An effective route to the synthesis of carbonated apatite crystals with controllable morphologies and their growth mechanism

Abstract

† Electronic supplementary information (ESI) available: XRD and FTIR analyses, additional TEM image, carbonate content calculation and solution chemistry calculation.Carbonated hydroxyapatite (CHAp) powders with controllable morphologies and sizes were successfully synthesized via hydrothermal treatment by using hexamethylenetetramine (HMT) as a hydroxide anion-generating agent in a phosphate-surplus precursor solution. The products were characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, and selected area electron diffraction. Results revealed that the morphologies (such as micro-rods, sheet-like-assembled flowers, shaft wheel-like structures, bur-like spheres, dumbbell-shaped structures, and microspheres) of the products could be well tailored by regulating the reaction acidity and time. A possible growth mechanism accompanied with the effects of HMT on crystal nucleation and growth was preliminarily proposed for the formation of the controllable structures. This work indicated that the use of HMT as a hydroxide anion-adjusting agent is an effective strategy to finely control the morphology of CHAp crystals.

Novel synthesis of AB-type carbonated hydroxyapatite hierarchical microstructures with sustained drug delivery properties

“…[9][10][11][12] Guo et al 13 fabricated hollow B-type CHAp microspheres by using calcium carbonated microspheres as sacrificial templates via a hydrothermal method. Shen et al 14 prepared B-type CHAp powders with controllable morphologies and sizes (microrods, sheet-like-assembled flowers, bur-like spheres) via hydrothermal treatment by using hexamethylenetetramine (HMT) as a hydroxide anion-generating agent. Ren et al 3 synthesized biomimetic AB-type CHAp nanoparticles with tunable size, morphology and ultrastructure via a hydrothermal route.…”

Rapid Flow Synthesis of a Biomimetic Carbonate Apatite as an Effective Drug Carrier

“…For characterization, natural bioapatite (bone and tooth enamel) samples and fully crystalline commercial synthetic HAp were initially investigated (Figure S1, Supporting Information) prior to synthetic apatite phases. The platelet-like morphology (Figure S1A, Supporting Information), presence of carbonate in the apatite structure (Figure S1C, Supporting Information), and lower crystallinity levels (Figure S1D, Supporting Information) are noticeable features of natural bioapatite. − , To check the specific type (A- or B-type) of CAp, FT-IR spectroscopy was utilized, and the presence of B-type CAp (CO 3 substituting for PO 4 ) was investigated based on the peaks at the v 2 (860∼870, <880 cm –1 ) and v 3 (1412∼1455 cm –1 ) regions. − ,, FT-IR spectroscopy was also applied to investigate the effect of varying carbonate source concentration − on synthetic carbonate apatite (Figure S2, Supporting Information). SEM imaging was employed to view the overall morphology and size, specifically for verifying the rounder platelet-like morphology of CAp ,− based on bioapatite samples (Figure S1A, Supporting Information) and a more elongated rod or needle-like morphology of HAp, ,,, and the general uniformity of the apatite nanocrystals was checked.…”

“…For CAp synthesis, the addition of carbonate may result in inconsistencies of the outcome, hence its limited application compared to HAp. ,, Innovative synthesis methods have been reported such as rapid mixing of aqueous solutions of a continuous computer-controlled reactor, mechanochemical–hydrothermal synthesis at room temperature, rapid hydrothermal flow synthesis with a sophisticated setup, ultrafast sonochemistry-assisted microwave process, and phase transformation on a polymer matrix . However, the most commonly applied method is aqueous precipitation via batch synthesis, typically under hydrothermal conditions followed by subsequent aging and heat treatment (calcination/sintering) procedures ,,,,− that can be lengthy and costly overall. In addition, so far, functionalizing both CAp and HAp as drug carriers has been carried out as a post-process via surface adsorption of therapeutic agents on fully formed apatites through batch methods, − ,− which has the chance of becoming problematic due to unwanted leakage of the drugs before reaching to the target tissue.…”