Rheological enhancement of mechanically activated α‐tricalcium phosphate cements

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Abstract
Most biocements are two- or three-component acid-based systems with large differences in the component particle sizes, which occurs by virtue of the differing processing routes. This work aimed to improve injectability and strength of a single reactive component cement, that is, mechanically activated α-tricalcium phosphate (TCP)-based cement by adding 13–33 wt % of several fine-particle-sized (d50 of 0.5–1.1 μm) fillers [dicalcium phosphate anhydrous (DCPA), titanium dioxide (TiO2), and calcium carbonate] to the monomodal α-TCP matrix (d50 = 9.8 μm). A high ζ-potential was measured for all particles in trisodium citrate solution. The fraction of α-TCP cement “injected” through an 800-μm hypodermic needle was found to be only 35% at a powder-to-liquid ratio of 3.5 g/mL. In contrast, the use of fillers decreased cement viscosity to a point, where complete injectability could be obtained. Mechanistically, these additives disrupted α-TCP particle packing yet decreased the interparticle spacing by a factor of ∼5.5 such that the electrostatic repulsion effect was enhanced. A strength improvement was found when DCPA and TiO2 were used as fillers despite the lower degree of conversion of these cements. Compressive strengths of precompacted cement samples increased from 70 MPa for unfilled α-TCP cement to 140 (110) MPa for 23 wt % DCPA (or TiO2) fillers as a result of porosity reduction. Strength improvement for more clinically relevant uncompacted cements was achieved by higher powder-to-liquid ratio mixes for filled cements such that maximum strengths of 90 MPa were obtained for 23 wt % DCPA filler compared with 50 MPa for single-component α-TCP cement. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 73B: 1–6, 2005