Setting solution concentration effect on properties of a TTCP/ DCPA-derived calcium phosphate cement

The present work was to investigate the effects of concentration of (NH₄)₂HPO₄ (diammonium hydrogen phosphate) setting solution on properties of a tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)-derived calcium phosphate cement. Experimental results indicated that working/setting time of the cement paste decreased with increasing (NH₄)₂HPO₄ concentration of the setting solution. After being immersed in Hanks' solution for 1 day or longer, the XRD intensities of initial TTCP and DCPA phases largely decreased, while apatite phase became dominant. More residual TTCP phase was observed in the 1 day-immersed cement prepared from higher concentration setting solutions. Compressive strength of the cement immersed for 1 day was consistently higher than that immersed for 30 min or 7 days. After being immersed for 1 day, the average CS value reached a maximal value (59 MPa) as (NH₄) ₂HPO₄ concentration was increased to 0.6 M, beyond that the cement strength decreased and maintained in a relatively high range of 47-54 MPa. Cells incubated with conditioned medium of Al₂O₃ powder and with blank medium exhibited similar average viability values (0.80 and 0.78, respectively). The OD value with extractions of cement decreased with increasing (NH₄)₂HPO₄ concentration of the setting solution. The average 0.25, 0.5 and 0.6 M-OD values were 0.78, 0.67 and 0.66, respectively. When setting solution concentration was greater than 0.6 M, the OD value sharply declined to 0.47.