Generation of a Porous Scaffold with a Starting Composition in the CaO-SiO\({}_{2}\)-MgO-P\({}_{2}\)O\({}_{5}\) System in a Simulated Physiological Environment  
[PERSON]  
1 Instituto de Ciencia de Materiales de Aragon, Dpto. Ciencia y Tecnologia de Materiales y Fluidos, Universidad de Zaragoza-CSIC, 50.018 Zaragoza, Spain; [EMAIL_ADDRESS] (L.G. ); [EMAIL_ADDRESS] (M.D.-  
enstatite (MgSiO\({}_{3}\)), and their combinations are suitable for tissue engineering that favors implant attachment to bone tissue, as they have the ability to generate a hydroxyapatite (HAp) layer in contact with simulated body fluid (SBF) and to stimulate the proliferation and adhesion of osteoblast cells. Among the multiphasic ceramics, Ca\({}_{3}\)(PO\({}_{4}\))\({}_{2}\)-CaSiO\({}_{3}\)[7; 8; 9], Ca\({}_{3}\)(PO\({}_{4}\))\({}_{2}\)-CaMg(SiO\({}_{3}\))\({}_{2}\)[10], CaSiO\({}_{3}\)-CaMg(SiO\({}_{3}\))\({}_{2}\)[11], and Ca\({}_{3}\)(PO\({}_{4}\))\({}_{2}\)-CaSiO\({}_{3}\)-CaMg(SiO\({}_{3}\))\({}_{2}\)[12] eutectics, also suitable for tissue engineering, have been widely studied for their bioactivity. The SBF solution mimics human blood plasma in terms of pH and ionic concentration. The choice of one or another ceramic material depends on the kinetics of HAp deposition, the degradation rate, or the enhanced mechanical behavior if load bearing properties are required. It is also well known that the presence of Ca, Mg, and Si ions can influence proliferation and osteogenesis-related gene expressions in the different stages of osteoblastic differentiation in a way that is favorable in the process of bone remodeling [13; 14]. The main disadvantages of ceramics, glasses, bioglasses, and bioactive crystals are their fragility when they have a porous structure, and their surfaces' limited bioactivity when they are completely dense [15; 16]. For this reason, some researchers have designed multiphasic ceramics with the ability of generating a porous structure by the dissolution of one of the phases in the presence of SBF. Moreover, an adequate selection of the phases enables one to adjust the mechanical properties, bioactivity, ion release, and resorption rate to the specific needs of the bone. However, the size of the porous structure formed is limited to the size of the resorbable phase, which is micrometric in the case of bioeutectics [8]. Nevertheless, surface microporosity might improve the bioactivity of the scaffolds, thereby enabling the adsorption of proteins and cells to a larger surface area. Phase dissolution occurs via the breaking of bonds catalyzed by the absorption of protons or hydroxyl ions to such bonds. In the case of Wollastonite dissolution, the release of Ca\({}^{2+}\) ions is accompanied by H\({}^{+}\) penetration deep into the structure, promoting silica tetrahedral condensation leading to the formation of a thin amorphous silica-rich layer at the surface. Such a layer slows down Wollastonite dissolution by decreasing the surface area exposed to the reactive fluid. This process influences the depth of the porous layer when a resorbable phase is present in a multiphasic bioceramic. Due to the consumption of protons (H\({}^{+}\)), the pH increase and the newly formed negative silica layer attracts positive ions, and this gives rise to the re-adsorption of Ca, Mg, and other ions such as HPO\({}_{4}\)\({}^{2}\)- and OH\({}^{-}\) from the media. The role of Mg\({}^{2+}\) ions in bone remodeling, skeletal development, human metabolism, and cellular processes such as bone cell adhesion and osteoblast proliferation is well established [17; 18]. [PERSON] et al. [19] reviewed the olivine dissolution rates in aqueous fluids and reported an initial non-stoichiometric release of Mg and SiO\({}_{2}\) due to the equilibration of the olivine (Forsterite) surface with the liquid, and this release was followed by an increase in Mg and SiO\({}_{2}\) concentrations in the liquid linearly with time. These ions are preferably released at low to neutral pH.