Formation of macropores in calcium phosphate cements through the use of mannitol crystals

Mannitol crystals with sizes ranging from approximate to 100 mum to approximate to 400 mum were mixed with calcium phosphate cement (CPC) powders that contained equimolar amounts of tetracalcium phosphate and dicalcium phosphate anhydrous. CPC-mannitol mixtures with mass fractions of(a) 0 % and (b) 10 % mannitol were mixed with cement liquid (1 mol/L Na2HPO4 solution) at powder-to-liquid ratio (P/L) of 4 g/mL. The hardening times (expressed in min) for the two mannitol-containing cements were (a) 5.3 +/- 0.3 and (b) 5.5 +/- 0.5 (n = 5). The cement pastes were packed into sample molds with an applied pressure of approximate to 2 MPa. Samples were removed from molds 4 h later and placed in water for 20 h causing complete dissolution of the mannitol and formation of macropores in the shapes of the mannitol crystals. Properties of the 24-h cement samples are as follows: Densities (expressed in g/cm(3)) of dried samples were (a) 2.05 +/- 0.03 and(b) 1.83 +/- 0.04 (n = 8). Macroporosities (expressed as volume fraction in %) were (a) 0 and (b) 10.9 +/- 1.7 (n = 8), and microporosities (expressed as volume fraction in %) were (a) 34.3 +/- 1.0 and (b) 30.6 +/- 0.6 (n = 8). Diametral tensile strengths (DTS) expressed in MPa were (a) 11.8 +/- 1.5 and (b) 7.6 +/- 0.9 (n = 8). Additional CPC-mannitol samples were prepared with P/L = 10 g/mL under a pressure of approximate to 660 MPa. The DTS (expressed in MPa) of these samples were (a ') 20.6 +/- 1.5 and (b ') 13.8 +/- 1.2 (n = 3).