In-situ Characterization of the Early Stages of Bio-Mimetic Calcium Phosphate and Calcium Carbonate Mineralization

Abstract

Biomineralization is an important and inspiring process where living organisms promote self-assembly of organic matrices in order to induce high control of calciumbased mineralization. The in-situ characterization of early stage bio-mimetic mineralization allows the nanoscale structures of mineral nucleation to be studied. This research thesis has characterised the formation of calcium phosphate and calcium carbonate using in-situ ellipsometry, X-ray and neutron reflectivity and small angle X-ray and neutron scattering as a means of probing the early stages of mineralization. Thin films of amorphous calcium phosphate were formed on the air-liquid interface of a simulated body fluid (SBF) using a zein protein and hexadecanoic acid (HDA) monolayer. Zein protein induced calcium phosphate films were formed by aggregation and fusion of hemispherical nanoparticles. HDA induced mineral films showed a flat continuous morphology. The mineral film thickness, obtained by ellipsometry, using HDA template were significantly thicker than that of zein-induced calcium phosphate films. X-ray reflectivity measurements on a diluted SBF revealed a mineral film that decreased in thickness while increasing in density. When the SBF concentration was doubled a very dense mineral film was detected with its increasing thickness over the 4 h experiment. Multilayered chitosan/iota-carrageenan films showed striking iridescence, when swollen in H2O, shifts from a golden to a blue sheen when mineralized using SBF or simulated seawater (SSW). The interfaces between the chitosan and iota-carrageenan bilayers were shown to increase in density, with small angle neutron scattering showing an increase in lamellar density with mineralization. The presence of Cu2+, Zn2+, Pb2+ and Cd2+ heavy metal ions at concentrations of 5 and 50 μg L-1 within the SBF and SSW were shown to inhibit scattering features arising from these dense interfaces. The kinetics of this template was studied using in-situ ellipsometry at the solid-liquid interface on a 2-bilayer film. The rate of biopolymer thickness increases with calcium phosphate and carbonate mineralization shown was increase with the presence of heavy metal ions.