For fixedly implanting a device for material or signal delivery or acquisition or a part of such a device in a human or animal body, an opening is provided in hard tissue of the body, the opening reaching through a hard tissue layer, e.g. through a cortical bone layer into cancellous bone underneath. The device includes a plug portion (P) and/or a cover portion (C) which includes a ring of a material having thermoplastic properties extending around the plug portion (P) or on a tissue facing surface of the cover portion (C). The opening provided in the hard tissue has a cross section at least in the area of its mouth that is adapted to the plug or cover portion such that the plug portion (P) can be introduced through the mouth of the opening or the cover portion (C) can be positioned over the mouth of the opening such that the ring extends around the opening, along its wall and/or on the hard tissue surface around its mouth.
