Platinum electrode and method for manufacturing the same

#The field of the invention relates to platinum electrodes and electroplating processes for deposition of platinum.

#Electrodes for stimulating body tissue by electrical stimulation are known in great variety. For the utility of an implantable stimulation or sensing electrode—especially one intended for long-term use in a tissue stimulator with a non-renewable energy source and that, therefore, must require minimal energy—a high electrode capacitance and correspondingly low electrical impedance is of great importance. Furthermore, without sufficiently low impedance, a large voltage may cause polarization of both the electrode and the tissue to which the electrode is attached forming possibly harmful byproducts, degrading the electrode and damaging the tissue.

#Because the ability of an electrode to transfer current is proportional to the surface area of the electrode and because small electrodes are necessary to create a precise signal to stimulate a single nerve or small group of nerves, many in the art have attempted to improve the ability of an electrode to transfer charge by increasing the surface area of the electrode without increasing the size of the electrode.

#FIG. 1 shows a platinum gray surface magnified 2000 times.

#FIG. 2 shows a shiny platinum surface magnified 2000 times.

#FIG. 3 shows a platinum black surface magnified 2000 times.

#Referring to FIG. 1, an illustrative example of a platinum gray surface coating for an electrode according to the present invention is shown having a fractal surface with a surface area increase of greater than 5 times the surface area for a shiny platinum surface of the same geometry, shown in FIG. 2, and an increase in strength over a platinum black surface, shown in FIG. 3. FIGS. 1, 2, and 3 are images produced on a Scanning Electron Microscope (SEM) at 2000× magnifications taken by a JEOL JSM5910 microscope (Tokyo, Japan). Under this magnification level it is observed that the platinum gray is of a fractal configuration having a cauliflower shape with particle sizes ranging from 0.5 to 15 microns. Each branch of such structure is further covered by smaller and smaller particles of similar shape. The smallest particles on the surface layer may be in the nanometer range. This rough and porous fractal structure increases the electrochemically active surface area of the platinum surface when compared to an electrode with a smooth platinum surface having the same geometric shape.

#Because no impurities or other additives such as lead, which is a neurotoxin and cannot be used in an implantable electrode, need to be introduced during the plating process to produce platinum gray, the surface can be pure platinum. Alternatively, other materials such as iridium, rhodium, gold, tantalum, titanium or niobium could be introduced during the plating process if so desired but these materials are not necessary to the formation of platinum gray.

#Platinum gray can also be distinguished from platinum black and shiny platinum by measuring the color of the material on a spectrodensitometer using the Commission on Illumination l*a*b* color scale. l* defines lightness, a* denotes the red/green value and b*, the yellow/blue value. The lightness value (called l* Value) can range from 0 to 100, where white is 100 and black is 0—similar to grayscale. The a* value can range from +60 for red and −60 for green, and the b* value can range from +60 for yellow and −60 for blue. All samples measured have very small a* and b* values (they are colorless or in the so-called neutral gray zone), which suggests that the lightness value can be used as grayscale for Platinum coatings.