טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentPokroy Boaz
SubjectInteraction between the Organic and Inorganic Phases in
Biogenic CaCO3
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Emeritus Emil Zolotoyabko
Full Thesis textFull thesis text - English Version


Abstract

Organisms produce a large number of minerals in the course of biomineralization. These biogenic minerals have been extensively studied for decades because of their fascinating characteristics, which are achieved as a result of the ability of living organisms to effectively control the polymorph selection and crystal morphology by means of organic macromolecules. Therefore, the key point in biomineralization is a detailed understanding of the mechanisms responsible for the interaction between the organic and inorganic phases. This is as yet an unresolved issue. For this reason we are still unable to mimic in the laboratory the growth processes developed by nature and benefit from artificially grown bio-composites. Our research is focused on studying such interaction in CaCO3, which is the most abundant biogenic mineral, existing in different structural forms: calcite, aragonite, vaterite, and amorphous calcium carbonate. We show that the organic phase controls not only the polymorphism, morphology and orientation of growing minerals, but in some sense even their atomic structure.

By using high-resolution x-ray powder diffraction on synchrotron beam lines we discovered anisotropic lattice distortions (maximally about 0.2%) in biogenic aragonite and calcite, as compared to their geological counterparts. This phenomenon was found to be widespread in many different mollusc shells investigated by us. The lattice distortions were attributed to organic molecules confined within the mineral lattice. The basis of this assumption is elaborated throughout this thesis.

Analysis of the entire set of experimental findings led to some new considerations concerning the role of intra-crystalline organic macromolecules in biomineralization. We believe that deeper understanding of the structure and microstructure of biogenic crystals will aid in the development of new approaches for growing organic/inorganic composite materials and controlling their properties on the molecular level.