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.