Design and Mechanical Properties Verification of Gradient Voronoi Scaffold for Bone Tissue Engineering

In order to obtain scaffold that can meet the therapeutic effect, researchers have carried out research on irregular porous structures. However, there are deficiencies in the design method of accurately controlling the apparent elastic modulus of the structure at present. Natural bone has a gradient porous structure. However, there are few studies on the mechanical property advantages of gradient bionic bone scaffold. In this paper, an improved method based on Voronoi-tessellation is proposed. The method can get controllable gradient scaffolds to fit the modulus of natural bone, and accurately control the apparent elastic modulus of porous structure, which is conducive to improving the stress shielding. To verify the designed structure can be fabricated by additive manufacturing, several designed models are obtained by SLM and EBM. Through finite element analysis (FEA), it is verified that the irregular porous structure based on Voronoi-tessellation is more stable than the traditional regular porous structure of the same structure volume, the same pore number and the same material. Furthermore, it is verified that the gradient irregular structure has a better stability than the non-gradient structure. An experiment is conducted successfully to verify the stability performance got by FEA. In addition, a dynamic impact FEA is also performed to simulate impact resistance. The result shows that the impact resistance of the regular porous structure, the irregular porous structure and the gradient irregular porous structure becomes better in turn. The mechanical property verification provides a theoretical basis for the structural design of gradient irregular porous bone tissue engineering scaffolds.

Design and Compressive Fatigue Properties of Irregular Porous Scaffolds for Orthopedics Fabricated Using Selective Laser Melting

An irregular porous structure plays a major role in bone tissue engineering, and it is more suitable for bone tissue growth than a regular porous structure. The response surface method was used to establish a relationship between the average pore size and the design parameters. The technology of selective laser melting was utilized to fabricate the porous Ti-6Al-4V scaffolds with an irregularity of (0.4) and porosities of (70, 80, and 90%) designed using the Voronoi-tessellation method. Compression tests of porous scaffolds showed an elastic modulus range of 0.84-1.97 GPa and an ultimate strength ranging within 21.0-99.1 MPa. The elastic modulus was mainly influenced by the porosity and heat-treatment process. Furthermore, the fatigue test results suggested that the number of cycles (9 × 10⁴ to 1.8 × 10⁶) was greatly influenced by the porosity and heat-treatment process. The heat treatment of annealing greatly improved the fatigue performance of porous scaffolds. The irregular porous scaffolds with lower porosity and after full annealing exhibited the best fatigue behavior.