Patent Publication Number: US-2012035647-A1

Title: Body lumen filters with large surface area anchors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Patent Application claims the benefit of and priority to U.S. Provisional Patent Application having Ser. No. 61/138,406, filed on Dec. 17, 2008, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates generally to medical devices and to body lumen filters in particular, such as body lumen filters with large surface area anchors and methods for filtering a body lumen. 
     2. Background and Relevant Art 
     Surgical procedures, including both invasive as well as minimally-invasive procedures, save countless lives each year. However, the instrument and processes used during such procedures sometimes create additional challenges. For example, many minimally invasive procedures are performed using highly specialized surgical tools that are introduced to the procedure site by way of the patient&#39;s vasculature. In particular, a catheter is introduced into the vasculature by way of a small incision. The catheter is then advanced into proximity with the procedure site. Thereafter, the surgical tools are advanced to the procedure site through the catheter. With the surgical tools thus at the procedure site, the surgical tools are then manipulated from the outside of the body. Accordingly, a surgical procedure can be performed with only a small incision. While such an approach can reduce the invasiveness of performing a surgical procedure, this approach can cause additional challenges. 
     In particular, as the catheter and/or surgical devices are advanced through the vasculature, their passage can cause arterial plaques, clots, or other debris commonly referred to as emboli to become dislodged and move with the blood as it circulates through the vasculature. As the emboli move downstream, they can encounter plaque or other obstructions within the bloodstream to form new clots or obstructions in the bloodstream. Such obstructions can result in partial or complete blockage of vessels supplying blood and oxygen to critical organs, such as the heart, lungs and brain. 
     Accordingly, filter devices have been developed to capture the emboli at safe locations. Vena cava filters are devices that are implanted in the inferior vena cava, providing a mechanical barrier to undesirable particulates. The filters may be used to filter peripheral venous blood clots and other particulates, which if remaining in the blood stream can migrate in the pulmonary artery or one of its branches and cause harm. 
     Therefore, a body lumen filter with large surface area anchors and methods for filtering a body lumen may be useful. 
     BRIEF SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     As described herein, a body lumen filter is provided that includes a body configured to move between a pre-deployed state and a deployed state. In the deployed state, the body has filtering openings defined therein. The body lumen filter also includes at least one anchor coupled to the body. The anchor may include a base and a bulbed portion. The bulbed portion may have a major cross-sectional dimension that is larger than a major cross-sectional dimension of the base. 
     In other examples, the body lumen filter can include a body configured to move between a pre-deployed state and a deployed state. The body lumen filter can also include a plurality of anchors secured to the body in which the anchors are configured to engage a body vessel at a deployment site with a force effective to maintain the body at the deployment site while having a surface area sufficient to prevent penetration of the anchors through an intima layer of the body vessel. 
     In other examples, a system is provided that can include a body lumen filter including a body having at least one anchor coupled to the body, the anchor including a base and a bulbed portion, the bulbed portion having cross-sectional dimensions that are larger than a largest cross-sectional dimension of the base. The system can also include a deployment device configured to move the body lumen filter between a pre-deployed state and a deployed state in which in the deployed state the body has filtering openings defined therein. 
     In another example, a method is described. The method may include longitudinally elongating the body of a body lumen filter such that the body lumen filter has a reduced dimension. The body lumen filter may be delivered to a desired deployment site within the body lumen. The body may be longitudinally reduced such that the body lumen filter has an enlarged dimension and the at least one anchor applies radial forces to an inner wall of the body lumen. 
     These and other features of the present invention will become more fully apparent from the following description and appended claims, or can be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe the manner in which the above-recited and other advantages and features of the invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical examples and are not therefore to be considered to be limiting of the invention&#39;s scope, examples will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1A  illustrates a body lumen filter in a deployed state according to one example; 
         FIG. 1B  illustrates the anchor of the body lumen filter of  FIG. 1A  in more detail; 
         FIG. 1C  illustrates a cross-sectional view of a bulbed portion of the anchor of  FIG. 1B ; 
         FIG. 2A  illustrates a body lumen filter in a pre-deployed state being introduced to a body lumen by a deployment device according to one example; 
         FIG. 2B  illustrates a body lumen filter in a deployed state and deployed in the body lumen according to one example; 
         FIG. 2C  illustrates a removal step of the body lumen feature according to one example; 
         FIG. 3  illustrates an exemplary anchor configuration according to one example; 
         FIG. 4  illustrates an exemplary anchor configuration according to one example; 
         FIG. 5  illustrates an exemplary anchor configuration according to one example; 
         FIG. 6  illustrates an exemplary anchor configuration according to one example; 
         FIG. 7  illustrates an exemplary anchor configuration according to one example; and 
         FIG. 8  illustrates a body lumen filter according to one example. 
     
    
    
     DETAILED DESCRIPTION 
     Devices and systems are provided herein for filtering a body lumen. By way of example only, a body lumen may include a blood vessel. Filtering may be performed by body lumen filters. For instance, embodiments of body lumen filters (e.g. including vena cava and/or other lumen filters), are described. Components of body lumen filters also are described. These components may include anchors and/or other components. In particular, the devices and systems provided herein include body lumen filters having a plurality of anchors with relatively large surface areas. The relatively large surface areas of the anchors can reduce the trauma associated with maintaining the body lumen filters at an intended location. 
     Some body lumen filters may be designed to capture and/or lyse particles of a particular size. Many body lumen filters may be generally tapered from a distal end toward a proximal end. For example, many body lumen filters may be generally cone shaped. Tapered body lumen filters may become misaligned within a body lumen. For instance, a tapered body lumen filter may be considered properly aligned within a body lumen or a longitudinal axis of the body lumen filter is generally aligned with a longitudinal axis of the body lumen at a deployment site. However, tapered body lumen filters, after delivery, may become improperly oriented such that the longitudinal axis of the implantable and filter is not aligned with a longitudinal axis of the body at the deployment site. 
     The body lumen filters and/or anchors described herein may be manufactured from any suitable material. For example, a body lumen filter and/or anchor may be, at least partially, formed from various materials including, but not limited to, nickel titanium and/or alloys thereof, stainless steel, cobalt chromium and/or alloys thereof, niobium tantalum and/or alloys thereof, other materials suitable for implantable stents, filters, or other implantable medical devices, and/or combinations thereof. Further, a body lumen filter and/or anchor may be, at least partially, formed of or include a radiopaque material and/or be coated with a radiopaque material to enhance visibility of the body lumen filter and/or the anchors. 
     These materials may include at least one beneficial agent incorporated into the material and/or coated over at least a portion of the material. The beneficial agents may be applied to body lumen filters that have been coated with a polymeric compound. Incorporation of the compound or drug into the polymeric coating of the body lumen filter can be carried out by dipping the polymer-coated body lumen filter into a solution containing the compound or drug for a sufficient period of time (such as, for example, five minutes) and then drying the coated body lumen filter, preferably by means of air drying for a sufficient period of time (such as, for example, 30 minutes). The polymer-coated body lumen filter containing the beneficial agent may then be delivered to a body vessel. 
     The pharmacologic agents that can be effective in preventing restenosis can be classified into the categories of anti-proliferative agents, anti-platelet agents, anti-inflammatory agents, anti-thrombotic agents, and thrombolytic agents. Anti-proliferative agents may include, for example, crystalline rapamycin. These classes can be further sub-divided. For example, anti-proliferative agents can be anti-mitotic. Anti-mitotic agents inhibit or affect cell division, whereby processes normally involved in cell division do not take place. One sub-class of anti-mitotic agents includes vinca alkaloids. Representative examples of vinca alkaloids include, but are not limited to, vincristine, paclitaxel, etoposide, nocodazole, indirubin, and anthracycline derivatives, such as, for example, daunorubicin, daunomycin, and plicamycin. Other sub-classes of anti-mitotic agents include anti-mitotic alkylating agents, such as, for example, tauromustine, bofumustine, and fotemustine, and anti-mitotic metabolites, such as, for example, methotrexate, fluorouracil, 5-bromodeoxyuridine, 6-azacytidine, and cytarabine. Anti-mitotic alkylating agents affect cell division by covalently modifying DNA, RNA, or proteins, thereby inhibiting DNA replication, RNA transcription, RNA translation, protein synthesis, or combinations of the foregoing. 
     Anti-platelet agents are therapeutic entities that act by (1) inhibiting adhesion of platelets to a surface, typically a thrombogenic surface, (2) inhibiting aggregation of platelets, (3) inhibiting activation of platelets, or (4) combinations of the foregoing. Activation of platelets is a process whereby platelets are converted from a quiescent, resting state to one in which platelets undergo a number of morphologic changes induced by contact with a thrombogenic surface. These changes include changes in the shape of the platelets, accompanied by the formation of pseudopods, binding to membrane receptors, and secretion of small molecules and proteins, such as, for example, ADP and platelet factor 4. Anti-platelet agents that act as inhibitors of adhesion of platelets include, but are not limited to, eptifibatide, tirofiban, RGD (Arg-Gly-Asp)-based peptides that inhibit binding to gpIIbIIIa or αvβ3, antibodies that block binding to gpIIaIIIb or αvβ3, anti-P-selectin antibodies, anti-E-selectin antibodies, compounds that block P-selectin or E-selectin binding to their respective ligands, saratin, and anti-von Willebrand factor antibodies. Agents that inhibit ADP-mediated platelet aggregation include, but are not limited to, disagregin and cilostazol. 
     Anti-inflammatory agents can also be used. Examples of these include, but are not limited to, prednisone, dexamethasone, hydrocortisone, estradiol, fluticasone, clobetasol, and non-steroidal anti-inflammatories, such as, for example, acetaminophen, ibuprofen, naproxen, and sulindac. Other examples of these agents include those that inhibit binding of cytokines or chemokines to the cognate receptors to inhibit pro-inflammatory signals transduced by the cytokines or the chemokines. Representative examples of these agents include, but are not limited to, anti-IL1, anti-IL2, anti-IL3, anti-IL4, anti-IL8, anti-IL15, anti-IL18, anti-GM-CSF, and anti-TNF antibodies. 
     Anti-thrombotic agents include chemical and biological entities that can intervene at any stage in the coagulation pathway. Examples of specific entities include, but are not limited to, small molecules that inhibit the activity of factor Xa. In addition, heparinoid-type agents that can inhibit both FXa and thrombin, either directly or indirectly, such as, for example, heparin, heparin sulfate, low molecular weight heparins, such as, for example, the compound having the trademark Clivarin®, and synthetic oligosaccharides, such as, for example, the compound having the trademark Arixtra®. Also included are direct thrombin inhibitors, such as, for example, melagatran, ximelagatran, argatroban, inogatran, and peptidomimetics of binding site of the Phe-Pro-Arg fibrinogen substrate for thrombin. Another class of anti-thrombotic agents that can be delivered is factor VII/VIIa inhibitors, such as, for example, anti-factor VII/VIIa antibodies, rNAPc2, and tissue factor pathway inhibitor (TFPI). 
     Thrombolytic agents, which may be defined as agents that help degrade thrombi (clots), can also be used as adjunctive agents, because the action of lysing a clot helps to disperse platelets trapped within the fibrin matrix of a thrombus. Representative examples of thrombolytic agents include, but are not limited to, urokinase or recombinant urokinase, pro-urokinase or recombinant pro-urokinase, tissue plasminogen activator or its recombinant form, and streptokinase. 
     One or more immunosuppressant agents may be used. Immunosuppressant agents may include, but are not limited to, IMURAN® azathioprine sodium, brequinar sodium, SPANIDIN® gusperimus trihydrochloride (also known as deoxyspergualin), mizoribine (also known as bredinin), CELLCEPT® mycophenolate mofetil, NEORAL® Cylosporin A (also marketed as different formulation of Cyclosporin A under the trademark SANDIMMUNE®), PROGRAF® tacrolimus (also known as FK-506), sirolimus and RAPAMUNE®, leflunomide (also known as HWA-486), glucocorticoids, such as prednisolone and its derivatives, antibody therapies such as orthoclone (OKT3) and Zenapax®, and antithymyocyte globulins, such as thymoglobulins. In addition, a crystalline rapamycin analog, A-94507, SDZ RAD (a.k.a. Everolimus), and/or other immunosuppressants. 
     Many body lumen filters may include hooks and/or other anchoring devices that pierce the inner wall of the body lumen to prevent filter migration. In some cases, piercing the inner wall of the body lumen may not be desirable. For instance, where the body lumen is already weakened. Body lumen filters that do not include hooks and/or other anchoring devices that pierce the inner wall of the body lumen may be subject to filter migration. 
     Thus, embodiments of the description relating to a body lumen filter with anchors having relatively large surface areas and methods for filtering a body lumen may be useful for facilitating filtering of a body lumen. 
       FIG. 1A  illustrates a body lumen filter  100  for filtering a body lumen, such as a blood vessel. As illustrated in  FIG. 1A , the body lumen filter  100  includes a body  105  having a plurality of expandable struts  110 . The expandable struts  110  are interconnected at junctions  115  in such a manner as to allow the body lumen filter  100  to be moved from a pre-deployed configuration to a deployed configuration. In at least one example, the pre-deployed configuration can be a relatively collapsed configuration. In such examples, the body lumen filter can be moved from the pre-deployed configuration to the deployed configuration by expanding at least a portion of the body lumen filter  100 . 
     In the illustrated example, the body lumen filter  100  can be expanded by providing relative separation between at least some of the expandable struts  110  and/or junctions  115 . The expandable struts  110  can be expanded in any suitable manner. In at least one example, the expandable struts  110  can be mechanically expanded by an expansion member, such as a balloon or other expansion member. In other examples the expandable struts  110  can be formed of a material that can resiliently move from a pre-deployed state to a deployed state due to the resilient nature of the material. 
     In  FIG. 1A  the body lumen filter  100  is shown in a deployed state. The body lumen filter  100  includes a first end  120  and a second end  130 . At least one anchor  140  is coupled to at least one of the first end  120  or the second end  130 . In the deployed state, filter openings  150  are defined between one or more of the expandable struts  110  and the junctions  115 . Further, in the example shown the first end  120  is narrower than the second end  130  such that the body lumen filter  100  has a generally tapered shape. 
     In other examples, the body lumen filter  100  may have different shapes, such as an hourglass shape, a generally parabolic shape, other shapes, or combinations thereof. Additionally, in the illustrated example the body  105  is formed of expandable struts  110 . In other examples, the body  105  can be formed of other components, such as helically wound wires, twisted wires, other elements or combinations thereof that form a plurality of filter openings  150 . 
     In the illustrated example, anchors  140  are secured to the expandable struts  110  on at least the second end  130 . The anchors  140  may have relatively high-surface areas as compared to a conventional anchor in which the anchor is achieved by bending an end of an expandable strut or other elongate portion of the body lumen filter away from a longitudinal axis of the body lumen filter  100 . The relatively high surface area of the anchor  140  can allow the anchor  140  to secure the body lumen filter  100  at a deployed position. The relatively high surface area may decrease the potential that the anchor  140  will pierce through the inner surface of the body lumen (i.e. an intima of a blood vessel) in which the body lumen filter is deployed. One exemplary configuration of an anchor  140  and an exemplary configuration of an associated body lumen filter will now be discussed in more detail. 
     As illustrated in  FIG. 1B , two of the expandable struts  110  meet at the junction  115 . The anchor  140  is shown extending away from a longitudinal axis of the body lumen filter and away from the junction  115 . In particular, the anchor  140  may include a base  160  secured to the junction  115 . Alternatively, the base  160  may be a portion of the body  105 . For instance, the anchor  140  may be connected to a strut  110 , a junction  115 , or other portions of the body  105 . The anchor  140  further includes a bulbed portion  170  that may be secured to the base  160 . 
     The bulbed portion  170  may include a first end  170 A and a second end  170 B. The anchor  140  can be described with reference to a primary axis  180  that can extend generally along a centerline of the anchor  140  and/or base  160 . The primary axis  180  can then extend along a portion of the bulbed portion  170  between the first end  170 A and the second end  170 B. The primary axis  180  is referenced for ease of discussion in describing a relative orientation and location of the bulbed portion  170  relative to the base  160 . In at least one example, the bulbed portion  170  can be offset relative to the primary axis  180  such that a majority of the bulbed portion  170  is oriented away from the primary axis  180 . 
     In the illustrated example, the bulbed portion  170  can have a three-dimensional shape in which at least part of the bulbed portion  170  has cross-sectional dimensions that are larger than a largest cross-sectional dimension of the base  160  or a portion of the body  105  to which the bulbed portion  170  may be connected (such as a strut  110 , a junction  115 , or other component). Cross-sectional dimensions can refer to the largest dimension of a cross-sectional portion when a cross section is taken normally relative to a center axis or line of the corresponding component. Such a center line can follow any path, including straight, curved, arced, other paths, or combinations thereof. In the illustrated example, the primary axis  180  can be co-linear with a center line of the base  160  such that cross sections of the base  160  are taken normally relative to the primary axis  180 . 
     In at least one example, the anchor  140  has as a three-dimensional elliptical shape, which can be referred to as an ovoid shape. Such a configuration may result in at least part of the bulbed portion  170  having a cross-sectional dimension that is larger than a corresponding dimension of the base  160  or a portion of the body  105  to which the bulbed portion  170  may be connected. 
     In the illustrated example, the second end  170 B of the bulbed portion  170  can be shaped such that the second end  170 B transitions smoothly to an intermediate portion  170 C. Further, the first end  170 A can be shaped to form a smooth transition between the base  160  and the central portion  170 C. In other examples, the transition can be step-wise, irregular, any other type of transition, or combinations of the same. Further, the first end  170 A and/or second end  170 B may be shaped similarly to the central portion  170 C such that there is generally no transition. The central portion  170 C in turn can have a generally smooth cross-sectional profile or can have an irregular cross-sectional shape as desired. 
       FIG. 1C  illustrates a cross-sectional view of the central portion  170 C of one exemplary bulbed portion  170  in more detail taken along section  1 C- 1 C in  FIG. 1B . In the illustrated example, the central portion  170 C can have a generally elliptical shape. Other cross-sectional shapes can include round or rounded cross-sectional shapes, sharply transitioned areas, as well as any other shapes or combinations thereof. Further, it will be appreciated that the central bulbed portion  170 C, as well as any other part of the bulbed portion  170  can have any shape desired to provide a relatively high-surface area for the anchor  140 . Various shape configurations can allow one or more anchor  140  to secure the body lumen filter  100  at a deployed location while reducing the penetration of the anchor  140  through the inner layer of the body lumen in which it is deployed. One exemplary process for deploying the body lumen filter  100  and the anchors  140  in particular will be described below. 
     Referring now to both  FIGS. 1B and 1C , the bulbed portion  170  can have a length of between about 1 mm and about 30 mm and a largest cross-sectional dimension of between about 0.10 mm and about 5 mm. The base  160  can have a largest cross-sectional dimension of between about 0.05 mm and about 1 mm. Accordingly, the anchor  140  can have a relatively large surface area. Further, an engagement surface area of the anchor  140 , which can be defined as the surface area of anchor  140  that may contact an inner surface of a body lumen. For instance, the engagement surface area may include one half of total surface area of the bulbed portion  170  can be between about 0.10 mm 2  and about 150 mm 2 . In another example, the engagement surface area may include the surface area of the hemisphere of the anchor  140  that may contact the inner surface of the body lumen. 
     The bulbed portion  170  may be shaped to conform to an inner surface of a body lumen. For example, the engaging surface may be generally rounded to approximate the curvature of the inner surface of the body lumen. 
     The body lumen filter  100  may be formed in any manner. In at least one example, the body  105  may be formed first, such as by etching, cutting, rolling, welding, or any combination of processes to form expandable struts  110 , junctions  115 , and/or bases  160 . Thereafter, the bulbed portions  170  may be formed on and/or attached to the bases  160 , junctions  115 , struts  110 , other portions of the base  105 , or combinations thereof. The bulbed portions  170  may be formed in any manner, such as through deposition processes, soldering, molding, other operations, or combinations thereof. The body lumen filter  100  can further include an engagement feature  190  coupled to a first end  120  thereof. 
       FIG. 2A  illustrates the body lumen filter  100  in a pre-deployed configuration and located within a deployment device  200 . The deployment device  200  is configured to deploy the filter  100  into a body lumen  205 . The body lumen  205  may include an inner layer  210  (i.e. intima layer), a medial layer  215 , an adventitial layer  220 , or combinations thereof. The deployment device  200  can include a housing  225  and/or a delivery mechanism  230  that may be actuated from a proximally located handle (not shown). A retrieval device  235  may be positioned within the delivery mechanism  230  and may similarly be actuated from the proximally located handle. The retrieval device  235  can include a retrieval feature  240  configured to engage the engagement feature  190  on the body lumen filter  100 . 
     As previously discussed, the body lumen filter  100  includes expandable struts  110  that are interconnected in such a manner as to allow the body lumen filter  100  to be moved from the pre-deployed state illustrated in  FIG. 2A  to a deployed state illustrated in  FIG. 2B . To deploy the body lumen filter  100 , the deployment device  200  is moved near a desired location within a body lumen  205  by using a catheter or other techniques. In one example, once the deployment device  200  is near the desired location, the delivery mechanism  230 , such as a plunger or other moveable member disposed within the housing  225 , may be advanced distally relative to the housing  225 , thereby driving the body lumen filter  100  from the housing  225  toward the desired location. In another example, the deployment device  200  may be advanced to the desired location, the delivery mechanism  230  may be advanced distally to abut the body lumen filter  100 , the housing  225  may be retracted to deploy the body lumen filter  100 , or combinations thereof. 
     As the body lumen filter  100  is deployed by the deployment device  200 , the body lumen filter  100  may move toward the deployed state. For instance, for a body lumen filter  100  formed from a shape memory material, moving the delivery mechanism  230  distally, moving the housing  225  proximally, or a combination of such movements, may release the body lumen filter  100  from within the housing  225  to transition to the deployed state of  FIG. 2B . 
     A resilient body lumen filter  100  is illustrated. Embodiments of the body lumen filter body  105  and/or anchor  140  can include a material made from any of a variety of known suitable materials, such as a shape memory material (SMM). For example, the SMM can be shaped in a manner that allows for restriction to induce a substantially reduced, generally linear orientation while within the housing  225 , but can automatically return to the memory shape of the body lumen filter  100  once extended from the deployment device  200 . SMMs have a shape memory effect in which they can be made to remember a particular shape. Once a shape has been remembered, the SMM can be bent out of shape or deformed and then returned to its original shape by unloading from strain and/or heating. Typically, SMMs can be shape memory alloys (SMA) comprised of metal alloys, or shape memory plastics (SMP) comprised of polymers. The materials can also be referred to as being superelastic. 
     Usually, an SMA can have any non-characteristic initial shape that can then be configured into a memory shape by heating the SMA and conforming the SMA into the desired memory shape. After the SMA is cooled, the desired memory shape can be retained. This allows for the SMA to be bent, straightened, compacted, and placed into various contortions by the application of requisite forces; however, after the forces are released, the SMA can be capable of returning to the memory shape. The main types of SMAs are as follows: copper-zinc-aluminium; copper-aluminium-nickel; nickel-titanium (NiTi) alloys known as nitinol; and cobalt-chromium-nickel alloys nickel-titanium platinum; nickel-titanium palladium or cobalt-chromium-nickel-molybdenum alloys known as elgiloy alloys. The temperatures at which the SMA changes its crystallographic structure are characteristic of the alloy, and can be tuned by varying the elemental ratios or by the conditions of manufacture. 
     For example, the material of a body lumen filter  100  can be of a NiTi alloy that forms superelastic nitinol. In the present case, nitinol materials can be trained to remember a certain shape, straightened in a shaft, catheter, or other tube, and then released from the catheter or tube to return to its trained shape. Also, additional materials can be added to the nitinol depending on the desired characteristic. The alloy can be utilized having linear elastic properties or non-linear elastic properties. 
     An SMP is a shape-shifting plastic that can be fashioned into a body lumen filter  100  in accordance with the present invention. Also, it can be beneficial to include at least one layer of an SMA and at least one layer of an SMP to form a multilayered body; 
     however, any appropriate combination of materials can be used to form a multilayered body lumen filter  100 . When an SMP encounters a temperature above the lowest melting point of the individual polymers, the blend makes a transition to a rubbery state. The elastic modulus can change more than two orders of magnitude across the transition temperature (Ttr). As such, an SMP can formed into a desired shape of a body lumen filter  100  by heating it above the Ttr, fixing the SMP into the new shape, and cooling the material below Ttr. The SMP can then be arranged into a temporary shape by force, and then resume the memory shape once the force has been applied. Examples of SMPs include, but are not limited to, biodegradable polymers, such as oligo(ε-caprolactone)diol, oligo(ρ-dioxanone)diol, and non-biodegradable polymers such as, polynorborene, polyisoprene, styrene butadiene, polyurethane-based materials, vinyl acetate-polyester-based compounds, and others yet to be determined. As such, any SMP can be used in accordance with the present invention. 
     A body lumen filter body  105  having at least one layer made of a SMM or suitable superelastic material and other suitable layers can be compressed or restrained in its delivery configuration within a delivery device using a sheath or similar restraint, and then deployed to its desired configuration at a deployment site by removal of the restraint as is known in the art. A body lumen filter body  105  made of a thermally-sensitive material can be deployed by exposure of the body lumen filter  100  to a sufficient temperature to facilitate expansion as is known in the art. It will be appreciated that the body lumen filter  100  can be mechanically expanded, such as by a balloon or other expanding device. 
     Continuing with the example illustrated in  FIG. 2B , as the body lumen filter  100  is moved toward the expanded state, the expandable struts  110  can be displaced to provide the filter openings  150 . The filter openings  150  can be sized to prevent particulates, such as at least one embolus, from passing through the body lumen filter  100  and/or to lyse particulates of greater than a desired size. While an embolus is trapped against body lumen filter  100 , blood may continue to flow over the embolus. The flow of blood over the embolus can dissolve the embolus through the body&#39;s lysing process. Additionally, the body lumen filter  100  may be coated with a beneficial agent that may facilitate lysing of the embolus. 
     The blood flow F exerts a fluid force on the body lumen filter  100  that would tend to move the body lumen filter  100  in the direction of the blood flow F. The anchors  140  may resist this force to generally maintain the body lumen filter  100  in or near an intended deployment location. In particular, frictional, compressive, and/or other forces between the body lumen filter  100  and the body lumen  205  may generally maintain the body lumen filter  100  at or near the intended deployment location, as will now be described in more detail below. 
     As the body lumen filter  100  is moved toward the deployed state, the anchors  140  may be moved into contact with the intima layer  210  of the body lumen  205 . In the deployed state, opposing anchors  140  can be separated by a distance that is slightly larger than the diameter of the body lumen  205  before the body lumen filter  100  is deployed. As a result, a tensile force can urge or press the bulbed portion  170  of one or more of the anchors  140  into contact with the intima layer  210 . 
     As the bulbed portions  170  are urged into contact with the intima layer  210 , the intima layer  210  can deform slightly to begin to conform to the shape of the bulbed portion  170 , which can result in compressive forces between the bulbed portion  170  and the body lumen  205 . 
     Further, this deformation can increase contact between the arcuate anchor  170  and the intima layer  210 . Frictional forces between two objects that are in contact typically depend on the normally applied force and the coefficient of friction between the two objects. The normally applied force depends on the area of contact and the pressure applied to that area. The coefficient of friction as well as the normal force necessary to maintain the body lumen filter  100  positioned in body lumen  205  may be relatively constant. Accordingly, increasing the surface area over which the arcuate anchor  170  applies the normal force can reduce the pressure the arcuate anchor  170  applies to the intima layer  210  of the body lumen  205 . Decreasing the pressure applied to the body lumen  205 , in turn, can reduce the possibility that the arcuate anchors  170  will pierce the intima layer  210 . 
     Accordingly, the relatively large surface area of the anchors  140  can help maintain the body lumen filter  100  at or near a desired deployment location in the body lumen  205 . Further, the relatively large surface area of the anchors  140  can reduce the likelihood that the anchors  140  will penetrate through the intima layer  210  and into the medial layer  215  and/or the adventitial layer  220 . Reducing penetration into the medial layer  215  may in turn reduce endothelial growth while and/or after the body lumen filter  100  is deployed. 
     At some point, it may be desirable to retrieve the body lumen filter  100 .  FIG. 2C  illustrates a step for retrieving the body lumen filter  100 . As illustrated in  FIG. 2C , retrieving the body lumen filter  100  can include positioning the deployment device  200  such that the housing  225  is positioned in proximity to the body lumen filter  100 . Thereafter, the retrieval device  235  can be moved into engagement with the engagement feature  190  on the body lumen filter  100 . In particular, the retrieval feature  240  can be advanced distally beyond the housing  225  and into engagement with engagement feature  190  or some other portion of the body lumen filter. Thereafter, the retrieval device  235  can be proximally relative to the housing  225  and/or the deployment mechanism  230  to thereby draw the body lumen filter  200  into the deployment device  200 . Once the body lumen filter  200  is located within the deployment device  200 , the deployment device  200  can be removed to thereby complete retrieval of the body lumen filter  100 . 
     Referring briefly again to  FIG. 1B , the first end  170 A and the second end  170 B can transition smoothly to the central portion  170 C. Further, the central portion  170 C can include a generally elliptical cross-sectional shape. Such a configuration can provide a bulbed portion  170  that can have arcuate or smooth edges. Referring again to  FIG. 2B , relatively smooth edges can distribute the compressive forces discussed above in a generally even manner across the bulbed portion  170  to thereby reduce the likelihood that the anchor  140  will pierce the intima layer  210 . Reducing the likelihood of penetration of the anchor  140  through the intima layer  210  can in turn reduce endothelial growth, which can reduce trauma associated with retrieval of the body lumen filter  100 , as described above. 
     Anchors can be provided having any number of shapes and configurations that have relatively high-surface area. These shapes can include shapes having rounded edges and/or non-rounded edges. Additional configurations of anchors with rounded configurations are shown in  FIGS. 3-7 . 
       FIG. 3  illustrates an anchor  143  having a bulbed portion  170 . As illustrated in FIG. 
       3 , the bulbed portion  170  is offset relative to the primary axis  180 . Further, the anchor  143  illustrated in  FIG. 3  has a second end  170 B that has a larger cross-sectional area than an intermediate portion  170 C. The intermediate portion  170 C in turn has a larger cross-sectional area than a first end  170 A of the bulbed portion  170 . 
     In another example illustrated in  FIG. 4 , an anchor  144  can include a bulbed portion  170  having a first end  170 A with a larger cross-sectional area than an intermediate portion  170 C. The intermediate portion  170 C can in turn have a larger cross-sectional area than a second end  170 B of the bulbed portion  170 . 
       FIG. 5  illustrates an anchor  145  that includes a bulbed portion  170  having second end  170 B that has a larger cross-sectional area than an intermediate portion  170 C. The intermediate portion  170 C in turn has a larger cross-sectional area than a first end  170 A of the bulbed portion  170 . Further, a primary axis  180  can pass more centrally through the bulbed portion  170 . 
     A similar configuration illustrated in  FIG. 6 , in which an anchor  146  includes a bulbed portion  170  having a primary axis  180  passing more centrally through the bulbed portion  170 . In the example illustrated in  FIG. 6 , a first end  170 A of the bulbed portion has a larger cross-sectional area than an intermediate portion  170 C. The intermediate portion  170 C can in turn have a larger cross-sectional area than a second end  170 B of the anchor  146 . 
     A further anchor  147  is illustrated in  FIG. 7 , in which an intermediate portion  170 C of the anchor  147  has a larger cross-sectional area than both a first end  170 A and a second end  170 B. In the illustrated example, a primary axis  180  passes substantially centrally through the bulbed portion  170 . 
     In the examples illustrated above, a primary axis has been described which is generally aligned or parallel to a base portion of the anchor. In other examples, the primary axis and the base portion can be oriented at an angle relative to each other. Such orientations can be combined with any of the configurations of the bulbed portions described above, as well as any other configuration of an anchor having large surface area. 
       FIG. 8  illustrates a body lumen filter  100 ′ according to one example. As illustrated in  FIG. 8 , the number of filter openings  150 , or cells, may increase toward the second end  130  of the body lumen filter  100 ′. A plurality of retrieval features  190 ′ may be positioned on various sides of the first end  120 . As illustrated, the retrieval features  190 ′ may be positioned on opposing sides. While two retrieval features  190 ′ are shown, the number of these retrieval features  190 ′ could also be three, four, or more. The retrieval features  190 ′ may incorporate radiopaque materials to facilitate retrieval of the filter  100 ′. In some embodiments, the retrieval features  190 ′ may be located anywhere along the filter  100 ′. 
     The present invention can be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.