Active metal brazing for joining glass-ceramic to titanium-a study on silver enrichment

Abstract

A hermetic encapsulation system for implantable telemetric electronic devices has been developed. It is based on the combination of a glass-ceramic material transparent to radio-frequency signals with commercially pure titanium. The materials were joined by active metal brazing, resulting in a multi-layer structure. The in vivo and in vitro behaviour of this metal-ceramic interface was studied. In vivo experiments consisted of subcutaneous implantation of capsules in piglets and pigs with different weights, while the in vitro tests consisted of electrochemical techniques aimed at characterizing the degradation behaviour of the interface. Electrochemical experiments were conducted at 37°C in a simulated physiological solution (Hank's Balanced Salt Solution; HBSS). Results show that a silver-rich phase was formed at the interface, both in living tissue and in HBSS. Chloride seems to have an important role in the reaction mechanism. The mechanical integrity of the capsules was not affected by this reaction under in vivo conditions.