The effect of surface silanol groups on the deposition of apatite onto silica surfaces: a computer simulation study

Computer modelling techniques were employed to investigate the effect of surface silanol groups on the strength of adhesion of apatite thin films to silica surfaces. To this end, we have studied a series of silica surfaces with different silanol densities and calculated their interaction with apatite thin films. Our findings indicate that apatite does not attach strongly to surface hydroxy groups, but that apatite should deposit at dehydrated silica surfaces, especially when the surface silicon and oxygen species rearrange to form O–Si–O links. Any dangling silicon and oxygen bonds at the silica surfaces are saturated by coordination to oxygen and calcium atoms in the apatite layer, but the extra reactivity afforded by these under-coordinated surface species does not necessarily lead to more favourable substrate/film interactions. The lowest energy silica/apatite interfaces are those where an undistorted apatite layer can be deposited on a regular, stable substrate surface. Our simulations support the suggestion, that in vivo surface hydroxy groups are first condensed to form O–Si–O bridges before deposition and growth of apatite.