Effect of smooth, porous and fractal surface structure on the properties of an interface

Recently, biomaterials research has focused on the creation of new materials. Mixing or doping of well-tried materials should aim to result in new physical or chemical properties, better tissue tolerability and improved long-term stability. We present another way of improving performance: the application of new technologies to well-known materials. The surface structure of a coating depends on the deposition technique. Hence, the transfer of, for example, sputtering technology to biotechnology may solve current problems with well-tried materials. This paper reports the influence of surface structure and area on the properties of pacemaker electrodes. Smooth electrodes were compared with porous electrodes produced by sintering and with fractal electrodes resulting from physical vapour deposition of iridium or titanium nitride. Micrographs revealed a slight enlargement of the surface area by sintering and an enormous enlargement with fractal coating. Analysis of electrochemical properties proved the advantages of fractal coating: the impedance spectra exhibited incomparable low impedances for frequencies down to 1 Hz and no afterpotentials could be detected. Clinical results confirmed the superiority of fractal electrodes. The stimulation thresholds were significantly reduced, P-and R-wave amplitudes were increased, and ventricular evoked responses and monophasic action potentials were able to be measured with clarity unknown so far.