Плазменная технология формирования поверхности электродов кардиостимуляторов из рутения

Abstract

The electric pacemaker (EP), a device for electrically stimulating the myocardium, is widely used for treating and rehabilitating patients who have suffered heart attacks and other heart diseases. Stable transfer of energy in impulses from the EP to the heart and the optimal coordination between the EP parameters and the pacemaker electrodes are the most important conditions for the EP operation. The electrode is electrically connected with the myocardium tissue mainly through capacitive coupling. To stimulate the myocardium, an electrical impulse with duration of 100–300 µs and energy of 1–5 μJ is required; with the stimulation threshold equal to 1 V, the coupling capacitance should be equal to 2–10 µF. When an electric potential is applied to the electrode, a double electric layer (DEL) appears in the blood electrolyte at the electrode surface. The DEL’s capacitive impedance is significantly higher than its ohmic resistance. The DEL is electrically equivalent to two series-connected capacitors, and its capacitance is determined by the capacitances of the DEL’s inner dense part and of its outer diffuse part. To improve the EP efficiency, the DEL capacitance should be increased. To do so, two methods are used: increasing the electrode surface area by extending its surface and increasing the surface adsorption by using special coatings. The modern pacemaker electrodes have the characteristic size of extended surface inhomogeneity equal to around 1 µm, which is larger than the DEL’s inner dense layer thickness, which is less than 1 nm. Therefore, for pacemaker electrodes, the size of the surface structure elements should be reduced down to 1 nm. Such structures of the "fuzz" type can be obtained by processing materials with plasma. A PLM plasma installation intended for obtaining an extended surface nanostructure on metals, including that of the “fuzz” type, has been constructed at the National Research University Moscow Power Engineering Institute. Electrodes of metals from the platinum group are the most promising ones; the iridium coating of the electrodes has the lowest capacitive impedance. Ruthenium (Ru) also belongs to the platinum group of elements. In this study, ruthenium, an element which is a chemical analog of iridium but having a number of technological advantages, has for the first time been proposed for coating the electrodes. Ruthenium is the only one of these elements that is naturally present in the human body. In addition, ruthenium is significantly cheaper than iridium. In the PLM installation, a nanostructured coating of ruthenium is produced on the electrode by sputtering Ru by means of a target in plasma discharge. It is proposed to test a few approaches, including that in which a “fuzz” type structure is produced on a titanium surface. After that, ruthenium can be sprayed onto this structure, or a “fuzz” type structure can be produced already on the deposited ruthenium layer. Such experiments open the possibility to develop a new technology for making the pacemaker electrodes with improved characteristics.