Highly ordered superstructures composed of inorganic nanoparticles appear in natural
and synthetic systems, however the mechanisms of non-equilibrium self-organization
that may be involved are still poorly understood. Herein, we performed a kinetic investigation
of the precipitation of calcium phosphate using a process widely found in microorganisms:
the hydrolysis of urea by enzyme urease. With high initial ratio of calcium ion to
phosphate, periodic precipitation was obtained accompanied by pH oscillations in a
well-stirred, closed reactor. We propose that an internal pH-regulated change in the
concentration of phosphate ion is the driving force for periodicity. A simple model
involving the biocatalytic reaction network coupled with burst nucleation of nanoparticles
above a critical supersaturation reproduced key features of the experiments. These
findings may provide insight to the self-organization of nanoparticles in biomineralization
and improve design strategies of biomaterials for medical applications.
