Patent Application
20160000985
The present invention relates to implantable medical devices associated with the creation of, and/or the maturation of an arteriovenous (AV) fistula access structure for hemodialysis.
AV Fistula (a connection between an artery and a vein) are a desired access structure for the dialysis of kidney failure patients.
About 42% of surgically created AV Fistula fail to mature; that is, the portion of the vein proximal the fistula fails to adapt physiologically to accommodate the higher arterial pressure. When this venous portion (or side of the AV fistula) matures, it becomes usable as a cannula access site for dialysis (
Patients without a mature AV Fistula require some other, less desirable form of dialysis access for the standard 3 times a week dialysis regimen until a mature fistula is available. Additionally, about a third of mature fistula fail in a year. The health of kidney failure patients without a functioning mature AV Fistula deteriorates at a more rapid rate than those with one. Deteriorating health makes the subsequent creation of a functioning mature AV Fistula less probable, necessitating a significant number of interventions or access procedures resulting in poorer survival rates. Thus, a significant number of interventions and procedures may be avoided or significantly delayed, significant cost savings realized and the survival rate of dialysis patients significantly improved by decreasing the failure to mature rate of newly created AV fistula and by reducing the rate at which mature fistula fail.
There is evidence that the shape of an arteriovenous fistula can affect long term durability. For example, Papachristou (2012) and Krishnamoorthy (2012) have indicated that a curved fistula is preferred to a straight fistula because the curved fistula results in greater flow rates, lesser differences in wall shear stress, greater venous dilatation, and less eccentric neointimal hyperplasia. Papachristou E and Vazquez-Padron R I. From basic anatomic configuration to maturation success. Kidney International 81: 724-726, 2012. Krishnamoorthy M K, Banerjee R K, Wang Y et al. Anatomic configuration affects the flow rate and diameter of porcine arteriovenous fistula. Kidney International 81: 745-750, 2012. In addition, Ene-lordache B et al (2013) have found that angle at the origin of a “side-to-end” arteriovenous fistula is very important. Their research indicates that an angle of 30 degrees is preferred over angles of 45, 60 or 90 degrees. Ene-lordache B, Cattaneo L, Dubini G, Remuzzi A. Effect of anastomosis angle on the localization of disturbed flow in “side-to-end” fistula for haemodialysis access. Nephrol Dial Transplant 28: 997-1005, 2013.
There are no known extravascular or perivascular devices available that can effectively and reliably assist a surgeon in maintaining a more desirable AV fistula construct. Accordingly, there is a need for a device that can aid in creating the correct anatomy by providing the appropriate support in the appropriate locations and in the appropriate configurations that promote long-term arteriovenous (AV) fistula patency.
The invention provides an extravascular or perivascular arteriovenous (AV) guide intended for being placed at an anastomosis to support and help achieve vein maturation. The apparatus is intended for being placed at an anastomosis to support and help achieve a vein maturation including an about 15 to 45 degrees, preferably about 30 degree, take-off angle (or less than about 45 degrees) between the vein and artery at the fistula. The apparatus is placed when the anastomosis is made and remains to help produce an about 30 take-off angle for the matured vein.
U.S. application Ser. No. 14/063,984 (attorney docket: 62571.770) (“'984 application”) disclose extravascular wraps for an AV fistula. Discussed therein are take-off angles for the venous portion of the fistula. The '984 application proposes an obtuse take angle, which is measured with respect to axis A in FIG. 2A of the '984 application, and a curved venous support portion for an AV guide. The present disclosure includes embodiments directed to an extravascular AV guide that instead provide an acute take-off angle and the venous support portion is comparatively straight or devoid of a curvature as described in the '984 application. U.S. application Ser. No. 14/253,719 (attorney docket: 62571.889) (“'719 application”) discloses embodiments of stents or support devices intraluminally placed at a fistula to support the same range of take-off angles as embodiments of an AV wrap disclosed herein.
The invention, in one aspect, is directed to a medical device supporting a desired venous take off angle θ of about 5, 10, 15, 20, 25, less than about 30 degrees, between about 20-45 degrees or between about 15 to 45 degrees relative to axis A in
According to some embodiments, the AV guide is sized to initially fit at least a vein portion distal of the fistula loosely and has an internal diameter in the range of 4-8 mm. A variety of sizes would be available depending on the patient anatomy. For example, an average outer diameter of a vein portion of the fistula is roughly 6 mm, so the AV guide would have an ID of 6 mm. According to some embodiments, the AV guide includes bioresorbable or non-bioresorbable wraps, cuffs or shells, respectively, which allow a surgeon to easily fit or place the wrap at the fistula. A tubular body is formed, according to some embodiments. In other embodiments a wire frame is made. In the case of a tubular body, the structure may be made from bioresorbable threads combined with a shell so that a channel or opening circumscribing the vein will easily open as the vein matures and radially presses outward. The venous portion of the AV guide may have a diameter of 4-10 mm and a length of 5-10 cm.
In accordance with the foregoing, there is an AV stent or scaffold, medical device, method for making such an AV stent or scaffold, a method of using an AV stent or scaffold, or method for assembly of a medical device comprising such a AV stent or scaffold, and/or a medical device comprising a balloon, having one or more, or any combination of the following things (1)-(35):
All publications and patent applications mentioned in the present specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. To the extent there are any inconsistent usages of words and/or phrases between an incorporated publication or patent and the present specification, these words and/or phrases will have a meaning that is consistent with the manner in which they are used in the present specification.
For purposes of this disclosure, the following terms and definitions apply:
When referring to a vein or artery prior to making a fistula, a “proximal end” refers to an end closest to the torso of the body, whereas a “distal end” refers to the end furthest from the torso of the body. In contrast, after the fistula is made, or when referring to a medical device's intended location relative to a fistula or anastomosis, the terms “proximal” and “distal” are instead intended to be made with respect to the relative location of the fistula or anastomosis. Thus, for example, the end of a AV Guide closest to the fistula will be called the “proximal” end and the end furthest from the fistula the “distal” end. Thus, generally speaking, prior to making the fistula the former terminology is used. And after the fistula is made “proximal” and “distal” always refers to a location relative to the fistula.
The terms “anastomosis” and “fistula” may be used interchangeably in this description. For purposes of the disclosure the two terms mean the same thing and refer to the arteriovenous (AV) type of anastomosis or fistula.
The terms “about” or “approximately” mean 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1.5%, 1%, between 1-2%, 1-3%, 1-5%, or 0.5%-5% less or more than, less than, or more than a stated value, a range or each endpoint of a stated range, or a one-sigma, two-sigma, three-sigma variation from a stated mean or expected value (Gaussian distribution). For example, d1 about d2 means d1 is 30%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, 1.5%, 1%, 0%, or between 1-2%, 1-3%, 1-5%, or 0.5%-5% different from d2. If d1 is a mean value, then d2 is about d1 means d2 is within a one-sigma, two-sigma, or three-sigma variance from d1.
It is understood that any numerical value, range, or either range endpoint (including, e.g., “approximately none”, “about none”, “about all”, etc.) preceded by the word “about,” “substantially” or “approximately” in this disclosure also describes or discloses the same numerical value, range, or either range endpoint not preceded by the word “about,” “substantially” or “approximately.”
A procedure for forming an AV fistula is explained in the documents incorporated by reference herein. As noted therein, after the fistula is formed, there is no guarantee that the vein will retain a desirable flow facilitating curve. An AV stent or scaffold according to the disclosure helps to maintain a desired venous shape to increase the patency period for the fistula. Importantly, the devices disclosed herein can promote increased flow rate through the fistula by affecting the flow characteristics/patterns such that there are no regions of low wall shear stress and/or less circular/stagnant flow along in the vein wall, which helps prevent a stenosis from forming at the fistula or adjacent portions of the vein. Preferably the AV stent or scaffold (or combination thereof) is such that it causes the vein to mature into a shape producing a relatively low acceleration (rate of direction change) of the flow as it is diverted from the artery to vein. Moreover, the shape minimizes or eliminates stagnant or circular blood flow and avoids the forming of low flow regions that result in minimal or no shear stress along the vessel walls. Dimensional goals for the fistula are to enlarge to a diameter on the order of 6 mm and lie no more than 6 mm beneath the skin surface.
Referring to
Referring to
Referring to
The half-tube vein portion 15a extends from the artery portion 12a at the angle θ, with respect to axis A; or a lower edge 17a of the portion 15a forms an angle of 180−θ with respect to a lower edge 16 of the artery portion 12a. In some embodiments the half-tube portion 15a is a half-cylinder extension of the half cylinder portion 12a. In alternative embodiments the portion 15a can be a half-frustum or form one hall of a portion 15a having a frustoconical shape whereby the smaller opening of the frustum is proximal the fistula and the larger opening distal of the fistula. In another embodiment the body shape for portion 15a has a first portion proximal the fistula that is constant in diameter (as illustrated) then flares out towards the distal end. The increased diameter provided in the alternative embodiments provides the space to allow the vein to increase in diameter while providing the structure proximal the fistula to support the take-off angle and proper vein maturation. The edge 17a can be straight so that the angle 180−θ is constant from the proximal to distal ends of the portion 15a; however, the corresponding edges forming the angle at 14 would decrease when moving from the edge portions proximal the fistula to distal the fistula.
In the foregoing embodiments of the cylindrical, or frusto-conical shapes of the portion 15, i.e., portions 15a and 15b combined, it will be appreciated that only the inner surface of the lower edge 17 may be needed to maintain the take-off angle by contact with the abluminal surface, just as the tongue structure described in the '719 application (intraluminal AV support) may be all that is needed to maintain the take-off angle from the luminal surface of the vessel. As such, the portion 15 can be shaped to have a taper or flared proximal end, or otherwise have an opening at the distal end that is larger than the opening at the proximal end, e.g., larger by a factor of 2, 4 or 6. This structure type helps avoid adversely interfering with the vein's maturation in response to increased blood flow through the fistula. Alternatively or in addition, in some embodiments upper edges 17b of portion 15 are not connected to each other, so as to reduce or avoid any resistance to the vein increasing in diameter during maturation. The slit or edge surfaces may be formed to have a zig-zag or wavy pattern as shown in the '984 application when the shell 10 is placed around the fistula.
Thus, the shell 10 when closed may provide sufficient space for the vein to expand during the remodeling process while maintaining the take-off angle. This is important as the vein portion of the fistula undergoes considerable positive remodeling and greatly enlarges in size. The venous portion of the shell 10 should have enough space to allow this enlargement. Or the portion 15 should be able to easily dilate if it is close fitting when implanted.
The space between the shell 10 and vessel abluminal surfaces may be filled with a hydrogel, which could be high molecular weight, shear-thinning, pre-crosslinked particles, or in-situ gelling. Examples include Healon (hyaluronic acid), PEG, two component glues such as fibrin glue, Bioglue, two-component PEG, Restylane type of particles, UV-curing, or Pluronics containing free drug, or microparticles or nanoparticles that elute drug. The filling may be used as a medium/vehicle to aid in the retention of drug-eluting particles at the therapy site.
The shell 10 can be made of either porous or nonporous materials. It is believed that a porous structure would be preferable for biocompatibility, tissue vitality, and tissue ingrowth. However, a monolithic or less permeable structure is possible.
Materials to accomplish this include: polyethylene terephthalate (e.g., DACRON), silicone, polyurethanes, polypropylene, polyesters, Pebax, silicones, polyisobutylene and ethylene-alphaolefin copolymers, acrylic polymers and copolymers, vinyl halide polymers and copolymers, poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene fluoride) (PVDF), poly(vinylidene chloride), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), poly(tetrafluoroethylene-co-vinylidene fluoride-co-hexafluoropropylene), polyvinyl ethers, such as polyvinyl methyl ether, polyacrylonitrile, polyvinyl ketones, polyvinyl aromatics, such as polystyrene, polyvinyl esters, such as poly(vinyl acetate), copolymers of vinyl monomers with each other and olefins, such as ethylene-methyl methacrylate copolymers, acrylonitrile-styrene copolymers, ABS resins, and poly(ethylene-vinyl acetate) copolymers, polyamides, such as Nylon 66 and polycaprolactam, alkyd resins, polycarbonates, polyoxymethylenes, polyimides, polyethers, poly(sec-butyl methacrylate), poly(isobutyl methacrylate), poly(tert-butyl methacrylate), poly(n-propyl methacrylate), poly(isopropyl methacrylate), poly(ethyl methacrylate), poly(methyl methacrylate), epoxy resins, poly(vinyl butyral), poly(ether urethane), poly(ester urethane), poly(urea urethane), poly(silicone urethane), polyurethanes, rayon, rayon-triacetate, cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellophane, cellulose nitrate, cellulose propionate, cellulose ethers, carboxymethyl cellulose, poly(ether ester), polyalkylene oxalates, polyphosphazenes, poly(fluorophosphazene), poly(phosphoryl choline methacrylate), polymers and co-polymers of hydroxyl bearing monomers such as 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), hydroxypropylmethacrylamide, PEG acrylate (PEGA), PEG methacrylate, poly(styrene-isoprene-styrene)-PEG (SIS-PEG), polystyrene-PEG, polyisobutylene-PEG, poly(methyl methacrylate)-PEG (PMMA-PEG), polydimethylsiloxane-co-PEG (PDMS-PEG), nitinol, and/or elgiloy.
The shell 10 can also be drug coated in order to prevent cell infiltration or control neointimal hyperplasia. Drugs to accomplish this include: everolimus, zotarolimus, ABT-578, sirolimus, umirolimus, biolimus, merilumus, myolimus, novolimus, temsirolimus, deforolimus, and AP23573. Alternatively, in other embodiments the shell 10 can be drug coated to encourage cell infiltration or to integrate the cover with the vein and/or arterialize it. Drugs for this include mitogens such as fibroblastic growth factor (FGF), basic FGF, platelet derived growth factor (PDGF), insulin like growth factor 1 (IGF-1), epidermal growth factor (EGF), granulocyte macrophage colony stimulating factor (GMCSF), human growth hormone (HGH), IL-1, TGF-B, and matrix metalloproteinases.
The shell 10 may also elute a vasodilator that promotes venous dilation. Possible drugs include a nitric oxide donor, nitroglycerine, papaverine, calcium channel blocker, adenosine, prostacyclin, epinephrine, prostaglandin, L-arginine, bradykinin, natriuretic peptides, alpha blockers, adenocard, sodium nitroprusside, or matrix metalloproteases.
Additional possibilities include agents that degrade the external structure of the vessel to permit expansion, such as collagenases, elastases, metalloproteinases; agents that promote inflammation that results in the release of factors the promote vessel expansion, such as interleukins 1, and TNF-alpha; and agents that block the effects of anti-inflammatory agents, such as blockers of IL-4, IL-10, IL-13, which are anti-inflammatory cytokines.
Referring to
Following the step illustrated in
Pure iron, martensitic; Carbonyl iron; Maghemite (Fe2O3); Magnetite (Fe3O4); Ferromagnetic iron; Ferrimagnetic iron; Superparamagnetic iron; and Iron oxide.
In some embodiments the shell 10 has eyelets that permit attachment of the shell 10 to adjacent tissues. These could be eyelets, loops, flanges, tabs or holes. A porous shell 10 would lend itself to direct suturing to the surrounding tissue.
According to some embodiments, the shell 10 is a hybrid where the shell is comprised of both bioresorbable polymer(s) and a durable polymer(s). The bioresorbable components hold the shell portion 15 at a smaller diameter which fits closely to the venous dimensions. As the bioresorbable portion degrades, the venous portion of the shell 10 easily dilates to a large diameter, which is set by the radial stiffness of the durable polymer component of the portion 15. According to one embodiment, the shell portion 15 is woven with both durable polymer filaments and bioresorbable polymer filaments where the durable ones are looser or can expand more once the bioresorbable filaments lose strength.
In general it is expected that the maturation process for the vein occurs within 12 weeks of forming the fistula. After this period, it is desirable to have at least the venous portion of the shell 10 bio-resorb or degrade to cause a significant loss in radial strength or stiffness of the shell portion surrounding or in contact with the maturing vein. According to some embodiments the shell may be made from, or portions thereof made from or strengthened by threads of the following material:
There is an average venous growth rate of 0.2 mm/week (Corpataus). As such, according to some embodiments the shell 10 is capable of allowing the vein to expand at this rate through loss of mechanical properties or through loss of mass. A rapidly degrading polymer such as PLGA with low mass is presently preferred. TABLE 1 below summarizes the properties of a vein over a 12-week period following formation of the fistula.
Brescia-Cimino hemodialysis access is the standard surgical technique used to make arteriovenous fistulas. See, e.g., Bagolan P1, Spagnoli A, Ciprandi G, Picca S, Leozappa G, Nahom A, Trucchi A, Rizzoni G, Fabbrini G., A ten-year experience of Brescia-Cimino arteriovenous fistula in children: technical evolution and refinements. J 1998 April; 27(4):640-4.
Referring again to
In some embodiments the shell 10 is instead formed from a compound that can be shaped as needed for the patient's vasculature at the time of the procedure. To achieve this end, there is a provided a sheet of biocompatible material that achieves cross-linking (to form a permanent shape) by moisture cure, temperature, UV curing etc. The possible materials include epoxy, urethane butylcyanoacrylate, Bioglue etc. The material may be permanent or durable, or the material may be bioresorbable. Once shaped and placed around the vasculature, the ends may be held together by magnets, as disclosed earlier.
In some embodiments the moldable sheet is thermoset. The sheet is stored in a freezer. The surgeon would remove it from the freezer and immediately begin to form it around the artery/vein shaping it and cutting it to fit. As the material warms, a crosslinking reaction takes place which hardens the wrap. There are many chemistries capable of accomplishing this process, including thiol or amine/N-hydroxysuccinimide (NHS), thiol/maleimide, amine/thioester, sulfhydryl/vinyl sulfone, thiol/acrylate, thiol/vinyl ether, thiol/allyl ether, thiol/thiol, and biotin/avidin.
The sheet (or wrap) is monolithic meaning it is not porous. A thermoset system is one in which chemical cross linking occurs. This transforms the sheet from something that is flexible and moldable to one which is rigid, or at least has a memory for a certain shape. The crosslinking chemistry needs to be rapid, selective and biocompatible. Crosslinking systems typically have at least two components, i.e., component A and component B, although more than two is possible. It is preferred for the blended A and B components to have a glass transition temperature (TG) less than 40° C. in the hydrated state, using a simple part A and part B system as an example. Each part is composed of prepolymer molecules with a specific chemistry on the polymer chains.
Part A has one type of chemical functional group, which will be called “A groups,” and part B will have “B groups.” The specific A or B group chemistry can be at the ends of the polymer chains or arranged along the backbone, depending from the polymer chains. The two parts A and B are blended by the manufacturer either at low temperature and/or rapidly. During storage, the sheet is frozen or kept cold to prevent the crosslinking reaction. TABLE 2 lists some types of chemistries for Groups A and B, which are suitable for use in the body.
These pairs of A and B groups will react with each other to from a cross link. The A and B groups may be attached to a durable or biodegradable backbone polymer. A list of useful durable polymer backbones includes silicone, polyethylene, polypropylene, polybutylene, polyisobutylene and ethylene-alphaolefin copolymers, polyvinyl chloride, polyvinyl methyl ether, polyvinylidene chloride, polyvinyl acetate, ethylene-methyl methacrylate copolymers, ethylene-vinyl acetate copolymers, poly(propylene fumarate), poly(n-butyl methacrylate), poly(sec-butyl methacrylate), poly(isobutyl methacrylate), poly(tert-butyl methacrylate), poly(n-propyl methacrylate), poly(isopropyl methacrylate), poly(ethyl methacrylate), poly(methyl methacrylate), polyurethane, cellulose acetate, cellulose butyrate, cellulose acetate butyrate, cellophane, cellulose nitrate, cellulose propionate, cellulose ethers, carboxymethyl cellulose, poly(ethylene glycol) (PEG), poly(ethylene oxide), poly(propylene oxide), poly(ether ester), polymers and co-polymers of 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), hydroxypropylmethacrylamide, PEG acrylate (PEGA), PEG methacrylate, methacrylate polymers containing 2-methacryloyloxyethyl-phosphorylcholine (MPC) and n-vinyl pyrrolidone (VP), methacrylic acid (MA), acrylic acid (AA), poly(styrene-isoprene-styrene)-PEG (SIS-PEG), polystyrene-PEG, polyisobutylene-PEG, poly(methyl methacrylate)-PEG (PMMA-PEG), polydimethylsiloxane-co-PEG (PDMS-PEG), poly(vinylidene fluoride)-PEG (PVDF-PEG), PLURONIC™ surfactants (polypropylene oxide-co-polyethylene glycol), poly(tetramethylene glycol), hydroxy functional poly(vinyl pyrrolidone), polyvinylidene fluoride, and poly(vinylidene fluoride-co-hexafluoropropylene).
A useful list of biodegradable polymers to which the A and B groups could be attached are collagen, gelatin, chitosan, alginate, fibrin, fibrinogen, starch, dextran, dextrin, hyaluronic acid, heparin, elastin, polyanhydrides, polyorthoesters, polyamino acids, poly(ester-amides), polyhydroxyalkanoates, poly(ester amides), polycaprolactone, poly(L-lactide), poly(D,L-lactide), poly(D,L-lactide-co-PEG) block copolymers, poly(D,L-lactide-co-trimethylene carbonate), polyglycolide, poly(lactide-co-glycolide), polydioxanone (PDS), polyorthoester, polyanhydride, poly(glycolic acid-co-trimethylene carbonate), poly(amino acids), poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-valerate) (PHBV), poly(3-hydroxyproprionate) (PHP), poly(3-hydroxyhexanoate) (PHH), poly(4-hydroxybutyrate), poly(4-hydroxyvalerate), poly(4-hydroxyhexanoate), poly(hydroxyvalerate), poly(tyrosine carbonates), poly(tyrosine arylates), poly(ester amide), poly(3-hydroxyalkanoates) such as poly(3-hydroxypropanoate), poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), poly(3-hydroxyhexanoate), poly(3-hydroxyheptanoate) and poly(3-hydroxyoctanoate), poly(4-hydroxyalkanaote), poly(4-hydroxybutyrate), poly(4-hydroxyvalerate), poly(4-hydroxyhexanote), poly(4-hydroxyheptanoate), poly(4-hydroxyoctanoate), poly(D,L-lactide), poly(D,L-lactide-co-caprolactone), poly(L-lactide), polyglycolide, poly(D,L-lactide-co-glycolide), poly(L-lactide-co-glycolide), polycaprolactone, poly(lactide-co-caprolactone), poly(glycolide-co-caprolactone), poly(dioxanone), poly(ortho esters), poly(anhydrides), poly(tyrosine carbonates), poly(tyrosine esters), poly(imino carbonate), and poly(glycolic acid-co-trimethylene carbonate).
For the thermoset sheet or wrap, after removal from the freezer, the surgeon would cut the wrap to shape (if needed) and then quickly place it around the artery/vein and anastomosis.
According to another embodiment the shell 10 is shaped from a porous sheet of material stored dry. In this embodiment, the sheet material is porous. The average pore size may be from 0.1 micron to 10 microns. Porous sheets can be made by lyophilization, leaching out of a porogen, a foaming process with an inert gas, mechanically by punching or drilling, or by lasing. Several chemistries are available that are responsive to moisture. Two preferred ones are isocyanate groups and cyanoacrylate groups. These chemistries don't require a Part A and Part B component. It would simply be one component with these groups attached (either all isocyanate or all cyanoacrylate). During storage, the sheet would be packaged in an impermeable package of some sort, preferably in an inert atmosphere. The physician would open the package, exposing the sheet to moisture. Exposure to moisture causes the groups to become reactive and initiates the cross linking reaction. This moisture can come from the ambient humidity, or exposure to biological fluids when implanted. The list of durable and biodegradable polymers to which the isocyanate or cyanoacrylate groups could be attached is the same as in the embodiment above.
According to another embodiment the shell 10 is made from a thermoplastic sheet (e.g. pebax, nylon, polyester, PLLA mesh) that is heated in a microwave then shaped around the artery when soft. The softening temperature would be above 37° C. but otherwise minimized or luminally insulated to minimize any thermal artery damage.
Thermoplastic polymers are those which can be processed via melt processing to form useful articles. They typically have a TG or melting point above ambient temperature. According to the embodiments a sheet or wrap could be stored at ambient temperature and the material can be monolithic or porous. It would be heated to temperature above 37° C., but when implanted in the body around the artery and vein, the temperature cannot be greater than about 47° C. Useful material would be a biocompatible material with a TG or melting point in the range of 37° C. to 50° C. Specific material which could achieve this are poly(ethylene-co-vinyl acetate), poly(ethylene-co-butyl methacrylate), poly(L-lactide-co-caprolactone), poly(L-lactide-co-trimethylene carbonate), poly(glycolide-co-caprolactone), and poly(glyolide-co-trimethylene carbonate).
According to another aspect of the disclosure there are flexible and interconnected wire clips configured to close around venous and arterial portions adjacent the fistula to support and maintain the take-off angle θ. For example, referring to
A benefit to having a spring clip, e.g., the clip illustrated in
The clips 32, 34 and 36 may be made from either a round or flat cross section wire. High yield and elastic material such as 300 Series Stainless may be used. The thickness of the wire (narrowest dimension for a flat) would be 250 um to 2000 um wire. Possible materials would include 304 Stainless Steel, 316 Stainless Steel, Chrome Vanadium ASTM A231 or Chrome Silicon ASTM A 401. According to some embodiments the material has an Elastic Modulus of at least 180 MPa with a Tensile Strength of at least 750 MPa.
Referring to
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As depicted in
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In
The above description of illustrated embodiments of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.
These modifications can be made to the invention in light of the above detailed description. The terms used in the claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the claims, which are to be construed in accordance with established doctrines of claim interpretation.
