Optimum Surface Texture Geometry
A surface geometry for an implantable medical electrode that optimizes the electrical characteristics of the electrode and enables an efficient transfer of signals from the electrode to surrounding bodily tissue. The coating is optimized to increase the double layer capacitance and to lower the after-potential polarization for signals having a pulse width in a pre-determined range by keeping the amplitude of the surface geometry with a desired range.
1 . A method for optimizing a coating on a substrate comprising the steps of:
a. providing a primary metallic component
b. providing a secondary reactive component;
c. depositing said primary and said secondary components on said substrate such that deposited atoms of said secondary reactive component react with atoms of said primary metallic component prior to solidifying;
d. wherein the reaction of said primary metallic component and said secondary reactive component results in a surface having pyramidal or tetragonal crystal structures defined thereon; and
e. varying the deposition parameters such that the average amplitude of said crystal structures falls within a desired range.
2 . The method of claim 1 wherein said varied deposition parameters are selected from a group consisting of pressure and power.
3 . The method of claim 2 wherein said deposition takes place under a pressure that will result in average amplitude of said crystal structures being with said desired range.
4 . The method of claim 3 wherein said primary metallic component is titanium, said secondary reactive component is nitrogen.
5 . The method of claim 1 wherein said desired range for the average amplitude of said crystal structures is approximately between 250 and 400 nanometers.
6 . The method of claim 1 wherein the sides of said pyramidal structures form an angle with the base of said pyramidal structures which is between 20 and 70 degrees.
7 . The method of claim 6 wherein said angle is 45 degrees.
8 . The method of claim 5 wherein the voltage on the double layer capacitance falls to within 30-50 mV of its unstimulated level with 18-22 ms of the trailing edge of the stimulation pulse.
9 . The method of claim 5 wherein the double layer capacitance of said coating is approximately 70 mF/cm 2 or above.
10 . The method of claim 1 further comprising the step of polishing said substrate prior to depositing said coating.
11 . The method of claim 10 wherein said surface is polished to an Ra of 11 micro-niches or less.
12 . The method of claim 10 wherein said surface is polished to an Ra of 8 micro-inches or less.
13 . The method of claim 1 wherein said primary metallic component is selected from the group consisting of Ti, Ta, Nb, Hf, Zr, Au, Pt, Pd and W.
14 . The method of claim 1 wherein said secondary reactive component is selected from a group consisting of nitrogen, oxygen and carbon.