PACKAGING AND COATING FOR BIO-ELECTRICAL STIMULATION AND RECORDING ELECTRODES

Abstract: A packaging system (11) for a bioelectrical stimulating and recording electrode (15) is provided. The system (11) includes a protective container (13) in which the electrode (15) is housed. A conductive biocompatible and bioresorbable liquid (17) partially fills the container (13) in order for the electrode (15) housed therein to be coated by the liquid (17). While the preferred conductive liquid (17) is glycerol, other liquids may be chosen for practicing the invention.

Description: PACKAGING AND COATING FOR BIO-ELECTRICAL STIMULATION AND RECORDING ELECTRODES Background of the Invention A. Field of Invention This invention relates to packaging for a bioelectrical electrode array, which can be used for stimulation, recording, or both, and more specifically, to a packaging system which includes a conductive liquid for ensuring electrical contact with the electrode that is bathed in the liquid. B. Description of the Prior Art A cochlear device is generally understood to be some type of implantable hearing aid which helps a specific class of patients for which conventional hearing aids are inadequate. As is well known, a cochlear device includes an electrode array of one or more electrodes which must perform appropriately for the device to function. Typically, the electrode or electrodes of a cochlear device may need to be remotely tested for open circuits after packaging. It is believed that one prior art packaging included a sealed compartment of saline solution. The sealed compartment, however, could only be ruptured once in order to enable electrical contact between electrodes, and thereby enable testing for open circuit electrodes. In particular, in such a package the water content will evaporate after the compartment is ruptured -- the test is thus essentially a "once only" test for open circuits. In other words, it cannot be conducted both immediately after packaging and immediately prior to implantation if the intervening time has been sufficient to allow water evaporation. Additionally, prior art packaging is known which includes a coating material made of polyvinyl alcohol. The polyvinyl alcohol is used to protect the electrode material. However, polyvinyl alcohol is not conductive, making electrode testing even more difficult. Moreover, polyvinyl alcohol increases the stiffness of the electrode material and makes its insertion more difficult. U.S. Patent No. 5,237,991 discloses a means for testing an electrical lead within its sterile package. The described device requires a dummy load to be connected to the electrodes within the sterile package by means of posts and setscrews. However such hardware adds complexity and expense to the device. Furthermore there is a risk of damage to the electrodes and inconvenience in that the dummy load must be removed before making use of the lead. Accordingly, it is desirable to provide a packaging system that overcomes the above disadvantages. Furthermore, multiple electrodes are used in biomedical applications apart from cochlear implants and so it is desirable to provide a packaging which is also suitable for use with these other types of electrodes. Summary of the Invention Generally speaking, in accordance with the invention, a packaging system for a bioelectrical stimulating and recording electrode is provided. The system includes a protective container, preferably semi-porous, in which the electrode is housed. A conductive biocompatible and bioresorbable liquid partially or wholly fills the container in order for the electrode housed therein to be coated by the liquid. While the preferred conductive liquid is a solution of 1 % by weight sodium chloride in glycerol, other liquids may be chosen for practicing the invention. It is therefore an object of the invention to provide an improved packaging system for a bioelectrical stimulating and recording electrode array. Still another object of the invention is to provide electrical contact between the electrodes of an array such that electrical contact will remain after a cochlear device has been packaged. Yet a further object of the invention is to provide a method for testing the operability of an electrode of a cochlear device. Still other objects and advantages of the invention will in part be obvious, and will in part be apparent from the following description. An advantage of the invention is that glycerol is a lubricative liquid which is currently used to allow deeper insertion of electrode arrays into the cochlear. The invention accordingly comprises a product and system possessing the features, properties and relation of components which will be exemplified in the product and system hereinafter described, and the scope of the invention will be indicated in the claims. Brief Description of the Drawings For a fuller understanding of the invention, reference is made to the following description, taken in connection with the accompanying drawings, in which: Fig. 1 is a cross-sectional view showing a bioelectrical stimulation and recording electrode contained in a packaging system made in accordance with the invention; Fig. 2 shows an enlarged view of the electrode array. Fig. 3 is an electrical schematic view. Detailed Description of the Preferred Embodiment Referring first to Fig. 1 , a packaging system generally indicated at 1 1 and made in accordance with the invention is now described. Packaging system 11 includes a protective container 13 in which a bioelectrical stimulating and recording electrode 15 is housed. The container 13 may constitute the whole package or it may form a separate compartment within a larger package. Container 13 may have a substantially tubular configuration and is made from silicone, or other similar material. Preferably, container or tube 13 is made of a semi-porous material which is substantially permeable to a sterilizing media such as ETO/steam. Preferably container 13 takes the form of a tear-away sheath. Packaging system 1 1 further includes a conductive biocompatible and bioresorbable liquid 17 for at least partially filling container 13. As can be appreciated, liquid 17 coats or otherwise bathes electrode array 15, including electrodes 15A-15C and others, as it is situated in container 13. Preferably, liquid 17 should have a boiling point significantly greater than that of water and a vapor pressure at storage temperature significantly less than that of water. Such properties reduce the likelihood of evaporation during storing of packaging system 1 1. Liquid 17 is held within the container by a seal 24 around the electrode array body 23 which is impermeable to the liquid. Alternatively, a larger container may be used for housing the complete electrode assembly. Of most importance is for liquid 17 to be conductive so that electrode array 15 can be tested for open circuits after packaging within system 1 1 as described below. The preferred liquid 17 is saline-doped glycerol, i.e., a solution of 1 % sodium chloride in glycerol, since it is substantially conductive and is more pliable than polyvinyl alcohol. Although saline-doped glycerol is the preferred liquid 17, other suitable high-boiling point biocompatible solvents include polyethylene glycol, propylene glycol, hyaluronic acid, and hydroxypropyl methylcellulose. Alternatively, a liquid containing biocompatible salts, such as potassium chloride, sulfates, nitrites and phosphates, may be used. As can be well appreciated, mixtures of more than one of these suitable liquids may be used, and some water may be added, or even small amounts of polyvinyl alcohol may be added. An important feature of the inventive system is that it enables remote testing of packaged bioelectrical stimulating and recording electrodes. This is because the liquid which bathes the electrodes in the packaging of the invention is both conductive and pliable. Referring to Fig. 2, a typical array 15 includes a plurality of electrodes 15A, 15B, etc. disposed near a distal end. Each electrode is connected to a corresponding wire 21 A, 21 B, etc. extending through a sleeve 23 and being exposed at end 25. Since all the electrodes are bathed in the liquid 17, they are effectively shorted to each other. Therefore, the electrodes can be easily tested for continuity. For example, a shown in Fig. 3, each electrode and its conductor can be tested by checking the continuity between 21 A, 21 B ... and 21 D, which may be considered a common return. Typically a limited current source and ammeter or continuity tester 19 are used to test for electrical continuity. If the array has only a single electrode, it may be tested by using liquid 17 for the return path. For example, a method for testing the electrical integrity of an implantable electrode array might consist of the following steps. Firstly the electrode bearing portion of the array is housed in a protective container containing an electrically conductive liquid. The array, container and liquid are arranged so that the electrodes are in electrical contact with the liquid while the electrode leads are allowed to protrude with the electrically conductive liquid being substantially sealed within the container as shown in Fig 1 for example. The next step is that for each electrode a current is passed between the lead connecting to that electrode and one of the other electrode leads. If current flows through the circuit, as might be detected with a conventional ammeter for example, then it can be deduced that the leads are intact and electrically connected to the electrodes, otherwise a problem is detected and the electrode array can be either disposed of or repaired. Packaged arrays which have tested satisfactorily are then stored until such time as they are required. Prior to implantation the packaged electrode arrays can be re-tested, once again by connecting a current source between the various electrode leads and monitoring for current flow as before. On the basis of the monitoring it can be decided if the electrode array is suitable for implantation. It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently obtained and, since certain changes may be made in the above system without departing from the spirit and scope of the invention, it is intended that all matter contained in this description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Claims: CLAIMS: 1. A packaging system for a bioelectrical stimulating and/or recording electrode array terminating in at least one electrode comprising: a protective container in which said electrode array is housed; a conductive biocompatible and bioresorbable liquid at least partially filling said container said electrodes being immersed in said liquid, said liquid being used to enable the testing of said electrode array for open circuits after packaging. 2. The system of claim 1 , wherein said container is semi-porous. 3. The system of claim 1 or 2, wherein said container is tubular in configuration. 4. The system of claims 1 to 3, wherein said container is made of a material which is substantially permeable to a sterilizing media. 5. The system of claims 1 to 4, wherein said container is a tear-away sheath. 6. The system of claims 1 to 5, wherein said liquid is a solution of a bicompatible salt in glycerol. 7. The system of claim 6, wherein said biocompatible salt is sodium chloride. 8. The system of claims 6 or 7 wherein said biocompatible salt is in proportion of approximately 1% by weight. 9. The system of claims 1 to 5, wherein said liquid has a boiling point significantly greater than that of water and a vapor pressure at storage temperature significantly less than water. 10. The system of claims 1 to 4, wherein the liquid is a solution of a biocompatible salt in a solvent selected from polyethylene glycol, propylene glycol, hyaluronic acid, and hydroxypropyl methylcellulose. 11. The system of claim 10, wherein said biocompatible salt is sodium chloride. 12. The system of claims 10 or 1 1 wherein said biocompatible salt is in proportion of approximately 1% by weight. 13. A method for testing the electrical integrity of an implantable electrode array, including at least two electrodes each electrode with at least one lead connected thereto, comprising the steps of : a) housing the electrode bearing portion of said array in a protective container containing an electrically conductive liquid whereby said electrodes are in electrical contact with said liquid and said leads protrude from said container and whereby said liquid is substantially sealed within said container; b) for each electrode lead connecting a limited current source between said lead and one other lead; c) monitoring the flow of current between said current source and one of the leads in step b); d) on the basis of the monitoring in step c) either storing said container and electrode array of step a) until implantation of the array is required or discarding said array or unpackaging said array for implantation.

Inventors: CARTER PAUL MICHAEL, MONEY DAVID KERRY, TABOR BRUCE, CARTER, PAUL, MICHAEL, MONEY, DAVID, KERRY, TABOR, BRUCE
Applicants: COCHLEAR LTD, COCHLEAR LIMITED
Application year: 1997
Main classification: A61N1
IPC codes: A61B5, A61F11, A61N1, G01R31, H04R25