## 1 Introduction  
Tissue engineering can be conceptualized as the use of a combination of cells, materials, and biochemical and physicochemical factors to improve or replace biological tissues [1]. Based on this, bone tissue repair-regeneration has been the focus and may be one the major applications of this discipline. A great number of strategies have been evolved over the past decades towards engineering tissue replacements, but the most common approach implies the use of reabsorbable synthetic materialsas scaffolds acting as a 3D-framework for cell growth in vitro. An ideal synthetic matrix for bone regeneration should fulfill some requirements as being bioactive and reabsorbed at medium term, displaying mechanical characteristics similar to bone tissue and, at the same time, possessing the ability to enhance cell proliferation while supporting tissue specific differentiation [2].  
Among various biomaterials, calcium phosphate-based ceramics (CaP) play a critical role as scaffold in bone tissue engineering. Previously, from 1960 to 1970, these materials have been widely used to repair bone defects because of their properties of biocompatibility, safety, unlimited availability, high cost-effectiveness ratio and similarity to mineral fraction of the bone [3]. CaP ceramics can be used alone or in combination with other ceramics or compounds as proteins or polymers [4; 5]. The biphasic CaP ceramics have some advantages over simple-phase ceramics by presenting favourable bioactivity and controllable biodegradation in vivo [6]. Besides, they can be used as a vector for therapeutic molecules. Alternatively, it has been demonstrated that they integrate directly in host bone tissue through formation of an apatite interface layer [7]. CaP ceramics can promote osteogenic cellular activities, mineral deposition and bone formation. Furthermore, the mineralization of the surface of these ceramics to form the apatite layer may facilitate quick protein fixing on the surface and consequently, promote cell adhesion, proliferation and osteogenic differentiation. For this reason, the surface mineralization prior to implantation by means of the use of simulated body fluid (SBF) may increase the bioactivity to improve the osteointegration with the host bone [8].  
The incorporation of specific ions into the chemical composition of bioceramics is expected to improve bone stimulating features. Silicon (Si) in CaP-based materials may play an important role in cell growth on the materials [9; 10]. Si is recognised because of its unique effect on osteoblastic differentiation and thus bone mineralization [11].  
Consequently, we have focused our attention on synthesizing a novel porous Si-Ca-P monophasic ceramic (SCP-c) by means of a solid-state reaction that was able to induce calcium deficient hydroxyapatite mineralization in simulated body fluid through the formation of two well differentiated Si-Carbonate-Hydroxapatite layers [12]. Moreover, its properties of degradability and stimulation of bone tissue formation [13] indicated that the ceramic material possesses osteoconductive in vivo properties. The traditional in vitro techniques evidenced the biocompatibility of the SCP-c and its potential ability to stimulate osteogenic differentiation [14]. However, little has been studied in depth about the impact on the osteogenic differentiation of a primary adult human mesenchymal stem cells (_ali_MSCs) culture. In order to ensure that this new biomaterial induces _ah_MSCs differentiation to osteoblasts and to know the route by which it acts, in this work we have investigated and monitored the expression of genetic markers involved in the osteogenic differentiation of _ah_MSCs as well as the expression of different proteins of the extracellular matrix and surface markers (surface antigens) to give greater consistency to our results.