Rapid Hardening Dual-Paste Premixed Cement for Bone Repair

Previously reported premixed calcium phosphate cements (CPC) were in the form of a single paste, which must be non-aqueous to achieve acceptable shelf-life. Such cements begin to harden after placement in bone defects where the moisture needed for cement setting is obtained from surrounding tissues.  OBJECTIVES: To develop and study properties of a dual-paste premixed cement, with one of the pastes being aqueous to provide the water needed for the setting reaction to occur. METHODS:  The aqueous paste of the cement contained 69 mass% monocalcium phosphate monohydrate and 31mass% of 2mol/L citric acid solution that also contained 0.4mass% hydroxypropyl methyl cellulose. The non-aqueous paste contained 48mass% tetracalcium phosphate, 18mass% dicalcium phosphate anhydrous (DCPA), 7mass% CaO, and 27mass% glycerin. The pastes, in separate containers, were subjected to an accelerated aging test (50°C for 7d) for stability evaluation. Equal amounts of each paste were mixed to produce samples for the property measurements. The hardened product was characterized by powder X-ray diffraction (XRD) for phase identification. RESULTS: Aging test results showed that both pastes were stable and did not lose reactivity. The mean (n=3) hardening time, measured by Gilmore needle method, was (10±1)min, similar to (10.3±1.2)min (p>0.05) reported for a conventional powder/liquid, citric acid-based CPC. The mean (n=4) 1-day compressive strength was (34.2±1.3)MPa, also similar to (31.6±5.0)MPa for the same CPC. XRD showed DCPA as the major cement product with dicalcium phosphate dihydrate and hydroxyapatite as minor products. CONCLUSION: The setting time and mechanical properties of the new dual-paste, water-containing premixed CPC were similar to those of a conventional powder/liquid CPC of similar chemical composition.  While the individual pastes were completely stable in the package, the new CPC provides the needed water so it hardens more uniformly and rapidly than previously reported single-paste premixed CPCs. Supported by NIDCR R01DE11789, ADAF, and NIST.