Effect of the Ionic Radius of Alkali Metal Ions on Octacalcium Phosphate Formation via Different Substitution Modes

Abstract

Octacalcium phosphate (OCP), a layered calcium phosphate compound, is an attractive material for new medical combination products, which are hybrid materials consisting of both drugs and biomaterials that have shown excellent therapy scores. OCP is fabricated primarily from soluble calcium salt via an aqueous-mediated hydrolysis process. The coexisting cations are likely to be incorporated into the OCP unit lattice during this process and affect the development of the OCP crystal structure and its thermodynamic stability. However, the key parameters of the coexisting cations, such as the ionic radii and charge number, that affect OCP formation are still unclear. In this study, we focused on the ionic radius of each monovalent ion of alkali metal ions (Li + , Na + , K + , Rb + , and Cs + ) for OCP incorporation and formation in a CaHPO 4 •2H 2 O (DCPD)-(NH 4 ) 2 HPO 4 system with alkali metal salts. There was little incorporation of Li into the OCP unit lattice at low concentrations, whereas Li was incorporated into the OCP unit lattice as a conjugate form of NH 4 and K, which have ionic radii that are larger than that of Ca, resulting in a HPO 4 −OH layered structure in the OCP unit lattice. The Na concentration increased hyperbolically and was incorporated into the OCP unit lattice, resulting in a HPO 4 −OH layered structure in the OCP unit lattice. By contrast, Li, K, and Rb resulted in the HPO 4 −OH layer in the OCP unit lattice at low concentrations and attenuated OCP formation at high concentrations. Cs only exhibited an attenuation effect on OCP formation. Considering the differences between the Ca ionic radius (1.00 Å) and those of alkali metal ions, the alkali metal ionic radii that were smaller than ∼1.5 times the Ca ionic radius could be incorporated into the OCP unit lattice, whereas those greater than ∼1.5 times the Ca ionic radius exhibited an inhibiting effect on OCP formation. In addition, Na particularly affects the OCP formation and its crystallinity unlike other alkali metal ions because of its similar ionic radius to Ca.

Fabrication of interconnected porous Ag substituted octacalcium phosphate blocks based on a dissolution-precipitation reaction

“…Co-existing NH 4 + (or NH 3 ) enabled the dispersion of Ag + ions in weak basic phosphate solutions as [Ag(NH 3 ) 2 ] + form. Furthermore, Na + ion as OCP inducer co-existed in the reaction solutions [ 27 , 28 ]. Thus, OCP foams with substituted Ag were fabricated successfully.…”

SBA-15 with Crystalline Walls Produced via Thermal Treatment with the Alkali and Alkali Earth Metal Ions

“…In particular, the size of the ion exhibits a certain relationship with the cell volume of the crystalline phase [52]. In that way, Na + ion having the ionic radius of 1.02 Å favors the transition to cristobalite (cell volume = 171 Å 3 , density = 2.32 g cm −3 , tetragonal) [52,61,62].…”

Cemp1-p3 Peptide Promotes the Transformation of Octacalcium Phosphate into Hydroxyapatite Crystals

“…P1-P4 are in the apatite layer, and P5 and P6 are in the HPO 4 -OH layers (Supplementary material, Figure S1). All PO 4 molecules in the OCP unit are conjugated to specific Ca 2+ ions in the OCP unit [13]. The morphological analysis of the sample was obtained by scanning electron microscopy that shows a series of micrographs of different areas and amplification.…”

“…The reasons for this are clear: apatites form the mineral component of bones and teeth, and calcium phosphates are also involved in several mineralization processes, including those that occur in pathological calcifications [9][10][11][12]. The great versatility of apatites in accepting a large variety of substitutional ions, complicates their study [13,14]. The role of octacalcium phosphate (OCP: Ca 8 H 2 (PO 4 ) 6 •5H 2 O) in bone formation remains inconclusive.…”