of the invention the tissue growth promoting component is selected from the group consisting of fibronectin, vascular endothelial growth factor, and fibroblast growth factor. 
         [0040]    In addition or in the alternative, the method of manufacturing a left atrial appendage closure device of the invention further comprises a step of attaching a hub to the plurality of bioabsorbable struts joined at their proximal ends, said hub being adapted to be releaseably attached to a distal end of a delivery shaft. 
         [0041]    In some aspects of the method of manufacturing a left atrial appendage closure device the invention, the hub is a bioabsorbable hub. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0042]      FIG. 1A  presents a lateral view of a left atrial appendage closure device of the invention. 
           [0043]      FIG. 1B  illustrates an alternate arrangement of the plurality of centrally joined struts of a left atrial appendage closure device of the invention. 
           [0044]      FIG. 2  presents an axial view of the left atrial appendage closure device of  FIG. 1A  as seen from the distal end thereof. 
           [0045]      FIG. 3  presents a partial cutaway view of a left atrial appendage closure device of the invention disposed in a distal portion of a delivery catheter. 
           [0046]      FIG. 4  presents a detail view of a releasable connection between a delivery shaft and a hub of a left atrial appendage closure device of the invention. 
           [0047]      FIG. 5  illustrates a plurality of centrally joined struts of a left atrial appendage closure device of the invention. 
           [0048]      FIGS. 6A and 6B  provide schematic cross-sectional views of portions of porous cap membranes of the invention which include a tissue growth promoting component. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    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 exemplify aspects of the claimed invention. 
         [0050]    Although some suitable dimensions, ranges and/or values pertaining to various components, features and/or specifications are disclosed, one of skill in the art, incited by the present disclosure, would understand desired dimensions, ranges and/or values may deviate from those expressly disclosed unless the context clearly indicates an intended limitation. 
         [0051]    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). 
         [0052]    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. 
         [0053]    It is noted that references in the specification to “an aspect”, “some aspects”, “other aspects”, etc., indicate that the aspect described may include a particular feature, structure, or characteristic, but not every aspect may necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect of the invention. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it would be within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described unless clearly stated to the contrary. 
         [0054]      FIG. 1A  shows a lateral view of an expanded self-expanding left atrial appendage closure device  100  and  FIG. 2  shows a axial view of the same device as seen from the distal end, which device comprises a plurality of bioabsorbable struts  122 , each having a proximal end and a distal end, which are joined at their proximal portions to form an umbrella-like support structure which is concave when viewed from a distal end of the plurality of proximally joined bioabsorbable struts; a porous cap  110  coextensive with the joined proximal portions of the bioabsorbable struts  122  and extending distally therefrom along at least a portion of the bioabsorbable struts  122 . In some aspects, at least some of the bioabsorbable struts of the umbrella-like support structure may be joined near their distal ends to form a closed support structure cage. 
         [0055]    Although the illustrated aspect of the invention has eight bioabsorbable struts  122 , it will be appreciated that more or fewer bioabsorbable struts, for example, 4, 5, 6, 7, 9, 10, or 12 struts, may be employed if desired. Generally fewer struts may reduce the diameter of a collapsed configuration of a left atrial appendage closure device  100  to facilitate delivery, while the addition of more bioabsorbable struts  122  may tend to provide a smoother wall sealing contour by allowing individual bioabsorbable struts  122  flex to a greater or lesser extent to accommodate variations in the shape of an ostium. In some aspects of the invention, at least some of the bioabsorbable struts may be joined at their distal ends to form a closed cage support structure. 
         [0056]    The proximal ends of the plurality of bioabsorbable struts  122  may assume a generally planar configuration adapted to span the ostium of a left atrial appendage before bending distally to provide a more cylindrical wall engaging portion. The joined proximal ends may form or include a hub  120  to be discussed in greater detail below. In some aspects of the invention, the hub  120  may be formed as a thickened region of the joined proximal ends of the plurality of bioabsorbable struts  122 . Although shown in the figures as slightly protruding proximally from the porous cap  110  in the figures for clarity of illustration, it will be appreciated that the hub may be constructed to be flush with the porous cap  110  or even slightly recessed therefrom. 
         [0057]    Bioabsorbable struts  122  may also include one or more optional barbs  124  to be discussed in greater detail later. 
         [0058]    The invention contemplates a variety of cross-sectional shapes and cross-sectional areas distributed along the length of the struts which are selected to control the rate of bioabsorption in a manner which provides adequate support during endothelialization, provides rapid bioabsorption when support is no longer required, and which minimizes the release of portions of the biodegradable struts  122  and/or the porous cap  110  membrane which might otherwise constitute undesirable particulate matter debris within the circulatory system. 
         [0059]    The bioabsorbable struts  122  and the resulting umbrella-like structure may be formed by any of the methods employed in the art to construct similar structures and may include injection molding, blow molding, machining, 3D printing and assembly from individual components. In certain aspects of the invention, the bioabsorbable struts  122  or  122 ′ and hub  120  may be formed as a separate membrane supporting structure as shown in  FIG. 5 . In some aspects of the invention, the bioabsorbable struts  122  may be formed from one or more of polyglycolic acid, polylactic acid, polycaprolactone, polyvalerolactone, poly(1,4-dioxane-2,3-dione), poly(1,3-dioxane-2-one), poly(p-dioxanone), poly(1,5-dioxepan-2-one), poly(β-R,S-malic acid), poly(α-malic acid), polyhydroxyalkanoates, mixtures or copolymers thereof, and the like. In an exemplary aspect, the bioabsorbable struts  122  may be formed from poly-4-hydroxybutyrate and copolymers thereof. 
         [0060]    The porous cap  110  of  FIGS. 1 and 2  may be viewed as providing a generally planar central region which is adapted to span an ostium of a left atrial appendage as well as transitioning to provide a generally cylindrical skirt which is adapted to lie along a lumen wall defined by a left atrial appendage and to improve the lateral sealing ability of the porous cap  110  within the left atrial appendage once the device is deployed. 
         [0061]    The porous cap  110  is formed from a bioabsorbable membranous material which may comprise one or more of polyglycolic acid, polylactic acid, polycaprolactone, polyvalerolactone, poly(1,4-dioxane-2,3-dione), poly(1,3-dioxane-2-one), poly(p-dioxanone), poly(1,5-dioxepan-2-one), poly(β-R,S-malic acid), poly(α-malic acid), polyhydroxyalkanoates, mixtures or copolymers thereof, and the like. In an exemplary aspect, the porous cap  110  membrane may be formed from poly-4-hydroxybutyrate and copolymers thereof. 
         [0062]    The porous cap  110  membrane may be a textile, a nonwoven, a braid, a laser cut sheet, an etched sheet or a 3D printed article. In some aspects, the porous cap  110  membrane may be formed by one or more of weaving, braiding, electrospraying, electrospinning, molding, vacuum forming, laser cutting, etching, and 3D printing. While the pores of the porous cap  110  membrane have been depicted as through pores for ease of illustration in some of the figures, it will be appreciated that for the purpose of promoting tissue ingrowth of endothelial tissue, some or all of the porosity may be disposed at or near the surface of the porous cap  110  membrane. Although illustrated in the figures as disposed over the bioabsorbable struts  122 , it will be appreciated that the porous cap  110  membrane may in the alternative be disposed within a support structure provided by bioabsorbable struts  122 . 
         [0063]    It also will be appreciated that it may be convenient to form the plurality of centrally joined bioabsorbable struts  122  and the porous cap  110  membrane simultaneously as an integrally formed object. In those aspects, it may be desirable to include one or more additional components of the left atrial appendage closure device  100  such as hub  120 , barbs  124  or their equivalents, a tissue growth promoter  112 ,  114 , and the like in the same forming operation. In addition, in such aspects the portions of the bioabsorbable struts  122  which are coextensive with the porous cap  110  membrane may be present as thickened portions of the porous cap  110  membrane rather than as distinctly separate features. 
         [0064]    The hub  120 , barbs  124  or their equivalents, a tissue growth promoter  112 ,  114 , and the like may also be introduced at different stages of the manufacturing operation if desired. Similarly, it may be desirable or convenient to use the same or different bioabsorbable polymers for various components of the left atrial appendage closure device as well as the same or different manufacturing processes for the fabrication of individual components to be assembled in separate steps of a manufacturing method. 
         [0065]    In the aspect of the invention illustrated in  FIGS. 1 and 2 , each bioabsorbable strut  122  includes an optional barb  124  which is sized and adapted to engage adjacent tissue to minimize migration of a deployed device. Although one barb  124  is shown on each bioabsorbable strut  122 , one of ordinary skill in the art would appreciate that this arrangement is only illustrative of an aspect of the invention. In other aspects, a strut or struts may have 0, 2, 3, or more barbs per bioabsorbable strut  122  and not every bioabsorbable strut  122  needs to have the same number of barbs  124  as its immediate neighbors. The simple barb  124  of  FIGS. 1 and 2  is intended to be representative of other structures known in the art to inhibit migration of an implanted device. For example, the simple barb  124  of  FIGS. 1 and 2  may be replaced by a two-tipped barb having one tip disposed generally in a proximal direction along the associated bioabsorbable strut while a second tip is disposed generally in a distal direction along the associated bioabsorbable strut  122 . Similarly, the barb  124  may be replaced with a roughened segment of exposed bioabsorbable strut  122  such that each protrusion from the roughened segment of exposed bioabsorbable strut  122  may be viewed as a tip of a barb  124 . Some barbs  124  may be integrally formed with the associated strut while other barbs  124  may be formed separately and attached to the bioabsorbable strut  122 . It will be appreciated that although the exemplary barbs  124  are illustrated as located at the distal margin of the porous cap  110  membrane, barbs  124  or their equivalents may be distributed at other locations along the associated bioabsorbable strut  122  and may extend outward from the surface of the porous cap  110  membrane as well as outward from more distal portions of the bioabsorbable struts  122 . As discussed above, barbs  124  or their equivalents, if present, also may be formed from the previously identified bioabsorbable polymer(s) using the known manufacturing processes. 
         [0066]    In the interest of promoting tissue growth into and across the portion of the porous cap  110  membrane located at the ostium of the left atrial appendage to permanently seal the ostium prior to the full bioabsorption of the left atrial appendage closure device  100 , the devices include a tissue growth promoting component  112 ,  114  which may be dispersed throughout the porous cap  110  membrane as shown in  FIG. 6A , preferentially absorbed near one or both surfaces of the porous cap  110  membrane, and/or applied as a coating to one or both surfaces of the porous cap  110  membrane as shown if  FIG. 6B . If desired or convenient, the tissue growth promoting component  112 ,  114  may also be present within or applied to other components of the left atrial appendage closure device  100  such as the bioabsorbable struts  122  and barbs  124  or their equivalents. 
         [0067]    In a further aspect related to the manufacturing of a left atrial appendage closure device  100 , a support structure shown in  FIG. 5  provided by bioabsorbable struts  122  comprising poly-4-hydroxybutyrate may be formed separately by, for example, injection molding and then positioned about a mandrel. In an alternate aspect of the manufacturing method, a support structure shown in  FIG. 1B , in which at least some of the bioabsorbable struts  122 ′ may also be joined at their distal end. In a separate step, a porous cap  110  membrane may be formed over a portion of the bioabsorbable struts  122  and the mandrel by electrospinning filaments of poly-4-hydroxybutyrate. In some aspects, the bioabsorbable struts  122  may be removed from the mandrel and a porous cap  110  membrane may be formed over a portion of the bioabsorbable struts  122  and the mandrel by electrospinning filaments of poly-4-hydroxybutyrate. The filaments may comprise a dispersed tissue growth promoter  112  as shown somewhat schematically in  FIG. 6A  or a tissue growth promoter  114  may be applied to the porous cap  110  membrane as a coating or as an adsorbed layer, as shown in  FIG. 6B , in a later step. 
         [0068]    The bioabsorbable left atrial appendage closure devices  100  of  FIGS. 1 and 2  may be delivered to the left atrial appendage using delivery catheters and approaches of the art. For example, the bioabsorbable left atrial appendage closure devices  100  of  FIGS. 1 and 2  may be caused to assume a first compact configuration adapted to be received within the distal end of a delivery catheter  200 , as shown in  FIG. 3 , prior to being advanced to the deployment site where the devices may be expelled by advancement of delivery shaft  230  and/or withdrawal of delivery catheter  200 . In such aspects, the bioabsorbable left atrial appendage closure device  100  may include a proximal hub  120  adapted to releasably mate with a delivery shaft  230 , one aspect of which is illustrated in  FIG. 4 . 
         [0069]    In the illustrated aspect of  FIG. 4 , the distal tip  240  of the delivery shaft  230  includes a male threaded portion and the corresponding mating hub  120  of the bioabsorbable left atrial appendage closure device  100  includes a female threaded aperture adapted to threadably engage the distal tip  240  for delivery through and from the delivery catheter  200 , including possible recollapse and repositioning within the delivery site before rotation of the deliver shaft and distal tip  240  unscrews the distal tip  240  from the mating hub  120  of the bioabsorbable left atrial appendage closure device  100 . It will be appreciated that engagement between the delivery site wall upon self-expansion of the bioabsorbable left atrial appendage closure device  100  to assume a second expanded configuration will provide the resistance necessary to allow the distal tip  240  to unscrew from the mating hub  120 . 
         [0070]    It also will be appreciated that other releasable mating connectors known in the art may be used. For example, the female threaded portion of the releasable mating connector may be formed within distal tip  240 , while the hub  120  includes a mating male threaded portion. In the alternative, friction fit couplings, pin and loop connectors, and even magnetic couplers may be used with due regard for bioabsorbability of the components of the hub  120 . The delivery catheter  200  and/or the delivery shaft  230  may include radiopaque markers to aid in positioning the left atrial appendage closure device  100  within the left atrial appendage. 
         [0071]    Although the illustrative examples described above relate to closure of a left atrial appendage, it is also contemplated that the device may be used close other ostia such as that of an aneurysm. In such an aspect, the size and shape of the generally planar central region of the proximal portions of the bioabsorbable struts and porous cap as well as the distal extent of the device as a whole may be modified to better match the ostium and depth of the aneurysm or other lumen. 
         [0072]    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.