Crystallization of an inorganic phase controlled by a polymer matrix

Abstract

BIOLOGICAL composite materials such as bones, teeth and shells consist of a polymer matrix reinforced by an inorganic phase which forms in the matrix¹. These materials are distinguished from synthetic composites by the high degree of organization and regularity displayed by the inorganic phase: inorganic minerals of uniform size, morphology and crystallographic orientation can be formed in ordered arrays in living cells. Such a process has until now not been realized in synthetic systems, although the recent interest in nanoscience^2–6has stimulated much research in the area. We report here an example of a synthetic process that produces composite materials analogous to those produced by natural biomineralization. The inorganic/organic in situ synthesized composites display controlled inorganic crystal size, morphology and orientation, which are determining features of type II, or matrix-mediated⁷, biocomposites. The synthetic factors that must be optimized to give biomimetic properties to synthetic composites are strong binding of the inorganic reagents by the organic matrix (molecular complementarity); good 'solvation' of the inorganic reagents by the polymer; and an ordered, regular polymer environment in which to induce nucleation (matrix preorganization)¹.