Patent Application
20100292744
1. Field Of The Invention
The present invention generally relates to implantable leads, and in particular to ring electrodes for usage in such implantable leads.
2. Description of the Prior Art
Body implantable electrical leads form the electrical connection between an implantable medical device (IMD), such as cardiac pacemaker, cardiac defibrillator or cardioverters, and body tissue, such as the heart, which is to be electrically stimulated. As is well known, the leads connecting the IMD with the tissue may be used for pacing/defibrillation and for sensing electrical signals produced by the tissue.
The implantable leads of today are complex arrangements, generally including multiple different lead elements of different materials and therefore having different characteristics. This makes the assembly process of a lead time consuming and complex. Furthermore, in most implantable leads at least some of the lead elements are connected through welding. Though this may work satisfactory for elements of same materials, welding elements having different material characteristics may impose new problems. There is risk that a weld between different materials may become brittle. Thus, there is generally a need of connecting lead elements of different materials and different material characteristics.
There is therefore a need for a lead manufacturing process that allows connecting lead elements of different materials. There is also a need for implantable electrical leads, where a risk of forming brittle welds is reduced. The present invention overcomes these and other drawbacks of the prior art arrangements.
It is a general object of the present invention to provide a ring electrode of an implantable medical lead having interconnected electrode material of differing materials.
It is another object of the invention to provide a manufacture of ring electrodes involving spark plasma sintering for directly or indirectly connecting an electrode member to a coil adapter.
Briefly, the present invention involves an implantable medical, electrical lead connectable to an implantable medical lead. The lead has a ring electrode in connection with its distal end. The ring electrode comprises an electrode member made of a first conducting material, such as titanium. This electrode member constitutes the portion of the ring electrode that provides stimulating pulses to adjacent tissue and/or sense the electrical activity of the tissue following implantation.
The ring electrode also has a coil adaptor made of a second conducting material, such as a metal alloy, e.g. a nickel-cobalt-chromium-molybdenum alloy. This adaptor has a proximal end connectable to a lead conductor that electrically connects the coil adaptor to a terminal electrode at the proximal end of the lead.
The coil adaptor is mechanically and electrically connected, directly or indirectly, to the electrode member at least partly by spark plasma sintering. This metal-connecting technique allows elements of different material characteristics to be reliably inter-connected even though the two materials cannot be securely inter-connected through traditional welding.
In a particular embodiment, the ring electrode also has a weld adapter functioning as a bridging unit between the electrode member and the coil adapter. In such a case, the weld adapter is electrically and mechanically connected to at least one of the electrode member and the coil adaptor through spark plasma sintering. The other element connection can be made with tradition welding as long as the two elements (electrode member and weld adaptor or coil adaptor and weld adaptor) are made or the same or at least inter-weldable materials.
The invention also encompasses a method of producing such a ring electrode of an implantable medical lead.
The invention offers the following advantages:
Other advantages offered by the present invention will be appreciated upon reading of the below description of the embodiments of the invention.
Throughout the drawings, the same reference characters will be used for corresponding or similar elements.
The present invention relates to implantable medical leads or catheters, and in particular to a distal end arrangement thereof and such distal lead arrangements having a ring electrode. The leads of the invention are adapted for connection to different implantable medical devices (IMDs), such as pacemakers, cardioverters, defibrillators and other implantable electrical medical devices.
The distal lead portion 102 also has a ring electrode 200 or indifferent electrode according to the present invention. This ring electrode 200 is provided for electrically stimulating adjacent tissue and/or for sensing electrical activity of tissue.
The connector assembly 140 at the proximal lead end 104 is adapted to electrically and mechanically couple the lead body 106 to the IMD. The assembly 140 comprises terminal contacts in the form of a tubular, rotatable pin terminal contact 146, often denoted connector pin 146, and a ring terminal contact 144, generally referred to as connector ring 144. These two contacts 144, 146 are positioned to engage corresponding electrical terminals within a receptacle in the IMD. In order to prevent ingress of body fluid into the IMD receptacle, the connector assembly 140 may be provided with spaced-apart sets of seals 142, well known in the art.
The present invention is not limited to be implemented into active fixation medical leads having electrically conducting helical screw-in fixation elements. In clear contrast, the teachings of the invention can be applied to leads having helical screw-in fixation elements that are not employed as stimulating/sensing electrodes, i.e. being made of non-conducting material and/or having no electrical contact with electrical terminals in the IMD. The invention can also be applied to passive fixation leads, where the helical screw-in fixation element is replaced by, for instance, a collar, tines or fines for anchoring the lead body to a selected tissue.
The IMD 300 can wirelessly communicate with an external device 400, non-limitedly illustrated as a programmer 400 in the figure. The external device 400 could alternatively be a physician's workstation, a home monitoring device or actually any data processing unit having capability of receiving data collected by the IMD 300 and preferably sending instructions and commands to the IMD 300. The external device 400 is preferably connected to a display screen 410 allowing display of the collected diagnostic parameters and data
The proximal portion of the sleeve 170 has a counterbore terminating at a distal end wall. An electrically conductive tubular abutment 164, such as of MP35N® or the like, L-shaped in cross section, has an axial portion connected, e.g. welded, to the proximal end of the helix shaft 160 and a flange projecting radially within the counterbore of the sleeve 170. Thus, the abutment 164 being secured to the shaft 160 is movable rotationally and axially with the shaft 160 relative to the sleeve 170.
Contained within the counterbore is an electrically conductive, expandable/contractable contact member, preferably in the form of a metallic compression spring 162 of, for instance, MP35N® or like material. In such a case, electrically continuity is thereby established between the collar 120 and the terminal contact pin of the connector assembly via the inner tube 150, the sleeve 170, the contact spring 162, the L-shaped abutment 164 and the inner conductor coil 190. The contact spring 162 is extended or contracted depending on the extension or retraction of the helix electrode 110.
An outer insulating tube 130, for instance of silicone rubber or polyurethane, a Elast-Eon® polymer (trademark of Aor Tech International, a polymer of silicone with polyurethane), such as Elast-Eon® 2A, 2D, 3A, 3LH or HF, extends between the proximal face of the collar 120 and the distal extremity of a ring electrode member 210. A corresponding insulating tube 130 also covers the main lead body by extending from the proximal extremity of the ring electrode 210 up to the connector assembly.
Projecting radially inwardly from the inner surface of the inner header tube 150 is a post 152 interposed between adjacent turns of the helix electrode 110. In this fashion, rotation of the helix electrode 110 forces the electrode 110 to advance or retract within the lead body header.
The ring electrode 200 of the present invention is in mechanical and electrical contact with a terminal of the collector assembly, such as the collector ring, through an outer coil conductor 192. The two coil conductors 190, 192 are electrically insulated by a longitudinally extending insulating tube 180, such as made of silicone rubber, polyeurethane, Elast-Eon® or the like. This insulator 180 is disposed between the coils 190, 192 to prevent electrical contact between the conductors 190, 192 and between the ring electrode member 210 and the inner conductor coil 190.
The figure schematically illustrates an embodiment of a ring electrode 200 according to the present invention. The ring electrode 200 comprises an electrically conducting electrode member 210 connected to a coil adapter 220 also made of a conducting material. This coil adapter 220 mechanically and electrically connects the electrode member 210 to the outer conductor coil 192.
The ring electrode 200 of the present invention comprises at least two ring elements 210, 220 made of different electrically conducting material. Thus, a first element is the actual electrode member 210 having a portion that faces the outside environment when implanted in a patient body. This electrode member 210 must therefore be made of a biocompatible conducting material having corrosion-resistance and material properties that are required for the rather harsh environment it will face following implantation.
Typical materials for the electrode member 210 include metal or metal alloy materials and preferably electrically conducting metal (alloy) materials. Examples of metal materials include platinum, titanium, tantalum, iridium and niobium, and different alloys thereof, such as titanium alloys or platinum/iridium (Pt/Ir) alloys, including Pt/Ir 90/10 or Pt/Ir 80/20. Also other metal alloy materials can be used including a nickel-cobalt-chromium-molybdenum alloy, such as MP35N® (trademark of SPS Technologies, Inc.) or 35N LT® (trademark of Fort Wayne Metals Research Products Corp.), or an iron-nickel-cobalt alloy, such as Kovar® (trademark of Carpenter Technology Corp.). A preferred conducting material of the electrode member 210 is titanium.
Traditionally the ring electrode member 210 is mechanically and electrically connected directly to the outer conductor coil 192. However, generally the conductor coil 192 is made of a second conducting material different from the material of the electrode member 210 or at least there is a desire to use a second different material. There may though be problems when connecting the electrode member 210 directly to the coil conductor 192 and where these two elements are made of different materials. For instance, the main connecting technique employed in lead assembly, welding, may cause problems as a weld between, for instance, a titanium electrode member and a MP35N® conductor coil may become brittle and may have problems withstanding the mechanical strain, which arise during implementation and use of the lead.
The present invention solves this problem by introducing a coil adapter 220 to the ring electrode 200. This coil adapter 220 acts like a bridge between the electrode member 210 and the conductor coil 192. The coil adapter 220 is made of a second conducing material, typically the same material as the outer conductor coil 192 or a matching material that allows formation of a reliable and robust electrical and mechanical connection to the conductor coil 192, preferably through welding, such as laser welding. Preferred materials of the coil adapter 220 include conducting metal (alloy) materials, such as platinum, titanium, tantalum, iridium and niobium, and different alloys thereof, such as titanium alloys or platinum/iridium (Pt/Ir) alloys, including Pt/Ir 90/10 or Pt/Ir 80/20. Also other metal alloy materials can be used including a nickel-cobalt-chromium-molybdenum alloy, such as MP35N® (trademark of SPS Technologies, Inc.) or 35N LT® (trademark of Fort Wayne Metals Research Products Corp.), or an iron-nickel-cobalt alloy, such as Kovar® (trademark of Carpenter Technology Corp.). A preferred conducting material of the coil adapter is MP35N® or 35N LT®. The coil adapter 220 is preferably made of the same material as the outer conductor or conductor coil 192, or at least a material that can be efficiently and reliably welded thereto.
The electrode member 210 and the coil adapter 220 of the present invention are mechanically and electrically connected at least partly through spark plasma sintering, which is described further herein. This means that the two ring electrode elements 210, 220 can be directly connected to each other through spark plasma sintering to thereby obtain a robust, strain- and corrosion-resistant mechanical and electrical connection between the coil adapter and the electrode member. Alternatively, spark plasma sintering is used for achieving an indirect connection between the coil adapter 220 and the electrode member 210. In this latter case, one or more additional ring electrode elements can be used for connecting the coil adapter 220 and the electrode member 210. Though, the connection of one such additional element to the coil adapter 220 and/or the electrode member 210 and/or the interconnection of two such additional elements are achieved through spark plasma sintering.
Thus, connecting the coil adapter 220 of the invention to the electrode member 210 at least partly by spark plasma sintering encompasses a direct mechanical and electrical connection between the elements by spark plasma sintering but also encompasses an indirect mechanical and electrical connection using one or more additional connection elements, where at least one connection between the elements of the ring electrode 200 is obtained through spark plasma sintering, though other such connections may be performed through other techniques, such as welding.
In a first implementation, the outer diameter of the distal adapter portion 222 matches the outer diameter of the proximal electrode portion 216. In such a case, the ends of the coil adapter 220 and the electrode member 210 are anchored together to form a ring electrode. This means that the circular distal end portion 222 of the coil adapter 220 will be connected by spark plasma sintering to the circular proximal end portion 216 of the electrode member 210.
In a second embodiment, an outer diameter of the distal adapter portion 222 matches the inner diameter of the proximal electrode portion 216. This means that the shoulder portion 222 is adapted for insertion, at least partly, into the bore 218 of the electrode member 210 as illustrated in
In a third implementation, an outer diameter of the proximal electrode portion 216 matches the inner diameter of the distal adapter portion 222. In this implementation, the proximal electrode portion 216 is inserted into the bore 228 of the coil adapter 220 and connected thereto through spark plasma sintering.
The coil adapter 220 preferably comprises a second outwardly protruding shoulder 224 covering the circumference or a portion of the circumference of the coil adapter 220. This shoulder 224 acts like a stop and possibly anchoring element to the outer conductor coil. Thus, the proximal coil portion is threaded on the proximal adapter portion 226 up to the coil adapter. At this position the conductor coil can be attached to the shoulder 224 or the lateral surface of the proximal adapter portion 226, typically by welding.
The ring electrode illustrated in
The distal FSR lead portion 102 comprises a header 158, such as made of titanium, extending from the sleeve 170 up towards the distal lead end. The opposite side of the header 158 is preferably connected to a marker ring 154, such as made of Pt/Ir. The marker ring 154 is covered by an insulating header cap 156, which can be made of any insulating material generally employed in medical leads, such as a silicone material, polyurethane, or Elast-Eon®. An insulating tubing 155 is provided around the header 158, extending down to covering at least a portion of the sleeve 170. This can also be made of different insulating materials, such as polytetrafluoroethylene (PTFE). This insulating tubing 155 electrically insulates the electrode member 214 of the ring electrode from the header 158 and the sleeve/coupling 170. The inner insulator 180 preferably extends, in this FSR lead, up to and covers at least an end portion of the insulating tubing 155. The remaining lead header elements are similar to those illustrated in
In this embodiment, the weld adapter 230 and coil adapter 220 are interconnected through spark plasma sintering. The weld adapter 230 is in turn welded to electrode member 210 to thereby form a mechanical and electrical connection between the coil adapter 220 and the electrode member 210 formed partly by spark plasma sintering.
It is anticipated by the present invention that in another embodiment, the proximal electrode portion 216 is instead partly inserted into the bore 238 of the weld adapter 230 and welded thereto. Alternatively, the diameter of the proximal electrode portion 216 matches the diameter of the distal weld adapter portion 232. In such a case, the two elements 210, 230 can be welded together end-to-end.
Furthermore, in an alternative embodiment the weld adapter 230 is made of the second conducting material, i.e. the same material as the coil adapter 220 or at least a matching material that can be welded thereto to form a reliable, robust and non-brittle weld therebetween. In such a case, the weld adapter 230 is connected to the electrode member 210 by spark plasma sintering. The resulting sub-assembly can then be connected to the coil adapter 220 by welding the weld adapter 230 to the coil adapter 210.
In an alternative embodiment, the weld adapter 240 and the coil adapter 220 are made of same or at least inter-weldable conducting materials. The weld adapter is then preferably first spark plasma sintering into the bore 218 of the electrode member 210 or around the proximal end portion of the electrode member 210. In the former case the distal end 223 of coil adapter 210 is introduced into the ring-shaped weld adapter 240 and welded thereto. In the latter case, the weld adapter 240 is introduced in the bore 228 of the coil adapter 210 and connected by welding.
According to the present invention “at least partly fabricated” means a sub-assembly that is either a completely fabricated ring electrode element or at least a partly fabricated raw or start material that can be formed into a fabricated element. As a consequence, at least partly fabricated encompasses providing powder, grain, granule or granulate particles of the first (in the case of coil adapter) or second (in the case of electrode member) conducting material compacted to a shape from which the final shape of the element can be fabricated and formed to a continuous body by spark plasma sintering. At least partly fabricated also encompasses a finally fabricated element that is to be connected, such as by spark plasma sintering, to another element of the ring electrode member. The expression also covers element bodies between these two extremes such as an continuous element body of the conducting material that is connected, such as by spark plasma sintering, to another element of the ring electrode assembly but having a shape different from the final shape of the element. In such a case, the element body can be further processed, such as turned, ground, etched, subjected to electrical discharge machining (EDM), milled, sawed, drawn, tumbled, swaged, forged, welded, following the connection to form the desired final shape and/or surface treatment.
Step S1 can therefore involve, for instance, providing powder particles of the first conducting material and forming, in a die, the particles to a desired shape. Alternatively, a fabricated coil adapter body of the second material, such as illustrated in
A next step S2 involves providing an at least partly fabricated electrode member made of a second conducting material. This step S2 can, in consistency with step S1, involve providing powder particles of the second material and compacting them to a desired shape. Alternatively, a fabricated electrode member having a shape as illustrated in
A next step S3 involves directly or indirectly connecting the coil adapter and the electrode member at least partly by spark plasma sintering. Furthermore, in the case any of the providing steps S1 and S2 involved providing material particles, the spark plasma sintering operation performed in step S3 also includes forming a continuous body of the material in addition to inter-connecting at least two ring electrode elements.
“Spark plasma sintering” or “SPS” is a sintering technique that applies, in addition to pressure, DC current/voltage pulses directly through a die containing a sample to be formed or samples to be inter-connected. The DC current pulses not only pass through the die by also through the actual sample(s) in the case of conductive samples. As a consequence, heat is generated internally through spark discharge between the particles occurring in the initial stage of the current-voltage pulse. The generation of spark impact pressure, Joule heat and the action of the electric field will result in efficient heating, plastic deformation promotion, high-speed diffusion and material transfer that give an opportunity to conduct low-temperature, short-time sintering of hard-to-sinter materials and bonding of dissimilar materials.
Spark plasma is formed initially of the sintering process and necks between the particles are created. After the initial process, surface, grain-body and volume-diffusion-processes and plastic flow contribute to densification while avoiding coarsening. SPS also facilitates a very high heating or cooling rate (several hundred ° K/minute), hence the sintering process is very fast. SPS is also sometimes denoted field assisted sintering technique (FAST) or pulsed electric current sintering (PECS) in the art.
Thus, the expression “spark plasma sintering” as used herein relates to a technique for forming inter-metal bonds between metal (alloy) bodies of different conductive materials through the application of pressure and DC current/voltage pulses through the die and the at least partly fabricated ring electrode elements of the invention.
The at least fabricated coil adapted can be in the form of powder/grain/granulate/granule particles of the first conducting material, preferably MP35N® or a similar alloy, formed in the die to the final shape of the coil adapter or at least into a body that can be further processed into the final coil adapter shape following the spark plasma sintering. Alternatively, the coil adapter is in the form of a continuous body, either finally fabricated or partly fabricated, inserted into the sintering die together with the titanium particles.
In a further embodiment, the coil adapter and the electrode member are in the form of finally fabricated or partly fabricated continuous bodies of the first and second conducting material, respectively. These two bodies are then inserted into the die and spark plasma sintered together to be directly inter-connected.
The above-described discussion of the at least partly fabrication form of the coil adapter and the electrode member also applies to this embodiment, in which the coil adapter and the weld adapter are inter-connected. As was described in the foregoing, in an alternative approach, an at least partly fabricated weld adapter made of the first conducting material is provided in the sintering die together with an at least partly fabricated electrode member made of the second conducting material. The two elements are mechanically inter-connected by spark plasma sintering and then the weld adapter is welded to the coil adapter.
A test body made of a preferred conducting material of the electrode member, i.e. titanium, and a preferred conducting material of the coil adapter, i.e. MP35N®, has been spark plasma sintered at a temperature of 800° C. for 1 minute. The test bodies had a diameter of 12 mm and a height of 3 mm and were sintered from MP35N® and titanium powder.
The SPS procedure of the present invention results in a diffusion-based joint between the materials. In a small transition zone around the joint, particles of the materials become inter-mixed to form the diffusion-based, seamless joint.
As is well known in the art, the temperature of the SPS process is dependent on, among others, the particular materials to be sintered and the thickness of the materials or the size of the material particles. Briefly, the sintering temperature should be below the lowest melting point of the materials to the sintered. Furthermore, the smaller the diameter of the material particles, generally the lower sintering temperature can be used. Care must also be taken for materials that are subject to phase transitions so that not an unaccepted, from mechanical and/or electrical properties point of view, is formed in the SPS process. The pressure that is applied during the SPS process is also material dependent and depends on the size of the sintered materials. Generally, the pressure per surface area is rather constant for a given material.
The optimal SPS sintering parameters can be determined by the person skilled in the art through routine tests and table look-ups regarding the particular material combinations. The above described parameter settings can be used as starting points in such an optimization process.
The electrochemical behavior of Ti (grade 2) sintered to MP35N® was investigated. The material combination Ti/MP35N® showed low current density during polarization. The current density is related to the corrosion rate, implying that the investigate material combination joint had low corrosion rate. A reason for this low current density may be attributed to the presence of protective oxide films. The protective oxide film of MP35N® consists of Cr2O3. The titanium has a passive surface film in the form of TiO2. This passive surface film contributes significantly to the corrosion resistance of the materials. The tested material combination showed good corrosion resistance in artificial physiological solutions.
An electrochemical investigation was also tested for another possible metal combination according to the invention, i.e. a Ptlr alloy and titanium. The metal combination showed low current density during polarization. The reason for this low current density is the protective oxide (TiO2) film and the inert behavior of Ptlr. Potentiodynamic polarization does not affect Ti and Ptlr at all or only to a minor degree. The material combination exhibited good corrosion resistance.
It will be understood to those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2007/001005 | 11/14/2007 | WO | 00 | 5/4/2010 |
