Brushite forming biocements made from strontium substituted beta-tricalcium phosphate: Fid-Bau Portal

Brushite forming biocements made from strontium substituted beta-tricalcium phosphate

Hamdan Alkhraisat, M. / Moseke, C. / Gbureck, Uwe

Incorporation of Strontium (Sr) ions into calcium phosphate bone cement may improve its osteointegrative properties and its suitability for therapeutic applications. Beta-tricalcium phosphate (TCP) was prepared by mixing CaHPO4 and CaCO3 in a molar ratio of 2.15:1 and sintering at 1400 deg C for 12 h followed by 6 h at 1000 deg C. Sr substitution in the resulting beta-TCP was achieved by replacing CaCO3 with SrCO3 in proportions varying from 0 - 100 %. The brushite cement pastes were produced in two different ways (mixing the TCP powder in an equimolar ratio with monocalcium phosphate and following addition of water (beta-TCP-MCPM-H2O system) or mixing the TCP powder with phosphoric acid of different concentration (beta-TCP-H3PO4-H2O system)). The temperature change during the setting reaction was measured with a thermocouple, placed in the middle of a bulk of cement paste from 10 g of powder. A polystyrene mould served as insulation against ambient temperature. Compressive strength of brushite cement cuboids (12 x 6 x 6 mm) was determined using a static mechanical testing machine. The temperature versus time curves were characterized by a rapid increase in the first minutes of the setting reaction and a relatively slow temperature decrease after the maximum had been reached. Rising Sr content in the beta-TCP resulted in a significant decrease of the highest temperature (equal to 55 deg C) and shifted the maximum to the right, indicating a deceleration of the setting reaction. Mechanical testing showed that Sr did not reduce the compressive strength of brushite cements prepared with MCPM and even significantly improved the mechanical properties of the cements prepared with phosphoric acid. Strontium ions incorporated in beta-TCP slow down its dissolution, thus maintaining lower pH for a longer period of time, which promotes the formation of more brushite crystals. Furthermore, the higher setting time of Sr-containing cements reduces the average crystal size and improves the compaction of the crystals. Hence, substitution of Ca by Sr in the beta-TCP-H3PO4-H2O system results in the formation of brushite cements with higher density and improved compressive strength.