3D printed Ti6Al4V bone scaffolds with different pore structure effects on bone ingrowth

Abstract

The microstructure of porous scaffolds plays a vital role in bone regeneration, but its optimal shape is still unclear. In this study, four kinds of porous titanium alloy scaffolds with similar porosities (65%) and pore sizes (650 μm) and different structures were prepared by selective laser melting. Four scaffolds were implanted into the distal femur of rabbits to evaluate bone tissue growth in vivo. Micro-CT and hard tissue section analyses were performed 6 and 12 weeks after the operation to reveal the bone growth of the porous scaffold. The results show that diamond lattice unit (DIA) bone growth is the best of the four topological scaffolds. Through computational fluid dynamics (CFD) analysis, the permeability, velocity and flow trajectory inside the scaffold structure were calculated. The internal fluid velocity difference of the DIA structure is the smallest, and the trajectory of fluid flow inside the scaffold is the longest, which is beneficial for blood vessel growth, nutrient transport and bone formation. In this study, the mechanism of bone growth in different structures was revealed by in vivo experiments combined with CFD, providing a new theoretical basis for the design of bone scaffolds in the future.

Keywords: Bone ingrowth; Bone scaffold; Computational fluid dynamics; Pore geometry; Selective laser melting.

Fig. 1

Schematic diagram of the design parameters of the four structures

Fig. 2

A Material universal testing machine; B DIA stress-strain curve

Fig. 3

a Exposure of the distal lateral condyle of the femur; b A defect (5 mm in diameter and 8 mm in depth) was drilled from the lateral femoral condyle of the rabbit at low speed; c Titanium scaffold implanted into the bone defect

Fig. 4

Schematic diagram of the CFD simulation boundary conditions

Fig. 5

a Photo of a 3D printed titanium scaffold for the mechanical experiments; b Photo of the four cylindrical scaffolds for the in vivo experiments; c Micro-CT reconstruction of the porous titanium scaffold; d Surface area of four kinds of porous titanium scaffolds measured after 3D reconstruction

Fig. 6

Stress-strain curves of the four kinds of scaffold structures

Fig. 7

a Micro-CT reconstruction of the distal femur of rabbits after 6 and 12 weeks of titanium scaffold implantation. White represents the bone scaffold, and yellow represents new bone. b The titanium scaffold was implanted in the distal femur of rabbits. *P < 0.05, **P < 0.001 compared with DIA

Fig. 8

Histological sections of dehydrated embedded samples of the bone scaffolds obtained at 6 weeks and 12 weeks were stained. Red represents the bone tissue, and black represents the scaffold. Original magnification: 10.0; scale bar: 1 mm

Fig. 9

Fluid simulation results of the four structures

Fig. 10

Velocity flow diagrams for the four structures