Zeta potential of alumina powders with different crystalline phases in simulated body fluids

The zeta potential of alumina (Al2O3) powder with different crystalline phases, prepared by heat treatment of boehmite, was measured in simulated body fluids in order to discuss the mechanism on in vivo formation of a calcium and phosphorus (CaP)-rich layer on bone cement containing δ-Al2O3-based bead powder. γ, δ, and θ-Al2O3 powders were obtained by heat treatment of boehmite powder at 600 °C, 900 °C, and 1025 °C, respectively. It was found that δ-Al2O3 gave a negative zeta potential in an acidic simulated body fluid, whereas γ-Al2O3 and θ-Al2O3 gave a positive potentials. During the bone fracture healing process, acidic conditions are maintained at the site of fracture for several days. Consequently, it is speculated that the negative surface potential of δ-Al2O3 in an acidic body fluid, similar to the fracture site, might be responsible for the in vivo formation of the CaP-rich layer on the overlying bone cement, given that the negatively charged surface of δ-Al2O3 would attract calcium ions from the surrounding body fluid, thereby facilitating the formation of the CaP-rich layer.