Artículos SCI

Porous biomorphic silicon carbide (bioSiC) is a structurally realistic, high-strength, and biocompatible material which is promising for application in load-bearing implants. The deposition of an osteoconductive coating is essential for further improvement of its integration with the surrounding tissue. A new strategy towards biomimetic calcium phosphate coatings on bioSiC is described. X-ray photoelectron spectroscopy (XPS) analysis shows that using 10-undecenoic acid methyl ester a covalently bound monolayer can be synthesized on the surface of the bioSiC. After hydrolysis it exposes carboxylic acid groups that promote the selective nucleation and growth of a very well-defined crystalline layer of calcium phosphate. The resulting calcium phosphate coating is characterized by X-ray diffraction and electron microscopy techniques. Further, ion beam imaging is employed to quantify the mineral deposition meanwhile, three-dimensional dual-beam imaging (FIB/SEM) is used to visualize the bioSiC/mineral interface. The monolayer is show to actively induce the nucleation of a well-defined and highly crystalline mixed octacalcium phosphate/hydroxyapatite (OCP/HAP) coating on implantable bioSiC substrates with complex geometry. The mild biomimetic procedure, in principle, allows for the inclusion of bioactive compounds that aid in tissue regeneration. Moreover, the mixed OCP/HAP phase will have a higher solubility compared to HAP, which, in combination with its porous structure, is expected to render the coating more reabsorbable than standard HAP coatings.

Aluminum incorporation into TiO ₂ has been studied in the TiO ₂-Al ₂O ₃ system as a function of pressure at temperatures of 900 and 1300 °C using commercial Al ₂TiO ₅ nanopowder as starting material. A new orthorhombic TiO ₂ polymorph with the CaCl ₂ structure has been observed in the recovered samples synthesized from 4.5 to 7 GPa and 900 °C and from 2.5 to 7 GPa at 1300 °C. The phase transition to the α-PbO ₂ type TiO ₂ phase takes place between 7 and 10 GPa at both temperatures. Two mechanisms of Al incorporation in TiO ₂ rutile have been observed in the recovered samples. The substitution of Ti ⁴⁺ by Al ³⁺ on normal octahedral sites is dominant at lower pressures. High pressure induces the incorporation of Al ³⁺ into octahedral interstices of the rutile structure, which is responsible for an orthorhombic distortion of the TiO ₂ rutile structure and gives rise to a (110) twinned CaCl ₂ type structure. This phase is probably a result of temperature quench at high pressure. Aluminum solubility in TiO ₂ increases with increasing pressure. TiO ₂ is able to accommodate up to 9.8 wt% Al ₂O ₃ at 7 GPa and 1300 °C. Temperature has a large effect on the aluminum incorporation in TiO ₂, especially at higher pressures. High pressure has a strong effect on both the chemistry and the microstructure of Al-doped TiO ₂. Enhanced aluminum concentration in TiO ₂ rutile as well as TiO ₂ grains with a microstructure consisting of twins are a clear indication of high-pressure conditions.