Patent Application: US-201213403790-A

Abstract:
an absorbable vascular filter is disclosed for deployment within a vessel for temporary filtering of body fluids . a preferred embodiment is the placement of such absorbable vascular filter within the inferior vena cava to filter emboli for the prevention of pulmonary embolism for a limited duration in time . once protection from pe is complete , the filter is biodegraded according to a planned schedule determined by the absorption properties of the filter components . hence the temporary absorbable vascular filter obviates the long term complications of permanent ivc filters such as increased deep vein thrombosis , neighboring organ puncture from filter fracture and embolization while also circumventing the removal requirement of metal retrievable ivc filters .

Description:
embodiments of the present invention will now be described in detail with reference to the drawings and pictures , which are provided as illustrative examples so as to enable those skilled in the art to practice the invention . notably , the figures and examples below are not meant to limit the scope of the present invention to a single embodiment , but other embodiments are possible by way of interchange of some or all of the described or illustrated elements . wherever convenient , the same reference numbers will be used throughout the drawings to refer to same or like parts . where certain elements of these embodiments can be partially or fully implemented using known components , only those portions of such known components that are necessary for an understanding of the present invention will be described , and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention . in the present specification , an embodiment showing a singular component should not be considered limiting ; rather , the invention is intended to encompass other embodiments including a plurality of the same component , and vice - versa , unless explicitly stated otherwise herein . moreover , applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such . further , the present invention encompasses present and future known equivalents to the components referred to herein by way of illustration . referring to the embodiment depicted in fig1 a - e , an absorbable vascular filter 1 consists of an outer , circumferential element 2 for supporting a plurality of absorbable filter capture elements ( 30 - 32 , 40 - 41 ). the capture elements are purposely designed to be biologically absorbed and / or degraded preferably in a sequential manner to avoid simultaneous detachment of the entire filter causing an unexpected embolus . sequential degradation can be controlled by the choice of absorbable polymers that possess different absorption profiles , diameter , and / or expiration dates . additionally , absorptive linkages may be incorporated to serves as detachment points during absorption . the sequential bioabsorption / biodegradation is illustrated in fig1 b - e where decomposition begins with the proximal capture elements 30 , progressing to the middle section capture elements 31 , and finally full bioabsorption / biodegradation as depicted in fig1 e . such engineered , sequential bioabsorption / biodegradation of the capture elements can be achieved with numerous synthetic materials . the goal is to select the absorbable filter materials to match a desired filter indwell time . per the prior background section , a filter indwell time of 6 weeks would be suitable for an ivc filter to prevent pe following trauma or in conjunction with major surgeries . synthetic materials which can be used to form the capture elements include : polydioxanone ( pdo , pds )— colorless , crystalline , biodegradable synthetic polymer of multiple repeating ether - ester units . in suture form , pds ii ( ethicon , somerville , n . j .) size 4 / 0 and smaller maintains 60 %, 40 %, and 35 % of its tensile strength at 2 , 4 , and 6 weeks respectively . for pds ii size 3 / 0 and larger , it retains 80 %, 70 %, and 60 % of its tensile strength at 2 , 4 , and 6 weeks respectively . in addition to providing wound support for 6 weeks , pds ii suture is fully absorbed in 183 - 238 days via hydrolysis making it a strong candidate for ivc filter applications . basically absorption is minimal in the first 90 days and is essentially complete in 6 months . finally , pds has a low affinity for microorganisms and possesses minimal tissue reaction . polytrimethylene carbonate ( maxon )— similar to pds in absorption profile yet with slightly higher breaking strength . maxon ( covidien , mansfield , mass .) maintains 81 %, 59 %, and 30 % of its tensile strength at 2 , 4 , and 6 weeks respectively , and is fully hydrolyzed in 180 - 210 days . polyglactin 910 ( vicryl )— braided multifilament coated with a copolymer of lactide and glycolide ( polyglactin 370 ). in suture form , vicryl ( ethicon ) size 6 / 0 and larger maintains 75 %, 50 %, and 25 % of its tensile strength at 2 , 3 , and 4 weeks respectively and is fully absorbed in 56 - 70 days . polyglycolic acid ( dexon )— similar to polyglactin , made from polyglycolic acid and coated with polycaprolate . dexon has similar tensile strength and absorption profile as polyglactin . poliglecaprone 25 ( monocryl )— synthetic copolymer of glycolide and e - caprolactone . monocryl ( ethicon ) maintains 50 %- 70 % and 20 %- 40 % of its tensile strength at 1 and 2 weeks respectively and is fully absorbed in 91 - 119 days . polylacticoglycolic acid ( plga ) copolymer of monomers glycolic acid and lactic acid . different forms and properties of plga can be fabricated by controlling the ratio of lactide to glycolide for polymerization . like the other synthetic absorbable materials , plga degrades by hydrolysis with the absorption profile dependent on the monomer ratio ; the higher content of glycolide , the faster degradation . however , the 50 : 50 copolymer exhibits the fastest degradation at 2 months . since the polymer degrades in the body to produce lactic acid and glycolic acid , both being normal physiological substances , plga poses minimal systemic toxicity . poly l - lactic acid ( pla ) is also a polymer made from lactic acid yet with considerable longevity . in soft tissue approximation , pla remains intact for 28 weeks , and is fully absorbed within 52 weeks . as an example of engineering capture elements to sequentially degrade following the period of pe protection , the proximal capture elements 30 , 41 could be fabricated with pds ii size 4 / 0 ( 0 . 15 mm dia . ), while the middle capture elements 31 , 40 fabricated with size 2 / 0 ( 0 . 3 mm dia . ), and finally the distal capture elements 32 fabricated with size 2 ( 0 . 5 mm ) pds ii suture . as an alternative to assembling a plurality of capture elements , the vascular filter can be fabricated with absorbable or non - absorbable composite mesh . candidates for a mesh capture system include polypropylene such as c - qur ( atrium medical corp . hudson n . h . ), polypropylene encapsulated by polydioxanone as in proceed ( ethicon , somerville , n . j . ), polypropylene co - knitted with polyglycolic acid fibers as in bard sepramesh ip composite ( davol , inc ., warwick , r . i . ), polyethylene terephathalate as in parietiex composite ( covidien , mansfield , mass . ), and eptfe used in dualamesh ( w . gore & amp ; assoc . inc ., flagstaff , ariz .). regarding the circumferential element 2 in fig1 , 2 , and 3 that serves to support the capture elements of the absorbable vascular filter and maintain filter positioning within the vessel upon expansion from a catheter , either an absorbable material such as described above or non - absorbable material can be utilized . a non - absorbable material would essentially serve as a permanent stent , lasting well beyond the life of the absorbable capture elements . this may be an important option in cases where the vessel needs assistance in maintaining patency . both types of circumferential elements 2 may incorporate barbs 79 ( refer fig2 ) to maintain filter positioning upon deployment . plausible non - absorbing materials for constructing the circumferential element include : nitinol , elgiloy , phynox , 316 stainless steel , mp35n alloy , titanium alloy , platinum alloy , niobium alloys , cobalt alloys , and tantalum wire . fig2 a - 2 h illustrate another embodiment of the absorbable vascular filter wherein the absorbable capture elements 60 - 64 are mounted to a simple circumferential element 2 held against the vessel wall 70 with optional barbs 79 . here again the circumferential element 2 can be fabricated with absorbable or non - absorbable materials of the like described above . an enlarged cross - sectional view of the capture element assembly 65 is shown in fig2 b . notice that the sequential degradation of the capture elements is achieved by varying the diameter of the chosen absorbable material . for example , the inner capture element 60 could be pds ii 4 / 0 ( 0 . 15 mm dia .) resulting in the fastest absorption as illustrated in fig2 d at time t 1 , followed by capture element 61 degradation being pds ii 3 / 0 ( 0 . 20 mm dia .) at time t 2 in fig2 e , followed by capture element 62 degradation being pds ii 2 / 0 ( 0 . 30 mm dia .) at time t 3 in fig2 f , followed by capture element 63 degradation being pds ii 0 ( 0 . 35 mm dia .) at time t 4 in fig2 g , and finally the degradation of the last capture element 64 constructed of pds ii 1 ( 0 . 40 mm dia .) at time t 5 in fig2 h . although these dimensions represent a specific example , any diameters within approximately 0 . 1 mm to 0 . 7 mm would suffice . overall , a gradual progression of degradation is designed purposely following a prophylactic window of 6 weeks for trauma and major surgery applications . referring to the embodiment depicted in fig3 a and b , a vascular filter 1 consists of an outer , circumferential stent 2 for supporting a plurality of collapsible filter capture elements ( 60 - 64 ) and to maintain vessel patency . the capture elements are purposely designed to be collapsible for catheter - based installation and to avoid end organ damage . the supporting stent 2 is shown to be fabricated as an artificial vascular graft supported by undulating supporting structures 3 . this vascular filter , which can be comprised of absorbable or non - absorbable filter capture elements , possesses various advantages over all conventional vascular filters , including permanent , temporary , and optional ivc filters . most importantly , the vascular filter is fabricated with a stent that serves as a circumferential mount for the capture elements in addition to providing vessel patency , and avoids endothelialization characteristic of metal filters with barbed struts . hence the increased incidence of dvt observed with metal ivc filters due to inherent vessel damage from the metal struts is likely obviated . the circumferential stent element 2 in fig3 a serves to support the capture elements of the vascular filter , in addition to maintaining vessel patency and maintaining stationary filter positioning within the vessel upon expansion . numerous types of stents conventionally employed as thoracic endoprostheses can be utilized . such stents would include gore tag , medtronic talent and valiant systems , and cook zenith tx2 system . in particular , the gore tag is comprised of an artificial vascular graft fabricated with a fluoropolymer ( expanded polytetrafluoroethylenee ptfe and fluorinated ethylene propylene or fep ) combined with a nitinol supporting structure . alternatively , the stent component of the vascular filter can be fabricated with only the supporting structure ( without the artificial vascular graft ) utilizing nickel - titanium alloy ( nitinol ), cobalt - chromium - nickel alloy ( elgiloy ), cobalt - chromium - nickel - molybdenum alloy ( phynox ), 316 stainless steel , mp35n alloy , titanium alloy , platinum alloy , niobium alloys , cobalt alloys , and tantalum wire . a specific embodiment of an absorbable vascular filter with sequential degradation was constructed , tested , and evaluated with assorted polydioxanone sutures ( sizes 3 - 0 , 2 - 0 , 0 , and 1 ) and is shown in fig4 a . the filter featured higher density webbing than shown in fig2 b to catch smaller emboli . polydioxanone was the preferred candidate polymer based on tension retention and absorption properties proven in wound approximation applications . tygon long flex lifetime tubing ( saint - gobain performance plastics , akron , ohio ) with 25 . 4 mm id similar to the ivc was utilized for the vessel wall wherein polydioxanone was fabricated into the various filter patterns shown . fig4 a sports webbed capture elements that are purposely designed for sequential or phased absorption to avoid simultaneous detachment of the entire filter during absorption . here varying diameter strands of polydioxanone ( size 3 - 0 , 2 - 0 , 0 and 1 ) were utilized to vary the time to complete absorption , in addition to varying the expiration dates . since the absorbable polymers initially break at the stress points during absorption , the webbed filters were designed to disintegrate into 8 pieces at length d / 2 , and 8 pieces sized d / 4 , where d is the inside diameter of the vessel . the objective is piecemeal disintegration , phased or sequential , to minimize free floating exposure of the polymer filter capture elements in circulation . fig4 b is the same webbed design but with uniformly sized polydioxanone suture for comparison . fig4 c is a radial filter design similar to conventional metal ivc filters yet sports the varying diameter sutures for sequential absorption . finally , fig4 d is a radial design constructed exclusively with polydioxanone size 2 - 0 . the primary endpoint for evaluating the absorbable polymers for vascular filter application was load at break as a function of time . in addition to the absorbable filters pictured in fig4 , several test cells were fabricated with the various absorbable polymer candidates for weekly destructive tensile testing . polymer characterization was performed utilizing the admet expert 7601 tensile testing machine with mtestquattro software ( norwood , mass .) at weekly intervals to yield stress vs . strain graphs in addition to the primary endpoint of load at break , and several secondary endpoints : ( i ) maximum stress ( tensile strength ), ( ii ) maximum strain (% elongation at break ), ( iii ) energy at break , and ( iv ) young &# 39 ; s modulus of elasticity . the admet machine was operated with a crosshead speed of 3 cm / min and outfitted with a high resolution 100 lb load cell and 2kn pneumatic grippers . the candidate absorbable polymers ( representing capture elements ) sewn into the test cells were embedded in a closed circulation system engineered to mimic human cardio physiology . at weekly intervals , the system was shut down to extract sutures of each size and type to perform destructive tensile testing . as a control , identical absorbable sutures were submerged into a static buffer bath ( stabletemp digital utility bath , cole - parmer , vernon hill , ill .) held at 37 ° c . and also tested on a weekly basis . the hypothesis being that the increased thermodynamics of the circulation system accelerates both absorption rate and tensile strength loss of the capture elements . the closed circulation system was constructed with thin walled ¾ ″ pvc with od 26 . 7 mm that fit snug inside the flexible 25 . 4 mm id tygon tubing that simulated the ivc . the heart of the system was a harvard apparatus large animal pulsatile blood pump ( holliston , mass .) that simulated the ventricular action of the heart . the harvard apparatus blood pump was operated near continuously for 22 weeks ( 913k l pumped ) with minor preventative maintenance . the heart rate was adjusted to 60 bpm , stroke volume between 60 and 70 ml , systolic / diastolic duration ratio 35 %/ 65 %, and systolic blood pressure varied from 120 mmhg ( simulated conditions for an arterial filter to prevent cerebral and systemic embolism ) to 5 mmhg ( simulated conditions for an ivc filter to prevent pe ). real time measurements were available from the upstream and downstream sensor manifolds . the sensors upstream from the absorbable filters under test included digital temperature , flow rate ( l / min ), total flow ( l ), and pressure ( mmhg ). downstream instrumentation included real time measurement of % oxygen , total dissolved solids ( tds in ppt ), and ph . tds monitoring was included to evaluate the absorption by - products less than 20 microns in size , while the downstream 80 micron in - line filter would catch fragments of suture from the filters and test cells . the 4 candidate absorbable vascular filters introduced in fig4 were installed in series along the upstream tubing , whereas 5 test cells containing absorbable suture for weekly destructive testing were installed in series along the downstream section of the in - vitro cardio test system . a 288w heating tape with thermostat was utilized to maintain 37 ° c . within the closed circulation system . finally , the circulating fluid was ph 7 . 4 phosphate buffer ( invitrogen , carlsbad , calif .) with a similar electrolyte profile as human blood . buffer was replaced weekly in an effort to maintain stable ph . absorption and tensile properties of the selected polymers were determined as a function of time until compete strength degradation in both the circulation system and control bath . the phosphate buffer in the circulation system was changed weekly as the ph decreased from 7 . 4 to an average 6 . 6 during each week . buffer was changed in the control bath only monthly due to better ph stability in the static environment . mean flow was 4 . 7 l / min while oxygen averaged 30 % and tds 8 . 8 ppt . the phased or sequential absorption of the webbed absorbable filter design is illustrated in the collage of fig5 . notice the filter begins to disintegrate during the 13th week and continues in a phased manner , losing only 1 or 2 capture elements per week thereafter , until complete disintegration in 22 weeks . initial fractures detected in the 13th week were located at the high stress points within the capture elements . since the apex of a capture element mounted to the circumferential support experiences twice the stress in comparison to the base of the capture element , the initial break will be at the apex . the capture elements that formed loops extending from the vessel wall to the center of the filter were constructed of polydioxanone size 1 and 0 with expiration date january 2012 , while the shorter capture elements that extended a quarter of the diameter were constructed of size 3 - 0 polydioxanone suture with an expiration date of january 2015 . the expiration date was seen to play a greater role than suture diameter in the rate of absorption since the smaller diameter suture fractured in week 17 , versus the larger diameter suture that fractured in week 13 . the planned disintegration of 8 elements of length d / 2 and 8 elements of length d / 4 for the webbed filter actually yielded smaller brittle fragments due to splintering and fragmenting . in fact the largest filter element captured from the webbed design by the downstream 80 um filter revealed a maximum sized fragment of 5 mm × 0 . 3 mm . perhaps the paramount characteristic under consideration for use in an absorbable vascular filter is the strength retention profile of the absorbable polymers as depicted in fig6 for polydioxanone in the in - vitro circulation system . as shown , polydioxanone initially exhibits moderate strength degradation , less than approximately 5 % per week for the initial 5 to 6 weeks , followed by rapid decline approaching 20 % per week thereafter . as a conservative summary for the initial 5 weeks in circulation , polydioxanone size 1 maintained about 10 kg strength , size 0 maintained 6 kg , size 2 - 0 maintained 4 kg , and size 4 - 0 maintained 1 . 5 kg . similar results were obtained from a buffer bath control for the initial 5 weeks . however , statistical difference was achieved at week 5 for size 0 ( p & lt ; 0 . 014 ), week 6 for sizes 2 - 0 and 1 ( p & lt ; 0 . 021 ), and week 7 p & lt ; 0 . 011 ). the proposed filter designs employ multiple strands serving as capture elements , hence the emboli load is distributed across n strands . therefore assuming equal distribution , the net emboli load that can be accommodated by the filter is a multiple , n , of the per strand load at break . consequently , a polydioxanone size 2 - 0 filter with 8 capture elements secured at the circumferential support would accommodate a net emboli load of 32 kg . an alternative method for accessing strength retention for the polymers is to chart the percentage strength retention as a function of time as shown in fig7 . here all polydioxanone sizes slowly lost strength for the first 5 weeks , then rapidly absorbed to negligible strength by the 10th week . specifically , polydioxanone within the in - vitro circulation system retained average strength for sizes 2 - 0 and larger of 88 % at 2 weeks , 85 % at 4 weeks , and 68 % at 6 weeks vs . ethicon &# 39 ; s in - vivo animal tissue approximation applications that yielded 80 % at 2 weeks , 70 % at 4 weeks and 60 % at 6 weeks per ethicon product literature . young &# 39 ; s modulus of elasticity ranged from 1 . 0 - 2 . 3 gpa for polydioxanone as shown in fig8 for the absorbable filter elements . notice that young &# 39 ; s modulus initially decreased ( polymer became more elastic ) as it was subjected to the buffer , reached a minimum at 6 weeks , then increased to approximately twice the initial value . this increase in young &# 39 ; s modulus for polydioxanone is indicative of the increased brittleness as it reached zero terminal strength , and was further observed during disintegration . this property may well be advantageous for the absorbable filter application . for example , as polydioxanone reached zero terminal strength and disintegrated , it splintered and fractured into smaller , brittle fragments thereby being potentially less harmful to downstream organs . further studies are required to determine the exact size of the terminal fragments in - vivo and evaluate potential pulmonary micro - infarcts . in conclusion from the in - vitro absorbable filter study , polydioxanone appears to be a strong candidate for absorbable vascular filters with sufficient strength retention to capture emboli for at least 6 weeks , then absorb rapidly over the next 16 weeks via hydrolysis into carbon dioxide and water . specifically polydioxanone size 2 - 0 was shown to conservatively maintain 4 kg load at break per strand throughout 5 weeks in circulation . hence a filter incorporating 8 capture elements would trap an embolus load of 32 kg ; or equivalently , an embolism would have to deliver 1600 kgmm of energy to break through the filter which is highly unlikely given that the pressure in the ivc is a mere 5 mmhg ( about 0 . 1 psi ). moreover , the webbed filter geometry with varied diameter capture elements and expiration dates was shown to disintegrate in a sequential or phased manner , releasing 1 or 2 small brittle filter fragments ( less than 5 mm × 0 . 3 mm each ) weekly in circulation from weeks 14 through 22 . together with polydioxanone being fda - approved and proven to be nonallergenic and nonpyrogenic , a catheter - deployed polydioxanone absorbable vascular filter would likely be an efficient and effective device for the prevention of pulmonary embolism . a preferred installation of the absorbable vascular filter is via intravenous insertion with a catheter requiring only a local anesthetic as illustrated in fig9 a - e . here the filter is collapsed and compressed within a delivery catheter comprised of an outer sheath 71 and internal applicator or stabilizer piston 73 on a central rod as illustrated in fig9 a . for ivc filter deployment , the delivery catheter is inserted into the patient &# 39 ; s vasculature of convenient location , such as the femoral vein or internal jugular . subsequently , the delivery catheter is fed through the vasculature typically over a guide wire until reaching the desired deployment location , often inferior to the renal veins . next the compressed filter 50 is allowed to expand upon sliding the exterior sheath 71 in the proximal direction while simultaneously pushing the stabilizer rod and piston 72 in the distal direction ( refer fig9 b ). once the exterior sheath 71 is withdrawn away from the filter , the stabilizing piston 73 can also be retracted as depicted in fig9 c . consequently as a thrombosis event releases an embolus 80 , the embolus is captured by the vascular filter and is prevented from traveling to the heart and lungs thereby preventing a potentially fatal pe ( refer fig9 d ). following the desired prophylactic time window for filter utilization ( approximately 6 weeks in many applications ), the filter is biologically absorbed resulting in the absence of any foreign material in the vessel as depicted in fig9 e . an alternative embodiment of the absorbable vascular filter 1 is portrayed in fig1 a with an integrated circumferential support 102 and capture basket 101 . here the circumferential support 102 and capture basket 101 are braided or woven much like a radial expansible stent that can be compressed in a catheter as described above prior to deployment . fig1 b is a top view of the absorbable vascular filter that displays the weave or braid of the capture basket 101 . the weave is shown to maintain a patent center 104 to allow insertion of a guide wire during catheter deployment . the appeal of this particular embodiment is that the entire absorbable vascular filter ( circumferential support and capture basket composed of the capture elements ) can be fabricated from a single filament with a designed radial force to prevent filter migration as described below . the integrated absorbable vascular filter shown in fig1 a and b yields a diametrically expandable and compressible tubular filter that exhibits a radial force with magnitude dependent on the materials chosen , angle phi ( φ ) of the crossing elements of the weave , and the amount of diameter over sizing employed . specifically , the angle important to establishing radial force is depicted as φ in fig1 . the larger the angle φ as it approaches 180 °, the greater the amount of radial force provided by the weave . typically φ is an obtuse angle , chosen between 90 and 180 °. for illustration , a simple cylindrical braided weave ( l = 7 , p = 4 ) is shown in fig1 cut in the longitudinal direction and placed flat on a surface revealing the looping pins 110 and braiding filament 103 . considering the weave as a series of sinusoid waveforms of period pτ ( see bold section of weave in fig1 ), where p is the number of looping pins traversed for one cycle of the sinusoid and τ is the pin - to - pin spacing , an algorithm can be derived to ensure that for a given set of parallel looping pins l that equidistantly span the circumference of the intended diameter of the vascular filter , each pin will be looped once and the final loop ending at the origin . the algorithm can be visualized by a table as shown in table 1 to indicate the relationship between l , p and the angle φ for any desired number of circumferential loops ( l ). l / p represents the fractional number of sinusoids traversed per circumference , and n represents the total number of turns around the circumference of the cylinder . essentially the weave creates sinusoids that are out of phase by a fixed increment until the final loop is achieved for which the final sinusoid is desired to be in - phase with the initial sinusoid . the in - phase condition requires the product n ×( l / p ) to be an integer . moreover , to ensure all pins are looped , the first integer to be formed by the product n ×( l / p ) must occur where n = p . for example with l = 7 and p = 4 , the first integer that appears in the row corresponding to p = 4 of table 1 is where n = 4 so this combination of l , p , and n will provide a successful braid wherein all pins will be utilized ( 7 across the top , 7 across the bottom ) and the final weave will terminate at the origin . it can be demonstrated that l must be an odd integer for a successful braid . it can further be shown that the angle φ can be expressed as φ = 2 tan − 1 ( pπr / l1 ) where r and l is the radius and length of the desired filter circumferential support 102 . the values for r and l used for calculating φ in table 1 were 0 . 625 and 1 . 5 inches respectively . also τ is easily computed from the relationship lτ = 2πr or τ = 2πr / l . fig1 depicts another braid combination where l = 7 and p = 6 . notice that the first integer to appear in the row for p = 6 in table 1 corresponds to n = 6 hence the braid will terminate successfully at the origin and all l pins looped once . further fig1 illustrates a method for forming the capture basket 101 as a simple continuous extension of the filament beyond the circumferential support 102 . as shown at the alternating looping points across the top of the circumferential support , the conical capture basket 101 is weaved by sequentially interlocking loops from adjacent loops 105 and extending a loop to the apex 106 . the apical loops from each extension 106 can be bonded together revealing a conical capture basket as shown in fig1 b with a patent center apex 104 . clearly other braided patterns can be employed to yield the pattern resolution sufficient to trap emboli of a desired size . although only a set of 7 looping pins were considered for simplicity in the above illustrations , a more likely number useful for an absorbable vascular filter for the ivc may well be 17 or 19 with φ & gt ; 100 °. specifically , an absorbable ivc filter with integrated circumferential support and capture basket was fabricated with a single 10 ft synthetic filament ( 0 . 5 mm diameter ) as shown in fig1 a and b with l = 17 , p = 16 , φ = 102 °, l = 1 . 5 ″, r = 0 . 625 ″, and τ = 0 . 23 ″. the self expandable ivc filter provides sufficient radial force to maintain placement in the ivc by the choice of the obtuse weave angle , 25 % oversized diameter ( to fit 1 ″ ivc diameter ), and wide diameter filament ( 0 . 5 mm ). alternatively , the above described integrated absorbable vascular filter can be constructed with multiple bonded filaments , although a single continuous filament may be preferable . although the present invention has been described with reference to specific exemplary embodiments , it will be evident to one of ordinary skill in the art that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the invention . accordingly , the specification and drawings are to be regarded in an illustrative rather than a restrictive sense . goldhaber s z , ortel t l . the surgeon general &# 39 ; s call to action to prevent deep vein thrombosis and pulmonary embolism , office of the surgeon general ( us ), national heart , lung , and blood institute ( us ). rockville ( md ). 2008 spencer f a , emery c , lessard d , anderson f , emani s , aragam j et al . the worcester venous thromboembolism study ; a population - 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