Properties of injectable apatite-forming premixed cements

Previous studies reported premixed calcium phosphate cements (CPCs) that were stable in the package and form hydroxyapatite (HA) as the product after exposure to an aqueous environment. These cements had setting times of greater than 60 min, which are too long to be useful for some clinical applications. The present study investigated properties of fast-setting HA-forming premixed CPCs that initially consisted of two separate premixed pastes: (1) finely ground (1.0 μm in median size) dicalcium phosphate anhydrous (DCPA) mixed with an aqueous NaH ₂PO ₄ solution, 1.5 mol/L or 3.0 mol/L in concentration, and (2) tetracalcium phosphate consisting of combinations of particles of two different size distributions, 5 μm (TTCP5) and 17 μm (TTCP17) in median size, mixed with glycerin. Equal volume of Pastes 1 and 2 were injected with the use of atwobarrel syringe fitted with a static mixer into sample molds. The molar Ca/P ratio of combined paste was approximately 1.5. Cements were characterized in terms of setting time (Gilmore needle), diametral tensile strength (DTS), and phase composition (powder x-ray diffraction, XRD). Setting times were found to range from (4.3 ± 0.6 to 68 ± 3) min (mean ± sd; n = 3), and 1-d and 7-d DTS values were from (0.89 ± 0.08 to 2.44 ± 0.16) MPa (mean ± sd; n = 5. Both the NaH ₂PO ₄ concentration and TTCP particle size distribution had significant (p μ 0.01) effects on setting time and DTS. Powder XRD analysis showed that low crystallinity HA and unreacted DCPA were present in the 1-day specimens, and the extent of HA formation increased with increasing amount of TTCP5 in the TTCP paste. Conclusion: Injectable HA-forming premixed CPCs with setting times from 4 to 70 min can be prepared by using DCPA and TTCP as the ingredients. Compared to the conventional powder liquid cements, these premixed CPCs have the advantages of being easy to use and having a range of hardening times.