Osteoblast response to hydroxyapatite doped with divalent and trivalent cations

The present in vitro study doped hydroxyapatite (HA) with various metal cations (Mg2+, Zn2+, La3+, Y3+, In3+, and Bi3+) in an attempt to enhance properties of HA pertinent to orthopedic and dental applications. X-ray diffraction material characterization indicated that the metal cations may have substituted for calcium in the HA crystal structure and that all of the doped HA formulations were single-phase and crystalline. Scanning electron microscopy analysis revealed a variety of grain sizes, depending on the dopant utilized. Energy-dispersive spectroscopy confirmed that the dopants added during synthesis were present and that all of the HA formulations synthesized were within the defined range of HA phase in the CaO-P2O5-H2O system. Lastly, Bi-doped HA had a slower dissolution rate than either undoped HA or HA doped with other cations when exposed to simulated physiological conditions for 21 days. In terms: of cell function, results provided the first evidence that osteoblasts, bone-forming cells, adhered and La3+ differentiated (as measured by alkaline phosphatase synthesis) in response to HA doped with trivalent cations (specifically, La, Y3+, In3+, Bi3+) at earlier time points than either HA doped with divalent cations (Mg2+, Zn2+) or undoped HA. Of the dopants examined, Bi3+ most enhanced osteoblast long-term calcium-containing mineral deposition. For these reasons, this study revealed for the first time the potential benefits of doping HA with Bi3+ according to criteria critical for bone prosthetic clinical success. (C) 2003 Elsevier Ltd. All rights reserved.