(67d) Reactivity Of Calcium Phosphate Cements In Dependence Of Particle Size, Crystal Phase And Crystallinity

A previous study investigated the use of amorphous tricalcium phosphate (TCP) nanoparticles for use in calcium phosphate cements in comparison to micron-sized α-TCP [1]. The development of a detailed understanding of the reaction mechanism as well as reaction kinetics and thermodynamics of hydraulic calcium phosphate cements is crucial to better fulfill future applications in orthopedic surgery. Therefore we have now investigated the reactivity of a series of different TCP-based apatite cements. A suitable set of materials with varying particle size, crystal phase and crystallinity was prepared using solid state reactions as well as flame spray synthesis. When particles with different particle size but the same crystal phase were used, the rate of the setting reaction changed, but the reaction mechanism remained the same. On the other hand, a change of crystal phase contributed to a change in thermodynamics. Specifically, the reaction of amorphous nanoparticles was limited by diffusion in contrast to apatite cements based on crystalline, micron-sized TCP which were limited by a surface reaction [2].

[1] T. J. Brunner, M. Bohner, C. Dora, C. Gerber and W. J. Stark, J. Biomed. Mater. Res. Part B: Appl. Biomater., 2007, DOI: 10.1002/jbm.b.30809.

[2] T.J. Brunner, R.N. Grass, M. Bohner, W.J. Stark, submitted to J. Mater. Chem., 2007