Functionally graded porous scaffolds in multiple patterns: New design method, physical and mechanical properties

Functionally Graded Porous Scaffold (FGPS) becomes an attractive candidate for bone graft due to its combination of better mechanical and biological requirements with the scaffold gradient to better mimic host tissue. This paper focuses on the graded change requirements of bio-porous scaffolds in terms of physical and mechanical properties. Gradients in three patterns (density, heterostructure and cell-size gradients) with Gyroid and Diamond unit cells were proposed based on Triply Periodic Minimal Surfaces (TPMS), and fabricated by Selective Laser Melting (SLM) using Ti-6Al-4V. Among them, cell-size gradient was described for the first time, realizing a variation of graded pore size on a specific way. Morphological properties of porous samples were characterized by micro-CT and SEM, followed by compressive tests for determining their mechanical behaviors. It was found that the TPMS method is an effective way to achieve gradients in multiple patterns which are comparable to natural tissue with respect to both continuous topology and interconnectivity. The porous surface area and pore size, could be controlled by the cell-size gradient without relatively density alteration, stabilizing the modulus and strength within 11% and 20%, respectively. Both Gyroid and Diamond structures possess a superior strength (152.6 MPa, 145.7 MPa) and comparable elastic modulus (3.8GPa) with natural cortical bone. Keywords: Functionally graded porous scaffold, Triply periodic minimal surfaces, Selective laser melting, Additive manufacturing, Mechanical behavior