Pure hydroxyapatite synthesis originating from amorphous calcium carbonate

Michika Sawada,Yasuharu Kanda,Shinya Yamanaka,Kandi Sridhar

doi:10.1038/s41598-021-91064-y

Michika Sawada, Yasuharu Kanda + Show 2 more

Open Access

https://doi.org/10.1038/s41598-021-91064-y

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Abstract

We report a synthesis strategy for pure hydroxyapatite (HAp) using an amorphous calcium carbonate (ACC) colloid as the starting source. Room-temperature phosphorylation and subsequent calcination produce pure HAp via intermediate amorphous calcium phosphate (ACP). The pre-calcined sample undergoes a competitive transformation from ACC to ACP and crystalline calcium carbonate. The water content, ACC concentration, Ca/P molar ratio, and pH during the phosphorylation reaction play crucial roles in the final phase of the crystalline phosphate compound. Pure HAp is formed after ACP is transformed from ACC at a low concentration (1 wt%) of ACC colloid (1.71 < Ca/P < 1.88), whereas Ca/P = 1.51 leads to pure β-tricalcium phosphate. The ACP phases are precursors for calcium phosphate compounds and may determine the final crystalline phase.

Highlights

We report a synthesis strategy for pure hydroxyapatite (HAp) using an amorphous calcium carbonate (ACC) colloid as the starting source
We demonstrate that pure HAp or β-tricalcium phosphate (β-TCP; Ca3(PO4)2) is synthesised by a reaction of ACC colloids with an orthophosphoric acid solution at room temperature and a subsequent calcination process
In addition to ACC, the broad pattern suggests the possibility of amorphous calcium phosphate (ACP), which is an intermediate state in crystalline calcium phosphate compounds[31,32,33,34]

Summary

Introduction

We report a synthesis strategy for pure hydroxyapatite (HAp) using an amorphous calcium carbonate (ACC) colloid as the starting source. We demonstrate that pure HAp or β-tricalcium phosphate (β-TCP; Ca3(PO4)2) is synthesised by a reaction of ACC colloids with an orthophosphoric acid solution at room temperature and a subsequent calcination process. To prevent the ACC transformation into crystalline calcium carbonate, the phosphorylation reaction of the ACC colloid was conducted in an acetone system.

Results

Conclusion