Sponge spicules as blueprints for the biofabrication of inorganic–organic composites and biomaterials

While most forms of multicellular life have developed a calcium-based skeleton, a few specialized organisms complement their body plan with silica. However, of all recent animals, only sponges (phylum Porifera) are able to polymerize silica enzymatically mediated in order to generate massive siliceous skeletal elements (spicules) during a unique reaction, at ambient temperature and pressure. During this biomineralization process (i.e., biosilicification) hydrated, amorphous silica is deposited within highly specialized sponge cells, ultimately resulting in structures that range in size from micrometers to meters. Spicules lend structural stability to the sponge body, deter predators, and transmit light similar to optic fibers. This peculiar phenomenon has been comprehensively studied in recent years and in several approaches, the molecular background was explored to create tools that might be employed for novel bioinspired biotechnological and biomedical applications. Thus, it was discovered that spiculogenesis is mediated by the enzyme silicatein and starts intracellularly. The resulting silica nanoparticles fuse and subsequently form concentric lamellar layers around a central protein filament, consisting of silicatein and the scaffold protein silintaphin-1. Once the growing spicule is extruded into the extracellular space, it obtains final size and shape. Again, this process is mediated by silicatein and silintaphin-1, in combination with other molecules such as galectin and collagen. The molecular toolbox generated so far allows the fabrication of novel micro- and nanostructured composites, contributing to the economical and sustainable synthesis of biomaterials with unique characteristics. In this context, first bioinspired approaches implement recombinant silicatein and silintaphin-1 for applications in the field of biomedicine (biosilica-mediated regeneration of tooth and bone defects) or micro-optics (in vitro synthesis of light waveguides) with promising results

Formation of filamentous carbon through dissociation of chromium carbide under hydrothermal conditions

Synthesis of filamentous carbon through the decomposition of chromium carbide was studied employing hydrothermal technique in the pressure and temperature range of 100–200 MPa and 350–800 °C respectively. It was found that chromium carbide dissociates into chromium oxide in the presence of water at temperature <400 °C. But, the formation of free elemental carbon as filamentous particles was noticed in the presence of organic compounds at temperatures above 600 °C. The organic compounds are known to dissociate to C–O–H supercritical fluids under hydrothermal condition. The supercritical fluids generated by the dissociation of organic compounds have great influence on the decomposition of chromium carbide. The scanning electron microscopic (SEM) studies of the experimental run products show that the fibrous or filamentous form of carbon was found with a few spherical shaped carbons, in the chromium carbide—organic compound runs. These carbon particles were solid curved filaments with a mean diameter of 50–100 nm. Micro Raman spectroscopic studies show that the filaments have sp 2 -hybridized carbon atoms