Abstract
Ionic substitution can affect essential physicochemical properties leading to a specific biological behavior upon implantation. Therefore, it has been proposed as a tool to increase the biological efficiency of calcium phosphate based materials. In the following study, we have evaluated the contribution of an important cation in nature, Mg2+, into the structure of previously studied biocompatible and biodegradable hydroxyapatite (HA) nanorods and its subsequent effect on its chemical, morphology, and bone mimetic articulation. Mg2+-substituted HA samples were synthesized by an aqueous wet-chemical precipitation method, followed by an hydrothermal treatment involving a Mg2+ precursor that partially replace Ca2+ ions into HA crystal lattice; Mg2+ concentrations were modulated to obtain a nominal composition similar to that exists in calcified tissues. Hydrothermally synthesized Mg2+-substituted HA nanoparticles were characterized by X-ray powder diffraction, FT-NIR and EDX spectroscopies, field emission scanning and high resolution transmission electron microscopies (FE-SEM, H-TEM). Molecular modeling combining ab initio methods and power diffraction data were also performed. Results showed that Mg2+-substitution promoted the formation of calcium deficient HA (cdHA) where Mg2+ replacement is energetically favored at Ca(1) position in a limited and specific amount directing the additional Mg2+ toward the surface of the crystal. The control of Mg2+ incorporation into HA nanorods gave rise to a tailored crystallinity degree, cell parameters, morphology, surface hydration, solubility, and degradation properties in a dose-replacement dependent manner. The obtained materials show qualities that conjugated together to drive an optimal in vitro cellular viability, spreading, and proliferation confirming their biocompatibility. In addition, an improved adhesion of osteoblast was evidenced after Mg2+-Ca2+ substitution.
Highlights
Notwithstanding the steady advances in material science field, the creation of calcium phosphate (CaP) ceramics analogous to the mineral matrix of calcified tissue remains one of the most ambitious goals of implants research, mainly due to the difficulty of simultaneously mimic the morphology and microstructure thereof.[1]
Mg2+- substituted hydroxyapatite powders (Mg2+- HA) of different composition were prepared supposing that Mg2+ ions would switch the calcium position in the HA lattice in order to obtain a nominal concentration equivalent to that exists in bone (MgI-HA) and dentin (MgII-HA); materials containing two to ten times the amount of Mg2+ in dentin are formulated (MgIII-HA and MgIV-HA) to evaluate the maximum capacity of Mg2+substitution into de HA framework
Results were compared with respect to HA, asterisks denote statistically significant differences (**p < 0.01). (b) Solubility product of different Mg2+- HA materials treated under physiological conditions at 37°C as a function of Mg2+ content. (c)
Summary
Notwithstanding the steady advances in material science field, the creation of calcium phosphate (CaP) ceramics analogous to the mineral matrix of calcified tissue remains one of the most ambitious goals of implants research, mainly due to the difficulty of simultaneously mimic the morphology and microstructure thereof.[1]. In the course of the study, HA nano-crystals affected the hydrodynamic environment of the protein network producing hybrid scaffolds with improved mechanical and thermal stability properties. It is recognized that the substitution of Ca2+ positions by Mg2+ in the surface of the crystal induces a chaotic state where ions are constantly swapped from the outer hydrated layer and expands the number of molecular layers of coordinated water; 13-14 all these events affect the material resorption abilities as well as its protein adsorption capacity and future cells adhesion. Our study follows with the analysis of Mg2+ substitution effect on the material hydrophilicity and degradation properties under osseous resorption conditions correlating the ion release with its biocompatibility in the presence of osteoblasts and endothelial cells. The results obtained from this work would contribute to a better understanding of the ionic substitution effect on the properties of precipitated phases and, to the design of raw materials for tissue engineered implants displaying enhanced bioactivity and specific ionic delivery abilities to treat bone diseases
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