Surface properties of bioactive TEOS-PDMS-TiO₂-CaO ormosils

Tetraethyl orthosilicate (TEOS)-polydimethyl siloxane (PDMS) ormosils with different amounts of Ti and Ca were prepared and characterized. Several surface properties such as specific surface area, porosity, fractality, dispersive and polar surface energies were determined and related with their in-vitro bioactivity. It has been found a dependence of the surface fractal dimension with the concentration of Ca²⁺ ions that induce the appearance of rough surfaces. The dispersive surface energy, γ _S ^d, increased with the incorporation of Ti or Ca and the presence of micropores, but Ca(NO₃)₂ precipitates in the surface coming from non-incorporated Ca lead to a decrease of the surface energy values. In relation with the polar surface energy, it has been observed that all ormosil materials presented amphoteric character with a larger presence of base surface sites than acid ones. The basicity of the surface increased with the concentration of Ti and Ca, while the acidity decreased. The in-vitro bioactivity of the surface was estimated by soaking samples in simulated body fluid (SBF) and afterwards characterized by means of X-ray diffraction (TF-XRD) and field emission scanning electron microscopy (FE-SEM). It has been observed that in vitro bioactivity is related with the polar surface characteristics of these materials, being necessary for the bioactivity, the presence of a highly polar surface with intermediate base/acid ratio and specific roughness.