Abstract

Surface porous silicon based ceramics are a class of materials with excellent mechanical, physical and chemical properties and for this reason they are widely used in different fields of application. The resultant properties of these material are due principally to the combination of the chemical composition (coordination with the Si atom) and the specific geometry of the pattern. These parameters are able to influence phenomena such as the biological activity, the exposed surface area and the thermal, mechanical and chemical resistance. Techniques used nowadays to synthesize these ceramics with a specific patter are usually really complicated, expensive and time-consuming with limitations for the large-scale industrial application. The Breath Figure method is a new fast and highly controllable technique that allows to decorate the surface of polymer films with different porous patterns. A large variety of starting materials can be used to perform this process, obtaining porous films with different characteristics and with a specific control on the entire process. In this work we used a UV cross-linkable polysiloxane as precursor for the Breath Figure process in order to combine the pattern procedure with the polymer derived ceramic method. Initially, the effects of the process variables on the final surface porosity was evaluated, identifying the parameters which most influence the final material. After the patterning, materials with different characteristics were pyrolyzed under different atmospheres in order to induce simultaneously the ceramic conversion and the chemical modification of the silicone structure. Three different porous silicon-based ceramics were obtained using flowing air, nitrogen and ammonia during the heat treatments, respectively: silicon dioxide, silicon oxycarbide and silicon oxynitride. All these material have been proposed as implant coating for different body districts, but recent studies demonstrated the potential application of silicon oxynitrides as bone implant coatings due to the enhanced bioactivity and osteoinductivity of the ceramic. For this reason in the second part of this work we evaluated the potential bioactivity of surface porous silicon oxynitrides in terms of bioactive silicon ions release capability and effects of different porosity degrees on cells behavior. Four different surface pattern were applied on titanium alloy disks and used for an in vitro characterization using human Mesenchymal Stem Cells and compared with uncoated titanium. The results indicated that the silicon ions release from the coating surface leads to an increase of the cellular activity with the porous pattern influencing the hMSC initial adhesion and proliferation.