MATERIAL SCIENCE MEETS MEDICINE – PRESENTATION ABSTRACTS BIOMINERALIZATION

Development of Functional Organic/Inorganic Hybrid Materials by Macromolecular Templates

Tatsuya Nishimura Department of Chemistry and Biotechnology, School of Engineering, University of Tokyo

1. Introduction: Preparation of functional materials through self-organization processes Biominerals such as bones, teeth, seashell nacre, scales of coccolithophores, and the exoskeletons of crustaceans are organic/inorganic hybrids with highly controlled hierarchical structures (Figure 1).1 Organisms exploit the mechanical, optical, and magnetic properties of these structures for a variety of purposes. In living organisms, these structures are formed under gentle conditions through self-organization processes that are controlled by macromolecular templates. The structures, properties, and formation processes of natural biominerals inspire new approaches to synthetically develop functional hybrid materials.2 In accordance with this idea, we previously reported the formation of thin films of Figure 1. (a) Schematic diagram inorganic crystals using a biomineralization approach.2g The outlining the formation process of nacre. resulting hybrid materials consisting of inorganic crystals (b) SEM image of a coccolithophore. (c) Cross-sectional SEM image of the and organic polymers exhibited a wide variety of exoskeleton of a crayfish. morphologies (Figure 2).3,4 Here we discuss our recent strategies for the development of new inorganic/organic hybrid materials such as unidirectionally oriented thin films, macroscopically oriented crystals, and hybrid thin films.5

2. Study of peptides isolated from crayfish exoskeletons6 Functional peptides play important roles in the formation of biominerals. Our research targets focus on structural control and lightweight materials with both high flexibility and mechanical strength. We designed and synthesized new recombinant peptides based on the functional peptide CAP- Figure 2. (a,b) SEM images of patterned structures on hybrid thin films. (c,d) 1, which was isolated from the crayfish exoskeleton. We Photographic images of amorphous have examined the effects of these peptides on the transparent hybrids consisting of CaCO /polymer templates. formation of calcium carbonate and organic hybrid materials 3

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MATERIAL SCIENCE MEETS MEDICINE – PRESENTATION ABSTRACTS BIOMINERALIZATION

in aqueous solution. In the presence of these recombinant peptides containing chitin-binding moieties, plate-like tripodal calcite crystals were formed on the chitin matrix with a unidirectional crystallographic orientation (Figure 3). Two kinds of interactions between the acidic part of the peptides and calcium ions and specific binding interactions of the peptides to chitin are essential in the formation of these oriented crystals and the control over specific morphologies. The crystallite size is indirectly proportional to the number of acidic units in the mutated peptides. This bio-inspired design Figure 3. SEM images of a tripodal of peptides controlling the inorganic/organic interface may CaCO3/chitin hybrid formed on a chitin open gateways to potentially highly versatile hybrid matrix. The image on the right is a magnified image of the surface of the structures. obtained crystal.

3. Orientation control of inorganic/organic hybrid materials7 Oriented calcite crystals can be obtained using simple acidic polymers with matrices that exhibit macroscopic liquid-crystalline order. In order to prepare functional biomineral-inspired hybrid materials, control over the orientation and structure of both inorganic and organic components on the macroscopic scale is crucial. Our methodology using liquid-crystalline templates for crystallization can be applied to the synthesis of novel highly organized hybrid structures. We are able to tune the chemical and self- organized structures of the template polymer matrix for the crystallization of inorganic crystals in order to produce oriented hybrid materials with interesting optical, electrical, and magnetic properties.

4. Conclusion We have prepared new organic/inorganic hybrid materials with hierarchical structure via self- organization processes under mild conditions using macromolecular templates. These approaches are inspired by biomineralization and can be applied to develop hybrid materials between a variety of inorganic crystals (including transition metal-based compounds) and organic functional macromolecules. The resulting materials show great potential in a wide range of applications such as energy devices, high strength eco-friendly materials, and biocompatible materials.

References: [1] L. Addadi, S. Weiner, Angew. Chem. Int. Ed. Engl., 1992, 31, 153. [2] a) T. Kato, Adv. Mater., 2000, 12, 1543; b) H. Cölfen, S. Mann, Angew. Chem. Int. Ed., 2003, 42, 2350; d) M. Umetsu, M. Mizuta, K. Tsumoto, S. Ohara, S. Takami, H. Watanabe, I. Kumagai, T. Adschiri, Adv. Mater., 2005, 17, 2571; e) K. Naka, Y. Chujo, Chem. Mater., 2001, 13, 3245; f) T. Kato, T. Sakamoto, T. Nishimura, MRS Bulletin, 2010, 35, 127. [3] T. Sakamoto, T. Nishimura, T. Kato, et al., Angew. Chem. Int. Ed., 2011, 50, 5856. [4] Y. Oaki, S. Kajiyama, T. Nishimura, H. Imai, T. Kato, Adv. Mater., 2008, 20, 3633. [5] T. Nishimura, H. Imai, Y. Oaki, T. Sakamoto, T. Kato, Chem. Lett., 2011, 40, 458. [6] H. Kumagai, R. Matsunaga, T.

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MATERIAL SCIENCE MEETS MEDICINE – PRESENTATION ABSTRACTS BIOMINERALIZATION

Nishimura, H. Nagasawa, K. Tsumoto, T. Kato, et al., Faraday Discuss., in press. [7] T. Nishimura, M. Yoshio, T. Kato, et al., Angew. Chem. Int. Ed., 2008, 47, 2800.

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