A.P. Legrand, H. Sfihi, N. Lequeux, J., Lemaître (Paris, France)
INTRODUCTION:
The composition and evolution of a brushite-type calcium phosphate cement was investigated by solid state NMR and X-ray during the setting process. The cement is obtained by mixing b-tricalcium phosphate [Ca3(PO4)2, b-TCP] and monocalcium phosphate monohydrate [Ca(H2PO4)2.H2O, MCPM] in presence of water, with formation of dicalcium phosphate dihydrate or brushite [CaHPO2.2H2O, DCPD].
METHODS:
1H, 31P solid state NMR, Phosphorus-Proton HetCor, X-ray. The setting follow-up of the mixture of the two extruded pastes was obtained by mixing with anhydrous acetone after pre-selected reaction times. Quenching was obtained through extraction of water by acetone during crushing of the mixture
RESULTS:
Fig. 1: 31P SPE-MAS NMR spectra of reference phosphates. Mono Calcium Phosphate Monohydrate [MCPM]; b-Tricalcium phosphate [b-TCP]; a and b calcium pyrophosphates [a and b-CPy]; Di-calcium phosphate dihydrate [DCPD]; Di-calcium phosphate [DCP].
Fig. 2: Setting process follow-up as a function of time, observed by 31P MAS SPE-NMR. To follow the evolution of the composition as a function of time, each total surface spectrum is set identical.
CONCLUSIONS:
Analysis of the initial b-TCP paste has shown the presence of b-calcium pyrophosphate [Ca2P2O7, b-CPy] and that of the initial MCPM a mixture of MCPM and dicalcium phosphate [CaHPO4, DCP]. Follow-up of the chemical composition by 31P solid state NMR enables to show that the chemical setting process is completed after 20 mn. The constant composition observed at the end of the process was determined: DCPD 65%; DCP 13%; b-TCP 22% (w %).
REFERENCES:
paper submitted to J Biomed Mater Research Part B: Applied Biomaterials.
ACKNOWLEDGEMENTS: We thank D. Brendlen, C. Pittet (Produits Dentaires SA, CH-1800 Vevey, Switzerland) for providing samples and discussions and M. Bohner for some reference phosphates.