Design of an inorganic dual-paste apatite cement using cation exchange

The use of hydraulic calcium phosphate cements (CPCs) as bone substitute is impaired by their relatively poor handling due to the need to mix a powder and a liquid during surgery. The aim of the present study was to assess the possibility to design CPCs as inorganic dual-paste cements, where both pastes would be stable for years, but would react as soon as they are mixed together. Results showed that aqueous pastes of alpha-tricalcium phosphate (alpha-TCP) powder could be stabilized for up to a year at room temperature by the use of 0.1 M Mg chloride solution. Adding a calcium chloride solution in a 1: 4 volume ratio activated alpha-TCP pastes provided the Ca/Mg ratio was larger than one. Mechanistic investigations suggest that Ca ions can displace Mg cations adsorbed at the surface of alpha-TCP particles to initiate alpha-TCP transformation to calcium-deficient hydroxyapatite and concomitant paste hardening. The compressive strength (29 MPa) was similar to that of commercial formulations (5-80 MPa). Other divalent cations (Ba, Ni, Sr) had a similar effect although with a different degree of efficacy.