The siliceous skeleton of demosponges is constructed of spicules. We have studied the formation of spicules in primmorphs from Suberites domuncula. Scanning electron microscopy and transmission electron-microscopical (TEM) analyses have revealed, in the center of the spicules, an axial canal that is 0.3-1.6 microm wide and filled with an axial filament. This filament is composed of the enzyme silicatein, which synthesizes the spicules. TEM analysis has shown that spicule formation starts intracellularly and ends extracellularly in the mesohyl. At the initial stage, the axial canal is composed only of silicatein, whereas membranous structures and fibrils (10-15 nm in width) can later also be identified, suggesting that intracellular components protrude into the axial canal. Antibodies against silicatein have been applied for Western blotting; intracellularly, silicatein is processed to the mature form (24 kDa), whereas the pro-enzyme with the propeptide (33 kDa) is detected extracellularly. Silicatein undergoes phosphorylation at five sites. Immunohistological analysis has shown that silicatein exists in the axial canal (axial filament) and on the surface of the spicules, suggesting that they grow by apposition. Finally, we have demonstrated that the enzymic reaction of silicatein is inhibited by anti-silicatein antibodies. These data provide, for the first time, a comprehensive outline of spicule formation.
There is a demand for novel bioactive supports in surgery, orthopedics, and tissue engineering. The availability of recombinant silica-synthesizing enzyme (silicatein) opens new possibilities for the synthesis of silica-containing bioactive surfaces under ambient conditions that do not damage biomolecules like proteins. Here it is shown that growth of human osteosarcoma SaOS-2 cells on cluster plates precoated with Type 1 collagen is not affected by additional coating of the plates with the recombinant silicatein and incubation with its enzymatic substrate, tetraethoxysilane (TEOS). However, the enzymatic modification of the plates by biosilica deposition on the protein-coated surface caused a marked increase in calcium phosphate formation of SaOS-2 cells as revealed by alizarin red-S staining to quantify calcium mineral content. The increased occurrence of calcium-phosphate nodules on the modified surface was also observed by scanning electron microscopy. These results suggest that by supporting calcium-phosphate deposition in vitro, biosilica (silicatein)-modified surfaces are potentially bioactive in vivo, by stimulating osteoblast mineralization function.
BiFeO
3
(BFO) nanoparticles (NPs) were synthesized using the sol-gel method at different calcination temperatures from 400 °C to 600 °C. XRD studies have confirmed that all BFO NPs show distorted rhombohedral crystals that match the R3c space group. We found evidence of local structural strain that develops with increasing particle size as suggested by TEM and Raman spectroscopy measurements. Magnetic measurements suggest that NPs have two distinct regimes: a ferromagnetic-like one at low temperatures and a superparamagnetic-like one at room temperature. The crossover temperature increases with NPs size, suggesting a size-dependent blocking magnetic regime. Similarly, local piezoelectric measurements at room temperature in single NP have confirmed a ferroelectric order with a NP size-dependent d
33
coefficient. An analysis of both the ferroelectric and the magnetic results suggest that ferromagnetism and ferroelectricity coexist at room temperature in NPs. Our results lead to the possibility of tailoring the ferroic order in multifunctional materials by means of NP size.
Softly, softly: VS2 nanotubes (see electron micrograph, layer separation 1.6 nm) are prepared from vanadium oxide nanotubes by a “chimie douce” process. The VS2 nanotubes are remarkably stable; the corresponding bulk compound is unstable unless it is intercalated with alkali‐metal atoms. The nanotubes reversibly intercalate copper with high capacity and thus could serve as precursors for conductors or contacts in electronic circuitry.
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