Biomineralization Processes on Natural and Synthetic Substrates

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Biomineralized materials such as molluscan shells are complex lamellar aggregates of inorganic single crystals and biopolymers that form at low temperature with exceptional strength and crystalline ordering. The biosynthesis process gives and incredible regularity to 1) inorganic and protein structure at nanoscale (atomic) dimensions, and 2) the initiation and termination of growth at mesoscale (is greater than approximately 0.1 microns) dimensions, thus generating the highly ordered microlaminate composite formation that gives the resulting biomaterial its strength and flexibility. This interdisciplinary research will investigate the fundamental chemical and stereochemical interactions which, at the molecular level control such biologically mediated mineral nucleation and growth at both the nano- and mesostructure level. Nucleation and growth of inorganic phases will be carried out from solutions at low temperatures and pressures on: i) inorganic and biological mineral templates; ii) synthetic organic templates with optically active groups and surface arrays of ionic sites similar to those found on biopolymeric templating surfaces in vivo; and iii) biogenic templating polypeptides. The proposed experiments will use a novel combination of synthesis and characterization techniques, including polypeptide sequencing and synthesis to form structure directing templates, in situ atomic force microscopy and grazing incidence X-ray diffraction. %%% Nature's use of templating involves material growth from solutions at low temperatures and pressures, a process that is currently only poorly understood and little used by materials scientists. Increasingly, it is becoming apparent that these new materials, which have been referred to as "chemically bonded ceramics", have exceptional flexural strength. The proposed activity of this research is expected to lead to the development of new methods for the low temperature synthesis of mechanically superior and/or highly oriented materials using nanostructure design and synthesis techniques. It is hoped that as more light is shed on templating mechanisms involved, templating kinetics will be improved and template-directed materials synthesis can be done on a faster time scale. While the research will initially be centered around the mineralization processes of molluscs, which specifically involves CaCO3 growth, all multicellular organisms appear to have evolved with chemically similar tools for carrying out genetic control over mineral nucleation and growth. We therefore expect that our experimentation will increase insight on related areas of biomineralization, including bone growth. By more fully realizing how mineralization is orchestrated in one particular species, the answers to more complex biomineralization problems will surely follow. Implications of our results for the medical field are foreseeable; bone nucleation growth is based on the same fundamental chemical and structural interactions as occurs in mollusc shells, except that the nucleating macromolecules are part of a bilipid membrane which encloses the mineralization space. Thus, the study of hydroxyapatite nucleation onto such lipid bilayer surfaces may follow. On the other hand, a greater understanding of soluble growth inhibitors can be useful for the prevention of undesirable crystal growth. Medical examples include dental plaque, organ stones, hardening of the arteries, and calcification of implanted heart valves. In industrial cooling systems, oil recovery systems, and municipal water supplies, undesirable water-formed scale deposits of CaCO3 and CaSO4 foul treatment facilities. New organic compounds may inhibit scale formation, be cost effective, and be useful over a larger range of temperatures, pH, and salinity.