Surgery – Miscellaneous
Reexamination Certificate
1999-04-15
2001-02-20
Hindenburg, Max (Department: 3736)
Surgery
Miscellaneous
C600S300000
Reexamination Certificate
active
06189536
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for protecting implantable devices from corrosion once the device is implanted, such as within a human body.
BACKGROUND
In many medical situations, it is desirable and often necessary to implant relatively small (micro) electromechanical devices for an extended period of time. For example, it may be desirable to continually administer fluid medication (either as a gas or a liquid) to a patient over an extended period of time. Examples of such treatments included the low dose continual administration of morphine for pain control, the administration of FUDR for cancer chemotherapy, the administration of baclofen for the treatment of intractable spasticity, and the like.
In such instances, a particularly desirable goal is to maintain a relatively constant level of medication in the patient's bloodstream. In order to accomplish this goal, relatively small fluid handling devices are implanted within a patient's body. However, both the medication and bodily fluids that may contact the micro fluid handling devices are typically corrosive. Thus, it is desirable to provide a corrosion-resistant layer to at least one surface of the micro fluid-handling device to prevent or limit corrosion. For example, Saaski et al. describe that a nominal layer of a corrosion-resistant substance may be deposited on a substrate by sputtering by using an e-beam evaporator, where suitable corrosion-resistant substances may be silicon, gold, platinum, chrome, titanium, zirconium, and oxides of silicon or these metals. It is further described that oxides may be formed by thermally oxidizing the corrosion-resistant substance in air after it has been applied to the substrate. See, U.S. Pat. Nos. 5,660,728; 5,702,618; and 5,705,070 all to Saaski et al.
SUMMARY OF THE INVENTION
What is yet needed is a method for protecting implantable devices from corrosion on at least one surface of the device, wherein that surface may or may not include a separate coating. For example, in a typical device fabrication process, a corrosion-resistant coating is applied to individual components along the fabrication process but prior to complete assembly of the device. Because typical coating methods utilize relatively high temperatures, coating a completely assembled device is generally not possible because the relatively high coating temperatures tend to be detrimental to electrical components which, in turn, ultimately adversely affects the functioning of the device.
Accordingly, one aspect of the present invention provides a method for protecting an implantable device from corrosion that includes providing a pulse waveform to at least one surface of the implantable device, thus eliminating the need to apply a separate coating to prevent corrosion.
However, if a coating is to be applied to a device, providing a pulse waveform to at least one surface including a coating of the implantable device can protect the device from corrosion that may occur through very small openings in the coating or through coating imperfections.
As used herein, “corrosion” refers to a complex electrochemical degradation of a conductive material (such as a metal or a metal alloy) or a semiconductive material (such as silicon or carbon) due to a reaction between such materials and the environment, usually an aqueous electrolyte-containing environment, such as an acidic or basic (alkaline) environment. In general, a corrosion product of such a material is in the form of an oxide of the material, such as a metal oxide, silicon dioxide, and the like. While not wishing to be bound by any particular theory, it is believed that corrosion occurs when the material (such as copper or silicon) contacts an electolytic solution and a mini-electrochemical circuit is formed when a small amount of the material dissolves in the water and combines with dissolved species. In forming the mini-electrochemical circuit, an imbalance of electrons between the solution and the surrounding material creates a minute flow of electrons, or current. So long as a current is allowed to flow, the material will continue to deteriorate, resulting in degradation and even pitting of the material.
A “corrosive fluid” is one that participates in the corrosion of a material. Typical corrosive fluids are aqueous solutions containing electrolytes that generally have an alkaline pH (i.e., greater than about 7.0). For example, a corrosive fluid can be a solution of a therapeutic agent (e.g., baclofen) or even a bodily fluid, such as blood.
A method in accordance with the present invention is suitable for any implantable device but is particularly well suited for micro electromechanical devices, such as implantable pumps, filters, valves, cardiac pacesetters, lead conductors and electrodes, prosthetic device, to name a few.
Thus, one aspect of the present invention provides a method for protecting an implantable device from a corrosive fluid comprising providing a pulse waveform to at least one surface of the implantable device, wherein a closed circuit is completed though the corrosive fluid. Preferably, the pulse waveform originates from at least one electrode on the at least one surface of the implantable device. The pulse waveform preferably has a frequency of about 100 KHz to about 1 MHz. The pulse waveform is preferably generated by a current having a voltage of about 1 volt to about 10 volts.
In one embodiment, the pulse waveform generated in the surface has a root mean squared of current of about 8.6 mA to about 0.029 mA, wherein the surface comprises silicon. However, one with skill in the art will recognize that the magnitude of the current may be dependent on the material to be protected and the composition of the corrosive fluid. Thus, some materials may require more or less current to shift them to a region of stability, as described herein.
The method may also include a second electrode, wherein the closed circuit is completed though the corrosive fluid from the at least one electrode and the second electrode. Therefore, the at least one surface of the implantable device is preferably located between the at least one electrode and the second electrode.
The at least one electrode is preferably formed from a material selected from the group consisting of a metal, a metalloid, and a combination thereof. Alternatively, the at least one electrode comprises a material having an electrical conductivity of at least 10
−6
mho/cm. More preferably, the at least one electrode comprises a metal selected from the group consisting of a refractory metal, a noble metal, and a combination thereof, including an alloy, a nitride, and an oxide of each. Even more preferably, the metal is selected from the group consisting of tantalum, titanium, zirconium, ruthenium, iridium, platinum, and a combination thereof.
In accordance with the present invention, the implantable device is preferably selected from the group consisting of a pacemaker, a pacemaker-cardioverter-defibrillator, an implantable neurostimulator, a muscle stimulator, an implantable monitoring device, an implantable fluid handling device, a defibrillator, a cardioverter/defibrillator, a gastric stimulator, a drug pump, and a hemodynamic monitoring device. In one embodiment of the present invention, the at least one surface of the implantable device is an exterior surface of the implantable device. In another embodiment, the at least one surface of the implantable device comprises an interior surface of the implantable device, however a combination of surface can be protected by a method in accordance with the present invention.
The corrosive fluid can be selected from the group of an aqueous solution of a therapeutic agent or a body fluid.
Another aspect of the present invention provides an implantable device comprising a first electrode attached to a surface of the implantable device and a second electrode each operatively connected to a waveform generator, wherein the second electrode is oriented such that the surface of the implantable device is between the
Haller Markus
Martinez Gonzalo
Hindenburg Max
Jaro Michael J.
Medtronic Inc.
Patton Harold
Woods Thomas F.
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