The effect of modification of KH2PO4 hardening liquid with H3PO4 and chitosan on setting reactions and compressive strength of calcium phosphate cement

The setting processes and mechanical properties of tetracalcium phosphate (TTCP) -monetite cements with H3PO4 and chitosan modified KH2PO4 hardening liquid have been studied. From XRD phase analysis, it was found that brushite was created in the first stage of the setting process by the interaction between phosphate compounds in hardening liquids and TTCP. Calcium deficient hydroxyapatite was the final product of the hardening process. The orthophosphoric acid addition to KH2PO4 hardening liquid caused lowering resistance to disintegration and an increase in the setting times of cements which allows the possibility for their control. Cement with pure KH2PO4 hardening liquid was resistant to wash-out immediately after mixing. Chitosan addition to KH2PO4 + H3PO4 hardening liquid of an amount around 1 wt.% did not affect change of setting time or improvement of disintegration behaviour of cement. Compressive strengths were around 80-100 MPa in cements soaked in SBF without an chitosan addition and chitosan caused an approximately 15% decrease in compressive strength. The compressive strength of calcium phosphate cements is more influenced by the hydroxyapatite particle morphology than their crystallinity.