The morphogenesis of hierarchically ordered, spherical aggregates of fluorapatite–gelatine-nanocomposites starts with elongated hexagonal prismatic seeds, followed by fractal branchings and the development of growing dumbbell states. The general principles of this dramatic process of self-organisation are not yet known but should be laid out already in the real structure of the central seed (P. Simon, W. Carrillo-Cabrera, P. Formanek, C. Göbel, D. Geiger, R. Ramlau, H. Tlatlik, J. Buder and R. Kniep, J. Mater. Chem., 2004, 14, 2218, ). Here we describe the structure and inner architecture of the fluorapatite composite seeds which consist of self-similar nano-subunits nucleated by gelatine macromelecules. Although grown without any cell activities, the biomimetic composite closely resembles natural biomaterials based on interactions between collagen and apatite.

Marine sponges of the subclass Keratosa originated on our planet about 900 million years ago and represent evolutionarily ancient and hierarchically structured biological materials. One of them, proteinaceous spongin, is responsible for the formation of 3D structured fibrous skeletons and remains enigmatic with complex chemistry. The objective of this study was to investigate the interaction of spongin with iron ions in a marine environment due to biocorrosion, leading to the occurrence of lepidocrocite. For this purpose, a biomimetic approach for the development of a new lepidocrocite-containing 3D spongin scaffold under laboratory conditions at 24 °C using artificial seawater and iron is described for the first time. This method helps to obtain a new composite as “Iron-Spongin”, which was characterized by infrared spectroscopy and thermogravimetry. Furthermore, sophisticated techniques such as X-ray fluorescence, microscope technique, and X-Ray diffraction were used to determine the structure. This research proposed a corresponding mechanism of lepidocrocite formation, which may be connected with the spongin amino acids functional groups. Moreover, the potential application of the biocomposite as an electrochemical dopamine sensor is proposed. The conducted research not only shows the mechanism or sensor properties of “Iron-spongin” but also opens the door to other applications of these multifunctional materials.