Patent Application
20100036470
The present invention relates to medical implants, and more specifically to fabrication of stimulation electrodes for cochlear implant systems.
Implantable neurostimulation electrodes are currently produced using manual and/or semi-automated methods for placing metal wires, metal traces, or stimulation contacts (all typically made of platinum or a platinum alloy) in electrically isolating material. This may be done manually, but manual work is very operator dependent and it is difficult to specify in sufficient detail to ensure reproducible results. Hand-made devices may therefore unintentionally be subject to significant variations in performance, which represents a technical problem. Furthermore, manual work is associated with extensive and time-consuming training of personnel.
Semi-automated processes can overcome some of these problems. Among the approaches currently used are photolithography, electroplating, and vapor depositioning of metal. Some conductive portions of the resulting structure may further be covered by thermal melt encapsulation or spin coating in an electrically insulating material as needed. These are described further, for example, in PCT Patent Application WO 2004064687, U.S. Patent Publication 2008027525, and U.S. Patent Publication 2006017273, which are incorporated herein by reference. Although precise and reproducible, these methods involve multiple individual procedural steps that include extensive use of chemicals, which may pollute materials that eventually are to be implanted, thus making purity control of chemicals a very important factor.
With existing electrode fabrication processes, it is possible to make structures in two dimensions (though quite difficult to control) and the height or thickness of the deposited metal is basically the same at different locations. But it is not practical to make three dimensional structures because physical masking of parts of the depositioning area—and therefore interruption of the process—would be needed. Thus, there are several technical problems involved with these methods.
Other semi-automated processes include removal of material from a sheet of metal to create predefined traces and pads. For example, U.S. Pat. No. 7,240,416 (incorporated herein by reference) suggests using embossing and electrical discharge machining or laser ablation. Embossing and selective material removal can facilitate making some three-dimensional structuring, but it may be limited by the thickness of the metal sheet used. Furthermore, it is generally not desirable to initially place a relatively large amount of metal (which is typically an expensive noble metal such as platinum or an alloy thereof) and then remove most of the metal to create individual traces and pads.
A method of fabricating an implantable stimulation electrode is described. An arrangement of conductive metal powder is provided atop an electrode substrate. A laser beam is then focused on the metal powder to form the stimulation electrode in a given geometry with given dimensions and supported by the electrode substrate.
In some specific embodiments, the metal powder may be blown onto the electrode substrate so that the stimulation electrode is formed by laser deposition of the metal powder. In other embodiments, the metal powder may be pre-layered on the electrode substrate so that the stimulation electrode is formed by laser sintering of the metal powder.
The given geometry may specifically be a two-dimensional geometry so that the stimulation electrode lies substantially in a plane, or a three-dimensional geometry so that the stimulation electrode has a three-dimensional geometry. The stimulation electrode may be formed in a recess in the surface of the electrode substrate, or above the surface of the electrode substrate.
The stimulation electrode may include at least one electrode contact for delivering an electrical signal to adjacent tissue. The electrode contact may include a layer of conductive surface structures for increasing the surface area of the electrode contact. There may be at least one conductive trace element for delivering the electrical signal to the electrode contact. In some embodiments, there may be multiple conductive trace elements and/or multiple electrode contacts. The electrode contact and the conductive trace element may have the same height or different heights.
The method may further include smoothing at least one surface of the stimulation electrode to reduce insertion trauma, for example, by electro-polishing or chemical etching. The stimulation electrode may be formed into multiple different metal layers. The metal powder may include at least one of platinum, iridium, gold, silver, palladium, tungsten, or an alloy thereof. The electrode substrate may be at least one of silicon, glass, polymer, or metal.
In any of the foregoing, the stimulation electrode may specifically be a cochlear implant electrode. And embodiments of the present invention also include an implantable stimulation electrode formed by any of the foregoing methods.
Laser depositioning of metal powder is a known technique for repairing metal parts (e.g. turbine blades) and for rapid prototyping. In this process, a laser beam is focused on a substrate (e.g. metal) and metal powder is blown onto the focus point. The laser energy heats the metal powder to create metal deposits on the underlying substrate. The process is controlled by parameters which include laser energy, laser spot size, and powder flow rate. When the laser and the powder injector are moved over the substrate, metal traces of a given thickness, width and height can be created. If the laser and the powder injector are moved up away from the substrate, three-dimensional structures can be created such as a spring shape standing up away from the substrate. This technology has been described for production of porous surfaces such as for bone implants (see, e.g., U.S. Patent Publication 2007202351, Canadian Patent 2,242,790, U.S. Patent Publication 2006073356, and U.S. Patent Publication 2002082741, which are incorporated herein by reference) and for depositing anti-microbial substances on implant surfaces (see, e.g., Patent Cooperation Treaty Publication WO 2008002750, which is incorporated herein by reference).
Selective laser sintering is similar to laser depositioning as discussed above, but instead of blowing in a metal powder, one or more layers of metal powder are pre-positioned on or in the substrate and sintered by the laser to create metal structures having a desired geometry and dimensions, depending in part on how many layers of metal powder are sintered.
Embodiments of the present invention use similar techniques to fabricate implantable stimulation electrodes. With existing laser technology, electrode structures can (theoretically) be created in widths and heights of down to ˜10 and ˜5 micrometers respectively. This level of detail is adequate for making high-density electrode arrays and conductors for implantation.
Laser depositioning of metal powder for making implantable stimulation electrodes can be flexible, simple, fast, reproducible, and highly automated. Relatively little equipment is needed and there are few process steps, most of which can be automated. Laser sintering on the other hand may be somewhat less flexible, but useful for making two-dimensional structures of limited height such as thin conducting trace elements such as wires and thin tissue contacts such as electrode contacts. Moreover, use of laser sintering avoids blowing possibly expensive noble metal powder around in the laser device. Depending on whether or not the excess powder can be re-collected and re-used, laser sintering may be more cost effective than laser depositioning.
Using either laser deposition or laser sintering a stimulation electrode may be formed into multiple different metal layers. For example, a layer of gold can be deposited first, and then followed by a layer of platinum on top. Alternatively, the core of a stimulation electrode could be made of a less expensive material having desired material characteristics, e.g., stainless steel, and then an outer layer of platinum or platinum alloy may be applied by laser deposition or laser sintering. In this way the electrical characteristics (such as the charge injection properties) and the mechanical characteristics (such as strength and flexibly) can be tailored to meet desired design objectives. The metal powder may specifically be one or more of platinum, iridium, gold, silver, palladium, tungsten, or an alloy thereof. The electrode substrate may be at least one of silicon, glass, polymer, or metal. The method may further include smoothing at least one surface of the stimulation electrode to reduce insertion trauma, for example, by electro-polishing or chemical etching.
The given geometry may specifically be a two-dimensional geometry so that the stimulation electrode lies substantially in a plane, or a three-dimensional geometry so that the stimulation electrode has a three-dimensional geometry. The stimulation electrode may be formed in a recess in the surface of the electrode substrate, or above the surface of the electrode substrate. And the stimulation electrode may include at least one electrode contact for delivering an electrical signal to adjacent tissue. The electrode contact may further include a layer of conductive surface structures for increasing the surface area of the electrode contact. There may be at least one conductive trace element for delivering the electrical signal to the electrode contact. In some embodiments, there may be multiple conductive trace elements and/or multiple electrode contacts. The electrode contact and the conductive trace element may have the same height or different heights.
The processes described above can be useful for creating two-dimensional and/or three-dimensional structures for implantable stimulation electrodes. The resulting structures can be adjusted and optimized to have desired mechanical properties. And a finished electrode can be created by one continuous process without interruption to form in a single integrated structure. The design structure of the stimulation electrode can be changed simply by changing a CAD file where the geometrical parameters for the electrode design are defined (and possibly some basic process optimization).
Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention. For example, in any of the foregoing, the stimulation electrode may specifically be a cochlear implant electrode. And embodiments of the present invention also include an implantable stimulation electrode formed by any of the foregoing methods.
This application claims priority from U.S. Provisional Patent Application 61/087,275, filed Aug. 8, 2008, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61087275 | Aug 2008 | US |
