Investigation of Apatite Deposition onto Charged Surfaces in Aqueous Solutions Using a Quartz-Crystal Microbalance |
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Authors: | Peixin Zhu Yoshitake Masuda Tetsu Yonezawa Kunihito Koumoto |
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Affiliation: | Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan |
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Abstract: | Hydroxyapatite (HAp) deposition onto positively charged surfaces (i.e., self-assembled monolayers (SAMs) terminated with NH2 head groups) and negatively charged surfaces (i.e., OH-SAMs (weak) and COOH-SAMs (strong)) soaked at 50°C in aqueous supersaturated solutions (1.5 SBF, pH 7.0–7.6; SBF = simulated body fluid) was investigated using a quartz-crystal microbalance. The results revealed that the solution conditions greatly influenced the formation of HAp on the charged surfaces. In a stable supersaturated solution of simulated body fluid (1.5 SBF, pH <7.4), more strongly negative surfaces had a more powerful induction capability for the heterogeneous nucleation of HAp (COOH > OH), whereas nucleation was obviously prohibited on a positive surface (NH2-SAM). On the other hand, after the calcium phosphate particles had nucleated homogeneously in an unstable soaking solution (1.5 SBF, pH ≧7.4), adhesion of the HAp microparticles to the NH2-SAM was observed. A two-step interaction is conceivable to describe the formation of HAp on the positive NH2-SAM: At the first stage, electrostatic interaction dominates the adhesion of HAp microparticles; at the second stage, hydrogen bonds possibly form between the HAp microparticles and the amino head groups of the NH2-SAM, for a firm bonding with the substrate, and the microparticles grow progressively into a thin film. The electrophoretic behaviors of the HAp microparticles confirmed this hypothesis. |
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Keywords: | apatite deposition nucleation |
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