Introduction

A way to treat bone defects is to use calcium phosphate (CaP) minerals. Two well-known CaP compositions are β-tricalcium phosphate (β-TCP; β-Ca₃(PO₄)₂) and monetite (DCP; CaHPO₄). Mostly they are synthesized over methods like high temperature processes or precipitation in aqueous solutions. Both lead to agglomerated and polydispersed particles. Our aim is therefore to assess a new approach to synthesize non-agglomerated and monodispersed CaP crystals based on the precipitation method in organic solvents.

Methods

Our work is based on the results of Tao et al.¹, where the CaP particles were produced with a single batch method. For our purpose a calcium salt solution was mixed with a phosphate salt solution. We used ethylene glycol as organic solvent. The temperature was typically in the range of 90 to 170°C. After a certain reaction time single crystalline particles precipitated out of this solution. The resulting product was washed, dryed and analyzed by SEM, XRD, and laser diffraction analysis.

Results

To vary size, shape and composition of the resulting particles, parameters like temperature, pH, reaction time and precursor concentration have to be changed. The size dispersion for batches resulting in β-TCP particles with a phase pure composition was below 10 % and in ideal cases even below 5 %. The size ranged from about 0.1 μm (nanoparticles) to 1.2 μm (hexagonal platelets) or in special cases even up to 8 μm when mixed with DCP. The parallelepiped-shaped DCP platelets had a length up to several micrometers. Their size dispersion was below 20-30 %, depending on the reaction temperature. The urchin-shaped monetite particles had a diameter of 2.8±0.7 μm; with a size dispersion of 25 %. All particles were non-agglomerated as indicated by the narrow and monomodal particle size distribution curves obtained by laser diffraction.

Conclusion

As our first research efforts show, it is possible to synthesize non-agglomerated and monodispersed calcium phosphate particles. Their size, shape and composition can be influenced by varying the reaction parameters. To investigate other compositions and shapes further studies have to be done.

REFERENCES: ¹ J. Tao, W. Jiang, H. Zhai, H. Pan, X. Xu, and R. Tang (2008) Crystal Growth & Design, 8(7), 2227.

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