Formation of calcium phosphates by vapour diffusion in highly concentrated ionic micro‐droplets

Abstract

In this work we have used the sitting drop vapour diffusion technique, employing the "crystallization mushroom" to analyze the evolution of calcium phosphate crystallization in micro-droplets containing high initial concentrations of Ca 2+ and HPO 4 2-. The decomposition of NH 4 HCO 3 solution produces vapours of NH 3 and CO 2 which diffuse through the droplets containing an aqueous solution of Ca(CH 3 COO) 2 and (NH 4 ) 2 HPO 4 . The result is the increase of pH by means of the diffusion of NH 3 gas and the doping of the calcium phosphate with CO 3 2-ions by means of the diffusion of CO 2 gas. The pH of the crystallization process is monitored and the precipitates at different times are characterized by XRD, FTIR, TGA, SEM and TEM techniques. The slow increase of pH and the high concentration of Ca 2+ and HPO 4 2-in the droplets induce the crystallization of three calcium phosphate phases: dicalcium phosphate dihydrate (DCPD, brushite), octacalcium phosphate (OCP) and carbonate-hydroxyapatite (HA). The amount of HA nanocrystals with needle-like morphology and dimensions of about 100 nm, closely resembling the inorganic phase of bones, gradually increases, with the precipitation time up to 7 days, whereas the amount of DCPD, growing along the b axis, increases up to 3 days. Then, DCDP crystals start to hydrolyze yielding OCP nanoribbons and HA nanocrystals.

Hydrothermal processing of hydroxyapatite nanoparticles—A Taguchi experimental design approach

“…Indeed, anionic sites within the HAp crystals are very susceptible to carbon dioxide originated from the atmosphere, so that carbonate ions (CO 3 2 À ) generated from CO 2 in the reaction solution can substitute hydroxyls or phosphates in the crystal lattice and based on this substitution, type A and type B of carbonated HAp are, respectively, formed [32,33]. Although the published data in the literature has led to some contradictory explanations regarding which bands correspond to the A-, B-, or mixed AB-type carbonate substitutions, but according to the results of IR analysis recently reported [32][33][34], the nanoparticles synthesized in the present study can be corresponded to the B-or mixed AB-type carbonated structures. Table 3 specifies the carbonated specimens and provides information on the sites where the carbonate groups were substituted.…”

Progress on the preparation of nanocrystalline apatites and surface characterization: Overview of fundamental and applied aspects

“…Numerous methods have been used for the synthesis of apatite crystals. They can be classified into the following categories: wet chemical precipitation [75][76][77], sol-gel synthesis [78][79][80], coprecipitation [24,81], hydrothermal synthesis [82][83][84], rapid or continuous precipitation from solution [85], mechanochemical synthesis [86], microwave processing [87][88][89][90], vapor diffusion [91][92][93], silica gel template [94], emulsion-based syntheses [95], electrospraying [96], electrospinning [97], flux cooling [98] and other methodologies producing (nano)crystals of various shapes and sizes [99,100]. Dorozhkin [5] has recently produced a review of those methods producing nanocrystalline apatites and has underlined that the interest for nanocrystalline apatites was quite recent.…”

Industrial‐scale fabrication of an osteogenic and antibacterial PLA/silver‐loaded calcium phosphate composite with significantly reduced cytotoxicity

“…It has been reported that Ca/P atomic ratios varying between 1.4 and 2.4 are often observed for hydroxyapatite prepared from solution co‐precipitation . Similarly, the additional carbon signal in the samples is most likely a result of carbonate impurities . Further investigation into preparation induced impurities should be performed in future studies.…”