Preparation of tricalcium phosphate/calcium pyrophosphate structures via rapid prototyping
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Custom made tricalcium phosphate/calcium pyrophosphate bone substitutes with a well-defined architecture were fabricated in this study using 3D powder printing with tricalcium phosphate (TCP) powder and a liquid phase of phosphoric acid. The primary formed matrix of dicalcium phosphate dihydrate (DCPD, brushite) was converted in a second step to calcium pyrophosphate (CPP) by heat treatment in the temperature range 1,100–1,300°C. The structures exhibited compressive strengths between 0.8 MPa and 4 MPa after sintering at 1,100–1,250°C, higher strengths were obtained by increasing the amount of pyrophosphate formed in the matrix due to a post-hardening regime prior sintering as well as by the formation of a glass phase from TCP and calcium pyrophosphate above 1,280°C, which resulted in a strong densification of the samples and compressive strength of >40 MPa.