Isolating the Effects of Mg²⁺, Mn²⁺ and Sr²⁺ Ions on Osteoblast Behavior from those Caused by Hydroxyapatite Transformation

Ionic trace elements such as Mg²⁺, Mn²⁺ and Sr²⁺ are very difficult to stabilize in the hydroxyapatite lattice, and they can induce phase transformations when subjected to thermal treatments. The effects of the ions themselves are often confused with the effects of the newly formed phases. Therefore, the objective of this work was to evaluate the effects of the ions isolated from the effects caused by the inherent phase transformations observed in these systems. WDXRF, XRD, FTIR and biological assays using mouse preosteoblastic cells (MC3T3-E1) showed the Mg²⁺ ions can stimulate cell differentiation even when segregated from the HA structure in the form of MgO. However, the presence of MgO considerably retards cell proliferation. At the same time, Mn²⁺ ions are able to increase cell proliferation and induce the production of high levels of ALP, regardless of whether they are inserted into the HA structure or segregated in the form of Mn₃O₄. Finally, the presence of Sr²⁺ in the HA lattice does not appear to directly affect cell behavior, since both the proliferation and production of ALP are comparable to those observed in the nondoped HA sample.

Keywords:
hydroxyapatite; trace element; osteoblast behavior; MC3T3-E1; phase transformation