SE430467B - Implantable carbon electrode - Google Patents

Description

15 20 25 30 35 H0 7702777-9 2 Direction electrodes, which consist of metals, such as e.g. platinum, causes a degeneration of the tissue adjacent to the electrode within a period of about 2 - H weeks, which is manifested by the formation of a non-irritable connective tissue layer. The consequence of this is a continuous rise of the excitation threshold, for the overcoming of which a large current is required. This also increases the excitation voltage, which can be divided into an ohmic loss of body resistance and a predominant loss of polarization occurring at the electrode, whereby the polarization proportion can be above the decomposition voltage of the water, whereby a secure fixation of the excitation electrode in the body is made more difficult. .

To eliminate this drawback, it has been proposed to use carbon or graphite-containing irritating electrodes, on the surface of which only a thin connective tissue capsule is formed. Due to their mechanical properties, however, the materials in question have not gained ground in practice for this purpose, since in particular the wear and the relative probability of breakage of human implants are disadvantageous and also the relatively high polarization voltage is not satisfactory. . The object of the invention is to make implantable carbon electrodes in such a way that they exhibit high mechanical stability and in long-term operation consume as little energy as possible.

This object is achieved according to the invention with a carbon electrode, the electrode head of which consists at least on the surface of pyrolytic carbon.

Pyro-carbon is formed from hydrocarbonaceous gases which decompose on the surface of a heated substrate. By controlling the separation conditions, such as separation temperature and pressure, the composition of the reaction gas and the retention time, it is possible to change the density and microstructure of the pyrolytic carbon within wide limits. However, the mechanical stability of nos pyro-carbon within these limits is greater than the stability of normal carbon and graphite bodies proposed for excitation electrodes. In addition, the fracture toughness of pyrolytic carbon can be further increased in a simple manner by simultaneous separation of stable carbide-forming elements. For comparison, the flexural strength strengths are: normal graphite pyrolytic carbon pyrolytic carbon with - about 10% kiaai about soo kn / mmz d Pyrolytic carbon is also extremely abrasion resistant and does not react with blood and other substances present in the body. up to 50 km / mma approx. SEK 159 / mmz 10 15 20 25 30 35 Ä0 3 7702777-9 The electrode head of the irritating electrode may in its entirety consist of pyrolytic carbon or contain a core of another material, the surface of which is coated with a layer of pyrolytic carbon. According to the invention, the thickness of this layer amounts to at least 0.05 mm. According to the invention, it is particularly advantageous to activate the pyrolytic carbon on the surface by a partial oxidation, by which is meant the formation of a surface provided with numerous etching holes and sack-like micropores. 1 The activation of the pyrocarbon takes place by oxidizing gases and vapors, oxidizing acids or also by electrochemical means. The electrode head is heated for this purpose, for example in an oxygen, air, water vapor or carbon dioxide-containing atmosphere to a temperature between H00 and 800 ° C for less than one hour, whereby the most favorable conditions can be determined by simple preliminary experiments.

By activating the pyrolytic carbon, the polarization losses which occur at the interface between the electrode and the tissue and which do not contribute to increasing the field strength in the adjacent irritable tissue can be kept very low. In this way, the implantable electrode according to the invention achieves both a slight encapsulation by connective tissue formation as well as a low energy consumption and in connection therewith good permanent operating conditions, since the current density at the stimulation threshold is not increased during the duration of the implantation.

The invention will be explained in more detail below by way of example.

An electrode prepared from a fine-grained graphite body was provided at a temperature of 120,000 in a propane atmosphere, the partial pressure of which was about 0.2 bar, with a layer of pyrolytic carbon. The carbon was deposited, until the formation of a closed surface layer, likewise in the pores of the graphite body, whereby the strength of the body approximately doubled. The thickness of the surface layer was 60-80 pm. A second electrode was prepared from a pyrolytic carbon body similarly produced by propane gas at a temperature of about 300 ° C, with a pronounced isotropic microstructure, and graded for activation for 1 hour at 850 ° C in a water vapor stream. These electrodes, and for comparison purposes, a platinum-iridium excitation electrode were implanted in the thigh of cats. The operating results are given in the following table: Electrode Pyrocol Pyrocol activated Platinum-Iridium At the beginning of the test current 0.18 mA 0.16 mA 0.15 mA voltage 0, Uü V 0, l2 V 0.16 V after 20 days current 0.17 mA 0.18 mA 0, U2 mA voltage 0, ü8 v 0.11 V 0.45 V 7702777-9 "-n Implantable electrodes with an electrode head of superficially activated pyrolytic carbon show a slight polarization according to the test results and are therefore suitable particularly for use as cardiac pacemaker electrode electrodes, since little energy is consumed for the induction process due to the small induction threshold increase, the life of the current source is high and it can also be performed small.

Claims (3)

5,770,277? -9 Patent claims An implantable carbon electrode, in which at least one surface layer of its electrode head consists of pyrolytic carbon, is characterized in that the pyrolytic carbon material has a surface with a microporous structure. An implantable carbon electrode according to claim 1, characterized in that the pyrolytic carbon material is partially oxidized. An implantable carbon electrode according to claim 1 or 2, characterized in that the thickness of the surface layer of pyrolytic carbon in the electrode head is at least 0.05 mm.