Biocompatibility of glass-encapsulated electronic chips (transponders) used for the identification of pigs.

The biocompatibility of electronic transponders encapsulated in two different types of glass was studied after they had been implanted subcutaneously into pigs for the purpose of identification. Rods of white crystal glass or green iron-containing glass were screened for superficial impurities by scanning electron microscopy and X-ray analysis, revealing a few crystalline and plaque impurities which were similar for both types of glass, and no differences in elemental composition. In vitro cytotoxicity tests using cell cultures of human dermal fibroblasts and haemolysis and clot formation tests in human blood after contact with the rods, showed that both types of glass were biocompatible. When implanted subcutaneously at the base of the ears of pigs for from three to 150 days, both types of transponder appeared to induce a similar connective tissue capsule, on average less than 0.2 mm in thickness, surrounding the rods. A classic foreign body reaction did not occur. It is concluded that the fibrous capsules were due to scar tissue formed around the glass rods as a result of the tissue being damaged when they were implanted. There were no significant differences between the reactions to the two types of glass. The subcutaneous implantation of glass-encapsulated transponders appears to be a good method for identifying pigs.