Bioinspired Synthesis of Organic/Inorganic Nanocomposite Materials Mediated by Biomolecules

Many organisms are capable of synthesizing organic/inorganic composites for protective or support purposes, such as bones, shells, and teeth. They exert a remarkable level of molecular control on particle size, structure, morphology, aggregation, and crystallographic orientation of these organic/inorganic structured materials. These materials often hierarchically arrange from nanoscale to macroscale (Feldheim and Eaton 2007; Dujardin and Mann 2002; Mann et al. 1993; Palmer et al. 2008; Estroff and Hamilton 2001; Aizenberg et al. 2005). For example, mollusks produce shells or nacres that contain a single distinct calcium carbonate crystalline phase, such as aragonite or calcite (Addadi et al. 2006). Magnetotactic bacteria produce Fe3O4 or Fe3S4 nanoparticles with well-defined sizes and shapes to recognize magnetic fields for alignment and migration (Dennis A. Bazylinski and Frankel 2004; Komeili 2007). Marine sponges produce silica spicules that have been demonstrated to possess light-guiding characteristics and may reach lengths of up to 3 m (Aizenberg et al. 2004; Sundar et al. 2003; Cattaneo-Vietti et al. 1996). In each of the examples listed above, and in many more examples in nature (Fig.1), specialized biomolecules, such as proteins, peptides, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and polysaccharides, have been found or are thought to play a critical role in directing the formation of these hierarchically assembled inorganic structures (Söllner et al. 2003; Müller et al. 2007). The participation of biomolecules in the nucleation and growth of crystals has attracted much research attention. Most notably, the proteins involved in directing the shape of these biomaterials have often evolved to recognize and bind selectively to one or more faces of the growing crystal. For instance, important matrix proteins involved in bone growth contain different function domains that orient the protein on hydroxyapatite nanocrystals and interact with target cell receptors (Gilbert et al. 2003). Nature has always been a source of inspiration for technical developments. Materials scientists consider the hierarchical structure of natural materials as a model for the development of new types of high-performance engineered materials (George and Ravindran 2010). The biomimetic approach could lead to the development of the controlled synthesis of inorganic nanophases, the crystal engineering of bulk solids, and the assembly of organized composite and ceramic materials (Mann et al. 1993).