Bones represent a family of biological materials with complex, hierarchically organized architecture. These diverse mineralized structures are excellently adapted to the variety of mechanical functions and stresses (Weiner et al. 1999; Beniash 2011). According to modern point of view, "bone is specific to vertebrates, and originated as mineralization around the basal membrane of the throat or skin, giving rise to tooth-like structures and protective shields in animals with a soft cartilage-like endoskeleton" (Obradovic-Wagner and Aspenberg 2011). In his excellent monograph, John Long (1995) described the origin and diversity of bone structures which I will now briefly summarize. Bone can be examined as the calcified tissue that supports the skeleton, external or internal, of vertebrates and shows a broad variety of mechanical adaptations at nano- and microscales (Currey 1984, 2002; Weiner and Wagner 1998; Fratzl et al. 2004). A functionally important mechanical property of bones is stiffness, both in the whole element sense and in the material sense (Horton and Summers 2009). Main components of bone include hydroxylapatite (HAP) (as inorganic part), nanofibrillar collagen fibres that support the in vivo development of mineralised bone, and corresponding vascular tissue that supplies blood to the living cell components of bone. Since publication by Kölliker (1859), the presence of cellular and acellular types in the bone of early vertebrates is well established. In spite of that the structures of these bone types are similar, the principal difference between them are the spaces in cellular bone for the osteocytes, which occur throughout this hard tissue.
Chitin of poriferan origin is a unique and thermostable biological material. It also represents an example of a renewable materials source due to the high regeneration ability of Aplysina sponges under marine ranching conditions. Chitinous scaffolds isolated from the skeleton of the marine sponge Aplysina aerophoba were used as a template for the in vitro formation of Fe2O3 under conditions (pH ∼ 1.5, 90 °C) which are extreme for biological materials. Novel chitin–Fe2O3 three dimensional composites, which have been prepared for the first time using hydrothermal synthesis, were thoroughly characterized using numerous analytical methods including Raman spectroscopy, XPS, XRD, electron diffraction and HR-TEM. We demonstrate the growth of uniform Fe2O3 nanocrystals into the nanostructured chitin substrate and propose a possible mechanism of chitin–hematite interactions. Moreover, we show that composites made of sponge chitin–Fe2O3 hybrid materials with active carbon can be successfully used as electrode materials for electrochemical capacitors.
Biological materials are a rewarding area of modern materials science, yielding both evolutionary insights and inspiration for biomimetic research. In particular, biocomposite structures are valuable sources of novel structures with unusual chemical properties, and they are very informative for the mechanisms of biomineralization. Here we describe a unique biocomposite of amorphous silica, crystalline aragonite, and chitin from species of the order Verongida, a group of marine sponges. The structures have been analyzed with a diverse suite of techniques, revealing a chitinous template for siliceous overgrowth containing aragonite-based crystal aggregates. Sponge chitin is an example of a specific template where two minerals in amorphous and crystalline forms are formed together with an organic molecule.
The first reports on the presence of zoochlorellae within the organelles of mesenchymal cells from freshwater sponges were published in the 19th century. Today, it is well-known that freshwater sponges can be found in association with different endosymbiotic algae. However, until now there has been no detailed information about the endosymbiotic chlorophyll-containing algae in the remarkable endemic green sponges from Lake Baikal. In our study we were able for the first time to isolate and identify endosymbionts from primmorphs cultivated in vitro, and to compare them with those from naturally occurring Lubomirskia baicalensis sponges. Structural as well as molecular biological investigations show that the endosymbiotic alga is a Mychonastes species closely related to M. huancayensis. Another novel aspect of our work was to show that it is possible to use primmorphs of endemic sponges for isolation and subsequent cultivation of their endosymbiotic algae. We employed a simple cold-water (3–4°C) approach for cultivating Mychonastes sp., both within sponge primmorphs and in culture.
