Bioceramic bone substitutes with programmed architecture were manufactured at room temperature in this study using a novel 3D printing process that combined 3D powder printing with calcium phosphate cement chemistry. During printing, biphasic α/β‐tricalcium phosphate (Ca3(PO4)2, TCP) powder reacted with a liquid component consisting of phosphoric acid solution to form a matrix of dicalcium phosphate dihydrate (CaHPO4·H2O, DCPD, brushite) and unreacted TCP. Printed samples showed compressive strengths between 0.9–8.7 MPa after printing depending on the acid concentration. A further strength improvement to a maximum of 22 MPa could be obtained by additional hardening of the samples in phosphoric acid for three one minute washes. After this treatment, the samples mainly consisted of brushite with minor phases of unreacted TCP and a lesser amount of dicalcium phosphate anhydrate (CaHPO4, DCPA, monetite). Hydrothermal conversion of brushite to DCPA resulted in an increase of porosity of approximately 13 % and a decrease of strength to 15 MPa, however the resorption rate in vivo was increased as demonstrated after intramuscular implantation over 56 weeks. Major advantages compared with commonly used sintering techniques are the low processing temperature, which enables the fabrication of thermally instable and degradable matrices of secondary calcium phosphates.

Direct printing of brushite and hydroxyapatite bioceramics at room temperature is used to construct model implants onto which the angiogenic compounds vascular endothelial growth factor (VEGF) and copper sulfate were adsorbed. This low‐temperature direct approach offers several practical advantages and may find application in bone grafting. The figure shows examples of complex shapes made of brushite.

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 degrees C. The structures exhibited compressive strengths between 0.8 MPa and 4 MPa after sintering at 1,100-1,250 degrees 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 degrees C, which resulted in a strong densification of the samples and compressive strength of >40 MPa.