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COATED ELECTRODE ARRAY HAVING
UNCOATED ELECTRODE CONTACTS
The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/687,495, filed Jun. 2, 5 2005, which application is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
The teachings of the present disclosure relate to external or implantable stimulation devices, e.g., cochlear prosthesis used to electrically stimulate the auditory nerve, spinal cord stimulation (SCS) devices used to provide therapy along the dura of the spinal cord, or other types of neurostimulation devices used to provide therapy to muscles or nerve tissue. More particularly, the teachings of the present disclosure relate to an implantable electrode array for use with, e.g., a cochlear stimulator, an SCS stimulator, or any type of neuro- 2o stimulation device used in the body to stimulate muscle or nerve tissue. Such stimulation devices, e.g., cochlear stimulator, are designed to place the electrode contacts of the electrode array generally along one side of the array so that when the array is implanted, e.g., in the cochlea, or other body 25 cavity, the side of the array whereon the electrode contacts are located can be positioned in close proximity to the cells that are to be stimulated, thereby allowing such cells to be stimulated with minimal power consumption.
Furthermore, the teachings of the present disclosure 30 includes electrode arrays which further include a bioresorbable material which improves performance and adds additional benefits to the electrode array. For example, where the array is implanted in the cochlea, the electrode side of the array may be positioned closest to the modiolar wall, thereby 35 placing all of the individual electrode contacts in close proximity to the ganglion cells and thereby in close proximity to the auditory nerve fibers, and in addition, the bioresorbable coated material, in time, could be absorbed and help minimize or eliminate any pressure within the cochlea or other 40 body cavity. When using the electrode array described herein in SCS applications, the electrode array may be placed in a location such that the electrical stimulation will create a tingling sensation felt by the patient known as paresthesia. SCS electrode arrays containing a bioresorbable material will 45 improve performance and add additional benefits to the electrode array and further improve the performance of the SCS stimulation therapy.
The hearing loss phenomenon, which may be due to many different causes, is generally of two types: conductive and 50 sensorineural. Of these, conductive hearing loss occurs where the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss may often be helped by use of conventional hearing aids, which amplify sound so that 55 acoustic information does reach the cochlea and the hair cells. Some types of conductive hearing loss are also amenable to alleviation by surgical procedures.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. This 60 type of hearing loss is due to the absence or the destruction of the hair cells in the cochlea which are needed to transduce acoustic signals into auditory nerve impulses. These people are unable to derive any benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, 65 because their mechanisms for transducing sound energy into auditory nerve impulses have been damaged. Thus, in the
absence of properly functioning hair cells, there is no way auditory nerve impulses can be generated directly from sounds.
To overcome sensorineural deafness, there have been developed numerous cochlear implant systems—or cochlear prosthesis—which seek to bypass the hair cells in the cochlea (the hair cells are located in the vicinity of the radially outer wall of the cochlea) by presenting electrical stimulation to the auditory nerve fibers directly, leading to the perception of sound in the brain and at least partial restoration of hearing function. The common denominator in most of these cochlear prosthesis systems has been the implantation into the cochlea of electrodes which are responsive to a suitable external source of electrical stimuli and which are intended to transmit those stimuli to the ganglion cells and thereby to the auditory nerve fibers.
A cochlear prosthesis operates by direct electrical stimulation of the auditory nerve cells, bypassing the defective cochlear hair cells that normally transduce acoustic energy into electrical activity in such nerve cells. In addition to stimulating the nerve cells, the electronic circuitry and the electrode array of the cochlear prosthesis performs the function of the separating the acoustic signal into a number of parallel channels of information, each representing the intensity of a narrow band of frequencies within the acoustic spectrum. Ideally, each channel of information would be conveyed selectively to the subset of auditory nerve cells that normally transmitted information about that frequency band to the brain. Those nerve cells are arranged in an orderly tonotopic sequence, from high frequencies at the basal end of the cochlear spiral to progressively lower frequencies towards the apex. In practice, this goal tends to be difficult to realize because of the anatomy of the cochlea.
Over the past several years, a consensus has generally emerged that the scala tympani, one of the three parallel ducts that, in parallel, make up the spiral-shaped cochlea, provides the best location for implantation of an electrode array used with a cochlear prosthesis. The electrode array to be implanted in this site typically consists of a thin, elongated, flexible carrier containing several longitudinally disposed and separately connected stimulating electrode contacts, perhaps 6-30 in number. Such electrode array is pushed into the scala tympani duct to a depth of about 20-30 mm via a surgical opening made in the round window at the basal end of the duct. During use, electrical current is passed into the fluids and tissues immediately surrounding the individual electrode contacts in order to create transient potential gradients that, if sufficiently strong, cause the nearby auditory nerve fibers to generate action potentials. The auditory nerve fibers arise from cell bodies located in the spiral ganglion, which lies in the bone, or modiolus, adjacent to the scala tympani on the inside wall of its spiral course. Because the density of electrical current flowing through volume conductors such as tissues and fluids tends to be highest near the electrode contact that is the source of such current, stimulation at one contact site tends to activate selectively those spiral ganglion cells and their auditory nerve fibers that are closest to that contact site. Thus, there is a need for the electrode contacts to be positioned as close to the ganglion cells as possible. This means, in practice, that the electrode array, after implant, should hug the modiolar wall, and that the individual electrodes of the electrode array should be positioned on or near that surface of the electrode array which is closest to the modiolar wall.
In order to address the above need, it is known in the art to make an intracochlear electrode array that includes a spiralshaped resilient carrier which generally has a natural spiral
shape so that it better conforms to the shape of the scala tympani. See, e.g., U.S. Pat. No. 4,819,647. The '647 U.S. patent is incorporated herein by reference. Unfortunately, while the electrode array with spiral-shaped carrier shown in the '647 patent represents a significant advance in the art, 5 there exists lack of sufficient shape memory associated with the carrier to allow it to return to its original curvature (once having been straightened for initial insertion) with sufficient hugging force to allow it to wrap snugly against the modiolus of the cochlea. 10
Thus, while it has long been known that an enhanced performance of a cochlear implant can be achieved by proper placement of the electrode contacts close to the modiolar wall of the cochlea, two main problems have faced designers in attempting to achieve this goal. First, it is extremely difficult 15 to assemble electrode contacts on the medial side of the an electrode array, facing the modiolus of the cochlea. Second, heretofore there has either been the need for application of an external (and perhaps unsafe) force, or a lack of sufficient shape memory, to allow the electrode (after initial straighten- 20 ing to facilitate insertion) to assume or return to the desired curvature needed to place the electrodes against the modiolar wall so that the curvature wraps snugly around the modiolus of the cochlea. As a result, the electrode contacts of the prior art electrodes are generally positioned too far way from the 25 modiolar wall.
Many cochlear electrode arrays of the prior art are made for insertion into a left cochlea, or a right cochlea, depending upon the orientation of the electrode contacts one to another. It would be desirable for a universal electrode array to be 30 made that could be used in either cochlea, left or right, without concern for whether the electrodes were orientated in a right or left side orientation.
During the insertion procedure of the modular hugging electrode, a pressure build-up occurs which may potentially 35 damage the modiolar wall structure of the cochlea. The pressure may become chronic causing discomfort and infection to the patient. It would thus be desirable to have a modiolar hugging electrode that can reduce the pressure buildup after insertion as well as reduce discomfort and infection. 40
It is thus evident that improvements are still needed in, e.g., implantable cochlear electrodes, particularly to facilitate assembling an electrode so that the electrode contacts are on the medial side of the electrode array, and to better assure that the electrode assumes a close hugging relationship with the 45 modiolus once implantation of the electrode has occurred without the internal pressure that the patient may experience within the cochlea.
Stimulation systems, e.g., cochlear, SCS, cardiac, brain or peripheral nerve stimulation systems, are further enhanced by 50 implementing the teachings of the present disclosure to the electrode array which is part of the system.
The teachings of the present disclosure addresses the above and other needs by providing a universal electrode array, adapted for insertion into either a left or right cochlea, which provides improved stability of electrode contact direction. All of the electrode contacts are spaced apart along one edge or 60 side of the array, termed the "medial side". The structure of the electrode array facilitates bending of the array with the electrode contacts on the inside of the bend, yet deters flexing or twisting of the array that would tend to position or point the electrode contacts away from the inside of the bend. Hence, 65 when inserted into the scala tympani duct of a cochlea, all of the electrode contacts on the medial side of the array gener
ally face the modiolus wall of the cochlea. Furthermore the electrode side includes a bioresorbable coated material which, over time, is absorbed and thereby reduces pressure buildup within the cochlea.
The term bioresorbable as used herein is intended to encompass the various known biocompatible materials that are resorbed or otherwise degraded over time within the vivo environment. The material composition should be biodegradable in vivo and yield degradation products which are themselves non-inflammatory and non-toxic. Biodegradability is desired to provide a natural resorbable process without the possibility of chronic tissue reaction to the foreign material. The rate of degradation of the material within the cochlea or any part of the body can be controlled by adjusting the yield composition as is known in the art of bioresorbable materials.
In one embodiment, small non-conductive bumps or humps are formed in the carrier between the electrode contact areas on the medial side of the array. These small bumps are made, e.g., from a soft silicone rubber, or equivalent substance. When inserted into the cochlea, the small bumps serve as non-irritating stand-offs, or spacers, that keep the electrode contacts near the modiolus wall, but prevent the electrode contacts from actually touching the modiolus wall. The bumps may also serve as dielectric insulators that help steer the stimulating electrical current in the desired direction, towards the modiolus wall, as taught, e.g., in U.S. Pat. No. 6,112,124, incorporated herein by reference. Furthermore the non-conductive bumps are coated with a bioresorbable material with a defined thickness which, over time, is absorbed to thereby reduce chronic placement pressure which may have been induced during the insertion of the electrode array into the cochlea. The bioresorbable material may also serve as a carrier for drugs and other materials that would improve performance of the electrode array. Such drugs are used to elicit a desired therapeutic or other result, e.g., to inhibit fibrous tissue or bone growth in the vicinity of the electrode contacts; or to promote healing of damaged tissue in the region of the electrode contacts, or to prevent infection and discomfort to the patient.
It is a further feature of the present disclosure described herein to provide an electrode array having non-conductive bumps coated with a bioresorbable material. The bioresorbable material should be non-toxic and have a reliable decomposition and absorption. The bioresorbable material can be any of one of various known materials such as polydioxanone, polycaprolactone, polyhydroxybutyrate, polyamino acid, polymers formed of alpha hydroxy acids, lactic acids, poly-L-lactic acids, polylactic-coglycolic acid polymers, polysaccharides as well as other suitable combinations thereof known in the art of bioresorbable materials. Other examples of bioresorbable materials may include: glycoaminoglycans, hydroxyethyl cellulose, oxidized celluloses, and suitable combinations thereof.
It is an additional feature of the teachings of the present disclosure to provide a bioresorbable material coated on the surface of the non-conductive bumps which may serve as carriers for drugs or other materials that can improve the performance of the electrode array. Representative drugs that may be used to coat the electrode array and/or the individual non-conductive bumps in accordance with this aspect of the teachings of the present disclosure include selected steroids, either naturally occurring or synthetic, or a Neuro-trophin selected to prevent neural degeneration and/or to promote neural regeneration.
It is a further feature of the teachings of the present disclosure to provide an electrode array used in SCS applications which includes a bioresorbable material on the electrode con