Control of structural and mechanical properties in bioceramic bone substitutes via additive manufacturing layer stacking orientation

Additive manufacturing (AM) is a promising approach for fabricating structures to serve as bone substitutes, or as biomaterial components in biphasic implants for repair of osteochondral defects. In this study, the three dimensional printing (3DP) AM process was investigated to determine the effect of powder layer orientation on mechanical and structural properties of fabricated parts. Five types of standard cylindrical parts were manufactured via AM with 0°, 30°, 45°, 60° and 90° stacking layer orientations relative to the vertical z-axis of the print bed, using amorphous calcium polyphosphate (CPP) powder of irregular particle shape, average aspect ratio ≈1.70 and particle size between 75 and 150 μm. It was concluded that layer orientation had an effect on porosity and compressive strength, based on induced powder particle orientation in the green part during powder layering. The resulting bulk porosity values ranged between 30.0 ± 2.4% and 38.2 ± 2.7%, while the compressive strength ranged between 13.50 ± 1.95 MPa and 45.13 ± 6.82 MPa. The orientation with the highest compressive strength was 90°, while orientations with the weakest compressive strength were 0° and 45°. Based on these results, it was established that AM-made parts are structurally and mechanically anisotropic. The stacking layer orientation which results in the highest strength performance along a preferred loading orientation can be implemented to further optimize mechanical strength of constructs along the maximum loading direction.