Design and Analysis of Three-Dimensional Printing of A Porous Titanium Scaffold

Objective: To develop suitable structural designs for the three-dimensional (3-D) printing of a porous titanium scaffold to fill bone defects in knee joints. Pore diameter and mechanic strength are key factors for the 3-D printing of porous titanium scaffolds. Methods: Fifteen different pore unit structural models of titanium scaffolds were designed with 3-D printing computer software; five different scaffold shapes were designed: imitation diamond-60°, imitation diamond-90°, imitation diamond-120°, regular tetrahedron and regular hexahedron. Each structural shape was evaluated with three pore diameters 400μm, 600μm and 800μm, and fifteen types of cylindrical models(diameter: 20mm; height: 20mm). Autodesk Inventor software was used determine the strength and safety of the models by simulating simple strength acting on the knee joints. We analyzed the data and found suitable models for 3-D printing of porous titanium scaffolds. Results: Fifteen different types of pore unit structural models were evaluated under positive pressure; the compressive strength was lower when the pore diameter(400μm, 600μm and 800μm) was larger, except for the regular tetrahedron structure. Under lateral pressure, the compressive strength was also lower when the pore diameter(400μm, 600μm and 800μm) was larger. Under torsional pressure, the strength of the imitation diamond structure was similar when the pore diameter(400μm, 600μm and 800μm) was larger, and the strengths of the regular tetrahedron and regular hexahedron structures were lower when the pore diameter(400μm, 600μm and 800μm) was larger. In each case, the compressive strength of the regular hexahedron structure was highest, that of the regular tetrahedron was second highest, and that of the imitation diamond structure was relatively low. Fifteen types of cylindrical models under a set force were evaluated, and the sequence of comprehensive compressive strength, from strong to weak was: regular hexahedron> regular tetrahedron> imitation diamond-120°> imitation diamond-90°> imitation diamond-60°. The compressive strength of cylinder models was higher when the pore diameter was smaller. Conclusion: The compressive strength differed among titanium scaffolds with different pore structures. The pore diameter and shapes of the pore structure were important factors influencing the compressive strength. The models of regular hexahedron, regular tetrahedron and imitation diamond-120°appeared to meet the conditions of large pore diameters and high compressive strength. The strength of each structure was lower when the pore diameter(400μm, 600μm and 800μm) was larger.