MXPA06007992A - Mri compatible implant comprising electrically conductive closed loops - Google Patents

Abstract

The present invention relates to an implant 100 which comprises a plurality of electrically-conductive closed loops (300A, 300B, 300C, 300D;120A, 120B, 120C, 120D each constituted from a plurality of loop portions such as struts (400, 500). The loops together form apertured walls of a cage with an interior volume, and the portions in any one said loop providing electrically-conductive pathways within which eddy currents are liable to be induced when the implant is subjected to an time-dependent external magnetic field, with each said loop comprising at least first and second said pathways. The implant is characterized in that the first and second pathways are arranged such that, in any particular magnetic field, the direction of the eddy current that would be induced in the second pathway is the reverse of the direction of the eddy current that would be induced in the first pathway, so as to mitigate the tendency of the implant to function in said magnetic field as a Faraday cage.

Description

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IMPLANT COMPATIBLE WITH MRl COMPRISING CLOSED LOOPES, ELECTRICALLY CONDUCTORS FIELD OF THE INVENTION This invention relates to an implant having a plurality of closed, electrically conductive loops, constituted by a plurality of portions which may be struts, the loops forming together walls with openings of a cage with an interior volume; providing the portions in any of said loops, electrically conductive paths, within which parasitic currents are susceptible to be induced when the implant is subjected to an external, time-dependent magnetic field; each loop having at least first and second current paths. The archetypal implant considered here is a tubular mesh to be delivered in a radially compact configuration, transluminally, by means of a catheter, and then expanded to a radially expanded deployed configuration at a residence site of the tubular mesh , inside a lumen of the body. However, the variety of implants is growing increasingly, and the inventors of the present contemplate the use of the invention in a wide variety of implants other than tubular meshes. A particular example is a filter, such as a vena cava filter, and a variety of grafts for body lumens. Thus, a tubular mesh of Palmaz and a tubular mesh in "Z" of Gianturco have struts, but the tubular wire mesh of Wallsten lacks said struts. Although the tubular meshes exhibit a tubular mesh matrix consisting of portions that resemble struts, terminating at ends corresponding to an abrupt change of direction, there are also tubular meshes made of a single smooth spiral of wire, or a plurality of webs. smooth spirals of wire, woven or woven or braided together (like the children's toy called "Chinese finger"). Any oxide layer on the surface of the wire will inhibit or deny the electrical conductivity of a wire portion to any other portion that is touching it. Although polymers are increasingly interesting and useful, metals are still important for tubular meshes, filters and tubular mesh grafts. In fact, the available variety of biocompatible metals is relatively small. Stainless steel and nickel-titanium alloys with shape memory are favored for the manufacture of tubular meshes and filters; but certain titanium alloys are widely used in particular implant applications. Tantalum is biocompatible, radio-opaque, and has an electrochemical potential similar to that of the nickel-titanium alloy with shape memory, which makes it useful for radio-opaque marking of nickel-titanium meshes. Other biocompatible materials, such as silver and gold, are also useful as radio-opaque markers. Mainly all these materials have good electrical conductivity, and thus, a tubular mesh made of one of those materials, is able to function as a Faraday cage.

In this application, the term "Faraday cage" is intended to have its usual meaning, connoting a shield or a screen surrounding a volume. The shield provided by a Faraday cage resists the penetration of an electromagnetic field into the interior volume, and also prevents the fields generated within the volume from leaving the volume. In this way, an implant that functions as a Faraday cage can prevent an external magnetic field, dependent on time, from penetrating the internal volume of the implant.

THE PREVIOUS BACKGROUND TECHNIQUE Magnetic resonance imaging (MRl) techniques are becoming increasingly important to image soft tissue structures in human and animal bodies. In these imaging procedures, the subject to be examined is subjected to a strong external magnetic field, independent of time (field B0), and superimposed on this magnetic field invariable with time, there is a magnetic field that depends on time (the B1 field is typically an alternating field of radio frequency (RF)), which interacts with the nuclei of the soft tissue structure, very often with the protons (H +) in the nuclei. If these two B fields are superimposed on another magnetic field having a field strength gradient across the field of view, position data can be extracted from the field of view, and an image constructed. Clearly, it would be useful to have a MRl mage of the biological structures or fluids within the lumen of a tubular mesh. However, when an image is taken of a field of view that includes a conventional metallic tubular mesh, little information can be derived from the portion of the image that corresponds to the lumen of the tubular mesh. The metallic tubular mesh works like a Faraday cage to shield the lumen against the Bi field, with the result that the lumen of the tubular mesh does not become clearly visible in an MRl image. It is an object of the present invention to provide implants that define an interior volume and that make available that volume and the areas adjacent to the implant, for MRl imaging, while retaining a useful mechanical operation of the implant. In the MRl apparatus, the B-¡field can induce eddy currents in any closed loop of electrically conductive material, whose plane is not parallel to the direction of its imposed magnetic field, dependent on time. A metallic tubular mesh to be delivered transluminally, from a wire material, a tubular material or a sheet material can be formed; and frequently it is a line of mesh-forming metal rings, arranged along the major axis of the tubular mesh. Regardless of whether the tubular mesh is to mention only a few examples) a woven tubular mesh, made of wire, or a tubular mesh cut with laser, made of tubular material, or a sheet material formed into a tube, the rings can be formed of metal struts that extend in a zigzag pattern around the circumference of each of the rings. The adjacent rings may be connected at one or several sites, here called the joining portions. Within the general structure of the tubular mesh, which defines the lumen walls of the tubular mesh, what can be called the matrix of the tubular mesh, there is typically a multiplicity of closed, electrically conductive loops, which need not be confined to be contained within a tubular mesh forming ring, but may include portions within two or more tubular mesh forming rings. It is possible that eddy currents are induced in these closed loops of the tubular mesh matrix, provided that the metal tubular mesh is within the field of view of a MRl machine, and that the time-dependent magnetic field vector passes through. of the area defined by the closed loop. The parasitic currents induced in the closed loop generate a magnetic field that is what provides the Faraday cage effect, hindering the possibility that the MRl device produces a useful image of the material that is inside the lumen of the tubular mesh. . Consequently, there have been various proposals to reduce or eliminate the induction of eddy currents in the tubular mesh that will be subjected to the fields within a MRl machine. A metallic tubular mesh, expandable, which is said to be compatible with MRl, is described in published US application No. 2002/01 88345 A1. The tubular mesh has discontinuities of non-conductive material. These eliminate the electrically conductive paths in the rings and loops of the tubular mesh. It is said that the discontinuities facilitate the MRl image formation of the tissue that is inside the lumen of the tubular mesh. The non-conductive material can be selected from various materials, such as adhesives, polymers, ceramics, mixed materials, nitrides, oxides, silicides and carbides. The discontinuity is preferably formed in such a manner, during the expansion, that the discontinuity is located where a compressive stress is suffered by the discontinuity. Advantageously, the discontinuities are arranged circumferentially along the tubular mesh forming rings. US-A-5,280,385 discloses a tubular mesh having at least one passive resonance circuit, with an inductance and a capacitance thanks to which its resonance frequency is essentially equal to the frequency of the applied RF field of the image forming machine MRl. The tubular mesh is essentially acting as a second resonance coil in the MRl system. A change in the signal response is produced in that way in a locally defined area in the tubular mesh, or around it, when a spatial resolution image is being taken. A metal endoprosthesis is described in WO 03/015662, which is said to not cause significant artifacts in images taken by magnetic resonance tomography (MRT), as a result of a combination of the production materials with a special design. The endoprosthesis is made of a material with a magnetization capacity similar to that of human tissue. The design of the stent is such that the members or wires of the stent run extensively along the longitudinal axis of the stent, without forming a closed circuit in a plane that is essentially perpendicular to the major axis of the stent. As the material of the stent is said to be suitable copper, gold, copper-gold alloys and silver-palladium alloys. The design of the endoprosthesis includes a spine to which annular elements are attached that perform the function of the endoprosthesis, by means of electrically non-conductive links. The ring elements do not exhibit closed electroconductive loops, in a plane perpendicular to the spine. In WO 03/075797 of the applicant, a medical implant is described having the shape of a tubular mesh, in which adjacent tubular mesh forming rings are connected in joint portions. The joining portions comprise conductivity interruptions to reduce, or even eliminate, the induction of eddy currents when the implant is exposed to the B-i field of a MRl machine. However, there are disadvantages associated with each of those previous proposals. The inventors of the present have started from the first principle, and have searched for ways to make the lumen of a metallic tubular mesh available for imaging in a MRl machine. One way to reduce the amount of eddy currents flowing is to increase the electrical resistance of the tubular mesh itself. It could form the tubular mesh of less conductive materials, make the current flow trajectories longer, or reduce its cross-sectional area, such as by replacing the thick and short struts of a tubular mesh matrix, with longer, thinner connectors and more convolved. However, this has consequences on the mechanical strength of the mesh, and on the steps involved in its manufacture. In another approach, the flow of parasitic currents could be inhibited through a tubular mesh matrix, eliminating or reducing the number of longitudinal electrical connections between adjacent tubular mesh forming rings., which extend around the lumen of the tubular mesh. This is a realistic approach within the field of tubular mesh grafts; where the structural integrity throughout the implant can be provided by the covering of the tubular mesh forming rings. To give an example of a tubular mesh graft with spaced tubular mesh forming rings, see WO 96/281 15. However, in isolated tubular meshes, separating the tubular mesh forming rings has consequences on the mechanical integrity of the mesh. tubular, whether it survives the rigors of the assembly and supply and how possible it is to manufacture such a tubular mesh. Thus, the inventors of the present sought other possibilities of making the MRl image more visible to the local volume of an implant and the areas adjacent to the implant.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention an implant is provided, as defined above, and is characterized by first and second current paths, which are arranged in any closed loop such that, in any particular electromagnetic field, the direction of the parasitic current that would be induced in the second current path, is inverse to the direction of the parasitic current that would be induced in the first current path, in order to mitigate the tendency of the implant to operate in the magnetic field as a cage of Faraday. The observation that the inventors have made of the problem is that an arrangement of conductive current paths in a loop, which is likely to give rise to eddy currents, is not a disadvantage, provided that, at the same time, there is another part of the current. same closed loop, electrically conductive, which is capable of inducing eddy currents of equal force, but in the opposite direction. In that way, the aggregate flow of current in the closed loop is zero (or almost zero), and so that the Faraday screen-shaping effect prevents the inner lumen of the implant from being reproduced in MRl image, so less is mitigated, or even eliminated. To take a very simple example, imagine a simple circular loop of conductive material, arranged in a plane transverse to an external magnetic field, dependent on time. Eddy currents will be induced in the loop. However, imagine keeping the loop at two diametrically opposed points, and then rotating a point 180 ° with respect to the other point. From the individual loop in a given plane, a figure of an eight has been created in the same plane, with portions of the closed individual loop crossing each other where the two lobes of figure eight have their crossing point. With the two intersecting portions electrically isolated, so that there is no short circuit at the crossing point, imagine what the effect will be within the conductive material with the figure of eight loop, exposing it to the same external magnetic field. In both lobes there will be a force to create eddy currents that flow in the "same" direction (dextrorotatory or levógiramente, depending on the direction of the magnetic field). However, when the parasitic currents flow in the same direction in both lobes, they will meet "head to head" at the point of crossing between the two lobes. None can flow, since they are equal and opposite, when the lobes have the same area. Consequently, no current flows. This principle applies regardless of the angle between the plane of the loop and the direction of the incident electromagnetic field, which varies with time. To fix the idea underlying the invention, it can be useful to imagine a piece of paper whose shape has "the figure of 8", with its upper surface green and its lower surface red, and with the field B-? in a direction normal to the plane of the paper. Field B-, "sees" two green circles, each of which is one of the lobes of "8". However, when one lobe is rotated 1 80 ° to the other, the Bi field sees a red and a green circle; both circles being coplanar and having the same area. The parasitic currents that would be induced to flow around the periphery of the red circle, cancel those that would flow around the periphery of the green circle. It is this simple principle that informs the development of the modalities of the present invention. The inventors have given this concept the name "balanced loop". Although the concept of balanced turn is at the heart of the current contribution to the technical field, however, a second effect has been found, which has been termed "inductive inhibition", which is important for facilitating image formation in lumens of the tubular mesh. Let's go back to the simplest case of the two parallel wires of electrically conductive material. If an AC current flows in one of those wires, then, by means of an induction process, the parasitic currents in the second wire will flow in a direction opposite to that of the first wire. Extending this principle, when several wires run close to each other and parallel to each other, then parasitic currents are caused to flow in the neighboring wires due to the current in any particular wire. The net effect of all these additional parasitic currents is that the effective resistance of each wire increases. This effect is often noted in the transformer and inductor winding and is commonly referred to as the "proximity effect". This effect can be used to deliberately increase the resistance of all the loops present in the implant, by making all the loops as convoluted as possible, and by running the loops as close to each other as possible, so that it rises to the maximum the effect of proximity. This has the effect of decreasing the currents that can flow in that implant, so that the visibility of the implant lumen in MRl imaging is improved. Turning now to the matrix structures of the actual tubular mesh, one can proceed with the idea of the figure of eight in the formation of an implant from a plurality of closed, electrically conductive loops, with each of those closed loops formed of a string of lobes arranged in line and extending in that line along the length of the cylinder of the tubular mesh, parallel to the cylinder axis of the tubular mesh. The lobes of this line are interspersed with crossing points where the conductor of the loop intersects with itself as it moves from one lobe through the crossing point to the adjacent lobe. It is contemplated that there is an electrical insulation between the two electrical conductors that intersect, at each crossing point. Obviously, the closed loop of several lobes can be created by successive 180 ° rotations of one end of the loop with respect to the other; and all these successive rotations may be in the same direction or, alternatively, in one direction and then in another direction to create successive crossing points, or in some other format. In any case, using our visualization of the "colored paper", the successive crosses produce alternating red and green lobes, all along the tubular mesh. In a modality in which all the lobes have the same area, there must be an even number of said nodes. However, modalities can be envisaged in which a smaller number of large area nodes are arranged with a larger number of small area nodes canceling, so that the supply of a parasitic current cancellation effect is an aggregate. Again with our paper image with one green side and the other red side, the B-t field must "see" the same total area added of red paper, that of green paper. These different formats will influence the mechanical properties of the resulting implant. However, one aspect that should be noted in all these constructions is that there is a double thickness of the electrical conductor at each crossing point. In many medical implants, it is a special reason to maintain the thickness of the implant wall, between the body tissue and the internal volume of the implant, as small as possible and as uniform as possible, so that these crossing points can be considered negative. double thickness. With the present invention, various known tubular mesh matrix constructions can be modified, as such, within the state of the art, to take advantage of some of the benefits of the inventive concept. For example, the applicant of the present form self-expanding tubular meshes from nickel-titanium alloy tubes, with shape memory, using a laser cutting tool to cut grooves in the wall thickness of the metal tube, in a configuration that allows the tube to expand radially when opening the angles between the struts that are created in the wall thickness of the metal tube, cutting a multiplicity of grooves through the wall thickness. Typically, the slots are all parallel to the longitudinal axis of the metal tube, so that, when the radius of the slotted tube is expanded, a sequence of zigzag struts extending around the circumference of the expanded metal tube is evident in a sequence of rings forming zigzag tubular mesh, stacked along the longitudinal axis of the metal tube. The flexibility of the tubular mesh thus formed varies with the number of links or links connecting each of the tubular mesh forming rings, to the next tubular mesh forming ring, axially adjacent thereto, along the entire length of the tubular mesh. In that way, the tubular mesh exhibits closed, electrically conductive loops around the lumen of the tubular mesh, and other closed loops that extend along the lumen, within the annular envelope of the tubular mesh. It can be seen that, when the adjacent tubular mesh forming rings are connected only by a link at only one point of the circumference of the metal tube, there is considerable freedom to move in relative flexure of a tubular mesh forming ring, with with respect to the next tubular mesh forming ring, adjacent. In fact, at the end, completely separate tubular mesh forming rings can be formed, and sandwiched between two layers of tubular graft material, so that the flexibility of the resulting tubular mesh graft, between two adjacent mesh forming rings, is limited. only by the rigidity of the graft material, and not by the material of the tubular mesh forming rings. However, for an uncovered tubular mesh, it is typical to provide a number of links between the adjacent tubular mesh forming rings, which is less than eight., by circumference, and frequently four per circumference. Then, said tubular mesh exhibits a multiplicity of closed loops of electrically conductive material, which extends within the externally time-dependent magnetic field of a machine for obtaining MRl images. There are closed conductive loops within each tubular mesh forming ring, and other closed conductive loops, which include portions of different, adjacent tubular mesh forming rings. Eddy currents will tend to flow in said loops. The precise distribution of eddy currents varies with the distribution of the links or joints within the tubular mesh forming rings, and between the adjacent tubular mesh forming rings. However, the previous proposals to expose the lumen of the tubular mesh to the MRl imaging, have involved the installation of one or more conductivity interruptions at some point on the circumference of each of the tubular mesh forming rings, closed loop The proposal of the inventors of the present is different. Suppose that each closed loop could be modified in some way (as the previous individual loop was modified to the figure of an eight), for example, to create within any of the closed loop portions in which eddy currents flow in one direction , that cancel exactly the effect of other portions in which the parasitic currents tend to flow in the opposite direction. The aggregate flow of eddy currents within said closed loop must be zero. It will be remembered that, in the figure of eight, by providing that the two lobes, that is, both halves, of the loop that has the shape of an eight, by means of the time-dependent Bi field, have an equal area, they extend in the same plane and are cut by the same direction and the same density of the incident field, each lobe "cancels" the other, so that the total flow of eddy currents induced in the loop that has the shape of an eight, is zero. In the previous discussion, the figure of eight is flat and the field -i is perpendicular to the plane that contains the two lobes. However, in a real tubular mesh, the lobes are not flat, but lie within the ring of the matrix of the tubular mesh. Looking from the end of the ring, and taking the upper part of the circle as a reference point "N", the lobes of the eight tab described above, are in a line parallel to the axis of the tubular mesh that runs to everything long axis and through the reference point N. Back to the piece of paper with red and green faces, imagine now the figure of eight wrapped on the cylinder of the tubular mesh, like a saddle on a horse, with the waist of the figure of eight coinciding with the reference point N, and a lobe on each side of the cylinder, touching almost the two lobes at point "S", at the other end of the diameter, with respect to "N". Think of a watch face, where N is 12. Then, S is six o'clock.

Consider now fields B-, incidents. One that is parallel to the axis of the tubular mesh does not "see" green or red at all. A BT field passing through the cylinder, perpendicular to the vertical diametrical plane that includes the reference points N and S, first "sees" an area of one color, when it enters the cylinder of the tubular mesh; but then, when it leaves the cylinder, it "sees" in the other color an area of equal size; on the other side of the vertical diameter, with respect to the first area. Thus, the figure of the eight "wrapped" or "wrapped" around the ring of the tubular mesh, is also a potential "balanced" loop. Note that there should be no crossing of the conductive trajectories in the waist of figure eight when moving from one lobe to the other (if there was one, then the Bi field, perpendicular to the axis of the tubular mesh, "would see" the same color of paper in both lobes through which passes successively, and then the two lobes would reinforce each other in the creation of parasitic currents). A modality that does not require the double thickness of a crossing point is clearly advantageous in the design of the tubular mesh. You have looked at two of the three orthogonal directions of an incident BT field. The third is the case of a B-¡field in the vertical diameter, which includes reference points N and S, and transverse to the longitudinal axis of the cylinder of the tubular mesh. It passes through an area that corresponds to the waist of the figure of eight, in N, but without said area in S, where the two lobes approach each other, but are not electrically united. If the waist area is large, then some eddy currents can be expected accordingly, because the area is not "balanced" in the sense explained here. In fact, with the tubular mesh struts arrays similar to those of conventional tubular meshes, the "waist" area can easily be confined to an area that fades to become small. Similarly, at the "opposite" point, at the waist, where the two "wrapped" lobes look at each other, they can easily separate at a negligible distance from a film of electrically insulating material. Obviously, said "wrapped" balanced coil can have: i) more than two lobes; and ii) it offers just as many tubular mesh forming functions as a tubular mesh with an analogous strut matrix, but which does not comprise any "balanced" spiral, as described herein The "wrapping" of a balanced loop around a mesh cylinder It is not confined to wrapping a loop in a plane transverse to the axis of the tubular mesh, but rather successive lobes of an endless loop can be arranged in a spiral path around the axis of the tubular mesh. explained above, the loop should consist of several lobes, where the area of the lobes cut by the Bi field on one side of the cylinder of the tubular mesh, is balanced by an equal and opposite lobe aggregate area, on the other side of the cylinder of the tubular mesh Two lobes, spaced 1 80 ° around the circumference of the tubular mesh ring is just the simplest example of the concept, with the tubular meshes created at From a laser-cut tube, the balanced turns will exhibit a plurality of lobes and may be arranged transverse to the axis of the tubular mesh, or spirally along it. In particular, a preferred arrangement is referred to in this application as the concept of "winding". According to the concept of winding, each of the endless loops spirals around the inner volume, preferably (although not necessarily) in an integral number of turns around the longitudinal axis of the tubular mesh. Thus, in a typical tubular mesh, a plurality of these "winding coils" defines a cage having a central longitudinal axis, and defines an interior volume that is tubular and centered on that axis. The tubular shape will often be cylindrical, although this is not necessarily the case. For example, it could have flared ends. At the circumference of the cage, in any cross section with respect to the length of the tubular mesh, co-operating portions of at least two of the winding turns constituting the cage will have to be found. A major advantage of both the "figure of eight" and the "wrapped" or "coiling" loops is that the canceling effect is independent of the orientation of the tubular mesh with respect to the direction of the B-i field. Thus, a tubular mesh that incorporates the concept does not form a Faraday cage whatever its orientation with respect to the B- field. Consequently, the damaging screen effects due to the Faraday cage are at least mitigated, if not eliminated. This makes said shaped tubular mesh to be particularly attractive, because the lumen or inner volume of the mesh can be imaged, using an MRl image forming machine, regardless of the orientation of the tubular mesh in relation to the direction of the field B- | . For structural integrity there may be connections between portions within each winding loop, and other connections between adjacent winding loops; and all these connections must include conductivity interruptions. It will be a special goal to reduce the number of electrically conductive links. The ability to install conductivity interruptions in these links will give the designer greater freedom to manipulate the mechanical properties of the implant thus formed. If these links do not have to include conductivity interruptions, then they can simply be formed from the material of the metal tube from which the implant is created. Otherwise, mechanical links can be contemplated, such as by forming brackets. If a link between adjacent winding loops will include a conductivity interruption, then it could be achieved by a layer of adhesive composition between cooperating shape adjustment portions, in the adjacent winding loops; or in a mechanical link that allows the relative movement of the two portions that form the link; an electrically insulating coating in one or both co-operating portions of the link. One way to provide said insulating coating is to deliberately build a sufficiently thick and robust oxide layer. Another way is by local deposition of a material, such as diamond-like carbon, on the surface portion of a link portion contacting a link portion of the adjacent winding ring. For a better understanding of the invention, and to show more clearly how the invention can be put into practice, reference will now be made, by way of example, to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram showing the principle of balancing eddy currents induced in two portions of a closed loop. Figure 2 is a schematic view of a part of an implant embodying the principle shown in Figure 1, open from a tubular configuration to a planar configuration. Figure 2A is a schematic view of the implant of Figure 2, not open to the planar configuration. Figure 3 is a schematic view of a balanced implant embodying the invention, which has been unwrapped along the major axis of the implant, from the tubular configuration to a planar configuration. Figure 3A is a schematic view of the implant of Figure 3, not open to a planar configuration. Figure 4 is a schematic view as in Figure 3, and showing four balanced strut loops, with insulating connections within the loop and between the loops. Figure 4A is a schematic view of the implant of Figure 4, without opening it to the flat condition. Figure 5 is a schematic view as in Figure 3, of a geometry that can be used to produce closed, balanced loops with insulating connections within the loop and between the loops. Figure 5A is a schematic view of the implant of Figure 5, unopened to the planar condition. Figure 6 is a perspective view of two tubular mesh forming rings, composed of struts arranged in a zigzag pattern, and in their radially small configuration, before deployment; and ring-to-ring connecting portions. Figure 7 is a perspective view of two tubular mesh forming rings, shown in Figure 6, but separated from one another. Figures 8 to 10 are schematic views of constructions for connecting portions. Figures 1 to 24 are isometric views of various joint constructions, in which: Figures 12 to 14 include a retaining strut; Figures 15 to 18 include a cord link; Figures 19 to 22c show a formed connecting piece; and Figures 23 and 24 show a mutual mechanical assurance between cooperating portions of the adjacent parts of the implant.

Figure 25 is a copy of Figure 4 of the applicant's WO 01/31 02; and Figure 26 is a portion of a tubular mesh matrix, in a side view, showing two forms of insulating gasket, in one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Typically, a tubular mesh is formed of metallic wire, or of a tubular matrix of metal struts, formed from seamless tubular material, or from rolled flat sheet material. Although the following description refers only to expandable tubular meshes, supplied transluminally, the principle of the present invention can be applied to medical implants in general, different from transluminal tubular meshes; such as implants installed in a body lumen by open surgery, filters, such as vena cava filters, fluid flow measuring devices, valves, such as heart valves or venous valves, etc. To prevent parasitic currents from flowing, it has been an alternative to eliminate the conductive links between the adjacent tubular mesh forming rings, which form the tubular mesh. However, this physically weakens the tubular mesh, so that it may not function properly, for example, it may not deploy properly and, once deployed, may not be strong enough to withstand arterial pressures. The connection of tubular mesh forming rings, by means of insulating joints, imposes additional manufacturing tasks and extra compliance charges with the regulatory authorities. The present invention is directed to reduce eddy currents, without unacceptable loss of operating capacity, by means of designs that are "balanced" electromagnetically with respect to an external field of MRl dependent on time. In the following, this category of tubular mesh is called tubular mesh "of balanced coil". The purpose is that any closed loop, electrically conductive, inside the tubular mesh, have opposite portions, so that the parasitic currents that are generated in one portion, are opposite to the parasitic currents that are generated in another portion of the closed loop. In this way, the two portions of the loop cancel or balance each other, and no eddy currents flow. Figure 1 illustrates an example of said geometry ("figure 8") to reduce, even eliminate, eddy currents that are induced in a metallic tubular mesh matrix, when exposed to a time-dependent magnetic field. The time-dependent magnetic field (field B ^ of an MRl imaging apparatus in Figure 1 is perpendicular to the plane of vision and goes to the page) A conductive loop 300 (solid line), which is part of a matrix of Metallic tubular mesh, can be divided into two parts, which are called "lobes"; namely: the portion marked "I" and the portion marked "I I". The currents induced in the loop 300 are indicated by dashed lines with arrows. Field B ^ induces levorotatory currents in both portions of loop 300; but due to the geometry of the loop 300, a levorotatory current in the "I" portion will flow as a right-handed current in the "I I" portion and vice versa. Thus, the two currents oppose each other, and the total amount of the current flowing through the loop 300 is reduced, even eliminated. The use of said "balanced" coil in the matrix of a tubular mesh can reduce, or even eliminate, the damaging effects of the Faraday cage screen, which undergo conventional tubular mesh matrix designs, in an MRl apparatus. With the present invention a tubular mesh can be formed from numerous separate loops, which are insulated from each other, and where each of those loops exhibits a "balanced" configuration, so that it reduces, or even eliminates, the total electromagnetic effect of the cage of the tubular mesh. Figure 2 illustrates a schematic view of part of a tubular mesh design, wherein each of twelve closed lobes, of multiple lobes, is elongated parallel to the lumen length of the tubular mesh. Thus, each of the loops forming the tubular mesh matrix is "balanced". The horizontal axis in Figure 2 represents the distance from one axial end to the other axial end of the tubular mesh; while the vertical axis represents the angle around the circumference of the tubular mesh. In such a manner, Figure 2 illustrates the tubular mesh in the planar configuration. Because the angular range goes from 0o to 120 °, only one third of the entire circumference of the tubular mesh is shown open to a flat condition, in Figure 2.

Each of four individual loops 300A, 300B, 300C, 300D, has a longitudinal direction parallel to the longitudinal axis of the tubular mesh, and extends the entire length of the tubular mesh 1 00. Figure 2 shows only part of the matrix of the tubular mesh. In total, the tubular mesh has twelve of these individual loops, arranged regularly around the circumference of the tubular mesh, so that the tubular mesh, in cross section, exhibits a regular dodecahedron configuration. Figure 2A shows this, and reveals the circumferential extension of 120 ° of the matrix portion of the tubular mesh, shown in Figure 2. The two upper loops 300A, 300B of Figure 2, illustrate one embodiment of the torsion required for obtain the "balancer" effect, and the two lower loops 300C, 300D show an alternative mode of twisting. In the two loops 300C, 300D, advancing along the wire on one side of the loop, from one end of the tubular mesh to the other, one side is always "on" or always "under" the wire on the other side, at each crossing point. However, in the loops 300A, 300B, following the same advance, one alternately passes over and under the wire of the other side, at each successive crossing point. However, in the work modes, a tubular mesh will similarly incorporate all the loops with the same torsion pattern, either that of the loops 300A, 300B, or that of the loops 300C, 300D. In the loops 300A and 300B, the length portion 400 is at the crossing points 600 alternately above and below the length portion 500. The loops 300A, 300B thus form what could be termed a "braided" tubular mesh loop. or ntra-coupled, which can be formed by unidirectionally twisting one end of a wire rectangle with respect to the other. Conversely, the crossing arrangement of the 300C loops, 300D could be obtained by simply "bending" half the length of each closed loop on the other half, so that all the zigzags of the second half of the length of the loop are above the zigzags of the first half of the length. The circles shown in Figure 2 indicate insulating connections 600, in which portions 400 and 500 of each individual loop are fixed together, in order to prevent undesired movement of those loop portions. Given the "braided" arrangement of the loops 300A, B, there should be less tendency for unwanted relative movement, so that there would be less need to fix each crossing point with a connection. The loops are held together by electrically insulating connections 800, from loop to loop; so that it may be possible to omit loop 600 connections within each loop. Portions 400 and 500 of a closed individual loop, however, must be electrically isolated from each other at each crossing point, along the entire length of that loop. Another possibility for not having to use the connections 600 within the loop, is to use a wire 200 that is woven above and below the loop sections 400 and 500, at the electrically insulating junctions 600; and fixing both ends of the wire 200 to the axial ends of each of the loops, to hold each loop together. Various methods are possible for isolating the crossing points, such as by inserting an electrically non-conductive element between the overlapping portions of each of the loops, or by coating the overlapping portions with a layer of non-conductive material. It is also contemplated to reduce the thickness of each of the overlapping portions locally at the crossing points, in order to avoid a double wall thickness of each of the loops at said crossing points. Another embodiment of a "balanced" design, which is referred to herein as a "winding" tubular mesh is illustrated schematically open in Figure 3, and not open, flat, in Figure 3A. The "winding" tubular mesh design consists of four closed, conductor strips, 120A, 120B, 120C and 120D; each of which spirals around the longitudinal axis of the tubular mesh. The vertical axis in Figure 3 indicates the longitudinal direction of the tubular mesh. The horizontal axis in Figure 3 indicates the winding angle at which each of the loops 120A, 120B, 120C and 120D is wound around the longitudinal axis of the tubular mesh. This "roll-up" tubular mesh approach, of course, is not limited to four strut loops, and the roll angle is not limited to that shown in Figure 3.

In Figure 3, four loops 120A, 120B, 120C and 120D are shown, which are insulated from one another in the positions of connecting joint 125 indicated by circles. Each loop is wound helically around the longitudinal axis of the tubular mesh; that is, they form a spiral around the tubular mesh. In this case, the length of each loop is such that it forms a spiral around the tubular mesh of 720 °, as shown more clearly in Figure 3A. To minimize the generation of eddy currents, regardless of the direction of the incident magnetic field, the winding angle must be an integer multiple of 360 °. The illustrated tubular mesh is made up of struts 4 mm long, with a length of 95 mm (24 struts). A zigzag tubular mesh forming ring, with 48 struts, also extends around the 360 ° circumference of the lumen of the tubular mesh, at any point along the entire length of the tubular mesh. For other tubular mesh lengths, other numbers of struts and other lengths and other numbers of loops will be indicated in the same way. Each loop consists of a multiplicity of metal struts joined end to end to create a zigzag pattern, which is wound around the longitudinal axis of the tubular mesh. Those portions of each of the four loops 120A, 120B, 120C and 120D, which are located at the same distance, for example, from the lower axial end of the tubular mesh matrix, are indicated in Figure 3 by row 1 , row 2, row 3, row 4, etc. The portion of the loop 120A in Figure 1 and the portion of the loop 120A in row 4 are on opposite sides of the tubular mesh matrix; that is, they are arranged 180 ° apart from each other. Two adjacent rings of 24 struts form a tubular mesh forming ring of 48 struts, or "row", with a circumference of 360 °; and each of said rows includes struts of each of the four winding loops. The tubular mesh has twelve such rows, and twelve tubular mesh forming rings within the total length of about 96 mm, so that each ring of struts has a length of 4 mm; each row a length of 8 mm (and each tubular mesh forming ring, a length of 8 mm). In a conventional tubular mesh, made of a tube, each tubular mesh forming ring is a closed, electrically conductive loop. By installing electrically insulating interruptions between the winding loops of the present invention, the creation, in the matrix of the tubular mesh, of the electrically conductive tubular mesh forming rings, of a conventional tubular mesh is avoided. With respect to loop 120A, the portion in row 1 and the portion in row 2 are electrically connected to a pair of parallel links 202, 204, which are insulated from each other. There are analogous, electrically insulating links 125 between the facing portions of the adjacent closed loops 120A, B, C, D. An alternative way of obtaining a "tubular winding mesh" is illustrated in Figure 4, which shows a mesh tubular consisting of four curl loops, each of which has six lobes. Figure 4 shows only a portion of the length of the implant. The entire implant needs to have a length such that each lobe of each loop has an equal and opposite "associated" lobe, which is disposed 180 ° apart from it, on the opposite side of the tubular mesh. Figure 4 is a schematic view showing four separate loops 140A, 140B, 140C and 140D, which are wound helically in the longitudinal direction about the axis of the tubular mesh. The vertical axis indicates the distance from one axial end of the tubular mesh to the other; while the horizontal axis indicates the angle to which each of the loops 140A, 140B, 140C and 140D is wound around the axis of the tubular mesh. Each loop is made up of zigzag metal struts, joined end to end with full electrical conductivity. The struts that make up a single zigzag line of one of the loops are electrically connected to the next zigzag adjacent line of the same loop, by a pair of parallel struts, insulated from each other and marked in FIG. 4 by the circles 126B. Additionally, portions of each winding loop are connected to portions of the adjacent winding loop in the same row, by a pair of parallel struts, indicated again by circles 126A. In other words, the tubular mesh matrix shown in Figure 4 has connections within the loop and between the loops; all of which include an electrical conductivity interruption, and are indicated by the circles of Figure 4. The insulating connections within the loop, within each of the loops, and the connections between the loops, between adjacent loops, extend in a trajectory that spirals around the longitudinal axis of the tubular mesh (in figure 3 they remain in equidistantly spaced diagonals). Following a hypothetical trajectory from an insulating board marked with a circle, to a neighboring insulating board, marked with a circle (see the dashed lines in Figure 4), there is at least one pair of struts 128A, 128B, which have been cut. in transverse direction, which makes a strong contrast with the design shown in figure 3. These additional cuts can increase the flexibility of the tubular mesh matrix, both in the longitudinal direction and in the transverse direction with respect to the matrix of the tubular mesh. Figure 4A more clearly reveals that each winding loop of Figure 4 is less wrapped than a full turn of the cylinder circumference of the tubular mesh matrix; in fact, only a quarter of a turn is wrapped from one end of the cylinder to the other. An implant having approximately four times the length of the portion of figure 4, satisfies the requirement of equilibrium of eddy currents, when each lobe of the loop has a corresponding and opposite lobe, to balance the currents. Referring now to Figure 5, this figure of the drawings illustrates a tubular mesh "winding" design, with only two closed loops 160A, 1 60B, which spiral around the longitudinal axis of the tubular mesh. Again the vertical axis in Figure 5 indicates the distance along the axial length of the tubular mesh; while the horizontal axis indicates the angle through which each of the loops has advanced around the longitudinal axis of the tubular mesh.

Figure 5 reveals that each of the two winding turns of Figure 5 extends around 450 ° circumference of the tubular mesh cylinder. The length of the tubular mesh is 48 mm, consisting of six tubular mesh forming rings. Obviously, a reduction in the length of the tubular mesh cylinder to 40 mm, and five tubular mesh forming rings, instead of six, would leave each winding loop extending exactly around one turn around the lumen of the tubular mesh. However, the winding turns of Figure 5 provide a "balanced" configuration because the lobes of each winding turn exhibit equal and "opposite" areas in terms of their parasitic current generating capacity. The small circles superimposed on the tip matrix in Figure 5 indicate both insulating connections within the loop and between the loops. In contrast to the tubular mesh design shown in Figure 4, transverse insulating connections are provided within the loop and between the loops, imparting additional rigidity to the design of the tubular mesh, particularly in the longitudinal direction. By selectively incorporating longitudinal and transverse insulating connections, both within the loop and between loops, structural rigidity can be altered as required, but the effects of a "balanced" design are maintained. The aspects shown in Figure 4 and Figure 5 are not limited to a tubular mesh matrix comprising four loops and two loops, respectively; they can be modified and combined, if necessary. The following is a description of how insulating connections can be made, in general, and in particular the insulating connections within the loop and between the loops; and therefore, reference is made to the applicant's previous international applications No. WO 01/32102, WO 02/15820, WO 02/047575 and WO 03/075797, all incorporated herein by way of this reference. In the illustrated modes, the tubular mesh is made of Nitinol®, a nickel-titanium alloy with shape memory. In other embodiments, the tubular mesh could be made of stainless steel or any other biologically compatible conductive material, capable of performing a tubular mesh function. It is conventional to form the network pattern of the tubular meshes of Nitinol® by laser cutting. The cutting of the cooperating frustoconical surfaces of the body portion of the tubular mesh is obtained by aligning the laser in the normal, ie radial, direction, thus intersecting the longitudinal axis of the tube of the tubular mesh. Once the slits in the workpiece of the tubular mesh tube are cut, most, but not all, of the vertices that axially connect two adjacent rings of the tubular mesh tube are separated; and only a few are left connected, in order to maintain an integral tubular structure of tubular mesh. The smaller the number of connected vertices, the greater the potential for the tubular mesh to bend out of a straight line when it is advanced along a tortuous path to the site of the elastic prosthesis. Additionally, the flexibility of the tubular mesh after deployment is also increased. As can be seen in figure 6, taken from the previous application WO 03/075797, the junctions 12 connecting two adjacent vertices 12A, 12B, at two ends of a tubular mesh ring 4 that look at each other, have a length that it is not zero, which, in turn, makes the overall structure in a radially compressed configuration more flexible so that it can be advanced more easily along a tortuous path within a lumen of the body. Figure 7 shows in more detail how the individual rings 4 of the tubular mesh are connected to one another. Here the cylinder of the tubular mesh is shown in its radially compact arrangement. In particular, attention is directed to the construction details of the connection points, that is, the junctions connecting the vertices 12A, 12B of the two adjacent rings 4. Figures 6 and 7 illustrate two zigzag rings 4, which comprise connecting struts 14A, 14B at both axial ends of each of the rings 4. All the connecting struts include a straight portion provided to increase the axial flexibility of the tube. the tubular mesh. The protruding portions of the connecting struts 14A, 14B can be classified into male portions, which have an arched head portion 16A, and female portions that have an arcuate recess portion 16B. The female portions comprise internal abutment surfaces for receiving the complementary arched male head portion. Both male and female portions have a frustoconical shape, a consequence of the laser cutting process, as described in WO 03/075797. Thus, due to the complementary male and female portions, they represent a shape adjustment when they are connected to each other, which gives the male and female portions excellent connection security and in this way, the joints are self-centering and self-centered. Aligners. Additionally, the main luminal and abluminal surfaces, outside which the arcuate head portion and the arcuate collapse portion are formed, share the same radius of curvature as the main surfaces of the zigzag rings. However, this does not necessarily happen when the cylinder of the tubular mesh is initially cut with laser from the flat sheet material. The number of these co-operating male and female portions in the adjacent zigzag rings is not limited to the number shown in Figure 6. The proportion of cooperating portions to hollows, i.e., the points at the axial ends of the rings in the that the connecting struts 14A, 14B are cut during the laser cutting process, can be up to 1 to 5, or even 1 to 6, depending on the design of the mesh structure used for the tubular mesh. It goes without saying that the number of male portions corresponds to the number of female portions. However, the number can be easily changed during the manufacture of the tubular mesh tube. It has been found that the heat generated during the laser cutting process oxidizes part of the metal surface, both of the male and female fitting portions, so that both portions are electrically isolated from each other in the assembled state. This oxide layer provides a portion of reduced or virtually zero electrical conductivity, which is effective to improve the MRl imaging of the lumen of the tubular mesh. The technology described in WO 03/075797, and the summary in the above passages, can be adapted to the provision of connections between the loops and connection within the loop, within the embodiments of the present invention. The experienced reader will appreciate that other additional ways or ways of providing portions of reduced conductivity between the two cooperating portions of two adjacent rings are conceivable, such as immersing one or both of the cooperating portions in an oxidizing agent, or irradiating one or both of the cooperating portions with a laser, thereby generating enough heat to oxidize its metal surface. It is conceivable that the oxide layer that occurs naturally on the surface of the metallic tubular mesh could be sufficient to provide the conductivity interruption, especially when the two cooperating portions are not in physical contact with each other.; so that there is a small gap between them. The thickness of an oxide layer generated by laser depends on the period of time and the intensity of the laser used for the irradiation of one of the cooperating portions. The thickness of this oxide layer must be sufficient so that, when the current induced by the external magnetic field exceeds a certain level, an inrush of current between two adjacent rings does not occur. The experienced reader will also appreciate that other ways of connecting two adjacent rings are obtainable. These alternatives include hook-type, plug-and-socket connections, tongue-and-groove type connections, pin-sleeve connections, clamp-on devices, glue-type connections, hinged-type connections, which further increase the axial flexibility of the tube. of the tubular mesh, eye-type and female-type connections, in which a female is fed through respective eyes at the axial ends of the rings and then the two ends of the thread are knotted to the eyes of the rings to keep together the Rings. It is also conceivable to use sleeves for connecting connecting struts projecting axially from two adjacent rings, thereby providing a tubular mesh structure in which there is no axial connection of two adjacent rings, except for the sleeves. The sleeves may be made of a material having low electrical conductivity. The protruding connecting struts of two adjacent rings may comprise the shape of a bone-like structure, that is, the diameter of the protruding portion increases toward its axial end. See figure 10, which is described below. When the male form fit portion is inserted into the female shape fit portion, these two portions remain together when the radial expansion of the tubular mesh tube is performed, solely because of its complementary fit. The male portion is inserted into the female portion radially inward, due to its radially tapered shape, so that, during radial expansion of the tubular mesh forming rings, the female portion can push the male portion radially outwardly, thereby pressing the male head portion further inwardly into the female sunken portion, against the internal stop surface recessed from the female portion. The friction between the complementary male and female portions can help improve the rigidity of the connection (see WO 02/15820). However, this effect is more susceptible to application in balloon-expandable tubular meshes, than it is in self-expanding tubular meshes. In self-expanding tubular meshes, when the tubular mesh is deployed by proximate proximate extraction from a sheath or outer sheath that confines it, the angle between the liberated portion and the undraped portion of the tubular mesh may be large enough to spring-off the strut coupling that unites the male and female portions, at the moment that is released from the sheath. A biocompatible adhesive may be used, although not necessary, to permanently fix two adjacent rings together. If the biocompatible adhesive is also non-conductive, the extra layer of oxide created can be omitted, for example, by immersing at least one of the ends of the two complementary form fitting portions, within an oxidizing agent. Suitable adhesives may include polymer-based adhesives, such as parylene, acrylate, silicone, PTFE and stable or biodegradable adhesives. An example of biodegradable adhesives includes lactide acids. It is believed that biodegradable adhesives are advantageous in that they make the structure of the tubular mesh more flexible after deployment, and once the biodegradation process has begun. It is also contemplated to coat the joining struts that protrude axially, with a non-conductive coating. Suitable coatings include diamond-like carbon (DLC), SiC, SiO2 coatings or ceramic coatings. The connection between two adjacent rings by means of two joint connecting struts, which look at each other, can be obtained by using the adhesive or the coating itself as a linker, or by bringing the joining struts to be very close to each other, so that a gap between them, for example, using a cuff; with which it is ensured that there is no direct contact between the joining ends neither inside nor outside the sleeve. However, this does not exclude that an adhesive or a coating is applied to the connected connecting ends. Methods for applying an adhesive and / or a coating include: physical vapor deposition (PVD), implantation, injection, dipping, welding, solder welding, brass welding, plasma deposition, flame spraying, etc. However, an experienced person will appreciate that other adhesives and coatings are conceivable as well as other methods for applying them. The joint between two adjacent tubular mesh forming rings, or even the adhesive itself or the coating itself, can be used as a carrier for drugs that inhibit restenosis. The drugs can be incorporated into the adhesive and / or the coating, and they will be released from it in dosed form, so as to prevent the occurrence of restenosis within the lumen of the tubular mesh. In figure 7, two tubular mesh forming rings in unassembled state are illustrated. As can be seen, the two male and female complementary shape adjustment portions are able to tightly fit together with reduced conductivity between them. The luminal surface of the joints 12 is flush with the luminal surface of the tubular mesh forming rings. However, this is not crucial to carry out the inventive concept. The luminal surface of the joints can be located radially inward with respect to the luminal surface of the tubular mesh forming rings. However, in order to provide unobstructed fluid flow through the lumen of the tubular mesh, the luminal surfaces of the junctions should preferably be flush with the luminal surfaces of the rings. Figure 8 shows a connecting joint between two connected tubular mesh forming rings, with complementary shape and fitting male portions, forming the joint between two tubular mesh forming rings, according to another preferred embodiment of the invention. The shape-fitting female portion is in the form of a fork 22 for receiving the male shape-fitting portion 24 within the depression at the center of the fork. Due to the laser cutting process, both male and female form fitting parts are frustoconical in shape. There is a separation between the male portion and the female shape adjustment portion. If a laser is used for cutting, the size of the male and female shape-fitting portions essentially corresponds to the dimension of the focus of the laser beam. However, the male and female shape adjustment portions can be produced separately, in which case the spacing between them can differ from the dimension of the laser focus. This separation must be taken into account to increase the flexibility of this type of structure. A through hole, drilled by laser, extends through the male and female shape-fitting portions, so that both through holes are aligned, in order to allow a pin 26 to be inserted through them, to fix the male portion of shape fit in the female shape fitting portion. The through holes can be created by means of a laser beam punch, either under manual control, under a microscope, or automatically, under the control of a microprocessor. It is preferable that the pin has a surface made of an electrically insulating material, such as an oxide layer. Also contemplated is the use of pins 26 made entirely of non-conductive material, such as polymer-based materials, ceramics, etc. Figure 9 shows another preferred embodiment of the connector joint used in the invention of the present application. Two tubular mesh forming rings are connected by means of cooperating portions 32, 34; both mesh forming rings are complementary in shape and have a through hole, through which a pin 36 can be inserted, so that the joint functions as a hinged joint. Again, due to the focus of the laser beam having a finite width, there is a gap or gap between the two complementary portions when connected; so that the connection allows a certain degree of pivotal movement when the tube of the tubular mesh is advanced along a tortuous path, within a vessel of the body. Each hinge pin 26, 36 can be mechanically fixed to the respective ends of the two complementary cooperating portions, such as by glue, or they can be fixed in some other way. Again the cylindrical surface of the pin is preferably electrically insulated. Figure 10 shows connecting struts 42, 44, provided with a bulbous cantilevered end 46, 48, respectively, and surrounded by a shrinkable sleeve 50. Each of the bulbous ends is treated to impart an oxide insulating layer 52, 54. The functional joint similarly to the knee joint. An experienced reader will understand that the various electrically insulating possibilities described above and in figures 6 to 10, and in the applicant's prior application WO 02/047575, are available to be applied to any of the sites in any of the described implants. further back, and with reference to figures 1 to 5 of the accompanying drawings. Among those possibilities are: i) mechanical friction adjustment devices, such as press fit for smaller size; the use of a thermal expansion effect; spring effects, the use of coatings and additives to change the friction properties of the surface; ii) mechanical interlocking devices, such as the use of tapered surfaces for basketed devices, or plastic deformation of portions, such as by twisting, to mutually locked portions; iii) the use of an additional component part of the joint, such as a micromolding plastic component, which is to be staked with heat or ultrasonically welded, laser welded or friction-adjusted in place; or the use of threads, fibers, fibrils or powder or polymer film, to join adjacent metal surfaces; iv) encapsulating the adjacent metal portions in the joint, such as by overmolding or other use of a form of containment around the joint, or by coating the joint with powder, and then subjecting it to laser concreting, concreting and surface fusion of a ceramic powder or cure of a resin by means of laser in a bath of the resin; v) welding by high resistance points in the joint; vi) connection by welding with brass, with a ceramic filling; vii) doping of the adjacent loop portion to join it in the joint. Within the scope of the present invention is contemplated a tubular implant formed by a sequence of three rings, in which the intermediate ring (which could be termed the "stuffing" in the "sandwich") is made of electrically insulating material, and the rings radially internally and externally to the intermediate ring are made of electrically conductive material. In that way, the outer rings contain the conduction paths necessary for the creation of the balanced turns of the present invention, while the intermediate ring provides the insulating mechanical connections between the separate electrically conductive paths. Conducting junctions are contemplated through the insulating ring to conduct electrically conductive path portions within any balanced turn. Various ways of forming the three-ring sandwich construction are contemplated. It can be started with a flat material, creating in it a network of conductive joints, then winding the device thus prepared, to create a tubular device according to the present invention. Otherwise, it can be split with a tubular material and create within it the balanced turns required by known techniques, such as laser cutting or chemical etching. See, for example, WO 96/033672 for an example of two conductive rings separated by an expanded polytetrafluoroethylene ring. The drawings of figures 12 to 24 reveal additional ideas for joint constructions; specifically proposing to form the joints in constructions such as the embodiment of Figure 5, in which two "joint categories" can be perceived. With reference to Figure 5, and moving along the horizontal axis, between 0 ° and 360 °, there are eight rows of joints, spaced at 45 ° angles around the 360 ° circumference of the tubular mesh. Each of these rows incorporates both kinds of board. The joints 150A lie between the adjacent side-by-side portions of any two different different closed loops or two portions of the same closed loop, within the tubular mesh matrix. In contrast, each joint 150B is between the nose-to-nose vertices of the adjacent zigzag tubular mesh forming rings. A joint of the category 150B between the nose and nose vertices of the following adjacent tubular mesh forming rings is a regular aspect of the tubular meshes formed by zigzag tubular mesh forming rings, and said joints are discussed in the context of Figures 6 to 10 of the present. The joints of the 150A category between the struts from side to side, are rather different, at least with respect to the tension pattern that said joint will experience during the deployment and use of the implant. Consequently, it is advisable to think again how such joints could be incorporated very attractively. Now back to other figures in the drawings, some of the joints indicated above are suitable for nose-to-nose connections, such as 150B, and others are more appropriate for a side-to-side connection, such as 1 50C in Figure 5. Thus, nose-to-nose connections are shown in Figures 12 to 16, 19 to 21 B and 24 of the drawings, while side-to-side joint connections can be seen in Figures 14, 17, 1 8, 22 23 of the drawings. One of the stimuli for the development of the new joint structures is the perception that the longevity and properties of the adhesives are not predictable. Any chance that a device can disassemble after deployment in the body is adverse. This is particularly difficult if, when such disassembly occurs, the parts of the implant move relative to other parts in such a way that the lumen into which the implant has been deployed could be occluded by any part of the disassembled device. However, in order to make effective joints available that are not (only) based on adhesive, as for example, the joint illustrated in Figure 11, a certain degree of three-dimensionality is indicated. The applicant is particularly interested in implants made of nickel-titanium alloy with shape memory. Initial experiments suggest that an implant with a wall thickness of 240 μm could be thinned or compressed locally to form a joint, up to a thickness of around 100 μm. This opens up many possibilities, as will be seen below. Returning first to FIG. 12, between the facing protuberances 60, 62 of the adjacent zigzag tubular mesh forming rings, a gasket is provided which places parallel fingers 64, 66 on the protuberance or nose 62, within the interdigital spaces between three parallel fingers 68, 70, 72, in the nose or protuberance 60. It will be appreciated that said structure multiplies the surface area of the bond with adhesive between the protuberances 60 and 62, for any given gap length between these two protuberances Additionally, adhesive joints are relatively weak in the detachment mode; but the interlocking finger design of Figures 12 and 13 is relatively resistant to any detachment, because the kind of stresses that would lead to detachment are resisted by outer fingers 70 and 72, which encapsulate the surfaces attached with adhesive. However, for greater security against disassembly, a retainer strip 74 may be added on the abluminal surface of the joint, and a similar strip 76 on the luminal surface of the joint. The material of the tubular mesh forming rings, in the form of a zigzag, can be made thinner between the protuberances 60 and 62, in the vicinity of the mutually locking fingers, in order to accommodate the strips 74 and 76, within a More or less general wall thickness of the device. As for the electrical insulation, it will be appreciated that the surfaces of the fingers that lock together can be electrically isolated from the fingers of the other component. As for the strips 74, 76, these could be made of metal and be welded to the outer fingers 70 and 72, and could even be welded to the intermediate finger 68, at the same time as they do not allow electrical contact between the strip 74, 76 and any of the fingers 64, 66. A coating of formable material is contemplated for surface uniformity, between the protuberances 60 and 62, and around the strips 74 and 76, to obtain a uniform surface contour, and to increase the resistance of the board. Now back to Figure 14, an analogous joint for a side-to-side joint point is illustrated, instead of a nose-to-nose joint point. The material protrudes from the facing surfaces of the adjacent parallel portions of the implant, and incorporates a wall thickness somewhat smaller than the overall wall thickness of the implant.

The protruding portions incorporate a dovetail joint between the portions 80 and 82 (and it will be appreciated that the surfaces of the dovetail are treated so as not to allow electrical conductivity through the tail joint of milano). As in Figure 13, a strip 84 can be provided through the dovetail joint on the abluminal surface of the device, and a similar strip (not shown) can be provided on the luminal surface; thus making negative any possibility that the male part 82 of the dovetail will slide out of the female portion of the dovetail, in an upward or downward direction, when seen in Figure 14. Again like in figure 13, the joint could be "encapsulated" in a formable material, which is electrically insulating, in order to confirm and reinforce the integrity of the joint. In continuing with the drawing of Figures 15 to 18, it is seen that these show variations on the subject of using a cord 90 to connect nose to nose, as shown in Figures 15 and 16, or portions side by side, as shown in FIGS. shown in FIGS. 17 and 18. In FIG. 15, locally thinned or compressed portions 96, 98 are disposed in close proximity from end to end, with cord 90 in the form of a closed loop covering the gap 1 00 the parts of nose implant with nose. The cord is conveniently a high strength polymer that can be welded so as to form the closed loop, after the cord has been passed through the holes 102 and 1 04, in the thinned portions 96 and 98, respectively. As with the embodiments described above, the entire joint area between the protuberances 60 and 62 can be "encapsulated" with an electrically insulating polymeric material, to reinforce the seal and confirm the electrical insulation between the protuberances 60 and 62. In Figure 16 each the thinned portion 96, 98 is provided with a pair of perforations 1 06, 1 08, with equal spacing, so that they can be arranged aligned, so that the cord 90 passes through the perforations 106, and then through the perforations 108, before being connected end to end, to form the closed loop of cord, which holds together the protuberances 60 and 62. Again the joined area can be encapsulated in formable polymeric material, to maintain the electrical insulation and the integrity of the board. Note the direction F that is indicated by the arrow in figure 16. When looking at figure 16, the abluminal surface of the implant is the upper surface seen in the drawing. The arrow F indicates the direction of deployment of the implant (by removal of a confining sheath in a direction opposite to arrow F), with the consequence that the zigzag tubular mesh forming ring, which includes the protrusion 62, is released by the retaining sheath before the sheath lightens the zigzag ring that includes the protrusion or nose 60. Accordingly, the tendency of the nose 62 to expand radially away from the nose 60, is resisted by the thin portion 96 remaining above. of the thin portion 98, radially outward from it. Thus, the stresses carried by the board during deployment of the implant are carried by the metal of the zigzag rings, rather than by the cord polymer 90. It will be appreciated that, if the thin portion 98 were overlapping the thin portion. 96 in Figure 16, and then the sheath is removed from right to left in Figure 16, with the implant deploying in the direction shown by arrow F, then it would pass to bead 90 the responsibility to retain the integrity of the joint when the nose 62 seeks to move upward (radially outward) relative to the thin portion 96. Since the implant is constructed in such a way as to work for the inherent strength of the overlapping joint shown in Figure 16, it must be more elastic to the forces carried by the implant during its deployment and loading, than the butt joint of figure 15. In both cases it is contemplated that the local thinning of the wall thickness of the implant for portions 96 and 98 would be 250 μm at about 50 μm on each side of the center line of the wall thickness; then serving a 50 μm diameter cord to join the two thinned portions. As for the flap joint of Figure 16, thinned portions that overlap each other, each of which has a thickness of about 50 μm, are contemplated for a general implant wall thickness of 250 μm. By now observing the cord systems for joining the side-to-side portions of the implant, a bead 90 is seen attached in Figure 17, for example by welding, to be formed into a closed loop, which sits in a locally formed depression. in adjacent portions side by side 92 and 94 of the implant. Typically, the implant has a wall thickness of 250 μm, the cord has a diameter of 50 μm, and the sags to receive the cord have appropriate dimensions to tightly accommodate the cord. Again, the joint area will be filled with adhesive or other formable polymer composition, to confirm the electrical insulation between the portions 92 and 94, and to improve the strength of the joint. It will be appreciated that it is not necessary for the cord to be made of electrically insulating material, provided that insulation can be provided between the conductive cord 90 and each of the portions 92 and 94 of the joint from side to side. Figure 1 8 offers the possibility of using a cord 90 of greater diameter and, therefore, of greater strength. Each of the portions 92 and 94 side by side is formed with a depression 1 10 on its luminal surface, and a stepped depression 1 12 on its abluminal surface; having an elongated slot 1 14 through the wall thickness of the implant and extending into each of the depressions 1 10, 1 12. Of that maneara, as seen in figure 18, there is space within the wall thickness total for a bead 90, even with a diameter of about 1 00 μm, without unacceptably weakening the mechanical strength of the side-to-side portions 92 and 94 of the joint area. Again, once the joint has been formed, the joint area can be filled with a formable, electrically insulating material, to maintain electrical insulation between the portions 92 and 94, and to increase the strength and integrity of the joint. Figure 1 9 offers an elegantly simple alternative for the cord 90 of Figure 15. Instead, a formed connecting piece 1 16, with a through groove 1 1 8 (or two blind grooves separated by a core) to receive the grooves. thin portions 96 and 98 may be offered to the facing protuberances 60 and 62, and then heated so that the material of the connecting piece 1 16 flows into the respective holes 102 and 104 in the thin portions 96 and 98. By cooling the connecting piece 1 16, a mechanical mutual locking is obtained which has high electrical insulation between the protuberances 60 and 62. Figures 20A and 20B show an alternative connecting piece 160, incorporating a central stop 162, and a pair of projections 164, 1 66, one on each side of the central stop. Each projection receives a respective hole of the holes 102, 104, in the relatively thinner portions 96, 98 and, when the thin portions are firmly seated in the connector part 160, the respective heads of the projections 164, 166 can be pressed and heated, so that the heads are on top of the flat surface of the thinned portions 96 and 98, so that they function in the manner of rivets. The embodiment of Figures 21A and 21B is effective without thermal formation. Rather each nose or protrusion 60 and 62 is provided with respective depressions on its luminal and abluminal surface, to receive corresponding arm portions 171, 172; each side of a central divider 162 in a connector piece 174, evidently functioning much like an office paper fastener, for retaining in its desired configuration end-to-end, the two protuberances 60 and 62.

As for a joint between two portions extending side by side, analogous to FIG. 17, consider FIGS. 22A, B and C. The two portions 92 and 94 are locally thinned on the larger surfaces abluminal 1 80 and luminal 1 82 of the implant, to accommodate the wall thickness of a connecting piece 184, around a pair of parallel holes 186 running along the connecting piece 1 84. Between each hole 1 86 and the corresponding side wall surface 190 of the connector piece 184, there is a slit 188, so that the deformation of the material of the connecting piece 184, on each side of the central insulating core 162, allows the connecting piece to pass over the corresponding thinned portions 180, 182 of the respective portions of side with side 92 and 94 of the implant. It will be appreciated that the connector piece 184 can be considered as a "double C piece". The open ends of each C, i.e., the slits 188, can be closed by conventional methods, such as hot stamping, laser welding or ultrasonic welding. Alternatively, an overmoulding technique could be employed to form a connector piece such as that indicated in Figures 22B and C, without further the need to provide the slits 188. Finally, mutual mechanical interlocks are suggested in the drawings of Figures 23 and 24. The drawing of Figure 23 shows the mutual locking of two adjacent "coiling loops" of this invention. The use of adhesive and polymeric materials at the expense of a helical h-zone of overlap between two adjacent winding loops, which are mutually locked and extend one over the other in a double thickness around the helix H. can be avoided. it avoids said double thickness by providing a thin protrusion 96 with a rectangular surface 192, in which its longer length direction extends towards the other part of the joint, in the facing protuberance 98. The thinned portion 98 of the second piece of nose 62, incorporates a portion 192 of hammerhead or T-shaped joint, which cooperates with the hole 1 92. The length of the transverse part of the T-shape is greater than the width of the hole 192, but not so large as the length of the orifice 192. Consequently, the piece T can be passed through the hole 192, and then rotated in the locking configuration shown in figure 24. Again the integrity of the joint is not it depends on the polymers or adhesives, although, again, the maintenance of the electrical insulation between the portions 96 and 98 dictates that an electrically insulating barrier be placed between these two portions. As with other illustrated embodiments, the joint area can be filled, or encapsulated, with formable polymeric material, electrically insulating, if not for joint reinforcement and increased electrical insulation, yes to increase the uniformity of the surface, which General is suitable for any implant that will unfold inside the body. The inventors have constructed and tested an embodiment of the present invention that corresponds to the matrix shown in Figure 5. The results of the test verify what is expected of the invention. The lumen of the matrix cylinder of the tubular mesh was visible in MRl images. The construction of the tested modality is revealed in the

Claims (12)

1. Figures 25 and 26, and is described below. Application WO 01/32102 of the applicant describes tubular, laser-cut, shape-memory nickel-titanium alloy meshes having tubular mesh forming rings spaced along the entire length of the tubular mesh, and joined together by bridges conductors, as seen in aspect 62 of Fig. 25. In Fig. 26 a similar structure is evident, except that some of the links are cut longitudinally and some transversely, to create the windings of the winding evident in Fig. 5, described before. The separation is achieved by means of the same laser that creates the strut matrix of the tubular mesh, from a precursor workpiece of the raw tubular mesh of N ITINOL. The longitudinally cut joints are as in Figure 17, except that the function of the band 90, in the test piece, is carried out by epoxy adhesive. The cross-cut joints resemble the joint described above with reference to Figure 12. Again epoxy adhesive was used on the test piece to join together, but electrically isolated, the two cooperating portions forming the joint of the figure 12. The matrix of the tubular mesh tested, exhibited two coils of winding, each of which extends the entire length of the matrix of the tubular mesh, and each of which exhibits an even number of lobes that, at added, they define equal and opposite areas, cut by an incident B-field, so that the summed flow of the eddy currents in each winding turn is essentially zero. The embodiments described above should be understood, with reference to the drawings, as examples of constructions within the scope of the claims that follow, and of the inventive concepts described above. CLAIMS 1 .- An implant characterized in that it comprises: closed loops, electrically conductive, forming a wall with openings of the implant, with an interior volume; each of the loops is formed of loop portions that provide electrically conductive current paths within which it is possible to induce eddy currents when subjected to an external time-dependent magnetic field; each of the loops consists of a first current path and a second current path; where the first current path and the second current path are arranged in such a way that, irrespective of the direction of the external magnetic field, the direction in which the stray current that would be induced by said field in the second current path is reversed to the direction of the parasitic current that would be induced simultaneously by the field in the first current path; which prevents the flow of eddy currents in each of the loops.
2. 2. The implant according to claim 1, further characterized in that each of the loops has loop portions formed as a first lobe and as a second lobe of a figure of eight; and further comprises a crossing point between the first lobe and the second lobe.
3. 3. The implant according to claim 2, further characterized in that it further comprises an electrically insulating seal between the two loop portions at the crossing point.
4. 4. The implant according to claim 2 or 3, further characterized in that each of the loops has additional lobes and additional crossing points between the lobes; such being the areas limited by the lobes that, in sum, the area limited by a series of lobes is equal to the area limited by the rest canceller of the lobes.
5. 5. The implant according to any of the preceding claims, further characterized in that the implant has a central longitudinal axis and the inner volume is tubular and centered on the shaft.
6. 6. The implant according to claim 1 or 5, further characterized in that each of the loops is wrapped around the axis in the form of a spiral, with an integral integral number of turns.
7. 7. The implant according to claim 6, further characterized in that the integral integral number of turns is at least three. 8. The implant according to claim 6 or 7, further characterized in that each of the loops that is wrapped around the shaft is inside a casing that is transverse to the axis. 9. The implant according to claim 6, 7 or 8, further characterized in that each of the loops is wrapped around the axis in a path that spirals around the axis, from one end of the implant to the other. 10. The implant according to any of claims 6 to 9, further characterized in that the passage of the spiral path is constant. 1 .- The implant according to any of the preceding claims, further characterized in that the loop portions correspond to struts that are joined together end to end, and can be deployed in use to form a zigzag pattern. 12. The implant according to any of the preceding claims, further characterized in that the plurality of loops is arranged mutually adjacent in the axial direction, and spaced along the axis. 13. The implant according to claim 12, further characterized in that the adjacent loops are connected to each other by electrically insulating links. 14. The implant according to any of the preceding claims, further characterized in that each of the loops includes a plurality of electrically insulating links connecting loop portions spaced from said loop. 15. The implant according to claim 1 3 or 14, further characterized in that each link is a mechanical coupling having a first cooperating link portion and a second cooperating link portion. 16. The implant according to claim 15, further characterized in that the cooperating portions can be moved with respect to each other. 17. The implant according to claim 16, further characterized in that the cooperating portions are constituted as a hook portion and an eye portion for receiving the hook portion.
8. 8. The implant according to any of claims 15, 16 and 17, further characterized in that it includes a layer of bonding material between the cooperating linking portions.
9. 9. The implant according to claim 18, further characterized in that the bonding material is ceramic. 20. The implant according to claim 1 8, further characterized in that the bonding material is an adhesive composition. 21. The implant according to any of claims 15 to 20, further characterized in that the mechanical coupling comprises fingers of mutual locking. 22. The implant according to any of claims 15 to 21, further characterized in that the mechanical coupling comprises surfaces that are mechanically coupled, in combination with at least one restriction strip that remains above the coupling surfaces. 23. The implant according to any of claims 13 to 22, further characterized in that each link includes a molded connector part. 24. - The implant according to any of claims 13 to 23, further characterized in that each link includes a portion that is locally thinned with respect to the thickness of the wall of the implant. 25. The implant according to any of the preceding claims, further characterized in that the wall of the implant is a tube with openings. 26. The implant according to any of the preceding claims, further characterized in that the implant is made of a nickel-titanium alloy with shape memory. 27. The implant according to any of claims 1 to 25, further characterized in that the implant is made of stainless steel. 28. The implant according to any of the preceding claims, further characterized in that the implant is a tubular mesh. 29. The implant according to claim 28, further characterized in that the tubular mesh is radially expandable from a radially compact delivery configuration to a deployed, radially larger configuration; and the tubular mesh is capable of being delivered transluminally by means of a catheter.30.- The implant according to any of claims 1 to 27, further characterized in that the implant is a filter. 31. The implant according to any of claims 1 to 27, further characterized in that the implant is a