Investigation of the Surface Elution Mechanism of Citric Acid-Coordinated Hydroxyapatite Nanoparticles in Biological Solutions

Abstract

We clarified the surface elution behavior of citric acid (Cit) ions from Cit-coordinated europium­(III) ion (Eu3+)-doped hydroxyapatite (CEH) nanoparticles in three different biological solutions (i.e., phosphate buffer (PB), carbonate buffer (CB), and simulated body fluid (SBF)). Specifically, the elution behavior of Cit from the CEH nanoparticles in SBF was clarified as compared with the cases in PB and CB. Based on the elution results of Cit from the nanoparticles, two-stepwise (i.e., initially dramatic and subsequentially gradual) elution behavior during the immersion was observed, which was mainly driven by the substitutional coordination of HPO4 2– and CO3 2– to the Cit ions on the nanoparticle surfaces. The Cit elution behavior by the immersion was effectively affected by the anions in the biological solutions. The substitutional coordination of HPO4 2– or CO3 2– to the Cit ions was the dominant driving force for the Cit ion elution chelating with Eu3+ and Ca2+ ions, which progressed significantly at the immersion time of 0–3 h in SBF. Subsequently, the complex reactions based on the substitutional coordination would become the equilibrium state at the immersion time of 3–12 h in SBF, suggesting the control of nanoparticle surface states by optimizing the Cit elution behavior. Therefore, we believe that the nanoparticles will be the base nanobiomaterials toward the application for drug delivery system carriers containing both photoluminescence and drug loading functions.

Biological Surface Layer Formation on Bioceramic Particles for Protein Adsorption

“…The substitutions at both sites are called type AB CHA [ 26 ]. CHA and CDHA particles have been investigated as nanocarriers for DDS based on the CHA/organic interface design [ 27 , 28 ].…”

“…CHA and CDHA particles have been investigated as nanocarriers for DDS based on the CHA/organic interface design [27,28].…”

Surface functionalization of hydroxyapatite nanoparticles for biomedical applications

“…By exploiting the interaction between the ions located at the Ca sites in HAp and the carboxyl ions of the citric acid molecule, the synthesis of hybrid NPs can be achieved. [224][225][226][227][228][229][230] In order to utilize the aforementioned nanomaterial system for specific cell visualization, the authors added citrate ions during the synthetic process for substituting Eu 3+ with the Ca sites of the HAp NPs (Fig. 15(a)).…”

Effective Thermal Diffusion of Eu(III) and F Ions into Hydroxyapatite Nanoparticles by Citric Acid Coordinative Mediation

“…According to previous reports, the coordination environment of Eu 3+ ions in Eu:HA may be changed through the interaction with organic molecules. − Citric acid (Cit) is an organic acid containing three carboxyl groups with a strong coordination ability (i.e., formation of the chelates) with various metal ions, − which can effectively coordinate with lead­(II) and cadmium­(II) ions , and can also coordinate with calcium­(II), terbium­(III), and europium­(III) ions for immobilizing various crystal surfaces. − In addition, the inhibition of crystal growth and the enhancement of crystal solubility occurred through the coordination effect, − and the dissolution–reprecipitation processes of the crystals are strongly related to ion replacement. , Moreover, it was suggested that Cit coordination could promote the replacement state change of Eu 3+ ions in HA. Furthermore, our group has elucidated the interactions between Cit and Eu:HA, which suppressed the photoluminescence (PL) deactivation caused by the adsorption of surface water molecules. − Thus, the control of the Cit coordination behavior can change the PL properties of the Eu 3+ ions in HA.…”