Control of nano size haydroxyapatite crystallization by polyelectrolytes

ABSTRACT Many current evolving technologies require crystallization strategies that provide control over the structure, size and morphology of inorganic crystals. This demand exists because many areas of materials fabrication involve particles of modal size and shape. However, although knowledge of the thermodynamic and kinetic factors which might regulate nucleation and control the crystal growth process is extensive, the reproducible fabrication of economic crystalline materials to specific design remains an elusive goal. Much of our awareness of molecular influences on oriented crystallization has come from the study of biomineralization. In general, biominerals are formed by the precipitation of calcium carbonate, calcium phosphate and other minerals within polymeric tissue matrices. It is thought that the organic polymer matrix is the key to the micro structural control. An understanding of biological solid-state interactions would therefore be of immense value in many areas. In this work the individual effect of polymeric additives for the hydroxyapatite (HAP) crystallization were investigated by seeding stable supersaturated calcium phosphate solutions with crystals. The seed crystals were characterized by SEM, BET, FT-IR, X-Ray powder diffraction methods. The polyacrylic acid, polymethacrylic acid homopolymers and poly(ethylene glycol-h-acrylic acid), poly(ethylene glycol-b-methacrylic acid) copolymers with different molecular weights and acid contents have been used as additives. Kinetic results of HAP crystallization were obtained using the constant composition method where the concentration of the reactants is kept constant during the course of the crystal growth experiment. The rate of HAP crystallization was affected by the polymer architecture and polymer concentration. The crystallization reactions were interpreted in terms of the Langmuir adsorption isotherm. In this study we have used phosphorus-containing polymers namely poly(vinylphosphonic acid-co-4vinylimidazole) copolymers for the induction of the overgrowth of HAP from aqueous supersaturated solutions. Keywords: Hydroxyapatite crystallization, nucleation, polymeric additives, biomineralization. xn