ACTIVE METAL BRAZING FOR JOINING GLASS-CERAMIC TO TITANIUM - A STUDY ON SILVER ENRICHMENT

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 commercia lly pure titanium. The materials were joined by active metal brazing, resulting in a multi-layer structure. The in vivo and in vitro behavio ur of this metal-ceramic interface was studied. In vivo experiments co nsisted of subcutaneous implantation of capsules in piglets and pigs w ith different weights, while the in vitro tests consisted of electroch emical techniques aimed at characterizing the degradation behaviour of the interface. Electrochemical experiments were conducted at 37 degre es C in a simulated physiological solution (Hank's Balanced Salt Solut ion;HBSS).Results show that a silver-rich phase was formed at the inte rface, both in living tissue and in HBSS. Chloride seems to have an im portant role in the reaction mechanism. The mechanical integrity of th e capsules was not affected by this reaction under in vivo conditions.