WO2024167983A1

WO2024167983A1 - Opto-electrical cochlear implant

Info

Publication number: WO2024167983A1
Application number: PCT/US2024/014705
Authority: WO
Inventors: Claus-Peter Richter; Joaquin CURY
Original assignee: Northwestern University
Current assignee: Northwestern University
Priority date: 2023-02-08
Filing date: 2024-02-07
Publication date: 2024-08-15
Anticipated expiration: 2025-08-08

Abstract

A cochlear implant includes an electrical driver that includes a plurality of current stimulators that deliver current pulses to neurons. The implant also includes a light source that delivers optical pulses to the neurons. The implant also includes an optical driver that includes a plurality of channels. The plurality of channels turn the light source on and off to control the optical pulses delivered to the neurons. The implant further includes a microcontroller operatively coupled to the electrical driver and the optical driver. The microcontroller maintains a clock to control timing of the current pulses and the optical pulses.

Description

OPTO-ELECTRICAL COCHLEAR IMPLANT

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the priority benefit of U.S. Provisional Patent App. No. 63/483,842 filed on February 8, 2023, the entire disclosure of which is incorporated by reference herein.

REFERENCE TO GOVERNMENT RIGHTS

[0002] This invention was made with government support under grant number R01- DC 18666 awarded by the National Institutes of Health/National Institute on Deafness and other Communication Disorders. The government has certain rights in the invention.

BACKGROUND

[0003] Cochlear implants (Cis) are devices that restore some hearing in individuals that are severely -to-profoundly deaf. More specifically, a cochlear implant is a surgically implanted neuroprosthesis that provides a person who has moderate-to-profound sensorineural hearing loss with sound perception. Today, more than 500,000 hearing impaired individuals have received a CI. As a result, Cis are considered one of the most successful neural prostheses in use.

SUMMARY

[0004] An illustrative cochlear implant includes an electrical driver that includes a plurality of current stimulators that deliver current pulses to neurons. The implant also includes a light source that delivers optical pulses to the neurons. The implant also includes an optical driver that includes a plurality of channels. The plurality of channels turn the light source on and off to control the optical pulses delivered to the neurons. The implant further includes a microcontroller operatively coupled to the electrical driver and the optical driver. The microcontroller maintains a clock to control timing of the current pulses and the optical pulses.

[0005] In one embodiment, the electrical driver includes a plurality of integrated circuits and a total of 24 current stimulators. In another embodiment, the optical driver includes a plurality of integrated circuits and a total of 16 channels that switch from constant to a pulse mode. In some embodiments, the plurality of channels turn the light source on and off between different current levels that are defined by input voltages. In another embodiment, the system includes a plurality of digital to analog converters that control the input voltages.

[0006] The implant can also include one or more waveguides that guide the optical pulses to the neurons. In one embodiment, each of the one or more waveguides includes tubing that is at least partially filled with a viscous polymer. In another embodiment, the implant includes a microphone operatively coupled to the microcontroller. In one embodiment, the electrical driver, the light source, the optical driver, and the microcontroller are formed as a 6-layers stack electrical circuit. In another embodiment, the 6-layers stack electrical circuit includes a dielectric in between layers and a plurality of vias, where the vias include through holes, blind vias, buried vias. In another embodiment, the 6-layers stack electrical circuit is formed into a single chip.

[0007] An illustrative method of operating a cochlear implant includes delivering, by an electrical driver, current pulses from a plurality of current stimulators to neurons. The method also includes controlling, by an optical driver that includes a plurality of channels, an on/off state of a light source to control optical pulses. The method also includes delivering, by the light source, the optical pulses to the neurons. The method further includes maintaining, by a microcontroller operatively coupled to the electrical driver and the optical driver, a clock to control timing of the current pulses and the optical pulses.

[0008] In some embodiments, the method includes turning the light source on and off between different current levels that are defined by input voltages. In other embodiments, the method includes controlling, by a plurality of digital to analog converters, the input voltages. One embodiment includes guiding, by one or more waveguides, the optical pulses to the neurons. In another embodiment, each of the one or more waveguides includes tubing that is at least partially filled with a viscous polymer.

[0009] In another embodiment, the electrical driver, the optical driver, and the microcontroller are formed as a 6-layers stack electrical circuit. In another embodiment, the 6-layers stack electrical circuit includes a dielectric in between layers and a plurality of vias, wherein the vias include through holes, blind vias, buried vias. In another embodiment, the method includes inserting the light source into scala tympani of a basal turn of a cochlea of a patient that receives the cochlear implant. In another embodiment, the light source comprises a plurality of light sources, and the method includes separating the light sources from one another to prevent interference. [0010] Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Illustrative embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like numerals denote like elements.

[0012] Fig. 1 depicts compound actual potential (CAP) amplitudes plotted versus radiant energy in accordance with an illustrative embodiment.

[0013] Fig. 2 depicts that triangular and ramp-up wave shapes are approximately 2-3 times more power efficient as comparable ramp-dow n and square pulses in accordance with an illustrative embodiment.

[0014] Fig. 3A depicts ABRs that were recorded during optical and electrical costimulation in a deaf white cat in accordance with an illustrative embodiment.

[0015] Fig. 3B depicts a typical histology of a middle turn in the deaf white cat in accordance with an illustrative embodiment.

[0016] Fig. 4 depicts results of the interaction of two optical stimuli that were delivered with 2 independent optical fibers at two sites along the cochlea separated by ~400pm in accordance with an illustrative embodiment.

[0017] Fig. 5 depicts a fabricated waveguide made by filling microtubing with OrmoComp in accordance with an illustrative embodiment.

[0018] Fig. 6 depicts a set of outputs for one electrical channel in accordance with an illustrative embodiment.

[0019] Fig. 7A depicts waveguide propagation losses for a wavelength of 535 nm in accordance w ith an illustrative embodiment.

[0020] Fig. 7B depicts waveguide propagation losses for a wavelength of 1375 nm in accordance with an illustrative embodiment.

[0021] Fig. 7C depicts waveguide propagation losses for a wavelength of 1460 nm in accordance with an illustrative embodiment. [0022] Fig. 7D depicts waveguide propagation losses for a wavelength of 1550 nm in accordance with an illustrative embodiment.

[0023] Fig. 8 depicts a schematic representation of the 6-layers stack in in the electrical circuit of an opto-electrical cochlear implant in accordance with an illustrative embodiment.

[0024] Fig. 9 depicts the ty pes of locations and vias present in the 6-layers stack electrical circuit in accordance with an illustrative embodiment.

[0025] Fig. 10 depicts the assignment of the layers in the 6-layers stack electrical circuit in accordance with an illustrative embodiment.

[0026] Fig. 1 1 depicts a schematic of the top layer of the 6-layers stack electrical circuit in accordance with an illustrative embodiment.

[0027] Fig. 12 depicts a view of the top layer of the 6-layers stack electrical circuit with through holes in accordance with an illustrative embodiment.

[0028] Fig. 13 depicts a view of the bottom layer that includes optical drivers in accordance with an illustrative embodiment.

[0029] Fig. 14 depicts a microcontroller soldered onto a small printed circuit board in accordance with an illustrative embodiment.

[0030] Fig. 15 depicts a conventional electrode fused with an array of optical sources in accordance with an illustrative embodiment.

[0031] Fig. 16 depicts components of a cochlear implant in accordance with an illustrative embodiment.

DETAILED DESCRIPTION

[0032] Cochlear implants (Cis) are devices that aim to restore at least some hearing in individuals that are severely-to-profoundly deaf. With traditional Cis, the performance of individual users varies largely. While some patients are able to communicate over the phone in different languages as a result of using a CI, others receive little benefit from Cis. For all of the users, noisy listening environments and music perception constitute a challenge. Contemporary cochlear implant devices all use electrical current to stimulate neurons. As determined by the electrode configuration and the electrical-tissue properties, the current spreads in the tissue and consequently does not allow stimulation of focused neuronal populations. The resulting overlap of stimulation fields limits use of neighboring electrode contacts. A goal of the proposed systems and methods is to overcome the limitations of electrical stimulation by using infrared neural stimulation (INS) in a human CI. It is believed that devices and strategies using optical stimulation will dramatically impact the existing multibillion-dollar neurostimulation market and positively impact patient outcomes.

[0033] It has been argued that performance of Cis could be improved by reducing the interaction between neighboring CI electrode contacts and subsequently creating more independent channels for stimulation. Described herein is an approach that uses photons to evoke responses from small populations of neurons. This approach takes advantage of the fact that optical radiation can be delivered more selectively to groups of target neurons. It is anticipated that with optical stimulation, neural prostheses with enhanced neural fidelity can be developed. Two methods for optical stimulation are currently under investigation, optogenetics and infrared neural stimulation (INS). The inventors have shown that stimulation with infrared light is feasible in animal models such as mice, gerbils, guinea pigs, and cats, including two genetically deaf animals models (a deaf white cat and VGLUT3 KO mice). Also, a hybrid opto-electrical cochlear implant has been developed for use in a human.

[0034] The spatial selectivity of both proposed optical methods, INS and optogenetics, has been shown to be comparable with that of acoustical stimulation. Stimulation with light in either method would overcome challenges related to electrical cunent spread in tissue. One of the methods, optogenetics, involves the delivery of a viral vector to express photosensitive ion channels in the membrane of the spiral ganglion neurons (SGNs). The rate at which the ion channel or optogenetic tool is expressed plays a crucial role, since low expression levels in the SGNs require larger photon flux rates for stimulation. Additionally, high expression rates of the optogenetic tool can irreversibly damage the cells. Studies on the optogenetic approach in the adult auditory system has shown a 46 % success rate for evoking a response after an adeno associated virus (AAV) transfer of a faster channel rhodopsin mutant, the CatCh. However, the injection of the viral vector decreased the number of SGNs by -25%. The loss of SGNs through the treatment might become a challenge in CI candidates who already have a substantially reduced number of auditory neurons. Even with fast ion channels, the pulse repetition rate, for which significant phase locking can be observed, is not above 250 pulses per second (pps) using optogenetics. The rate limiting factor for the pulse repetition is the -4 millisecond (ms) delay for the response following the stimulus. In gerbils, the radiant energy required to evoke auditory brainstem responses (AB Rs) during cochlear stimulation is 4 microJoules (pJ)/pulse and 2 pj to reach behavioral thresholds. [0035] In contrast to optogenetics, INS does not involve the expression of a photosensitive ion channel with a viral vector. During INS the fluid and tissue absorb the photons and the energy is converted into heat. Spatially and temporally confined heating evokes action potentials in the SGNs. The challenge for INS is the delivery of heat to the target structure(s), which needs to be removed or dissipated to prevent thermal damage during stimulation. The results show that for optogenetics and INS, pulse repetition rates and radiant energies to stimulate the auditory system are similar. At present, tissue heating limits the rate of stimulation to about 250 pulses per second (pps) at a maximal radiant energy of 25 pj/pulse. Lowering the radiant energy⁷ for INS would allow for faster repetition rates. The inventors have addressed this limitation by using a more efficient wavelength for INS (A, =1375 nanometers (nm)), through optimized pulse shapes such as ramp-up pulses, and through the use of combined optical stimulation and electrical stimulation.

[0036] As background, the principle of INS works through temporally and spatially confined heating. It has been shown that irradiation of neural tissue with blue light evokes action potentials, and target wavelengths have been identified for use in safe neural stimulation. For example, several suitable wavelengths in the near infrared and infrared (e.g., 1840 nm and 2100 nm) spectrums have been identified for which optical sources are available for stimulation. Upon the absorption of a photon by the water in the tissue, its energy is converted into heat, inducing a rapid temperature change, which then evokes an action potential. Temporally and spatially confined heating depolarizes the cell by changing the membrane capacitance, resulting in a depolarizing inward current. The change in capacitance can result from changes in membrane thickness or from small-diameter nanopores in the membrane.

[0037] Furthermore, it has been demonstrated that transient receptor potential cation channels of the vanilloid group (TRPV) are involved. These channels are temperature sensitive and are highly calcium selective. The data has demonstrated that intracellular calcium homeostasis changes during INS. Spatially and temporally confined heating, which occurs during INS, also results in stress relaxation waves. A consideration is whether or not the resulting pressure is the dominating effect in cochlear INS. Results have been presented where cochlear INS did not evoke responses in deaf animals. Those findings differ from reports that showed responses in deaf animals missing hair cells. The argument for direct interaction between the radiation and the neurons comes from single unit recordings done in the inferior colliculus and masking experiments in the guinea pig. [0038] Additionally, INS evokes ABRs in congenitally deaf mice and deaf white cats. As discussed below, one of the deaf mouse models lacks the vesicular glutamate transporter-3 (VGLUT3-/-) and does not release glutamate at the inner hair cell afferent synapse. The deaf white cats do not have remaining hair cells and a largely reduced population of SGNs. Also, the Atohlf/kiNeurogl gene manipulated mice show no ABR response to acoustical stimuli, but did exhibit responses to INS.

[0039] Parameters for the optical cochlear implant (oCI) can include a radiation wavelength, energy’ on target, pulse shape and duration, a combination of different types of stimulation, the number of optical sources to use, etc. In one embodiment, a radiation wavelength of 1375 nm can be used by the system. Alternatively, a different wavelength value may be used (e.g., 1350, 1360, 1380, 1390, 1400, 1450, etc.). The photon absorption in water is similar between 1460 and 1860 nm. However, the technology for small optical sources is well advanced for radiation wavelengths between 1370 and 1600 nm wavelengths because these wavelengths are used in communication networks, which are advanced technology⁷ when compared to the technology’ available around 1860 nm. In particular, radiation at / = 1550 nm has the same penetration length in water as radiation at /.= ! 860 nm, the wavelength used to study INS. To explore the possibility of using 1550 nm for INS the inventors have directly compared the possibility of evoking auditory responses at both wavelengths in the same animal. Stimulation with both radiation wavelengths is comparable. Furthermore, the inventors have tested optical sources at 1375 nm and found that the optical sources are about 3 times more power efficient than sources for 1550 nm or 1860 nm and that INS is more efficient at 1375 nm. Fig. 1 depicts compound actual potential (CAP) amplitudes plotted versus radiant energy’ in accordance with an illustrative embodiment. As shown, the energy required to evoke a 60 pV CAP was about 4 times smaller at 1=1375 nm when compared to the energy at /.- 1860 nm.

[0040] In one embodiment, the energy on target for the system can be between 0-500 milliwatts (mW). Alternatively, a different energy’ on target may be used. Both flat and angle polished optical fibers were used to determine the radiant energy required for stimulation. The radiant power to stimulate with infrared light was typically' below 80 mW. It is noted that those values were taken from experiments at 1860 nm and square pulses and do not reflect the more efficient stimulation at 1375 nm and ramp-up pulse shapes. [0041] In some embodiments, the system can utilize a 100-JJ.S ramp-up pulse shape. Alternatively, the system may use a different duration and/or shape. It has been determined that the membrane of a neuron has two capacitive components, an electrical component and a temperature dependent component that interact and have to be considered during optical stimulation. The inventors have used equations to predict the responses to pulses, with an energy profile that follows a square, ramp-up, ramp-down, or a triangle. Modeling showed that the ramp-up waveform and the triangular waveform were more power efficient to increase the tissue temperature. Corresponding experiments in cats and in guinea pigs confirmed that among the tested pulse shapes the ramp-up pulses are the most efficient for stimulation. Amplitude traces were obtained in 4 cats. Fig. 2 depicts that triangular and ramp- up wave shapes are approximately 2-3 times more power efficient as comparable ramp-down and square pulses in accordance with an illustrative embodiment.

[0042] In one embodiment, combined optical and electrical stimulation can also be used by the system. Combined optical and electrical stimulation reduces the radiant energy required for INS in deaf white cats, as show n in Fig. 3. All of the cats tested were profoundly deaf with no response to acoustic stimuli up to 120 dB SPL (re 20 pPa). Histology showed severe degeneration of the cochleae with missing organs of Corti, loss of outer and inner hair cells, and reduced number of SGNs to less than 7% of the counts found in control animals. ABRs were recorded in response to electrical pulses between 0 pA and 1400 pA and in response to the laser pulses (X = 1860 nm, radiant energy (Q) = 0-164 pj/pulse, pulse repetition rate (PR) = 10 Hz. and pulse width (PW) = 100 ps). Responses evoked by optical stimulation were only seen if the neuron counts were larger than 7% of counts in normal hearing animals.

[0043] Fig. 3A depicts ABRs that were recorded during optical and electrical costimulation in a deaf white cat in accordance with an illustrative embodiment. The optical pulses were delivered 1 ms before biphasic electrical pulses. No responses were observed for electrical or optical stimulation alone. However, the combined opto-electrical stimulation resulted in responses. It was determined that the low number of remaining SGNs is the likely cause for the high stimulus levels required for stimulation. Fig. 3B depicts a typical histology of a middle turn in the deaf white cat in accordance with an illustrative embodiment. The organ of Corti on the basilar membrane is missing completely , and the spiral ganglion neuron counts in Rosenthal’s canal (arrow) are largely reduced. In Fig. 3B. the scale bar = 100pm. [0044] The number of optical sources to be used by the system was also considered. The inventors have evaluated the spatial selectivity of INS in acutely damaged cochleae of guinea pigs. The stimulated section along the cochlear spiral ganglion was estimated from the responses obtained from neurons in the central nucleus of the inferior colliculus (ICC). Spatial tuning curves were significantly narrower for INS than for acoustic stimulation. On average, the spread of activation evoked by optical stimuli was 357 pm, versus 383 pm for acoustic pure tone stimuli. The interaction between two optical sources was determined by the reduction of compound action potential amplitude. From Fig. 4 it can be seen that the optical sources should be separated by at least 400-500 pm to avoid interactions. As described below, optrodes can be assembled from individual light sources, which are placed into scala tympani and connected with small (~25 pm) platinum wires with the pulse generator. Small laser diodes (100x250x450 pm³) that could be used would result in optrodes with about ~25 optical channels. This is about three times more than the 8 independent channels achieved in contemporary Cis.

[0045] Fig. 4 depicts results of the interaction of two optical stimuli that were delivered with 2 independent optical fibers at two sites along the cochlea separated by ~400pm in accordance with an illustrative embodiment. The outcome measure was the reduction of the response to a probe light pulse (second pulse) by a 2 ms proceeding pulse (masker). The results show that the response to the probe stimulus is unmasked, indicating that at 400 pm little interaction occurs.

[0046] Critical placement and orientation of the sources was also explored. Optical fibers were beveled at their ends and the beveled surfaces were coated with dielectric mirrors such that the beam path was to the side and not along the optical axis of the fiber (i.e., side firing fibers). The fibers were inserted along scala tympani of the basal turn of the guinea pigs to quantify the effect of the orientation of the beam path on the ability to stimulate the neurons. The largest response was obtained while SGNs were irradiated by the laser. Deviations of ±45° in orientation from the maximum response were acceptable (the compound action amplitude decreased less than 6 dB).

[0047] With respect to safety, using a high stimulation rate and/or high pulse energy, the delivery of infrared light bears the risk of thermal damage to the tissue. C APs were used to determine the injury thresholds in guinea pig cochleae. The selected optical parameters for INS were the wavelength (Z= I 869 nm), the pulse duration (100 ps), the pulse repetition rate (250 pps), and the radiant energy (0 to 127 pj/pulse). For up to 5 hours of continuous irradiation, no functional damage was observed for a 250 pps repetition rate and radiant energies up to 20 pj/pulse. Cochlear histology from animals exposed to 98 or 127 pj/pulse at 250 pps did not show a decrease of spiral ganglion neuron or hair cell counts. The inventors also examined cats chronically implanted with an optical fiber to stimulate the cochlea with infrared radiation. Stimulation for 4 weeks, 8 hours per day, did not result in a change in the electrophysiological responses. SGN counts and post-implantation tissue growth, which was localized at the optical fiber, were similar in chronically stimulated and sham implanted cochleae.

[0048] Electronic design of the proposed device involved power considerations, component considerations, layout considerations, etc. Power calculations are based on a long term behavioral study in cats, and on the experiments on channel interaction during optical stimulation in guinea pigs. During the behavioral study, responses were obtained with a 200 pulses/s repetition rate, a 100 ps pulse length, and 12 pj radiant energy. The channel interaction found in guinea pigs suggests that in the human cochlea 18 independent channels can be achieved with optical stimulation. A battery with a 3,000 mAh capacity is required to power the optical stimulation over an 18 hour period with laser diodes (CHIP- 176) from SemiNex (Danvers, MA) and IC-HG current laser switches (IC House, Bodenheim, Germany). This value is within 6,300 mAh of the capacity of batteries used in Medtronic implants.

[0049] With respect to circuit design, in one embodiment, the opto-electrical CI (oeCI) includes four main blocks: A) an electrical driver including two integrated circuits (ICs) with a total of 24 current stimulators providing current pulses up to 2.5 mA and containing chargerecovery circuits. B) An optical driver having three ICs with a total of 16 channels switching from constant to pulse mode (1 kHz). These channels can turn on and off light sources (e.g., laser diodes, light-emitting diodes (LEDs), etc.) between different current levels defined by input voltages. The inputs are controlled by a IC that includes 16 digital-analog converters (DACs). C) An ultra-low power 32-bit microcontroller. D) A MEMS microphone. As discussed in more detail below, circuits were designed in a 6-layers PCB (size 3.5x3.5 cm²) using the software Altium Design 2019 (USA) and manufactured by the foundry OSH Park (USA). [0050] Additionally, to deliver light along the cochlea, two strategies were explored. The first strategy involved inserting light sources arrays into scala tympani of the basal turn of the cochlea. The second strategy involved delivering light using bundles of polymeric waveguides. To manufacture the waveguides, the inventors used a polyimide microtubing (MicroLumen Inc., USA) with an outer and inner diameters of 132 pm and 100 pm, respectively. The polyimide tubing served as the cladding for the waveguide. The waveguide's core was a viscous polymer OrmoComp (Kayaku Advanced Mate-rials, USA) aspirated into the tubing. Exposure to ultraviolet light cured the polymer within a few minutes. The inventors fabricated waveguides of at least 2 cm in length and measured the propagation and bending losses.

[0051] Fig. 5 depicts a fabricated waveguide made by filling microtubing with OrmoComp in accordance with an illustrative embodiment. The propagation losses were obtained by coupling light (wavelengths 535-1550nm) into the waveguide and recording the energy at the tip. After this measurement, the waveguide was shortened by 1 mm and the energy was measured again. To determine the waveguide's bending losses, the inventors recorded the radiant energy' at the tip of the waveguide while straight and while bent (360°) at various radius of curvature (2 mm and 4 mm).

[0052] Fig. 6 depicts a set of outputs for one electrical channel in accordance with an illustrative embodiment. The current was passed along a 0.5 kQ-resistor to generate a voltage difference. Similar results were obtained for the optical channels. The OrmoComp waveguide's propagation losses were 9.78 ± 3.53, 1.52 ± 0.55, 2.43 ± 0.60, 2.79 ± 1.28 dB/cm, at wavelengths of 535, 1375, 1460, and 1550 nm, respectively. The bending losses at the same wavelengths for 2 mm curvature were 8.61 ± 0.92, 2.54 ± 1.06, 2.41 ± 0.68 and 1.80 ± 0.19 dB, correspondingly. For 4 mm, the bending losses are 4.99 ± 1.78, 0.44 ± 0.31, 0.75 ± 0.05 and 0.82 ± 0.22 dB, respectively. Fig. 7A depicts waveguide propagation losses for a wavelength of 535 nm in accordance with an illustrative embodiment. Fig. 7B depicts waveguide propagation losses for a wavelength of 1375 nm in accordance with an illustrative embodiment. Fig. 7C depicts waveguide propagation losses for a wavelength of 1460 nm in accordance with an illustrative embodiment. Fig. 7D depicts waveguide propagation losses for a wavelength of 1550 nm in accordance with an illustrative embodiment. In Figs. 7A-7D, the dashed line represents the average. [0053] In an illustrative embodiment, the implant has 24 electrical channels and 18 optical channels. In order to have a small implant, the inventors chose a 6-layers design. Typically, most electronic circuits have two layers. Adding more layers provides more space for tracks and connections. This approach, while much more complex as well as expensive, is suitable for the opto-electrical CI (oCI). Each layer is separated by dielectrics. More importantly, the device uses blind/buried vias. These are connections between internal layers. Fig. 8 depicts a schematic representation of the 6-layers stack in in the electrical circuit of an opto-electrical cochlear implant in accordance with an illustrative embodiment. For each layer and dielectric, the selected materials and their thickness is shown. Fig. 9 depicts the types of locations and vias present in the 6-layers stack electrical circuit in accordance with an illustrative embodiment. As shown, some vias are through holes (from top to bottom), some are blind (e.g., top layer to layer 2), and some are buried (e.g., layer 1 to layer 4).

[0054] Fig. 10 depicts the assignment of the layers in the 6-layers stack electrical circuit in accordance with an illustrative embodiment. It is noted that the dielectrics between layers are not shown in Fig. 10. Fig. 11 depicts a schematic of the top layer of the 6-layers stack electrical circuit in accordance with an illustrative embodiment. Fig. 12 depicts a view of the top layer of the 6-layers stack electrical circuit with through holes in accordance with an illustrative embodiment. In one embodiment, the size of the entire board is approximately 3 cm by 3 cm, but a different size may be used in alternative embodiments. In Fig. 12, the top layer includes two electrical drivers on the superior border and the 24 electrical output channels. At the bottom is shown a voltage regulator for fixing the power supply for the chips above. On the right side of the circuit are the different connections (CS, MOST MISO and Clock) for serial peripheral communication (SPI) with a microcontroller. In addition, there is an empty⁷ place on the inferior right side of the board that is designated for the optical output channels. Fig. 13 depicts a view of the bottom layer that includes optical drivers in accordance with an illustrative embodiment.

[0055] As discussed, the top layer holds the electrical drivers (24 electrical channels), and the bottom layer holds the optical drivers (18 optical channels). In alternative embodiments, a different number of channels (electrical or optical) may be used. Layers 1 (LI) and 4 (L4) are the ground planes (reference for the top and bottom, respectively). Layer 2 (L2), the signal layer, provides space for the tracks coming from the top when the space in the top is not sufficient. To this end. the signals from the electrical drivers are sent to L2 through blind vias. Layer 3 is used for the power plane and can also be used for some tracks from the optical drivers (botom). It is important to highlight that the notation for each layer as well as its function, might vary’ in alternative implementations. For example, in one embodiment, the 6-layers design can have one ground layer instead of two. The reason for these changes is related to the returning current path. By placing ground close to the top and botom layers, the returning current path is close to the electronic components. When the returning current path is not fully defined (leakage), because the ground plane is away from the signal layer, crosstalk or abnormal functioning of the circuit may occur.

[0056] Regarding the processor (or microcontroller) for the system, initial designs containing less optical and electrical channels used a microcontroller soldered in a feather board. This approach was useful as prototyping, however the feather boards from Adafruit are too big for an implant. Aiming to decrease the size of the oCI, the inventors choose a microcontroller STM32WB55 with Bluetooth protocol and on-chip antenna. In alternative embodiments, a different type of microcontroller may be used. Fig. 14 depicts a microcontroller soldered onto a small printed circuit board (PCB) in accordance with an illustrative embodiment. Specifically, the microcontroller is soldered onto a small PCB (~2 cm by 1.4 cm), which in turn is soldered onto a larger PCB for programming via micro-USB, STP-link, etc. It is noted that the inventors established footprints in a PCB for the microcontroller to keep the size of the implant small.

[0057] In an illustrative embodiment, the microcontroller is programmed with the STM32 environment (IdeCube) and the coding in C can be uploaded to the microcontroller via USB or another method. Because the microcontroller will control the peripheral devices (INTAN chip and IC-Haus chips), the inventors first set the configuration for the SPI interface (serial peripheral interface). This protocol for communication between a master and their slaves (peripheric devices) is widely used and provides a sufficient speed for data transmission compared to other protocols such as I2C. The communication of the INTAN chip (electrical driver) with the microcontroller involves configuration of 4 different lines (Chip select, clock, MOSI and MISO). Once the chip select is set low (OV). a train of pulses coming from the microcontroller (clock) are sent to the INTAN chip. During the transition of the clock signal from low to high, a bit is sent through the MOSI line to the INTAN device. The INTAN device sends streams of 32 bits. The first 16 bits are the address in the memory' of the INTAN chip and the following 16 bits are the command (could be the amplitude or polarity of the stimulation pulse, etc.) [0058] The coding strategy for the proposed system is described below. For electrical stimulation alone, a code called Frequency modulated phase coding (FMPC) can be used. The code is unique for its method of the decision making when optical or electrical or combined optical and electrical stimulation \\ i 11 be used. The version for optical stimulation includes electrical and optical stimuli and is christened optical Frequency Modulated Phase Coding (oFMPC). The optical frequency-modulated phase coding (oFMPC) strategy to encode acoustical information in cochlear implants may or may not modulate the amplitude, and uses the amplitude or energy of the acoustical signal to calculate the spike probability. At high energy levels the probability that a pulse is generated is high, and fast pulse repetition rates result. Moreover, the amplitude of the pulses is modulated by a nonlinear function modeling the input-output function of a hair cell. At low sound energy levels, the probability for a pulse is low and the resulting pulse repetition rate is slow. Again, the amplitude of the pulses is modulated by a nonlinear function modeling the input-output function of a hair cell. In addition to the sound energy the phase is considered in the calculation. The probability for a pulse is maximum at integer times between subsequent pulses that correspond to the center frequency of the selected frequency band, and is close to zero at the other times. Thus, envelope information is encoded by the rate and level of the stimulus, and temporal fine structure is recovered from the acoustical signal and the center frequency of the selected subband. Additionally, the broadness of the frequency band determines whether phase balanced biphasic electrical pulses are sub-threshold, which helps optical stimulation, or suprathreshold, which stimulates without the delivery of optical pulses.

[0059] The inventors have designed several prototypes of the proposed opto-electrical hybrid cochlear implant, and measured their size, stiffness, and insertion force into an acrylic human size model. Fig. 15 depicts a conventional electrode fused with an array of optical sources in accordance with an illustrative embodiment. For demonstration, light sources emitting at 405 nm were used, but different light source wavelengths can be used in alternative embodiments. The results were compared with the results obtained with similar measurements done with five Hi -Focus JI sample cochlear implant electrodes. The inventors have also built a prototype in which an existing Hi-focus CI electrode w as extended by three optical sources. The subsequent characterization of the electrode showed an approximate 10% increase in size at the tip of the electrode and a 30% increase in stiffness at the very tip where the optical sources are found. At sites, where the thickness of the silicon layer was reduced, the stiffness of the modified electrode was about 10% less than the Hi-focus CI electrode. In future iterations, the stiffness will be decreased by reducing the diameter of the backbone for the optical sources from 125 pm to 25 pm.

[0060] In an illustrative embodiment, any of the operations or calculations described herein can be performed by a computing system that includes a processor, a memory, a user interface, a transceiver (receiver and/or transmitter), etc. The operations can be stored as computer-readable instructions in the memory'. Upon execution by the processor of the computer-readable instructions, the computing system performs the operations, calculations, etc. described herein. As an example, Fig. 16 depicts components of a cochlear implant in accordance with an illustrative embodiment. The cochlear implant includes a computing system 1600 which can be in communication with a network 1635 in one embodiment.

[0061] In one embodiment, components of the computing system 1 00 can be incorporated into a stacked circuit board, as described herein. The computing system 1600 includes a processor 1605, an operating system 1610, a memory' 1615, an input/output (I/O) system 1620. a network interface 1625, and a CI application 1630. The computing system is also in communication with a light source(s) 1640, which can be any type of light source described herein, and current stimulator(s) 1645. In alternative embodiments, the computing system 1600 may include fewer, additional, and/or different components. The components of the computing system 1600 communicate with one another via one or more buses or any other interconnect system.

[0062] The processor 1605 can be in electrical communication with and used to control any of the system components described herein. For example, the processor can be used to execute the CI application 1630, control the hardware, process hearing data, run algorithms, etc. The processor 1605 can be any type of computer processor known in the art, and can include a plurality of processors and/or a plurality of processing cores. The processor 1605 can include a controller, a microcontroller, an audio processor, a hardware accelerator, a digital signal processor, etc. Additionally, the processor 1605 may be implemented as a complex instruction set computer processor, a reduced instruction set computer processor, an x86 instruction set computer processor, etc. The processor 1605 is used to run the operating system 1610. which can be any type of operating system.

[0063] The operating system 1610 is stored in the memory 1615, which is also used to store programs, received measurements/data, network and communications data, peripheral component data, the CI application 1630, and other operating instructions. The memory 1615 can be one or more memory systems that include various types of computer memory such as flash memory, random access memory (RAM), dynamic (RAM), static (RAM), a universal serial bus (USB) drive, an optical disk drive, a tape drive, an internal storage device, a nonvolatile storage device, a hard disk drive (HDD), a volatile storage device, etc.

[0064] The I/O system 1620 is the framework which enables users and peripheral devices to interact with the computing system 1600 to perform system updates, control system settings, etc. The I/O system 1620 can also include one or more buttons or other controls, etc. that allow the user to interact with and control the computing system 1600. In some embodiments, the I/O system 1620 also includes circuitry and a bus structure to interface with peripheral computing devices.

[0065] The network interface 1625 includes transceiver circuitry (e.g., a transmitter and a receiver) that allows the computing system 1600 to transmit and receive data to/from other devices such as remote computing systems, servers, websites, etc. The network interface 1625 enables communication through the network 1635, which can be one or more communication networks. The network 1635 can include a cable network, a fiber network, a cellular network, a wi-fi network, a landline telephone network, a microwave network, a satellite network, etc. The network interface 1 25 also includes circuitry' to allow device-to- device communication such as Bluetooth® communication.

[0066] The CI application 1630 can include software and algorithms in the form of computer-readable instructions which, upon execution by the processor 1605, performs any of the various operations described herein such as determining/controlling a radiation wavelength, determining an amount of energy⁷ on target, determining pulse shape and duration, determining/controlling the number of light sources 1640 to use, controlling an amount of current delivered by the current stimulator(s) 1645, controlling the microphone, processing sensed data, acting as the optical and/or electrical driver, etc. The CI application 1630 can utilize the processor 1605 and/or the memory 1615 as discussed above. In an alternative implementation, the CI application 1630 can be remote or independent from the computing device 1600, but in communication therewith.

[0067] The word "illustrative" is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, "a" or "an" means "one or more.” [0068] The foregoing description of illustrative embodiments of the invention has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and as practical applications of the invention to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

WHAT IS CLAIMED IS:

1 . A cochlear implant comprising: an electrical driver that includes a plurality of current stimulators that deliver current pulses to neurons; a light source that delivers optical pulses to the neurons; an optical driver that includes a plurality of channels, wherein the plurality of channels turn the light source on and off to control the optical pulses delivered to the neurons; and a microcontroller operatively coupled to the electrical driver and the optical driver, wherein the microcontroller maintains a clock to control timing of the current pulses and the optical pulses.

2. The cochlear implant of claim 1, wherein the electrical driver includes a plurality of integrated circuits and a total of 24 current stimulators.

3. The cochlear implant of claim 1, wherein the optical driver includes a plurality of integrated circuits and a total of 16 channels that switch from constant to a pulse mode.

4. The cochlear implant of claim 1, wherein the plurality of channels turn the light source on and off between different current levels that are defined by input voltages.

5. The cochlear implant of claim 4, further comprising a plurality of digital to analog converters that control the input voltages.

6. The cochlear implant of claim 1, further comprising one or more waveguides that guide the optical pulses to the neurons.

7. The cochlear implant of claim 6, wherein each of the one or more waveguides includes tubing that is at least partially filled with a viscous polymer.

8. The cochlear implant of claim 1, further comprising a microphone operatively coupled to the microcontroller.

9. The cochlear implant of claim 1, wherein the electrical driver, the light source, the optical driver, and the microcontroller are formed as a 6-layers stack electrical circuit.

10. The cochlear implant of claim 9, wherein the 6-layers stack electrical circuit includes a dielectric in between layers and a plurality of vias, wherein the vias include through holes, blind vias, buried vias.

11. The cochlear implant of claim 9, wherein the 6-layers stack electrical circuit is formed into a single chip.

12. A method of operating a cochlear implant, the method comprising: delivering, by an electrical driver, current pulses from a plurality of current stimulators to neurons; controlling, by an optical driver that includes a plurality of channels, an on/off state of a light source to control optical pulses; delivering, by the light source, the optical pulses to the neurons; maintaining, by a microcontroller operatively coupled to the electrical driver and the optical driver, a clock to control timing of the current pulses and the optical pulses.

13. The method of claim 12, further comprising turning the light source on and off between different current levels that are defined by input voltages.

14. The method of claim 12, further comprising controlling, by a plurality of digital to analog converters, the input voltages.

15. The method of claim 12, further comprising guiding, by one or more waveguides, the optical pulses to the neurons.

16. The method of claim 15, wherein each of the one or more waveguides includes tubing that is at least partially filled with a viscous polymer.

17. The method of claim 12, wherein the electrical driver, the optical driver, and the microcontroller are formed as a 6-layers stack electrical circuit.

18. The method of claim 17, wherein the 6-layers stack electrical circuit includes a dielectric in between layers and a plurality of vias, wherein the vias include through holes, blind vias, buried vias.

19. The method of claim 12, further comprising inserting the light source into scala tympani of a basal turn of a cochlea of a patient that receives the cochlear implant.

20. The method of claim 12, wherein the light source comprises a plurality of light sources, and further comprising separating the light sources from one another to prevent interference.