Fast-hardening premixed cements form hydroxyapatite/brushite mixtures as products

Previously reported premixed calcium phosphate cements (CPC) form hydroxyapatite (HA) or brushite (DCPD) as product.  These CPCs typically have long setting times.  Objectives: To develop premixed CPCs that harden rapidly and form a mixture of HA and DCPD with any desired proportion. Methods: All cements consisted of two premixed pastes: (1) monocalcium phosphate monohydrate (MCPM) mixed with 2mol/L citric acid, and (2) tetracalcium phosphate in median particle sizes of 5µm (TTCP5) and17µm (TTCP17) mixed with glycerin.  Mass fraction of TTCP5/(TTCP5+TTCP17) was used to control the cement hardening time.  Cements were prepared by combining pastes 1 and 2 with different mass ratio to produce a molar Ca/P ratio of approximately 1.50 to 1.04. Cement hardening time (at 32°C) was measured by Gilmore needle method, initial strength was assessed by a penetration test, and phase composition of set cement was analyzed by powder X-ray diffraction.  Results: All cements with TTCP5 fraction of 0.33 hardened instantly and were unsuitable for preparing test specimens. With TTCP5 fraction of 0.14, the setting times were (in min; mean±sd; n=3) 3±1, 2±1, and 1±0 for the three cements with paste1/paste2 mass ratios of 0.25, 0.50, and 1.0, respectively. When the TTCP5 fraction was reduced to 0.07, the setting times were 8±1, 5±1, and 3±1 for the three cements. Both TTCP5 fraction and paste mass ratio had significant (p<0.05) effects on setting time. Penetration test results showed that all cement developed a strength >24 MPa within 10 min. After incubation in a physiological-like solution for 4 days, the phases present were DCPD, HA+DCPD, and HA for the three cements. Conclusion: Fast setting premixed CPCs with a wide range setting times and product compositions, ranging from HA to DPCD, can be prepared by using MCPM and TTCP as the major ingredients. Supported by NIH grant DE11789, ADAF and NIST.