Water absorption characteristics of modified hydroxyapatite bone cements

Water absorption characteristics of a range of modified hydroxyapatite (HA)-reinforced poly(ethyl methacrylate)-n-butyl methacrylate (PEMA-nBMA) bone cements have been established. From gravimetric measurements, the kinetics of successive absorption and desorption cycles, equilibrium uptake, diffusion coefficients and solubility data have been determined. In general, the water uptake could be modelled by the classical laws of diffusion. The introduction of the HA reduced the water uptake of the bone cement, with a further decrease if the HA filler was surface treated with a silane coupling agent. However, the system comprising the silicated silanated HA-filled cement produced a large uptake of water, with relatively low diffusion coefficients, which is attributed to the presence of soluble sites in the matrix.