a biocompatible medical implant has at least one part thereof composed of ceramic material with the formula na x k y nbo 3 , wherein 0 ≦ x ≦ 0 . 8 , 0 . 2 ≦ y ≦ 1 , and x + y = 1 . the ceramic material can be polarized to give the implant spatially varying piezoelectric properties . signals can be measured from the respective piezoelectric regions of the selectively polarized ceramic material to provide an indication of the degree of fixation of the implant to surrounding tissue .