Patent Application
20100305673
The present invention relates to medical implants, and more specifically to a new type of implantable electrode for implant systems.
Present day implantable electrodes such as cochlear implant electrodes require considerable amount of hand assembly during manufacturing. Individual thin platinum wires of about 25 μm in diameter with about 4 μm of polytetrafluoroethylene (PTFE) insulation must be cut to size and manipulated without compromising the insulation. The wires must be stripped of insulation at the ends and welded to thin platinum foils which have been cut to size, usually around 500 μm in diameter. Each individual wire must be placed one by one into a mold and assembled into a multi-channel structure before then being silicone injection molded. Demolding of the long electrodes then must take place without causing damage to the structure. There are some manufacturing rejects, for example, due to open or short circuits between wires, or poor welding of contacts. Silicone overflow onto the contact surfaces also cause some further rejects. The electrode making process is extremely labor intensive, a significant percentage of rejected electrodes is unavoidable, and maintaining adequate quality is problematic. Moreover, this highly manual work process is strongly operator dependent and it is difficult to specify in enough detail to ensure reproducible results. Hand made devices may therefore unintentionally be subject to significant variations in performance. Furthermore, the manual work is linked with extensive and time consuming training of personnel.
Semi-automated electrode fabrication processes can overcome some of the hurdles described above. Currently that typically involves photolithography and electroplating or vapor depositioning of metal (see e.g. WO2004064687, US2008027525, US2006017273; incorporated herein by reference) followed by thermal melt encapsulation or spin coating in an electrically insulating material to cover the conductive parts of the structure as needed to allow for adequate electrical stimulation. Although such semi-automated processes are precise and reproducible, they involve many individual process steps, some of which include extensive use of chemicals. Such chemicals may pollute materials that eventually are to be implanted, thus making purity control of chemicals and cleaning of electrodes very important factors. With existing processes it is possible to make structures in 2 dimensions—the height/thickness of the deposited metal is typically about the same at different depositioning locations—but it is not practical to make three dimensional structures because that would require physical masking of portions of the depositioning area and consequent interruption of the process.
Other semi-automated fabrication processes include removal of material from a sheet of metal to create predefined traces and pads (see e.g. U.S. Pat. No. 7,240,416, incorporated herein by reference, which suggests using embossing and electrical discharge machining or laser ablation). Embossing and selective material removal can facilitate making some three dimensional structures, but this 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 (typically an expensive noble metal such as platinum or an alloy thereof) and then remove the majority of it for creating individual traces and pads.
A method of producing an implantable electrode device starts by providing an electrode substrate for structural support. An electrode network of wires and contacts is developed over portions of the electrode substrate based on inkjet deposition of conductive metal material for electrically connecting an implant processor device to targeted tissue in a patient. A portion of the electrode network is selectively covered with a biocompatible encapsulation layer to provide electrical insulation for the covered portion of the electrode network, while also leaving exposed portions of the electrode network to allow electrical contact with adjacent tissue.
In further specific embodiments, the metal material may include platinum material such as a platinum-based ink and/or a platinum alloy material. For example, a metallic ink may contain metal nanoparticles or be based on a complex of platinum ions and surrounding ligands. Providing the electrode substrate may include initially treating the electrode substrate with at least one of a primer treatment and a plasma activation treatment to increase wettability of the metal material to the electrode substrate. Developing the electrode network also may include heat treating one or more portions of the electrode network for sintering. Developing the electrode network also may include developing selected portions of the electrode network to have a greater metal thickness than unselected portions of the electrode network. The greater metal thickness may include electroplated metal and/or inkjet deposited metal, and the selected portions may include selected exposed portions of the electrode network.
At least one of the substrate and the encapsulation layer may be formed of a silicone material. Providing the electrode substrate may include developing electrode channels by photo-resist processing for containing portions of the electrode network. The exposed portions of the electrode network are developed based on at least one of laser ablation, wet chemical removal, plasma etching, and mechanical treatment. Selectively covering a portion of the electrode network with the encapsulation layer may be based on at least one of spray coating, spin coating, inkjet printing, a thermal melting, and an injection molding process. The exposed portions may include one or more recessed portions wherein the exposed portion has a surface recessed below the surface of the adjacent encapsulant layer.
Developing the electrode network also may include inkjet printing the conductive metal material into recesses on the electrode substrate, which may be formed by embossment or injection molding in the electrode substrate. Developing the electrode network also may include inkjet printing the conductive metal material into recesses on a transfer plate, heat treating the conductive metal to form the electrode network, covering the electrode network with the electrode substrate, attaching the electrode substrate to the electrode network, and removing the electrode network and electrode substrate from the transfer plate.
Embodiments of the invention also include an implantable electrode device. An arrangement of conductive metal material is developed by inkjet deposition into an electrode network of wires and contacts for electrically connecting an implant processor device to targeted tissue in a patient. An electrode substrate beneath the electrode network provides structural support to the electrode network. A biocompatible encapsulation layer selectively covers a portion of the electrode network and providing electrical insulation for the covered portion of the electrode network, and leaves exposed portions of the electrode network to allow electrical contact with adjacent tissue.
In further specific such embodiments, the metal material may include platinum material such as a platinum-based ink. The metal material may be derived from a metallic ink containing metal nanoparticles or be based on a complex of platinum ions and surrounding ligands. The electrode substrate may include at least one of a primer treatment and a plasma activation treatment to increase wettability of the metal material to the electrode substrate. In other specific embodiments, one or more portions of the electrode network may be heat treated for sintering. The electrode network also may be developed so that selected portions of the electrode network have a greater metal thickness than unselected portions of the electrode network. The greater metal thickness may include electroplated metal and/or inkjet deposited metal, and the selected portions may include selected exposed portions of the electrode network.
The exposed portions of the electrode network may be developed based on at least one of laser ablation, wet chemical removal, plasma etching, and mechanical treatment. The encapsulation layer may be based on at least one of a spray coating, a spin coating, an inkjet printed coating, a thermal melted coating, and an injection molding process.
The exposed portions may include one or more recessed portions wherein the exposed portion has a surface recessed below the surface of the adjacent encapsulant layer. At least one of the substrate and the encapsulation layer may be formed of a silicone material. The electrode substrate may include electrode channels developed by photo-resist processing for containing portions of the electrode network. Or, the electrode network may be developed by inkjet printing the conductive metal material into recesses on the electrode substrate, which may be formed by embossment or injection molding in the electrode substrate. The electrode network also may be developed by inkjet printing the conductive metal material into recesses on a transfer plate, heat treating the conductive metal to form the electrode network, covering the electrode network with the electrode substrate, attaching the electrode substrate to the electrode network, and removing the electrode network and electrode substrate from the transfer plate.
Various embodiments of the present invention are directed to a streamlined automated process to make implant electrode devices for neuro-stimulation which assembles platinum wires, electrode contacts and insulators in just a few steps, and with the ability to scale up as demand grows. Such an automated process can be implemented by adapting inkjet printing technology and metal-containing inks to inkjet print the electrode device onto a substrate (e.g. thin polymer film) to create a desired structure of conducting wires and stimulation contacts. Subsequent encapsulation of the printed electrode structures in electrically insulating polymer may then be done, for example, by thermal melting or spin coating. Such an inkjet printing process can be automated, flexible, comparably simple, and fast to ensure high reproducibility, thereby overcoming many of the challenges found in currently used and described alternative methods of manufacturing implantable electrode devices.
In one specific embodiment, the printed track of an individual wire 203 on the electrode substrate 201 typically has a width of about 100 μm and a height of a few hundred nm. These dimensions are in an interesting range for small multi-channel electrode devices 200 where multiple wires 203 and stimulation contacts 204 are used. The thin electrode network 202 enables the electrode device 200 to be highly flexible so that its mechanical properties are appropriate for in-vivo use such as, for example, cochlear implant electrode arrays that are inserted into the highly curved cochlea. On the other hand, very thin wires 203 can tend to have unduly high electrical resistance, which may be a problem due to the energy loss (resistance is a function of the cross-section area of the metal structure). To overcome this problem, several printing passes may be used to build up the material height of the wires 203 and thereby lower the electrical resistance.
In some specific embodiments, the conductive metal material of the electrode network 202 may include platinum material such as a platinum-based ink and/or a platinum alloy material. For example, a metallic ink may contain metal nanoparticles or be based on a complex of platinum ions and surrounding ligands. In some specific embodiments, the electrode substrate 201 may have been pre-treated with at least one of a primer treatment and a plasma activation treatment to increase wettability of the metal material to the electrode substrate 201. A metallic ink may not initially be conductive until it is sintered so as to either (depending on the ink formulation) fuse the platinum nanoparticles or cause reduction of the platinum complex in order to form solid metallic platinum. Thus, developing the electrode network 202 may include heat treating one or more portions of the electrode network 202 for sintering.
Once the electrode network 202 is developed, a portion of it is selectively covered with an encapsulation layer 501 in
In the embodiment shown in
For some applications such as high-density electrodes or particularly small electrodes (e.g., cochlear implant electrodes), there may be problems related to spreading of the metallic ink over the surface of the substrate 201. If needed, the printability may be enhanced by matching the surface energy of the ink to the substrate 201 or by treating the surface of the substrate 201, for example, with a plasma treatment. Alternatively,
An inkjet printing process as described above to manufacture an implantable electrode device can be fast, simple, flexible, reproducible, and highly automated. Little complicated equipment is needed and there are relatively few process steps needed to make both two-dimensional and three-dimensional electrode network structures. And there is no need to waste expensive surplus material as in some other manufacturing methods since only the metal that is actually used for the electrode network is actually printed and used.
Structures using different metals can be produced in the same process by having ink cartridges with different inks. For example, in this way the electrode stimulation contacts can be coated or plated with a different metal than the bulk metal of the other portions of the electrode network. It is also possible to tailor the electrical and mechanical properties of the electrode device in a single process by printing structures that include elements which serve a mechanical purpose without necessarily being electrically active. For example, structures of non-conductive materials can be printed in the same manufacturing process by using printing cartridges with an appropriate material (e.g. a structural polymer). This also allows printing of structures for electrical insulation.
In addition, changing the design parameters of the manufactured structures is relatively simple with only simple changes in a CAD file where the geometrical parameters for the electrode design are defined and possibly some basic process optimization. In a case of printing into recessed geometries, the process for creating the recesses may also need to be changed.
For more background information on inkjet printing in embossed polymer structures refer to C. E. Hendriks, P. J. Smith, J. Perelaer, A. M. J. van den Berg, U. S. Schubert, Invisible Silver Tracks Produced by Combining Hot-Embossing and Inkjet Printing, Adv. Funct. Mater., 18, 1031-1038, (2008), incorporated herein by reference.
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.
This application claims priority from U.S. Provisional Patent Application 61/181,475, filed May 27, 2009, incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61181475 | May 2009 | US |
