Surface properties of bioactive TEOS–PDMS–TiO 2 –CaO ormosils Aitana Tamayo • Lucı ´a Te ´llez • Marlene Rodrı ´guez-Reyes • M. Alejandra Mazo • Fausto Rubio • Juan Rubio Received: 13 November 2013 / Accepted: 11 March 2014 / Published online: 3 April 2014 Ó Springer Science+Business Media New York 2014 Abstract 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 Ca 2? ions that induce the appearance of rough surfaces. The dispersive surface energy, c S d , increased with the incorporation of Ti or Ca and the pre- sence of micropores, but Ca(NO 3 ) 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 char- acteristics of these materials, being necessary for the bio- activity, the presence of a highly polar surface with intermediate base/acid ratio and specific roughness. Introduction During the last four decades, an important and extensive work has been carried out in the bioactive materials area [1–3]. The development of Bioactive Glass (45S5, Bio- glass TM ) by Hench et al. [1] entailed the opening of a new class of materials, and since then, a large number of glas- ses, glass ceramics, ceramics, polymer and hybrid com- posites have been thoughtfully studied as potentially bioactive materials [1, 2, 4–6]. Among the substances investigated, bioactive glasses are probably the most attractive materials because they can be prepared with a chemical composition similar to hydroxyapatite Ca 10 (PO 4 ) 6 (OH) 2 . Furthermore, these glasses exhibit several advantages in comparison to synthesized hydroxyapatite because of their high formation rate of bone-like tissue when placed in SBF due to the presence of Si–OH bonds into the network and the dissolution products (calcium and silicate ions) [7]. The relatively poor mechanical properties of the glassy materials constraints the use of these bioactive glasses to low stressed areas. However, the use of organically mod- ified silicates (ormosils) is intended to fulfil the mechanical requirements of a large number of structures [6, 8–11]. Several ormosil materials prepared by the sol–gel process using tetraethyl orthosilicate (TEOS), polydimethylsilox- ane (PDMS) and Ca(NO 3 ) 2 have shown bioactivity in terms of formation of bone-like structures [12, 13], and it has been demonstrated that the incorporation of Ti increased the mechanical resistance of the materials with- out affecting the biocompatibility [14]. The presence of Ca 2? ions and silanol groups (Si–OH) in ormosils is observed to be a requirement for inducing spontaneous deposition of the biologically active apatite layer from the SBF [10, 15]. This conclusion was extracted A. Tamayo (&)  M. A. Mazo  F. Rubio  J. Rubio Instituto de Ceramica y Vidrio, CSIC, Kelsen, 5, 28049 Madrid, Spain e-mail: aitanath@icv.csic.es L. Te ´llez  M. Rodrı ´guez-Reyes ESIQIE-Instituto Polite ´cnico Nacional, UPALM-Zacatenco, 07738 Mexico, DF, Mexico 123 J Mater Sci (2014) 49:4656–4669 DOI 10.1007/s10853-014-8169-4