Embryonic States of Fluorapatite–Gelatine Nanocomposites and Their Intrinsic Electric-Field- Driven Morphogenesis: The Missing Link on the Way from Atomistic Simulations to Pattern Formation on the Mesoscale By Paul Simon, Elena Rosseeva, Jana Buder, Wilder Carrillo-Cabrera, and Ru ¨diger Kniep* 1. Introduction With respect to structure, ordering, and nanocomposite formation, the biomimetic system fluorapatite (FAP)–gelatine bears strong resemblance to the biosystem hyd- roxyapatite-collagen which plays a decisive role in the human body as functional materials in the form of bone [1] and teeth. [2] The morphogenesis of FAP–gelatine nano- composites grown by double diffusion into a gelatine–gel matrix offers the advantage of revealing a concise sequence of shape development, [3–16] whereas bone and teeth are formed by much more complex pro- cesses with involvement of cell activities in a living system. In former investigations, [3–6] we showed that on the micrometer-scale the biomimetic composite (containing about 2–3 wt% protein) starts its shape develop- ment with a hexagonal prismatic seed which transforms via growing dumbbell states to a finally (slightly notched) sphere. This kind of morphogenesis is schemati- cally presented in Figure 1 and indicates that the fractal splitting procedure is best described as an outgrowth phenomenon, which immediately implies that the central hexagonal prismatic seed bears the intrinsic code for its further shape development. Detailed investigations on the central hexagonal prismatic seeds have already been performed and showed that these specimens FULL PAPER www.afm-journal.de [*] Prof. R. Kniep, Dr. P. Simon, E. Rosseeva, J. Buder, Dr. W. Carrillo- Cabrera [+] Max-Planck-Institut fu¨r Chemische Physik fester Stoffe No ¨thnitzer Str. 40, 01187 Dresden (Germany) E-mail: kniep@cpfs.mpg.de E. Rosseeva Department of Crystallography Saint Petersburg State University Universitetskaya Nab 7/9 199034, Saint Petersburg (Russia) [+] This author’s name was changed from Wilder German Carrillo- Cabrera on 16.11. 2009, after online publication. DOI: 10.1002/adfm.200900843 The shape development of fluorapatite (FAP)–gelatine nanocomposites is revealed by means of HRTEM investigations starting from molecular dimensions up to the formation of mesoscaled (elongated) hexagonal prisms. The composite nature of the aggregates is proved by IR spectroscopy and by chemical analyses on all states of shape development. The initial states are characterized by triple-helical fiber protein bundles, which are mineralized step-by-step forming and fixing nanoplatelets of FAP in a mosaic arrangement. After being fully mineralized the bundles form elongated composite nanoboards. In the next step of the growth process the boards aggregate to bundles of boards which are in a more or less parallel alignment with respect to each other. By adding up more and more composite nanoboards a critical size is reached and an electric field is developed, which takes over control and directs the further development of the aggregates. This kind of electric-field- directed growth of the elongated polar nanoboards additionally leads to the formation and inclusion of protein nanofibrils into the growing composite aggregate. By this method, cone-like nanofibril structures develop along the long axis of the aggregates accompanied by more perfect parallel alignment of the composite boards within the aggregates. Further shape development is characterized by adding up composite nanoboards, in particular to increase the third dimension in volume. This thickening process preferably takes place in the middle part of the elongated aggregates and finally proceeds to their basal ends until a perfect hexagonal prismatic seed is formed, which then is ready for further shape development on the micrometer scale. 3596 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2009, 19, 3596–3603