Flexible neural implant with improved insertion and fixation characteristics

Abstract

The present invention relates to a substantially planar neural electrode array, the electrode array comprising: a flexible base; a connector cable attached to the base; one or more flexible shafts protruding from the base, the shafts being arranged to protrude from the same surface of the base in the same plane so as to form a comb-like structure, each of the one or more shafts comprising one or more electrode contacts, the electrode contacts being electrically coupled to the connector cable; a first reinforcing layer extending over the base and a proximal portion of the one or more shafts, the proximal portion being adjacent to the base; and a second resorbable reinforcing layer extending over a distal portion of the one or more shafts, the distal portion being remote from the base, with an overlap between the first reinforcing layer and the second resorbable reinforcing layer. Furthermore, the present invention relates to a neural implant comprising one or more electrode arrays according to the present invention. Furthermore, the present invention relates to a method for manufacturing an electrode array according to the present invention.

Description

[Technical Field]

[0001] The present invention relates to a thin, flexible electrode array for large-scale (high-resolution) neural signal recording and neural stimulation in the brain or neural tissue. More specifically, it relates to the insertion of multiple needle-like or interdigitated arrays of such electrodes, thus forming a 3D array. It has features that allow for improved insertability and subsequent mechanical stabilization. [Background technology]

[0002] Increasing evidence suggests that flexible neural electrode arrays are superior to stiffer, typically larger, silicon- or metal-based electrode arrays in terms of scar tissue formation and long-term performance. A possible explanation is the reduction of damage or irritation caused by continuous movement of the implant relative to the brain. Typically, such flexible electrode arrays are fabricated using thin-film technology on a flat carrier substrate, such as a silicon wafer, and then released from the carrier. Common materials used for flexible electrode arrays are polyimide or parylene-C isolation layers and noble metal electrical connections, as well as electrode materials such as platinum, iridium oxide, carbon nanotubes, or PEDOT. A typical shape is an array of needles, also called shafts or strands, derived from one or more common bases. The bases are intended to be placed outside the neural tissue, while the electrode-containing needles are intended to penetrate the inside.

[0003] To enable high-resolution interaction with large volumes of neural tissue, 3D arrays of electrodes need to be inserted. Essentially, flexible electrode arrays are too weak to penetrate the meninges or even brain tissue by themselves, and it has long been established that flexible neural electrode arrays need to be temporarily reinforced during insertion (either by a coating or external means such as an insertion shuttle).

[0004] To avoid the so-called "needle-bed effect," which significantly increases the required insertion force, it is common not to insert the electrodes of a flexible array all at once. Instead, one-by-one or row-by-row insertion is used.

[0005] Existing methods for inserting 3D arrays of flexible needles or strands involve the use of rigid insertion needles that grasp the electrode strands and insert them one by one. This method is difficult to scale up to a large number of insertion points. One expensive and complex improvement to alleviate this is the use of robotic-assisted surgery to reduce the lengthy procedure requirements, as disclosed, for example, in U.S. Patent Application Publication No. 20210007808.

[0006] Another method uses rigid (metal or silicon-based) insertion vehicles (or shuttles) to which flexible planar (2D) arrays are temporarily attached with a biocompatible, water-soluble substance such as polyethylene glycol. The use of interdigitated versions of such insertion vehicles allows for row-by-row insertion, significantly speeding up the implantation procedure, as disclosed, for example, in U.S. Pat. No. 10,214,001.

[0007] However, in our research, we encountered several drawbacks to this method. (a) This method does not scale well to very thin flexible electrode arrays. When arrays are typically thinner than 10–20 microns, they have little remaining rigidity, increasing the likelihood of the implant being pulled out during retraction of the insertion vehicle. Furthermore, (b) after unintentional removal, it is impossible to reinsert the implant because it is too weak to be inserted on its own, and there is no way to reattach the implant to the insertion vehicle during surgery. (c) The retraction of the insertion vehicle causes additional tissue damage.

[0008] Yet another method involves coating flexible planar 2D arrays with dissolvable or bioabsorbable reinforcing materials such as polyethylene glycol, PGA, PLGA, dextran, or sucrose. Such methods, as disclosed in U.S. Patent No. 10,335,519, have demonstrated the ability to insert single strands of thin, flexible electrodes with little damage and leaving a scar volume much smaller than the original volume occupied by the absorbable material.

[0009] However, this method may also be the easiest way to go beyond a simple single needle and insert larger arrays constructed from several combs or other shapes. It does not require complex manipulation and is useful for inserting large 3D arrays by hand or with simple instruments. The impracticalities of the shuttle-based method described above (no possibility to reinsert the implant, additional tissue damage due to shuttle retraction) are essentially avoided.

[0010] When investigating the latter method, our experiments revealed several weaknesses of the simple, straightforward coating technique when applied to planar interdigitated arrays, weaknesses that are not apparent when coating a single needle. Without a reinforcing coating, the base of a thin, flexible implant is often not rigid enough for insertion. Furthermore, when the entire implant is coated using conventional dip-coating techniques, the coating tends to form bridges between adjacent needles. As a result, inserting the implant into neural tissue requires much more force and causes much more tissue damage. An alternative is to not use the dip-coating technique. However, dip-coating results in sharp needle tips. Therefore, if the bridging issue can be resolved, dip-coating remains the preferred coating method.

[0011] Furthermore, planar electrode arrays inserted in this manner are only weakly attached to the underlying tissue and are supported only on their thin sides by the protruding shaft and by the connectors. The array should be fixed in place, not simply floated above the brain surface.

[0012] A sufficiently rigid and thick coating on the base of the array can help the electrode array stay in place. However, if the base is coated with the same dissolvable or bioabsorbable coating as the electrode needles, this reinforcement often wears off over time, leading to implant failure.

[0013] Fourth, the bases of planar arrays tend to be subjected to torsional forces from the cables connecting them to the electronic circuitry required to read out or control the electrodes, which tend to twist the bases downward and pull the attached needles out of the neural tissue.

[0014] Finally, it is difficult to connect the base of a thin, flexible electrode array to a superstructure that allows for better anchoring on the surface of the neural tissue. Summary of the Invention [Problem to be solved by the invention]

[0015] Therefore, there remains a need for flexible neural electrode arrays with improved insertion and fixation characteristics. [Means for solving the problem]

[0016] According to a first aspect of the present invention, a substantially planar neural electrode array is disclosed, the electrode array comprising: a flexible base; a connector cable attached to the base; one or more flexible shafts projecting from the base, the shafts being arranged to project from the same surface of the base in the same plane so as to form a comb-like structure, each of the one or more shafts comprising one or more electrode contacts, the electrode contacts being electrically coupled to a connector cable; and Equipped with - the first reinforcing layer extends across the base and a proximal portion of the one or more shafts, the proximal portion being adjacent the base; and a second absorbable or dissolvable reinforcing layer extending over a distal portion of the one or more shafts, the distal portion being spaced from the proximal portion; It is characterized by There is an overlap between the first backing layer and the second absorbent backing layer.

[0017] Preferably, there is substantially no overlap between the second absorbent backing layer and the base. In the context of the present disclosure, a "neural electrode array" should be understood as a device that is implantable into the neural tissue of a human or other mammal and intended for neural signal recording and / or neural stimulation of the tissue.

[0018] In the context of this disclosure, the adjective "flexible" means that the electrode array has a stiffness substantially less than that of current state-of-the-art silicon microneedle arrays for neural recording, such as the Utah array or NeuroPixels devices. Those skilled in the art will appreciate that the stiffness of an electrode array is a function of both the array's geometry and the elastic modulus of the material from which it is fabricated. While the electrode array is substantially fabricated from a material with an elastic modulus significantly lower, often by several orders of magnitude, than the metallic or ceramic materials typically used in implants, those skilled in the art will appreciate that the elastic modulus of this material may still be several orders of magnitude higher than the elastic modulus of neural tissue in humans or other mammals. Thus, in the present invention, the electrode array derives its flexibility primarily from its planar shape and limited thickness in the out-of-plane direction. Compared to more conventional neural electrode arrays fabricated substantially from silicon, the electrode array of the present invention has at least an order of magnitude greater flexibility.

[0019] In the context of the present disclosure, the adjective "absorbable" or "bioabsorbable" should be understood as "capable of being broken down and absorbed by the body of a living human or other mammal after being inserted into the body, leaving substantially no foreign matter within the body, and not causing a persistent inflammatory response within the body." The adjective "dissolvable" should be understood as "capable of being excreted by the body of a living human or other mammal after being inserted into the body, leaving substantially no foreign matter within the body, and not causing a persistent inflammatory response within the body." Those skilled in the art are aware of such bioabsorbable or dissolvable materials.

[0020] The electrode array according to the present invention is substantially planar, i.e., two of its dimensions are substantially greater than the third dimension. The electrode array comprises a substantially planar base to which shafts, also called needles or strands, are attached. All of these shafts are substantially in the same plane. The shafts are substantially in the same plane as the base of the electrode array. All of the shafts protrude in the same direction from the same side of the base of the electrode array. Thus, the electrode array has a comb-like structure, which is well known to those skilled in the art.

[0021] Electrode arrays are primarily constructed from flexible, biocompatible, and electrically insulating materials. These materials, typically polymers such as polyimide or parylene-C, are well known to those skilled in the art. Planar electrode arrays made from these materials are typically orders of magnitude more flexible than traditional metal or silicon-based electrode arrays. Internally, electrode arrays contain traces of conductive material. These traces connect electrode contacts on the shaft, where they are not covered by electrically insulating material, to connector cables that connect to the base of the electrode array. Electrode arrays can contain tens to hundreds of electrode contacts.

[0022] The first reinforcing layer extends over the base of the electrode array and the proximal portion of the electrode array shaft (the portion connecting to the base). The first reinforcing layer does not have to cover the entire surface area of ​​the base and proximal portions. The first reinforcing layer may only partially cover the base and proximal portions of the needle. The first reinforcing layer may extend partially or completely over the base and proximal portions without completely covering them; for example, the first reinforcing layer may feature a notch. An example of a first reinforcing layer that extends over the entire base and proximal portions without completely covering them is a reinforcing layer in the form of a honeycomb structure. The first reinforcing layer does not need to have a uniform thickness throughout its entire area.

[0023] The first reinforcing layer is made of a biocompatible, electrically insulating material. Preferably, the material is not soluble in body fluids or aqueous solutions. Preferably, the material is not bioabsorbable. Suitable materials for the first reinforcing layer include ceramics or polymers such as polyimide, Parylene-C, or UV-curable USP VI class epoxies. The first reinforcing layer increases the stiffness of the base and proximal portions of the electrode array primarily through the effect of increased thickness. The elastic modulus of the material for the first reinforcing layer may be lower, equal to, or higher than the elastic modulus of the material comprising the base and needles of the electrode array.

[0024] The second reinforcing layer extends over the distal portion (the portion furthest from the base) of the electrode array shaft. The second reinforcing layer is made of a biocompatible, electrically insulating material. Preferably, the material of the second reinforcing layer is soluble in body fluids or aqueous solutions. Preferably, the material of the second reinforcing layer is bioabsorbable. The second reinforcing layer can be made of, for example, polyethylene glycol, PGA, PLGA, dextran, or sucrose.

[0025] An important parameter in selecting a material for the second reinforcing layer is the time required for the material to degrade or bioabsorb. If the time required for complete absorption of the second reinforcing layer after implantation of the electrode array into neural tissue is longer than 3–4 weeks, fluid-filled voids are likely to remain around the shaft of the electrode array. In this case, contact between the array's electrode contacts and the surrounding neural tissue is insufficient for the array to function properly. Furthermore, adhesion of the array to the neural tissue will be very poor. On the other hand, if the material of the second reinforcing layer degrades or dissolves very rapidly under certain circumstances, the second reinforcing layer may lose its functionality before or during implantation of the electrode array. This can occur, for example, with a second reinforcing layer made from sucrose when exposed to the temperature and humidity typical of an operating room. For these reasons, the second reinforcing layer is preferably made from a material with an absorption time of less than 4 weeks but more than a few hours, such as certain types of PLGA.

[0026] The second reinforcing layer increases the stiffness of the distal portion of the electrode array primarily through the effect of increased thickness. The modulus of elasticity of the material of the second layer may be lower than, equal to, or higher than the modulus of elasticity of the material comprising the needles of the electrode array.

[0027] The preferred thickness of the second reinforcing layer is 50 to 200 microns, more preferably 100 to 150 microns.

[0028] There is an overlap between the first and second reinforcing layers so that the shaft is reinforced along its entire length. In the overlapping region, the second reinforcing layer is preferably applied over the first reinforcing layer. Preferably, the overlap between the first and second reinforcing layers is 50 microns or greater. Preferably, the overlap between the first and second reinforcing layers is 500 microns or less.

[0029] When the needles of an electrode array are inserted into a coating bath to apply the second reinforcing layer, the coating tends to form a meniscus between adjacent needles in the array. Those skilled in the art will appreciate that the meniscus formed can be concave or convex, depending on the contact angle between the shaft surface and the coating. Typically, the material used to apply the second reinforcing layer is attracted to the uncoated shaft surface material such that the contact angle is less than 90°, forming a concave meniscus. This is the case, for example, for PLGA coatings applied to polyimide or parylene-C. Alternatively, if the contact angle between the material used to apply the second reinforcing layer and the uncoated shaft surface material is greater than 90°, a convex meniscus will form. In typical material combinations that result in the formation of a concave meniscus, the apex of the meniscus corresponds to the bottom of the concave meniscus. Alternatively, in material combinations that result in the formation of a convex meniscus, the apex of the meniscus corresponds to the top of the convex meniscus.

[0030] If the apex of the meniscus does not contact the base of the array, the coating layer adheres to each individual needle without forming a coating bridge between adjacent needles upon retraction of the array from the coating bath. In contrast, if the apex of the meniscus does contact the base of the array, a coating bridge forms between adjacent needles upon retraction of the array from the coating bath. In the latter case, application of the second reinforcing layer transforms the electrode array from a comb-like structure to a wedge-like structure. This is undesirable because insertion of a wedge-like structure into neural tissue requires much greater force than insertion of a comb-like structure, causing much more damage to the neural tissue.

[0031] To avoid the formation of coating bridges between adjacent needles during application of the second reinforcing layer, there is preferably substantially no overlap between the second reinforcing layer and the base of the electrode array. Those skilled in the art will appreciate that the amount of overlap between the second reinforcing layer and the base of the electrode array that can be tolerated without forming coating bridges will depend, among other factors, on the material of the needles, the base and first reinforcing layer, the composition of the coating bath, and the conditions of coating application, such as the temperature or retraction rate of the electrode array from the coating bath. Preferably, the proximal portions of the needles of the electrode array (over which the first reinforcing layer extends) have a length greater than the overlap distance between the first reinforcing layer and the second reinforcing layer.

[0032] An advantage of the electrode array is that the first and second reinforcing layers reinforce the base and shaft of the flexible electrode array, thus allowing the shaft of the electrode array to be inserted into neural tissue or brain meninges of a human or other mammal.

[0033] A further advantage of the electrode array is that the second reinforcing layer dissolves or absorbs after insertion, allowing the shaft to subsequently move with the neural tissue into which the electrode array is inserted, while the first reinforcing layer preferably remains rigid enough to allow the base of the electrode array to remain in place and does not degrade.

[0034] An additional advantage is that the first reinforcing layer increases the thickness of the base of the electrode array, thereby increasing the contact area between the base of the electrode array and the surface of the neural tissue into which the electrode array shaft is inserted. As a result, the electrode array is more likely to stay in place due to the increased support and friction provided by this larger surface area. Furthermore, it allows for attachment to a support platform as described in claims 7 and 8.

[0035] An additional benefit of the electrode array is that the second reinforcing layer does not substantially overlap the base. As a result, no coating bridges form between two adjacent shafts during application of the second reinforcing layer. Therefore, each shaft is completely coated, but the space between the shafts is not bridged by the second reinforcing layer. As a result, only the individually coated needle-shaped shafts need to penetrate the meninges and neural tissue, reducing the force required to insert the electrode array and resulting in less tissue damage.

[0036] In the remainder of this disclosure, a partial realization of an electrode array according to the first aspect of the invention that includes a base and one or more shafts, but does not include the first and second reinforcing layers, may be referred to as an "uncoated electrode array."

[0037] In the remainder of this disclosure, a partial realization of an electrode array according to the first aspect of the invention, comprising a base, one or more shafts, and a first reinforcing layer, but not a second reinforcing layer, may be referred to as a "partially coated electrode array."

[0038] In the remainder of this disclosure, the "coated base" of the electrode array refers to the base of the electrode array together with the first reinforcing layer applied to the base.

[0039] In some embodiments of the electrode array, the proximal portion has a length of at least 50 microns and not more than 500 microns. Preferably, the proximal portion has a length greater than the overlap distance between the first and second reinforcing layers.

[0040] The advantage of judiciously selecting the length of the proximal section is that it simultaneously achieves three goals. First, the needles of the array can be reinforced along their entire length through the overlap between the first and second reinforcing layers. Second, the extent to which the first reinforcing layer, which is preferably neither dissolvable nor absorbable, protrudes into the tissue upon insertion of the electrode array can be limited. Third, the formation of coating bridges between adjacent needles of the electrode array can be avoided.

[0041] In some embodiments of the electrode array, the distal tip of the shaft of the electrode array has a tip angle of less than 45°, where the tip angle is defined as the sharpest angle found at the distal tip of the shaft. Preferably, the distal tip of the shaft is wedge-shaped or pyramidal.

[0042] An advantage of these embodiments is that electrode arrays with sharper tip angles require less force to insert into neural tissue.

[0043] In some embodiments of the electrode array, the coated base of the electrode array comprises one or more orifices.

[0044] An advantage of these embodiments is that tissue can grow through the orifices, thereby securing the electrode array in place. Alternatively, the orifices can be used to secure the electrode array to another surgically introduced mechanical structure. This can be achieved, for example, by a click mechanism or by a biocompatible adhesive or polymer. Preferably, the orifices used to secure the array to tissue extend through the thickness of the base of the array and the first reinforcing layer and have a diameter on the order of tens of microns. Preferably, the base of the electrode array includes more than 10 such orifices. Preferably, the orifices used to secure the array to the mechanical structure have a diameter on the order of hundreds of microns. Preferably, the orifices are dispersed throughout the coated base of the electrode array. Preferably, the orifices are arranged in a two-dimensional pattern on the coated base of the electrode array.

[0045] In some embodiments of the electrode array, the connector cable is a split multi-core serpentine cable. In the context of this disclosure, the term "multi-core" means that the connector cable includes two or more wires, each of which is a conductor surrounded by electrical insulation. Preferably, the connector cable includes one wire for each electrode contact of the electrode array. Preferably, each electrode contact of the array is electrically connected to a separate wire of the connector cable. Alternatively, the connector cable may include fewer or more wires than the number of electrode contacts of the electrode array. In a first alternative, two or more electrode contacts may be connected to the same wire, or one or more electrode contacts may be left unconnected. In a second alternative, two or more wires may be connected to the same electrode contact, or one or more wires may be left unconnected. Each of the wires of the cable may include a solid conductor or a stranded conductor.

[0046] Preferably, all of the wires of the cable are not grouped together in a single sheath, but rather the wires are distributed across multiple separate sheaths. For example, in a connector cable with 16 wires, these wires can be distributed across four separate sheaths, with each sheath containing four wires. Thus, in this example, the connector cable is made up of four separate cables, each of which has a smaller cross-section (each of which has four wires and one sheath) than the cross-section of a cable with 16 equivalent wires and one sheath. Preferably, these separate cables are not attached to each other except at their respective ends. Preferably, each of the separate cables is pre-formed into a serpentine shape.

[0047] An advantage of these embodiments is that the torsional stiffness of the split multi-core cable is lower than the torsional stiffness of a single multi-core cable carrying an equivalent number of wires of an equivalent cross section due to the lower polar moment of inertia of the separate cables.

[0048] A further advantage of these embodiments is that the pre-formed serpentine cable has extra length and is therefore stretchable.

[0049] Due to its lower torsional stiffness and stretchability, the split multi-core serpentine connector cable reduces the torsional forces exerted on the electrode array due to the twisting and pulling of the connector cable, which is almost unavoidable during surgery. By limiting the torsional forces transmitted to the electrode array, the split multi-core serpentine cable reduces the likelihood of damaging or dislodging the electrode array.

[0050] According to a second aspect of the present invention, a neural implant is disclosed, the device comprising: - one or more neural electrode arrays according to claim 1; -Electronics unit and Equipped with The connector cables of one or more electrode arrays are electrically connected to the electronics unit.

[0051] The implant's one or more neural electrode arrays are implantable into the neural tissue of a human or other mammal for the purpose of neural signal recording and / or neural stimulation of the tissue.

[0052] Preferably, the electronics unit is implanted between the neural tissue and one or more protective layers surrounding the neural tissue, for example, in the case of implantation of an electrode array in the brain, the electronics unit may be implanted between the meninges of the brain and the skull.

[0053] Preferably, the electronics unit comprises a system for wireless power transmission so that the implant can receive power from a device located outside the body of the human or other mammal in which it is implanted. Those skilled in the art will know systems suitable for wireless power transmission over short distances, such as, for example, inductive power transmission.

[0054] Preferably, the electronics unit comprises a system for wireless data communication so that it can send and receive data to and from devices located outside the body of the human or other mammal in which the implant is implanted. Those skilled in the art know systems suitable for wireless data communication over short distances, such as, for example, NFC or Bluetooth®.

[0055] In some embodiments of the device, the base of the one or more electrode arrays is mechanically connected by the platform. Preferably, the base of the one or more electrode arrays comprises an orifice and is mechanically connected to the platform by a mechanism such as a click mechanism or by a biocompatible adhesive or polymer.

[0056] Preferably, the platform is made of a biocompatible material that is not dissolvable or absorbable by the body of a living human or other mammal. Suitable materials are well known to those skilled in the art, including, for example, titanium, PMMA, or silicone. Preferably, the platform is not implanted within neural tissue, but floats above the neural tissue, and is not connected to the skull.

[0057] An advantage of these embodiments is that by mechanically connecting the electrode array(s) to the platform, the mechanical stability of the electrode array(s) is increased. By increasing the mechanical stability of the electrode array(s), the platform reduces the likelihood of damaging or dislodging the electrode array(s).

[0058] In some embodiments of the device, where the device comprises a platform connected to one or more electrode arrays of the device, the platform is created in situ.

[0059] For example, in the case of implantation of an electrode array into the brain, the platform can be created in situ, and a temporary opening in the skull (necessary for implantation of the electrode array) can serve as a mold for casting the platform, for example, from fast-curing biocompatible silicone.

[0060] An advantage of these embodiments is that the shape of the platform can be adapted to the surface shape of the underlying neural tissue.

[0061] A further advantage of these embodiments is that dedicated attachment of the platform to living tissue is not required: after skull closure, the platform can remain in place due to conformance with the underlying brain surface and pressure from the overlying skull surface.

[0062] In some embodiments of the device, one or more electrode arrays are stored in a removable holder, which separates the one or more electrode arrays from each other. This holder serves as temporary storage for the one or more electrode arrays; the holder is generally not implanted and is preferably discarded during surgery. Optionally, the holder is adapted to be reusable as a platform for mechanically connecting the bases of one or more inserted electrode arrays, as described above. In the latter case, the holder is not discarded during surgery.

[0063] An advantage of these embodiments is that the holder protects the electrode array or arrays from mechanical damage or contamination during storage or transport.

[0064] A further advantage of these embodiments is that the holder separates one or more electrode arrays from sticking together.

[0065] A further advantage of these embodiments is that the holder allows for easier grasping of the electrode array.

[0066] According to a third aspect of the present invention, there is provided a method for manufacturing a neural electrode array according to claim 1, the method comprising the steps of: - providing a planar substrate; - coating a planar substrate with a sacrificial layer; - depositing at least a first layer of an electrically insulating material on the sacrificial layer; - depositing one or more metal traces and electrode contacts on the first layer; - depositing and patterning at least a second layer of electrically insulating material over the first layer and the metal traces; - applying a first reinforcing layer; applying a second absorbent backing layer; Includes:

[0067] The electrically insulating material used for at least the first and second layers is flexible and biocompatible. Examples of suitable materials include polyimide or parylene-C. Preferably, the materials used for the first and second layers are the same. The second layer is patterned to completely cover the metal traces, except for the electrode contacts and bond pads.

[0068] The surface of the planar substrate serves as a substrate for fabricating the electrode array. An example of a suitable substrate is a silicon wafer. Depending on the specific method selected for applying the first reinforcing layer, the neural electrode array can be released from the substrate before or after application of the layer. Release can be achieved, for example, by dissolving the sacrificial layer described above.

[0069] Optionally, the planar substrate can be anisotropically patterned and etched to create a mold for the neural electrode array in the substrate, and the mold is shaped to transfer the pointed pattern to the shaft of the electrode array built on top.

[0070] In some embodiments of the method, the first reinforcing layer is applied using a first dip-coating process and the second reinforcing layer is applied using a second dip-coating process.

[0071] The electrode array is released from the substrate before undergoing a first dip-coating process. In the first dip-coating process, the base of the electrode array and the proximal portion of the shaft of the electrode array are coated by immersion in a coating bath. The immersion begins on the side of the base opposite the side from which the shaft protrudes. The electrode array is further immersed in the coating bath until the base and the proximal portion of the shaft are immersed in the bath. The first dip-coating process forms a first reinforcing layer on the base of the electrode array and the proximal portion of the shaft.

[0072] In the second dip-coating process, the distal portion of the electrode array shaft is coated by insertion into the coating bath. Insertion begins at the distal end of the shaft opposite the end where the shaft connects to the electrode array base. The electrode array is further inserted into the coating bath until the distal portion of the shaft is submerged in the bath. As the shaft is inserted into the coating bath, capillary tension causes the coating material to form a concave meniscus between adjacent shafts. If the shaft is inserted into the coating bath until the apex of the concave meniscus contacts the base of the electrode array, the coating will form a coating bridge between adjacent shafts when the implant is retracted from the coating bath. To avoid this phenomenon, the electrode array shaft is slowly inserted until the apex of the concave meniscus is within a predetermined distance of the base of the electrode array. This distance is selected so that bridging cannot occur between the electrode array shafts. After reaching its maximum insertion depth, the electrode array is retracted. The base of the electrode array is not inserted into the coating bath during the second dip-coating process. The base of the electrode array does not contact the coating bath during the second dip-coating process, which forms a second reinforcing layer on the distal portion of the shaft of the electrode array.

[0073] An advantage of these embodiments is that the two-step dip coating process ensures coverage of the electrode array, since in each of both steps the electrode array can be clamped in a position where it is not inserted into the coating bath.

[0074] An additional advantage of these embodiments is that the second dip coating process reduces the tip angle at the distal end of the shaft.

[0075] A further advantage of these embodiments is that the second dip coating process does not form coating bridges between the individual shafts of the electrode array because the base of the electrode array does not contact the coating bath.

[0076] In some embodiments of the method, the first reinforcing layer is applied using a molding process and the second reinforcing layer is applied using a dip coating process.

[0077] The electrode array is released from the substrate before undergoing a molding process. In the molding process, the electrode array is inserted into a prefabricated mold. Then, a first reinforcing layer material is placed into the mold. The mold is configured so that the first reinforcing layer material covers the base and proximal portions of the shaft of the electrode array. After the first reinforcing layer hardens, the electrode array is released from the mold. Then, a second reinforcing layer is applied to the electrode array using a dip coating process.

[0078] The dip coating process is similar to the second dip coating process described above. The advantages of the dip coating process are similar to the advantages of the second dip coating process described above.

[0079] The advantage of these embodiments is that the geometric shape of the first reinforcing layer can be freely chosen.

[0080] In some embodiments of the method, the first reinforcement layer is applied using a wafer-scale deposition process and the second reinforcement layer is applied using a dip-coating process.

[0081] In the deposition process, the first reinforcing layer is deposited before the electrode array is released from its carrier substrate. Those skilled in the art will recognize suitable techniques for the deposition of the first reinforcing layer; one possible example is the use of lithographic deposition.

[0082] The electrode array is released from the substrate before undergoing the dip-coating process, which is similar to the second dip-coating process described above. The advantages of the first dip-coating process are similar to those of the second dip-coating process described above.

[0083] An advantage of these embodiments is that the first reinforcement layer can be deposited on a wafer scale, which may improve batch-to-batch consistency, cost and throughput scalability, and manufacturing precision.

[0084] In some embodiments of the method, the first reinforcing layer is manufactured separately from the uncoated electrode array. The first reinforcing layer can be manufactured using any suitable process known to those skilled in the art, such as a molding process or a deposition process. Manufacturing the first reinforcing layer can include laser cutting. The first reinforcing layer is then attached to the uncoated electrode array, after which the second reinforcing layer is applied using a dip-coating process. The first reinforcing layer can be attached to the uncoated electrode array using any suitable attachment known to those skilled in the art, such as by gluing with a biocompatible adhesive or by thermal means.

[0085] The dip coating process is similar to the second dip coating process described above. The advantages of the dip coating process are similar to the advantages of the second dip coating process described above.

[0086] An advantage of these embodiments is that the manufacturing process for the first reinforcing layer can be freely selected, thereby allowing the manufacturing of the electrode array to be optimized for cost, precision or throughput.

[0087] In some embodiments of the method, the planar substrate is a silicon wafer. Preferably, the {111} crystal plane of the wafer is inclined at a substantially acute angle relative to the surface of the wafer, allowing the wafer to be anisotropically patterned and etched to create a mold for the neural electrode array within the wafer. In these embodiments, deposition of at least a first layer of electrically insulating material onto the sacrificial layer partially fills the substrate.

[0088] In the context of this disclosure, a substantially acute angle is an angle less than 54.7°, which is the inclination between the {111} crystal planes and the surface of a standard (100) silicon wafer.

[0089] An advantage of these embodiments is that the {111} crystal planes of silicon are non-etching in wet anisotropic etchants such as KOH and TMAH. Etch mask deposition, lithographic mask patterning, and anisotropic etching of the wafer according to these embodiments produces pits with near-atomically sharp tips that can be used as substrates for the fabrication of electrode arrays. Electrode arrays fabricated using this substrate have sharp tip angles at the distal end of the shaft, thereby reducing the force required for insertion into neural tissue. [Brief explanation of the drawings]

[0090] [Figure 1] 1A and 1B illustrate schematically an embodiment of a partially coated electrode array according to the present invention, including a first reinforcing layer but not a second reinforcing layer. [Figure 2] 1 shows a schematic representation of an embodiment of an electrode array according to the present invention, comprising a first reinforcing layer and a second reinforcing layer; [Figure 3] 3 shows a schematic cross section of the entire embodiment of FIGS. 1 and 2 along line AA'. [Figure 4] 10A-B illustrate schematically the formation of a fluid meniscus between adjacent shafts during application of the second reinforcing layer using a dip coating process. [Figure 5]1A and 1B illustrate schematically one embodiment of a connector cable for an electrode array according to the present invention. [Figure 6] 1A and 1B illustrate schematic diagrams of an embodiment of an electrode array for insertion into the brain of a human or other mammal. [Figure 7] 1 shows a schematic representation of an embodiment of an implant according to the invention. [Figure 8] 1 shows a schematic representation of an embodiment of an implant with a removable holder according to the present invention. [Figure 9] 1 illustrates schematically an embodiment of an implant with a platform according to the present invention. [Figure 10(a)] 1A-1C show schematic steps of a method for manufacturing an electrode array according to the present invention. [Figure 10(b)] 1A-1C show schematic steps of a method for manufacturing an electrode array according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0091] While the present disclosure will be described with reference to particular embodiments, they are illustrative of the present disclosure and should not be construed as limiting. It will be understood that the present disclosure is not limited by what has been particularly shown and / or described, and that alternative or modified embodiments may be developed in light of the overall teachings of the present disclosure. The drawings described are only schematic and are non-limiting.

[0092] References throughout this specification to "an embodiment" or "one embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present disclosure. Thus, the appearances of the phrase "in an embodiment" or "in one embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment, although they may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[0093] FIG. 1 schematically illustrates one embodiment of a partially coated electrode array according to the present invention. The electrode array 1 according to FIG. 1 is substantially planar, i.e., two of its dimensions are substantially larger than the third dimension. The electrode array comprises a substantially planar base 20 to which shafts 10, also called needles, are attached. All of these shafts 10 are substantially in the same plane. The shafts 10 are substantially in the same plane as the electrode array base 20. All of the shafts 10 protrude in the same direction from the same side of the electrode array base 20. Thus, the electrode array 1 has a comb-like structure, which is well known to those skilled in the art. Preferably, the uncoated electrode array, comprising the base 20 and the shafts 10, has a thickness greater than 0.5 microns, more preferably greater than 1 micron. Preferably, the uncoated electrode array, comprising the base 20 and the shafts 10, has a thickness less than 100 microns, more preferably less than 50 microns.

[0094] The electrode array is made from a flexible, biocompatible, electrically insulating material. These materials, such as polyimide or parylene-C, are well known to those skilled in the art. Internally, the electrode array contains traces of conductive material (not labeled in FIG. 1 ). These traces connect electrode contacts 30 on the shaft 10, where they are not covered by the electrically insulating material, to a connector cable (not shown in FIG. 1 ) that connects the base 20 of the electrode array 1. Preferably, the conductive material of the traces and electrode contacts is selected from platinum, gold, iridium oxide, carbon nanotubes, or PEDOT.

[0095] In the illustrated embodiment, the spacing between the shafts is constant, but this spacing may be variable. Preferably, the electrode array includes more than one shaft, more preferably more than five shafts, even more preferably more than 10 shafts, and most preferably more than 15 shafts. Preferably, the electrode array includes fewer than 200 shafts, more preferably fewer than 100 shafts, even more preferably fewer than 50 shafts, and most preferably fewer than 35 shafts. Preferably, each of the shafts has a width of 10 to 500 microns. Preferably, the distance between the shafts is 0.5 mm or more. Preferably, the distance between the shafts is 1 mm or less. Preferably, the tip angle of the shaft 10 at the distal end 12 is less than 45°. More preferably, the tip angle of the shaft 10 at the distal end 12 is less than 30°. Even more preferably, the tip angle of the shaft 10 at the distal end 12 is less than 20°. The smaller the tip angle, the easier it is for the electrode array to penetrate tissue.

[0096] Preferably, the electrode contacts are evenly spaced along the length of the shaft. Preferably, the electrode array comprises one or more electrode contacts per 10 mm of shaft length, more preferably two or more electrode contacts per 10 mm of shaft length, even more preferably five or more electrode contacts per 10 mm of shaft length, and most preferably ten or more electrode contacts per 10 mm of shaft length. Preferably, the electrode array comprises no more than 100 electrode contacts per 10 mm of shaft length, more preferably no more than 50 electrode contacts per 10 mm of shaft length, and even more preferably no more than 20 electrode contacts per 10 mm of shaft length. Those skilled in the art will understand that the number of electrode contacts can be adapted to the neural tissue into which the electrode array is inserted, as well as the specific purpose of the electrode array. Those skilled in the art will also understand that the spacing of the electrode contacts is a compromise between the resolution for recording or stimulating neural tissue and the manufacturing complexity of the electrode array.

[0097] In the illustrated embodiment, the various shafts have different lengths, although these lengths may be the same. In the illustrated embodiment, the various shaft lengths increase or decrease monotonically, although the variation in shaft length may follow any pattern. Preferably, the shaft lengths are such that upon insertion of the electrode array into neural tissue, the majority of the electrode contacts are located in the gray matter. Preferably, the shaft lengths are such that upon insertion of the electrode array into neural tissue, the electrode contacts are distributed as a substantial portion of the thickness of the gray matter layer in the target region.

[0098] For example, to probe the gray matter of the human visual cortex, the shortest shaft of the electrode array is preferably longer than 0.2 mm, more preferably longer than 0.5 mm, and even more preferably longer than 1 mm. The shortest shaft of the electrode array is preferably less than 3.5 mm, more preferably less than 3.0 mm, and even more preferably less than 2.5 mm. The longest shaft of the electrode array is preferably longer than 20 mm, more preferably longer than 25 mm, and even more preferably longer than 30 mm. The longest shaft of the electrode array is preferably less than 60 mm, more preferably less than 55 mm, and even more preferably less than 50 mm. This allows the shortest shaft to probe the entire thickness of the gray matter layer above the gyrus of the visual cortex, and the longest shaft to probe the entire extent of the gray matter layer adjacent to the sulcus of the visual cortex. Those skilled in the art will understand that the length of the shaft can be adapted to the neural tissue into which the electrode array is inserted as well as the specific purpose of the electrode array.

[0099] The first reinforcing layer 40 extends over the base 20 of the electrode array 1 and the proximal portion of the shaft 10 of the electrode array 1 (the portion connecting to the base 20). The first reinforcing layer 40 is made of a biocompatible, electrically insulating material. By extending over the proximal portion of the shaft 10, the first reinforcing layer 40 reinforces the shaft at a location that experiences the greatest mechanical stress upon insertion of the electrode array into neural tissue. Preferably, the first reinforcing layer 40 extends over the proximal portion of the shaft 10 a distance of 50 microns or more. Preferably, the first reinforcing layer 40 extends over the proximal portion of the shaft 10 a distance of 500 microns or less. Preferably, the first reinforcing layer 40 has a thickness of 100 microns or more. Preferably, the first reinforcing layer 40 has a thickness of 500 microns or less.

[0100] Preferably, the material of the first reinforcing layer is not soluble in body fluids or aqueous solutions. Preferably, the material of the first reinforcing layer is not bioabsorbable. The material of the first reinforcing layer may have an elastic modulus that is lower than, equal to, or higher than the typical elastic modulus of neural tissue in humans or other mammals. Suitable materials for this layer include UV-curable USP Class VI epoxies. Those skilled in the art will appreciate that the thickness of the first reinforcing layer may depend, among other things, on the material of the first reinforcing layer. For example, for a first reinforcing layer composed of epoxy, a thickness of approximately 250 microns may be appropriate.

[0101] In the embodiment of Figure 1, the base 20 and first reinforcing layer 40 include multiple orifices 21. After insertion of the electrode array, connective tissue mag grows through these orifices, thereby locking the electrode array in place. Alternatively, the electrode array may be glued in place using a biocompatible adhesive or polymer, with the orifices providing additional surface area for attaching the adhesive or polymer to the electrode array.

[0102] Preferably, the orifices used to secure the array to tissue extend through the thickness of the base of the array and the first reinforcing layer and have a diameter on the order of tens of microns. Preferably, the orifices used to secure the array to the mechanical structure have a diameter on the order of hundreds of microns. Preferably, the orifices cover more than 10% of the surface area of ​​the base of the electrode array.

[0103] Figure 2 shows a schematic representation of one embodiment of an electrode array according to the present invention. The embodiment of Figure 2 corresponds to the embodiment of Figure 1 with the addition of a second reinforcing layer 50. All features of the embodiment of Figure 1 are present in the embodiment of Figure 2, but for ease of reading they are not necessarily labelled.

[0104] The second reinforcing layer 50 extends across the distal portion of the shaft 10 of the electrode array 1. The second reinforcing layer 50 is made of a biocompatible, electrically insulating material. For example, the second reinforcing layer may be made of polyethylene glycol, PGA, PLGA, dextran, or sucrose. Preferably, the second reinforcing layer material is soluble in body fluids or aqueous solutions. Preferably, the second reinforcing layer material is bioabsorbable. The second reinforcing layer increases the stiffness of the distal portion of the electrode array primarily through the effect of increased thickness. The modulus of elasticity of the second layer material may be lower, equal to, or higher than the modulus of elasticity of the material comprising the needles of the electrode array. Those skilled in the art will appreciate that the required thickness of the second reinforcing layer may depend, among other things, on the material of the second reinforcing layer and, in the case of the shaft, on its shape. For example, for a second reinforcing layer composed of PLGA, a diameter of approximately 120 microns appears appropriate for each coated shaft of the array.

[0105] There is an overlap between the first reinforcing layer 40 and the second reinforcing layer 50 so that the shaft 10 is reinforced along its entire length. In the overlap region, the second reinforcing layer 50 is preferably applied over the first reinforcing layer 40. Preferably, the degree of overlap between the first reinforcing layer and the second reinforcing layer is 50 microns or more. Preferably, the degree of overlap between the first reinforcing layer and the second reinforcing layer is 500 microns or less.

[0106] When the second reinforcing layer 50 is applied using a dip coating process, there is substantially no overlap between the second reinforcing layer 50 and the base 20 of the electrode array 1 to avoid the possibility of bridging between the shafts 10.

[0107] Figure 3 shows a schematic cross-section of the entire embodiment of Figures 1 and 2 taken along line A-A'. The top of Figure 3 shows a cross-section of the embodiment of Figure 1. One electrode contact 30 is shown schematically. The bottom of Figure 3 shows a cross-section of the embodiment of Figure 2. The second reinforcement layer 50 overlaps the first reinforcement layer 40, ensuring reinforcement along the entire length of the shaft. The second reinforcement layer 50 covers the electrode contact 30. The electrode contact 30 can only come into contact with neural tissue once the second reinforcement layer 50 has dissolved or absorbed after insertion. Preferably, the second reinforcement layer 50 is applied using a technique that results in a sharp tip at the distal end 12 of the shaft 10. Dip coating is the most well-known and most economical of these techniques. The second reinforcement layer applied using a dip coating process typically follows the tip angle of the uncoated shaft within the plane of the shaft.

[0108] FIG. 4 schematically illustrates the application of a second reinforcing layer to a partially coated electrode array 1 using a dip-coating process. In this process, the distal portion of the electrode array shaft 10 is coated by insertion into a coating bath 200. Insertion begins at the distal end of the shaft opposite the end where the shaft connects to the electrode array base 20. The electrode array 1 is further inserted into the coating bath 200 until the distal portion of the shaft 10 is submerged in the bath. As the shaft 10 is inserted into the coating bath 200, capillary tension causes the coating material to form a concave meniscus 201 between adjacent shafts. If the shaft 10 is inserted into the coating bath 200 until the apex 202 of the concave meniscus 201 contacts the base 20 of the electrode array 1, the coating forms a coating bridge between adjacent shafts when the array 1 is retracted from the coating bath 200.

[0109] To avoid this phenomenon, the shaft 10 of the electrode array 1 is slowly inserted until the apex 202 of the concave meniscus 201 is within a predetermined distance of the base 20 of the electrode array 1. This distance is selected so that bridging cannot occur between the shafts 10 of the electrode array 1. After reaching its maximum insertion depth, the electrode array 1 is retracted. The base 20 of the electrode array 1 is not inserted into the coating bath during the dip-coating process. The base 20 of the electrode array does not contact the surface of the coating bath during the dip-coating process.

[0110] Preferably, the electrode array 1 is inserted deep enough into the coating bath 200 so that the surface of the fluid meniscus 201 overlaps the first reinforcing layer 40. This ensures that the second reinforcing layer applied by the dip coating process will overlap the first reinforcing layer 40.

[0111] FIG. 5 schematically illustrates one embodiment of a connector cable for an electrode array according to the present invention. In the embodiment of FIG. 5, the connector cable 32 is a split multicore serpentine cable comprising 16 wires 33. The wires 33 are individually insulated and grouped in pairs within a protective sheath. Each of the wires 33 in the cable 32 may comprise a solid conductor or a stranded conductor. Eight groups of two wires 33 each connect to the base 20 of the electrode array 1 at one end. At the other end, the eight groups of wires 33 preferably connect to a common electrical connector (not shown in FIG. 5). Preferably, the eight separate wire groups are not attached to each other between their ends. Preferably, the eight separate wire groups are pre-formed into a serpentine shape. Compared to a connector cable that groups all 16 wires together in a common protective sheet, a connector cable including eight groups of two wires each has a much lower polar moment of inertia. Those skilled in the art will be able to calculate the polar moment of inertia of a cable. Depending on the amount of wire, the splitting method, and the materials involved, the polar moment of inertia of a split cable such as that shown in FIG. 5 can be one to two orders of magnitude smaller than that of a non-split cable carrying the same amount of wire of equal cross-section. Because of its lower moment of inertia, the embodiment of connector cable 32 in FIG. 5 reduces the torsional forces exerted on electrode array 1 due to twisting and pulling on connector cable 32, which is almost unavoidable during surgery. By limiting the torsional forces transmitted to electrode array 1, split multicore serpentine cable 32 reduces the likelihood of damaging or dislodging electrode array 1.

[0112] Figure 6 shows a schematic representation of an embodiment of an electrode array inserted into the brain of a human or other mammal. The human or other mammal brain has a folded surface structure including gyri or ridges 500 and sulci or fissures 501. Internally, the brain is substantially composed of gray matter 502 and white matter 503, with the gray matter being found primarily in a layer several millimeters thick along the brain's surface.

[0113] In the embodiment of FIG. 6, the electrode array 1 is inserted into the brain of a human or other mammal through the surface of the gyrus 500. The array shaft 10 is inserted into the gyrus 500 while the base 20 and connector cable 32 are not. For some purposes, it is important that the electrode contacts on the shaft extend over a significant portion of the gray matter 502. This is the case, for example, for visual prostheses whose purpose is to induce visual perception through electrical stimulation of the visual cortex. Because it is known that a geometric mapping exists between the gray matter of the visual cortex and the geometry and resolution of the perceived image, it is considered particularly important that the electrode contacts of the visual prosthesis be distributed over a significant portion of the gray matter of the visual cortex.

[0114] While the gray matter 502 directly overlying the gyri 500 is easily accessible for insertion of the electrode array 1, the gray matter 502 embedded in the sulci 501 is not easily accessible. A possible solution to this problem is the insertion of electrode arrays 1 with shafts 10 of different lengths, as shown in Figure 6. The shaft shape shown in Figure 6 allows the electrode array to probe the gray matter adjacent to the sulci 501 without unnecessarily penetrating into the white matter 503.

[0115] 7 shows a schematic diagram of an embodiment of an implant according to the present invention. In the illustrated embodiment, the implant 100 comprises three electrode arrays 1. However, those skilled in the art will understand that the number of electrode arrays can be freely selected depending on the location and purpose of the implant. Each electrode array is connected to an electronics unit 110 by a connector cable 32.

[0116] Preferably, the electronics unit 110 is implanted between the neural tissue and one or more protective layers surrounding the neural tissue. When the device 100 is implanted, for example, in the brain, the shaft of the electrode array 1 is inserted through the meninges into the neural tissue. Preferably, the electronics unit 110 is attached between the meninges and the skull.

[0117] Preferably, the electronics unit 110 includes a system for wireless power transmission so that the implant can receive power from a device located outside the body of the human or other mammal in which it is implanted. Those skilled in the art will know systems suitable for wireless power transmission over short distances, such as inductive power transmission.

[0118] Preferably, the electronics unit comprises a system for wireless data communication so that it can send and receive data to devices located outside the body of the human or other mammal in which the implant is implanted. Those skilled in the art know systems suitable for wireless data communication over short distances, such as, for example, NFC or Bluetooth.

[0119] 8 shows a schematic representation of an embodiment of an implant with a removable holder according to the present invention. In a typical embodiment of the implant 100, there are approximately 20 electrode arrays 1. To allow for orderly insertion, the electrode arrays can be pre-sorted on a removable holder 120 or platform assembled on a permanent part of the implant 100.

[0120] The holder 120 protects the electrode arrays 1 from mechanical damage or contamination during storage or transport, separates the electrode arrays 1 from sticking together, and allows the electrode arrays 1 to be grasped more easily.

[0121] During implantation of the implant 100 into the brain, the electronics unit 110 is attached to (or placed in a recess within) the skull, and then the electrode arrays 1 are inserted sequentially into the brain. Finally, the holder 120 is removed. The holder 120 may be 3D printed from a biocompatible polymer (PEEK or polyamide) and features vertical protrusions that keep the electrode arrays 1 separated from each other during storage, transport, sterilization, and surgery.

[0122] Figure 9 shows a schematic representation of one embodiment of an implant 100 according to the present invention, comprising a platform 130, an electronics unit 110, and a plurality of electrode arrays 1. In the embodiment of Figure 9, the base of the one or more electrode arrays 1 is mechanically connected by the platform 130. Preferably, the base of the one or more electrode arrays 1 comprises an orifice and is mechanically connected to the platform 130 by a mechanism such as a click mechanism or by a biocompatible adhesive or polymer.

[0123] Preferably, platform 130 is made from a biocompatible material that is not dissolvable or absorbable by the living human or other mammalian body. Suitable materials are well known to those skilled in the art and include, for example, titanium, PMMA, or silicone. Preferably, platform 130 is not implanted within neural tissue, but floats above the neural tissue.

[0124] As already mentioned above, in some embodiments of the present invention the platform may be used as a holder for storing and transporting the electrode array.

[0125] 10(a) and 10(b) schematically illustrate steps in a method for fabricating an electrode array according to the present invention. In the first step 400 of the fabrication method, a substrate 300 is provided. Preferably, this substrate 300 is a silicon wafer. Although not shown in FIG. 10, in some embodiments, this substrate is a (113) silicon wafer that has been patterned using anisotropic wet etching to form shallow molds in the substrate, improving the sharpness of implants built on top.

[0126] In step 401, a sacrificial layer 301 is applied to the substrate. This sacrificial layer serves the purpose of enabling the release of the electrode array from the substrate 300. Those skilled in the art will be aware of suitable materials to use as the sacrificial layer and suitable methods for applying the sacrificial layer. For example, the sacrificial layer 301 can be deposited using sputter coating.

[0127] In step 402, a first layer of electrically insulating material 302 is deposited on the sacrificial layer 301. Preferably, layer 302 is made of a flexible, biocompatible and non-bioabsorbable material. For example, suitable materials for realizing layer 302 are polyimide or parylene-C.

[0128] In step 403, a conductive layer 303 is deposited on the electrically insulating layer 302. The conductive layer 303 is patterned to form the electrical traces 31 and electrode contacts 30 of the electrode array (not labeled in FIGS. 10(a) and 10(b)). Layer 303 is preferably made from a biocompatible conductive material such as platinum, gold, iridium oxide, carbon nanotubes, or PEDOT.

[0129] In step 404, a second layer of electrically insulating material 304 is deposited over the electrical traces 31 and electrode contacts 30. Preferably, layer 304 is made of a flexible, biocompatible, and non-bioabsorbable material. For example, suitable materials for realizing layer 304 are polyimide or parylene-C. Preferably, the material of layer 304 is substantially the same as the material of layer 302. Preferably, the deposition process used is such that layers 302 and 304 blend seamlessly with each other. Layers 302 and 304 together form the flexible, electrically insulating backbone of the implant.

[0130] In step 405, an etch mask 305 is deposited over layer 304. Subsequently, the etch mask 305 is patterned.

[0131] In step 406, the electrically insulating layers 302 and 304 are etched, with both the conductive layer 303 and the dedicated etching mask 305 acting as etching masks. Because both layers 303 and 305 function as etching masks and layers 303 and 305 are each individually patterned, a single etching step can create several features. Preferably, in step 406, electrode contacts 30 are defined on the shaft 10 of the electrode array by etching away the insulating layer 304 in the appropriate locations. Preferably, bond pads 306 for making connection with the connector cable 32 (not shown in FIGS. 10(a) and 10(b)) are created in the same manner during step 406. Preferably, the outline 307 of the electrode array is defined in step 406 by etching away both layers 302 and 304. In some embodiments of the method, etching the distal end 12 of the electrode array shaft 10 increases the sharpness of the shaft 10, for example, by etching a staircase pattern on the distal end 12.

[0132] In step 407 , a first reinforcing layer 40 is applied over the base portion 20 and the proximal end of the shaft 10 .

[0133] In step 408 , the partially coated electrode array is released from the substrate 300 by dissolving the sacrificial layer 301 .

[0134] In step 409, a second reinforcement layer 50 is applied using a dip coating process to obtain an embodiment of an electrode array 1 according to the present invention.

[0135] Preferably, the connector cable 32 is manufactured as an integral part of the array, such that the conductive core of the cable is continuous with the electrical traces and electrode contacts, and the insulating mantle of the cable is continuous with the electrical insulating layer of the array. [Explanation of symbols]

[0136] Reference sign 1. Electrode array 10. Shaft of electrode array 11 Proximal end of shaft 12 Distal end of shaft 20 Base of the electrode array 21 Orifice 30 electrode contacts 31 Metal Trace 32 connector cable 33 Connector cable wires 40 First reinforcement layer 50 Second reinforcement layer 100 implants 110 Electronics Unit 120 Holder 130 Platform 200 Coating bath 201 Meniscus 202 Meniscus apex 300 boards 301 Sacrificial Layer 302 First layer of electrical insulating material 303 Conductive layer 304 Second layer of electrical insulating material 305 Etching Mask 306 Bond Pad 307 Electrode Array Contour 400 First step of the manufacturing process 401 Second step of the manufacturing process 402 Third step of the manufacturing process 403 Fourth step of the manufacturing process 404 Fifth step of the manufacturing process 405 Sixth step of the manufacturing process 406 Seventh step of the manufacturing process 407 Eighth step of the manufacturing process 408 9th step of the manufacturing process 409 Tenth step of the manufacturing process 500 cerebral folds 501 Groove 502 Gray matter 503 White matter

Claims

1. A substantially planar neural electrode array (1), comprising: - a flexible base (20), - a connector cable (32) attached to said base (20); one or more flexible shafts (10) projecting from said base (20), said shafts (10) being arranged to project from the same surface of said base (20) in the same plane so as to form a comb-like structure, each of said one or more shafts (10) comprising one or more electrode contacts (30), said electrode contacts (30) being electrically coupled to said connector cable (32); Equipped with a first reinforcing layer (40) extending over said base (20) and a proximal portion of said one or more shafts (10), said proximal portion being adjacent to said base (20); an absorbable or dissolvable second reinforcing layer (50) extending over a distal portion of said one or more shafts (10), said distal portion being spaced from said base portion (20); It is characterized by An electrode array (1) in which there is an overlap between said first reinforcing layer (40) and said second reinforcing layer (50).

2. 2. The electrode array (1) of claim 1, wherein the proximal portion has a length of at least 50 microns and at most 500 microns.

3. 3. The electrode array (1) of claim 1 or 2, wherein the distal tip (12) of the shaft (10) has a tip angle of less than 45°.

4. Electrode array (1) according to any of claims 1 to 3, wherein the base (20) comprises one or more orifices (21).

5. Electrode array (1) according to any one of claims 1 to 4, wherein the connector cable (32) is a split multi-core serpentine cable.

6. A neural implant (100), comprising: - one or more neural electrode arrays (1) according to claim 1, an electronics unit (110); Equipped with A neural implant (100), wherein the connector cables (32) of the one or more electrode arrays (1) are electrically connected to the electronics unit (110).

7. 7. The implant (100) of claim 6, wherein the bases (20) of the one or more electrode arrays (1) are connected by a platform (130).

8. The implant (100) of claim 7, wherein the platform (130) is created in an intracranial opening.

9. An implant (100) according to any one of claims 6 to 8, wherein the one or more electrode arrays (1) are stored in a removable holder (120), the holder (120) separating the one or more electrode arrays (1) from each other.

10. 2. A method for manufacturing a neural electrode array (1) according to claim 1, said method comprising the steps of: - providing a planar substrate (300); - coating said substrate (300) with a sacrificial layer (301); - depositing at least a first layer of an electrically insulating material (302) on said sacrificial layer (301); - depositing one or more metal traces (31) and electrode contacts (30) on said first layer (302); - depositing at least a second layer of an electrically insulating material (304) on said first layer (302) and on said metal traces (31); - applying said first reinforcing layer (40); - applying said second reinforcing layer (50); A method comprising:

11. 11. The method of claim 10, wherein the first reinforcing layer (40) is applied using a first dip coating process and the second reinforcing layer (50) is applied using a second dip coating process.

12. 11. The method of claim 10, wherein the first reinforcing layer (40) is applied using a molding process and the second reinforcing layer (50) is applied using a dip coating process.

13. The method of claim 10, wherein the first reinforcing layer (40) is applied using a deposition process and the second reinforcing layer (50) is applied using a dip coating process.

14. 11. The method of claim 10, wherein the first reinforcing layer (40) is manufactured separately from the uncoated electrode array, the first reinforcing layer (40) is attached to the uncoated electrode array, and the second reinforcing layer (50) is applied using a dip coating process.

15. 15. The method of any of claims 10 to 14, wherein the planar substrate (300) is a single crystal silicon wafer, the {111} crystal planes of the wafer (300) being inclined at a substantially acute angle relative to the surface of the wafer (300), and the surface being anisotropically patterned and etched to create a mold for the neural electrode array (1) in the wafer (300).

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