Single Solid Ingredient Based Calcium Phosphate Cements

Previously reported calcium phosphate cements (CPC) contained two or more calcium-containing ingredients.  We report new CPCs that require only a single solid ingredient. Objectives: To evaluate setting and mechanical properties of single solid ingredient-based CPCs.  Methods: The solid cement component was tetracalcium phosphate (TTCP), α-tricalcium phosphate (α-TCP), or β-tricalcium phosphate (β-TCP), prepared in a furnace and ground in non-aqueous media to obtain desired medium particle sizes of 5µm to 20µm. The cement liquid was a solution ([Ca]=0.72mol/L, [P]=1.88mol/L, pH 2.06) saturated with respect to dicalcium phosphate dihydrate (DCPD), prepared by a previously reported method [Chow and Brown, JDR 1975].  Cement powder and liquid were mixed (P/L=1.5) to produce samples for setting time (Gilmore needle) and compressive strength (CS) measurements. The hardened products were characterized by powder X-ray diffraction (XRD) for phase identifications. Results: The setting times (n=3) were (10.3±0.6)min≈(11.0±1.0)min>(32.3±2.1)min (p<0.05) with TTCP, α-TCP, and β-TCP, respectively, as the cement powder. One-day wet CS (n=3) values were (21.7±0.8)MPa≈(22.5±1.3)MPa>(5.4±0.6)MPa (p<0.05), respectively. XRD results showed that the cement products were hydroxyapatite(HA)+unreacted TTCP, HA+DCPD, and DCPD+unreacted β-TCP, respectively. None of the above single ingredient-based cements would harden when water or a sodium phosphate solution was used as the liquid. It was speculated that the relatively fast setting of these CPCs was a result of rapid formation of DCPD as soon as the cement powder and liquid were mixed. The overall acid-base balance allowed subsequent HA formation in the cases of TTCP and α-TCP-containing cements. The low solubility of β-TCP prevented HA formation in that cement. Conclusions: Single solid ingredient-based CPCs harden rapidly and form poorly crystalline HA and DCPD as products. These CPCs may be advantageous in terms of forming more resorbable products and simpler manufacturing processes. Supported by NIDCR grant R01DE11789, ADAF, NIST, and Nihon University.