Material characterization and in vivo behavior of silicon substituted alpha-tricalcium phosphate cement.

The possibility and biological effects of substituting silicon in alpha-tricalcium phosphate (alpha-TCP) by way of solid-state reaction have been evaluated. alpha-TCP powders with varying substitution amounts (1 and 5 mol % Ca2SiO4) were synthesized by reacting mixtures of CaCO3, Ca2P2O7, and SiO2, at a rate of 4 degrees C(min)(-1) to 1100 degrees C, left to dwell for 2 h and then heated to 1325 degrees C at 4 degrees C(min)(-1) and left to dwell for a period of 4 h. The powders were then rapidly quenched in air. Si incorporation could be verified by X-ray diffraction analysis, indicating an increase of the lattice volume with increasing Si content from 4284.1(8) to 4334(1) A3 for pure alpha-TCP and alpha-Si5%TCP, respectively. The hydrolysis of milled alpha-SiTCP powders was monitored by isothermal calorimetry, and the compressive strength of set cements was tested. The results showed changes in speed and amount of heat released during reactivity tests and a decrease in mechanical strength (60, 50, and 5 MPa) with increasing Si content. In vitro bioactivity of the set cements after soaking in simulated body fluid for 4 weeks was also tested. The formation of a bonelike apatite layer on the surface of the set cements could be observed and was thickest for 1%Si (20 microm). These results were in good agreement with the in vivo studies performed, which showed strong evidence that the cement containing 1% silicon doped alpha-TCP enhanced mesenchymal cell differentiation and increased osteoblast activity compared with alpha-TCP.