Ability of a novel biomimetic titanium alloy cage in avoiding subsidence and promoting fusion: a goat spine model study

Clinically used intervertebral cages have several bottleneck problems, such as lack of osteogenic properties and high subsidence rate. This research aims to design a novel biomimetic titanium alloy cage through three improvements: cross-sectional shape mimics, Young's modulus matches and osteogenic property enhances. Two inner porous structures (1450–200 μm and 800–200 μm) were selected, and the Young's modulus were 540.7 MPa (similar to cancellous bone) and 1139.2 MPa, respectively. Shape of the cages was designed by radiographic images and assistant softwares to make the dense border contact the peripheral cortical bone of the vertebrae. Hydroxyapatite (HA) biocoating was performed through the slurry foaming and impregnation method, and the average thickness was approximately 40 μm. The biocoated and nonbiocoated cages were then implanted in goats' intervertebral space. During the 6-month follow-up, the lordosis angle and disc space height maintained well in all groups. Histological results showed a significant increase in bone ingrowth area between the nonbiocoating and biocoating groups, meaning a great enhancement of osteogenic properties by HA biocoating. The osseointegration also improved greatly. Additionally, the fusion condition of Young's modulus matching cages, before or after biocoating, was superior to that of unmatched cages. The results demonstrated that biomimetic designs could help avoid subsidence and promote fusion.