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Hermann Ehrlich et al. intercalated chitosan/layered silicate nanocomposites prepared to develop robust and stable sensors useful for anionic detection in aqueous media as reported on [50, 51]. We suggest that silica-chitin and silica-NAG (-poly NAG) composites could be highly optimized biocompatible structures that would support and organize functional tissues if applied in tissue engineering of bone and cartilage replacements similar to silica-chitosan-based biomaterials [52]. Experiments on biocompatibility of silica-chitin and silicaNAG composites derived in vitro are currently in progress.

4. CONCLUSION
Chitin and poly-N-acetyl glucosamine are well investigated materials of biological origin with wide fields of application in biomedicine because of their unique multifunctional engineering mechanical properties and biocompatibility [53–56]. With respect to polysaccharides, including sponge chitin, it is theoretically possible that inorganic Si binds after the macromolecular structure has been formed. An alternative, more plausible from stereochemical considerations [49], would consist in the incorporation of preformed mono-or disaccharide Si derivatives during the synthesis of the polysaccharide chain. The finding of nanostructured silica-chitin biocomposites as structural scaﬀolds of glass sponge skeletons introduces a new aspect into the discussion surrounding the chemistry, diversity, and nanolocalization of these materials. Chitin as a template for biomineralization probably belongs to the basic pattern of the Metazoa.

ACKNOWLEDGMENTS
This work was partially supported by a joint RussianGerman program “DAAD-Mikhail Lomonosov.” We thank Professor H. Lichte for the possibility to use the facilities at the Special Electron Microscopy Laboratory for highresolution and holography at Triebenberg, TU Dresden, Germany. The authors are deeply grateful to Mariana Tasso, Heike Meissner, Gert Richter, Axel Mensch, and Ortrud Trommer for helpful technical assistance.