Hydroxyapatite coating on porous polyurethane facilitated by tetraethoxysilane

Biomimetic growth of calcium phosphate compounds on porous polyurethane (PU) treated with tetraethoxysilane (TEOS) and soaked in simulated body fluid (SBF) solution was studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Fourier transformed infrared spectroscopy–attenuated total reflectance (FTIR–ATR). Polyurethane was treated with TEOS in order to produce silanol groups which stimulated the growth of hydroxyapatite when immersed in SBF solution. Polyurethanes that were not treated with TEOS did not show calcium phosphate growth upon immersion in SBF solution. The Ca and P determined by EDAX and inductively coupled plasma spectroscopy (ICP) analysis revealed that the surface layer was not stoichiometric hydroxyapatite, but carbonated, containing hydroxyapatite with a Ca/P ratio of 1.5–1.6. This was confirmed by FTIR–ATR.     

Preparation of Nanoparticles of Barium Ferrite from Precipitation in Microemulsions

Magnetic nanoparticles of barium ferrite (BaFe₁₂O₁₉) have been synthesized using a microemulsion mediated process. The aqueous cores of water-in-oil microemulsions were used as constrained microreactors for the precipitation of precursor carbonate and hydroxide particles. These precursors were then calcined at 925°C for 12h, during which time they were transformed to the hexagonal ferrite. The pH of reaction was varied between 5 and 12, and it was found that the fraction of non-magnetic hematite (-Fe₂O₃) in the particles varied with the pH of reaction, thus affecting the magnetic properties of the particles. The same precursor particles were also prepared by bulk co-precipitation reaction for comparison. It was found that the microemulsion derived nanoparticles of barium ferrite had both higher intrinsic coercivity (H_c) and saturation magnetization (_s) than the particles derived from bulk co-precipitation. Particles were analyzed by electron microscopy, X-ray diffraction, differential thermal analysis (DTA), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The best barium ferrite particles produced by the microemulsion synthesis method yielded an intrinsic coercivity of 4310Oe and a saturation magnetization of 60.48emu/g.