Properties of Injectable Apatite Forming Premixed Cements

A previously reported premixed calcium phosphate cements (CPC) forms hydroxyapatite (HA) as product but had setting time greater than 60 min [Takagi et al., 2003].  Objectives: To study properties of fast-hardening HA-forming premixed CPCs. Methods: All cements consisted of two premixed pastes: (1) dicalcium phosphate anhydrous (DCPA) mixed with 1.5mol/L or 3.0mol/L NaH₂PO₄, 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.  Equal volume of pastes 1 and 2 were injected with the use of a two-barrel 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).  Results: Setting time (in min; mean±sd; n=3) ranged from 68±3 for [NaH₂PO₄]=1.5mol/L and TTCP5 fraction=0 to 4.3±0.6 for [NaH₂PO₄]=3mol/L and TTCP5 fraction=1.0. Both the NaH₂PO₄ concentration and TTCP5 fraction and their interaction had significant (p<0.01) effects on setting time. DTS values (in MPa; n=5) ranged from 2.3±0.4 to 0.9±0.2. Both the NaH₂PO₄ concentration and TTCP5 fraction had significant (p<0.01) effects on DTS. XRD analysis showed that low crystallinity HA and unreacted DCPA were present in the 1-day specimens, and the extent of HA formation was increased with increasing TTCP5 fraction. Conclusion: Injectable HA-forming premixed CPCs with setting times from 4 to 70 min can be prepared by using DCPA and TTCP as the major ingredients. Compared to conventional powder/liquid cements, these premixed CPCs have the advantages of easy to use, good shelf-life, controllable hardening times. Supported by NIH grant DE11789, ADAF and NIST.