A range of bio-ceramics can induce calcium phosphate nucleation in simulated body fluids over timescales of hours to days. Such in-vitro behaviour is well correlated with in-vivo bone and tissue bonding ability. We demonstrate and discuss here how the "bio-activity" of porous silicon films might be tailored by manipulation of layer microstructure, chemical composition, and surface electrical charge. The kinetics of in-vitro calcification can be accelerated to occur within hours, suggesting that silicon bio-chips might be developed that could rapidly bond in-vivo with living tissue and bone. Crown