. . "When the polymer employed for the device to control'the flow of medicament is made of a polymer which has a tissue reaction e.g. silicone, polyvinyl alcohol, Teflon and most of the other polymers which are tissue irritating, it is preferred to eliminate the tissue irritation by employing a polymer of a hydroxyalkyl acrylate or methacrylate, e.g. a HEMA polymer, as a thin biocompatible overall coat" . .