Polarization and Corrosion Studies of Porous and Solid Anodes for Implantable Power-Generating Electrodes

An implantable power source for driving a pacemaker consisting of a hybrid cell utilizing a sacrificial porous aluminum anode and a catalytic cathode for reducing oxygen is considered. Porous aluminum anodes show a significant improvement in polarization over a solid aluminum anode under in vitro transient operating conditions found with certain types of pacemakers. However, the in vivo transient behavior of porous aluminum anodes is only slightly better than solid aluminum anodes. Using in vivo and in vitro linear polarization studies, the corrosion of solid aluminum has been determined to be more than an order of magnitude less than that of solid zinc. The weight loss of aluminum due to corrosion is less than 3.0 percent that of the aluminum needed to supply the faradaic current to the pacemaker. A hybrid cell consisting of an aluminum anode and a porous palladium-black cathode has powered a commercially available pacemaker. Further histopathologic evaluation of tissues surrounding anodes is needed before selecting either zinc or aluminum as an anode material.