pectus excavatum, mini-movers, and it's magnet

Pectus Excavatum is a relatively common chest deformity in which the sternum grows inward. While this deformity is rarely serious particularly bad cases can result in reduced cardiac output and decreased lung capacity. Normally this condition is pretty expensive to correct and very painful , due to that many people decide to not go through the procedure, however a new procedure is being tested called the magnetic mini-mover procedure. In this procedure a neodynium magnet is (as I understand it) placed on the breastbone of a child(14 and under) and the wearing of a brace around the chest which has another magnet mounted to it. Over time the two magnets attract each other and reform the deformed breastbone. The reason this is relevant is that for the life of me I cant seem to find out what they are using for biocompatibility, and of all of the albeit the small procedures performed I haven't seen a single report of rejection. I've looked through a good amount of articles but couldn't find a good answer from a reliable source, and this seems like something that would very beneficial for us to know.