Resorbable porous or polycrystalline silicon implants impregnated with a beneficial substance can be used for slow release of a substance over a long time. Porous or polycrystalline implants, particularly of silicon, impregnated with a beneficial substance are new. Independent claims are included for the following: (a) a method of impregnating a porous semiconducting material with a substance by allowing molten impregnate substance to pass into the pores of the semiconductor (b) implants having a large number of holes which contain beneficial substance and which are closed by bio erodable doors of different thickness, to stagger the release of the beneficial substance over time as the doors are breached.
