Spin casted mesoporous silica coatings for medical applications

Abstract

Self-assembling organic/inorganic sol–gel systems were used to prepare mesoporous silica coatings that can qualify for medical applications. The cationic surfactant cetyltrimethyl ammonium chloride (CTAC) or an amphiphilic triblock copolymer were utilized as templates or structure-directing agents, and tetraethylorthosilicate (TEOS) as the silica precursor. Thin films could be applied on different substrates (glass, silicon, and titanium) by spin casting of the sol–gels. X-Ray diffraction analyses indicated that well ordered hexagonally packed mesostructures with unit cells of 3 and 13 nm, when CTAC and triblock copolymer were used, respectively, could be fabricated. Parameters such as CTAC/TEOS molar ratio and gel formation time highly affected the resulting structure, so the optimum values were established. A competition occurs between the formation of cylindrical mesochannels on the substrate and homogeneous nucleation of the silica in the sol–gel solution to form spherical particles. Therefore, a growing presence of silica particles on the spin casted coatings happens as the gel formation time is increased above ∼60 s, which results in poorer mesoporous films. When a triblock copolymer was used as template, a preferred alignment of the mesostructure was observed independently of the substrate. The removal of the organic template to hollow the pores was accomplished by photocalcination (selective ultraviolet irradiation). The resulting mesoporous silica coatings were able to induce apatite formation after 1 week of immersion in a simulated body fluid in physiological conditions, which is a sound indication of a bioactive behavior when tested in vivo. These results indicate that the coatings prepared by the methodology described in this work may be valid candidates to be used on implants.