The animation* by Dr. Tseng
Biomineralization refers to the course of forming minerals with high degree of order controlled by living organisms . This phenomenon is going on extensively in various kinds of organism, for instance, diatom, shell, oyster, pearl, skeleton and tooth, etc. The research aim in our lab is to investigate the mineralization process for the complex inorganic- organic hybrid biominerals formation and try to exploit bimimetic strategy to fabricate hierarchical structure. The materials include:
1. Calcium Carbonate
Calcium carbonate exhibits various polymorphs such as calcite, vaterite, aragonite and amorphous phase. Among these phases, vaterite is the metastable phase which does not exist for a long time and easily transform to calcite. We have successfully synthesized vaterite single crystal by using biomolecules (gelatin) as a stabilizer for vaterite (Fig .1A ). Surprisingly, it was found that the porous single crystals are formed by the aggregation of vaterite nanoparticles. This non-classical crystallization results in the formation of porous vaterite single crystals (Fig.1B).
2. Calcium Phosphate
Calcium phosphate minerals are known to exist in various polymorphs. They have the biomedical significance due to they are major inorganic component of bones and teeth. Especially, octacalcium phosphate (OCP) and hydroxyapatite (HAp) are supposedly the key phases involve in the bone and teeth formation. Both the morphogenesis and mechanisms for the OCP to HAp transformation are investigated in our lab. The HAp nanorods were successfully produced by a single-crystal-to-single- crystal transformation process (Fig .2A ). The unchanged morphology of the minerals during the phase transformation may explain why the hierarchical structure can be preserved as phase transformation is processed in biology. In addition, the detail molecular mechanism of OCP to HAp transformation was resolved by various solid-state NMR techniques. The study provided the mechanistic model for central dark line formation in fossils and human dentin (Fig.2B).
Biosilica such as diatom displays high level hierarchical and complex structure which is accomplished under mild physiological conditions. Up to now, the fabrication of this complex diatom-like structure is still a challenge. We try to use the amphiphilic properties of long-chain polyamines, which are supposedly involving in the formation of biosilica to activate the hydrolysis and condensation reaction of silicate to form the complex structure similar to diatom.
4. Zinc Oxide
Recently, our lab successfully developed a method to grow ZnO hierarchical structure made of nanoplates by adopting bimineralization strategy (Fig .4A ). The as-synthesized ZnO crystals exhibited whispering gallery model emission which may be used as a resonator application. Thus the ZnO crystals were further grown on the substrate to achieve higher level hierarchical structure for devices applications (Fig. 4B and 4C ).