Patent Publication Number: US-2023132996-A1

Title: Bevel tip expandable mouth catheter with reinforcing ring

Description:
FIELD OF INVENTION 
     The present invention generally relates devices and methods for removing acute blockages from blood vessels during intravascular medical treatments. More specifically, the present invention relates to retrieval catheters with expandable tips into which an object or objects can be retrieved. 
     BACKGROUND 
     Clot retrieval aspiration catheters and devices are used in mechanical thrombectomy for endovascular intervention, often in cases where patients are suffering from conditions such as acute ischemic stroke (AIS), myocardial infarction (MI), and pulmonary embolism (PE). Accessing the neurovascular bed in particular is challenging with conventional technology, as the target vessels are small in diameter, remote relative to the site of insertion, and highly tortuous. These catheters are frequently of great length and must follow the configuration of the blood vessels in respect of all branching and windings. Traditional devices are often either too large in profile, lack the deliverability and flexibility needed to navigate particularly tortuous vessels, or are not effective at removing a clot when delivered to the target site. 
     Many existing designs for aspiration retrieval catheters are often restricted to, for example, inner diameters of 6 Fr or between approximately 0.068-0.074 inches. Larger sizes require a larger guide or sheath to be used, which then necessitates a larger femoral access hole to close. Most physicians would prefer to use an 8 Fr guide/6 Fr sheath combination, and few would be comfortable going beyond a 9 Fr guide/7 Fr sheath combination. This means that once at the target site, a clot can often be larger in size than the inner diameter of the aspiration catheter and must otherwise be immediately compressed to enter the catheter mouth. This compression can lead to bunching up and subsequent shearing of the clot during retrieval. Firm, fibrin-rich clots can also become lodged in the fixed-mouth tip of these catheters making them more difficult to extract. This lodging can also result in shearing where softer portions breaking away from firmer regions of the clot. 
     Small diameters and fixed tip sizes are also less efficient at directing the aspiration necessary to remove blood and thrombus material during the procedure. The suction must be strong enough such that any fragmentation that may occur as a result of aspiration or the use of a mechanical thrombectomy device cannot migrate and occlude distal vessels. When aspirating with a fixed-mouth catheter, a significant portion of the aspiration flow ends up coming from vessel fluid proximal to the tip of the catheter, where there is no clot. This significantly reduces aspiration efficiency, lowering the success rate of clot removal. 
     Large bore intermediate and aspiration catheters and/or those with expandable tips are therefore desirable because they provide a large lumen and distal mouth to accept a clot with minimal resistance. The bore lumen of these catheters can be nearly as large as the guide and/or sheath through which they are delivered, and the expandable tip can expand to be a larger diameter still. When a clot is captured and drawn proximally into a tip with a funnel shape, the clot can be progressively compressed during retrieval so that it can be aspirated fully through the catheter and into a syringe or cannister. 
     In many examples, the fixed-mouth catheters and those with expandable tips can have an underlying braid as the primary supporting backbone. The use of braids in catheter support is not a novel concept, and typical examples can be readily found in the art. The braid can often be as simple as bands wrapped spirally in one direction for the length of the catheter which cross over and under bands spiraled in the opposite direction. The bands can be metallic, fiberglass, or other material providing effective hoop strength to reinforce the softer outer materials of the body. However, supporting braids can also have a very high sectional stiffness the point where they do not meet the flexibility criteria for many procedures or cannot be made soft enough for use in fragile vessels without causing substantial trauma. Conversely, the low section stiffness and hoop strength of many braids means that, during an aspiration procedure, the applied suction can collapse the tip before a clot is engaged. 
     Further catheter advances have shown evidence that a larger aspiration catheter tip surface area can lead to increased aspiration efficiency and an enhanced interface with a clot. Designs with angled bevel tips have been shown to improve interaction with a lodged clot, as a beveled tip offers a larger mouth area for aspiration and ingestion than a flat tip. An in vitro study by Vargas et al. demonstrated an improvement of nearly 70% in the incidence of complete ingestion of a clot when using a bevel tip catheter compared to a flat tip control device (Vargas et al., Journal of NeuroInterventional Surgery 2021; 13:823-826). As such, there is potential that a beveled tip can reduce the total number of aspiration attempts for a successful procedure, reduce the added complication associated with stentriever usage, and/or lead to more frequent TICI 2C revascularization grades with lower mRS scores. Despite this, greater support can be required to prevent tip collapse due to the reduced hoop stiffness resulting from an annular beveled shape as compared to a right cylinder. 
     As a result, the tip must be compliant enough to be advanced easily through a guide or sheath in a collapsed state, while being strong enough to withstand aspiration forces without collapsing. Combining these needs without significant tradeoffs can be tricky. There remains a need for improved catheter designs attempting to overcome these design challenges. The presently disclosed designs provide devices and methods capable of addressing the above-stated deficiencies. 
     SUMMARY 
     It is an object of the present designs to provide devices and methods to meet the above-stated needs. The designs can be for a clot retrieval catheter capable of remove a clot from cerebral arteries in patients suffering AIS, from coronary native or graft vessels in patients suffering from MI, and from pulmonary arteries in patients suffering from PE, or from other peripheral arterial and venous vessels in which a clot is causing an occlusion. The designs can also resolve the challenges of aspirating clot material utilizing an expandable tip capable of the suction energy/work required to deform these clots while having the structure to resist collapse during the procedure. 
     In some examples, a catheter can have a proximal elongate shaft with a proximal end, a distal end, a large internal bore, and a longitudinal axis extending therethrough. The elongate shaft can have a shaft braid configured around a low friction inner liner. The braids can serve as the backbone and support for the catheter shaft. The interlacing weave of the braid can be any number of materials or patterns known in the art and can have a varied density and composition along the length of the shaft. 
     In many examples, the catheter can have an expandable distal tip section extending from the distal end of the elongate shaft. The tip section can have a collapsed delivery configuration and an expanded deployed configuration. The tip can be radially collapsed for delivery through an outer guide sheath and can assume a funnel shape profile in the expanded configuration. The tip can have an outer polymeric membrane or jacket supported by an underlying braid. The distal end of the tip section can have a reinforcing ring on the braid and define a mouth that has a beveled profile forming an angle not perpendicular to the longitudinal axis of the catheter. The ends of the braid can be cut, or the wires can follow one spiral direction distally and then invert proximally back on themselves at the distal end to form the other spiral direction. The braid of the expandable distal tip section can accommodate radial expansion, and therefore can have variable PPI and cell angles to balance allowable expansion of the funnel tip with radial force capabilities. 
     The tip and shaft braids and can be monolithically formed or joined separately. In some examples, the tip and shaft braids can be made from the same material, or they can be different materials. In one example, the distal wires of the tip braid can be of Nitinol or another shape memory superelastic alloy composition allowing them to be heat set to the desired expanded diameter of the tip during manufacturing. 
     In other examples, the tip and shaft braids can have wires of differing thickness so that there is a hinging effect between the distal tip and the shaft while navigating the catheter through bends in the anatomy. A hinge can allow the distal tip section to be kept relatively short to reduce the tendency to elongate or shorten under tensile or compressive loading. 
     Longitudinally, the elastically expanded shape of the tip can be a substantially funnel shape flared radially from the shaft, so that in the transverse plane the tip section has a circular cross section in both the collapsed delivery configuration and the expanded deployed configuration. In one case, the circular profile of the tip section in the collapsed delivery configuration can define a center which is coincident with the longitudinal axis of the elongate body. Alternately, the circular profile of the tip section in the expanded deployed configuration can result in a center that is radially offset from the longitudinal axis. 
     The reinforcing ring can be disposed around the perimeter of the distal mouth of the expandable distal tip section. At least a portion of the ring can define a mouth plane forming an acute angle with respect to the longitudinal axis of the catheter when the distal tip section is in the collapsed delivery configuration. This angle can be similar or different when the tip section is deployed to the expanded configuration. In one example, the angle can be in a range between approximately 30 degrees and approximately 60 degrees. In another more specific instance, the angle can be approximately 45 degrees, 
     The reinforcing ring can be polymeric, metallic, or other suitable materials capable of adding stiffness and shape to the distal end of the tip section. In a preferred example, the reinforcing ring can be a shape memory alloy such as Nitinol which can be heat set to a desired expanded inner diameter larger than a collapsed inner diameter when the distal tip section is in the expanded deployed configuration. In another example, the reinforcing ring can overmolded to the braid. In a further alternative, the ring can be PVC or other appropriate density polymer. 
     During manufacturing, the reinforcing ring can be welded to the distal braid of the tip section. In other examples, brazing, friction welding, adhesives, or other means can be used to attach the reinforcing ring. 
     To facilitate consistent expansion and folding of the expandable tip section, the reinforcing ring can have a plurality of relief features in the circumferential profile. In some designs, the relief features can be machined into the ring, or the ring can be formed in a mold to have the features. The braid wires of the tip braid can be cut to follow the contours of the relief features at the distal end of the tip section. In another case, the braid wires can be wound around the perimeter and relief features of the reinforcing ring. 
     The features can be, for example, keyhole shapes having a parallel section and a rounded section extending proximally from the distal edge of the perimeter of the reinforcing ring. In another case, the relief features can be axial slots or other geometry extending proximally from the distal perimeter of the mouth formed by the reinforcing ring. The features can have portions which are parallel to the longitudinal axis or form an angle with respect to the axis. 
     The features can reduce the cross section profile of at least a portion of the tip section. The features can also be axially or longitudinally offset from the oblique mouth plane. This effective reduction in material due to the relief features encourages folding along specific planes around the circumference of the tip. The features can be spaced equally around the ring circumference such that the folding during collapse into an outer sheath is symmetric about the longitudinal axis. Alternatively, the features can be intermittently spaced so that folding is encouraged along certain planes advantageously. In addition, the relief features can form an angle with the axis in order to bias the collapse of the tip section in certain directions. 
     Other catheter designs of the present disclosure can have a proximal elongate shaft having proximal end, a distal end, and a tubular shaft braid defining a lumen and a longitudinal axis extending therethrough. The shaft can terminate distally at a radiopaque marker band. An expanding distal tip section can be disposed at the distal end of the elongate shaft and have a supporting tip braid and a reinforcing ring attached to the distal end of the tip braid. 
     The marker band can be a radiopaque material or can include a radiopaque coating or filler material. The material can be compatible with the materials of the shaft braid and tip braid so that the braid ends can be welded or otherwise attached to the marker band and the band serves as a joint between sections. In some examples, the proximal end of the supporting tip braid can be welded to the marker band. In another example, the distal end of the shaft braid can be welded to the marker band. In further examples, welding or adhesives are used to connect the shaft braid to the tip braid and the combined structure can be attached to the band. 
     The distal tip section can have a collapsed delivery configuration and an expanded deployed configuration. The reinforcing ring at the distal end of the tip section can have a plurality of relief features or cutouts spaced equally around the longitudinal axis. The cutouts can reduce the cross sectional profile around the perimeter of the reinforcing ring. At least a portion of the reinforcing ring can be planar to define a mouth plane which forms an acute angle with the axis when the tip section is in the collapsed delivery configuration, the expanded deployed configuration, or both. At least a portion of each of the relief features can be offset from the mouth plane so as to extend proximally from the mouth plane. 
     The profile of the distal tip section can be substantially symmetric with respect to the longitudinal axis when in the collapsed delivery configuration, but asymmetric or offset when in the expanded deployed configuration. A center of the expanded tip can be radially offset from a center of the catheter shaft. 
     Polymer membranes or jackets can be wrapped around the shaft braid and the tip braid. The jackets can be placed in an axial series and be selected from materials that are melt-miscible with each other so that adjacent layers help to hold together the underlying braid between them. Materials can also be chosen so that the stiffness of different sections of the catheter can be varied in a stepwise or continuous fashion. The cooperation between the braids and the polymer jackets can yield a catheter which has both a thin wall but is also highly kink resistant. 
     Some or all of the distal tip section can be covered or encapsulated within a distalmost tip jacket. The tip jacket can be of a very soft material so as to have the most atraumatic vessel crossing profile. For example, a low durometer Pebax can be used having a hardness is the range of approximately 42 Shore A to approximately 72 Shore A. Alternatively, a Neusoft layer can be reflowed to encapsulate the tip of 62 Shore A or even 42 Shore A. 
     The distalmost polymer tip jacket can be trimmed to follow the contours of the reinforcing rings around the mouth of the tip section of the catheter. The distal edge of the tip jacket can mirror that of the reinforcing ring including circumferential gaps to follow the outline of the relief features of the ring. In an alternate example, the tip jacket can be trimmed to a circular or ovular end of the beveled tip but be webbed over the cutouts of the relief features. A further design can have the tip jacket extending distally beyond the distal edge contours of the reinforcing ring as a soft lip overhanging the ring. 
     Other aspects of the present disclosure will become apparent upon reviewing the following detailed description in conjunction with the accompanying figures. Additional features or manufacturing and use steps can be included as would be appreciated and understood by a person of ordinary skill in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and further aspects of this invention are further discussed with reference to the following description in conjunction with the accompanying drawings, in which like numerals indicate like structural elements and features in various figures. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating principles of the invention. The figures depict one or more implementations of the inventive devices, by way of example only, not by way of limitation. It is expected that those of skill in the art can conceive of and combine elements from multiple figures to better suit the needs of the user. 
         FIG.  1    is a view of a distal portion of a clot retrieval catheter with an expandable tip according to aspects of the present invention; 
         FIG.  2    illustrates a side view of the catheter of  FIG.  1    according to aspects of the present invention; 
         FIG.  3    shows a close in view of the catheter tip section of  FIG.  2    in the collapsed delivery configuration according to aspects of the present invention; 
         FIG.  4    depicts an end on view of the catheter tip section of  FIG.  3    according to aspects of the present invention; 
         FIG.  5    shows a reinforcing ring of the catheter tip section according to aspects of the present invention; 
         FIG.  6    illustrates the catheter tip section of  FIG.  2    in the expanded deployed configuration according to aspects of the present invention; 
         FIG.  7    is an end on view of the tip section of  FIG.  6    according to aspects of the present invention; 
         FIG.  8    is a view of a catheter being advanced through a bend in the vasculature according to aspects of the present invention; 
         FIG.  9    illustrates a catheter deployed at a target site according to aspects of the present invention; 
         FIG.  10    is a view of another example of the distal portion of a clot retrieval catheter according to aspects of the present invention; 
         FIG.  11    depicts another example of the distal portion of a clot retrieval catheter according to aspects of the present invention; and 
         FIGS.  12   a - 12   c    shows ways in which the reinforcing ring and tip jacket can be oriented according to aspects of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Specific examples of the present invention are now described in detail with reference to the Figures. The designs herein can be for a clot retrieval catheter with a large internal bore and a distal tip section that can self-expand to a substantially funnel shape with a diameter larger than that of the guide or sheath through which it is coaxially delivered. The designs can have a proximal elongate body for the shaft of the catheter, and a distal tip with an expanding braided support structure and outer polymeric jacket to give the tip atraumatic properties. The tip section can have a reinforcing ring at the distal end which serves to add hoop strength and prevent the braid and jacket from collapsing under the suction of aspiration. The catheter&#39;s tip designs can also be sufficiently flexible to navigate highly tortuous areas of the anatomy while being able to recover its shape and maintain the inner diameter of the lumen when collapsed into a delivery configuration or displaced in a vessel. 
     Accessing the various vessels within the vascular, whether they are coronary, pulmonary, or cerebral, involves well-known procedural steps and the use of a number of conventional, commercially-available accessory products. These products, such as angiographic materials, mechanical thrombectomy devices and stentrievers, microcatheters, and guidewires are widely used in laboratory and medical procedures. When these products are employed in conjunction with the devices and methods of this invention in the description below, their function and exact constitution are not described in detail. Additionally, while the description is sometimes in the context of thrombectomy treatments in intercranial arteries, the disclosure may be adapted for other procedures and in other body passageways as well. 
     Turning to the figures,  FIG.  1    illustrates a clot retrieval catheter  100  of the designs disclosed herein. The catheter can have an elongate shaft  110  and a tip section  210  attached distally thereto. The tip section  210  can radially expand to provide better aspiration efficiency and a larger distal mouth  218  for ingesting an occlusive clot. The mouth  218  of the tip section can be provided with a slanted or beveled distal surface at an angle with the longitudinal axis  111 , which presents an oblique mouth with an even greater area for aspiration and clot ingestion. A reinforcing ring  211  can be incorporated at the distal end  214  of the tip section  210  to retain the braid  220  structure of the tip in an expanded funnel shape during aspiration and facilitate wrap down when withdrawn into an outer sheath. The catheter can have one or more radiopaque marker bands  116  to identify various transition points and terminal ends of the device during a procedure. 
     The braided sections of the shaft and the tip can be formed monolithically or in discrete sections. In many cases, four or more discrete braided sections of differing flexibility can be used. It can be appreciated that the different braided sections of the tip and shaft braids can have different geometries and weave patterns to achieve desired properties for that portion of catheter. Through choice of physical parameters and materials, different flexibility and stiffness characteristics can thus be given to different sections of the catheter  100  to meet clinical requirements. 
     The elongate shaft can have a backbone consisting of shaft braid sections and enclosed by an axial series of outer body jackets  160 . Similarly, the tip section  210  can have tip braid  220  surrounded by one or more polymeric tip jackets  180 . The jackets can be made of various medical grade polymers known in the art, such as PTFE, polyether block amide (Pebax®), or Nylon. 
     The braid  220  in the distal tip section  210  can have nitinol wires formed into the expanded free shape of the funnel profile when expanded. Nitinol braid wires like those of the tip braid can be used for the proximal braid  120  of the shaft  110  as well, but less expensive stainless steel wires can also be substituted to perform in these regions for stiffness and with less cost. 
     As used herein, “braided sections”, “braids”, and similar terms are used collectively to describe the support structure for the catheter shaft and tip. This type of catheter construction is commonly known in the art. The terms can refer to segments within a single monolithic braid that have different physical properties (PIC count, braid angle, etc.) and/or configurations and does not necessarily mean two distinct structures bonded together. Alternately, the terms can refer to a collective of distinct sections which are knitted together. 
     The marker band  116  can be positioned at or on the distal end of the shaft  110  and the proximal end of the tip section  210 . The marker band can be platinum, gold, and/or another metallic collar, or alternatively can be coated with a compound giving substantial radiopacity. The band can be kept relatively short in length, for example between 0.3-1.0 mm, in order to minimize the impact on shaft flexibility. The band  116  can be crimped in place or slid onto a mandrel and later adhered to the ends of braided sections. In some examples, the band  116  can also function as a joint between the braids of the tip section  210  and the shaft  110 , allowing for the braided sections of each to be quickly manufactured separately to any of a number of desired lengths and joined together at the band. If the catheter length is the typical 1350 mm of many designs, the tip section  210  can be approximately 100 mm in length, leaving a 1250 mm shaft  110  terminating at a proximal luer. The use of specific metallics such as platinum (which can be welded to both stainless steel and Nitinol) for the sleeve of the marker band  116  can replace the use of adhesives or other means and create a more robust joint. 
     The lumen of the catheter shaft can be sized so the catheter  100  is compatible with commonly-sized and readily available guide sheaths. A low friction inner liner can be disposed beneath the braid  120 , facilitating use of the lumen for the delivery of auxiliary devices, contrast injection, and direct distal aspiration to a clot face. Preferred liner materials can be fluoropolymers such as polytetrafluoroethylene (PTFE or TFE), ethylene-chlorofluoroethylene (ECTFE), fluorinated ethylene propylene (FEP), polyvinyl fluoride (PVF), or similar materials. Depending on the material chosen, the liner can also be stretched to alter the directionality of the liner material (e.g., if the liner material has fibers, an imposed stretch can change a nominally isotropic sleeve into a more anisotropic, longitudinally-oriented composition) to reduce the wall thickness as required. 
     The body jackets  160  and tip jackets  180  can be butted together to form a continuous and smooth outer surface for the catheter shaft. The polymeric jackets can be reflowed or laminated in place along the length of the elongate shaft  110  and tip section  210 . The applied heat can allow the outer polymer to fill the interstitial sites between the braids. This flow can also help to fix the jackets axially so they cannot slide distally. 
     These outer jackets can have varying durometer hardness to create, in conjunction with the braided structures, a proximal portion of the catheter with more column stiffness (by durometer hardness, flexure modulus, etc.) and transition into a distal portion with more lateral flexibility. In some examples, the body jackets can have a hardness in the range between approximately 25 to approximately 72 Shore D. The tip jacket  180  or jackets can have a distalmost jacket with the least stiffness for the most atraumatic vessel crossing profile. 
       FIG.  2    shows a profile view of the distal portion of the catheter  100  of  FIG.  1   . As disclosed, a distal marker band  116  approximately 0.8 mm in length can be included just proximal of the polymeric tip jacket  180  to give radiopacity near the distal end  214  of the tip section  210 . The marker band  116  can be platinum or another suitable noble metal and can be crimped over, under, or between the assembly of the braids  120 ,  220  of the shaft  110  and tip section  210 . The band  116  can also be situated at or near the distal end  114  of the shaft and at least 5 mm and up to 10 mm or more from the distal end  214  of the tip section  210 . Alternatively, or in addition, the reinforcing ring  211  of the distal tip section  210  can also be constructed of radiopaque material or be coated or embedded with such material to illuminate the final distal terminus of the device when interacting with a clot. 
     The catheter shaft  110  can have one or more axial spines (not shown) extending with the shaft braid  120  along the longitudinal axis  111 . The spine or spines  117  can counteract tensile elongation and contribute to the push characteristics of the shaft. This can be especially beneficial for when a large stiff clot becomes lodged at the distal end of the catheter and subjects the spine  110  to large tensile forces as the catheter is retracted into a larger outer sheath for removal from the vessel. The spine can be positioned beneath the braid, threaded between weaves of the braid, located on the outer diameter of the braid, or some combination of these. The spine can be composed of metallics, a polymeric, or composite strands such as Kevlar. In other examples, the spine can be a thread or other structure capable of supporting tensile loads but not compressive loads. In some preferred examples a liquid crystal polymer (LCP), such as Technora, can be utilized which is easy to process and offers high tensile strength without sacrificing any lateral flexibility. 
     When the catheter  100  is transiting to the target site or being retracted back into an access catheter/outer sheath in the collapsed delivery configuration shown, the tip section  210  can be wrapped radially down to compress the braid  220  and fold at the location of the relief features  224  around the circumference of the reinforcing ring  211 . In the access catheter, the tip section  210  can have a collapsed inner diameter  215  that is the same or nearly the same as the inner diameter  115  of the elongate shaft  110 . 
     As shown in  FIG.  1    and  FIG.  2   , the distal end  214  of the tip section  210  can have a beveled surface inclined at an angle  217  with respect to the longitudinal axis  111 . A beveled surface can increase aspiration efficiency and present a larger mouth area for improved clot ingestion, which can result in improved reperfusion and recanalization outcomes when compared to catheters with non-beveled tips. As such, a beveled tip can potentially reduce the number of passes required for a successful procedure or reduce the added complication involved with the introduction of mechanical clot retrieval devices. 
     When the tip section  210  is in the collapsed state, the beveled distal surface of the annular mouth  218  of the tip section  210  can reside on an inclined plane  213  at an acute angle  217  with the longitudinal axis  111 . The plane  213  can reside at an angle of at least approximately 10 degrees up to at least 60 degrees with respect to the axis. For a more atraumatic profile during navigation, a preferable angle  217  can be in a range from approximately 30 degrees to 60 degrees, or, more specifically, can be approximately 45 degrees. 
     To be compatible with whichever widely adopted outer guide and/or sheath is chosen, the inner diameter  115  of the catheter shaft  110  and the collapsed inner diameter  215  of the expandable tip section  210  can be sized and scaled appropriately. The cross sections of the tip section and shaft can be largely symmetric when collapsed, so that for example a 5 Fr catheter targeting vessels approximately 2.0 mm in diameter can have shaft/tip inner diameters  115 ,  215  of approximately 0.054 inches. Similarly, a 6 Fr catheter targeting vessels approximately 2.3-3.4 mm in diameter can have shaft/tip inner diameters  115 ,  215  of approximately 0.068-0.074 inches. A larger nominally 8 Fr catheter for less remote clots can have shaft/tip inner diameters  115 ,  215  of approximately 0.082-0.095 inches. In most situations, the actual design upper bounds of the tip diameter  215  when collapsed is limited by friction and other delivery forces when traversing within an outer guide or sheath. 
     The reinforcing ring can have a variety of shapes determining the profile of the distal end  214  of the tip section  210 , as seen in a closer view of the collapsed tip illustrated in  FIG.  3   . The ring  211  can be affixed around the distal edge of the tip braids  220  through welding or brazing. In one example, the reinforcing ring  211  can be a nitinol member which tightly grips the underlying braid and is set to a free shape which elastically stretches the distal portion of the tip section radially when sprung to a larger diameter in the deployed condition outside of a guide or sheath. Alternately, the ring  211  can be polymeric and overmolded, injection molded, or spray or dip coated onto the braided layer using masking. 
     The length and contour of the tip section  210  as tapered in a substantially funnel shape from the distal end  214  when expanded can be tailored through the design of the pattern of the tip braid  220  and reinforcing ring  211 . As mentioned, the wires of the braid  220 , in addition to or instead of the ring element, can have shape memory characteristics and heat set to the designed elastic free shape desired. For example, a shorter funnel section can offer the benefits of good hoop stiffness and flexibility through having a shorter lever distance to hinge off the elongate shaft  110 . Additionally, a shorter funnel can also be tailored to minimize stretch and deformation in the more distal of the outer polymer tip jackets  180 . Alternatively, a longer funnel with a shallower taper can better interact with and more gradually compress a clot over the length of the tip to reduce the risk of lodging. 
     The reinforcing ring  211  can be formed as a single piece of uniform thickness or can be varied in thickness at particular sections. In  FIG.  3   , the ring  211  can have a slightly greater thickness  221  to stiffen the web or ligaments between the relief features  224 , as these sections make up the majority of the mouth perimeter and can provide the greatest radial force to resist aspiration forces. The ring  211  can transition to a lesser thickness  222  in the region of the relief features  224  to further bias folding and collapse of the tip along these planes. The tip jacket  180  can also be trimmed to follow the contours of the reinforcing ring  211  (including trimmed proximally around the relief features  224 ) so as not to add further stiffness in these regions while maintaining symmetry in folding. 
     The relief features  224  can be a keyhole-shaped protrusions extending proximally from the distal perimeter of the reinforcing ring  211  at the catheter mouth  218 . A keyhole shape can have two parallel sections  225  running from the beveled annular portion of the ring  211  and terminating in a rounded section  226  acting as a stress reducer and articulating enabler for the ring structure. The keyhole relief features  224  allow the ring “open” and “close” by hinging about the rounded section  226 , enabling the distal tip  210  expand and collapse repeatedly without failure. The interrupting nature of the relief features  224  around the mouth  218  means they also function as flanges or keys during and post-manufacturing to aid in locating and securing the reinforcing ring  211  to the underlying braid  220 . 
       FIG.  4    depicts an end on view of the distal tip section  210  in the collapsed delivery configuration. When constrained within an outer sheath, the collapsed inner diameter  215  of the tip section can be approximately equal to the inner diameter  115  of the shaft  110 . Depending on the final design profile of the reinforcing ring  211 , the tip section and shaft can be concentric about a common center  117  when the tip is collapsed, or they can be offset. The annular mouth  218  can be an ellipse residing on the beveled plane inclined from the longitudinal axis  111 . 
     Four relief features  224  spaced 90 degrees apart, as seen in the perspective view of the reinforcing ring  211  in  FIG.  5   , help the tip section  210  to wrap down evenly and symmetrically while maintaining the inner diameter of the mouth  218  for use with ancillary devices. It should be noted that a larger or smaller number of relief features can be anticipated. The features can be spaced evenly around the longitudinal axis to promote symmetric folding of the tip section. For example, six relief features can be employed spaced 30 degrees apart. Alternatively, in some other examples, the reinforcing ring  211  can incorporate an odd number or relief features, or the features can be spaced in a non-symmetric fashion around the mouth so as to bias folding in certain directions of planes. 
     The keyhole shaped relief features  224  of this example of the reinforcing ring  211  can each have two parallel sections  225  joined proximally by a rounded section  226 . Each relief feature can thus serve as an aperture allowing radial expansion of the tip section. As illustrated in  FIG.  6   , the mouth  218  of the tip section  210  can expand from a collapsed diameter  215  to a larger inner diameter  230  in the expanded deployed configuration. The beveled distal end can define an expanded mouth plane  228  inclined at an acute angle  219  with respect to the longitudinal axis  111 . The beveled profile allows for a larger inlet area for ease of ingesting firm clots and allows the clot to be compressed more gradually over a greater length of the tip, improving the chances of the clot can be completely ingested and aspirated through the shaft of the catheter. 
     One or both of the reinforcing ring  211  and the wires of the tip braid  220  can be Nitinol or another shape memory superelastic alloy so that the solid-state phase transformations can be designed to dictate the constrained delivery and unconstrained deployed diameters of the tip. The tip braid  220  can be trimmed to follow the contours of the reinforcing ring  211  and the ring can be welded or brazed over the ends of braid wires such that the tip section is pulled open into a funnel shape when allowed to expand. The reinforcing ring  211  can be heat set to a free shape with a larger expanded inner diameter  230  when the catheter  100  is deployed from the outer sheath. When collapsed, the reinforcing ring  211  and tip braid  220  can have an inner diameter approximate that of the catheter bore when constrained. Alternately, the wires of the braid can also be drawn filled tubing (DFT) shape memory alloy with a platinum core such that the braid is visible under fluoroscopy. 
     A further benefit of using a superelastic material for the braid wires and using the reinforcing ring as the primary structural support element for the tip section  210  is that the catheter walls can be relatively thinner without sacrificing performance characteristics such as flexibility or crush strength, adding robustness to tortuous bends for the tip section  210 . The thinner walls allow a larger effective bore size for aspiration. 
     Radiopaque marker bands can be included at different axial points along the length of the catheter  100  for visibility under fluoroscopy during a procedure. In the example illustrated, a marker band  116  can illuminate the location of the distal end  114  of the shaft  110  to give an attending physician an indication of where the expandable capacity of the catheter begins. The band shown can be platinum strip or other noble metal with a relatively short length of between approximately 0.025-0.030 inches and a thin wall thickness (approximately 0.0005 inches) to minimize the impact on flexibility and the outer diameter of the catheter. 
     As  FIG.  6    and  FIG.  7    show, when the tip section  210  is expanded the central axis and a large portion of the tip can be offset from the nominal longitudinal axis  111  of the shaft  110 . The center  232  of the tip section can thus migrate radially away from being coincident with the shaft center  117  to become more asymmetric as the tip expands. Having an offset shape, and an oblique distal mouth  218 , can increase lateral flexibility so the tip section  210  can better track and deflect of vessel walls when being advanced to a target site.  FIG.  8    shows the beveled shape of the tip section  210  being able to deflect away from a tight bend when tracking in the vasculature  10 , with the proximally extending cutouts of the relief features  224  allowing the tip section to respond and flex in the presence of localized forces. In many situations, when at a target site the catheter can also be manipulated and torqued so that the beveled mouth  218  of the tip section  210  is in-plane with the clot face, providing an increased access area for better clot management at the interface. 
     The expandable tip section  210  can be designed to be advanced through the vasculature in the expanded state. In these examples, the expandable tip can have a maximum inner diameter in the expanded state approximately equal to the diameter of a target vessel just proximal of the target clot. In most examples, the expanded funnel tip can be sized to have a larger inner diameter than the inner diameter of an outer sheath and/or guide through which it is delivered. 
     During delivery, the collapsed inner diameter  215  of the tip section can be approximately the same as the nominal diameter  115  of the catheter shaft section. When expanded, the expanded inner diameter  230  of the tip section  210  can be scaled linearly with the nominal diameter  115  of for the vessels to be accessed. For example, a catheter with an inner diameter of approximately 0.070 inches in the shaft can have a tip section  210  with a maximum inner diameter  230  of approximately 0.090 inches in the expanded deployed configuration. Similarly, catheters with shafts in other common sizes, such as 5 Fr up to 9 Fr, can also be envisioned with flared tip diameters  230  which scale accordingly, for an overall range of approximately 0.075-0.200 inches. 
     When using a catheter  100  of the present disclosure to clear an occlusion from a body vessel, the catheter with the tip collapsed can be advanced through an outer catheter or sheath  30  to a location proximal of a vessel occlusion, as depicted in  FIG.  9   . The sheath  30  is typically placed as close to the occlusive clot as practical, but the location can depend on the destination vessel size and the relative tortuosity of the vasculature needed to reach it. For example, in the case of a middle cerebral artery occlusion, the outer catheter might be placed in the internal carotid artery proximal of the carotid siphon. If for example the target occlusion is in an M1 vessel, a typical guide or outer sheath will need to be maintained in a position well proximal of these vessel diameters and the aspiration catheter  100  advanced independently. 
     As illustrated, the guide sheath  30  can be parked well upstream of the occlusive clot, and the catheter  100  advanced from the distal end  32  of the guide sheath to deploy to the expanded state. If pure aspiration proves insufficient to dislodge a clot, a microcatheter  50  can be used to deploy a stentriever or other devices known in the art. The combined stentriever and efficient aspiration through the enlarged bevelled tip section can act together to increase the likelihood of first pass success in removing a clot  40 . 
     Once the clot has been dislodged from the vessel walls it can be progressively compressed through the funnel-shape of the expandable tip of the catheter and through the lumen into a cannister or syringe. As the reinforcing ring provides support against collapse of the tip, a more flexible braid can be used to allow for additional localized radial expansion. Instead of the stentriever being withdrawn through the stationary lumen, the catheter  100  can also direct the aspiration vacuum to the clot face while being withdrawn in tandem with the stentriever so that a composite clot (comprised of friable regions and fibrin rich regions) is held together to prevent embolization. For a particularly firm clot, this additional expansion of the tip section can protect and shelter a lodged clot while the catheter itself is withdrawn. 
     Contrast can be injected to determine the extent to which the vessel is patent. Clot retrieval devices may be rinsed in saline and gently cleaned before being reloaded into the microcatheter for additional passes, if required. 
     Another alternative design for the distal tip section  210  of the catheter according to the present disclosure is illustrated in  FIG.  10   . The beveled mouth  218  is determined by the perimeter of a reinforcing ring  211  having two relief features  224  spaced 180 degrees apart having exaggerated rounded sections  226 . The relief features  224  can extend proximally from the mouth  218  such that at least a portion is offset from the angled plane of the bevel. A lesser number of relief features can increase the overall stiffness and available hoop strength of the reinforcing ring  211 . This allows the ring to be used with a tip braid  220  of less density, offering a greater capacity for expansion. 
     Further, a configuration having two relief features  211  diametrically opposed as shown defines a bending plane for the tip section  210  passing through the two features. Alternately, additional relief features can be incorporated, including other geometric shapes that define additional planes. 
     The wires of the braid  220  of the tip section  210  can be cut and trimmed to the desired contours of the reinforcing ring  211  around the distal mouth  218 . In this way the braid can resemble the end of a stent with free ends for greater flexibility and ease of manufacture. Alternatively, the wires of the underlying braid can be wound in one direction towards the distal end  214  of the tip section. Upon reaching a distal terminus, the wires can be inverted and wound proximally in the opposite direction. As a result, the inverted ends are also more atraumatic for additional manufacturing cost. In this example, the inverted ends of the braid can also be wrapped around the reinforcing ring  211  to improve the strength of the joint. 
       FIG.  11    illustrates a design for the distal tip section  210  of the catheter where the reinforcing ring  211  has relief features  224  in the form of a series of axial slots  227  symmetric about the longitudinal axis  111 . The axial slots  227  can be wide arcing loops extending proximally toward the marker band  116  from the beveled mouth plane  213  and enclose the tip braid  220  therein. Although there are many cases where the axial slots  227  or other relief features can substantially parallel the longitudinal axis  111 , in other examples they can have parallel sections or a slot centerline which is angled or in a helix with respect to the axis. The use of a slot for the relief features can offer a more simplified manufacturing process compared to keyholes or other irregular geometric options. 
     The distalmost tip jacket  180  can be trimmed to follow the contours of the reinforcing ring  211  and relief features or can extend a longitudinal distance distally to overhang beyond the distal end of the ring. In the example shown in  FIG.  11   , the tip jacket extends beyond the perimeter of the reinforcing ring  211  in the regions of the axial slots  227  to yield a planar surface for the bevelled mouth  218  at the distal end  214  of the tip section  210 . In some examples, the longitudinal distance of the overhang can be in a range from approximately 0.1 mm to approximately 1.0 mm. In a more specific example, this longitudinal distance can be in a range between 0.5 mm to approximately 0.8 mm. 
     The tip jacket  180  can also be the softest of the jackets used on the catheter and can cover approximately the distal 90 mm of the length. The additional integrity provided by the reinforcing ring  211  allows increasingly soft jacket materials to be implemented. Generally, a hardness in a range between approximately 42 Shore A to approximately 72 Shore A can be preferred. In one more specific example, a Neusoft jacket with a hardness of approximately 62 Shore A can be reflowed to form the tip jacket  180 . In another case, an even softer Neusoft layer of approximately 42 Shore A can be used. 
     Cross sections demonstrating various examples of the layered layout of the reinforcing ring  211 , tip jacket  180 , and tip braids  220  of the distal tip section  210  are shown in  FIGS.  12   a - c   . The jacket  180  can be applied and adhered to the braid and ring through dip coating, reflow, lamination, or other suitable method. In the example shown in  FIG.  12   a   , the reinforcing ring  211  structure runs radially outside and over of the braid  220 , which is encapsulated by the tip jacket  180 . This layout enables the reinforcing ring to protect the distal jacket from abrasion or tearing, especially for instances when a softer, more fragile jacket is utilized. The edges of the reinforcing ring can have a radii or chamfer to protect the traversed vascular beds. 
     The alterative shown in  FIG.  12   b    can be used for when a slightly harder, more durable material is chosen for the jacket. The jacket-encased braid  220  can be positioned radially outboard and adhered to the exterior surface of the reinforcing ring  211 . In this configuration, the reinforcing ring is used to “push” the braid and jacket material outward as the tip section  210  is expanded. Similarly, the reinforcing ring will “pull” the braid and jacket material inward as the tip section is collapsed into an outer sheath. 
     In a further example, an arrangement where the braid  220  is sandwiched by the reinforcing ring  211  and the outer tip jacket  180  completely encapsulates both the braid wires and reinforcing ring is portrayed in  FIG.  12   c   . To form this construction, a thin inner jacket layer can be disposed on a flared mandrel and the mandrel loaded proximally into the distal end of the braid/reinforcing ring combination to radially expand the tip section. A thin elastic outer polymer layer of the tip jacket extrusion can be threaded or stretched over the flared mandrel and pushed over the flared section to expand the undersized material of the extrusion. The combined inner and outer layers of the tip jacket  180  can then be reflowed in place and the flared mandrel removed from the catheter assembly. 
     With a sandwiched braid and the jacket material encasing all of the underlying assembly, the configuration in  FIG.  12   c    can offer the most uniform “push” and “pull” forces acting on the tip section. Additionally, a fully-homogenous jacket edge is formed at the distal end  214  of the tip section  210 . 
     The invention is not necessarily limited to the examples described, which can be varied in construction and detail. The terms “distal” and “proximal” are used throughout the preceding description and are meant to refer to a positions and directions relative to a treating physician. As such, “distal” or distally” refer to a position distant to or a direction away from the physician. Similarly, “proximal” or “proximally” refer to a position near or a direction towards the physician. Furthermore, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. 
     As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. More specifically, “about” or “approximately” may refer to the range of values ±20% of the recited value, e.g., “about 90%” may refer to the range of values from 71% to 99%. 
     In describing example embodiments, terminology has been resorted to for the sake of clarity. As a result, not all possible combinations have been listed, and such variants are often apparent to those of skill in the art and are intended to be within the scope of the claims which follow. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents that operate in a similar manner to accomplish a similar purpose without departing from the scope and spirit of the invention. It is also to be understood that the mention of one or more steps of a method does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, some steps of a method can be performed in a different order than those described herein without departing from the scope of the disclosed technology.