Indirect three dimensional printing of Apatite-Wollastonite structures for biomedical applications

Abstract

The main goal of the current study was to investigate the capabilities of the indirect three-dimensional printing (3DP) process when used in combination with bioceramic Apatite-Wollastonite (A-W) powders and to evaluate the mechanical properties of the printed parts. A-W glass ceramic is a bioactive material that is used clinically for bone substitutes due to its suitable mechanical properties. Additive manufacturing approaches, especially 3DP, have been shown to produce 3D complex structures via computer aided design. A-W with weight % of 4.6 MgO, 44.7 CaO, 34 SiO2, 16.2 P2O5 and 0.5 CaF2 was used in the present study. The approach taken to indirect 3DP was: (i) blending of the A-W with maltodextrin (MD) powder; (ii) using a Z Corp Z310plus 3D printer to selectively print binder into sequentially deposited thin layers of the blended powders in order to build up a 3D structure; (iii) heat treating the 3D printed parts to 1150°C to burn off the MD and sinter the A-W to create a consolidated 3D structure. Phosphate glass infiltration was used to fill the porosities and increase the mechanical strength of the sintered parts. Bioactive phosphate glass with weight % of 6.22 Na2O, 71.29 P2O5, and 22.49 CaO was used because it can dissolve faster than A-W. The flexural strength, Young’s modulus, porosity and shrinkage were measured on various samples printed from the seven powder blends (PBs). PBs with 30% MD and zb®60 binder were required for the parts to develop sufficient strength. PBs 1, 4, and 5 develop the highest strength after sintering. PB1 contains A-W particle sizes in the range of 53-90 μm, PB4 contains A-W particle sizes in the range of 0-53 μm and PB5 contains mixed particle size ranges (78.5% in the range of 53-90 μm with 21.5% in the range of 0-53 μm). Average flexural strengths of 23.65 MPa, 35.64 MPa, and 25.68 MPa were achieved for PB1, PB4, and PB5, respectively. The average strength of PB5 increased to 31.34 MPa after glass infiltration. In all cases, the increase in strength is a result of the increased consolidation during sintering, as indicated by the observed reduced porosity. Indirect 3D printing of A-W structures can be used to create strong, highly porous structures, but care must be taken to appropriately select binder and processing parameters. Moreover, this is a promising approach for fabrication in bone tissue engineering.