Combined effect of strontium and pyrophosphate on the properties of brushite cements

In this study we report the synthesis of strontium-containing brushite cement with good cohesion and a diametral tensile strength (DTS) of 5 MPa. The cement powder, composed of β-tricalcium phosphate (β-TCP) and monocalcium phosphate, was adjusted by different concentrations of strontium and pyrophosphate ions. The cement liquid phase was 2 M phosphoric acid solution. The cement cohesion and mechanical properties were measured after being aged in water for 24 h at 37 °C. It was found that at low concentration both strontium and pyrophosphate ions inhibit the cement setting reaction. However, the final setting time was significantly reduced when SrCl₂ increased from 5 to 10 wt.% at pyrophosphate concentrations equal to or higher than 2.16 wt.%. The incorporation of strontium ions did not increase the DTS of brushite cements significantly. In contrast, the addition of pyrophosphate ions did increase the DTS of brushite cements significantly. When both ions were added simultaneously, the brushite cement with a Sr²⁺ content of 5 wt.% had the highest DTS value. Nevertheless, the DTS values of Sr-containing cements were significantly reduced if the pyrophosphate concentration was higher than 2.16 wt.%. The Sr²⁺ ions had a negative effect on brushite cement cohesion, although the solid weight loss started to decrease at Sr²⁺ concentrations higher than 5 wt.%.