Analysis of particle size distribution of hydroxyapatite crystallites in the presence of synthetic and natural polymers.

The particle size distribution (PSD) of suspended hydroxyapatite crystallites both at equilibrium and during crystal growth has been measured by a laser scattering technique. Addition of high-molecular-weight polyacrylate (PAA/C) resulted in appreciable crystallite aggregation, probably by polymer bridging of particles. In contrast, a lower-molecular-weight PAA was unable to bridge the hydrodynamic gap between particles and resulted in an overall dispersion. The addition of human serum albumin also markedly influenced the PSD and, with concomitant change in zeta potential to more negative values, resulted in dispersion due to steric interaction and electrostatic repulsion between the particles. The complex behavior of human saliva is illustrated by its tendency both to aggregate and to disperse hydroxyapatite crystallites, displaying the combined effects of different adsorbing macromolecules.