Patent Description:
The electrochemical performance of an electrode is one of the highest priority areas for optimization of leads and cuffs for use in neuromodulation and other applications. In neuromodulation, high performing electrodes lead to achieving safe and efficacious delivery of therapy. Ensuring that the electrode is high performing takes more than material selection and development. Even if electrode material and its charge injection capability have been optimized for the target therapy, the leads may still fail to achieve target electrochemical performance when the charge injection surfaces are blocked by contaminants or other non-conductive manufacturing residues. In scenarios where there are silicone flashes on the charge injection surfaces of the electrodes from the lead manufacturing and assembly process, the electrochemical performance can be highly compromised and variable from lead to lead, making it challenging to tune the system to optimize for the therapy.

Known solutions for addressing this problem have shortcomings. One solution is the use of thin film technology to integrate the electrode onto the substrate directly, skipping the molding step entirely. The disadvantages of this approach are that thin film materials are not soft enough and are not as well-proven as silicone for chronic implant applications. Furthermore, this presents less manufacturing freedom to fine tune the three-dimensional form factor of the neural interface device (e.g., a cuff or a paddle electrode) to fit highly variable anatomy and demographics of patients.

<CIT> discloses an implantable cuff electrode comprising an inner elastic body having a cylindrical inside surface and an exterior surface extending longitudinally along a length, the inner elastic body having a plurality of apertures formed radially therethrough at circumferentially spaced locations, wherein the inner elastic body includes a first longitudinal split extending through the length, a plurality of electrodes, each electrode being positioned at least partially within a corresponding aperture, an insulating material including a second longitudinal split, the insulating material being positioned over all of the exterior surface of the inner elastic body and the plurality of electrodes, wherein the second longitudinal split is aligned with the first longitudinal split, and wherein the first longitudinal split and the second longitudinal split together form an expandable access point to enable positioning of the cuff electrode over a target nerve, and a cover tube positioned over the insulating material.

A detailed failure analysis by the inventors revealed that the electrodes can be partially covered in silicone flashes from the molding process. These silicone "flashes" that cover the electrode surface reduce the effective surface area through which therapy can be delivered. Silicone flash may occur as a result of pressurized and heated silicone leaking around the edges of the electrode during manufacturing.

The present disclosure addresses the problems discussed and describes an inventive electrode assembly and method of making an electrode assembly. According to an embodiment, a method for use in making an electrode assembly comprises the steps of assembling electrode(s) onto a first-shot of molded silicone with positioning-assist windows; tagging down the electrode in place with implant-grade adhesive, electrically connecting the electrode(s) via laser or resistance welding with an intermediate electrically conductive wire or coil; applying an adhesive backfill over the electrode(s) and interconnect; and applying a second-shot of material over the adhesive backfill and electrodes.

In one particular embodiment, the first-shot, second-shot, and adhesive backfill may all be comprised of silicone, but different materials may be used for each shot as well as the backfill. In addition, the first-shot may hold the electrodes or electrode pads in their desired position with blind pockets formed to match their profile. The second-shot, injected during high-pressure molding, may be applied after the adhesive backfill has cured. The adhesive backfill material may be applied such that it seals off any gap between the metal electrodes and first-shot, preventing silicone from the second-shot molding to lead through the cracks to get on top of the electrode on the tissue facing surface.

In an embodiment, there is provided a method for use in making an implantable electrode assembly for neuromodulation, comprising: forming a first layer of material including a hole formed therein; positioning an electrode in the hole in the first layer of material; connecting an electrical lead to the electrode; applying a backfill material over the electrode, the electrical lead connection, and a portion of the first layer sufficient to seal any gap between the electrode and the hole; and applying a second layer of material over the backfill material.

In an embodiment, there is provided an electrode assembly, comprising: a first layer of material having a hole formed therein; an electrode connectable to a lead configured to fit within the hole; a backfill applied over the electrode and any exposed portion of the lead and an electrical connection between the electrode and the lead; and a second layer of material applied over the backfill and a portion of the first layer; and wherein the backfill fills any opening between the electrode and the first layer, thereby blocking any leakage path between the electrode and the second layer that could cover a portion of an exposed surface of the electrode.

In an embodiment, there is provided an electrode assembly for neuromodulation, comprising: a first layer of material having an opening; an electrode connectable to a lead provided at least partly in the opening; a backfill provided over the electrode, the backfill covering an edge of the electrode and at least a part of an electrical connection between the electrode and the lead; and a second layer of material provided over the backfill and a portion of the first layer, wherein the backfill blocks any opening between the electrode and the first layer for reducing leakage path between a target contact surface of the electrode and the second layer.

Detailed features of the disclosure are set forth below.

The disclosure relates to systems and devices for stimulating a nerve intra- or extra-venously through use of an implantable device that includes one or more electrodes positioned toward the distal end of a lead or within a neural interface device, including a cuff or a flat paddle lead, implanted within or around the outside of a blood vessel, for example an artery, a vein or nerve or a bundle of nerves such that the electrodes are in contact with surface tissue. Stimulation of the nerve may be defined by the delivery of electricity (e.g., electrical pulses) to a neuron, a nerve cell, a nerve bundle, or other target location of the nervous system that excites the neuron, nerve cell, nerve bundle, or other target location.

<FIG> depicts an example system including an implantable device <NUM> formed of a flexible, biocompatible material, such as a biocompatible thermoplastic elastomer, a soft polymer substrate, etc., that may be used to stimulate a nerve using current induced in the implantable device by a source <NUM> (not otherwise shown in <FIG>). The implantable device <NUM> show in <FIG> is an extra-vascular device in the form of a cuff that is wrapped around a nerve or blood vessel (not shown). The implantable device <NUM> is merely provided as an example and may come in many different shapes, configurations, sizes, etc. For example, the implantable device is not required to be fully wrapped around a target, may be paddle-like and used in both extravascular and intravascular applications, or other configurations for stimulating nerve tissue.

The implantable device <NUM> may include one or more electrodes <NUM>, sensors or arrays of the same, each array comprising one or more sets of electrodes or sensors. In some embodiments, each electrode <NUM> may be configured to emit electrical fields to stimulate a nerve proximate to the implantable device <NUM>. Each set of electrodes <NUM> within electrode array may include one or more individual electrodes for this purpose.

Each electrode <NUM> (or a set of such electrodes, etc.) may be coupled to an electrically conductive wire or coil lead <NUM> (<FIG>), such as a micro-coil lead, made substantially out of conductive material to a high-density, flexible interconnection (not shown). In some embodiments, for example, the conductive wire or coil leads <NUM> may be comprised substantially (e.g., <NUM> or <NUM> percent by weight) out of metals such as platinum, stainless steel (e.g., MP35N or titanium. Other metals, such as gold, may also be used. As depicted in <FIG>, the electrode <NUM> may be connected in series and/or parallel to other electrodes to provide multiple channels for increased selectivity of the parameters of the emitted electric field (e.g., magnitude, direction, location, etc.). In some embodiments, this arrangement may provide for more targeted and efficient stimulation of a nerve.

The electrode <NUM> may be coupled through the leads <NUM> to one or more other components (not shown) of implantable device <NUM>, such as a main lead body for the neural interface device, a control circuit, a battery, capacitive storage and/or other chargeable storage elements, etc., as necessary or desirable. In an embodiment, each electrode <NUM> is connected (i.e., welded or other suitable technique) to a lead <NUM> and then connected to a flexible interconnection lead (not shown) of the neural interface device <NUM>. The interconnection lead can connect directly to the lead body or provide an electrical connection between the leads <NUM>, either in series or parallel as desired. The lead <NUM> may be a micro-coil or other suitably flexible lead. The interconnection lead can also (and/or alternatively) connect directly to the lead body or provide an electrical connection between the electrodes <NUM>, either in series or parallel as desired. The interconnection lead may be a micro-coil or other suitably flexible lead. Thus, in some embodiments, the lead <NUM> may refer to both the lead <NUM> and the interconnection lead. In other embodiments, the lead <NUM> may be comprised solely of interconnection leads. In other embodiments, the lead <NUM> may be comprised solely of interconnection leads between electrodes <NUM> and comprised of an interconnection lead as a portion of lead <NUM> connectable to the lead body.

The electrode <NUM> may be a sensor or array of sensors that measure a physical or temporal parameter associated with implantable device <NUM> and/or its surroundings. For example, in one embodiment, the set of sensors may include sensors for measuring the electrical potential between two points. In addition, the set of sensors may include other sensors for measuring other characteristics such as pressure, temperature, time, resistance, conductance, electrical/magnetic flux, and so forth. Each sensor in the set of sensors may be coupled to any other component of implantable device <NUM>, such as the control circuit, the electrodes <NUM>, energy sources, etc..

Each of the components of implantable device <NUM> may be formed within or affixed into the soft polymer substrate <NUM> so that the substrate supports the formed or affixed components. In certain embodiments, the substrate <NUM> may comprise a single piece of flexible polymer material, such as silicone, to facilitate implantation into a patient and manipulation therein. In some embodiments, the substrate <NUM> may comprise a plurality of layers of material with various components, such as electrode <NUM> or arrays, sensors and wires or coils <NUM> positioned between the layers. In an embodiment, a first layer may be formed in a mold in which heated silicone is injected under pressure, i.e., "shot" into the mold. A series of holes in the first-shot layer may be formed by the mold or cut into the first layer once it has cured. Once the holes have been created, one or more electrodes may be placed in each whole, with each electrode then be connected to the wires or coils <NUM>, typically by welding the lead to a back of the electrode. Once the electrodes and leads are welded, a second-shot layer of heated and pressurized flexible polymer material may be placed over the back of the electrodes to seal the electrodes between the first-shot and second-shot layers and maintain their positions within their respective holes.

The following method has been found to be consistently effective at preventing silicone flashes of the kind described above. <FIG> is a cross-section along the line A-A of <FIG>. As shown in <FIG>, a first layer <NUM> of material, which may be a first-shot of silicone, polymer, or biocompatible thermoplastic elastomer material, or biocompatible thermoplastic polyurethane. The first layer <NUM> of material may be configured to include one or more holes <NUM>, each of which may hold a metal electrode <NUM> in a desired position. The electrode <NUM> is positioned in the hole <NUM> so that a front side of the electrode is approximately co-planar with an exposed surface of the first layer <NUM>. A backfill <NUM> of material, such as a silicone adhesive, may then be overlaid on the backside of electrode <NUM> without using heat or pressure, or at least without using pressure so as to form a seal over the electrode and a portion of the first layer, thereby closing any remaining opening between the electrode <NUM> and the first layer <NUM> around the edges of the hole <NUM>. A second layer <NUM> of material like the first layer may then be applied over the backfill <NUM>.

The backfill <NUM> may comprise a material of different hardness compared to that of the first layer <NUM> and the second layer <NUM>. For example, the backfill <NUM> may comprise a softer (or less stiff) material compared to the first layer <NUM> and the second layer <NUM>. In one example, the hardness of the first layer <NUM> and the second layer <NUM> may be around <NUM> Shores A - <NUM> Shores A, favourably <NUM>-<NUM> Shores A, favourably <NUM>-<NUM> Shores A; and the hardness of the backfill <NUM> may be ≥<NUM> Shores A, favourably ≥<NUM> Shores A, favourably ≥<NUM> Shores A, favourably ≥<NUM> Shores, favourably ≥<NUM> Shores (e.g. measured using a shore durometer).

In an embodiment, instead of using a first layer and a second layer of the same material, each layer may be of a different material. For example, the first layer may be made of a stiffer durometer of silicone or polymeric material so that it is more difficult for the metal electrode to tear through the first layer and potential cut into the neurovascular bundle (NVB) to which the neural interface devices is being applied. The second layer may then be of a different material with different stiffness or the same material (silicone) with lower durometer configured to elicit more favorable tissue reaction or to help the neural interface device form factor be more pliable, which may be beneficial for lowering the pressure exerted on the NVB, and thereby reduce the risk of mechanically induced tissue damage. In the event two layers of different materials or stiffness are utilized, it is desirable to prevent the two layers from mixing uncontrollably because variations in mechanical modulus distribution can lead to the neural interface device that may deform due in unpredictable ways due to a buildup in residual stress. An improved control of the two layers can be achieved by using the method of manufacture described in this disclosure.

The backfill <NUM> may be applied after connecting the electrode <NUM> to a lead <NUM> as shown in <FIG>. The lead <NUM> may be connected to the electrode <NUM> using laser welding or other suitable technique and provide an electrical connection between the electrode and a lead body (not shown) or an interconnection lead as described above. For example, at least one of the following may be used for an electrical connection between the lead and the electrode: welding (laser or resistance), crimping and conductive adhesive.

Applying the backfill <NUM> over the lead connection to the electrode <NUM> may serve to further secure the lead connection over time. The second layer <NUM> of material may be applied only after the backfill <NUM> is cured.

Referring to <FIG>, a method of manufacturing an electrode assembly in accordance with the present disclosure includes the steps denoted S1 through S6:.

Other biocompatible materials may be used in place of silicone, such as other biocompatible polymers. Likewise, different biocompatible materials may be used as a backfill versus only silicone adhesive.

Claim 1:
A method for use in making an implantable electrode assembly (<NUM>) for neuromodulation, comprising:
forming a first layer of material (<NUM>) including a hole (<NUM>) formed therein;
positioning an electrode (<NUM>) in the hole (<NUM>) in the first layer of material (<NUM>);
connecting an electrical lead (<NUM>) to the electrode (<NUM>);
applying a backfill material (<NUM>) over the electrode (<NUM>), the electrical lead connection, and a portion of the first layer (<NUM>) sufficient to seal any gap between the electrode (<NUM>) and the hole (<NUM>); and
applying a second layer of material (<NUM>) over the backfill material (<NUM>).