TECHNICAL FIELD

The present invention relates to medical implants, and more specifically to an implantable electrode arrangement for cochlear implant systems.

BACKGROUND ART

A normal ear transmits sounds as shown inFIG.1through the outer ear101to the tympanic membrane102which moves the bones of the middle ear103that vibrate the oval window and round window openings of the cochlea104. The cochlea104is a long narrow duct wound spirally about its axis for approximately two and a half turns. It includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The cochlea104forms an upright spiraling cone with a center called the modiolar where the spiral ganglion cells of the acoustic nerve113reside. In response to received sounds transmitted by the middle ear103, the fluid-filled cochlea104functions as a transducer to generate electric pulses which are transmitted to the cochlear nerve113, and ultimately to the brain.

Hearing is impaired when there are problems in the ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea104. To improve impaired hearing, auditory prostheses have been developed. For example, when the impairment is related to operation of the middle ear103, a conventional hearing aid may be used to provide acoustic-mechanical stimulation to the auditory system in the form of amplified sound. Or when the impairment is associated with the cochlea104, a cochlear implant with an implanted electrode can electrically stimulate auditory nerve tissue with small currents delivered by multiple electrode contacts distributed along the electrode.

FIG.1also shows some components of a typical cochlear implant system where an external microphone provides an audio signal input to an external signal processor111in which various signal processing schemes can be implemented. The processed signal is then converted into a digital data format for transmission by external transmitter coil107into the implant108. Besides receiving the processed audio information, the implant108also performs additional signal processing such as error correction, pulse formation, etc., and produces a stimulation pattern (based on the extracted audio information) that is sent through an electrode lead109to an implanted electrode array110. Typically, this electrode array110includes multiple stimulation contacts112on its surface that provide selective stimulation of the cochlea104.

The electrode array110contains multiple electrode wires embedded in a soft silicone body referred to as the electrode carrier. The electrode array110needs to be mechanically robust, and yet flexible and of small size to be inserted into the cochlea104. The material of the electrode array110needs to be soft and flexible in order to minimize trauma to neural structures of the cochlea104. But an electrode array110that is too floppy tends to buckle too easily so that the electrode array110cannot be inserted into the cochlea104up to the desired insertion depth. A trade-off needs to be made between a certain stiffness of the electrode array110which allows insertion into the cochlea104up to the desired insertion depth without the array buckling, and certain flexibility of the electrode array110which keeps mechanical forces on the structures of the scala tympani of the cochlea104low enough.

Damage and trauma cause bleeding, inflammation, perforation of soft tissue, tears and holes into membranes, and fracture of thin osseous structures. The resulting damage to the inner ear, for example, may cause loss of surviving hair cells, retrograde degeneration of the dendrite which innervates the organ ofCorti, and in the worst case, spiral ganglion cell death in the Rosenthal's canal. Cell death means quantitatively less neural tissue is available for stimulation, and qualitatively, that less frequency-tuned fibers are available to represent frequency information.

Cochlear implant electrode array designs and surgical techniques attempt to minimize the trauma of implantation surgery so that the insertion of the electrode array into the cochlea may be as smooth and resistance free as possible, both at the apical tip and elsewhere on the outer surface of the electrode array. In some cases, there may be resistance during the electrode insertion. For example,FIG.2shows a cross-sectional view of a cochlea104during insertion of the electrode array110through an electrode opening201wherein the apical tip202contacts the outer lateral wall203at the first turn. When that occurs, the surgeon either stops the insertion with only a partial length of the electrode array110inside the cochlea104, or the surgeon increases the insertion force to push the electrode array110beyond the resistance point, creating trauma inside the cochlea104.

The size and mechanical characteristics of the electrode array are critical parameters for the best patient benefit. Some electrode array designs are pre-curved, though a drawback of that approach is that a special electrode insertion tool is needed which keeps the electrode array straight until the point of insertion. As documented by Erixon et al.,Variational Anatomy of the Human Cochlea: Implications for Cochlear Implantation, Otology & Neurotology, 2008 (incorporated herein by reference), the size, shape, and curvature of the cochlea varies greatly between individuals, meaning that a cochlear implant electrode array must match a wide range of scala tympani (ST) geometries. Furthermore, recently published research by Verbist et al.,Anatomic Considerations of Cochlear Morphology and Its Implications for Insertion Trauma in Cochlear Implant Surgery, Otology & Neurotology, 2009 (incorporated herein by reference) has shown that the human ST does not incline towards the helicotrema at a constant rate, but rather there are several sections along the ST where the slope changes, sometimes even becoming negative (i.e. downwards). The location and grade of these changes in inclination were also found to be different from individual to individual. Consequently, CI electrode arrays should be highly flexible in all directions in order to adapt to individual variations in curvature and changes in inclination of the ST for minimal trauma implantation.

It is known to provide a fluid delivery channel within the electrode array to deliver therapeutic drugs and/or insertion lubricants to the outer surface of the electrode array. For example, one such arrangement is described in U.S. Patent Publication 2017/0028182 (incorporated herein by reference in its entirety).

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to an implantable electrode arrangement for a cochlear implant system. An elongated electrode array is configured for insertion into a patient cochlea. The electrode array has a central longitudinal axis and an outer surface with multiple simulation contacts for delivering electrical stimulation signals to adjacent cochlear neural tissue. A fluid delivery channel is located within the electrode array parallel to the central longitudinal axis and has at least one fluid delivery port for delivering lubricant fluid from the fluid delivery channel to the outer surface of the electrode array. The fluid delivery port and the lubricant fluid are configured to produce a lubrication region close to the outer surface of the electrode array proximal to the fluid delivery port during insertion of the electrode array into the patient cochlea so as to reduce insertion resistance at an adjacent section of lateral wall of the patient cochlea.

In further specific embodiments, the lubricant fluid may be characterized by forming a solid lubrication region between the electrode array and the lateral wall when contacting perilymph fluid within the patient cochlea. The electrode array may include an apical end containing the least one fluid delivery port. The outer surface of the electrode array may have an outer lateral side containing the at least one fluid delivery port. The at least one fluid delivery port may be multiple fluid delivery ports or a single fluid delivery port.

There may be at least one fluid reservoir connected to the fluid delivery channel and containing the lubricant fluid, wherein the at least one fluid reservoir is configured for non-reversible collapse under compression pressure for delivery of the lubricant fluid through the at least one fluid delivery port without developing back suction into the fluid delivery channel. The at least one fluid reservoir may include a metal layer configured for the non-reversible collapse. The at least one fluid reservoir may be multiple fluid reservoirs or a single fluid reservoir.

