WO2025111366A1

WO2025111366A1 - Cochlear implant device, method of making and using

Info

Publication number: WO2025111366A1
Application number: PCT/US2024/056717
Authority: WO
Inventors: Chong XIE; Lan LUAN; Elsa ACOSTA; Wonil SOHN; Pavlo ZOLOTAVIN
Original assignee: William Marsh Rice University
Current assignee: William Marsh Rice University
Priority date: 2023-11-20
Filing date: 2024-11-20
Publication date: 2025-05-30
Anticipated expiration: 2026-05-20

Abstract

A cochlear implant system and method of use is disclosed. The system includes a flexible cable, a core connected to the flexible cable, a branched electrode connected to the core, where branches of the branched electrode extend away from the core, a plurality of electrode contacts on the branches of the branched electrode, and an encapsulation encapsulating the core, the branched electrode, and the electrode contacts. Further, a method of fabricating a cochlear implant electrode is disclosed, including forming a network of electrical traces with a plurality of branches, where each electrical trace includes a flexible dielectric material and metallic wires, where each electrical traces forms a communication channel between a printed circuit board and a neural contact site and depositing a polymer onto the network of electrical traces, and curing the polymer to form the cochlear implant electrode.

Description

COCHLEAR IMPLANT DEVICE, METHOD OF MAKING AND USING

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] This invention was made with government support under Grant No. U01NS 115588 awarded by the National Institutes of Health. The government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Unites States Provisional Application Serial No. 63/601,125, filed October 13, 2023, entitled, “Cochlear Implant Device, Method of Making and Using the Implant, and Method of Making the Neural Electrodes” which is hereby incorporated by reference.

BACKGROUND

[0003] Hearing loss is a globally prevalent form of disability, with over 430 million people estimated to have moderate to complete hearing loss that require rehabilitation. Sensorineural hearing loss (SNHL) can be caused by damage to the cochlea that impairs its mechanism to transduce incoming sounds into neural signals. Patients with severe to profound SNHL are often treated with cochlear implants (CI) inserted inside the helical duct of the cochlea called scala tympani (ST). Cis bypass the impaired hearing transduction at the cochleae and directly stimulate the auditory neurons to activate them and elicit sound perception.

[0004] Despite a long history of cochlear implants, the number of stimulation sites on Cis has remained up to just 24, which is far below the number of some 30,000 auditory neurons inside cochlea. Such limited resolution stems from the conductive nature of the inside of cochlea in which CI is implanted, which causes the stimulating current to spread and blurs the specificity of stimulation. Various efforts have been made to mitigate the impact of current spread by reducing the distance between the contacts and the auditory neurons within the inner wall of cochlea to lower the current required to activate these neurons. However, no significant improvement has been accomplished yet, largely limited by the conventional cochlear implant electrode (“CI electrode”) designs consisting of linear contact arrays on a cylindrical electrode body. [0005] Implantable neural electrodes are widely used in treating neurological disorders such as Parkinson’s, epilepsy, hearing loss, and hold promising potentials in treating depression, paralysis, blindness, and many others. Existing medical implantable electrodes have proven to be working reliably for chronic uses in many human patients but are unable to provide single neuron recording or spatial localization of stimulation due to low channel-count. While there have been numerous strategies to address this problem by using thin-film microfabrication technology, they have intrinsic limitations in device robustness and long-term in vivo stability.

SUMMARY

[0006] This summary is provided only to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

[0007] In general, in one aspect, embodiments relate to a cochlear implant system including a flexible cable, a core connected to the flexible cable, a branched electrode connected to the core, where branches of the branched electrode extend away from the core, a plurality of electrode contacts on the branches of the branched electrode, and an encapsulation encapsulating the core, the branched electrode, and the electrode contacts.

[0008] In general, in another aspect, embodiments relate to a method of fabricating a cochlear implant electrode, including forming a network of electrical traces comprising a plurality of branches, where each electrical trace comprises a flexible dielectric material fabricated using photolithography, and metallic wires deposited using e-beam evaporation, sputtering, or chemical vapor deposition, and where each electrical traces forms a communication channel between a printed circuit board at a first end of the electrical trace and a neural contact site at a second end of the electrical trace. The method further includes depositing a polymer onto the network of electrical traces and curing the polymer to form the cochlear implant electrode.

[0009] In general, in yet another aspect, embodiments relate to a method of placing a cochlear implant system. The method includes inserting the cochlear implant system in a rolled-up format into a cochlea, where the cochlear implant system includes a flexible cable, a core connected to the flexible cable, a branched electrode connected to the core, a plurality of electrode contacts on each of the branches of the branched electrodes, an encapsulation encapsulating the core, the branched electrode, and the electrode contacts, and a degradable hydrogel coating on the encapsulation. The method further includes degrading the hydrogel coating inside the cochlea thereby unrolling the cochlear implant within the cochlea and contacting the electrode contacts with an inner wall of the cochlea.

[0010] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

[0011] Specific embodiments of the disclosed technology will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency. The advantages and features of the present invention will become better understood with reference to the following more detailed description taken in conjunction with the accompanying drawings in which:

[0012] FIG. 1 (Prior Art) shows a cross-section through a human ear with an implanted conventional cochlear implant;

[0013] FIG. 2 (Prior Artjdcpicts cross-sections through a human cochlear in accordance with one or more embodiments;

[0014] FIGs. 3(Prior Art) A and 3B depict a cochlear implant electrode locations;

[0015] FIG. 4 depicts a self-unrolling cochlear implant system in accordance with one or more embodiments;

[0016] FIGs. 5A - 5C depict elements a self-unrolling cochlear implant system in accordance with one or more embodiments;

[0017] FIG. 6 depicts a self-unrolled CI electrode in various stages of rolling in accordance with one or more embodiments; [0018] FIGs 7 A and 7B depict a self-unrolled CI electrode immediately after insertion into the cochlea and after self-unrolling in accordance with one or more embodiments;

[0019] FIG. 8 depicts a flowchart describing various steps of fabrication of a selfunrolled CI electrode in accordance with one or more embodiments;

[0020] FIG. 9 depicts the network of electrical traces of a self-unrolled CI electrode in various stages of fabrication in accordance with one or more embodiments;

[0021] FIG. 10 depicts a CI electrode in various stages of fabrication in accordance with one or more embodiments;

[0022] FIG. 11 depicts a flowchart in accordance with one or more embodiments;

[0023] FIG. 12 depicts a flowchart in accordance with one or more embodiments; and

[0024] FIGs. 13A-13E shows photographs of elements of Clelectrodes in accordance with one or more embodiments.

DETAILED DESCRIPTION

[0025] In the following detailed description of embodiments disclosed herein, numerous specific details are set forth in order to provide a more thorough understanding disclosed herein. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0026] Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers does not imply or create a particular ordering of the elements or limit any element to being only a single element unless expressly disclosed, such as by the use of the terms “before,” “after,” “single,” and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements. [0027] In the following description of FIGs. 1-13, any component described with regard to a figure, in various embodiments disclosed herein, may be equivalent to one or more like-named components described with regard to any other figure. For brevity, descriptions of these components will not be repeated with regard to each figure. Thus, each and every embodiment of the components of each figure is incorporated by reference and assumed to be optionally present within every other figure having one or more like-named components. Additionally, in accordance with various embodiments disclosed herein, any description of the components of a figure is to be interpreted as an optional embodiment which may be implemented in addition to, in conjunction with, or in place of the embodiments described with regard to a corresponding like-named component in any other figure.

[0028] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a horizontal beam” includes reference to one or more of such beams.

[0029] Terms such as “approximately,” “substantially,” etc., mean that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0030] It is to be understood that one or more of the steps shown in the flowcharts may be omitted, repeated, and/or performed in a different order than the order shown. Accordingly, the scope disclosed herein should not be considered limited to the specific arrangement of steps shown in the flowcharts.

[0031] The present disclosure relates to a high channel-count, self-unfolding branched cochlear implant (“CI”) electrode designed to enable high- specificity, high-frequency resolution stimulation of cochlea by using its self-unfolding mechanism to reliably position the contacts close to the cochlear inner wall, reducing the contact-to-neuron distance effectively mitigating the current spread, and lowering the current activation threshold, thereby enabling high- specificity stimulation. Methods of fabricating and using the cochlear implant are also described. [0032] Embodiments disclosed herein generally relate to a cochlear implant system, a method for making the cochlear implant system, a method for making the neural electrodes of the cochlear implant system and a method for placing the described cochlear implant system. While the present disclosure discusses cochlear implants specifically, as will be understood by those skilled in the art, the electrodes described herein may be applied to a number of different use cases where medical electrodes are employed. The neural electrodes described herein are highly tunable in terms of their dimensions and number of electrode contacts. As such, they can be optimized for different use cases outside of cochlear implants.

[0033] The current disclosure describes a strategy that combines the robustness of conventional medical electrodes with the high capacity enabled by thin-film microfabrication technology. This is a platform technology that may boost the channel-count of existing medical electrodes by at least 10 times, while maintaining comparable robustness and long-term device stability.

[0034] Described herein is a 200+ channel, rolled-up, self-unrolling branched electrode CI design aimed to reduce the current threshold for cochlear stimulation and enable higher-resolution stimulation. The electrode unrolls and expands to approach all sides of the scala tympani (ST) walls, reducing the contact- to-neuron distance (See FIGS. 7B). The high channel-count branched CI electrode may enable high-resolution stimulation by facilitating closer contacts-to-nerve distance to effectively mitigate the current spread and improve stimulation specificity.

[0035] FIG. 1 depicts a cross-section of a human skull (100) with a conventional CI system in place. Positioned externally, behind the ear (102), are located a microphone (112), speech processor, external magnet, and RF transmitter. These elements capture the sound signals, process them, and encode the transmission from the external transmitter (110) to an inner RF receiver placed internally to the bones of the skull (104).

[0036] Inside the cranium, typically near the inner surface of the bone of the skull (104), an inner RF receiver and internal pattern generator (IPG) (114) is implanted. From the IPG (114) a flexible cable (116) carries electrical signals generated by the IPG (114) to a conventional CI electrode (108) inserted into the cochlea (106). [0037] Acoustic signals (sound) detected by the microphone (112) are converted into electrical impulses and sent to the external transmitter (110) where they are converted into wireless signals, typically RF signals. These RF signals are received by the inner receiver which is used by the IPG (114) to generate an electrical stimulation pattern to the CI electrode, which is inserted into the scala tympani (220) of the cochlea.

[0038] FIG. 2 illustrates the structure of the cochlea (106) in more detail. The human cochlea (106), an element of the inner ear, is a spiral or helical-shaped chamber that curves about 2.5 times around a central pillar called the modiolus (232), which houses the spiral ganglion neurons (SGN) and auditory nerve fibers - the cochlear nerve. The helix of the cochlea (106) is divided into three chambers: the scala tympani (“ST”) (220), the scala vestibuli (226), and the scala media (222). The first two are filled with perilymph, and the scala media (222) is filled with endolymph. The differences in ion concentrations between these liquids allow for the hair cells located in the organ of Corti (226) to convert the mechanical energy of sound waves into electrical brain signals within the cochlear nerve (228). The cochlear nerve (228) then sends the electrical signal to the brain, encoding temporal information and other stimulus features.

[0039] A normally functioning ear (102) includes three sections: outer, middle, and inner ear. At the outer ear (102), the acoustic waves start their travel through the auditory pathway until they reach the middle ear’s small bones: the malleus, incus, and stapes. The primary function of these ossicles is to amplify and perform impedance-matching to convey the information of sound waves from the air-filled middle ear into the inner ear, specifically to the cochlea’s oval window. The propagated wave travels through the cochlear duct, which is filled with a fluid called perilymph. It reaches the hair cells, which play a crucial role in transducing the mechanical wave into an electrical stimulus for the cochlear nerve (228).

[0040] An important feature of the cochlea (106) is its tonotopic map, with each location of the cochlea (106) tuned to a specific sound frequency. The cells at the base of the cochlea (106) are specifically sensitive to high-frequency sounds, while the apex (helicextrama) (234) encodes the lower frequencies. Due to this tonotopic arrangement, the cochlea (106) can encode the frequency of the sound and stimulate the correspondent cochlear nerve fibers.

[0041] Cis aim to bypass the damaged portion and directly stimulate the cochlea nerve fibers with electrical pulses. Cis take advantage of the tonotopic map of the cochlea. The low frequencies are encoded to be delivered at the base of the cochlea, and higher frequencies toward the apex. By delivering electric current stimulation, the electrodes play the stimulation role that would normally be performed by hair cells. In this way, current excitation can be delivered to the auditory nerve at the location tuned to the frequency of interest, which in turn stimulates the auditory cortex and creates the perception of sound.

[0042] FIG. 3A depicts the issues caused by current spreading or dispersion in conventional Cis. The helical structure of the cochlea (106) ensures that the typical position adopted by an implanted CI electrode lies at or near the lateral wall (300) of the ST (220) separated from the spiral ganglions (230) in the organ of Corti (226) by approximately the radial distance of the ST (220). The ST (22) itself is filled with highly electrically conductive perilymph liquid. Two challenges arise from this sub- optimal separation. The first is a need for a greater amplitude of stimulation than would be necessary is the CI electrode (108) and the auditory nerves in the spiral ganglion (230) were in immediate proximity to one another, and the second is the current spreading (302) permitted by the separation. Current spread (302) describes the tendency of signals from a single CI electrode contact to influence or stimulate a large number of nerves within the spiral ganglion (230), including nerves that cover a spatial region of the organ of Corti (226) that is significantly greater than the spatial extent of the CI electrode contact itself. The resulting loss of resolution decreases the fidelity of the sound perceived by the patient. Further, although there are as many as 30,000 individual nerves in the cochlea (106), each of which may in principle be stimulated, the problem of current spreading implies that adding more, and more densely spaced, CI electrode contacts is of limited utility in providing a unique stimulus to each of these nerves.

[0043] FIG. 3B displays a more advantageous disposition of the CI electrode (108) achieved by the devices and methods described herein. In FIG. 3B, the CI electrode (108) is positioned immediately adjacent to the spiral ganglions (230) containing the individual auditory nerves. Accordingly, the amount of current spreading is much reduced, and in addition, the amplitude of the signal provided by each CI electrode contact may be much lower than for the typical CI electrode position, shown in FIG. 3 A, while still achieving the same level of stimulation to the auditory nerves.

[0044] FIG. 4 depicts an embodiment of the CI system (400) disclosed herein. At one end of the CI system (400) lies the electrical circuits embodied in a printed circuit board (“PCB”) (406), that may be connected to IPG (114). The IPG (114) receives RF signals from the external transmitter (110) and, conveys the RF signals to the PCB (406) that generates electrical signals to be transmitted using a network of electrical traces, running through a flexible cable (404) connecting the PCB to the contacts of the self-unrolling CI electrode (402), and hence to the auditory nerves in the spiral ganglion (230) of the cochlea. Prior to implantation of the self-unrolling CI electrode (402) into the cochlea, the branches of the self-unrolling CI electrode (402) are wound or coiled around the core (504) of the self-unrolling CI electrode (402) to form a cylindrical form having a diameter significantly less than that of the ST (220).

[0045] In accordance with one or more embodiments, FIG. 5A depicts the selfunrolling CI electrode (402), and elements thereof, prior to winding or coiling the branches (502) around the core (504). The self-unrolling CI electrode (402) includes a core (504), that in some embodiments may be stiffened with a stiffening wire (506), such as a titanium wire, and a number of branches (502) attached at one end of the branch to the core (504) and free or unattached at the other end of the branch.

[0046] In some embodiments, the branches (502) may be attached to the core (504) at an angle other than 90 degrees (as shown), while in other embodiments the branches (502) may be attached at 90 degrees. In still other embodiments, the branches (502) may be attached to the core (504) at varying angles, or example as a fan with one or more branches (502) at less than 90 degrees, one or more branches (502) at 90 degrees, and one or more branches (502) at more than 90 degrees. The angle at which the branches (502) attach to the core (504) should not be regarded as limiting to the scope of the disclosed invention.

[0047] In some embodiments, such as the embodiment shown in FIG. 5A, the branches (502) may have differing lengths. For example, the branch lengths near the tip of the self-unrolling CI electrode (402) furthest from the PCB (406) may have a shorter length than the branches (502) nearer the IPG (406). This design choice may be driven by the smaller internal dimensions of the ST (220) nearer the helixextrema (234) than nearer the base of the cochlea. However, in other embodiment, the branches (502) may all have the same length irrespective of their location on the self-unrolling CI electrode (402), or the branches (502) located near the PCB (406) may have a shorter length than the branches (502) farther from the PCB (406). The comparative length of each of the various branches (502) should not be interpreted as limiting to the scope of the disclosed invention.

[0048] Typically, a disclosed self-unrolling CI electrode (402) may have 15 to 25 branches, however some embodiments may have either more or less than this range of branches (502). For example, in some embodiments, the self-unrolling CI electrode (402) may have as many as 50 branches or as few as 5 branches. However, the number of branches (502) should not be interpreted as limiting the scope of the invention.

[0049] Similarly, each branch may have 6 to 8 electrode contacts, although some embodiments may have a number of electrode contacts greater or lesser than this range. Again, the number of electrode contacts should not be regarded as limiting the scope of the disclosed invention. In some embodiments, each branch may have the same number of electrodes

[0050] For example, a CI electrode (402) with 25 branches, each with 8 electrodes contacts would be a total of 200 electrode contacts with which to stimulate the cochlear nerves in the spiral ganglion - far exceeding the numbers previously available.

[0051] FIG. 5A further shows an expanded view of a branch of the self-unrolling CI electrode (402) in accordance with one or more embodiments. Each branch may include a portion of a network (510) made up from a plurality of electrical traces (518), with each electrical trace connecting an electrode contact (508) to the PCB (406) and configured transmit electrical signals configured to stimulate the auditory nerves, a described in connection with FIG. 3B.

[0052] FIGs. 5B and 5C show a portion of a branch (502) of the CI electrode in greater detail. FIG. 5B shows a plan view of the portion, while FIG. 5C shows a cross-section of the portion. FIG. 5B show three electrode contacts equally spaced along the branch. However, in some embodiments the spacing of the electrodes along the branch may not be equal. FIG. 5B also shows an optional stiffening wire (506) running along the core (504) of the CI electrode. Although the stiffening wire (506) is intended to stiffen the rolled CI electrode to ease insertion into the cochlea in some embodiments the stiffening wire (506) may be omitted. The presence of absence of the stiffening wire should not be interpretated as limiting the scope of the invention.

[0053] FIG. 5C shows a cross-section of the portion of the branch of the CI electrode. The cross-section illustrated runs through the center of the electrode contacts (508). In addition to the stiffening wire (506) within the core (504) the cross-section shows the silicone encapsulation (512) network of electrical traces, including the flexible dielectric material (514), electrical traces (518) and the metallic balls (516a, 516b) connecting an electrode contact (508) to each electrical traces (518).

[0054] To insert the self-unrolling CI electrode (402) into the cochlea (106) during the implantation of the CI system (400) the self-unrolling CI electrode (402) must first be transformed into a geometry that facilitates insertion, namely a long, small diameter cylinder and maintained in that geometry until insertion is complete. Specifically, the branches (502) of the self-unrolling CI electrode (402) may be rolled around the core (504) of the self-unrolling CI electrode (402) as shown in FIG. 6. Initially, FIG. 6 shows the flat self-unrolling CI electrode (402) prior to rolling, as previously displayed in FIG. 5A. In addition, FIG. 6 shows a partially rolled self-unrolling CI electrode (520). The rolling may be performed in either a clockwise or an anticlockwise manner without departing from the scope of the invention. Further a fully rolled self-unrolling CI electrode (522) is displayed on completion of the rolling operation. However, without further action, the rolled self-unrolling CI electrode (522) will, by design, automatically unroll or “self-unroll”. This automatic unrolling is clearly undesirable prior to insertion into the cochlea (106). To prevent the selfunrolling from occurring, the rolled self-unrolling CI electrode (522) may be partially or fully coated or encased in a material whose properties will inhibit unrolling before insertion but will permit self-unrolling after insertion. For example, the coated rolled self-unrolling CI electrode (524) may be coated in a gel, such as a hydrogel, that may safely and harmlessly dissolve, or weaken when immersed for a period of time in the perilymph liquid filling the ST.

[0055] FIG. 7A shows the coated rolled self-unrolling CI electrode (524) immediately after insertion into the ST (220) of the cochlea. By design the diameter of the coated rolled self-unrolling CI electrode (524) is significantly less than the smallest dimension of the ST (220) to allow the coated rolled self-unrolling CI electrode (524) to be inserted or threaded into the helically shaped ST (220). After insertion of the coated rolled self-unrolling CI electrode (524) the coating is allowed to physically and chemically interact with the perilymph liquid filling the ST (220) until the coating is dissolved or sufficiently weakened to permit the self-unrolling CI electrode (524) to unroll and to conform, at least in part, to the inner surface of the ST (220). In embodiments where the angle between the branches (502) and the core (504) of the self-unrolling CI electrode (700) is other than 90 degrees the unrolled branches (502) may form a helical shape around interior surface of the ST (220). Since the ST (220) itself has the form of a helix wound around the modiolus (232), the unrolled branches (502) of the self-unrolling CI electrode (402) may form as superhelix, i.e., a helix within a helix.

[0056] The branches (502) of the unrolled self-unrolling CI electrode (700) are pressed against or in near proximity to the walls of the ST (220) (including the portions of the walls of the ST (220) that contain the auditory nerves) in many, if not all, places along the length of the branches (502). Consequently, the electrode contacts (508) transmitting the cochlear nerve stimulating electrical systems are in near proximity to the cochlear nerves to be stimulated. As a result, as explained in FIGs. 3 A and 3B, the current spreading effect is minimized allowing the amplitude levels of the stimulating electrical signals to be minimized and significantly constraining the number of cochlear nerves activated by each electrode contact (508). As a result of this higher resolution “focusing” of the stimulation of the cochlear nerves it becomes useful to increase the number of electrode contacts (508) receiving unique electrical signals from the IPG (114) via the PCB (406). For example, the disclosed selfunrolling CI electrode (700) may have 200 or more electrode contacts (508) in comparison to the 10 to 20 electrode contacts of conventional CI electrodes.

FABRICATION [0057] In accordance with one or more embodiments, the self-unrolling CI electrode, such as self-unrolling CI electrode (402) may be fabricated using four main stages: Fabrication of Flexible Electrical Devices, Manufacturing of Metal Foil Contacts, Rivet Bonding, and Encapsulation. FIG. 8 depicts a summary of the steps in the fabrication process.

Microfabrication ofthin-film electrical interconnects'.

[0058] As shown in FIG. 9, microfabrication may be used to create a network (510) of electrically conducting pathways, i.e., electrical traces (518), that provide an electrical interconnection between the functional metal contacts that touch the tissue containing the nerves, i.e., spiral ganglions (230), and the PCB (406) and IPG (114). The steps of the microfabrication process include using photolithography combined with e- beam evaporation for the metal deposition to fabricate a sequence of layers of electrically insulating; conductive; and further insulating layers, to form a network (510) of electrical traces (518). In some embodiments, the insulating material may be a flexible electrically insulating material, such as polyimide (“PI”).

[0059] As an initial step (902) a silicon wafer (950) may be obtained, and a sacrificial nickel (“Ni”) layer (952) deposited on top of the silicon wafer (950) to enable the release of the flexible probes once the fabrication process is over. Next a thin flexible dielectric material layer (954), such as polyimide (“PI”), may be deposited, for example, using a spin-coating method to provide for insulation and encapsulation of the electrical paths to be subsequently laid. For example, the thin flexible layer may be 5pm thick, although in some embodiment the thin flexible layer may be only 1pm while in others the thin flexible layer may be 12pm thick. The thickness of the thin flexible layer should not be interpreted as limiting the scope of the disclosed invention. This layer may be soft-baked on a hot plate at a first temperature and the oven-baked using a varying temperature-time schedule. For example, the layer may be soft-baked at 65 °C and then oven-baked for approximately 12 hours under a varying temperature-time schedule that reaches a maximum 350°C.

[0060] After oven-baking, in step (904) a lift-off resist (LOR) layer (956) is spin-coated and baked, followed by a positive photoresist layer (958). [0061] Once the photoresist layer (958) is deposited, photolithography may be used to expose the design pattern (960) of the network (510) of electrical traces (518), in step (906). For example, maskless photolithography equipment (e.g., SF-100 Lightning, Bruker) may be used. To develop the exposed pattern, the wafer (including the silicon layer, nickel layer, dielectric material, lift-off resist, and positive photoresist layer (958)) may be immersed in a microposit developer, such as MF 319, for a short period of time, such as 75 seconds.

[0062] Next, in step 908, in some embodiments, metal may be deposited using e-beam evaporation to form the electrically conducting traces (518), while in other embodiments other mean for depositing metal, such as sputtering and/or chemical vapor deposition may be used. In some embodiments, the electrical traces (518) may include a composite of chromium (“Cr”) and gold (“Au”). For example, the electrical traces (518) may consist of layers of lOnm of Cr, 180nm of Au, and a top layer of lOnm of Cr. As will be appreciated by those skilled in the art, the deposited metals are not limited to Au and Cr. Other suitable metal combinations known in the art may be used. Photolithography equipment may then be used to expose the pattern for a hard mask that will protect the areas where the PI should remain intact. As noted above, maskless photolithography equipment may be used. To develop the exposed pattern, the wafer (including the silicon layer, nickel layer, dielectric material, lift-off resist, and positive photoresist layer (958)) may be immersed in a microposit developer, such as MF 319, for a short period of time, such as 75 seconds. The subsequent lift-off of the LOR layer (956) is achieved by immersing the wafer overnight in acetone, followed by a bath in MF 319 for 75 s. Once life-off is achieved, the electrical traces (518) remain.

[0063] In step (910) a second thin flexible dielectric material layer (954), such as a 5pm-layer of PI may be spin-coated and baked on top of the electrical traces (518), to achieve the encapsulation of the electrical traces (518).

[0064] After the installation of the second thin flexible dielectric material layer (954), and layers of LOR (956) and positive resist may be added, in step (912), to create a hard mask that defines the electrode outline. [0065] In step (914), the hard- mask pattern (defining the outline of the CI electrode) may be exposed using photolithography equipment and developed in MF 319. On top of this layer, a 200nm layer of titanium (“Ti”) may be deposited, in step (916) and the composite wafer immersed in acetone overnight for lift-off of the LOR, then finished with a bath in MF 319. At this point in the process, Ti covers the electrodes outline, allowing excess PI to be removed through dry etching (i.e., etching using a plasma of reactive gases), in step (918). This procedure creates the final PI cable outline and the holes needed to expose the contacts.

[0066] Penultimately, in step (920), the Ti hard mask is removed by hydrofluoric acid (“HF”) etching, followed by Cr etching to remove any residue on top of the exposed contacts.

[0067] For further handling, the Ni sacrificial layer (952) may be removed, in step (922) with a chemical etchant to release the Pl-encapsulated metallic traces.

Metal Foil Contacts

[0068] A metallic foil (1006) may be cut, e.g., laser-cut, into the desired electrode geometry and arrangement. To allow for metallic foil handling, processing, and later bonding to the electrical traces (518), a temporary adhesive (1004) may be used to fix the metallic foil (1006) to a glass substrate (1002), as shown in step (1000) of FIG. 10. Once the metallic foil (1006) is mounted, and a first layer of bonding balls (1008) has been placed (see details in the “Rivet Bonding” section), a laser may be used, in step (1100) to cut the contacts into the shape, size, and arrangement desired.

[0069] In some embodiments, stainless steel foil is coated with Cr and Au using e-beam evaporation to serve as the conductive electrode material. For example, the contact’s cross-section includes 10pm stainless steel foil, a lOnm Cr layer, and 180nm of Au. In other embodiments, the choice of material may be Platinum-Iridium (“Pt-Ir”), which is the benchmark in commercial cochlear implants, or Iridium-Oxide (“IrOx”) electrodes, commonly used in microfabricated neural probes involving electrodes with dimensions similar to those disclosed herein. Both materials exhibit features that favor chronic stimulation, due to their inert properties and current injection, because of their low impedance. [0070] As disclosed above, the metallic foil (1006) may be temporarily secured to a solid substrate to facilitate handling and processing through the various stages of the assembly process. Two steps are particularly important when choosing the mounting method, one being the laser-cutting of the contact sites and the second being the bonding of the metallic foil contacts to the electrical traces (518).

[0071] The first constraint is that the metallic foil must lie as flat as possible to ensure uniformity of the laser focus when moving along the surface. Differences of tens of microns between points are enough to prevent the metallic foil from cutting appropriately. Moreover, this surface uniformity allows consistent results throughout a single probe and between iterations.

[0072] The second constraint relates to the stability during exposure to fluctuating temperatures. In the rivet bonding stage, described below, the substrate is exposed to high temperatures that might impact the adhesion strength between the metallic foil (1006) and the solid substrate, causing a premature detachment of the metallic foil (1006) contacts or bonding failure. During the application of ultrasonic force to bond the contacts, the selected temporary adhesive (1004) must secure the metallic foil (1006) in place despite the temperature induced and whether the metallic foil (1006) has already been cut into small electrodes.

[0073] In some embodiments, wax may be used as a temporary adhesive (1004) while in other embodiments thermal release tape may be used. For example, wax-based temporal adhesive (1004) may be Crystalbond 590, with a reported flowing point of 150°C. To start the application, the wax and the glass substrate may be heated up to 130°C. A small amount of melted wax is placed on the heated substrate while still on the hot plate, followed by a piece of metallic foil (1006). The composite sample may then be removed from the heat and compressed, for example between Teflon sheets. A hydraulic heat press may be used to distribute the wax evenly. For example, the sample may be placed between the heated pressing plates (140°C) for 10 minutes before applying any pressure to ensure that the wax is flowing again and that the pressure is not applied to hardened material. Afterward, the pressure may be increased, for example to 1 MPa for 5 minutes, followed by 5 minutes under 2MPa. Before releasing the pressure, the sample may be cooled, e.g., to 60°C to ensure the wax is hard enough to retain its shape, avoid movement, and prevent bubble formation.

[0074] In other embodiments, a thermal release tape with a release temperature, such as 200°C, may be used. To mount the sample using this method, the tape is cut into rectangular pieces of the same size as the metallic foil to be secured. The bottom part of the tape, containing conventional adhesive, is attached to the glass substrate using a roller to apply pressure, avoid air bubbles, and ensure adhesion. Afterward, the clear acetate covering the heat-release adhesive is removed from the tape’s top surface, and the sample is mounted on top again using a roller.

[0075] Once the metallic foil (1006) is mounted on a solid substrate, the first layer of bonding balls (1008) is placed on the location of the desired contacts. This ensures a clean surface and a strong attachment between the bonding ball and the metallic foil before any laser debris contaminates the area. After completing this step, the sample is aligned with a laser that cuts the contacts into the desired shape, size, and arrangement.

Rivet Bonding

[0076] In step (1020), an automatic wire bonder may be used to attach the metallic foil (1006) contacts to the electrical traces (518), employing a rivet bonding technique. This technology may employ ultrasonic force and heat to bond a metallic ball, generated from a metallic thread, with a sample placed on the mounting stage. For example, an initial gold (Au) ball may be bonded to the center of each foil contact position. Then, the outlines of the metallic foil contacts are laser-cut. Subsequently, the electrical trace is aligned on top of the metallic contacts by aligning the electrical trace-holes to the extruding gold balls (1008). The first layer of gold balls (1008) serves as anchors during probe alignment procedure, and to hold the electrical trace temporarily. In step (1300) once all the electrical traces are in place, a second round of gold balls (1308) is placed on top of the first round of gold balls (1008), creating a rivet bonding that bonds the metallic foil contacts to the electrical trace.

[0077] The same procedure is used to bond the backend of the electrical traces (518) to a flexible printed circuit board (“PCB”) (406). The flexible PCB (406) is mounted on a glass substrate (1002), a first round of Au balls is applied, followed by the PI cable alignment, and finishing with a second round of gold balls to form the rivet.

Encapsulation

[0078] In step (1040), before releasing the electrode and removing the excess metallic foil, a layer of silicone encapsulation (1042) may be applied, for example, using blade- casted with an automatic Doctor blade film coater. In some embodiments, a mix of two silicones, e.g., Sylgard 184 and Sylgard 186, may be used, with a ratio of 1:1 by weight. This mixture provides an advantageous balance of flexibility and adhesive strength. The encapsulation thickness may be about 100 pm, which allows full coverage of the bonding balls, providing dielectric properties and robustness to the bond strength. However, the thickness of the encapsulation may be varied based upon the needs of each individual device. Moreover, this layer directly contributes to the overall device stiffness, which is crucial for the insertion stage, while still featuring flexible properties relevant to the stages of rolling, insertion, and deployment. In some embodiments, the encapsulation may be cured at a temperature of about 125°C, which is below the activation temperature of the heat release tape, to avoid premature release of the metallic foil (1006) from the substrate (1002).

[0079] Once the silicone encapsulation (1042) is fully cured, the sample may be heated, for example on a hot plate, to release the temporary adhesive (1004) and release the electrode, as shown in step (1050). Immersion in a cleaning agent, such as isopropyl alcohol (IPA), and sonication at 35°C for 15 minutes may be used to remove any residual adhesive. In addition, the bottom of the metallic foil may be wiped with IPA and air-dried before removing the excess foil.

[0080] FIG. 11 shows a flowchart (1100) for a method of fabricating a cochlear implant electrode, in accordance with one or more embodiments. The method begins in step (1102) by forming a network (510) of electrical traces (518) as described above with reference to FIG. 9. Each electrical trace includes a flexible dielectric material fabricated using photolithology, and metallic wires deposited using e-beam evaporation. Each electrical trace (518) may form a communication channel between a PCB (406) at a first end of the electrical trace and a neural contact site at a second end of the electrical trace. The network (510) of electrical traces (518) may include a plurality of branches.

[0081] For each electrical trace, step (1104) an electrode contact (508) may be formed at the neural contact site of the electrical trace by rivet bonding a metallic foil to the second end as described above with reference to FIG. 10.

[0082] In step (1006) the first end of the electrical trace may be rivet bonded to the printed circuit board. In some embodiments, the rivet bonding of the metallic foil may include laser-cutting the metallic foil into a desired geometry for the network (510) of electrical traces (518) and fixing the metallic foil to a glass substrate (1002) using a temporary adhesive (1004). In some embodiments, the rivet bonding of the metallic foil, for each neural contact site, may include bonding a first metallic ball to a center of the neural contact site, laser-cutting the metallic foil around the neural contact site, aligning an electrical trace on top of the foil contact, and bonding a second metallic ball on top of the first metallic ball. In some embodiments, the metallic foil may be a gold foil and the first and second metallic balls may be a first and a second gold balls.

[0083] In step (1108) a polymer may be deposited onto the network (510) of electrical traces (518) and in step (1110) the polymer may be cured to form the cochlear implant electrode. In some embodiments, the polymer may be polydimethylsiloxane.

[0084] FIG. 12 shows a flowchart (1200) for a method of placing or implanting a CI system (400) in accordance with one or more embodiments. In step (1202) a CI system (400) may be inserting in a rolled-up format into a cochlea. The CI system (400) may include a flexible cable, a core (504) connected to the flexible cable, a branched electrode connected to the core (504), a plurality of electrode contacts (508) on each of the branches (502) of the branched electrode, and an encapsulation encapsulating the core (504), the branched electrode, and the electrode contacts (508), and. a degradable hydrogel coating on the encapsulation. In some embodiments the encapsulation material may be polydimethylsiloxane. In some embodiments, the hydrogel may be gelatine. Ine one or more embodiments branched electrode may include a polyimide polymer [0085] In step (1204) the hydrogel coating may be degraded inside the cochlea thereby unrolling the cochlear implant within the cochlea.

[0086] In step (1206) the electrode contacts (508) may make contact with an inner wall of the cochlea. In one or more embodiments, the unrolled cochlear implant may connect the inner wall of the cochlea along a trajectory with a superhelical geometry.

EXAMPLES

[0087] The Examples described herein were made according to the methods described above. FIG. 13A shows a magnified photograph, taken with a digital light microscope, of a self-unrolling CI electrode (402) after nickel etching (See Step 922) before rivet bonding and encapsulation, while still attached to a temporary supporting framework (1302). The active length of the self-unrolling CI electrode (402) is 27 mm (~ linch) and 25 branches (502) radiate from the core (504). The network (510) of electrical traces (518) can be seen running along the core (504) with a portion of the electrical network running up each branch (502) to connect to each of the eight electrode contacts (508) disposed on each branch (502).

[0088] FIG. 13B shows a picture taken with a digital light microscope of the selfunrolling CI electrode (402) after rivet-bonding, encapsulation, and removal from the temporary supporting framework. FIG. 13C shows a higher magnification photograph of a portion of six of the branches (502) seen in FIG. 13B. On each branch four or the eight electrode contacts (508) may be seen in greater detail.

[0089] FIG. 13D shows a photograph of a coated rolled self-unrolling CI electrode (402) (524) prior to insertion into a synthetic cochlea (shown in FIG. 13D). The length of the coated rolled self-unrolling CI electrode (402) is approximately 27 mm and its diameter approximately 500 pm. FIG. 13E shows a photograph of the coated rolled self-unrolling CI electrode (402) (524) inserted into a synthetic translucent cochlea (1324) but before the coating dissolved to release the branches, and the same electrode after self-unrolling within the synthetic translucent cochlea (1324) to form an unrolled self-unrolling CI electrode (402) (1326). [0090] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claims

CLAIMS What is claimed:

1. A cochlear implant system comprising: a flexible cable; a core connected to the flexible cable; a branched electrode connected to the core, wherein branches of the branched electrode extend away from the core; a plurality of electrode contacts on the branches of the branched electrode; and an encapsulation encapsulating the core, the branched electrode, and the electrode contacts.

2. The system of claim 1, wherein the electrode contacts comprise a platinum-iridium composite.

3. The system of claim 1, wherein the branched electrode comprises a number of branches between 10 branches and 25 branches.

4. The system of claim 1, wherein each electrode contact of the plurality of electrode contacts comprises between 6 electrode contacts and 10 electrode contacts.

5. The system of claim 1, wherein the electrode comprises a polyimide polymer.

6. The system of claim 1, wherein the cochlear implant system is configured to be rolled up such that the branches are rolled around the core, thereby providing a rolled-up cochlear implant having a cylindrical shape.

7. The system of claim 6, wherein the rolled-up cochlear implant system is configured to be unrolled and have a superhelical geometry in a cochlea.

8. The system of claim 6, wherein the rolled-up cochlear implant further comprises a degradable hydrogel coating on the encapsulation.

9. A method of fabricating a cochlear implant electrode, comprising: forming a network of electrical traces comprising a plurality of branches, wherein each electrical trace comprises a flexible dielectric material fabricated using photolithography, and metallic wires deposited using e-beam evaporation, sputtering, or chemical vapor deposition, wherein each electrical traces forms a communication channel between a printed circuit board at a first end of the electrical trace and a neural contact site at a second end of the electrical trace, and depositing a polymer onto the network of electrical traces; and curing the polymer to form the cochlear implant electrode.

10. The method of claim 9, wherein the rivet bonding the metallic foil further comprises: laser-cutting the metallic foil into a desired geometry for the network of electrical traces; and fixing the metallic foil to a glass substrate using a temporary adhesive.

11. The method of claim 10, wherein the rivet bonding the metallic foil further comprises, for each neural contact site: bonding a first metallic ball to a center of the neural contact site; laser-cutting the metallic foil around the neural contact site; aligning an electrical trace on top of the foil contact; and bonding a second metallic ball on top of the first metallic ball.

12. The method of claim 11, wherein the metallic foil comprises gold foil and the first and second metallic balls comprise a first and a second gold ball.

13. The method of claim 9, wherein the flexible dielectric material comprises a polyimide material.

14. The method of claim 9, wherein forming the network of electrical traces comprises, for each electrical trace: forming an electrode contact at the neural contact site of the electrical trace by rivet bonding a metallic foil to the second end, and rivet bonding the first end of the electrical trace to the printed circuit board.

15. The method of claim 9, further comprising: rolling up the branches of the cochlear implant electrode to provide a rolled-up cochlear implant electrode having a cylindrical shape; and coating the rolled-up cochlear implant electrode with a degradable hydrogel to provide a cochlear implant system.

16. A method of placing a cochlear implant system comprising: inserting the cochlear implant system in a rolled-up format into a cochlea, wherein the cochlear implant system comprises: a flexible cable; a core connected to the flexible cable; a branched electrode connected to the core; a plurality of electrode contacts on each of the branches of the branched electrode; an encapsulation encapsulating the core, the branched electrode, and the electrode contacts; and a degradable hydrogel coating on the encapsulation; degrading the hydrogel coating inside the cochlea thereby unrolling the cochlear implant within the cochlea; and contacting the electrode contacts with an inner wall of the cochlea.

17. The method of claim 16, wherein the branched electrode comprises a number of branches between 10 branches and 25 branches.

18. The method of claim 16, wherein each electrode contact of the plurality of electrode contacts comprises between 6 electrode contacts and 10 electrode contacts.

19. The method of claim 16, wherein the unrolled cochlear implant has a superhelical geometry in the cochlea.

20. The method of claim 16, wherein the electrode comprises a polyimide polymer.